Tonight’s sky of new research

A GLIMPSE of Dark Matter: JWST Constraints on Early Structure Formation

Julian B. Muñoz, John Chisholm, Seiji Fujimoto+13 more

• Astrophysics of Galaxies
• High Energy Physics - Phenomenology

AstronomerUsing UV luminosity functions from JWST GLIMPSE lensing observations and legacy Hubble and Subaru data, the authors constrain small-scale matter clustering during reionization at z ∼ 7. After marginalizing over astrophysical uncertainties, they find a matter power spectrum consistent with cold dark matter down to sub-Mpc scales, with 1σ uncertainties of 0.2 dex at k = 3–9 Mpc⁻¹ and 0.5 dex at k = 9–27 Mpc⁻¹. These are the smallest scales probed at these early times. For thermal-relic warm dark matter, they obtain m_WDM > 3.2 keV at 95% confidence, independently of lower-redshift probes. The results extend small-scale dark-matter tests into a new redshift window; consistency with cold dark matter does not establish its identity.

PublicEarly galaxies can reveal how dark matter gathered into small clumps, because those clumps must exist to host the galaxies. The researchers used measurements of the abundance of galaxies at different ultraviolet brightnesses from JWST, Hubble and Subaru to study this process during an early period called reionization. Allowing for uncertainties in galaxy physics, they inferred a pattern of matter clustering consistent with the cold-dark-matter model on scales smaller than a megaparsec. For one alternative model, thermal-relic warm dark matter, they set a particle-mass lower limit of 3.2 keV at 95% confidence. This is a new test using early galaxies, not a detection of dark-matter particles or proof that the cold model is correct.

Young explorerWe cannot see dark matter, but its clumps give galaxies places to form. Scientists studied how many young galaxies there were and how brightly they shone to learn about those clumps long ago. What they found fits an idea called cold dark matter, though there is still room for uncertainty. The study gives scientists more clues, but it does not tell us exactly what dark matter is.

Disentangling constraints on S₈ from the high and low redshift CMB

Joann Jones, Ualype de Andrade Uchôa, Scott Dodelson

AstronomerThe authors separate primordial and lensing information in CMB parameter inference by marginalizing over lensing with a principal component analysis. This avoids conflating high- and low-redshift information when testing the ΛCDM prediction for clustering growth. Combining Planck 2018, ACT DR6, and SPT-3G D1, the primordial CMB prefers S8 = 0.795 ± 0.022, consistent with DES's S8 = 0.789 ± 0.012. Here S8 combines the present-day linear clustering amplitude σ8 with the matter density parameter. CMB lensing instead implies stronger clustering. Both the inferred excess lensing and the improvement in agreement with DES depend on the prior on the summed neutrino mass. Nevertheless, removing lensing information shifts the CMB inference toward agreement with DES across the prior choices considered.

PublicSome analyses suggest that the universe's oldest light implies more matter clumping today than galaxy surveys find. But this ancient light also carries information added later, when intervening matter bends its path through gravitational lensing. The researchers developed and applied a method to separate these contributions. Using combined CMB data from Planck, ACT, and SPT, they find that the primordial-light component implies a present-day clustering measure consistent with the Dark Energy Survey. The lensing component points to stronger clustering. How large that excess is, and how much agreement improves, depends on assumptions about the total mass of neutrinos. Removing the lensing information moves the CMB estimate toward the galaxy-survey result for all assumptions examined.

Young explorerScientists want to know how lumpy the universe is. Very old light gives them clues, but its journey past other matter bends it and adds more clues. The researchers separated the clues. The oldest-light clues gave an answer that agreed with a galaxy survey, while the bending clues suggested more lumps. Some details still depend on what scientists assume about the masses of tiny particles called neutrinos.

The Redshift-Space Cluster-Galaxy Cross-Correlation as a Probe of Gravity on Cosmic Scales

Nicole Marcelina Gountanis, David H. Weinberg, Andrés N. Salcedo+1 more

• General Relativity and Quantum Cosmology

AstronomerThis Fisher-matrix forecast assesses DESI BGS tests of gravity using the redshift-space cluster–galaxy cross-correlation and its sensitivity to cluster infall velocities. Mock catalogs combine AbacusSummit N-body simulations, an HOD galaxy model, and a log-normal cluster mass–observable relation. Departures from GR are represented by a single factor, F_G, rescaling halo infall velocities. After marginalizing over HOD, mass–observable, and cosmological parameters, the forecast gives σ(F_G) = 0.033 at z ≈ 0.3, sufficient within this framework to distinguish representative f(R) and Galileon models from GR at ≳4σ. These are projected sensitivities, not observational constraints or detections of modified gravity. The dominant limitation is degeneracy with scatter in the cluster mass–observable relation; no individual HOD parameter shows a strong degeneracy with F_G. Perfect knowledge of the galaxy–halo connection would yield σ(F_G) ≈ 0.015, and adding galaxy autocorrelations could recover some of that improvement. The same data vector forecasts σ(Ω_m) = 0.010 and σ(σ_8) = 0.010, with only moderate correlations with F_G. The method offers a prospective quasi-linear-scale gravity test complementary to other modified-gravity probes and weak-lensing cluster mass profiles.

PublicResearchers used simulated galaxy catalogs to estimate how well the DESI Bright Galaxy Survey could test Einstein’s theory of gravity by studying how galaxies fall toward galaxy clusters. They forecast that the survey could measure a factor describing departures from the predicted infall speeds with an uncertainty of about 3.3% near redshift 0.3. Within their modeling framework, that would be precise enough to distinguish selected examples of two alternative gravity theories from Einstein’s theory at a statistical significance of roughly four sigma or more. This is a prediction of the survey’s potential, not a measured disagreement with Einstein. The main obstacle is uncertainty in how reliably observable cluster properties indicate cluster mass. Better knowledge of how galaxies occupy their surrounding matter halos, and additional measurements of galaxy clustering, could improve the test.

Young explorerGravity pulls galaxies toward big groups of galaxies. Scientists made pretend galaxies on computers to work out how well a galaxy survey could check Einstein’s rules for gravity. Their calculation suggests it could tell some different rules apart. They have not found that Einstein is wrong. To make the check better, they need to know more about how heavy the galaxy groups are.

Probing Cosmology with Diffusion Models: Memorization, Generalization, and Parameter Estimation

Jiaming Pan, Nicholas Kern

AstronomerUsing HI fields from the CAMELS IllustrisTNG simulations, the authors train diffusion-model surrogates and examine how training-set size affects memorization, one- and two-point statistics, and cosmological parameter inference. At fixed model size, smaller, less diverse training sets produce memorized samples and miscalibrated parameter densities. A surrogate can pass visual, pixel-value-distribution, and power-spectrum convergence tests yet yield overconfident cosmological posteriors. With sufficient training-set information to support generalization, posterior density estimation can be well-calibrated. These simulation-based tests motivate adding explicit generalization checks to inference pipelines using neural surrogates; agreement with the tested summary statistics alone is insufficient.

PublicAI models can provide cheaper substitutes for costly simulations of the universe, but convincing-looking output does not necessarily support trustworthy scientific conclusions. The researchers trained diffusion models on simulated neutral-hydrogen fields. With the model size held fixed, models trained on smaller, less varied datasets memorized training examples and produced estimates of cosmological parameters that were too confident. This could happen even when the generated fields looked right and matched both the distribution of field values and the power spectrum, which describes patterns across scales. Training data with enough information allowed the models to generalize and could produce appropriately calibrated uncertainty estimates. The study therefore recommends testing whether an AI model generalizes beyond its training examples before using it for cosmological inference. These findings come from tests using simulations, not observations of the universe.

Young explorerScientists tested an AI helper that makes pretend maps of hydrogen in space, using examples from computer-made universes. When it learned from too few different examples, it copied maps it had seen before. Its maps could look good and pass some checks, but its guesses about the universe could still sound too sure. With enough different examples, it could learn to make new maps and give better estimates of how sure its guesses were. The lesson is to check that the helper has really learned, not just remembered.

Early Dark Energy Crowds Out Interacting Dark Energy

William Giarè, Jeremy Sakstein

AstronomerThe authors test whether a dark-sector interaction can further relieve the Hubble tension in a cosmology containing early dark energy (EDE), an independent late-time dark energy fluid with w approximately −1 coupled to cold dark matter, and a cosmological constant. The data strongly favor the non-interacting limit: the best fit effectively reduces to standard EDE, with EDE supplying most of the increase in H0 and little statistical gain from the coupling. Dark-matter-to-dark-energy transfer can raise H0 further, but worsens the low-redshift fit. Because the CMB tightly constrains the early-time physical matter density, additional transfer requires a lower present-day matter abundance, which Type Ia supernovae strongly disfavor. The authors find this restriction especially severe after EDE has raised H0 and argue that the mechanism applies to a broad class of post-recombination interactions. Allowing a Chevallier-Polarski-Linder dynamical equation of state does not change their conclusions.

PublicThis study asks whether energy passing from dark matter to dark energy could help explain the disagreement over how fast the universe is expanding, once early dark energy is already included. In the models tested, the data favor little or no exchange. Early dark energy accounts for most of the increase in the inferred expansion rate. Transferring additional energy from dark matter to dark energy can push that rate higher, but it also leaves too little matter today to fit observations of Type Ia supernovae well, given the early matter density constrained by the cosmic microwave background. The authors find that this trade-off becomes especially restrictive when early dark energy has already increased the expansion rate. Their analysis suggests a similar limitation for a broad class of interactions occurring after recombination, and allowing dark energy's equation of state to change over time does not alter the conclusion. This is a test of possible models, not evidence that such energy transfer occurs.

Young explorerScientists disagree about how fast the universe is growing. This study tested an idea in which an early burst of something called dark energy helps explain the difference, and dark matter then gives energy to dark energy. In their models, that extra sharing could make the universe grow faster, but it would leave too little dark matter to match what exploding stars tell us. The information they used fit better with little or no sharing. So this extra idea did not help much in their tests; they did not discover that the sharing really happens.

Core-collapse universality for inelastic self-interacting dark matter halos

Evan Batteas, Alexander Brisebois, Maheen Hemani+6 more

• High Energy Physics - Phenomenology

AstronomerThis theoretical study models gravothermal collapse in dark matter halos with velocity-dependent elastic and dissipative self-interactions. Within a gravothermal fluid framework, the authors derive an effective cooling rate for upscattering into an excited state followed by decay, with emitted states removing energy from the halo. Numerical solutions for spherically symmetric halos follow both core growth and collapse. Unlike the universal evolutionary trajectories of purely elastic models, the inelastic models show substantially more diverse evolution. The authors nevertheless identify a hidden parametric universality and use it to derive a semi-analytic collapse-time formula for arbitrary velocity-dependent elastic and inelastic cross sections, avoiding further simulations within this framework. These are modeling results, not observational findings.

PublicThe researchers use mathematical models and computer simulations to study how dark matter halos could evolve if dark matter particles collide and sometimes lose energy. In the modeled process, a collision puts a particle into an excited state; when it returns to its ground state, emitted states carry energy out of the halo. The simulations follow spherical halos as their central cores grow and later collapse. Allowing energy loss produces a wider variety of histories than collisions that conserve energy. Even so, the researchers find a shared mathematical pattern and derive a formula to estimate collapse times for different collision properties without running new simulations. The findings describe these theoretical models, not observed dark matter behavior.

Young explorerThe scientists made computer models of big clouds of dark matter. In their models, tiny bits of dark matter can bump into each other and sometimes send energy out of the cloud. They watched the pretend clouds' middles grow and later squeeze inward. Clouds that could lose energy changed in more different ways, but the scientists found a hidden pattern. They used it to make a math shortcut for figuring out how long the squeezing would take in their models. They did not watch real dark matter clouds do this.

Simulating and Characterizing Non-Gaussian Small-Scale Polarized Emission

Mark A. Bishop, Brandon S. Hensley, Krzysztof M. Gorski+2 more

• Astrophysics of Galaxies

AstronomerThe authors introduce a stochastic framework for small-scale Galactic foreground emission, using polarized synchrotron observations as an example application. The motivation is that foreground amplitudes exceed the target primordial CMB B-mode signal, while current simulations cannot stochastically reproduce the filamentary, non-Gaussian structure of the interstellar medium. The framework generates many independent realizations that inherit large-scale morphology and include tunable anisotropic, multifractal, and advected non-Gaussian features, controlled by a small set of physically interpretable parameters. Tests on synthetic fields show that Minkowski functionals and structure functions partially capture variations in non-Gaussianity that standard power spectra do not adequately describe. This is a foundation for future foreground simulation suites, not a reported detection of primordial B modes or a demonstration of improved cosmological constraints.

PublicEmission from our own Galaxy can overwhelm the faint primordial polarization signal that researchers seek in the cosmic microwave background. This work introduces a way to generate many different simulated versions of the Galaxy’s fine-scale emission, using observations of polarized synchrotron emission as an example. The simulations retain shape information from larger scales while adding adjustable, complex patterns, including threadlike structures that existing simulations struggle to reproduce randomly. Tests show that mathematical tools sensitive to shapes and changes across scales capture some, but not all, of the simulated complexity. The work provides a basis for future simulation collections; it does not report a discovery of the sought-after primordial signal.

Young explorerScientists want to study a very faint pattern in light from the early universe, but light from our own galaxy gets in the way. The researchers made a new way to create many pretend pictures of that galactic light, with twisty, threadlike shapes. The pretend pictures keep clues from bigger shapes seen in the sky. Their tests can describe some of the complicated shapes, but not all of them. This is a step toward making better pretend skies, not a discovery of the faint pattern.

The scale of homogeneity in DESI Data Release 1

Cullan Howlett, L. Giani, Elizabeth G. O'Brien+65 more

AstronomerUsing DESI DR1, the authors apply a counts-in-spheres estimator to nearly 5 million galaxies and quasars in six independent redshift bins spanning 0.1 < z < 2.1. They measure the correlation dimension D₂(r), defining the homogeneity scale R_H by convergence to within 1% of its homogeneous asymptotic value. All tracers show a transition to homogeneity; galaxy R_H ranges from 93.8 (+0.9/−0.7) to 142.6 (±1.4) h⁻¹ Mpc, depending on tracer redshift, galaxy bias, and modelling. A cosmology-dependent reconstruction of the underlying matter scale decreases monotonically with redshift, in excellent agreement with ΛCDM predictions. North–South Galactic Cap offsets reach approximately 10%, largely attributable to fiber assignment effects reproduced in simulations. Toy-model tests identify inhomogeneous universes except for rather finely tuned observer configurations. Accounting for these qualifications, the authors interpret the measurements as strong evidence for the cosmological principle over the surveyed redshift range. The reconstructed matter scales agree with, and are substantially more precise than, previous WiggleZ and SDSS constraints.

PublicOn sufficiently large scales, does the universe's clumpy distribution of galaxies become approximately uniform? Researchers tested this using nearly 5 million galaxies and quasars from the first DESI data release. By counting objects inside spheres of different sizes, they found a clear transition toward uniformity for every tracer population studied. The inferred transition scale depends on the population, its redshift, and the modelling used. A model-dependent estimate for the underlying matter distribution agrees closely with predictions of the standard ΛCDM cosmological model. An important complication is a difference of up to about 10% between measurements in two sky regions, largely explained by effects of assigning observing fibers in simulations. Separate toy-model tests also reveal unusual observer configurations that could mislead the method. With these caveats, the findings strongly support—but do not prove—the cosmological principle of large-scale uniformity.

Young explorerGalaxies make clumps in space. Scientists counted almost five million galaxies and other bright objects to ask whether those clumps look more evenly spread when we look at bigger and bigger regions. They found that they do. Their counting tools can affect the answer, so they checked those effects with computer pretend-universes. The results are strong clues that space looks fairly even on very big scales, not absolute proof.

Gravitational Wave Background from Metastable Current-Carrying Cosmic Strings

Ivan Rybak, Rinku Maji, Qaisar Shafi

AstronomerThis theoretical study models the stochastic gravitational-wave background from networks of current-carrying metastable cosmic strings, including possible vorton formation phenomenologically. The authors construct a fast, accurate analytical spectral template for pulsar timing array (PTA) frequencies and relate the low-frequency slope to string-network parameters. At LIGO-Virgo-KAGRA (LVK) frequencies, they derive an analytical expression constraining the scale-invariant component. Comparison with current PTA and LVK constraints identifies parameter regions that can match PTA observations but are in tension with LVK limits. For these regions, interpreting the PTA signal with this model would require additional mechanisms to suppress high-frequency emission; the study does not establish a cosmic-string origin for the signal.

PublicThe researchers explore whether hypothetical cosmic strings carrying currents could produce a background of gravitational waves consistent with observations. Their model allows for the possible formation of structures called vortons and provides formulas for predicting the signal across frequency ranges studied by pulsar timing arrays and LIGO-Virgo-KAGRA. Some model settings can agree with the pulsar timing observations but conflict with LIGO-Virgo-KAGRA limits. Those settings would need an additional process to weaken the predicted high-frequency waves. This is a test of a possible explanation, not a detection of cosmic strings.

Young explorerScientists wondered whether tiny, string-like things that might exist in space could make ripples in space. They used math to work out what those ripples might be like. Some versions could fit one set of clues, but predict too many fast ripples for another set. Those versions would need something to make the fast ripples weaker. The scientists have not shown that these space strings are real.

Machine Learning Based Classification of Type 1 Active Galactic Nuclei

Jie Li, Xu-Liang Fan

AstronomerThe study develops a photometry-based random-forest classifier to distinguish type 1 quasars from type 1 Seyfert galaxies, with potential application to large all-sky surveys and candidate selection among broad-line AGNs. PCA indicates partial separation between the classes. Reported F1 scores are 0.967 for quasars and 0.791 for Seyferts; raising the classification threshold can yield a higher-purity Seyfert sample. Applied to a sample cross-matched with DESI DR1, the classifier gives high quasar precision and recall relative to spectroscopic classifications. Many RF-selected Seyferts are less-luminous sources labeled as quasars spectroscopically; Seyfert performance is also good if these sources are instead treated as Seyferts, making that assessment conditional on their interpretation. Median SEDs and Seyfert fractions resemble those of the training sample, whereas spectroscopic Seyfert fractions are lower at all redshifts. The results support recovery of Seyfert-like features at least for objects resembling the training population, not unrestricted generalization.

PublicResearchers developed a machine-learning method that uses brightness measurements to distinguish type 1 quasars from type 1 Seyfert galaxies. It classified quasars more successfully than Seyfert galaxies, although a stricter selection threshold can produce a Seyfert sample with fewer contaminants. In a sample matched to DESI DR1, its quasar classifications agreed well with classifications based on spectra. The Seyfert results were less clear-cut: many dimmer objects labeled as Seyferts by the model were called quasars by the spectroscopic method. Treating those objects as Seyferts improves the model's apparent performance, but does not establish which label is correct. Overall, the method recovered properties resembling those of its training examples; its reliability for different populations remains uncertain.

Young explorerScientists taught a computer to sort space objects into two groups called quasars and Seyfert galaxies using measurements of their light. It did better with quasars. For some objects, the computer and another sorting method disagreed, so the right answer is not settled. It seems best at finding Seyfert galaxies like the examples it learned from.

Gravitational Dark Matter Production from Spectator Field in R²-Higgs Inflation

Arnab Samanta, Rajesh Mondal, Tanmoy Modak

• High Energy Physics - Phenomenology

AstronomerThis theoretical study investigates gravitational production of a spectator dark-matter candidate χ in multifield R²-Higgs inflation, with χ coupled to gravity through ξχχ²R. Using the doubly covariant formalism in the Einstein frame, the authors derive background and linear fluctuation equations. They find that production and the subsequent comoving relic abundance depend strongly on χ’s effective mass, identifying regions where cancellations in its effective mass-squared yield the required relic abundance. They also suggest that preheating involving Higgs and Goldstone fields may play a critical role in accounting for the observed dark-matter density; this is a model-based possibility, not an observational detection.

PublicThe researchers use mathematical calculations to explore whether gravity during the very early universe could have produced dark matter. In their model, a proposed dark-matter field interacts only through gravity, and the amount produced depends strongly on its effective mass. They identify cases where contributions to the mass-squared cancel, allowing the model to produce the amount of dark matter needed today. Processes involving the Higgs and Goldstone fields during an early stage called preheating may also be important. These are theoretical findings, not evidence that this proposed dark matter has been detected.

Young explorerScientists used maths to ask how the young universe might have made dark matter, invisible stuff in space. In their idea, gravity could help make it. Their sums show that some settings could leave the right amount, and other things happening in the young universe might help too. This is a possible explanation, not something they have shown really happened.

Testing Extended Exponential Infrared Teleparallel Gravity with CMB, DESI, and PantheonPlus

Mahmoud Hashim, Jackson Levi Said, Waleed El Hanafy+1 more

• General Relativity and Quantum Cosmology

AstronomerThe authors constrain an extended exponential infrared EExpIR f(T) teleparallel gravity model with an additional parameter b controlling late-time dynamics. Phase-space analysis selects the cosmological branch from two solution branches and motivates a prior range for b. In this model, torsion supplies an effective dark-energy component that evolves smoothly from quintessence-like to phantom behavior, while standard early-time cosmological behavior is recovered. Combining Planck, ACT, and SPT CMB measurements with DESI BAO, PantheonPlus supernovae, and the SH0ES calibration yields b = 0.573 (+0.016, −0.060) and H0 = 70.67 (+0.31, −0.35) km s⁻¹ Mpc⁻¹ at 68% confidence. Bayesian evidence finds EExpIR f(T) and ΛCDM statistically indistinguishable with CMB data alone; the full dataset including SH0ES weakly favors ΛCDM.

PublicThe researchers tested an alternative theory of gravity against measurements of the early and present-day universe. In this theory, a feature of gravity called torsion plays the role of dark energy, and an extra adjustable parameter controls how the universe evolves at late times. The theory predicts changing dark-energy-like behavior while retaining the standard picture of the early universe; this behavior is a property of the model, not a direct observational discovery. The team used measurements of the cosmic microwave background, galaxy clustering, and exploding stars, together with the SH0ES calibration, to constrain the model. Measurements of the cosmic microwave background alone do not distinguish it statistically from the standard ΛCDM model. When all the data are included, the comparison weakly favors ΛCDM rather than the alternative.

Young explorerScientists tested a different idea about gravity to see how well it explains the way our universe grows. They compared the idea with measurements of the universe from long ago and more recent times. The oldest-light measurements could not clearly choose between the new idea and the usual one. With all the measurements together, the usual idea did a little better. So this test does not show that the new idea is better.

Towards constraining cosmology with HI--galaxy cross-correlations from MeerKLASS

G. Autieri, M. Spinelli, Z. Chen+14 more

AstronomerThis proof-of-concept analysis infers cosmological parameters from the cross-correlation power spectrum of MeerKLASS 2019 L-band HI intensity maps and overlapping WiggleZ galaxies at z ≈ 0.43. The end-to-end pipeline includes foreground cleaning and a likelihood model incorporating single-dish observational effects. In the most optimistic case, with astrophysical nuisance parameters fixed, it yields H0 = 65.3 (+5.8/−10) km s⁻¹ Mpc⁻¹ and Ωm = 0.44 (+0.12/−0.30), at 68% confidence. Allowing the HI amplitude to vary under an informative prior preserves most of the constraining power and shifts results by less than 1σ. Tests with synthetic data show that neglecting observational effects can bias parameters by up to 2.5σ and underestimate uncertainties; this is not a measured bias in the real-data results. Varying foreground-mode removal and the fitted scale range shifts inferred parameters by less than 0.5σ. The results are consistent with concordance cosmology and support the pipeline’s robustness under the tested choices, providing a foundation for future MeerKLASS and SKAO inference rather than a definitive precision measurement.

PublicResearchers combined MeerKLASS radio maps of neutral hydrogen with the locations of WiggleZ galaxies to estimate the universe’s expansion rate and matter content. This was a proof-of-concept test of a complete analysis process on real data, and its estimates are consistent with the standard cosmological model. The tightest reported limits rely on fixing uncertain astrophysical quantities; allowing the hydrogen signal’s strength to vary, while using informative prior knowledge, changes the results only modestly. Tests with simulated data show that ignoring observational effects can skew estimates and make them appear more precise than they are. Changing how foreground signals were removed and which scales were analyzed also produced relatively small shifts. The work supports the method’s use in future studies, but is not a definitive precision measurement.

Young explorerScientists compared a radio map of hydrogen gas in space with where galaxies are. They used the matching patterns to estimate how fast the universe is growing and how much matter it has. Their answers fit the usual picture of the universe, but are still uncertain. Tests with pretend data showed that leaving out details of how the observations work can give misleading answers. This is an early check that their method works.

Probing the local primordial non-Gaussianity with clustering of FRB dispersion measure and galaxies

Indranil Das, Gilbert Holder

AstronomerThis forecasting study combines the angular dispersion-measure auto-spectrum, DM–galaxy cross-spectrum, and galaxy auto-spectrum to constrain local primordial non-Gaussianity through its scale-dependent bias in the free-electron and galaxy fields. For a DESI-like luminous-red-galaxy sample and FRBs covering 35% of the sky, the forecast uncertainty is sigma(f_NL) ≈ 5 for either 10,000 or 100,000 bursts, at fixed Planck 2018 cosmology and marginalising over three astrophysical bias parameters. The constraint remains robust when the six ΛCDM parameters are also marginalised over with Planck priors. At these burst counts, the galaxy auto-spectrum dominates; the DM contribution increases with sample size and becomes decisive for larger samples anticipated in the SKA era, with sigma(f_NL) ≈ 2 forecast for 10 million bursts. These are projected sensitivities, not measured constraints.

PublicThe researchers estimate how combining fast radio bursts with a galaxy survey could test whether the early universe's fluctuations departed from a Gaussian statistical pattern. They use three kinds of information: patterns in the bursts' dispersion measures, which probe free electrons; patterns in galaxy positions; and the relationship between the two. For their assumed surveys covering 35% of the sky, either 10,000 or 100,000 bursts gives a predicted uncertainty of about 5 on the parameter f_NL, with most of the constraining power coming from galaxies. A much larger sample of 10 million bursts could reduce that uncertainty to about 2, making the burst measurements decisive. These are forecasts under specified survey and modelling assumptions, not a detection of primordial non-Gaussianity; the smaller-sample forecast remains robust when cosmological parameters are allowed to vary subject to Planck constraints.

Young explorerScientists want to learn about patterns from when the universe was very young. They worked out how much they might learn by studying where galaxies are and how short flashes of radio waves travel through space. In their calculations, the galaxies provide most of the clues when there are fewer flashes. With many more flashes, the flashes could help a lot more. This is a prediction about what future measurements could teach us, not something they have discovered yet.

Running cosmological constant in light of recent CMB-BAO data

A. Racioppi, M. Vijar

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerThe authors revisit single-field slow-roll inflation driven by a cosmological constant with a logarithmic radiative correction, treating its relative amplitude δ as a free parameter of either sign. For positive δ, predictions interpolate between logarithmic and linear inflation. CMB-only compatibility is limited to a narrow region near the 2σ boundary at relatively large δ, whereas including BAO permits a broad parameter range. For negative δ, slow roll fails at small field values and the predictions are excluded by the data. Including the effective mass contribution within the logarithmic correction changes this conclusion: the potential develops a local maximum and becomes hilltop-like, allowing compatibility with CMB-only constraints, though agreement with combined CMB-BAO constraints is possible only at 2σ. These are model-to-data consistency findings, not a detection of the proposed inflationary mechanism.

PublicThis study tests a model of inflation, an early period of cosmic expansion, against cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) data. The model is driven by a cosmological constant modified by a logarithmic quantum correction whose size and sign are allowed to vary. With a positive correction, only a narrow range is compatible with CMB data alone, near the edge of the 2σ constraints; adding BAO data allows a much wider range. The basic negative-correction version is ruled out by the data and loses the approximation used in the calculation at small field values. However, including an effective mass contribution changes the model into a hilltop-like form that can match CMB-only constraints, while matching the combined data is possible only at 2σ. Compatibility does not establish that this model describes how inflation actually happened.

Young explorerScientists tested a math idea about how the universe expanded very early on. They compared its predictions with clues from space. Changing one part of the idea made it fit some clues better than others. One version did not fit, but adding a mass effect changed its shape to look like a hill and helped it fit some clues. Even then, it only just fit the combined clues. This does not mean scientists have proved the idea is what really happened.

Cosmic birefringence tomography with radio galaxies I: Testing birefringence solutions to the CMB-BAO tension

Toshiya Namikawa, Fumihiro Naokawa, Richard Battye+1 more

AstronomerThe study uses low-redshift radio galaxies to independently constrain ALP-induced cosmic birefringence in two scenarios that could alleviate the mild BAO–CMB tension through a large rotation during reionization: an nπ phase ambiguity in recent isotropic birefringence measurements, and energy injection from cold dark matter into ALPs. Fitting rotation angles estimated from radio-galaxy jet morphologies and polarization angles by Battye, Jackson & Browne (2026), the authors exclude absolute values of the integer n greater than or equal to 1 at more than 2σ for log10(mφ/eV) approximately less than or equal to −30.7. The energy-injection fit is consistent with no injection, although it slightly favors nonzero injection relative to the no-injection case. These constraints come from about 3000 radio galaxies and remain subject to possible astrophysical uncertainties and statistical fluctuations. Larger low-redshift samples for tomographic birefringence studies are advocated, not reported as a result.

PublicLight's polarization describes the orientation of its electromagnetic oscillations. This study tests whether hypothetical axionlike particles could rotate that orientation as light travels through space. The proposed models could ease a mild disagreement between recent baryon acoustic oscillation measurements and cosmic microwave background observations by producing a large rotation during reionization. Researchers fitted rotation estimates derived from the shapes of radio-galaxy jets and their polarization directions, using about 3000 galaxies. For a model in which existing measurements could miss integer multiples of π in the rotation, the data rule out an absolute value of the integer n of 1 or greater at more than 2 standard deviations when log10(mφ/eV) is approximately −30.7 or lower, where mφ is the particle mass. A second model, in which cold dark matter supplies energy to axionlike particles, is consistent with no energy transfer, despite a slight relative preference for some transfer. Neither finding establishes that these particles exist. Possible astrophysical uncertainties and statistical fluctuations motivate future studies with more nearby radio galaxies.

Young explorerLight has a direction it wiggles in, and scientists wonder whether tiny, unseen particles might turn that direction as light travels. They used clues from about 3000 radio galaxies to test two ideas that might help explain a small disagreement between measurements of the universe. The galaxy clues argued against some versions of one idea. For the other idea, where dark matter gives energy to the tiny particles, the clues still fit no energy being given, even though they leaned a little toward some being given. This does not show that the particles are real. Things happening in the galaxies and chance could affect the clues, so scientists want to study more galaxies.

Cosmological axion-photon interactions with a nonminimal dark gauge sector

Hao Jiao, Dong-Won Jung, Nils A. Nilsson

• High Energy Physics - Phenomenology

AstronomerThe authors study the cosmological evolution of radiation and dark radiation with nonminimal axion-photon-dark photon couplings. These Chern-Simons-type interactions can convert energy between photons and dark photons and rotate radiation polarization, potentially producing CMB spectral distortions and cosmic birefringence. Using the observed CMB monopole spectrum, they constrain the photon-dark photon energy-conversion fraction, which depends on the couplings and axion-field evolution. They further show that the parity-odd mixing term φF B̃ can partially relax bounds on the standard axion-photon coupling φF F̃ inferred from current cosmic-birefringence limits. These are constraints and model-dependent implications, not reported detections of conversion or dark photons.

PublicThe study explores how hypothetical particles called axions and dark photons could affect light as the universe evolves. In the model, their interactions could transfer energy between ordinary light and dark photons and rotate light’s polarization. Both effects could leave traces in the cosmic microwave background, the radiation left over from the early universe. The authors use its observed overall spectrum to limit how much energy could have been converted. They also show that including an additional interaction could partly loosen existing limits on the interaction between axions and ordinary light. The work does not report a discovery of axions or dark photons.

Young explorerSpace still has a faint glow from when the universe was very young. Scientists studied an idea in which tiny things we have not discovered could take energy from that glow or change how its light wiggles. They used measurements of the glow to limit how much energy could have moved. They also found that adding another possible interaction could make one earlier limit less strict. This does not mean they found those tiny things.

A deep learning approach to member identification and mass estimation in galaxy clusters

Zicheng Wang, Liping Fu, Wei Du+9 more

AstronomerThe authors develop and test a two-stage probabilistic deep-learning framework on mock cluster catalogues, rather than observational data. An LSTM assigns galaxy membership probabilities using projected phase-space proximity; these probabilities weight projected phase-space density maps used by a Bayesian neural network to infer dynamical masses and predictive uncertainties. The membership probabilities are well calibrated, with the mean membership-probability contour of 0.5 broadly tracing the empirical member–interloper transition. A 0.5 membership threshold balances completeness and purity, with high completeness inside projected radius r200. Membership weighting reduces the fiducial mass estimator’s residual scatter to 0.120, a 19.5% improvement over the unweighted baseline, but predictive uncertainty calibration is not uniform across BNN models. Controlled mock tests show substantial sensitivity to miscentring: using the brightest cluster galaxy instead of the gravitational centre lowers the median inferred mass by up to 47.6%, with larger reductions at larger offsets. Removing 40% of eligible non-central galaxies within r200 instead lowers the median inferred mass by 6.1% relative to complete catalogues.

PublicGalaxies mistakenly counted as members of a galaxy cluster can distort estimates of its mass. The researchers tested an artificial-intelligence method on mock galaxy-cluster catalogues. One network estimates each galaxy’s probability of belonging to a cluster, and a second uses those probabilities to estimate the cluster’s mass and its uncertainty. Giving likely members more weight reduced the scatter in mass-estimation errors by 19.5% compared with the unweighted method. However, the reported uncertainties were not consistently calibrated across the mass-estimation models. The mock tests also revealed a strong dependence on where the cluster’s centre is placed: using the brightest cluster galaxy instead of the gravitational centre lowered the median mass estimate by as much as 47.6%. Removing 40% of eligible galaxies other than the central galaxy within the study’s specified cluster radius had a smaller effect, lowering the median estimate by 6.1%. These are results from mock tests, not a demonstration on real cluster observations.

Young explorerA galaxy cluster is a big group of galaxies. Some galaxies can look like they belong to the group when they really do not. Scientists taught a computer to guess which galaxies belong, then use those guesses to work out how much mass the group has. They tried this with pretend galaxy groups, and it helped make the mass guesses less scattered. But choosing the wrong middle of a group could make the computer guess much too little mass. The computer also was not always good at saying how unsure it was. These tests used pretend groups, not real ones.

Low-variance renoising for weak gravitational lensing shear estimation

Xiangchong Li

AstronomerThe authors derive a general first-order noise-bias cancellation condition for renoising: the distribution of the shear-transformed original noise plus added noise with an assigned shear dependence must be independent of shear to first order. This permits estimation of the renoised ellipticity’s shear response from the known added-noise realization alone. Standard rotation renoising, used by Metacalibration and AnaCal, satisfies this condition but doubles the noise variance; it also yields AnaCal’s analytical response estimator. The authors construct an alternative, spectral renoising, that adds only a small fraction of the original noise variance. For homogeneous Gaussian noise, the added field is an independent, scaled-down copy of the image noise, with an assigned shear response obtained through a fixed filter determined by the noise power spectrum deconvolved by the point spread function. In image simulations, spectral renoising maintains multiplicative shear bias at the 10^-3 level and increases effective galaxy number density by about 20% at the faint end. These performance results are simulation-based, not observational measurements.

PublicMeasuring tiny stretches in galaxy images can be biased by the images’ random noise. An existing correction adds specially rotated noise to cancel the leading bias, but doubles the noise variance. The authors derive a general rule for how added noise can provide this cancellation and develop a new method called spectral renoising that adds much less noise. For noise with uniform, Gaussian statistics, the method uses an independent, weaker copy of the image noise and a mathematical filter. In simulated images, it keeps the fractional calibration bias in the stretching measurement at about one part in a thousand while increasing the effective number of usable faint galaxies by about 20%. These are simulation results; the abstract does not report a test on real observations.

Young explorerGalaxy pictures have random speckles that can make their shapes tricky to measure. One way to help is to add special extra speckles, but that makes the pictures noisier. The researchers worked out a new way that adds fewer speckles. When they tested it on pretend galaxy pictures made by a computer, it kept shape measurements accurate and helped them get more useful information from faint galaxies. They have not reported testing it on real sky pictures here.

Cosmological constraints on extra radiation and early dark energy with lepton asymmetry and varying quark masses

Yo Toda

• High Energy Physics - Phenomenology

AstronomerThis analysis combines Planck CMB, DESI DR2 BAO, Pantheon+ supernovae, and primordial helium and deuterium measurements to constrain extra radiation and axionlike early dark energy (EDE), allowing primordial lepton asymmetry or light-quark-mass variation during BBN. With extra radiation and lepton asymmetry both free, the inferred parameters are N_eff = 3.27 ± 0.16, ξ = 0.017 ± 0.011, and H_0 = 69.24 ± 0.92 km s⁻¹ Mpc⁻¹. Positive lepton asymmetry offsets the helium enhancement from extra radiation, permitting a higher inferred H_0 even with the LBT helium measurement, which agrees with standard BBN. For EDE, abundance data constrain the higher baryon densities associated with larger EDE fractions because these lower predicted deuterium; lepton asymmetry does not alleviate this restriction. Positive light-quark-mass variation instead raises predicted deuterium, allowing larger EDE fractions and higher inferred H_0, while leaving the extra-radiation constraint nearly unchanged. In the extra-radiation model, allowing lepton asymmetry also weakens the 95% upper bound on summed neutrino mass from 0.0640 to 0.0777 eV. These are model-dependent constraints, not detections of the proposed ingredients.

PublicMeasurements of the universe’s expansion and its oldest light can be combined with primordial helium and deuterium abundances to test ideas about the early universe. This study examines extra radiation and a proposed early form of dark energy, while allowing either an early imbalance between leptons and antileptons or changes in light-quark masses during the formation of the first nuclei. In the extra-radiation model, a positive lepton imbalance can counteract the predicted increase in helium, allowing a higher inferred expansion rate today. For early dark energy, deuterium measurements limit how much can be present: larger amounts are associated with higher ordinary-matter densities that predict too little deuterium. A lepton imbalance does not ease that limit, but a positive change in light-quark masses can, because it increases predicted deuterium. Allowing the lepton imbalance also loosens the upper limit on total neutrino mass in the extra-radiation model. These findings describe what the tested models can accommodate, rather than establishing that these early-universe changes occurred.

Young explorerScientists look at very old light and the amounts of helium and a special kind of hydrogen to learn about the baby universe. They tested ideas about extra radiation and a kind of energy that might have been there long ago. Those ideas change how much helium and special hydrogen the universe should have made. In their calculations, one change can balance out another, letting some models fit the clues while allowing the universe to be expanding faster today. But not every change helps every idea. The study does not show that these things really happened; it shows which ideas can fit the clues.

Efficient GLS map-making and assessment of 1/f noise impact for future CMB satellite missions

Marta Monelli, Guillaume Patanchon, Avinash Anand

• Instrumentation and Methods for Astrophysics

AstronomerThe authors introduce STITCH (STatistical Inpainting for Timeline CHunks), a preprocessing method designed to reduce boundary artifacts in circulant generalized least-squares CMB map-making. GLS is optimal for stationary Gaussian noise with known covariance, but the computationally efficient circulant approximation introduces edge effects in finite data chunks. STITCH extends chunks with synthetic samples so that the extended timelines are statistically consistent with the assumed circulant noise model, allowing use of standard efficient solvers. In simulations, it substantially suppresses boundary residuals and brings noise power spectra close to those obtained when the circulant approximation holds. The authors also report negligible impact on recovered signal, including large-scale E-to-B leakage, in their tests. Separately, noise simulations for representative LiteBIRD-, Planck-, and PICO-like scanning strategies support an empirical fit linking temporal 1/f noise parameters to angular noise spectra. That characterization applies to the configurations studied; these are simulation-based findings, not results from mission observations.

PublicMeasurements of the polarization of the cosmic microwave background can be contaminated by noise that stays correlated over time, making it harder to search for primordial B-mode patterns. Fast methods for turning these measurements into sky maps use a mathematical approximation that can create artificial features at the edges of data segments. The researchers propose STITCH, which adds statistically matched synthetic samples to each segment before it is processed. In simulations, this greatly reduces the edge artifacts while retaining the efficiency of the existing mapping method. Their tests also find negligible effects on the recovered sky signal, including unwanted mixing between two polarization patterns called E and B. The team separately uses simulations of scanning strategies resembling those of LiteBIRD, Planck, and PICO to model how time-dependent noise appears at different angular sizes on the sky. These findings characterize the simulated configurations rather than demonstrate performance on actual mission data.

Young explorerScientists want to make pictures of very old light from space, but unwanted wiggles in their measurements can get in the way. When a fast computer method works on short pieces of those measurements, it can leave false marks near the ends. The scientists made a helper called STITCH that adds pretend measurements at the ends, with wiggles that fit the noise. In computer tests, this made the false marks much smaller and barely changed the space-light pattern they wanted to keep. They also tested how different ways of looking around the sky spread the noise across a picture. These were computer tests, not new measurements of space.

Dwarf Galaxy Reticulum II's MeerKAT L-Band Observation: Constraining WIMP Dark Matter

Phillip Badenhorst, Michael Sarkis, Yin-Zhe Ma+5 more

• High Energy Physics - Phenomenology

AstronomerMeerKAT L-band observations at 1.3–1.5 GHz measure the radio surface-brightness profile of the dwarf spheroidal galaxy Reticulum II. Combining these measurements with theoretical WIMP-annihilation models gives 95% confidence upper limits on the annihilation cross-section of approximately 10^-26 cm^3 s^-1 for WIMP masses of roughly 10–200 GeV, conditional on the adopted uniform magnetic field and diffusion constant. The proposed emission mechanism is synchrotron radiation from annihilation-produced electrons and positrons in the galaxy’s magnetic field; the limits do not establish a dark matter detection. Poorly constrained magnetic fields remain a major source of model dependence, motivating better magnetic-environment characterisation to exploit future facilities such as the Square Kilometre Array.

PublicResearchers used MeerKAT radio observations to measure how radio brightness varies across the dwarf galaxy Reticulum II. They compared those measurements with models in which hypothetical dark matter particles called WIMPs annihilate, producing electrons and positrons that could emit radio waves in magnetic fields. This comparison places upper limits on how strongly WIMPs could annihilate for a range of particle masses; it is not a detection of dark matter. The limits depend strongly on assumptions about the galaxy’s poorly known magnetic field and how the charged particles spread. Better knowledge of these conditions will be important for future searches with the Square Kilometre Array.

Young explorerScientists used a radio telescope to study a small galaxy called Reticulum II. They were looking for radio signals that might be made if certain kinds of invisible dark matter particles meet and turn into other particles. They did not show that they had found dark matter. Instead, they worked out limits on how often this could happen, using a model. Those limits depend on things about the galaxy that scientists do not yet know well, especially its magnetic field.

Mapping cluster angular momentum with the rotational kinetic Sunyaev-Zel'dovich effect

Jack Y. L. Kwok, Bernardita Ried Guachalla, William R. Coulton+2 more

• Astrophysics of Galaxies

AstronomerThe authors present an optimal multifrequency matched filter for reconstructing a noisy projected intracluster-gas angular-momentum vector field from microwave maps through the rotational kinetic Sunyaev-Zel'dovich dipole. The filter separates rkSZ from much larger miscentered tSZ, cosmic microwave background, and infrared background contributions, improving on the comparison stacking and filtering methods. A coherent-rotation model, validated against TNG-Cluster and TNG300-1 simulations, uses differentially rotating concentric shells with constant equatorial tangential velocity and a mass- and redshift-independent ratio v_tan/V_c,200c = 0.18. Simons Observatory forecasts give cumulative detection SNRs of approximately 53, 25, and 6 for idealized catalogs above log10(M_200c/M_sun) thresholds of 14, 14.5, and 15, respectively, assuming perfectly known spin directions and cross-correlation with external rotation proxies. These are model-based forecasts, not observational detections. Potential applications include rotational non-thermal pressure in cluster mass calibration, spin alignments, and clustering biases.

PublicGas rotating coherently inside a galaxy cluster could leave a two-sided pattern in the microwave sky through the kinetic Sunyaev-Zel'dovich effect. The authors develop a method that combines microwave maps at different frequencies to extract this faint pattern from much stronger signals and estimate the gas's projected rotation direction, though individual estimates would be noisy. They test a simple model of the rotating gas against simulations and use it to forecast what the Simons Observatory could detect. Combining many clusters could produce a strong detection under idealized assumptions, especially that their spin directions are perfectly known from outside information. The study offers a framework for future measurements, rather than reporting an observed detection, with possible uses in understanding cluster rotation and improving cluster mass estimates.

Young explorerA galaxy cluster is a big group of galaxies with gas between them. If that gas spins together, it could make a tiny two-sided mark in the microwave sky. The scientists made a way to look for that mark among much stronger signals. They checked their idea using computer simulations and predicted that looking at many clusters together could help reveal it, if the spin directions were known perfectly. They have not reported finding the mark in real sky observations.

Benchmarking Quantum Neural Networks Developed for MBHB Coalescence in the Context of LISA Space Mission

Maria-Catalina Isfan, Laurentiu-Ioan Caramete, Ana Caramete

• Instrumentation and Methods for Astrophysics
• General Relativity and Quantum Cosmology
• Data Analysis, Statistics and Probability

AstronomerThis study benchmarks quantum, hybrid quantum-classical, and classical machine-learning architectures for massive-black-hole-binary signal detection and merger prediction relevant to LISA. Models are trained on labelled Sangria training data from the LISA Data Challenge and evaluated on its corresponding blind dataset, rather than on LISA observations. Several quantum models match or exceed classical detection baselines; the best hybrid post-VQC model identifies all signal samples in the blind dataset. That finding alone does not establish a zero false-positive rate. For merger detection and coalescence-time estimation, the standard variational quantum classifier is the most reliable model tested, localising all detected merger events with the lowest localisation errors. The study also examines performance, model complexity, and quantum-circuit resource trade-offs. No universal quantum advantage is found; the reported benefits are task-specific, supporting further investigation for future LISA analysis pipelines.

PublicResearchers tested whether quantum machine learning could help analyse gravitational-wave signals from pairs of massive black holes for the future LISA mission. Using training and blind-test datasets from the LISA Data Challenge, they compared quantum, mixed quantum-classical, and conventional methods. Several quantum models matched or outperformed conventional alternatives at finding signals. One mixed model found every signal sample in the blind test, though this does not mean it made no false alarms. A different quantum model was most reliable at identifying mergers and estimating when the black holes coalesced. These are benchmark results, not findings from LISA observations. Quantum methods were not better across the board, but some may be useful for particular analysis tasks.

Young explorerWhen two huge black holes come together, they make ripples in space. Scientists tested different computer helpers on a practice dataset to see which could find those ripples and tell when the black holes joined. Some helpers used quantum methods, a different way of computing. Some did very well, but no kind was best at everything. These were tests, not discoveries made by LISA.

Phenomenological implications of cosmic (super)strings with time-varying tension

Anastasios Avgoustidis, Edmund J. Copeland, Adam Moss+3 more

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThe study compares five models of time-dependent cosmic-string or cosmic-superstring tension with the conventional constant-tension case. Such evolution could arise from strings composed of evolving moduli fields or from direct coupling to evolving scalar fields. The authors evaluate gravitational-wave contributions and effects on the cosmic microwave background, and perform an MCMC analysis. The evolving-tension models produce potentially interesting gravitational-wave spectral signatures at frequencies between those covered by current pulsar timing array and interferometer data. However, these signatures are not unique to such strings, limiting identification with current data. Evolving-tension strings fit the gravitational-wave data as well as other favoured models; this does not establish their existence. The abstract reports no specific cosmic microwave background constraints.

PublicCosmic strings are hypothetical defects that might have formed in the early universe. This study explores what would happen if their tension changed over time rather than staying constant. The researchers tested five models, calculating their gravitational-wave signals and effects on the cosmic microwave background. Their analysis predicts distinctive-looking features in the gravitational-wave signals at frequencies between those covered by current pulsar timing and interferometer measurements. But other sources could produce similar features, so these are not clear identifiers of cosmic strings. Models with changing tension fit the gravitational-wave data as well as other favoured explanations, without proving that cosmic strings exist.

Young explorerImagine tiny threads that might have formed when the universe was very young. Scientists do not know whether these cosmic threads really exist. They used five mathematical models to explore what might happen if the threads changed how tightly they pulled. The models suggest patterns in ripples in space, but other things could make similar patterns. So the scientists cannot use those patterns to say they have found cosmic threads.

Extracting non-Gaussian information of line-intensity maps with weighted skew spectra

Eleonora Vanzan, Azadeh Moradinezhad Dizgah, Ely D. Kovetz

• Astrophysics of Galaxies

AstronomerThis study presents the first application of optimally weighted skew spectra to galaxy-hosted line-intensity mapping, accounting for luminosity-weighted clustering and shot noise and an unknown mean intensity. Idealized real-space Fisher forecasts consider SPHEREx-like Hα surveys over 0.2 ≲ z ≲ 4.6 in deep-field and noisier all-sky configurations. On perturbative scales, assuming fixed emitter redshift evolution, four skew spectra—including one matched to shot noise—recover bispectrum constraints on biases, shot noise and cosmological parameters to within a few percent. Joint power-spectrum and skew-spectrum analysis forecasts constraints on second-order-to-linear bias ratios in each redshift bin, despite the individual biases remaining degenerate with mean intensity. Their evolution can therefore be measured without an emitter model. For emission depending only on halo mass, these ratios reflect luminosity-weighted halo biases; testing their evolution could probe assembly-history or environmental dependence. These ratios are inaccessible to the tree-level real-space power spectrum alone. At z ≲ 3, the all-sky configuration is forecast to detect bias-ratio departures of order 0.1 at 3σ; deep fields perform better in the highest-redshift bins. These are forecasts, not survey measurements.

PublicMaps of the combined light from galaxies contain information in patterns involving three locations, but analyzing all those patterns is cumbersome. This study forecasts that four compact summaries can preserve nearly all the parameter-constraining information in those three-location patterns, under the stated assumptions. The calculations consider idealized SPHEREx-like surveys of hydrogen emission, rather than actual observations. Combining these summaries with the usual two-location statistics could reveal how galaxies’ light traces matter across cosmic time, even when the maps’ average brightness is unknown. This could test how emission relates to the dark-matter halos hosting galaxies, including possible links to their histories or surroundings. The forecasts favor wide coverage at lower redshifts and deeper observations in the highest-redshift bins.

Young explorerImagine a map of light from lots of galaxies. Scientists calculated a way to keep important clues from complicated patterns in just four simpler summaries. Future maps could use these clues to learn how galaxy light follows matter in space. This is a prediction from calculations, not something measured in the sky yet.

At the EDGES of MADness: phenomenology of relic millicharged atomic dark matter

Eleonora Vanzan, Kimberly K. Boddy, Ely D. Kovetz

• High Energy Physics - Phenomenology

AstronomerThe authors investigate millicharged atomic dark matter (MAD), in which dark recombination leaves a small residual ionized component that acquires a tiny electric charge through kinetic mixing. Using a modified CLASS cosmological Boltzmann solver, they identify parameter regions compatible with CMB, large-scale structure, supernova, laboratory, and astrophysical constraints. These regions overlap the window associated with the EDGES excess-absorption claim: fractional electric charges of roughly 10^-6–10^-4 and a millicharged component below one percent of the total dark matter abundance. This is a model-viability result, not a detection. Although the abstract considers the EDGES result unlikely to originate at Cosmic Dawn, it predicts distinctive MAD cosmological signatures accessible to upcoming 21-cm observations.

PublicCould a tiny portion of dark matter carry a very small electric charge? This study explores a model in which dark matter behaves like an analogue of hydrogen: most of its charged constituents combine into dark atoms, leaving a small charged remainder. The authors' calculations find versions of this model that satisfy existing observational and experimental limits. Some also fall within the range proposed to explain an unusually strong radio absorption signal reported by EDGES. However, that signal is considered unlikely to come from the early-universe era called Cosmic Dawn, and the study does not detect dark matter. The model predicts distinctive effects that upcoming observations of the 21-centimetre radio signal could test.

Young explorerScientists are trying to understand invisible stuff in space called dark matter. In this study, they used a computer to explore an idea: dark matter might make tiny dark atoms, leaving a little bit with a very small electric charge. Their calculations show that this idea could fit what we know so far, but they have not found these dark atoms. A strange radio signal helped inspire the study, though it probably did not come from the early universe as first hoped. Future radio observations could help test the idea.

Theoretical Consistency and Observational Constraints on Entropic Cosmology

Yunliang Ren, Xiaofeng Yang, Xuwei Zhang+3 more

• General Relativity and Quantum Cosmology

AstronomerMotivated by DESI DR2 indications of potentially evolving dark energy, the authors examine three entropic cosmology models with driving terms H², H² + Ḣ, and H² + Ḣ + H⁴. They assess early-universe consistency, the Trans-Planckian Censorship Conjecture (TCC), and Quintom-B crossing, and constrain the models with Pantheon+, DESI DR2 BAO, and Planck 2018 CMB distance priors. Model A is simplest but struggles to satisfy both early-universe consistency and the TCC. Model B differs only slightly in observational fit while being more compatible with the theoretical constraints. Model C does not improve the fit; its full-data analysis uses a first-order perturbative treatment for numerical stability. Observationally favored and theoretically preferred parameter regions do not fully overlap, suggesting that further development is needed for consistency across cosmic epochs.

PublicRecent DESI results hint, but do not establish, that dark energy may change over time. Motivated by this possibility, the researchers test three versions of entropic cosmology against astronomical data and theoretical requirements. The simplest version has difficulty meeting requirements concerning the early universe and a theoretical conjecture. A second version fits the observations only slightly differently but fares better against those requirements. Adding another correction in the third version does not improve the fit, although that model was analyzed using an approximation to keep the calculations stable. The settings favored by observations do not fully match those favored by theory, leaving these models in need of further development.

Young explorerScientists tried three math ideas for how the universe grows. They checked the ideas against things astronomers have measured and against rules they wanted the ideas to follow. The simplest idea had trouble with the rules. A second idea followed the rules better, but adding even more math in the third did not make it match the measurements better. None gave a fully matching picture, so the scientists think these ideas need more work.

Going off the (momentum) grid: A simple implementation of noncold relics in linear Boltzmann solvers

Arad Nasiri, Murali Saravanan, Caio B. de S. Nascimento

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerThe authors implement the Dispersive Fluid Approximation (DFA) in CLASS to capture the scale-dependent sound speed of noncold relics. In numerical tests within the standard ncdm module, it substantially improves cross and neutrino power spectra relative to the default fluid approximation and reduces cold dark matter power-spectrum errors by up to an order of magnitude, with a 1–4% total runtime increase. They also present the first open-source Generalized Boltzmann Hierarchy (GBH) implementation, which integrates out the momentum dependence of relic perturbations. Combined with the DFA and tested on massive neutrinos, the GBH reproduces the matter power spectrum to better than permille accuracy and cosmological parameter constraints to better than 0.05 sigma, at computational cost comparable to the standard implementation. The authors argue, rather than demonstrate here, that the GBH is particularly suitable for nonthermal relics with distributions that vary over time or parameter space. Both implementations are publicly available.

PublicThis work improves software calculations of how matter is distributed across the universe, rather than reporting new astronomical observations. The researchers added two methods to the CLASS cosmology program for handling components such as massive neutrinos. One method, the Dispersive Fluid Approximation, makes a fluid-based shortcut more accurate: in tests, it reduced errors in the calculated cold dark matter power spectrum by as much as a factor of ten while increasing total computing time by only 1–4%. The second method simplifies the equations by removing the need to track the particles’ momentum dependence explicitly. Used together and tested on massive neutrinos, the methods reproduced the matter power spectrum to better than 0.1% and cosmological parameter constraints to better than 0.05 standard deviations, at a computing cost comparable to the standard approach. The researchers suggest the second method could be especially useful for more complicated particle distributions; that broader usefulness is an argument, not a demonstrated result here. The software is publicly available.

Young explorerScientists use computers to work out how matter is spread around the universe. Some shortcuts make the computer faster but can make its answers less exact. These scientists made better ways to do the sums. In tests with particles called neutrinos, their new methods gave answers very close to the usual calculations without taking much more computer time. They shared their computer code so others can use it. This is a better way to calculate things, not a new discovery made by looking at the sky.

Toward a Complete Interpretation of Global 21 cm Absorption Signals Using the Radio CMB

Hannah Fronenberg

• Astrophysics of Galaxies

AstronomerThe authors propose combining the global 21 cm signal with the excess optical depth imprinted on radio-wavelength CMB anisotropies by resonant absorption in high-redshift neutral hydrogen. Unlike the global brightness temperature, this optical depth depends on the gas spin temperature alone, potentially breaking the cold-gas versus excess-radio-background degeneracy and isolating the radio background temperature without astrophysical modelling. Forecasts for four interferometric configurations indicate that a compact 55 × 55 array of 6 m dishes observing for 4000 hours could detect an EDGES-like optical depth at 4.2σ; fiducial cosmic dawn histories would require roughly ten times more collecting area. These are sensitivity forecasts, not detections. Global-signal measurements remain challenged by Galactic foregrounds, ionospheric effects, and instrumental systematics.

PublicRadio signals from the era of the first stars could reveal how those stars heated the surrounding gas. But even a convincing detection can be ambiguous: an unusual absorption signal, such as the one reported by EDGES, could reflect colder gas or a stronger radio background. The researchers propose separating these explanations by also measuring how hydrogen absorbs patterns in the cosmic microwave background at radio wavelengths. Together, the two measurements could reveal the radio background temperature without modelling the astrophysics of the first stars. Their forecasts suggest that a compact array of 55 × 55 dishes, each 6 metres across, observing for 4000 hours could detect the absorption effect expected for an EDGES-like case at 4.2σ significance. More standard cosmic-dawn histories would need roughly ten times the collecting area. This is a proposed method, not a new detection, and foreground emission, Earth's ionosphere, and instrument effects remain obstacles.

Young explorerScientists want to learn about the first stars by listening for radio signals from long ago. One signal can be puzzling: is the gas colder, or is there more radio light behind it? The researchers suggest checking a second clue—how the gas blocks some leftover light from the early universe. Using both clues could help tell the difference. Their calculations suggest a big group of radio dishes might spot this second clue if it is strong enough, but they have not measured it yet.

Cosmological lensing as a jump process

Galymzhan Baltabay, Ville Vaskonen

AstronomerThe authors develop a jump-process description of the joint probability distribution of lensing convergence and shear in the Born approximation. For independent lenses, they solve a compensated Kolmogorov-Feller equation in Fourier space and extend the treatment to clustered lenses through their two-point correlation function. Fourier-Hankel inversion gives the joint distribution of convergence and shear magnitude and hence the magnification distribution, including its high-magnification tail, without sampling noise. These distributions train an updated FLUMEN emulator for likelihood-based inference across cosmologies. As forecasts rather than observational constraints, samples of 10,000 Roman supernovae, 100,000 Rubin supernovae, 300 Einstein Telescope standard sirens, and 12 LISA standard sirens are estimated to constrain sigma_8 to 4.8%, 5.1%, 8.5%, and 19%, respectively, with all other cosmological parameters fixed.

PublicMatter between us and a distant source can bend its light, changing its apparent shape and brightness. This study develops a mathematical method for calculating the probabilities of these gravitational-lensing effects, treating successive lenses as separate changes along the path. The method includes a treatment of clustered lenses and calculates the distribution of magnification, including rare, very large magnifications, without sampling noise. The authors use these calculations to train an updated FLUMEN tool for comparing cosmological models. They forecast that specified samples of supernovae and gravitational-wave sources from Roman, Rubin, the Einstein Telescope, and LISA could measure how strongly matter is clumped, with estimated precision ranging from 4.8% to 19%. These are projections, not measurements, and assume that the other cosmological parameters are fixed.

Young explorerStuff in space can bend light like a lens, making faraway things look brighter or stretched. The researchers made a new way to calculate how likely different amounts of bending and brightening are, even very big ones. They used those calculations to teach a computer tool. They think future studies of exploding stars and ripples in space could use this tool to learn how clumpy the universe is. That is a prediction, not something they have measured yet, and it assumes other facts about the universe stay fixed.

Cosmological tests of chameleon dark energy with dark sector coupling

Jia-Qi Wang, Zong-Kuan Guo, Shao-Jiang Wang

• High Energy Physics - Phenomenology

AstronomerRecent DESI BAO measurements favor a matter density parameter different from that preferred by Planck CMB observations; combined with supernova data, they suggest an evolving dark energy equation of state crossing w = -1. This study constrains a chameleon model in which a canonical scalar field nonminimally coupled to dark matter drives late-time acceleration. At early times, the field evolves under its potential and coupling, with an effective mass much larger than the Hubble parameter. The dark-energy-to-dark-matter transfer case improves the best-fit χ² by 7.25 relative to ΛCDM, comparably to the reverse-transfer case. Joint sampling of both coupling directions favors a nonzero interaction at 3.3σ within this model. Modified dark matter evolution yields an effective dark energy equation of state crossing w = -1 near z ≃ 0.5 without introducing a phantom field; this is a model-dependent interpretation, not a direct detection of energy transfer.

PublicMeasurements of cosmic expansion from DESI and observations of the early universe from Planck favor different amounts of matter. Together with supernova data, these observations suggest that dark energy may change over time. The researchers test a possible explanation in which a field responsible for dark energy exchanges energy with dark matter. A version transferring energy from dark energy to dark matter fits better than the standard cosmological model, with a similar improvement for transfer in the opposite direction. Considering both directions together, the analysis favors an interaction at a statistical level of 3.3 sigma within the tested model, rather than establishing that such an exchange occurs. The model can make dark energy's inferred behavior cross a key dividing value, w = -1, without introducing a phantom field.

Young explorerMeasurements of space give scientists clues that do not quite agree about how much matter the universe has. Scientists tested an idea in which dark energy, linked to space growing faster, can trade energy with dark matter. This idea fits the observations better than the usual model, but that does not prove the trade really happens. In their model, the trade can make dark energy seem to change as the universe grows.

UNIONS: Red and blue alignments of DESI DR1 galaxies

R. Paviot, C. Murray, M. Kilbinger+9 more

• Astrophysics of Galaxies

AstronomerThe study measures intrinsic alignments by cross-correlating DESI DR1 spectroscopic samples with UNIONS galaxy shapes over up to 2400 deg², fitting three-dimensional galaxy–galaxy and galaxy–shape multipoles with NLA and TATT models. BGS, LRG, and ELG samples are split by colour and stellar mass. Halo masses are measured through galaxy–galaxy lensing for red BGS galaxies and extended to LRGs using the resulting stellar-to-halo mass relation. Red galaxies show strong radial alignment, but its amplitude is not a single power law over halo masses of 6 × 10^11–3 × 10^13 h⁻¹ solar masses: it is nearly flat at low mass and rises steeply above a break at 1.3 × 10^13 h⁻¹ solar masses. Massive blue BGS galaxies show tangential alignment at 3.3σ, described by the authors as the most significant nonzero blue-galaxy alignment detection to their knowledge. Low-mass blue BGS galaxies and ELGs are consistent with zero alignment. At current precision, the data do not favour TATT over NLA. These measurements address an important systematic in weak-lensing cosmology.

PublicGalaxies can have preferred orientations of their own, complicating studies that use gravitational lensing to investigate the universe. By combining DESI galaxy data with UNIONS measurements of galaxy shapes, researchers measured how these orientations depend on galaxy colour and mass. Red galaxies show strong radial alignment. Its strength changes little in lower-mass dark matter halos, then increases steeply above a characteristic halo mass, rather than following one simple trend. Massive blue galaxies in the BGS sample instead show a sideways, or tangential, alignment detected at a statistical significance of 3.3 sigma. The authors describe this as the strongest detection of blue-galaxy alignment known to them. Lower-mass blue BGS galaxies and the emission-line galaxy sample show no clear alignment signal, though that does not establish that their alignment is exactly zero. The measurements cannot currently distinguish between the two alignment models tested.

Young explorerGalaxies are huge groups of stars, and they do not always point in random directions. The researchers found that red galaxies tend to line up pointing inward, while some big blue galaxies tend to line up sideways. They did not find a clear pattern for some other galaxies. These patterns matter because they can make it harder to learn about space by looking at galaxy shapes.

OCCAMS: A Multi-Task Learning-Based Investigation of the CMB Power Spectra

Ankit Mandal, Rahul Shah, Md. Wali Hossain+3 more

• Instrumentation and Methods for Astrophysics
• Machine Learning

AstronomerThe study tests variational autoencoders with 5, 6 or 7 latent variables, trained through multi-task learning on CLASS-generated CMB TT, TE and EE spectra over multipoles 2–2500. No cosmological model is built into the network, although its training spectra are simulated. Fits are compared with Planck 2018 data using chi-squared, AIC, BIC and Bayesian evidence; latent–parameter correspondence is assessed after training using normalised mutual information. Across three reconstruction-loss configurations and two weighting strategies, four of six combinations improve from 5 to 6 variables but not beyond, and 6 variables are best or nearly best in five combinations. This supports a six-variable representation within the tested setups, matching the number of free parameters in the standard approach rather than establishing a universal minimum. Semi-automated weighting gives clearer disentanglement, whereas completely automated weighting has higher evidence at 5 and 6 variables. The latent variables associated with τ and A_s share almost no information, consistent with large-scale polarisation separating these parameters. The results support a compact, data-driven parametrisation, with a trade-off between interpretability and fit.

PublicResearchers tested whether a neural network could describe patterns in the cosmic microwave background without having a cosmological model built into its design. They trained it on computer-generated temperature and polarisation spectra, then compared its fits with Planck 2018 measurements. They tried representations with five, six and seven hidden variables—adjustable quantities the network learns. Six worked best or nearly best in five of six tested setups; adding a seventh generally did not improve the fit. Six is also the number of free parameters in the standard cosmological approach, but matching that count does not mean the network independently recovered the same physical quantities. One training strategy made the learned variables easier to interpret, while another scored better by Bayesian evidence for five and six variables. The study supports a compact description of these patterns, with conclusions limited to the approaches tested.

Young explorerScientists taught a computer to copy patterns in very old light from space. First it practised with patterns made by another computer. Then they checked its answers against real measurements. They let it use five, six or seven hidden knobs to make the patterns. Six knobs worked best, or almost best, in most of their tries. That does not mean six knobs will always be enough. Some ways of teaching also made the knobs easier to understand.

An Empirically Calibrated [C II] Luminosity-Halo Mass Relation for Line Intensity Mapping

Oliver Jeong, Martin White

• Astrophysics of Galaxies

AstronomerThis study constrains the [C II] intensity-mapping power spectrum using a double-power-law halo mass–luminosity relation calibrated solely on [C II] observations, rather than scaling relations from other regimes or simulations. Inputs are mean intensities from tomographic cross-correlation at 0.4<z<4.2 and luminosity-function measurements and limits near z=0 and at 4.3≲z≲8. The four parameters are fitted independently at z=4.5 and 5.5 without assuming evolution, and jointly across 0<z<7, with attention to modeling-dependent uncertainty. The inferred power-spectrum shape is well constrained: clustering peaks exceed the shot-noise floor by factors of 45 (23–93) and 64 (38–112), with clustering–shot-noise crossings near k=0.37 and 0.44 h Mpc⁻¹, respectively. Amplitudes remain substantially less certain: 0.5–0.6 dex for clustering and 0.7–0.9 dex for shot noise. The model indicates that the signal originates in halos accessible to current galaxy surveys, hosting Lyman-break galaxies and Lyα emitters, with luminosity-weighted bias of 4–5. These are data-calibrated inferences, not direct measurements of the high-redshift power spectrum.

PublicAstronomers want to map the early universe using light emitted by ionized carbon in star-forming galaxies. A key question is whether these maps will reveal how galaxies cluster, rather than mainly fluctuations caused by individual emitters. This study uses existing carbon-line observations to constrain a model linking a galaxy’s carbon emission to the mass of its surrounding halo. The model indicates that, at two early epochs, the clustering signal should rise well above the fluctuations from individual sources on some spatial scales. The predicted pattern is better constrained than its overall strength, which remains substantially uncertain and depends on modeling assumptions. The analysis also suggests that the signal comes from halos hosting galaxy populations accessible to current surveys. It is a prediction constrained by existing observations, not a direct detection of that early-universe clustering pattern.

Young explorerScientists want to make a map of faraway galaxies using a special kind of light. They used light already studied to build a model of what the map might look like. The model suggests that groups of galaxies should make a clearer pattern than the speckles from separate galaxies. But scientists are still unsure how strong the light in that map will be.

Field-level inference under pressure: the information content of the thermal Sunyaev-Zel'dovich field

Carmen Embil Villagra, Adrian E. Bayer, William R. Coulton+6 more

AstronomerThis simulation-based study compares field-level CNN inference with angular power spectrum and Minkowski functional (MF) constraints for the highly non-Gaussian tSZ field. Using 10,000 simulated Compton-y maps, the authors jointly vary the cold dark matter density fraction Ωc, clustering amplitude σ8, and electron pressure profile parameters P0 and β to represent astrophysical uncertainty. They report the first field-level tSZ analysis and the first application of simulation-based inference to its MFs. The CNN yields tighter constraints than the conventional summaries in noiseless simulations. With realistic Simons Observatory-like noise after component separation, however, the combined MFs and power spectrum give constraints comparable to the CNN. These simulation results motivate applying both approaches to real data; they are not constraints from observations.

PublicThe thermal Sunyaev–Zel’dovich sky signal contains information about the universe that a standard measure of its patterns, the angular power spectrum, does not fully capture. Researchers tested ways to extract that extra information using 10,000 simulated maps, varying both properties of dark matter and uncertain descriptions of electron pressure. They compared a neural network that analyzes whole maps with simpler, interpretable measures of map shapes and patterns. In simulations without noise, the neural network gave tighter estimates of the model parameters. When noise resembling that expected for the Simons Observatory was included, combining the simpler measures performed about as well as the neural network. The findings suggest promising ways to analyze future real data, but the tests used simulations rather than observations.

Young explorerScientists made 10,000 pretend sky pictures on a computer to test ways of learning about the universe. They compared a computer trained to study whole pictures with simpler ways of counting shapes and patterns. When the pictures had no added noise, the trained computer gave more precise answers. When the pictures had noise like that expected in telescope maps, the simpler tools worked about as well when used together. This was a practice test with pretend pictures, not a finding from the real sky.

Circular Axion String Loop Simulations: Field Theory and Effective Description

Mathieu Kaltschmidt, Javier Redondo, Ivan Rybak+2 more

• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThe study benchmarks axion-string dynamics using the collapse of an initially static circular loop in Minkowski spacetime, rather than a cosmological network. It compares field-theory simulations of conventional complex-scalar and high-tension Klaer–Moore models with renormalised Nambu–Goto–Kalb–Ramond (NGKR) solutions over dimensionless tensions of approximately 3–100. Both approaches converge toward the Nambu–Goto limit with corrections proportional to inverse tension. However, NGKR gives a leading correction to the halving-time that is 20–35% larger than in the field-theory simulations; at high tension, the NGKR value agrees with an independent perturbative calculation to 0.2%. The late-time axion spectrum agrees with NGKR in the infrared but develops additional ultraviolet structure. The authors attribute this structure to collapse events, including an outgoing wave front carrying a sizable energy fraction and the loop’s rebound. These controlled results provide a benchmark for understanding radiation from cosmological string networks, not a direct simulation of those networks.

PublicUsing simulations and mathematical equations, researchers studied how a circular axion-string loop shrinks and releases radiation. They chose a simplified setting without cosmic expansion to compare different descriptions of the same collapse. As string tension increased, the descriptions moved toward the same limiting behavior, but they still differed in the correction to the time needed for the loop to shrink by half. The radiation patterns agreed at long wavelengths, while the simulations showed extra structure at short wavelengths. The researchers interpret that structure as arising from events during collapse, such as an outward-moving wave carrying substantial energy or the loop bouncing back. This is a controlled theoretical test, not an astronomical observation, intended to improve understanding of more complicated cosmic string networks.

Young explorerScientists used computers and math to study a shrinking loop called an axion string. They compared different ways of describing how it shrinks and sends out waves. The answers were similar, but not exactly the same. Some extra wave patterns might come from the loop bouncing back or sending a wave outward. They studied this on computers, not by seeing a loop in the sky.

Primordial Gravitational Waves in Loop Quantum Cosmology: Regularization Ambiguities and Initial State Dependence

Mah Noor Jamil, Parampreet Singh

• General Relativity and Quantum Cosmology

AstronomerThe authors compute primordial tensor spectra across the bounce in standard loop quantum cosmology, mLQC-I, and mLQC-II, using hybrid and dressed metric prescriptions with a Starobinsky potential. The emergent de Sitter contracting branch of mLQC-I requires dedicated initial states: de Sitter modes for the dressed metric prescription and a Hankel-function solution for the hybrid prescription. For 60 and 65 inflationary e-foldings, the pivot-scale tensor-to-scalar ratio matches standard inflation with the same potential. The calculated r(k) cancels effects shared by the scalar and tensor sectors, varies slowly in the scale-invariant regime, and oscillates around the pivot value at smaller k. Oscillations adjacent to the scale-invariant regime are insensitive to adiabatic order, whereas lower-k peaks and spikes depend on it. For a fixed initial state, regularization dependence persists in the infrared, with long-wavelength modes retaining signatures of the bounce and pre-bounce branch. The authors propagate normalized spectra to CMB B-mode spectra and discuss observational prospects; these are theoretical predictions, not reported detections.

PublicThis theoretical study asks whether a cosmic bounce could leave traces in primordial gravitational waves. The authors calculate predictions for three versions of loop quantum cosmology, using two ways to describe fluctuations through the bounce. For two choices of inflation's duration, the predicted balance between gravitational-wave fluctuations and density fluctuations matches standard inflation at a reference scale. At longer wavelengths, that balance develops oscillations. Some features are insensitive to how the starting state is specified, while other peaks depend on that choice. The longest wavelengths also retain differences between the models' mathematical treatments of the bounce. The authors calculate how these predictions would appear in the cosmic microwave background's B-mode polarization and discuss prospects for observation, but report no detection of a bounce.

Young explorerCould the universe have squeezed down and then bounced into growing bigger? Scientists used math to explore that idea and work out what tiny ripples in space might look like. Some of their predicted wiggles change when they choose different ways for the universe to start, while others stay similar. They also worked out how the ripples might leave patterns in the universe's oldest light. These are ideas to look for, not signs of a bounce that anyone has found.

Inelastic Kinetic Decoupling in WIMP Leptogenesis: A Minimal Z₄ Model

An Liu, Hong-Hao Zhang

• High Energy Physics - Phenomenology

AstronomerThis theoretical study considers a minimal Z4-symmetric Standard Model extension with singlet Dirac dark matter χ and WIMP leptogenesis. Kinetic equilibrium is maintained mainly by inelastic χL ↔ χ̄Ψ conversion. A sizable mass splitting suppresses conversion more rapidly during cooling than in the near-elastic regime, enabling earlier kinetic decoupling even away from resonance. The authors derive an effective momentum-transfer rate from the full inelastic collision operator and solve coupled Boltzmann equations for the abundance, dark matter temperature, and B−L asymmetry. Early kinetic decoupling can substantially alter the relic abundance, although annihilation-induced heating can mitigate this near resonance. Changes to the asymmetry require production to overlap appreciable kinetic disequilibrium; the largest scan deviations occur mainly for x_lep ≳ x_cd. After the authors' constraints are imposed, asymmetry production typically ends before chemical decoupling, leaving the final asymmetry essentially unchanged. They also generate photon spectra with Pythia and evaluate the Fermi-LAT dwarf-spheroidal likelihood, but the abstract reports no indirect-detection outcome.

PublicThe researchers study a proposed dark matter particle whose annihilations could create an imbalance between leptons and their antiparticles in the early universe. Their calculations explore when dark matter stops exchanging energy efficiently with its surroundings. In this model, a larger mass difference between particles involved in that exchange makes it shut down earlier as the universe cools. Solving equations for the evolving particle population and temperature shows that this earlier loss of thermal contact can substantially change how much dark matter remains. Heating from annihilations can reduce that effect near a resonance. The lepton-related imbalance can also change if it is still being produced during this loss of thermal contact. However, after applying their constraints, the authors find that production typically ends early enough to leave the final imbalance essentially unchanged. This is a theoretical study, not a detection of dark matter; the abstract describes a gamma-ray comparison but gives no result from it.

Young explorerScientists used math to explore an idea about dark matter, something we cannot see directly. In their idea, dark matter could stop sharing heat with other particles earlier as the universe cooled. That could change how much dark matter was left. It could also change a tiny imbalance between other particles and their opposites, but in the cases that passed their checks, that imbalance usually stayed almost the same. They have not shown that this idea is what really happened.

Elliptic master integrals and the one-loop cosmological wavefunction

Amara McCune, Matthew D. Schwartz

• High Energy Physics - Theory

AstronomerThis theoretical study uses a bootstrap approach to compute exactly the one-loop triangle wavefunction coefficient for a conformally coupled scalar. Although its master integrals are elliptic, the elliptic periods cancel, leaving the flat-space wavefunction coefficient expressible in dilogarithms. The authors attribute the cancellation to the loop-integrand residue on the elliptic sector being a flat-space amplitude rational in loop momentum. The one-loop box behaves differently: it is not polylogarithmic even with one external leg at each site. Its threshold discontinuity involves elliptic integrals, for which the authors provide closed-form expressions. For the special case of regular-tetrahedron momenta, K3-surface periods enter the box loop integrand. These are exact mathematical results, not observational findings.

PublicCalculations describing particles in cosmological theories can contain unusually complicated mathematical functions. This theoretical study shows that those functions sometimes cancel unexpectedly. Using an exact calculation, the researchers find that a triangle-shaped one-loop contribution has a flat-space expression built from simpler functions called dilogarithms, despite expectations that elliptic functions would be needed. They explain the cancellation through a connection to particle-scattering mathematics. A related box-shaped contribution does require more complicated mathematics: elliptic integrals appear in its behavior at a threshold. For one special arrangement of momenta, its underlying calculation also contains mathematical quantities associated with a K3 surface. The work concerns theoretical calculations rather than measurements of the universe.

Young explorerScientists use maths to study tiny particles and the universe. They worked out a difficult calculation drawn like a triangle. Some tricky pieces canceled out, making the answer simpler than expected. But a calculation drawn like a box still needed trickier maths. This was a discovery about calculations, not something seen through a telescope.

Constructing likelihoods for a non-Gaussian gravitational-wave background

Tore Boybeyi, Vuk Mandic, Joseph Romano

• General Relativity and Quantum Cosmology
• High Energy Astrophysical Phenomena
• Instrumentation and Methods for Astrophysics

AstronomerThis methodological study reformulates searches for the non-Gaussian stochastic gravitational-wave background from stellar-mass compact binaries using the characteristic function of data from multiple detectors. The background’s non-Gaussianity reflects its origin in a finite number of individual mergers. The authors show that existing searches emerge as limiting cases and that alternative approximations to the characteristic function can yield new searches, providing a systematic route to approximate sufficient statistics. They illustrate the framework with an exactly solvable toy model; the abstract reports neither an observational detection nor demonstrated performance on realistic data.

PublicThe combined gravitational waves from a finite number of mergers involving compact objects of stellar mass do not form a perfectly Gaussian background. This paper presents a mathematical framework for searching for that background in data from several detectors. It connects existing search methods as special cases and shows how different mathematical approximations can be used to construct new ones. The authors illustrate the approach with a simplified model that can be solved exactly, rather than reporting a detection or establishing how well it works on real observations.

Young explorerWhen very small, heavy objects in space join together, they make ripples in space. Ripples from many such events can mix together. The researchers made a new math recipe for looking for that mixture with several detectors. Their recipe connects older ways of searching and offers ways to make new ones. They tried the math on a simple pretend example, not on real signals from space.

Unifying stochastic and deterministic signals: a practical search for the intermittent binary black-hole background

Tore Boybeyi, Vuk Mandic, Joseph Romano

• General Relativity and Quantum Cosmology
• High Energy Astrophysical Phenomena
• Instrumentation and Methods for Astrophysics

AstronomerThe authors propose a likelihood-based search for the intermittent gravitational-wave background from individually unresolved stellar-mass binary black-hole mergers. This background is expected to exist but has not yet been detected. The method unifies model-agnostic cross-correlation and deterministic template-based searches through a truncated likelihood ratio, marginalized over merger extrinsic parameters. It represents two-detector data using approximate sufficient statistics: higher-order cross-moments weighted by generalized overlap reduction functions. The authors show that almost all Bayesian evidence and population information comes from merger-induced inter-frequency correlations captured by these higher-order terms, making likelihoods that neglect those correlations suboptimal. Validation on one year of simulated Advanced LIGO data indicates that a catalog-informed analysis combining detected and unresolved mergers can infer the peak of the BBH population's redshift distribution; this is not a detection or population measurement from observational data.

PublicMost black-hole mergers are too faint for today's gravitational-wave detectors to identify individually. Together, these weak events should produce an intermittent background of ripples in spacetime, but that background has not yet been detected. The researchers propose a new search that combines two existing approaches and exploits connections between different frequencies produced by the same merger. They find that these connections carry nearly all the statistical evidence and information about the merger population in their analysis. In a test using one year of simulated Advanced LIGO data, their method combined information from individually detected mergers and unresolved events to infer where the merger population's redshift distribution peaks. This demonstrates potential in simulations, not a discovery in actual detector data.

Young explorerWhen two black holes join together, they make ripples in space. Many of these ripples are too tiny for our detectors to notice one at a time. Scientists think the tiny ripples together make a hidden background, but no one has found it yet. These researchers made a new way to look for patterns in those ripples. It worked in a computer test with pretend detector data, but they have not yet found the hidden background in real data.

Are Black Hole and Cosmological Horizon Thermodynamics Necessarily Inequivalent?

Zachary J. Hoelscher

• High Energy Physics - Theory
• General Relativity and Quantum Cosmology

AstronomerThis theoretical study examines a conjectured generic inequivalence between cosmological-horizon and black-hole thermodynamics using a toy universe containing one non-rotating black hole and a positive cosmological constant. In the Nariai limit, where the black-hole mass reaches its maximum allowed value, the authors impose strict parity invariance on the background quantum field theory. Within a semiclassical treatment that neglects the exact Nariai equilibrium’s instability under quantum fluctuations, they find that an observer cannot readily distinguish the local physics near the two horizons. This does not establish generic equivalence. The authors propose that a consistent quantum-gravity description of such universes should give the leading semiclassical entropies of the two horizons related microscopic origins near this limit.

PublicCould the boundaries associated with a black hole and with an expanding universe have related physics? The authors explore this question mathematically in a simplified universe with one non-spinning black hole and a positive cosmological constant. They consider a special limit in which the black hole has its greatest possible mass and assume that the quantum-field physics is unchanged by mirror reflection. Under these conditions, and while ignoring an instability caused by quantum fluctuations, they find that an observer would have difficulty telling the physics near the two boundaries apart. This is a theoretical finding, not an observation, and it does not show that the boundaries are generally equivalent. The authors propose that a theory of quantum gravity should explain their entropies through related microscopic physics near this special limit.

Young explorerScientists used math to imagine a universe with one black hole. They compared what happens near the black hole’s edge with what happens near another kind of edge, called the universe’s horizon. In a very special version of their model, the physics near the two edges was hard to tell apart. But they made special rules and left out an effect that could upset the model. So this does not mean the two kinds of edge are always alike. They suggest that a deeper theory should explain how the two are connected.

Looking for gravitational waves with orbital dynamics: GUEST mission and the μHz band of Gravitational Waves

Diego Blas

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerThese proceedings review the use of gravitationally bound orbits as resonant detectors of microhertz gravitational waves and ultra-light dark matter. The microhertz band lies between the bands probed by pulsar timing arrays and LISA. It is expected to contain an extension of the signal recently found by pulsar timing arrays if that signal arises from a population of gravitational-wave sources; signals associated with the early Universe, primordial black holes or dark matter are also possibilities. The authors describe GUEST (Gravitational Universe Exploration with Satellite Tracking), a mission concept recently proposed to ESA’s F-class call: two dense, passive, retroreflector-covered spheres in highly eccentric Earth orbits, tracked by a global laser-ranging network. The abstract presents a review and mission proposal, not a new detection.

PublicThe authors explore a proposed way to search for gravitational waves in a frequency range between those studied by pulsar timing arrays and LISA. This range could reveal signals linked to the early Universe, primordial black holes or dark matter, but those possibilities are not detections. It should also contain a continuation of a signal recently found by pulsar timing arrays, provided that signal comes from a population of gravitational-wave sources. The paper reviews how gravitational waves or ultra-light dark matter could affect the orbits of gravitationally bound objects. It then describes GUEST, a mission concept proposed to the European Space Agency: two dense spheres with laser reflectors would follow highly elongated orbits around Earth while a worldwide network tracks them with lasers.

Young explorerScientists have an idea for looking for very slow ripples in space. They propose putting two heavy balls with special reflectors into long, stretched-out paths around Earth. People on the ground would use lasers to track how the balls move. Ripples in space, or a possible kind of invisible matter, could affect their paths. This is a plan for a search, not news that the balls have found anything.

Diamonds in the sky: the shape of gravitational waves from cosmic string cusps

Auclair Pierre, Gharib Chams, Steer Danièle

• General Relativity and Quantum Cosmology

AstronomerThis theoretical analysis revisits gravitational-wave emission from cosmic string cusps beyond the treatment of Damour and Vilenkin. The authors identify two features they believe have not previously been described: at a fixed frequency, the angular emission pattern is diamond-like rather than concentrated within a cone, and its maxima lie in two directions slightly offset from the cusp velocity. They explain these features using simplified examples and examine two limiting cases with enhanced total radiated power: a diamond stretched in a particular direction and vanishing higher-order derivatives at the cusp. They also statistically estimate the importance of these effects for a population of odd-harmonic loops. The abstract reports theoretical findings, not an observational detection, and gives no numerical estimates of the enhancements or their prevalence.

PublicA theoretical study explores how cusps on cosmic strings would emit gravitational waves. Its calculations indicate that, at any chosen frequency, the waves form a diamond-like pattern across the sky rather than being concentrated within a cone. The strongest emission points in two directions slightly away from the cusp’s direction of motion. The researchers also examine two special cases that increase the total power emitted and statistically estimate how important these effects are in one modeled population of string loops. These are theoretical findings, not observations of cosmic strings or their waves.

Young explorerScientists used math to study how a sharp point on a possible space string could send out ripples in space. Their work says the ripples would spread in a diamond-like shape, with the strongest ripples going a little to either side of where the point moves. They also studied special cases that could make more powerful ripples. They did not report seeing these strings or ripples in the sky.

Beyond χ²: Ensemble null tests for reliable scientific discovery

Adrian E. Bayer, David N. Spergel

• Methodology
• Instrumentation and Methods for Astrophysics
• Data Analysis, Statistics and Probability
• Quantitative Methods

AstronomerThe authors propose ensemble null tests that compare multivariate distributions against references from observations or simulations, preserving structure that averaging or scalar summaries can obscure. In cosmic microwave background simulations, these tests detect systematic effects missed by conventional chi-squared tests. Applied to Gaia data, they detect velocity asymmetry with sensitivity comparable to an informed search. A CRISPR-screen demonstration identifies a DNA-damage control mismatch and the cellular profiles driving it. These examples support the method’s potential to expose unrecognized systematic errors, but do not establish that it will detect every such error.

PublicHidden errors can slip through standard scientific checks, especially when many measurements are compressed into an average or a single score. The authors propose comparing the patterns of several measured properties together with reference patterns from observations or simulations. In simulated cosmic microwave background data, the method finds systematic errors missed by a conventional statistical test. In Gaia observations, it detects an asymmetry in velocities as sensitively as a search designed to look for it. In a gene-editing experiment, it also reveals a mismatch in a DNA-damage control and identifies the cell profiles responsible. These demonstrations suggest a broader way to check for unexpected problems, not a guarantee that all hidden errors will be found.

Young explorerSometimes scientists miss a problem when they turn lots of measurements into just one number. These researchers suggest looking at many parts of the measurements together and comparing their patterns with examples. Their check found hidden problems in pretend data about light from space. In real space data, it spotted a difference in how things were moving, and in a cell experiment it found that a comparison used for checking did not match. This could help scientists catch more mistakes, but it does not mean they can catch every mistake.

Analytic Gravitational Wave Spectrum in Next-to-Minimal Bouncing Cosmology

Changhong Li

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerThe authors propose next-to-minimal bouncing cosmology by adding an earlier evolutionary phase to the four-phase minimal model, whose single-power-law gravitational-wave spectrum faces tension with the ΔN_eff bound when interpreting the PTA signal and has required trans-Planckian bounce energies. Using their propagation-matrix method with improved matching, they derive an analytic broken-power-law spectrum. Its low- and high-frequency tilts depend on the equations of state of the added and original contraction phases, respectively; amplitudes also depend on transition-time scales. This flexibility permits a PTA-band signal alongside a scale-invariant or red-tilted high-frequency branch, offering a route to compatibility with ΔN_eff. For the scale-invariant branch, a pointwise benchmark gives ρ_s↓^(1/4) ≲ 2.65 m_pl, with m_pl the reduced Planck mass. This is a conservative comparison estimate: integration over the illustrative frequency interval yields a tighter bound, leaving an upper limit of order the reduced Planck scale. These are theoretical results, not observational confirmation of a bounce.

PublicThis study proposes a version of a bouncing universe, in which contraction is followed by expansion rather than a singular beginning. A simpler bouncing model struggles to explain the signal studied by pulsar timing arrays without conflicting with limits on extra radiation in the early universe or requiring extremely high bounce energies. Adding an earlier stage changes the predicted gravitational-wave background: its strength can vary differently at low and high frequencies. This could allow the model to account for a pulsar-timing signal without producing too much gravitational-wave radiation at higher frequencies. The work provides a theoretical possibility, not evidence that a cosmic bounce happened. Its example energy constraint remains around the reduced Planck scale, and the precise bound depends on how the predicted spectrum is evaluated.

Young explorerImagine the universe squeezing smaller and then bouncing out bigger. Scientists made a math model with one extra step before the bounce. That step could help the model explain a signal scientists are studying, without making too many tiny ripples in space at other frequencies. This is an idea they worked out with math, not proof that the universe really bounced.

Closing the Mass Window for Stupendously Large Black Holes

Christopher Gerlach, Yann Gouttenoire, Antonio J. Iovino+1 more

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerThe authors find that primordial black holes in the Stupendously Large Black Hole mass range, M ≳ 10^11 solar masses, would generate isocurvature perturbations exceeding current Planck cosmic microwave background limits. They therefore exclude these objects as a significant dark matter component, rather than ruling out their existence altogether.

PublicThe study concludes that black holes formed in the early universe, with masses roughly 100 billion times the Sun’s mass or greater, cannot make up a significant share of dark matter. Such black holes would produce variations in the universe’s composition larger than allowed by Planck observations of the cosmic microwave background, the light left over from the early universe. This does not rule out the existence of these black holes.

Young explorerScientists studied the idea that some of the universe’s hidden matter could be enormous black holes made when the universe was very young. They found that if these black holes made up a big share of the hidden matter, they would change the pattern in the universe’s oldest light too much. So these giant black holes cannot explain much of the hidden matter, though some could still exist.

From the Solar System to cosmological distances: a complete formalism for gravitational wave astrometry

Gabriele Perna, Nicola Bellomo, Vincenzo Roatti+1 more

AstronomerThe authors develop a framework for calculating gravitational-wave-background-induced astrometric deflections without the usual infinite-distance approximation. It accommodates sources at distances comparable to the gravitational-wave wavelength, such as asteroids, and nontrivial three-dimensional source distributions, such as Milky Way stars. The formalism offers a way to probe frequencies beyond those accessible to pulsar timing arrays, extending to millihertz waves also detectable by LISA. Harmonic signal-to-noise forecasts, including correlations between different probes, yield SNR greater than one for the cases considered. A Fisher forecast suggests potential constraints at the percent level for a flat background. These are theoretical forecasts, not an astrometric detection.

PublicA background of gravitational waves can alter both the arrival times of pulsar signals and the apparent positions of stars and asteroids. This study develops a way to calculate those apparent shifts while accounting for how far away the objects are, rather than treating them as infinitely distant. The approach could explore gravitational-wave frequencies beyond those probed by pulsar timing, reaching the millihertz range also detectable by LISA. For the cases studied, the authors forecast signals stronger than the estimated noise and suggest that a background with a flat spectrum could potentially be constrained at the percent level. The work predicts possible measurement capabilities; it does not report a new detection.

Young explorerGravitational waves are ripples in space that can make stars and asteroids look as if they move a tiny bit. Scientists made a new way to work out these tiny shifts that pays attention to how far away each object is. Their calculations suggest that looking for these shifts could help scientists learn about the ripples. They have not spotted the shifts in this study; they are working out what future measurements might tell us.

Simultaneous determination of Hubble constant and cosmic baryon density: Forecasts for the synergy between FRBs and emerging probes

Peng-Ju Wu, Bo-Yang Zhang, Ji-Guo Zhang+3 more

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerThe study forecasts joint constraints on H0 and the cosmic baryon density Ωb by combining FRBs with probes having different degeneracy directions: GW standard sirens, strong-lensing time delays, or 21 cm intensity mapping. FRBs alone have a severe H0–Ωb degeneracy. Under nominal observational expectations, each pairing yields forecast precisions better than 1% on H0 and 1.5% on Ωb within ΛCDM. Precision degrades as dynamical-dark-energy model complexity increases. In a model-independent framework, FRB+GW and FRB+strong-lensing time delays achieve forecast precisions better than 1.5% and 3%, respectively. Optimistic observational scenarios would improve these forecasts significantly. These are prospective constraints, not observed resolutions of the Hubble tension or missing baryon problem.

PublicAstronomers face two puzzles: conflicting measurements of how fast the Universe expands and a shortfall in the ordinary matter accounted for nearby. Fast radio bursts could help investigate both, but their information alone cannot cleanly separate the expansion rate from the cosmic density of ordinary matter. This study forecasts how pairing bursts with gravitational waves, delays between strongly lensed images, or 21 cm radio mapping could overcome that limitation. Under expected observing conditions and the ΛCDM cosmological model, each pairing could measure the expansion rate to better than 1% precision and the ordinary-matter density to better than 1.5%. The forecasts depend on the cosmological model and observational assumptions; they do not establish that either puzzle has been solved.

Young explorerScientists want to know how fast the Universe is growing and where some hard-to-find matter is hiding. Quick flashes of radio waves give clues, but the clues get tangled together. This study says that combining those flashes with other kinds of space clues could help untangle them. The numbers describe how well future measurements might work, not puzzles already solved.

Diffusive dark fluids with Planck-2018 and DESI BAO DR2 Measurements

Shambel Sahlu, Amare Abebe

• General Relativity and Quantum Cosmology

AstronomerThe authors constrain a diffusive dark-fluid cosmology, in which energy transfers between two dark components, using Planck 2018 CMB measurements combined with DESI DR2 (2024) BAO data. They report H₀ = 67.27 (+0.54/−0.55) and 68.35 (+0.31/−0.29) km s⁻¹ Mpc⁻¹. They quote respective discrepancies of 1.90σ and 1.72σ relative to the Planck value of 67.4 ± 0.5 km s⁻¹ Mpc⁻¹, although the abstract does not explain the calculation of those significances or distinguish the fits yielding the two estimates. They also compute scale-dependent density contrasts and matter power spectra to examine interaction effects relative to ΛCDM. These are model-based constraints and calculations, not a direct detection of energy transfer; the abstract does not establish a resolution of the H₀ discrepancy.

PublicThe study tests a model in which two dark components of the universe exchange energy through diffusion. Using measurements of the cosmic microwave background and patterns in the distribution of matter, the researchers estimate the universe’s expansion rate within this model. Their two estimates lie near the quoted Planck reference value. They also calculate how the proposed energy exchange would affect the growth and distribution of cosmic structure, comparing it with the standard cosmological model. The work tests an idea against observations; it does not show directly that this energy exchange occurs or establish that disagreements over the expansion rate have been solved.

Young explorerScientists tested an idea that two invisible parts of the universe might pass energy between them. They used clues from very old light and patterns in where things are in space to work out how fast the universe could be growing. They also calculated how this sharing might change the way matter gathers into clumps. It is an idea they are checking, not something they have proved is happening.

Probing non-Gaussianity during reheating with SIGW in the LISA band

Gabriele Perna, Guillem Domènech

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study examines how non-standard reheating evolution modifies the scalar-induced gravitational-wave spectrum while accounting for primordial non-Gaussianity. The authors find characteristic spectral features associated with choices of w and c_s^2, and argue that reheating dynamics can suppress or enhance the signal, affecting its detectability. Fisher forecasts explore different w values and scans over signal amplitude and central frequency to assess detection prospects for interferometers such as LISA. These are model-dependent predictions and forecasts, not reported detections.

PublicThe researchers investigate whether the Universe’s evolution during an early period called reheating could leave distinctive patterns in gravitational waves generated by primordial fluctuations. Their calculations account for departures from a simple Gaussian statistical pattern in those fluctuations. They predict that different reheating conditions could strengthen or weaken the wave signal and change its spectrum. Forecasts explore whether an interferometer such as LISA could detect it, depending on the model and the signal’s strength and characteristic frequency. The study does not report an observed signal.

Young explorerThe very young Universe may have made tiny ripples in space. Scientists used maths to explore how an early time called reheating might change those ripples, making them stronger or weaker and giving them different patterns. They think a detector called LISA might be able to notice some of these patterns, but this study has not found the ripples.

Synergy between CSST and future gravitational-wave detectors: Probing primordial black holes by cross-correlating dark sirens with galaxies

Ya-Nan Du, Ji-Yu Song, Jing-Fei Zhang+1 more

• Astrophysics of Galaxies
• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerThis forecast tests whether GW clustering bias can statistically distinguish mergers of astrophysical black holes from those of primordial black holes (PBHs), whose environments and biases are expected to differ. The study cross-correlates the CSST photometric galaxy survey with mock GW catalogs for two future networks: ET2CE, comprising the Einstein Telescope and two Cosmic Explorer detectors, and BDET2CE, which adds the space-based baseline Decihertz Interferometer Gravitational-Wave Observatory. CSST combined with 10 years of ET2CE observations is forecast to reveal a PBH contribution when PBHs account for more than about 40% of the total merger rate; BDET2CE lowers the forecast threshold to about 20%. Sharper sky localization preserves small-scale clustering information otherwise erased by positional errors. These mock-catalog results suggest a promising, largely independent statistical route to identifying PBHs, not an observed detection.

PublicBlack holes formed from stars and primordial black holes are expected to merge in different cosmic environments. Researchers explored whether comparing the locations of gravitational-wave events with the distribution of galaxies could distinguish these populations statistically. Using simulated event catalogs, they forecast that the Chinese Space-station Survey Telescope combined with 10 years of observations from the future Einstein Telescope and two Cosmic Explorer detectors could reveal a primordial contribution if it exceeds about 40% of all mergers. Adding a proposed space-based gravitational-wave observatory lowers the forecast threshold to about 20%, because more precise event locations preserve patterns on smaller scales. This is a forecast for future observations, not evidence that primordial black holes have been found.

Young explorerWhen black holes join together, they send out ripples in space. Scientists think black holes made from stars and black holes from the early universe may join in different kinds of places. They used pretend maps to test whether future tools could compare the ripple locations with where galaxies are. Their test suggests that tools that point more precisely could make it easier to spot signs of the early-universe black holes, if those black holes make up enough of the joining pairs. They have not found them with this test.

Consistency test of the large-scale structure with Bernardeau-Nishimichi-Taruya transform of the KiDS-Legacy survey

Shiming Gu, Ziang Yan, Ludovic van Waerbeke+10 more

AstronomerThe first KiDS-Legacy k-cut cosmic shear analysis uses the Bernardeau-Nishimichi-Taruya transform to localise lensing kernels and exclude selected physical scales. Removing k ≥ 0.33 Mpc⁻¹ from the pseudo-Cℓ data vector yields S₈ = 0.798 with uncertainties of −0.045/+0.045 when the Gaussian covariance component is calculated from the theoretical data vector. This agrees within 0.1σ with both the fiducial bandpower result and the uncut pseudo-Cℓ posterior, indicating no significant nonlinear astrophysical feedback bias at KiDS-Legacy precision. With the Gaussian covariance instead calculated from the observed data vector, the same scale selection yields S₈ = 0.717 with uncertainties of −0.046/+0.047. Additional cuts reveal a mild preference for lower S₈ on larger physical scales, with a maximum low- versus high-k difference of 1.80σ. Mock tests suggest that an interplay between covariance prescription and data vector, rather than either alone, may produce this behaviour. The analysis demonstrates k-cuts as both a systematics-mitigation tool and a pipeline diagnostic.

PublicResearchers analysed the subtle distortions of galaxy images in the KiDS-Legacy survey using a method that removes information from selected physical scales. This helps test whether complicated astrophysical effects on smaller scales distort estimates of S₈, a measure of matter clustering. When part of the statistical uncertainty model was calculated from theoretical predictions, excluding small-scale information gave S₈ = 0.798, with an uncertainty of about 0.045, closely matching earlier and uncut analyses. That indicates no significant bias from those astrophysical effects at this survey’s precision, not proof that such effects are absent. Calculating that uncertainty component from the observations instead gave a lower value, 0.717, with similar uncertainty. Further tests found a mild tendency for larger scales to favour lower values. Simulated-data tests suggest that the interaction between the measurements and the uncertainty calculation may explain this behaviour. The method can therefore help both limit astrophysical complications and check analysis procedures.

Young explorerScientists looked at tiny changes in how galaxies appear to learn how clumpy the universe is. They tried leaving out the smaller-scale details, which can be tricky to understand. With one way of working out how uncertain their answer was, they got almost the same answer as before. With another way, they got a less clumpy answer. Tests with pretend data suggest that how the measurements and calculations work together might matter. The tests offer a clue, not a sure explanation.

photo-3x2-pt: Cosmology from cosmic shear and galaxy clustering with a single photometric galaxy catalog

Takashi Hamana

AstronomerA joint HSC-Y3 photo-3x2-pt analysis combines angular power spectra of galaxy clustering, galaxy–shear cross-correlation, and cosmic shear. The authors use pseudo-Cℓ estimators and template deprojection to mitigate galaxy-density systematics. Bayesian inference accounts for intrinsic alignments, galaxy bias, magnification, baryonic feedback, and source-redshift uncertainties. Assuming a flat cold dark matter model, they obtain a 68% credible interval of 0.76 ≤ S8 ≤ 0.81, consistent with previous HSC-Y3 cosmic-shear analyses and approximately 25% tighter. Measured B-mode spectra are consistent with zero. Separately, tests on mock catalogs resembling HSC-Y3 support unbiased recovery of key cosmological and nuisance parameters within those tests.

PublicResearchers combined three related measurements from the Hyper Suprime-Cam year-3 galaxy catalog: galaxy clustering, weak-lensing distortions of galaxy shapes, and the relationship between the two. Assuming a flat cold dark matter model, they inferred a 68% credible range of 0.76 to 0.81 for the cosmological parameter S8. This agrees with earlier analyses using HSC-Y3 galaxy-shape distortions alone, but gives an approximately 25% tighter constraint. The analysis accounts for several astrophysical effects and measurement uncertainties. Separate tests using simulated catalogs showed that the method could recover the input values of important parameters without bias in those tests.

Young explorerScientists looked at patterns in where galaxies are and how their shapes look stretched. Putting these clues together helped them narrow down a number in their model of the universe. Their answer agreed with earlier work but was more precise. They also tried their method on pretend galaxy catalogs to check that it could find the numbers put into those tests.

Conformally Coupled Scalar- Field Dark Energy: Cosmological Dynamics with Early- and Late- Measurements

Shambel Sahlu, Abunie Gezahegn, Amare Abebe+2 more

• General Relativity and Quantum Cosmology

AstronomerThe study investigates a scalar-field dark energy model conformally coupled to dark matter, with an interaction proportional to the trace of the dark matter energy-momentum tensor. It adopts C(phi) proportional to (1+phi)^m, where m controls the coupling, to study the direction and magnitude of energy transfer. The authors compare conformally interacting dark energy, uncoupled scalar-field dark energy, and standard LambdaCDM using CMB, BAO, and Type Ia supernova data, with MCMC inference in COBAYA and a modified CLASS. The supplied abstract ends before reporting parameter constraints or model-comparison results, so it does not establish evidence for an interaction or a preference over LambdaCDM.

PublicThe researchers test a model in which dark matter and dark energy can exchange energy, with dark energy represented by a mathematical field. They compare this idea with a version without that interaction and with the standard cosmological model, using measurements of the early universe, galaxy-clustering patterns, and exploding stars. The proposed energy exchange is part of the model, not a reported detection. The supplied abstract cuts off before giving results, so it does not say which model fits best or how strong any exchange might be.

Young explorerScientists are testing an idea that two mysterious parts of the universe, called dark matter and dark energy, might pass energy to each other. They use measurements of space to compare this idea with other ideas. But this description stops before telling us what they found, so we cannot say whether the idea worked.

Tangled τ: Planck CMB Constraints on Flash Reionization

Param Upadhyay, Elisa G. M. Ferreira, Evan McDonough

AstronomerThe authors present the first Markov Chain Monte Carlo fit of a flash-reionization model within ΛCDM to Planck PR4 CMB temperature, polarization, and lensing data. This proposed transient high-redshift ionization episode is mildly preferred by PR4, but its redshift is broadly allowed and tightly correlated with the peak ionization fraction. At fixed flash redshifts of 20 and 25, the inferred peak fractions are respectively 0.24 (+0.13/−0.07) and 0.15 (+0.07/−0.05). Standard ΛCDM parameters show no significant shifts, and the total optical depth is not appreciably increased: τ = 0.061 ± 0.007 versus 0.059 ± 0.006 for standard tanh reionization. Replacing PR4 with PR3 removes the mild preference, yielding 95% confidence upper limits of 0.28 and 0.18 on the peak fraction at the same respective redshifts. The analysis therefore constrains a possible flash rather than establishing its occurrence.

PublicCould the early universe have experienced a brief extra episode in which electrons were stripped from atoms? The researchers tested this proposed “flash reionization” by fitting a cosmological model to Planck measurements of the cosmic microwave background. The PR4 data mildly favor a flash, but leave its timing uncertain and link that timing closely to how much gas was ionized. Including a flash does not significantly change the usual cosmological parameters or the inferred total optical depth, which describes the chance that background light scattered from free electrons. The conclusion also depends on the data release: using Planck PR3 instead gives only upper limits on the flash strength, rather than a preference for one. These results do not establish that a flash happened.

Young explorerScientists wondered if the gas in the very young universe had a short extra time when tiny electrons were knocked loose from atoms. They checked this idea using measurements of light left over from the early universe. One set of measurements gives a small hint that it might have happened, but another does not. Adding this possible event also leaves their usual picture of the universe almost unchanged. They have not shown that it really happened.

Cosmic Birefringence from Large Lepton Asymmetry

Kentaro Kasai, Ippei Obata

• High Energy Physics - Phenomenology

AstronomerThe paper investigates a vector Chern-Simons coupling between the neutrino current and photons as a possible source of isotropic CMB birefringence. In what the authors describe as the first analysis of neutrino-current-induced anisotropic birefringence, they find theoretically that lepton-number isocurvature fluctuations can produce an important large-scale signal, while gravitationally induced anisotropy dominates on small scales in comparison with the axion-like-particle scenario. They also show that a large lepton asymmetry generated by the Affleck-Dine mechanism can account for the observed isotropic birefringence. A possible connection to recently reported low helium-4 abundances in Subaru EMPRESS and ACT is discussed, rather than established.

PublicLight from the cosmic microwave background can carry clues to new physics through a rotation of its polarization, or the orientation of its light waves. This paper explores whether a proposed interaction between neutrinos and light could explain the observed rotation that is uniform across the sky. The authors calculate that this interaction could also produce variations across the sky: fluctuations in the balance of leptons and antileptons could matter on large scales, while gravitational effects would dominate on small scales. They show that a large imbalance produced by a mechanism called Affleck-Dine could explain the uniform rotation, but this does not establish that neutrinos are its cause. They also discuss a possible, unconfirmed connection to recently reported low helium-4 abundances.

Young explorerVery old light from space has a direction, a little like an arrow, that can turn as it travels. Scientists studied an idea that tiny particles called neutrinos might help turn those arrows. Their calculations suggest this idea could explain a turn seen across the sky and could make the turning different in different places. But they have not proved that neutrinos really caused it.

TDCOSMO 2026: A 3% measurement of the Hubble constant from strong lensing and stellar kinematics

TDCOSMO Collaboration, Simon Birrer, Michele Cappellari+26 more

AstronomerThe blind TDCOSMO-2026 analysis uses 11 strongly lensed quasars with measured time delays. Improvements include spatially resolved kinematics for nine systems, six from JWST-NIRSpec; JWST-NIRCam imaging replacing HST for three lens models; direct axisymmetric dynamical modeling of resolved data; and line-of-sight convergence estimates based on Euclid Flagship simulations. The baseline inference, combining TDCOSMO-2026 with a DES-Dovekie prior on Ωm in flat ΛCDM, is H0 = 71.1 (+2.4/−2.3) km s⁻¹ Mpc⁻¹, with 3.3% uncertainty accounting for the mass-sheet degeneracy. Consistent SLACS and SL2S samples improve the precision to 3.0%. Replacing DES-Dovekie with the DESI-DR2 BAO likelihood gives fully consistent results, and H0 remains consistent across the tested open ΛCDM and dark-energy extensions. Combining TDCOSMO+SLACS+SL2S with both DESI-DR2 and DES-Dovekie disfavors w = −1 at 2.3–2.5σ in the three tested dark-energy extensions, a modest indication rather than a definitive exclusion. Reported values include w0 = −0.88 (+0.04/−0.05) in wφCDM and w0 = −0.85 (+0.07/−0.06) in w0waCDM; wa = −0.48 (+0.46/−0.44) remains consistent with zero.

PublicResearchers used measured light-arrival delays from 11 strongly lensed quasars to estimate how fast the universe is expanding today. Their analysis combines observations with models, including improved motion measurements and imaging, and simulations used to estimate the effects of matter along the light’s path. Assuming a flat universe with a cosmological constant and cold dark matter, and using a matter-density constraint from the DES-Dovekie supernova sample, they infer an expansion rate of 71.1 (+2.4/−2.3) kilometres per second per megaparsec, with 3.3% uncertainty. Adding two other lens samples improves the precision to 3.0%. The expansion-rate estimates agree across the alternative cosmological models tested. Combining the lens results with supernova and baryon acoustic oscillation data gives a modest statistical preference against a cosmological constant in three tested dark-energy models. This is not a firm discovery that dark energy changes over time; the reported parameter describing its variation remains consistent with no change.

Young explorerScientists studied light from 11 very faraway bright objects. Gravity bends their light, and some of it arrives later than the rest. Those delays helped the scientists work out how fast the universe is growing. Their answers agreed when they tried different models. They also found a small hint that dark energy might not behave as simply as expected, but the hint is not strong enough to be sure.

TDCOSMO 2026: new insights on the Hubble tension from strong lensing time delays

TDCOSMO Collaboration, Simon Birrer, Michele Cappellari+26 more

AstronomerA blind hierarchical analysis of 11 multiply imaged quasars in the TDCOSMO-2026 sample yields H0 = 71.1 (+2.4/−2.3) km s⁻¹ Mpc⁻¹ in flat ΛCDM, using DES-Dovekie supernova constraints on Ωm. The analysis combines time delays, HST and JWST lens imaging, and axisymmetric dynamical models constrained by JWST-NIRSpec, VLT-MUSE, and Keck-KCWI spectroscopy. The reported 3% precision accounts for the mass-sheet degeneracy, and the measurement is independent of the local distance ladder. Combinations of independent late-universe probes remain in tension with the Planck CMB prediction when methods based on Type-Ia supernovae, Cepheids, or the tip of the red giant branch are excluded individually. A no-supernova combination, substituting DESI BAO constraints on Ωm and adding independent non-supernova late-universe probes, gives 3.7σ tension with Planck; a combination excluding the local distance ladder entirely retains 2.7σ tension. These significance levels describe combined probes, not the quasar measurement alone.

PublicResearchers used 11 quasars whose light is split into multiple images by gravitational lensing to measure how fast the universe is expanding today. They combined differences in the images’ arrival times with detailed imaging and measurements of motion in the lensing galaxies. Assuming a flat cosmological model with a cosmological constant and cold dark matter, and using supernova data to constrain the matter content, they obtained a Hubble constant of 71.1 (+2.4/−2.3) kilometres per second per megaparsec, about 3% precision. This measurement does not rely on the local distance ladder. When combined with other independent late-universe measurements, the disagreement with the prediction from Planck observations of the early universe persists even when selected measurement methods are removed. A combination using no supernova data differs from Planck by 3.7 standard deviations; excluding the local distance ladder entirely leaves a 2.7-standard-deviation difference. These checks support the persistence of the disagreement but do not establish its cause.

Young explorerThe universe is getting bigger. To help measure how fast, astronomers watched light from 11 very faraway bright objects. Gravity makes their light take different paths, so we see more than one picture of each object, with the light arriving at different times. Those timing differences helped the astronomers estimate how fast space is stretching. Their answer still has some uncertainty and depends on their model of the universe. When they put it together with other measurements, it still did not quite match the answer predicted from light left over from the early universe—even when they left out some measuring methods. This study does not tell us why the answers differ.

A cosmological intercept tension in local distance ladders

Haotian Dong, Marek Biesiada, Zhoujian Cao+1 more

AstronomerUsing Pantheon+ data, the authors test consistency between Type Ia supernovae in Cepheid hosts and the Hubble-flow supernova sample in forward and backward directions. Within flat ΛCDM, they impose Planck-CMB priors on one sample, infer the supernova absolute-magnitude calibration, and transfer it to the other; perfect alignment would recover the input Hubble constant. Redshift corrections based on the Manticore-Local peculiar-velocity reconstruction shift the forward H₀ estimate from 74.30 (+1.18/−1.20) to 71.37 (+1.23/−1.18) km s⁻¹ Mpc⁻¹, and the backward estimate from 60.83 (+0.98/−0.97) to 63.25 (+0.95/−0.93) km s⁻¹ Mpc⁻¹, both toward the input CMB constraint. The magnitude–redshift intercept discrepancies fall from 6.8σ to 3.9σ and from 7.3σ to 4.3σ, respectively. Accounting for volumetric bias further reduces the residual discrepancy to approximately 1.7σ. These model-dependent consistency checks indicate partial alleviation, not a definitive resolution of the Hubble tension, and motivate further scrutiny of velocity modeling, sample selection, and calibration systematics.

PublicAstronomers use a distance ladder to estimate how quickly the universe is expanding, but its results disagree with estimates based on the cosmic microwave background. This study checks whether two stages of the ladder—Type Ia supernovae in galaxies containing Cepheid stars and a more distant supernova sample—give consistent answers. Using Pantheon+ data and assuming a flat ΛCDM cosmological model, the researchers transfer a calibration between the samples in both directions. Corrections for galaxies’ local motions, based on a reconstruction of those motions, move both inferred expansion rates closer to the microwave-background input. The statistical mismatches shrink from 6.8σ and 7.3σ to 3.9σ and 4.3σ. Accounting for an additional effect called volumetric bias reduces the remaining discrepancy to about 1.7σ. The analysis suggests that local motions and sampling effects matter, but does not establish that the broader expansion-rate disagreement is solved.

Young explorerScientists use bright exploding stars to help measure how fast the universe is growing. But different ways of measuring do not quite agree. This team checked whether two steps in one measuring method fit together. Galaxies have their own motions as well as moving with the growing universe. When the team used a model to account for those extra motions, the answers fit better. Accounting for another effect in how the galaxies are sampled made the remaining mismatch smaller still. That is encouraging, but it does not prove the whole puzzle is solved.

Supernova cooling from neutrino-devouring dark matter

Yugen Lin, Chih-Ting Lu, Ningqiang Song

• High Energy Physics - Phenomenology

AstronomerThe authors investigate fermionic dark-matter production through a neutrino-devouring process inside core-collapse supernovae, where the resulting energy loss could cause excessive cooling. Using state-of-the-art supernova simulation data and the full time evolution, they derive interaction limits rather than report a dark-matter detection. Their exclusions reach DM-electron scattering cross sections of 10^-51–10^-58 cm² for keV–MeV masses and DM-nucleon cross sections of 10^-49–10^-56 cm² for 0.1–100 MeV masses, potentially improving on direct-detection limits by several orders of magnitude. Complementary cosmological, astrophysical, collider, and direct-detection constraints cover larger cross sections. The analysis also excludes almost the entire parameter window in which electron-coupled fermionic dark matter in the keV–MeV range supplies an order-unity fraction of the dark matter.

PublicAn exploding star can help test ideas about dark matter: if hypothetical particles carry away too much energy, they could make the star cool excessively. This study uses supernova simulations, including how the explosion evolves over time, to investigate a process in which neutrinos are consumed to produce a proposed type of dark-matter particle. The authors derive limits on how strongly these particles could interact with electrons and with protons or neutrons. For some particle masses, the limits can be several orders of magnitude stronger than those from direct searches. They also rule out nearly all of the studied possibilities in which light, electron-coupled particles of this type make up a substantial fraction of dark matter. These are simulation-based constraints on a hypothetical particle, not a discovery of dark matter.

Young explorerWhen a big star explodes, it loses heat. Scientists wondered whether tiny, invisible particles called dark matter could take away too much of that heat. They used computer models of exploding stars to test this idea. Their work says that many possible ways these particles might behave would cool the star too much, so those possibilities are ruled out in their study. They did not find dark matter.

False Alarm Rates in Detecting Gravitational Wave Lensing from Astrophysical Coincidences: Insights with Model-Independent Technique GLANCE

Aniruddha Chakraborty, Suvodip Mukherjee

• General Relativity and Quantum Cosmology
• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerThis study quantifies astrophysical false positives in model-independent searches for gravitational-wave lensing: unrelated, unlensed events can mimic a lensed pair. Applying GLANCE to a simulated population of merging binary black holes, the authors find that approximately 0.01% of event pairs can be falsely classified as lensed at a lensing threshold signal-to-noise ratio of 1.5, with apparent inter-event delays of roughly 1,000 days or more. They characterize the false alarm rate across source masses, delay times, and lensing magnification parameters to assess where GLANCE can confidently identify lensed pairs at current LIGO sensitivity. These are simulation-based findings, not a confirmed lensing detection. The authors anticipate that the technique will help assess lensing false alarm rates for next-generation detectors observing larger source populations.

PublicMassive objects between a gravitational-wave source and Earth can bend the waves, potentially making one event appear as multiple detections. But two unrelated events can also look like such a repeat. The researchers tested this source of confusion by running the GLANCE search method on simulated mergers of pairs of black holes. At the chosen detection threshold, about 0.01% of event pairs could be mistakenly labeled as lensed, with apparent gaps of about 1,000 days or longer. They also examined how false alarms depend on the black holes’ masses, the time between events, and the lensing magnification, using current LIGO sensitivity. This is a simulation study, not an observed lensing discovery; the method may also help evaluate false alarms in future detectors.

Young explorerWhen black holes come together, they make ripples in space. Something very heavy in the way can bend those ripples, so one event might seem to happen more than once. Scientists used pretend black-hole events on a computer to test a way of spotting these repeats. They found that two different events could sometimes fool the test. They did not find a real bent-ripple event in this study.

Dark Matter Interpretation of the Super-Kamiokande Antineutrino Excess and Predictions for JUNO

Alessandro Granelli, Silvia Pascoli, Salvador Rosauro-Alcaraz

• High Energy Physics - Phenomenology

AstronomerSuper-Kamiokande reports a small excess of electron antineutrino events around 20 MeV in its search for the diffuse supernova neutrino background. The authors interpret the excess as a possible signature of thermal dark matter with a mass of tens of MeV and predominantly neutrino-producing s-wave annihilation. They note that this mass scale fits naturally within rich dark-sector extensions of the Standard Model. This is a proposed interpretation, not a dark matter detection; neutrino experiments, including JUNO, are expected to test it in the coming years.

PublicSuper-Kamiokande has reported a small excess of electron antineutrinos—particles it was looking for as part of a search for neutrinos from supernova explosions throughout the universe. The authors suggest that the excess might instead be a sign of dark matter particles annihilating mainly into neutrinos. Their proposed dark matter particles would have masses of tens of MeV. The excess does not establish that dark matter is responsible. Experiments including JUNO are expected to test this explanation in the coming years.

Young explorerA big particle detector called Super-Kamiokande found a few more tiny particles than expected. Scientists suggest they might come from dark matter, a mysterious kind of matter. In this idea, two dark matter particles meet and turn into other tiny particles. But nobody knows yet if that is what happened. Other experiments, including one called JUNO, will help check the idea.

LIGO, LISA and Ultralight Axion-like Dark Matter

Lawrence M. Krauss

• High Energy Physics - Phenomenology

AstronomerThis theoretical reassessment of interferometric searches for axion-like dark matter through induced photon birefringence treats the interplay of DM coherence length, arm length, and detector transfer function within the Krauss (2019) framework. It distinguishes cancellation when the coherence length exceeds the arm length from random-walk suppression when it is shorter. For LIGO, the Fabry-Pérot arm-cavity response sharply peaks near the cavity free spectral range, reproducing Nagano et al.; a naive single-pass estimate substantially overstates sensitivity. For LISA with previously proposed polarization-sensitive modifications, the projected accessible range is approximately 4 × 10^-19–4 × 10^-16 eV. With realistic optical-metrology noise, the projected coupling reach is a few × 10^-13 GeV^-1 or below, improving on the CAST bound over most of the band by up to about two orders of magnitude. Annual and sidereal Galactic-DM-wind signatures are discussed as candidate-signal discriminants. Local substructure with anisotropic velocity dispersion could shift and enhance sensitivity in particular mass windows. These are sensitivity calculations and interpretations, not a reported ALP detection.

PublicSome proposed dark-matter particles could subtly change the polarization, or orientation, of light. This study recalculates how gravitational-wave detectors might search for that effect, accounting for how consistently the dark-matter field behaves across a detector and how the detector processes light. For LIGO, treating light as making only one trip along an arm makes the prospects look substantially better than the detailed calculation supports. For LISA, proposed changes that make it sensitive to polarization could allow searches that outperform the existing CAST limit by up to about a factor of 100 over part of the relevant particle-mass range. That is a prediction, not a detection. The authors also discuss how daily and yearly patterns could help distinguish candidate signals, and how local dark-matter structure could change the search sensitivity.

Young explorerScientists wonder whether invisible stuff called dark matter might gently change how light wiggles. They worked out how giant light-measuring machines could look for this clue. Their calculations say one machine, LIGO, would have a harder time than a simple guess suggests. Another, LISA, might search well if changed in a proposed way. This study did not find dark matter; it worked out how to look for it.

Wave Optics Effects from Gravitational Wave Propagation Through Dark Matter Halos

Annamalai P. Shanmugaraj, Roland Haas, Erik Schnetter+1 more

• General Relativity and Quantum Cosmology

AstronomerThe authors present a numerical scheme for evolving linearised plane gravitational waves through stationary, spherical structures in weak and strong gravity, retaining all 10 components of the Einstein equations for Gaussian, NFW and Burkert potentials. The simulations address the breakdown of geometric optics when structure sizes are comparable to the wavelength and show that scattering depends strongly on the potential distribution, not just lens mass. In the Gaussian models, waves do not follow null geodesics in either gravity regime; for the strong-gravity Burkert model, the wave's convexity reverses upon exit. Differences from linearised scalar-wave predictions are of order unity inside the central potential but fall to a few percent after passage. These are simulation results, not detections; future GW detectors and pulsar timing arrays could potentially detect such signatures and constrain dark matter spikes or halos.

PublicGravitational waves are often treated as following ray-like paths, but that approximation can fail when they encounter structures about as large as their wavelength. Using computer simulations, the authors find that the waves' scattering depends not only on how much mass a structure contains, but also on how that mass is distributed. In some models, the waves depart from the paths predicted by the ray approximation; in one strong-gravity model, the curvature of the wave reverses as it leaves the structure. A simpler wave model differs substantially from the gravitational-wave calculation near the structure's centre, but the difference falls to a few percent after the waves pass through. These effects have not been reported as observations here. Future gravitational-wave detectors and pulsar timing arrays might detect them, potentially revealing information about dark matter structures.

Young explorerGravitational waves are ripples in space. Scientists used computers to see what happens when these ripples pass through big clumps of matter. In their pretend computer worlds, the ripples changed in different ways depending on how the matter was spread out, not just how much there was. The scientists have not seen these changes in real waves yet. Future tools might spot them and help us learn about dark matter, a kind of matter we are trying to understand.

No evidence of vorticity production from irrotational turbulent gravitational collapse yet

Axel Brandenburg, Evangelia Ntormousi, Jennifer Schober

• Fluid Dynamics
• Astrophysics of Galaxies

AstronomerDirect numerical simulations test whether gravitational collapse generates the vorticity thought necessary for small-scale dynamo action. The calculations omit magnetic fields and adopt a barotropic equation of state, keeping pressure and density gradients parallel; vorticity production is therefore restricted to viscous effects and vortex dynamo-type amplification. Within the parameter space accessible at the available resolution, these effects are linked to the initial irrotational turbulence rather than induced by collapse. The authors attribute some earlier barotropic numerical evidence to subgrid-scale modeling and do not reproduce it in direct simulations. They still expect vorticity production and associated small-scale dynamo action at sufficiently large Reynolds numbers, especially with baroclinic effects, but do not demonstrate that regime here.

PublicWhen matter collapses under gravity, it gains energy that might drive turbulent motion and help strengthen magnetic fields. But the magnetic-field mechanism considered here is thought to need swirling motion, whereas collapse mainly produces motion without swirl. In computer simulations with no magnetic field and a simplified relationship between pressure and density, the researchers found that swirl production was linked to the starting turbulence, not generated by collapse itself. Some earlier evidence for collapse-driven swirl appears to have come from how simulations modeled unresolved motions. The findings apply only to the conditions these simulations could resolve; the authors still expect swirl and magnetic-field amplification under other, more demanding conditions.

Young explorerWhen gravity pulls stuff together, it moves faster. Scientists wondered whether that could also make little swirls that might help magnetic fields grow. In their computer experiments, the swirls were connected to how the stuff moved at the start, not to gravity pulling it together. These experiments had limits, so the scientists think swirls could still grow in other conditions.

Theoretical Aspects of Direct Waves in Kerr Black Holes: Pole-Splitting Method for Ringdown Analysis

Nao Nakamoto, Naritaka Oshita, Hiroki Takeda

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThis theoretical study describes direct waves (DWs) from a particle plunging into a Kerr black hole in the extreme-mass-ratio regime. Their source-driven complex frequency reflects the particle’s orbital motion, including within the ergoregion. The authors identify the DW contribution from the quasinormal-mode (QNM) pole sector as part of dynamical QNM excitation. Apparent horizon-mode poles cancel at every order of a consistent near-horizon expansion of the trajectory, homogeneous radial solution, and complete point-particle source, assuming geodesic motion near the horizon. This does not exclude transient DWs near the ergosurface or potential barrier. A new pole-splitting method separates the transfer function into QNM-pole and non-pole components without the frequency-dependent time shift introduced by QNM filtering. For simulated quasi-circular plunges into moderately and rapidly rotating black holes, the non-pole waveform’s frequency and decay rate agree qualitatively with theoretical predictions over finite intervals. These findings suggest, but do not establish observationally, that DWs could probe the ergoregion and gravitational redshift.

PublicCould waves produced by a small object falling into a spinning black hole reveal its surroundings? This theoretical study explores direct waves, whose frequency and fading reflect the falling object’s motion. The calculations show that certain apparent wave contributions associated with the horizon cancel, provided the object follows a freely falling path near the horizon. Brief direct-wave signals could still arise elsewhere nearby. The researchers developed a mathematical method to separate simulated waveforms into contributions associated with the black hole’s characteristic oscillations and a remaining component. For some simulated plunges, that remaining component’s frequency and fading roughly match the theory for limited periods. This is not an astronomical detection, but it supports the possibility of using direct waves to study the region around spinning black holes and gravitational redshift.

Young explorerScientists used math and computer-made waves to study a tiny object falling into a huge, spinning black hole. They asked whether the waves could tell us about the strange space nearby. Part of the computer-made signal behaved roughly as their math suggested, but only for a short time. They have not seen this happen with a real black hole yet.

Neutrino Direct Simulation Monte Carlo: Accurate modeling of out-of-equilibrium decaying cosmological relics

Kensuke Akita, Miguel Escudero, Oleksii Ihnatenko+1 more

• High Energy Physics - Phenomenology

AstronomerThis computational study extends Neutrino Direct Simulation Monte Carlo (νDSMC) to nonstandard cosmologies in which decaying relics inject energy at MeV temperatures and drive neutrinos out of equilibrium. The framework jointly evolves relics, neutrino spectra, the electromagnetic plasma, and cosmic expansion, coupled to Big Bang nucleosynthesis. It includes direct and inverse relic decays, neutrino flavor conversion, quantum statistics, and pion production by energetic neutrinos. Across the scenarios tested, the authors report excellent agreement with independent quantum-kinetic or quasi-classical Boltzmann solutions. They find that νDSMC accommodates more physical processes and is substantially faster for strongly nonthermal neutrino populations, making broad parameter scans practical. For large departures from equilibrium, momentum-averaged approximations can predict the wrong sign of the change in the effective number of neutrino species and substantially incorrect primordial nuclear abundances. These are simulation and method-comparison results, not observational evidence for decaying relics.

PublicThe researchers improved a computer model of a possible early universe in which hypothetical leftover particles decay and release energy, disrupting the usual energy distribution of neutrinos. Their model follows how these particles, neutrinos, other matter, and the universe’s expansion interact, and predicts consequences for cosmic radiation and the first light elements. In the cases tested, it closely agrees with independent calculations and runs substantially faster when neutrino energies are far from their equilibrium distribution. The study also finds that shortcuts that average over neutrino momenta can give seriously misleading predictions, sometimes even reversing the predicted direction of a change in cosmic radiation. The work provides a tool for testing possible new physics; it does not establish that these hypothetical decays occurred.

Young explorerScientists made a better computer model of the universe when it was very young. They asked what might happen if some leftover particles broke apart and gave energy to tiny particles called neutrinos. Their tests showed that taking too many shortcuts can give wrong answers about the first kinds of atoms. This is a computer study, not a discovery that those leftover particles were really there.

Magnetically Charged Black Holes from Grand Unified Theory

Tanmay Vachaspati, Anja Wachowitz

• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThis theoretical scenario links magnetic monopoles predicted by Grand Unified models to the collapse of transient, biased domain walls produced by a weakly broken discrete symmetry. For a range of the symmetry-breaking parameter, collapse can form magnetically charged extremal black holes lighter than approximately 1 kg; Hawking evaporation and Schwinger production of monopole pairs are expected to prevent their survival to the present. For still smaller parameter values, black holes may instead have astrophysical masses above 10^15 g and sub-extremal magnetic charge, with Q approximately 10^8 for the authors’ canonical parameters. The residual monopole energy density also depends on the symmetry-breaking parameter and can satisfy all observational constraints when that parameter is sufficiently small. These are theoretical possibilities, not reported detections.

PublicSome theories that unify particle physics predict magnetic monopoles and temporary structures called domain walls in the early universe. This work explores how those walls could collapse into magnetically charged black holes. Depending on how weakly a particular symmetry is broken, the black holes could weigh less than about a kilogram or more than a billion tonnes. The lighter ones are not expected to survive until today because of processes that remove their mass and magnetic charge. For sufficiently weak symmetry breaking, the amount of leftover monopoles could also fit all observational limits. The abstract describes theoretical possibilities, not observed black holes or monopoles.

Young explorerImagine temporary walls in the very young universe falling in on themselves. Scientists describe a theory in which this could make black holes with a special kind of magnetism. Some could be tiny and would not be expected to last until today; others could be much heavier. This is an idea about what might happen, not something the scientists say they have seen.

Hot off the Stacks: X-rays in Romulus25, Part I - Comparisons to Observations from eRosita

N. Nicole Sanchez, Andrew Benson, Gwen Rudie+7 more

AstronomerThe study forward-models 0.5–2.0 keV emission from hot CGM gas (T > 10^6 K) in more than 750 Romulus25 galaxies with 10.0 < log(M*/M☉) < 11.5, using pyXSIM and SIXTE. Stacked surface-brightness profiles in six stellar-mass bins are generally brighter than the observational comparisons, particularly in the inner CGM. Mean CGM X-ray luminosities also exceed observations across most of the mass range, although the Milky Way-mass end is in relative agreement with observations and most of the other simulations considered: EAGLE, TNG, and SIMBA. Because Romulus25 lacks metal-line cooling, the authors also test a zero-metallicity emission model. This reduces mean luminosities by nearly an order of magnitude and improves agreement with observations, especially at Milky Way masses; it is an alternative emission prescription, not a measurement of CGM metallicity.

PublicThe researchers used the Romulus25 computer simulation to study the hot gas surrounding more than 750 galaxies. They created mock X-ray observations and compared the predicted brightness with real observations. The simulated gas was generally too bright, especially closer to the galaxies, although average total X-ray output agreed relatively well for galaxies around the Milky Way’s mass. The team also tested an emission model with no elements heavier than helium, motivated by the simulation’s lack of cooling through metal emission lines. That choice lowered the predicted X-ray output by nearly a factor of ten and improved agreement, particularly for Milky Way-mass galaxies. This test does not establish that real galactic gas lacks heavy elements.

Young explorerGalaxies have very hot gas around them that shines in X-rays, a kind of light our eyes cannot see. Scientists made pretend X-ray pictures of galaxies in a computer and compared them with real pictures. Most of the pretend gas shone too brightly, especially near the galaxies. Galaxies about as big as our Milky Way were a closer match. When the scientists changed which ingredients could make the pretend gas shine, it became much dimmer and matched better. That was a computer test, not proof of what the real gas is made of.

Resolving the thermal component of stellar feedback with the "anchor-and-refine" scheme in galactic simulations

Chengzhe Li, Hui Li, Wei Cui+4 more

AstronomerThis simulation study introduces an anchor-and-refine supernova feedback scheme to preserve hot gas when galaxy-scale calculations cannot resolve supernova cooling radii. A host cell anchored near each star particle retains a thermal-feedback reservoir. Resolved events deposit all supernova energy thermally into that cell; otherwise, the host cell is refined and terminal momentum is deposited into neighboring cells. Idealized tests agree with high-resolution simulations, reproducing superbubble properties and retaining hot interiors without artificial cooling. In an isolated Milky Way-mass galaxy simulation, the scheme produces finer X-ray-emitting structures, a sharply defined X-ray-bright central mid-plane, and smoother star formation than pure hybrid feedback. Hot gas dominates outflow mass loading, with the mass-loading factor plateauing near 0.2 above z = 1 kpc. Phase decomposition indicates a steady, energy-driven hot wind, while cooler outflows weaken with height through radiative cooling and gravitational fallback. These simulation results support future galaxy-scale and cosmological zoom-in applications, rather than demonstrating performance in those broader settings.

PublicThe researchers developed a way to model how exploding stars heat and push gas in computer-simulated galaxies. Such simulations often lack the detail needed to keep the hot gas around young stars from cooling artificially. The new method preserves a hot-gas reservoir near simulated stars and adjusts how it adds heat and outward pushes according to the available resolution. In simplified tests, it agrees with more detailed simulations. In a simulated isolated galaxy with the mass of the Milky Way, it reveals finer structures in X-ray-emitting gas and makes star formation steadier than a comparison method. The calculations indicate that hot gas maintains a steady galactic wind, while cooler outflows weaken as they cool and fall back under gravity. These are simulation findings, not observations; broader applications remain future work.

Young explorerWhen stars explode, they can heat gas and push it through a galaxy. Scientists made a new way to show this in a computer galaxy, keeping hot gas from cooling too quickly by mistake. In their computer test, hot gas kept flowing outward, while cooler gas slowed down or fell back. This was a model, not a galaxy they watched.

Extra! Extra! X-ray Emission!: X-rays in Romulus25, Part II - Physical Drivers of X-ray Emission in the CGM

N. Nicole Sanchez, Andrew Benson, Gwen Rudie+4 more

AstronomerUsing Romulus25 simulations of L* galaxies, the authors find a strong correlation between hot CGM gas mass, defined by T > 10^5.5 K, and X-ray emissivity, with a secondary dependence on the hot gas's mean metallicity. They interpret these correlations using PIONEER zoom-in simulations of Milky Way-mass galaxies, which use genetic modification and the same physics as Romulus25. In these simulations, the combined energy injection from stellar and AGN feedback sets the hot CGM mass, while mean temperature and metallicity shape its soft X-ray spectrum: at fixed hot gas mass, metal-rich halos are brighter than metal-poor halos. The authors infer that metallicity may bias X-ray observations of Milky Way-mass galaxies; this is a simulation-based interpretation, not a demonstrated observational bias.

PublicComputer simulations suggest that the X-ray brightness of hot gas surrounding galaxies like the Milky Way depends on both how much hot gas is present and its composition. The researchers find that energy released by stars and active galactic nuclei together determines the amount of hot gas in their simulated galaxies. The gas's temperature and abundance of elements heavier than helium also affect its X-ray emission: for the same hot gas mass, gas richer in these elements appears brighter. This suggests that X-ray observations could favor galaxies with element-rich gas halos, rather than simply revealing which galaxies contain the most hot gas. The possible observational bias is inferred from simulations, not established by observations in this study.

Young explorerGalaxies can have very hot gas around them that shines in X-rays, a kind of light our eyes cannot see. Scientists made computer models of galaxies to learn why some of this gas shines more brightly. In their models, stars and active galaxy centers give energy to the gas. How much hot gas there is, how hot it is, and what it is made of all help decide how brightly it shines. Even the same amount of hot gas can shine differently if its ingredients change. That could make some galaxies easier to spot in X-rays, but the scientists have not shown that this happens in real observations.

Not so dead after all: young stars in the massive S0 NGC 3115

João P. V. Benedetti, Alexandre Vazdekis, Anna Ferré-Mateu+3 more

AstronomerSOAR/Goodman spectroscopy and U-band line-strength fitting reveal evidence for a small young stellar component in the massive isolated lenticular galaxy NGC 3115. Assuming a bulk stellar population plus constant star formation over the past 1 Gyr, posterior inference gives a central young stellar mass fraction of 0.69% with uncertainties of +0.09 and −0.15 percentage points, falling to zero beyond 1 kpc in the fitted model. The inferred component follows kinematic structure and is concentrated in the pressure-supported region. Alternative UV-bright models, including extreme horizontal branch stars, fit less well and require mass fractions the authors deem unphysical. The authors interpret the central component as residual star formation fueled internally, potentially by recycled stellar material; this fuel source is not directly established. They argue that similar gradients across early-type galaxies support ubiquitous residual star formation, although this study directly measures only NGC 3115.

PublicA galaxy that looks old and inactive in visible light may still contain a small population of young stars. By fitting models to spectra of the galaxy NGC 3115, researchers inferred that young stars account for about 0.69% of its central stellar mass, with the fitted contribution falling to zero beyond roughly 1,000 parsecs from the centre. This estimate assumes that the young population formed steadily over the past billion years. Models using other ultraviolet-bright stars instead gave poorer fits. The researchers suggest that material shed by existing stars could fuel this small amount of central star formation, but they have not demonstrated that source of fuel. They interpret the finding, alongside similar patterns in other early-type galaxies, as evidence that low-level star formation may be widespread in galaxies once thought inactive.

Young explorerNGC 3115 is a galaxy that looks as though it mostly has old stars. Scientists studied its light and used models to work out what kinds of stars might be there. Their best-fitting model says a tiny bit of the stars’ total weight near the middle belongs to young stars, with none needed farther out. They think old stars might give off material that helps make new stars, but they do not know for sure. Even a galaxy that looks quiet may still be making a few stars.

Ejected and Rejected: Strong Scatterings in Dense Star Clusters

Adam Distler, Nicholas C. Stone

• High Energy Astrophysical Phenomena

AstronomerThis theoretical study quantifies rare strong scatterings in collisional stellar systems, whose evolution is otherwise dominated by weak, small-angle encounters. For isotropic, spherically symmetric distribution functions representing globular and nuclear star clusters, the authors derive the exact differential rate distribution of velocity kicks, its boundaries, and approximate rate scalings. They extend the framework to approximate energy- and angular-momentum-kick rates in nuclear clusters and apply it to ejections and the cancellation of prospective extreme mass ratio inspirals (EMRIs). In some regimes, saturation of the strong-kick distribution and breakdown of the weak limit complicate ejection rates, likely enhancing loss cone shielding. The calculations also suggest that strong scatterings likely cancel a sizable fraction of proto-EMRIs, but the impact on the true EMRI rate remains to be established.

PublicIn dense star clusters, most gravitational encounters give stars small nudges, but rare close encounters can deliver much stronger kicks. This theoretical study calculates how often kicks of different sizes occur in idealized, spherical clusters with no preferred direction of motion. The authors then estimate changes in orbital energy and angular momentum to investigate objects being ejected and prospective extreme mass ratio inspirals—objects spiraling toward a much more massive companion—being disrupted before they develop. Their calculations suggest that strong encounters likely prevent a sizable fraction of these prospective inspirals. They also find that ejection rates become complicated in some circumstances, where weak-kick approximations break down. These are theoretical findings, not observations, and further work is needed to determine how much strong encounters change the actual inspiral rate.

Young explorerIn a crowded group of stars, gravity usually gives each star tiny nudges. Sometimes, a very close meeting gives a much bigger shove. The scientists used math to work out how often these shoves might happen. Their calculations suggest that big shoves could send some objects out of the group or stop many objects from slowly spiraling toward a much heavier partner. They still need to work out how much this changes the number of spirals that really happen.

Simulation-Informed Dust Masses in Typical 6<z<14 JWST Galaxies

Jed McKinney, Dhruv T. Zimmerman, Desika Narayanan+5 more

AstronomerDirect dust detections in typical z>8 galaxies remain untenable, although rest-frame UV/optical spectro-photometry suggests dust is present. Informed by cosmological zoom-in simulations with on-the-fly dust evolution, the authors develop a dust-mass estimator using stellar half-light radii and UV/optical attenuation. The method reproduces observed lower-redshift trends but diverges from Milky Way-based calibration factors by up to approximately 1.5 dex. Applied to observed JWST galaxies at 6<z<14, it yields inferred dust masses of approximately 10^3–10^5 solar masses, consistent with ALMA upper limits rather than direct dust detections. The findings suggest early supernova-driven dust enrichment followed by efficient grain destruction in hot gas. A tabulated calibration is provided for future dust-mass inference across stellar masses and redshifts.

PublicDust is suggested by the light from very distant galaxies, but directly detecting it in typical galaxies beyond redshift 8 remains out of reach. Guided by simulations that track how dust evolves, the researchers developed a way to estimate dust mass from a galaxy’s apparent stellar size and how much its ultraviolet and visible light is dimmed. The method matches observed trends in less distant galaxies, while its calibration can differ substantially from one based on the Milky Way. Applied to JWST observations of galaxies at redshifts between 6 and 14, it gives estimated dust masses of roughly 1,000–100,000 times the Sun’s mass. These are indirect estimates consistent with ALMA’s upper limits, not direct detections. The findings suggest that supernovae supplied dust early on and that hot gas later destroyed dust grains efficiently.

Young explorerSome very faraway galaxies seem to have dust because their light looks dimmed, but that dust is too hard to spot directly. Scientists used computer models to make a new way to guess how much dust there is, using how big the galaxies look and how much their light is dimmed. Their guesses fit the limits from other telescope observations, but they are not direct sightings of the dust. The work suggests that exploding stars may have supplied dust early on, and hot gas later broke many dust grains apart.

No Significant Excess in Typical Variability in CLAS+ Changing-Look AGN Candidates in Rubin DP2

Lilianne Nakazono

AstronomerRubin DP2 samples CLAS+ changing-look AGN candidates approximately 1,000–9,000 days after their comparison epochs, testing whether enhanced short-term optical variability persists after spectral transitions. Band-by-band comparisons with a photometrically quiescent quasar control detect no significant median peak-to-peak amplitude excess for turn-on, turn-off, or intermediate states in either of two bands, and no median absolute magnitude-change difference as a function of time lag. The r-band amplitude distributions are broader than the control distribution; only the intermediate-state broadening is formally significant after multiple-comparison correction. This may hint at a high-amplitude subpopulation, rather than a general enhancement in typical variability.

PublicThe study used Rubin observations to ask whether candidate galaxies with changing active centers keep flickering more strongly after changes in their spectra. Observed about 1,000–9,000 days after earlier comparison observations, these candidates showed no statistically significant increase in typical short-term brightness swings relative to a comparison group of quasars with quiet brightness behavior, in either of two color bands. Typical brightness changes also showed no detected difference as a function of the time between measurements. However, the range of brightness-swing sizes was wider in the r band. This widening was statistically significant only for candidates in an intermediate state after accounting for multiple comparisons. It could point to a subset with unusually large swings, but does not establish one.

Young explorerSome galaxies have bright centers that can change how they look. The researchers checked whether centers thought to be changing kept flickering more than a quieter group. They did not find a clear difference in the usual size of the flickers. But one group had a wider mix of small and big flickers in one kind of light. That might mean a few centers flicker extra strongly, but the researchers are not sure yet.

The Carousel Lens III: Joint lens convergence and source kinematic modeling

William Sheu, Xiaosheng Huang, Tania M. Barone+9 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe authors introduce a datacube-level forward-modeling component for the Carousel Lens, jointly parameterizing the lens convergence profile and the unlensed source’s line-of-sight velocity, velocity dispersion, and surface brightness. Spatially resolved kinematics provide additional ray-traceable constraints unavailable from imaging alone, while modeling [OII] emission isolates one source redshift and removes foreground lens and line-of-sight light contamination. Applied to deep VLT/MUSE observations of the quadruply imaged star-forming galaxy at z = 1.432, the framework yields an Einstein radius of 12.816 arcsec (+0.005/−0.007) and logarithmic slope γ = 1.412 ± 0.002. Their statistical uncertainties are approximately 2–2.5 times smaller than in the corresponding flat emission-line map model; this does not establish a comparable reduction in systematic uncertainty. The source shows strong rotation, lies confidently on the star-forming main sequence, and has an inferred central black hole mass of log(M_BH/M_sun) = 7.89 ± 0.51. Application to other sources and lens systems is a proposed extension, not a demonstrated result here.

PublicThe Carousel Lens magnifies and distorts a distant star-forming galaxy into four images. This study uses not just those images’ shapes and brightness, but also information about how gas moves across them. The researchers model the full set of spatial and spectral measurements from VLT/MUSE observations, focusing on an oxygen emission line to separate the distant galaxy’s light from contaminating light. Compared with a model using only the emission-line map, this approach reduces the statistical uncertainties in two lens properties by roughly a factor of 2–2.5. It does not show that systematic modeling uncertainties have been eliminated. The analysis also finds strong rotation in the distant galaxy, places it among typical star-forming galaxies, and infers a central black hole mass. The authors propose extending the method to other lensed sources.

Young explorerGravity can bend a faraway galaxy’s light so we see four pictures of it. Scientists studied those pictures and clues about how the galaxy’s gas moves. Using both helped them work out more precisely how the light was bent. They also found that the faraway galaxy is spinning strongly. Their answers still have some uncertainty.

Tidal shells as clocks of galaxy mergers and tests of cosmological models

Ivana Ebrová, Michal Bílek, Elisabeth Sola+2 more

AstronomerStellar shells are concentric, arc-like tidal features produced in galaxy mergers that encode information about merger histories and host gravitational potentials. Comparing observations with cosmological simulations, the authors find that simulations predict a substantial population of shells larger than 100 kpc, whereas such systems are rarely observed—a potentially important discrepancy, rather than an established failure of the simulations. Given the differing shell-system scales, they focus on merger histories, using a shell-identification method to estimate merger times for nearby massive prolate rotators and comparing these with simulated histories. The abstract reports no quantitative outcome of that comparison. Ongoing deep imaging with the Milankovic telescope aims to enlarge the observational sample for future studies.

PublicGalaxy mergers can leave concentric arcs of stars called shells, which preserve clues to the merger and the host galaxy’s gravity. This study compares observed shells with those in computer simulations. The simulations predict many very large shells, more than 100 kiloparsecs across in scale, but shells this large are rarely observed. This could signal an important mismatch between simulations and reality, though the abstract does not establish its cause. The researchers also estimate when mergers occurred in a sample of nearby massive galaxies that rotate around their long axes, and compare those estimates with simulated merger histories; no outcome of that comparison is given. Work with the Milankovic telescope is underway to expand the sample with deep images.

Young explorerWhen galaxies come together, they can leave curved trails of stars, like rings. These trails give scientists clues about what happened. Computer models predict many very big star rings, but scientists rarely see rings that big in real galaxies. They do not yet say why the two are different. They also use the rings to work out when galaxies joined together, and they are taking more pictures with a telescope so they can study more galaxies.

Turbulent gas-rich discs at high redshift: Chaotic orbits and rapid bulge formation at high gas fraction

Johan M. Villa-Alatorre, Joss Bland-Hawthorn, Thor Tepper-Garcia+2 more

AstronomerN-body/hydrodynamic simulations using the nexus framework indicate that bars emerging in high-redshift discs have different orbital characteristics from their low-redshift counterparts. Among bar-supporting orbits, the chaotic fraction exceeds 60% in models with gas fractions above 60%, but is close to zero for gas fractions at or below approximately 60%. In the 80% and 100% gas-fraction simulations, emerging bars collapse within approximately 1 Gyr into rotationally supported, oblate central bulges, soon after chaotic orbits become dominant. The gravitational potential steepens rapidly during this interval, and orbit integrations show that trajectories departing from the evolving mean field are more likely to be chaotic. The authors interpret these findings as evidence that rapidly evolving central potentials drive orbital chaos and that the bars subsequently collapse through violent relaxation. Identical radial profiles for particles of different masses provide supporting evidence for rapid relaxation. These are simulation results and a proposed physical interpretation, not direct observations of galactic bars collapsing.

PublicComputer simulations suggest that elongated stellar structures called bars can behave differently in gas-rich galaxies in the early universe than in galaxies closer to the present day. In models with more than 60% gas, over 60% of the orbits supporting the bar are chaotic; in models with roughly 60% gas or less, almost none are. In the simulations with 80% and 100% gas, the bars collapse within about a billion years, forming flattened, rotating central bulges. This happens soon after chaotic orbits become the majority. The researchers argue that the rapidly changing gravity near the centre makes the orbits chaotic and allows the bar to reorganize quickly. The simulated particles’ matching radial distributions across different masses support this interpretation, but the study does not directly observe this process in real galaxies.

Young explorerScientists made galaxies in a computer to see what happens to long groups of stars called bars. In some galaxies with lots of gas, the stars’ paths became hard to predict, and the bars changed into squashed, spinning lumps in the middle. The scientists think quickly changing gravity helps make this happen. This happened in their computer models; they did not watch real galaxies do it.

Unveiling the Shock-Excited Molecular Environment in the Orion Protostar HOPS 370

Somnath Dutta, Koshvendra Singh, Devendra K Ojha+6 more

AstronomerTANSPEC spectroscopy over 1.94–2.52 μm on the 3.6-m DOT reveals prominent H₂ ro-vibrational emission toward the embedded Class 0/I source HOPS 370, including 1–0 S, 2–1 S, and 1–0 Q transitions. The same-upper-level 1–0 Q(3) and 1–0 S(1) lines yield A_V = 23.24 ± 1.25 mag and A_K = 2.50 ± 0.13 mag. The 2–1 S(1)/1–0 S(1) flux ratio of 0.12 ± 0.01 supports thermal excitation and disfavors UV fluorescence as the dominant mechanism. Assuming optically thin emission and local thermodynamic equilibrium, the excitation diagram gives T_ex = 2078 ± 215 K and N(H₂) = (1.93 ± 0.93) × 10^20 cm⁻². The derived ortho-to-para ratio, 2.45 ± 0.21, lies below the high-temperature equilibrium value of 3 and is interpreted as evidence of substantial shock-driven thermal processing. Together, the diagnostics favor predominantly warm, shock-heated H₂, most likely associated with the protostellar outflow.

PublicNear-infrared observations of HOPS 370, a young star still deeply buried in surrounding material, reveal strong emission from hydrogen molecules. Comparing two emission lines allowed the researchers to estimate how much intervening material dims the light. Other line comparisons favor gas heated by shocks rather than emission driven mainly by ultraviolet light. Assuming the emission is optically thin and the molecules are in local thermal equilibrium, the team inferred a temperature of about 2,080 kelvin and estimated the amount of molecular hydrogen along the line of sight. The relative abundance of two forms of molecular hydrogen also suggests substantial heating by shocks, although it remains below the expected high-temperature equilibrium ratio. The combined evidence points to warm gas most likely associated with material flowing outward from the forming star, rather than establishing that connection directly.

Young explorerA baby star called HOPS 370 is hidden deep inside a dusty blanket. Scientists looked at infrared light from tiny hydrogen molecules nearby. The light gives clues that the gas is very hot, probably because shocks have heated it. The scientists think this hot gas is likely part of material streaming away from the baby star, but they are not completely sure.

Age-Resolved Vertical Motions in the Milky Way Warp: A Localized Enhancement in Intermediate-Age Populations

Xiaoyue Zhou, Xiaodian Chen, Haifeng Wang+3 more

AstronomerUsing APOGEE DR19 spectroscopy, the authors estimate ages for 222,355 red giants and combine Gaia astrometry with geometric distances to analyze 168,824 stars in five age bins spanning 0–10 Gyr. The warp-related radial vertical-velocity profile of the 0–2 Gyr population broadly agrees with those of classical Cepheids and young open clusters. At 9 ≤ R < 12 kpc, mean vertical velocities for the 2–4 and 4–6 Gyr populations exceed those of the youngest bin by 1.48 ± 0.46 and 1.49 ± 0.52 km/s, respectively. At R ≈ 12–13 kpc, however, the profiles of populations spanning 0–6 Gyr agree within uncertainties. The intermediate-age enhancement survives the reported robustness tests and may indicate smaller effective kinematic warp onset radii for those populations. Earlier perturbations combined with the present-day warp, or population-dependent vertical structure, remain possible explanations rather than established causes.

PublicThe Milky Way’s disk is warped, and comparing the motions of stars of different ages can help researchers understand its history. This study estimates ages for more than 222,000 red giant stars and analyzes the motions of about 169,000 of them using Gaia data and distance estimates. Between 9 and 12 kiloparsecs from the Galactic center, stars aged 2–6 billion years have average vertical velocities about 1.5 kilometers per second higher than stars aged 0–2 billion years. Farther out, around 12–13 kiloparsecs, the measurements show no clear difference among these age groups within their uncertainties. The younger stars also show a broadly similar warp-related motion pattern to other young stellar groups. The difference closer in persists through the authors’ checks, but its cause is uncertain: it could reflect where warp-related motion begins, the combined influence of past disturbances and today’s warp, or differences in how the stellar populations are distributed vertically.

Young explorerOur galaxy is a huge disk of stars, but it is bent instead of perfectly flat. Scientists compared how stars of different ages move up and down. In one part of the galaxy, a middle-aged group had a slightly higher average up-and-down velocity than a younger group. Farther out, they could not clearly tell the groups’ motions apart. The scientists checked the pattern, but they do not yet know exactly why it happens. Old disturbances, the galaxy’s bend today, or how the stars are spread above and below the disk might help explain it.

The Influence of Hubble Expansion on the Future Merger of the Milky Way and Andromeda

Yufan Zhou, Tianchi Zhang, Shihong Liao+3 more

• Cosmology and Nongalactic Astrophysics

AstronomerIdealized N-body simulations compare the future MW–M31 interaction under pure Newtonian, ΛCDM, and w0waCDM scenarios, varying galaxy masses and proper motions within current observational constraints. Hubble expansion has negligible effects at low M31 tangential velocities, especially for mergers within a Hubble time. Above 66.5 km/s, ΛCDM runs show noticeable merger delays relative to Newtonian runs and potentially different final outcomes, although the isolated-pair approximation and assumed expansion history break down in these cases. Delays are smaller in w0waCDM, and including M33 and the Large Magellanic Cloud reduces merger-time differences. The actual importance of expansion remains contingent on better determinations of galaxy masses and proper motions.

PublicComputer simulations explore whether the universe’s expansion could change a possible future merger between the Milky Way and Andromeda. Expansion makes little difference when Andromeda’s sideways motion is slow. With faster sideways motion, some simulations predict a later merger or even a different eventual outcome. Those cases also stretch the validity of treating the galaxies as an isolated pair and of the assumed expansion history, so they are not firm forecasts. Adding the galaxies M33 and the Large Magellanic Cloud reduces the timing differences. Better measurements of the galaxies’ masses and motions are needed to establish how much expansion really matters.

Young explorerOur Milky Way and another huge group of stars called Andromeda might someday join together. Scientists made computer models to see whether the universe growing bigger could change that. In the models, growing space hardly mattered when Andromeda moved slowly sideways, but it could make the galaxies join later when that sideways motion was faster. Adding two other galaxies made the difference smaller. The models are simplified and may not work well for some possible futures, so scientists still need to learn more before knowing what will happen.

GRAVITY-RESOLVE: A comprehensive image reconstruction tool for Galactic Center observations with GRAVITY

K. Abd El Dayem, N. Aimar, P. Amaro-Seoane+83 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors revise GRAVITY-RESOLVE, an image-reconstruction code for Galactic Center observations with ESO’s VLTI/GRAVITY, to improve depth, runtime, and joint reconstruction of spatially separate pointings. Applied to recent data including GRAVITY-faint mode, the code produces its first GRAVITY image reconstructed from visibility phases and amplitudes. A joint reconstruction of nine separately acquired 2025 datasets demonstrates near-infrared mosaicking over approximately 409.6 × 409.6 mas, or 3390 × 3390 AU. Point-source injection tests, rather than direct detections at the quoted threshold, yield an estimated limiting magnitude of m_K ≈ 20.0 within 25 mas of the field center for reconstructions using closure phases and visibility amplitudes. The authors report the discovery of two faint stars, S303 and S304, and a computational runtime reduction by a factor of at least approximately ten.

PublicResearchers have improved software that turns observations from GRAVITY, an instrument at ESO’s Very Large Telescope Interferometer, into near-infrared images of stars at the center of our galaxy. They combined nine separately collected datasets from 2025 into one image covering a region about 3,390 times the Earth–Sun distance on each side, and report discovering two faint stars, S303 and S304. Tests that added artificial stars to real data suggest the software can recover sources as faint as about magnitude 20 in the K infrared band near the image center; this is an estimated sensitivity, not a claim that every star that faint was detected. The revised software also cuts computation time by a factor of at least about ten, supporting further searches for faint stars.

Young explorerScientists made a computer program better at turning telescope clues into pictures of stars in the middle of our galaxy. They joined nine sets of observations into one bigger picture and found two faint stars, called S303 and S304. They also put pretend stars into the telescope data to test how faint a star the program might find. Those pretend stars were a test, not new discoveries. The improved program takes about one-tenth as much time as before, or even less.

The nature of the Norma arm as a bar-driven star-forming shock front

Hillary Davis, Joss Bland-Hawthorn, Thor Tepper-Garcia+2 more

AstronomerNew N-body and hydrodynamic simulations support an alternative interpretation of masers associated with young high-mass stars previously assigned to a Norma-arm segment extending from one end of the Galactic bar. The authors argue that these masers trace the bar’s Quadrant I shock front, or dust lane, rather than a spiral arm or the bar-supporting x1 stellar orbits. Conditional on this association, they infer bar semi-major and semi-minor half-lengths of approximately 4.3 ± 0.2 and 2.3 ± 0.2 kpc, an inclination angle of 20 (+5/−2) degrees, and a pattern speed ≲40 km s⁻¹ kpc⁻¹. This simulation-based interpretation implies a star-forming bar dust lane and favors a long, slow bar, while raising questions about the conventional spiral-arm picture.

PublicSome masers—associated with young, massive stars—have been used to trace what was thought to be part of the Milky Way’s Norma spiral arm. Using new computer simulations of stars and gas, the researchers argue that these masers instead mark a shock front along a dusty lane of the Galaxy’s central stellar bar. If that interpretation is correct, stars are forming in the bar’s dust lane. Matching the masers to the simulated shock front also suggests that the bar is long and slowly rotating. These conclusions depend on the proposed identification; they are not a direct confirmation that the masers belong to the dust lane, and they raise questions about the Milky Way’s spiral structure.

Young explorerOur galaxy has a bar-shaped group of stars in its middle. Scientists found clues near young, big stars that seemed to belong to one of the galaxy’s curling arms. Now, computer models suggest those clues might instead sit along a dusty edge of the bar, where stars are being born. If the models have the right idea, the bar is long and turns slowly. Scientists are still working out which picture is right.

Kinematic methods of spiral nature identification: limitations and applicability

Valeria S. Kostiuk, V. D. Zozulia, A. A. Marchuk+3 more

AstronomerThe authors assess phase reversal and velocity harmonic dominance as diagnostics of spiral structure using toy models and mock data from TNG50 simulations. For bar resonances, phase reversal gives reliable corotation estimates only when the bar is aligned with the disc minor axis. Its spiral-arm results are not consistently reliable, motivating use alongside another kinematic diagnostic. Velocity harmonic dominance more robustly distinguishes density-wave, kinematic, and dynamic spirals, though some orientation sensitivity remains; rotation-curve uncertainties have little effect on its results. An illustrative application to observations of NGC3938 suggests multiple spiral modes, consistent with recurrent modes, but this interpretation rests on indirect evidence. The authors propose combining independent tests to classify observed spirals; validation of the strategy's predictive power awaits application to a larger sample.

PublicAstronomers still debate how galaxies form their spiral arms. This study tests two ways of interpreting galactic motions, using simplified models and simulated observations. One method, called phase reversal, can be misleading: its reliability depends on viewing orientation, and it should not be used alone to study spiral arms. The other, velocity harmonic dominance, more reliably separates several competing explanations for spiral patterns, although orientation still matters somewhat. When applied to observations of the spiral galaxy NGC3938, the methods suggest that multiple spiral patterns may be present, consistent with a picture in which such patterns recur. That interpretation is based on indirect evidence, not a definitive identification. The authors propose combining several independent checks and testing this approach on more galaxies.

Young explorerSome galaxies have big, curvy arms, but scientists are not sure how those arms form. They tried two ways of studying how a galaxy moves, first using pretend galaxies made with models and computer simulations. One way could give misleading answers depending on how the galaxy was turned. The other worked better, but was not perfect. They also studied a real galaxy called NGC3938. It might have several spiral patterns, but the clues do not prove that. The scientists suggest using several checks together and trying them on more galaxies.

Chemodynamical Study and Evidence for Hot Compact Companions to Blue Straggler Stars in Berkeley 31

Deniz Cennet Çınar, D. Bisht, Ing-Guey Jiang+2 more

AstronomerA study combining Gaia DR3 astrometry, Gaia-ESO DR5.1 spectroscopy, and multi-wavelength photometry identifies 329 probable members of Berkeley 31. Derived parameters include a distance of 6024 ± 181 pc, E(B−V) = 0.148 ± 0.047 mag, [Fe/H] = −0.36 ± 0.04 dex, mean [α/Fe] = 0.21 ± 0.04 dex, and systemic radial velocity of 57.89 ± 0.08 km/s. The isochrone age, 3.7 ± 0.2 Gyr, agrees with the chemical-clock estimate of 3.72 ± 1.42 Gyr. About 38% of main-sequence stars are unresolved binary candidates with mass ratio q ≳ 0.5. The authors identify 62 blue stragglers and two yellow-straggler candidates; 48 blue stragglers and both yellow-straggler candidates are newly reported. Multi-wavelength SEDs, including Swift/UVOT data for 28 blue stragglers, reveal clear ultraviolet excesses in two objects, consistent with a hot white-dwarf companion and a pre-extremely-low-mass white-dwarf companion, respectively. The derived guiding radius is 12.29 ± 0.29 kpc and orbital eccentricity is 0.11 ± 0.01. Comparison with an estimated chemical birth radius suggests moderate outward migration of the guiding center, while the current orbital position also contributes to the radial displacement. The results characterize Berkeley 31 as an intermediate-age, metal-poor outer-disk cluster.

PublicAstronomers combined measurements of stellar motions, spectra, and light at different wavelengths to study Berkeley 31, a star cluster in the Milky Way’s outer disk. They identified 329 probable members and estimated that the cluster is 3.7 ± 0.2 billion years old and 6024 ± 181 parsecs away. Its stars are relatively poor in iron. About 38% of its main-sequence stars are candidates for unresolved pairs, with the smaller star at least roughly half as massive as the larger one. The study also identifies 62 blue stragglers—stars that appear unusually young for their cluster—and two yellow-straggler candidates. Two blue stragglers emit extra ultraviolet light, consistent with hot, compact stellar companions, although those companions are not established by this evidence alone. Comparing the cluster’s calculated orbit with an estimate of where it formed suggests that its orbit has shifted moderately outward through the Galaxy; its current position along that orbit also helps explain its distance from its estimated birthplace.

Young explorerBerkeley 31 is a faraway group of stars that is about 3.7 billion years old. Astronomers studied how the stars move and shine to work out which ones probably belong together. Some may be pairs that look like one star because they are so far away. A few look younger than the rest. Two of those give off extra ultraviolet light, which our eyes cannot see. That light could come from tiny, hot stars beside them. The astronomers also found clues that the group’s path around our galaxy has moved farther outward since it was born.

On The Scaling Relations Between Black Holes And The Galaxy/Bulge Mass And Their Connections With The Black Hole Occupation Fraction

Emanuele Contini, J.K. Jang, Jinsu Rhee+2 more

AstronomerUsing the semianalytic model FEGA25 with the YS200 cosmological simulation as its reference volume, this study examines predicted black hole mass relations with total stellar mass and bulge mass. Black hole mass thresholds chiefly bias the low-host-mass regime; selected relations approach the intrinsic, uncut relations at higher host masses. Morphology also matters: increasingly bulge-dominated galaxies preferentially occupy higher stellar masses. Neither relation shows clear systematic evolution over z=0–3 in FEGA25. The hydrodynamical zoom-in simulation NewCluster likewise shows no clear monotonic evolution, but has larger scatter, especially at high host masses. The authors interpret FEGA25's behavior as consistent with a broadly preserved statistical connection between black hole and galaxy growth. Black hole occupation fraction and scaling relations provide complementary constraints: lower occupation generally accompanies stronger selection offsets, but neither uniquely determines the other. At fixed occupation fraction, bias depends on the host property and underlying black hole mass distribution. At z=0, FEGA25 agrees with available observational constraints while predicting greater scatter and bending toward lower host masses.

PublicComputer models explore how a black hole's mass relates to the mass of its galaxy's stars and central bulge. In the FEGA25 model, excluding smaller black holes mainly changes the apparent relationships for lower-mass galaxies; the effect fades for more massive hosts. Galaxy structure matters too, with more bulge-dominated systems tending to have higher stellar masses. Across the modeled redshift range, neither FEGA25 nor the comparison simulation NewCluster shows a clear, consistent trend in how these relationships evolve, although NewCluster produces more scatter. The study also finds that similar average mass relationships can occur even when very different fractions of galaxies contain black holes, so both kinds of information are needed. FEGA25 matches available present-day observations, but its prediction of more scatter and a bend in the relationships for lower-mass galaxies remains a model prediction.

Young explorerScientists used computer models to study black holes and their galaxies. In the models, leaving out small black holes changed the pattern most for smaller galaxies. The models did not show a clear, steady change in the pattern over time. They also showed that similar patterns can hide different numbers of galaxies with black holes. These are computer-model findings, not new sightings in space.

The coupled evolution of nuclear star clusters and intermediate-mass black holes in a dwarf-galaxy merger

Christian Partmann, Rachel S. Somerville, Michaela Hirschmann+2 more

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena

AstronomerSimulations of an equal-mass, gas-rich dwarf-galaxy merger test whether nuclear star clusters (NSCs) enable intermediate-mass black hole (IMBH) pairing, hardening, and growth. Each progenitor contains a 1,000-solar-mass IMBH inside a million-solar-mass NSC. The model couples GRIFFIN interstellar-medium and stellar physics at 4-solar-mass gas resolution to KETJU regularised post-Newtonian black hole dynamics; accreting black holes provide no feedback. Without NSCs, 1,000–10,000-solar-mass IMBHs reach only 50–200 pc separations and capture no gas. With NSCs, the clusters coalesce within about 500 Myr, the IMBHs form a binary within a few Myr, and scattering predominantly of old NSC stars drives merger about 340 Myr later. Gas capture grows the holes to 110,000 and 41,000 solar masses. Stellar feedback and cluster motion suppress capture during the starburst; later accretion occurs in brief, supernova-regulated episodes. Binary scattering and an approximately 175 km/s merger recoil leave a larger, rotating, flat-cored NSC; the remnant escapes the cluster but remains in the galaxy. The model predicts an increasing stellar tidal disruption rate toward coalescence and LISA detectability to high redshift. These simulation results support NSCs as a route past IMBH delivery and hardening bottlenecks, subject to the adopted modelling assumptions.

PublicA computer simulation explores how dense star clusters at the centres of small galaxies could help black holes meet, grow, and merge. In the model, two gas-rich galaxies collide, each carrying a black hole initially 1,000 times the Sun’s mass inside a central star cluster. Without these clusters, the black holes remain far apart and capture no gas. With the clusters, encounters with stars bring the black holes together, while captured gas increases their masses to 110,000 and 41,000 Suns. Exploding stars help regulate this feeding. The simulated merger kicks the resulting black hole out of the central cluster, but not out of the galaxy, and leaves the cluster larger with a flattened central density profile. The authors predict that LISA could detect such mergers even at high redshift. These are model results, not observations; notably, the simulation omits feedback from the feeding black holes.

Young explorerScientists used a computer to imagine two small galaxies coming together. Each had a black hole surrounded by a crowded group of stars. In their computer model, the star groups helped the black holes get close enough to join together. The black holes also grew by taking in gas. After joining, the new black hole got a kick that sent it out of its star group, but it stayed inside the galaxy. This is what happened in the model, not something the scientists watched happen in space.

ARRAKIHS: The observability of tidally stripped satellites in a Milky Way-like halo

Abram Pérez-Herrero, Y. Revaz, S. Roca-Fàbrega+34 more

AstronomerHigh-resolution N-body simulations investigate the visibility of tidal debris from dwarf galaxies with Plummer stellar distributions embedded in cuspy or cored dark matter haloes, orbiting in a static Milky Way-like disc, bulge, and halo potential. Idealised surface-brightness maps sampled every 0.5 Gyr over 10 Gyr quantify the projected area brighter than limits of 29–32 mag arcsec−2, spanning depths relevant to ARRAKIHS, LSST, and Euclid. Within the simulated grid, detectability depends most strongly on progenitor stellar mass, orbital configuration, and evolutionary stage. Extended debris is recovered predominantly from initially more radial configurations, mainly with eccentricity proxy e₀ ≳ 0.75. Progenitors with stellar masses of 10^8–10^9 solar masses dominate detectable area; 10^6–10^7 solar-mass systems can lose stars without producing detectable debris. Detectable area varies non-monotonically as streams form, phase-mix, and fade below the adopted limits. Cuspy and cored models evolve similarly in this metric, with differences smaller than orbit-driven scatter. These are idealised simulation findings, not measured survey detection rates.

PublicDeep images are revealing faint trails of stars around galaxies like the Milky Way. This study uses computer simulations, rather than new observations, to investigate when trails from disrupted dwarf galaxies would be visible. In idealised images, visibility depends chiefly on the dwarf’s stellar mass, its orbit, and how far its disruption has progressed. More massive dwarfs dominate the visible debris, while smaller ones can lose stars without leaving a detectable trail. Extended trails appear mainly on initially more radial orbits. Visibility does not change steadily: trails form, spread out, and can become too faint to see. Models with centrally concentrated versus flatter dark matter distributions produce similar changes in visible area, with orbital differences having a larger effect. The calculations assume a fixed Milky Way-like gravitational environment, so they are not direct predictions of actual survey detection rates.

Young explorerLittle galaxies can leave faint trails of stars as they travel around a bigger galaxy. Scientists made computer models to see when those trails might show up. Bigger little galaxies usually made more visible trails, but some trails became too spread out and faint to see. These are model results, not new pictures of real trails.

The extragalactic science of the KMOS VVVX-GalCen spectroscopic survey II: Discovery of a galaxy cluster at z = 0.089 behind the Galactic plane

E. O. Schmidt, C. Valotto, C. Villalon+33 more

AstronomerThe first extragalactic results from the KMOS VVVX-GalCen Spectroscopic Survey identify a poor galaxy cluster in the Zone of Avoidance using near-infrared spectroscopy. Of 19 photometric candidates in a VVV NIRGC III overdensity, 16 were observed with VLT/KMOS and yielded reliable radial velocities: 14 form a compact structure at mean redshift 0.089 ± 0.001, while two are foreground galaxies. The rest-frame line-of-sight velocity dispersion is 560 (+110/−120) km/s. This implies an indicative dynamical M200 of 1.9 (+0.7/−1.1) × 10^14 solar masses, with the important limitation that the sampled members lie within the cluster core, approximately 0.4 r200. Thirteen of the 14 members lie within the fitted near-infrared red sequence’s 2σ scatter; both foreground galaxies lie outside it. These observations demonstrate how spectroscopy can distinguish a physical galaxy concentration from a chance line-of-sight projection in a region where photometry alone is insufficient.

PublicAstronomers have identified a galaxy cluster hidden behind the Milky Way, in a region where our own galaxy makes the wider universe difficult to survey. Images had revealed 19 possible galaxies grouped on the sky, but images alone could not establish whether they belonged together. Near-infrared spectra provided reliable velocities for 16 candidates: 14 form a compact cluster, while two are closer foreground galaxies. The spread in the cluster galaxies’ velocities suggests a mass of roughly 190 trillion times the Sun’s mass, placing it in the relatively modest, or poor-cluster, category. That mass estimate is provisional and has substantial uncertainty, because the observations sample only the cluster’s central region. The study shows how near-infrared spectroscopy can help uncover and characterize galaxy clusters obscured by the Milky Way.

Young explorerOur Milky Way makes some faraway galaxies hard to see. Astronomers used a special kind of light called near-infrared light to study some galaxies that looked close together in the sky. Their measurements showed that 14 belong to one faraway group, while two others are closer to us. How fast the galaxies move gives the astronomers a clue about how heavy the group is, but they are not sure of its exact weight because they studied only its middle.

Environmental Quenching of Satellite Galaxies out to z 0.4 with GAMA and DEVILS

Megan Oxland, Matías Bravo, Laura Parker+2 more

AstronomerUsing satellite samples from GAMA and DEVILS with consistently derived galaxy properties and environments, this observational study investigates environmental quenching to z~0.4 while minimizing cross-survey systematic biases. Projected phase space serves as a proxy for infall time, rather than a direct measurement. The authors quantify quenched fractions and offsets from the star-forming main sequence, finding consistent trends across the surveys: satellite star formation declines relative to the main sequence at approximately 0.14 dex/Gyr following inferred infall. Visually classified early- and late-type systems show similar declining trends. No significant redshift evolution is detected between the surveys, supporting the interpretation that group and cluster environments have had comparable effects on satellite star formation over the past approximately 4.5 Gyr.

PublicGalaxies that become satellites within groups and clusters tend to make fewer new stars. This study compares observations from the GAMA and DEVILS surveys, using consistent methods to reduce differences caused by how the surveys measure galaxies and their surroundings. Because the time each galaxy entered its group or cluster is not directly known, the researchers estimate it using clues from the galaxy’s position and motion. They find that star formation falls steadily relative to the typical level for star-forming galaxies, with similar trends for different galaxy shapes. They detect no significant change in these patterns across the past roughly 4.5 billion years, suggesting that group and cluster environments have affected satellite galaxies similarly throughout that period.

Young explorerGalaxies are huge families of stars, and some live together in bigger groups. Scientists looked at galaxies in these groups and used clues to guess when they joined. They found that galaxies that joined longer ago tended to make fewer new stars. Galaxies with different shapes showed similar patterns. The scientists did not find a clear change in this pattern between more recent times and billions of years ago.

Odds Estimation for Supermassive Black Hole Binaries in Local Core Galaxies

C.J. Harris, Kayhan Gültekin

• High Energy Physics - Theory

AstronomerThe study combines IllustrisTNG massive-galaxy assembly histories with a semi-analytic core-scouring model to estimate the probability that a core galaxy hosts a bound supermassive black hole binary at z=0. Binary evolution includes dynamical friction, stellar hardening, and gravitational-wave emission. Logistic regressions use stellar mass deficit, stellar mass, central density, central velocity dispersion, and effective radius, achieving pseudo-R² = 0.51 ± 0.03, accuracy = 0.95 ± 0.01, precision = 0.92 ± 0.03, and recall = 0.82 ± 0.04 on simulated systems. Modeled uncoalesced binaries have separations peaking near 0.3 pc, with only about 0.3% emitting in the pulsar timing array band. Applied to observed core galaxies, the model assigns eight nearby galaxies a greater-than-50% hosting probability; these are candidates, not confirmed binaries. Messier 86 (NGC 4406), also identified independently as a candidate, is highlighted for follow-up.

PublicPairs of supermassive black holes are expected to form when massive galaxies merge, but finding them is difficult. Researchers combined simulated galaxy histories with a model of how black hole pairs evolve and affect stars near galaxy centers. They then used five galaxy properties to estimate which galaxies might contain a pair. The method performed well in simulations; when applied to observations, it flagged eight nearby galaxies as more likely than not to host two bound supermassive black holes. These are model-based candidates, not discoveries of confirmed pairs. Messier 86 stood out as a promising target for future observations because an independent approach had also identified it as a candidate. The simulations suggest that most surviving pairs are closely spaced and only a small fraction emit gravitational waves in the frequency range probed by pulsar timing arrays.

Young explorerWhen two big galaxies join together, their giant black holes may become a pair. Scientists used computer models to look for clues that a galaxy might have two black holes instead of one. Their model picked eight nearby galaxies that might hide a pair, but it has not proved the pairs are there. One galaxy, called Messier 86, looks especially worth checking.

Detailed chemo-dynamical characterization of four elusive Milky Way star clusters

D. A. Alvarez Garay, E. Ceccarelli, D. Massari+17 more

• Solar and Stellar Astrophysics

AstronomerVLT/X-shooter spectroscopy provides line-of-sight velocities and chemical abundances for BH 140, Garro 01, BLISS 1, and Kim 3. The study reports the first spectroscopic metallicity and alpha-element characterization of BH 140, the first comprehensive chemical characterization of Garro 01 and BLISS 1, and the first spectroscopic metallicity for Kim 3. BH 140, Garro 01, and BLISS 1 have [Fe/H] approximately -0.7 dex and enhanced alpha-element abundances; Kim 3 has [Fe/H] approximately -1.8 dex. Orbital analysis places Garro 01 and BH 140 within 1.5 kpc of the Galactic plane, with Garro 01 on a notably circular orbit. The authors favor in situ origins for both, while noting that BH 140's high eccentricity and mild alpha-element deficiency leave alternatives open. They classify BLISS 1 as accreted, on a high-energy, high-LZ prograde orbit reaching approximately 8 kpc above the plane, but find no clear dynamical association with a known progenitor. In tension with that classification, its chemistry appears to favor an in situ origin, potentially connected to the Aleph substructure. Kim 3's high-energy, low-LZ orbit is tentatively linked to the Elqui stream.

PublicAstronomers used spectra from the Very Large Telescope to measure stellar motions and chemical compositions in four faint Milky Way star systems: BH 140, Garro 01, BLISS 1, and Kim 3. The first three are relatively rich in elements heavier than helium compared with Kim 3, which is much more metal-poor. An analysis of their paths through the Galaxy suggests that Garro 01 and BH 140 probably formed within the Milky Way, although BH 140's elongated orbit and some chemical evidence leave other origins possible. BLISS 1 presents a puzzle: the researchers classify it as having arrived from outside the Galaxy, yet its chemistry seems more consistent with formation inside it. They find no clear orbital link to a known parent system and suggest a possible connection with the Aleph substructure. Kim 3 may be associated with the Elqui stream, but that link remains tentative.

Young explorerScientists studied the light from four faint groups of stars to learn what they are made of and how they move. One group, Kim 3, has much less iron than the other three. The scientists think two groups probably formed in our Milky Way galaxy, but they are not completely sure. Another group gives mixed clues about where it came from. Kim 3 might be connected to a trail of stars, but that is not certain either.

3-Methoxy-1-propanol Rotational Spectroscopy and Radio Astronomical Search toward NGC 6334I

D. Archie Stewart, Laurent Margulès, Roman A. Motiyenko+1 more

AstronomerThe authors measured portions of the centimeter, millimeter, and submillimeter rotational spectrum of the most stable conformer of 3-methoxy-1-propanol. They used the resulting experimental rotational parameters to simulate its spectrum under the physical conditions of NGC 6334I MM1 and searched the ALMA dataset previously used to identify 2-methoxyethanol. No transitions of 3-methoxy-1-propanol were identified, yielding a column-density upper limit of 7.5 × 10^15 cm^-2. This limit is consistent with a decline in column density from 2-methoxyethanol to 3-methoxy-1-propanol comparable to that from methoxymethanol to 2-methoxyethanol, but does not constitute a detection of the larger molecule.

PublicResearchers searched for 3-methoxy-1-propanol, a larger relative of two alcohol molecules already identified toward the young stellar source MM1 in the NGC 6334I star-forming region. They first measured parts of the molecule’s rotational spectrum in the laboratory, then used those measurements to predict its signals under conditions in MM1 and compare them with existing ALMA observations. They found no identifiable signals from the molecule. Instead, they established an upper limit on its amount along the line of sight: 7.5 × 10^15 molecules per square centimeter. That limit is consistent with these related alcohol molecules becoming less abundant as they get larger, although the largest molecule remains undetected.

Young explorerScientists have already found two related kinds of tiny molecules near a star that is still forming. They looked for a bigger relative by measuring the light signals it can make in a laboratory, then working out what those signals would look like near the young star. They did not find its signals in the telescope observations. That does not mean it is not there: there may be too little to spot. The search puts a limit on how much could be hiding there, and fits the idea that the bigger relatives are rarer.

The origin of UV emission in extremely low-mass satellite galaxies: Insights from Leo T

S Amrutha, Mousumi Das, Daniel Vaz+1 more

AstronomerA UVIT far-ultraviolet study of Leo T, the lowest-mass known gas-rich galaxy with recent star formation, identifies 30 FUV star-forming clusters and derives their areas, luminosities, and star formation rates. The authors report that the cluster FUV luminosities confirm the absence of massive O- and B-type stars. Cross-matching with Hubble and MUSE catalogs identifies main-sequence, blue-loop, horizontal-branch, and emission-line stars. Upper main-sequence and emission-line stars concentrate near the optical center, while lower main-sequence and blue-loop stars are more extended. Five of the six FUV-emitting stars with MUSE spectroscopy have [Fe/H] ≤ -3. The NUV–r color profile indicates that populations younger than 1 Gyr dominate the UV emission at radii below 185 pc. No identified clusters are associated with the previously detected CO clouds, whose inferred star formation efficiencies are extremely low. The cluster distribution suggests, but does not establish, a directional interaction with the Milky Way.

PublicLeo T is a small companion galaxy of the Milky Way and the lowest-mass gas-rich galaxy known to have formed stars recently. Using ultraviolet images, researchers identified 30 star-forming clusters and estimated their properties. Their ultraviolet brightness supports the absence of massive O- and B-type stars. Matching ultraviolet sources with other observations revealed several kinds of stars, with some groups gathered near the galaxy’s center and others spread farther out. Five of the six ultraviolet-emitting stars studied with MUSE spectroscopy are extremely poor in elements heavier than helium. The galaxy’s ultraviolet-to-visible color indicates that stars younger than a billion years dominate its ultraviolet light within about 185 parsecs of the center. None of the identified clusters coincide with the previously detected molecular gas clouds, which have extremely low estimated star formation efficiencies. The pattern of clusters hints at an interaction with the Milky Way, but does not prove one.

Young explorerLeo T is a little galaxy near our Milky Way that has made stars recently. Scientists looked at it in ultraviolet light, a kind of light our eyes cannot see, and found 30 groups where stars have formed. The light suggests that Leo T has no stars of two very big kinds called O and B. Some kinds of stars gather near the middle, while others are spread farther out. The scientists also found that the star groups do not sit on the gas clouds they studied, and those clouds seem to be making very few stars. The way the groups are arranged might be a clue that the Milky Way is affecting Leo T, but scientists are not sure.

Probing Multi-formation Channels of Dark Matter-Deficient Galaxies in a Simulated Universe

Sanghyeon Han, Ho Seong Hwang, Jaehyun Lee

AstronomerUsing the IllustrisTNG100 cosmological hydrodynamical simulation, the authors identify two formation channels for dark matter-deficient galaxies, defined by a dark matter-to-stellar mass ratio below unity. Acquired systems initially form within massive dark matter halos and subsequently lose most of their dark matter; inborn systems form with little or none. Acquired systems show stronger temporal variations in mass content, size, and kinematics and tend to form closer to neighboring galaxies in large-scale overdense regions than inborn systems. Inborn systems evolve more mildly, with most stars forming in situ from gas that was already metal-enriched and associated with other galaxies. Tidal interactions and filamentary gas flows are suggested contributors to compact gas-clump assembly, rather than established mechanisms. These simulation findings support at least two formation channels, with potentially multiple pathways for the inborn population; they are not observational detections.

PublicA computer simulation of galaxy formation suggests two ways galaxies can end up with less dark matter than mass in stars. Some begin inside massive dark matter halos and later lose most of their dark matter. Others form with little or no dark matter from the start. In the simulation, the first group changes more strongly in mass, size, and stellar motions and tends to form closer to neighboring galaxies in crowded regions. The second group changes more gently, and most of its stars form within the galaxy itself. The gas that supplies those stars was previously associated with other galaxies and already contained elements heavier than helium. Gravitational interactions and streams of gas may help gather this material into compact clumps, but the exact formation pathways remain uncertain. These are simulation results, not observations of real galaxies.

Young explorerScientists used a computer to explore how galaxies—big groups of stars—might form with very little invisible stuff called dark matter. In their computer universe, some galaxies started with lots of dark matter and then lost most of it. Others were born with hardly any. The first kind changed a lot over time, while the second kind changed less. Most stars in the second kind grew inside their own galaxy from gas that had been linked to other galaxies. Pulls from nearby galaxies and streams of gas might help gather that gas together, but scientists are not sure exactly how. This is what happened in the computer model, not something this study watched happen in the sky.

The Peculiar Astrometric Behaviour and Radio Structure of the Quasar 1524-136 Revealed with Very Long Baseline Interferometry

Angelina Osetrova, Sándor Frey, Oleg Titov+2 more

AstronomerHistorical VLBI astrometry shows an apparent position shift exceeding 0.1 arcsecond in the radio quasar 1524-136 (J1526-1351) between the 1990s and 2010s, despite sub-milliarcsecond measurement precision. The source has an extended, roughly 0.4-arcsecond, highly asymmetric and non-collinear jet structure. An analysis of historical VLBI astrometry and imaging, together with Gaia optical astrometry, attributes the shift to changing radio brightness structure: at X band, approximately 8.4 GHz, the core brightened substantially relative to the northern jet's terminal hotspot, moving the brightness peak and hence the measured VLBI position from the hotspot to the core. Similar changes could affect other radio sources and the stability of the VLBI celestial reference frame.

PublicA quasar's measured radio position changed dramatically between the 1990s and 2010s, but the analysis attributes this apparent jump to a change in which part of the source was brightest, rather than a physical leap across the sky. Researchers examined historical radio measurements and images, along with optical position information from Gaia. They found that the central region of quasar 1524-136 brightened relative to a bright spot at the end of its northern jet. At the radio frequency conventionally used to measure positions, the brightest point switched from that distant spot to the center, shifting the recorded position by more than 0.1 arcsecond. Similar changes could occur in other radio sources, so understanding them matters for keeping the radio-based map of reference positions in the sky stable.

Young explorerAstronomers saw that a faraway object called a quasar seemed to jump to a new place in the sky. They found that its middle had become brighter compared with a bright spot at the end of one of its jets. Their radio measurements followed the brightest spot, so the quasar's recorded place changed when a different part became brightest. It was an apparent jump, not evidence that the whole object suddenly moved. Other objects might do this too, which could make astronomers' sky maps harder to keep steady.

Hoag-type Galaxies: A Photometric Study of the Cores and Rings of Thirty Systems from the DESI Legacy Survey

Jingshuo Yang, Cheng Li

AstronomerVisual inspection of two machine-learning ring-galaxy catalogues identified 30 apparent Hoag-type systems in DESI imaging. Analysis of Legacy Surveys g, r, and z images, with two-dimensional core subtraction for ring measurements, finds predominantly red-sequence cores and a broader ring colour distribution extending toward the blue cloud. The cores broadly follow early-type mass scaling relations, but relative to mass-matched SDSS controls tend to be slightly bluer, smaller, denser, and less concentrated, with lower Sérsic indices. Among the 16 systems with SDSS group information, 14 (87.5%) are centrals, versus approximately 64% of mass-matched early-type controls; additional matching in central–satellite status substantially reduces differences in halo mass and large-scale overdensity. Ring stellar-mass surface density and normalized width decrease with increasing core-plus-inner-halo to ring mass ratio. In a simplified core-plus-ring model, most core R90 values fall inside the outermost stable circular orbit, while rings frequently span the unstable interval. The authors interpret the core properties as allowing a secular contribution but requiring more complex assembly than a simple diffuse-pseudobulge origin. A high central fraction may aid gas retention and ring survival, while the diversity of rings leaves multiple formation pathways open.

PublicResearchers identified 30 galaxies that appear to have the unusual Hoag-type shape: a smooth central core separated from an outer ring. Measurements from imaging show that the cores are mostly red, while the rings have a wider range of colours, including bluer ones. Compared with galaxies of similar stellar mass in an early-type comparison sample, the cores tend to be slightly bluer, smaller, and more densely packed, but less centrally concentrated in their light profiles. Of the 16 systems with information about their galaxy groups, 14 are the central galaxy rather than a satellite. The authors suggest that this status could help them retain gas and preserve their rings, but this is an interpretation rather than a demonstrated cause. A simplified model also places parts of many rings in a region where circular orbits would be unstable. The observations do not establish a single origin: the cores suggest a complicated assembly history, and different rings may have formed in different ways.

Young explorerThese galaxies look a little like a smooth middle with a separate hoop around it. Scientists found 30 galaxies that seem to have this shape. In the pictures, the middles are mostly red, but the hoops come in more colours, including blue. The scientists measured both parts to look for clues about how they formed. They still do not know the whole story, and different galaxies might have made their hoops in different ways.

Detection of HNCOH+ in the interstellar medium

M. Rey-Montejo, I. Jimenez-Serra, M. Sanz-Novo+12 more

• Solar and Stellar Astrophysics

AstronomerThe authors report the first interstellar detection of the metastable O-protonated isomer HNCOH+ toward G+0.693-0.027, using an ultra-deep survey with the Yebes 40-m, IRAM 30-m, and APEX telescopes spanning nearly 150 GHz of bandwidth between 31 and 275 GHz. They derive a column density of (9.9 ± 0.5) × 10^12 cm^-2 and an abundance relative to H2 of (7.3 +1.3/-1.0) × 10^-11. The measured HNCOH+/H2NCO+ column-density ratio is 3.8 +0.5/-0.4, despite H2NCO+ being the more stable isomer. This observational result is consistent with recent kinetic calculations favoring HNCOH+ formation, rather than directly establishing its formation pathway. The detection expands the known interstellar inventory of NCO-bearing molecules and supports the view that isomer abundances need not track thermodynamic stability.

PublicAstronomers report the first detection in interstellar space of HNCOH+, a previously predicted charged molecule, in the Galactic Center cloud G+0.693-0.027. Using a broad survey from three radio telescopes, they found it to be about four times as abundant as H2NCO+, a more stable form with the same atomic composition but a different arrangement. That finding agrees with calculations predicting that chemical reactions favor the formation of HNCOH+, although the observations alone do not establish how it forms. The discovery adds to the known space molecules containing the NCO chemical group and illustrates that the more stable form of a molecule is not necessarily the more common one.

Young explorerScientists used three telescopes to find a tiny molecule in a cloud far away in space. People had predicted it would be there, but no one had found it in space before. It has the same kinds and numbers of atoms as another molecule, but they are put together differently. The newly found kind is less stable, yet the scientists found about four times as much of it. That is a clue that how molecules are made can matter, not just how stable they are.

Dust growth in the early Universe: insight from the NewCluster spin-off simulation

J. K. Jang, Yohan Dubois, Francisco Rodriguez Montero+7 more

AstronomerA cosmological zoom-in simulation of galaxies at z≈5, using an evolving two-species, two-size dust model, yields three metallicity-dependent phases. At log(Z/Z☉)<−1, stellar ejecta dominate the dust supply, producing shallow, featureless UV extinction with a normalized wavelength dependence resembling the Calzetti attenuation law. At −1≤log(Z/Z☉)<−0.5, efficient silicate accretion drives rapid growth and SMC-like extinction. At log(Z/Z☉)≥−0.5, efficient carbonaceous grain growth produces a more balanced mixture and Milky-Way-like extinction. Recent clustered supernova feedback strongly suppresses local dust-to-metal ratios in the simulation. However, simulated dust masses and dust-to-metal ratios fall below current observational inferences for high-redshift galaxies. The modeled depletion patterns suggest that the assumed fixed Fe-bearing olivine composition may be too restrictive; metallicity-dependent grain compositions are a proposed remedy, not an established result.

PublicA computer simulation explores how dust develops in galaxies in the early Universe. It predicts three stages as galaxies become richer in elements heavier than helium: dust supplied mainly by stars, rapid growth of silicate dust, and then more efficient growth of carbon-based dust. These stages change which ultraviolet wavelengths the dust blocks most strongly. The simulation also finds that recent groups of stellar explosions can leave nearby regions with much less dust relative to their heavy-element content. But the simulated galaxies contain less dust than astronomers currently infer from observations of distant galaxies. The researchers suggest that allowing the chemical makeup of dust grains to change as galaxies become enriched might help explain the mismatch; this remains an interpretation to investigate.

Young explorerScientists used a computer to imagine how dust grows in galaxies long ago. In their model, stars first supply the dust. Then different kinds of dust grow as more ingredients become available, changing how the dust blocks light. Exploding stars can also leave nearby places with less dust. But the model makes less dust than astronomers think those faraway galaxies have. The scientists wonder whether changing the ingredients in their pretend dust could help, but they have not shown that yet.

Feeding or Fleeing: The Impact of Enhanced Early Black Hole Growth on Circumgalactic Clumps at z > 6

Floor van Donkelaar, Lucas Tortora, Debora Sijacki

• High Energy Astrophysical Phenomena

AstronomerTwo cosmological zoom-in simulations of the same massive halo at z > 6 compare dense circumgalactic clumps in the fiducial Fable model and Fable-SE, which enhances early black hole growth through mild super-Eddington accretion. At the resolution studied, clump gas masses, sizes, and associated stellar masses have broadly similar distributions; the main differences are in abundance, metallicity, and radial evolution. Fable-SE produces substantially more metal-enriched clumps, including an outward-moving population during its strong AGN-driven blow-out phase at z ≲ 7, with some clumps passing beyond the virial radius. These structures are associated with disturbed HI-rich gas and relatively high gas densities. Inward migration nevertheless dominates overall. The simulations indicate that both filamentary accretion and feedback shape dense CGM clump populations, with strong early AGN activity associated with outward migration of enriched structures containing relatively cool gas.

PublicComputer simulations explore how dense gas clumps form and move around a massive galaxy in the early universe. The researchers compared two versions of the same simulated system, one allowing its central black hole to grow faster early on. At the resolution tested, the clumps had broadly similar ranges of gas mass, size, and accompanying star mass. Their numbers, chemical enrichment, and movements differed more. The faster-growing-black-hole model produced substantially more clumps enriched in elements heavier than helium. During a strong gas-expulsion episode driven by the active black hole, some dense, relatively cool clumps moved outward, even beyond the halo's boundary. Most clump migration was still inward overall. These are simulation findings, not direct observations, and they suggest that both incoming gas streams and black-hole-driven activity shape the gas surrounding young massive galaxies.

Young explorerScientists used two computer models to study clumps of gas around a big galaxy when the universe was young. In one model, the black hole in the middle grew faster. That model made more gas clumps with heavier ingredients. When the active black hole drove a strong rush of gas outward, some clumps went outward too, even past the edge of the galaxy's surrounding region. But overall, clumps mostly moved inward. This happened in computer models, so it is a clue about how real galaxies might work, not something the scientists watched happen in space.

The stellar orbit distribution of 24 late-type galaxies observed by MUSE

Le Zhang, Ling Zhu, Jesús Falcon-Barroso

AstronomerThe study uses archival MUSE stellar kinematics for 24 nearby late-type galaxies, with coverage to at least one effective radius. Kinematics extracted with GIST and pPXF were fitted with axisymmetric Schwarzschild models constructed using dynamite. Orbits were classified by circularity as cold, warm, hot, or counter-rotating, and their luminosity fractions within one effective radius were calculated. The inferred orbital structures confirm mass-dependent trends previously identified in CALIFA galaxies and reproduced in IllustrisTNG simulations. The authors also examined component morphology and calculated edge-on flattening for the cold, warm, and combined hot plus counter-rotating components. Warm components are common in the low-mass late-type spirals studied, suggesting dynamically warmer, vertically thicker discs than in more massive spirals. This interpretation remains tentative because of the limited sample size.

PublicResearchers studied the motions of stars in 24 nearby galaxies using archival MUSE observations and models of stellar orbits. They estimated how much of each galaxy’s light comes from stars following different kinds of orbits. Their results support previously reported links between galaxy mass and stellar orbital structure, which have also been reproduced in simulations. In the lower-mass spiral galaxies studied, stars commonly occupy a category of orbits described as dynamically warm. Here, warm refers to stellar motion, not temperature. The authors interpret this as a possible sign that these galaxies have thicker discs and less orderly stellar motions than more massive spirals, but stress that the small sample makes this conclusion tentative.

Young explorerStars move around inside galaxies, but they do not all follow the same kinds of paths. Scientists studied how stars move in 24 nearby galaxies and used computer models to work out their paths. In the smaller spiral galaxies they studied, many stars seemed to follow less tidy paths. This might mean those galaxies have puffier discs of stars than bigger spirals. The scientists are not sure yet, because they studied only a small group of galaxies.

A MUSE and MeerKAT study of dynamics and star formation in HCG 16

Ixaka Labadie-García, Enrique Pérez, Julián Garrido+2 more

AstronomerThe study combines MUSE Hα maps and pyPipe3D stellar population synthesis with a high-resolution MeerKAT HI cube to investigate the interaction history of the five-galaxy, Phase 2 compact group HCG 16. Spatially resolved star formation histories indicate a major episode beginning about 400–500 Myr ago, coincident with the inferred close passage of NGC 848, and continuing in some members until at least 50–60 Myr ago. The observed HI distribution is highly perturbed, although HCG 16a retains a nearly regular disk; HCG 16b has associated Hα tails. The authors interpret the NGC 848 passage as a probable trigger for star formation, but not a sufficient explanation for the current starbursts in HCG 16c and 16d. They favor multiple interactions over a single strong encounter as the explanation for the group's evolution.

PublicAstronomers studied gas and the history of star formation in HCG 16, a compact group of five galaxies. Their analysis indicates that a major period of star formation began about 400–500 million years ago and lasted in some galaxies until at least 50–60 million years ago. Its beginning coincided with a close passage by the galaxy NGC 848, which the researchers suggest probably helped trigger it. They also found that the group's neutral hydrogen gas is strongly disturbed, although one galaxy retains a nearly regular gas disk, while another has tails traced by glowing hydrogen. The close passage alone cannot explain the intense star formation happening now in two members. The authors conclude that several interactions between the galaxies better explain the group's history than one strong encounter.

Young explorerFive galaxies live close together in a group called HCG 16. Scientists studied their gas and stars and found signs that they started making lots of stars a very long time ago. One galaxy passing near the others probably helped start this, but it does not explain all the stars being made now. Much of the gas is jumbled up, too. The scientists think the galaxies have tugged on one another several times, rather than having just one big meeting.

Channelled versus Isotropic Accretion of Galaxy Groups onto Clusters: Kinematics, Spin Alignment, and Assembly Bias

Ankit Singh, Frazer Pearce, Meghan Gray+4 more

• Cosmology and Nongalactic Astrophysics

AstronomerThis simulation study tests whether groups’ accretion routes affect their spin, kinematics and orbits. Using DisPerSE filaments in MDPL2, the authors classify 212,704 group–cluster infall pairs across 27,029 clusters into primary, secondary, primary-outskirt and isotropic channels. Primary and secondary groups change from predominantly filament-parallel to perpendicular spin at log10(Mflip/[h⁻¹ M☉]) = 13.07 and 13.12; their 0.05-dex difference is consistent with zero. These thresholds lie 1.3–1.4 dex above the field value and remain radially flat to 7 R200; isotropic groups show no flip. In the primary channel, the threshold increases with filament linear mass density. Matching group mass, cluster mass and distance preserves a positive trend but leaves its amplitude uncertain at 0.07–0.58 dex. At 2 R200, primary groups show 85% velocity–filament alignment. Isotropic groups fall in 150–180 km/s faster and more radially out to 5 R200. At matched distance, their pericentres are predicted to be up to 10% smaller; primary groups’ smaller pooled pericentres instead reflect their greater proximity to clusters. These are simulation findings and orbital predictions, with observational tests proposed using wide-area spectroscopic surveys.

PublicA computer simulation suggests that the route a galaxy group takes toward a galaxy cluster is linked to how it spins and falls inward. Researchers classified more than 212,000 group–cluster infall pairs. Groups arriving along cosmic filaments tend to spin along those filaments at lower masses and across them at higher masses. The transition occurs at higher group masses in denser cluster-connected filaments, although the size of that trend remains uncertain after matching other properties. Groups arriving from the open field fall faster and more directly inward. At equal distance from a cluster, they are predicted to pass up to 10% closer to its centre than groups on directly connected filaments. These results come from a simulation, not observations; large spectroscopic surveys could test them.

Young explorerGalaxy families can travel toward bigger galaxy crowds along space paths, or come in from other directions. Scientists used a computer model to watch them. Families taking different routes spun and moved differently. Those coming from outside the paths moved faster and more straight toward the crowd. The model suggests they could pass closer to its middle, too. Scientists still need to check what real galaxies do.

SDSS-V LVM: Mapping of plasma temperatures in the Lagoon Nebula reveals the origin of long-standing chemical abundance discrepancies

Amrita Singh, Guillermo A. Blanc, Kathryn Kreckel+18 more

AstronomerThe authors present the first spatially resolved IFU observations of O++ recombination lines (RLs) and collisionally excited lines (CELs) across a Milky Way H II region, M8. They map the long-standing abundance discrepancy, in which CELs yield lower abundances than RLs, and find a tight correlation between its magnitude and the temperature difference inferred using classical CEL and hybrid RL/CEL diagnostics. Interpreting the data with a plasma temperature perturbation model, they conclude that electron-temperature fluctuations drive the discrepancy in M8. They identify the diagnostic temperature difference as an observational proxy for fluctuation amplitude. The correlation constrains the mean electron temperature; adopting that temperature reconciles the CEL and RL abundances. The stated result concerns M8 rather than establishing a universal explanation for all nebulae.

PublicFor more than 80 years, two ways of reading the light from glowing gas have given different estimates of its chemical makeup. Researchers mapped this mismatch in the Lagoon Nebula using two kinds of light emitted by doubly ionized oxygen. They found that the chemical disagreement closely tracks the difference between two temperature estimates. By interpreting these observations with a model, they conclude that variations in electron temperature cause the mismatch in this nebula. Using the mean temperature constrained by their analysis brings the two oxygen-abundance estimates into agreement. The study also offers a way to measure how temperature variations affect such estimates.

Young explorerScientists read light from a glowing cloud in space to work out how much oxygen it has. Two ways of reading that light gave different answers. Their observations and a model point to warmer and cooler patches of gas as the reason. Using an average temperature made the two answers agree for this cloud, called the Lagoon Nebula.

Can the ∼5 kpc starburst ring in MW create eROSITA bubbles?

Mukesh Singh Bisht, Kartick C. Sarkar

AstronomerHydrodynamic simulations test whether a star-forming ring at a Galactic radius of about 5 kpc can account for the symmetric eROSITA bubbles. The authors find that ring-driven energy injection alone cannot reproduce the bubbles and argue that compact energy injection from the Galactic Center is required. Their simulations support interpreting the bubbles as a nuclear outflow, without identifying whether central star formation or the central supermassive black hole supplies the energy. The conclusion is simulation-based rather than a new observational determination of the source.

PublicWhat powered the eROSITA bubbles in our Galaxy: activity near its center, or a ring of forming stars farther out? The researchers tested the ring explanation using computer simulations of gas motion. In their simulations, the ring alone could not produce the bubbles' symmetric shape; a concentrated energy source at the Galactic Center was needed. This supports an origin in an outflow from the Galaxy's center, but does not settle whether the energy came from central star formation or the central supermassive black hole.

Young explorerOur galaxy has shapes called the eROSITA bubbles. Scientists used a computer to test whether a ring of places where stars are being born could make them. In their computer tests, the ring could not make the right matching shapes by itself. The tests suggest the bubbles need a push from the middle of our galaxy, but they do not tell us exactly what gave that push.

What kinds of strong star--black-hole encounters in AGN disks occur, and how often?

R. O'Shaughnessy, Z. Rosenberg, J. Nordhaus

• High Energy Astrophysical Phenomena

AstronomerThis modeling study examines stellar and black-hole encounters in active galactic nucleus disks. It includes stochastic initial relative velocities, strong-encounter cross-sections for single- and binary-mediated interactions calculated with direct two-body Hill or isolated three-body dynamics, and repeated encounters incorporating energy loss through stellar encounters and the supermassive black hole’s tidal field. The encounter model is combined with parametric natal stellar and binary populations, varying binary fraction and period distribution. In the fiducial disk model, single-single interactions dominate encounter counts, but binary-mediated interactions produce 68% of collisions. Most encounters are approximately parabolic, and stochastic relative velocities are comparatively substantial, driven by gravitational perturbations from disk fluctuations and neighboring bodies. These are model results, not observational measurements; the authors also provide semianalytic approximations for downstream applications.

PublicStars and black holes in disks around active galactic nuclei can pass close to one another or collide. This study models how those encounters depend on their speeds, whether they belong to bound pairs, and the effects of repeated encounters and the central supermassive black hole’s gravity. In the researchers’ reference disk model, encounters between two unpaired bodies are the most common, yet interactions involving bound pairs account for 68% of collisions. The model also finds that gravitational disturbances from the disk and nearby bodies make an important contribution to relative speeds. These findings come from calculations rather than observations, and the collision percentage applies to the reference model.

Young explorerStars and black holes can meet in a disk around a galaxy’s giant black hole. Researchers used a math model to explore these meetings. In their example, meetings involving pairs caused most crashes, even though meetings between objects traveling alone happened more often. This is a model, not something they watched happen.

Celia: Catalog Embeddings Learned from cosmologIcal simulAtions

Xiaowen Zhang, Matthew Ho, Anshul Kumar+3 more

• Cosmology and Nongalactic Astrophysics

AstronomerCelia is a self-supervised foundation model that compresses simulated subhalo catalogs and galaxy properties into embedding vectors. It is pretrained without parameter labels on the IllustrisTNG, SIMBA and Astrid CAMELS suites and their N-body counterparts through masked-property reconstruction and teacher-representation prediction. Linear models fitted to the embeddings recover Ωm with R²=0.999 and σ8 and both supernova-feedback amplitudes with R²≥0.97 in all three suites. For the unseen Swift-EAGLE code, a linear model trained on the three original codes predicts Ωm with r=0.985; linear models fitted on 20 labeled simulations achieve r≥0.94 for Ωm, σ8 and one supernova-feedback amplitude. Simple power laws in simulation parameters describe the leading principal components of embedding variation within each suite. These simulation-based results support a shared representation of galaxy catalogs, with intended applications to inference, emulation and comparison of galaxy-formation models; the abstract reports no test on observed galaxy catalogs.

PublicDifferent computer simulations describe galaxy formation in different ways, making their outputs difficult to compare. The researchers developed Celia, an AI model that turns simulated galaxy catalogs into compact numerical summaries. Its initial training does not require labels identifying the simulations’ physical settings. Simple models subsequently fitted to these summaries accurately recover settings related to matter density, cosmic clustering and the effects of supernovae in the three simulation families used for training. The summaries also work well for a fourth simulation code that Celia had not encountered, including tests using just 20 labeled simulations. The researchers present this as a common framework for comparing simulations and potentially extracting information about the universe. The reported successes concern simulated catalogs, not observations of real galaxies.

Young explorerScientists make pretend universes on computers to learn how galaxies form. Different computer programs make them in different ways. The scientists built an AI helper called Celia that turns long lists of pretend galaxies into short sets of numbers. Other simple computer tools used those numbers to work out some of the settings that made the pretend universes. This worked well even with a new program Celia had not seen before. It could help scientists compare their pretend universes, but these tests were not done with real galaxies.

A compact NH₂D source without NH₃ counterpart in the S187 high-mass star-forming region

E. A. Trofimova, I. I. Zinchenko, C. Henkel+3 more

AstronomerObservations with the 20-m OSO telescope at approximately 72–112 GHz, analyzed with non-LTE modeling, confirm a compact NH2D source no larger than about 0.2 pc in S187, at a projected distance of no more than about 0.3 pc from luminous IRAS 01202+6133. Lower-frequency observations mapped the area; higher-frequency observations sampled only the NH2D peak. Emission from about 20 molecules was detected, but only the DCO+ (1–0) peak coincides with the NH2D clump. No known source or NH3 emission peak is associated with it, although a dust-continuum enhancement lies approximately at its position. Temperature indicators yield about 20–30 K, possibly tracing the surrounding material rather than the clump. The intrinsic NH2D linewidth of about 0.4 km/s implies subsonic or transonic turbulence. The ortho/para line-intensity ratio is consistent with an abundance ratio of 3, and NH2D/NH3 may be about unity. The authors interpret the data as suggestive of a cold, dense, gravitationally stable core, possibly pristine, embedded in warmer material; higher-angular-resolution observations are needed to verify this picture.

PublicRadio observations confirm a small concentration of deuterated ammonia—a form of ammonia containing heavy hydrogen—near a luminous source in the S187 star-forming region. Such strong enrichment in heavy hydrogen is unusual in this environment. The concentration is no more than about 0.2 parsecs across and has no matching peak in ordinary ammonia emission, though a dust enhancement lies nearby in the same position. Of about 20 molecules detected, only DCO+ has an emission peak that lines up with the deuterated ammonia. The narrow ammonia line indicates relatively gentle gas motions. Temperature estimates of about 20–30 kelvin may describe the surrounding gas rather than the concentration itself. The observations suggest, but do not establish, a cold, dense pocket that is stable against gravitational collapse and may contain pristine material. Sharper observations are needed to test that interpretation.

Young explorerAstronomers used a radio telescope to find a small cloud of gas near a bright object where stars are forming. The cloud shows a special kind of ammonia made with heavy hydrogen, but ordinary ammonia does not have a matching bright spot there. The gas seems to move gently. The scientists think this might be a cold pocket inside warmer gas, perhaps holding material that has changed very little. They need a sharper look to find out if that idea is right.

Playing CHESS with stars II. Homogeneous analysis of high-resolution optical spectra for a sample of 135 giants in 14 bulge globular clusters

S. Özdemir, R. Smiljanic, J. E. Martínez Fernández+3 more

• Solar and Stellar Astrophysics

AstronomerA homogeneous analysis of archival high-resolution UVES spectra measures abundances in 135 giants across 14 Galactic bulge globular clusters. The CHESS pipeline derives atmospheric parameters on a reference-star scale, with spectrum-synthesis abundances for 14 elements and NLTE corrections for Na, Mg, Al, Si, Ca, Y, Ba, and Eu. The analysis uncovers a Li-rich giant in NGC 6723 with A(Li) = 1.68 after 3D NLTE corrections. Observed Na abundance spreads indicate that the sample contains both first- and second-generation stars. Relative to halo clusters, the bulge clusters show a lower low-metallicity [α/Fe] plateau and a more gradual decline toward higher metallicity. Sc abundances are below solar and lower than those of disk stars at comparable metallicity, a difference potentially relevant to unresolved Sc nucleosynthesis questions. No cluster exhibits a significant heavy-element abundance spread. Most clusters have [Ba/Eu] approximately 0.0, interpreted as evidence for contributions from both s- and r-process nucleosynthesis. Negative [Ce/Nd] in clusters with [Fe/H] < -0.5 supports predominantly r-process production of these elements in those clusters. These abundance patterns provide empirical constraints on the bulge’s chemical evolution; the nucleosynthetic origins remain interpretations of the measured ratios.

PublicOld star clusters in the Milky Way’s central bulge preserve chemical clues to the region’s history. Researchers reanalyzed archived high-resolution spectra of 135 giant stars in 14 clusters, using a consistent method to measure their chemical makeup. They found a previously unrecognized lithium-rich giant in the cluster NGC 6723. Differences in sodium abundance indicate that the sample includes distinct stellar populations. Compared with clusters in the Galaxy’s halo, the bulge clusters also show different patterns of certain elements relative to iron. Their scandium abundances are lower than those of disk stars with comparable iron content, potentially offering clues to how scandium forms. No cluster showed a statistically significant spread in heavy-element abundances. Ratios of particular heavy elements suggest contributions from both slow and rapid neutron-capture processes, with rapid capture likely dominating the production of cerium and neodymium in the lower-metallicity clusters. These origins are interpretations of the chemical evidence, not directly observed production events.

Young explorerStars contain different kinds of ingredients. Scientists studied light from 135 big stars in 14 groups near the middle of our galaxy to find out what ingredients they have. They spotted one star with lots of lithium and found differences in sodium between stars. These clues help scientists piece together the galaxy’s past, though they do not tell the whole story.

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VIII. First interstellar detection of fully deuterated methyl cyanide

A. Belloche, J. K. Jørgensen, M. N. Drozdovskaya+12 more

AstronomerAn ALMA COMPASS imaging spectral survey detected all three deuterated isotopologs of methyl cyanide toward the northern binary component of L1551 IRS5, including the first reported interstellar detection of CD3CN. Column densities were derived assuming local thermodynamic equilibrium. The inferred D/H ratio rises by about half an order of magnitude with each successive level of deuteration, resembling the pattern measured for methanol in several other low-mass protostars. The authors interpret this as evidence that methyl cyanide forms predominantly on dust-grain surfaces during the cold prestellar phase. However, a factor-of-two difference between methyl cyanide and methanol D/H ratios admits alternative explanations: gas-phase chemistry during warm-up could contribute approximately equally to methyl cyanide production, or methyl cyanide and its deuterated isotopologs could form somewhat earlier than methanol in the prestellar phase. These interpretations remain untested by models that follow methyl cyanide deuteration through CD3CN; none has yet investigated that full sequence.

PublicAstronomers using ALMA report the first detection in interstellar space of CD3CN, a form of methyl cyanide in which three hydrogen atoms are replaced by deuterium, a heavier form of hydrogen. They also detected the two less-deuterated forms toward the northern member of the young binary system L1551 IRS5. Their abundance estimates assume local thermodynamic equilibrium. The pattern of deuterium enrichment resembles that seen in methanol and suggests that methyl cyanide forms mainly on dust grains in the cold period before a star forms. This is an interpretation, not a direct observation of the chemistry. A difference between the deuterium enrichment of methyl cyanide and methanol could mean that reactions in warming gas also make a substantial share of methyl cyanide, or that it forms earlier than methanol. Chemical models have not yet explored methyl cyanide with all three hydrogen substitutions, leaving these explanations unresolved.

Young explorerScientists used a telescope called ALMA to find a special kind of molecule near a baby star. It is called CD3CN, and three of its hydrogen atoms are the heavier kind of hydrogen. This is the first time scientists have found this molecule in the space between stars. They found two related kinds there, too. The clues suggest these molecules may have been made on tiny, cold dust grains before the star formed. But scientists are not sure of the whole story: some might have been made later in warmer gas, or they might have formed earlier than another molecule they compared them with.

On the Proper 3D Modeling of Orbits in Wide Binary Gravity Tests

Kyu-Hyun Chae

• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerThe author introduces and tests a Bayesian MCMC orbit-reconstruction algorithm for wide binaries that treats the semimajor axis a as an explicit free parameter. Tests on the α-Cen AB–Proxima system and the Chae et al. sample of 36 wide binaries find that, when an observational constraint is included, this formulation is equivalent to an implicit-a algorithm enforcing an internal consistency relation involving the physical sky-plane separation s. The approach requires precise 3D relative positions and velocities, with essentially exact sky-plane angular coordinates and sufficiently precise distances for the stated consistency relations to be readily applied. The paper presents modeled orbits for α-Cen AB–Proxima under both Newtonian and Milgromian (MOND) gravity. It argues that a recent inference favoring Newtonian gravity from the 36-system sample may result from arbitrarily enlarged errors in some relative-position or velocity components, rather than establishing that explanation conclusively. The discussion emphasizes system-specific parameters, follow-up observations of anomalous systems, and Bayesian MCMC methods for low-acceleration gravity tests.

PublicWidely separated stars bound together by gravity can help test how gravity works when its pull is weak, but the tests depend on accurate positions, velocities, and careful orbit modeling. This study tests a method that lets an orbit’s size vary explicitly during the calculation. Using the Alpha Centauri AB–Proxima system and a sample of 36 wide star pairs, the author finds that the method agrees with an alternative approach when the appropriate observational constraint is included. The study also calculates possible orbits for the Alpha Centauri system under Newtonian gravity and an alternative called MOND; these are model calculations, not a reported choice between the theories. The author argues that a recent claim supporting Newtonian gravity from the 36 pairs may depend on artificially enlarged measurement uncertainties. The paper stresses the need for parameters tailored to each system and further observations of unusual cases.

Young explorerSome stars are far apart but still held together by gravity. Scientists can use their positions and movements to work out how they might travel around each other. The author checked two ways of doing this and found that they agree when the same measured information is properly included. The author also drew possible star paths using two different ideas about gravity. That does not tell us which idea is right. The paper says careful measurements matter, and unusual star pairs need another look.

The IRAC Distant Cluster Survey

Karolina Garcia, Anthony H. Gonzalez, Mark Brodwin+9 more

AstronomerThe IRAC Distant Cluster Survey (IDCS) identifies 825 galaxy cluster and group candidates in Boötes using PZWav and photometric-redshift probability distributions from twelve-band optical and infrared imaging. The catalog spans 0.08 < z < 2.0, with median z = 0.93 and 147 candidates at z ≥ 1.5. At the adopted S/N ≥ 4 threshold, simulations for z < 1.5 indicate 93% purity and 50% completeness at log(M200c/M☉) = 13.74 ± 0.01; these performance estimates are not established here for the higher-redshift sample. Comparison with spectroscopy gives a photometric-redshift scatter of σz/(1+z) = 0.017. A total of 80 candidates, including 18 previously published ISCS systems, are confirmed spectroscopically and/or through X-ray observations. DESI DR1 supplies redshifts for 38 systems at 0.12 < z < 0.93, including 23 newly confirmed clusters, each with at least 10 spectroscopic members. Their measured median velocity dispersion is approximately 490 km/s, corresponding to a median halo mass of 1.1 × 10^14 solar masses. Comparison with 39 independently confirmed literature clusters gives a median centroid offset of 211 kpc. The catalog is presented as a resource for large-scale structure, environmental galaxy evolution, and cluster-detection calibration for surveys including LSST, Roman, and Euclid.

PublicAstronomers have compiled a catalog of 825 possible galaxy clusters and smaller galaxy groups in a sky region called Boötes. They selected these candidates using optical and infrared images in twelve wavelength bands to estimate galaxy redshifts, which help distinguish systems along the line of sight. The catalog covers a broad redshift range, including 147 candidates at redshift 1.5 or higher. So far, 80 candidates have been confirmed using spectroscopy, X-ray observations, or both; the rest remain candidates. DESI spectroscopy newly confirmed 23 clusters. In a subset of 38 systems with at least ten spectroscopically identified members each, galaxy motions imply a median total halo mass of about 110 trillion times the Sun’s mass. Simulations suggest that, below redshift 1.5, 93% of selected candidates are genuine systems, while only half of systems are recovered at a specified lower mass scale. Those estimates do not establish the catalog’s reliability at higher redshifts. The catalog is intended to support studies of how galaxies evolve in crowded environments and to help test cluster-finding methods for future surveys.

Young explorerGalaxies are huge collections of stars, and some galaxies gather in groups. Astronomers looked at pictures of space and made a list of 825 places where galaxy groups might be hiding. Other observations have already helped them check that 80 of these places really contain groups or clusters. The others still need checking. Computer tests suggest their search works well for part of the list, but it can miss some groups, and the farthest-away candidates are less certain. The list can help astronomers study galaxies that have lots of neighbors.

From Dispersion to Metallicity: Probing the Milky Way Circumgalactic Medium with Fast Radio Bursts

Manami Roy, Sanskriti Das, Smita Mathur+2 more

AstronomerA statistical analysis of 25 FRB sightlines constrains the metallicity of the hot Milky Way CGM by combining metallicity-dependent oxygen-absorption DM estimates with metallicity-independent FRB DMs. For assumed diffuse baryon fractions in the IGM and intervening halos of f_d = 0.0, 0.6, and 0.8, bootstrap median metallicities are respectively 0.12 (+0.09/-0.04), 0.26 (+0.18/-0.12), and 0.39 (+0.26/-0.20) times solar. The f_d = 0.8 case yields super-solar metallicities along multiple sightlines, which the authors regard as implausible for the Milky Way CGM. They interpret enrichment above expectations for IGM accretion, even under their conservative f_d = 0.0 assumption, as strong empirical evidence that the CGM efficiently retains a substantial fraction of metal-enriched galactic feedback material. Significant sightline-to-sightline differences in inferred metallicity suggest an anisotropic, multiphase CGM shaped by feedback and accretion.

PublicThe Milky Way is surrounded by gas that can both supply the galaxy and receive material expelled from it. Researchers used 25 lines of sight toward fast radio bursts, together with oxygen absorption estimates, to infer how enriched the hot surrounding gas is in elements heavier than helium. The estimated median enrichment ranges from about 12% to 39% of the Sun’s level, depending on assumptions about gas between galaxies and in intervening galactic halos, with substantial uncertainty in each estimate. The highest assumed diffuse gas fraction also produces some estimates above the Sun’s enrichment level, which the authors consider implausible. They interpret the findings as evidence that much of the enriched material expelled by the Milky Way remains in its surrounding gas. Differences between directions suggest that this gas is uneven and has multiple phases, rather than forming a uniform reservoir.

Young explorerOur galaxy has lots of hot gas around it. Scientists studied quick flashes of radio waves passing through space, along with clues from oxygen, to work out what is in that gas. They think it holds onto lots of material that the galaxy has pushed out, and that the gas is different in different directions. They are not sure exactly how much of each ingredient is there, because the answer depends partly on how much other gas the radio waves passed through.

PRISMS GHZ8: Evidence for a Young Burst and Potential Merger Activity at z=10.23

Ruqiu Lin, Jorge Zavala, Javier Álvarez-Márquez+26 more

AstronomerJWST/MIRI LRS spectroscopy of the UV-bright galaxy GHZ8 at z=10.23, magnified by μ=1.23, detects the Hβ–[OIII] complex at approximately 5σ and Hα at approximately 4σ. NIRCam morphological decomposition reveals a bright, extended main component and a faint, compact southeastern component separated by 0.16 arcseconds, approximately 600 pc. Their demagnified UV absolute magnitudes are −19.91±0.10 and −18.03±0.15, with UV slopes of −2.53±0.22 and −3.45±0.49, respectively. The blue continua indicate young stellar populations; the authors interpret GHZ8-SE’s extreme slope as requiring an extremely young, interstellar-medium-poor population with an ionizing-photon escape fraction of 0.6–1.0. UV and Hα luminosities combined with spectro-photometric SED fitting allow either a recent, short-lived burst now in its final phases or continuous star formation lasting less than 50 Myr in GHZ8-main. The authors present this as evidence for bursty star formation, although the continuous-star-formation alternative remains viable. A merger-induced starburst is a possible interpretation, requiring deeper imaging or spatially resolved kinematics for confirmation.

PublicJWST observations reveal two closely spaced parts of GHZ8, a bright ultraviolet galaxy in the early Universe: a larger, brighter main region and a smaller, fainter companion region. The telescope also detected emission from hydrogen and oxygen. Both regions have blue ultraviolet light, indicating young stars. The researchers interpret the smaller region’s exceptionally blue light as evidence for extremely young stars with little surrounding interstellar material, allowing an estimated 60–100% of their hydrogen-ionizing light to escape. This is an inference from the light, not a direct measurement of escaping radiation. For the main region, the observations and modeling allow either a brief burst of star formation that is winding down or steady star formation over less than 50 million years. A merger might have triggered a burst, but stronger evidence is needed. The study helps investigate why some early galaxies shine so brightly and how they may have contributed to cosmic reionization.

Young explorerA space telescope looked at a faraway galaxy called GHZ8 and saw a big bright part and a little faint part close together. Their blue light tells scientists they have young stars. Scientists think lots of special light may escape from the little part. The big part may be finishing a quick burst of making stars, or it may have been making stars steadily for a short time. The two parts might be coming together, but scientists need a closer look to know.

Combining Multiple Incomplete Astronomical Surveys to Estimate Galaxy Flux Distributions

Maximilian Autenrieth, David A. van Dyk, Vinay Kashyap+3 more

• Applications
• Instrumentation and Methods for Astrophysics

AstronomerThe authors propose a hierarchical Bayesian framework for estimating a galaxy population’s X-ray flux distribution from non-representative X-ray and optical surveys. A broken power law, formulated as a mixture of Pareto distributions, models the flux distribution. The method combines two or more surveys with different incompleteness functions, using deeper surveys to help constrain the X-ray log(N)-log(S). Dedicated survey simulations inform the missing-data corrections, including corrections for sources detected in neither survey; these rely on a well-calibrated characterization of incompleteness. In a simulation study designed to mimic the Chandra Deep Field South (CDF-S), the model accurately recovers the flux distribution despite high systematic incompleteness. The authors also apply the method to CDF-S data, but the abstract reports no specific findings from that application.

PublicFaint galaxies can escape detection in surveys, leaving an incomplete picture of how their X-ray brightnesses are distributed. The authors propose a statistical method that combines X-ray and visible-light surveys, accounting for their different chances of missing faint sources. Deeper surveys help fill gaps in the X-ray picture, while simulations help determine corrections even for galaxies missed by both surveys. The method depends on accurately understanding those missing-source patterns. Tests with simulated data resembling the Chandra Deep Field South recovered the underlying brightness distribution accurately, even when many sources were systematically missed. The method was also applied to real data from that field, but the abstract does not describe the results of that application.

Young explorerSome galaxies are too faint for a sky survey to spot. The researchers made a new counting method that uses two kinds of sky surveys together to work out how many galaxies have different X-ray brightnesses, including ones the surveys miss. They tried it on a pretend sky, where they knew the answer, and it worked well even when many galaxies were missed. It needs good clues about which galaxies the surveys might miss. They also used it on real sky data, but this summary does not tell us what they found there.

Modeling the Ages and Chemical Abundances of Elliptical Galaxies

Nicole Marcelina Gountanis, David H. Weinberg, Aliza G. Beverage+3 more

AstronomerSpectroscopy of elliptical galaxies shows increasing stellar age, mean metallicity, and [Mg/Fe] with stellar mass or velocity dispersion. This study uses one-zone galactic chemical evolution models with flexible star formation histories to interpret SSP-equivalent ages, [Mg/H], and [Mg/Fe] at z ~ 0 and z ~ 0.7. SSP fits to synthetic composite spectra recover values close to the light-weighted, logarithmically averaged model ages and abundances. With supernova yields fixed to Milky Way-motivated values, the predicted abundance–age relations are surprisingly insensitive to the detailed star formation history; older populations have higher [Mg/Fe]. Within these models, matching observed trends requires higher star formation efficiency and weaker outflows in more massive galaxies. A core-collapse yield ratio calibrated to the Milky Way plateau, [Mg/Fe]cc ~ 0.45, underpredicts elliptical-galaxy [Mg/Fe] by 0.05–0.1 dex. Raising the yield ratio to 0.55 improves agreement but leaves a residual shortfall. A self-enriching terminal burst, which could lower the light-weighted age and raise [Mg/Fe], is discussed as a possible resolution, not an established finding.

PublicObservations show that more massive elliptical galaxies tend to have older stars, more heavy elements, and more magnesium relative to iron. The researchers modeled how star formation and chemical enrichment could produce these patterns, comparing their models with galaxies at two cosmic epochs. Tests with simulated spectra showed that the usual fitting method gives ages and chemical abundances close to averages weighted toward the stars contributing more light. In the models, changing the detailed timing of star formation had surprisingly little effect on the relationships between age and chemical composition. Matching the observed trends required more massive galaxies to form stars more efficiently and lose less gas through outflows. However, models using supernova element yields guided by Milky Way observations still predicted too little magnesium relative to iron. Increasing the assumed magnesium-to-iron yield helped but did not fully resolve the mismatch. One proposed explanation is a final burst of star formation that enriches itself, making the galaxy appear younger and more magnesium-rich; the study does not establish that this happened.

Young explorerAstronomers looked at big groups of stars called elliptical galaxies. The bigger ones tend to have older stars and a different mix of ingredients, including more magnesium compared with iron. The scientists made computer models to try to explain this. But their models still gave too little magnesium compared with iron, even after they changed how much exploding stars make. One idea is that these galaxies made a last burst of stars that changed their mix of ingredients and made them look younger. That is a possible explanation, not something the scientists have proved.

A prevalent population of normal-mass central black holes in high-redshift massive galaxies

Junyao Li, Yue Shen, Ming-Yang Zhuang

AstronomerTo mitigate selection biases favoring luminous, overmassive SMBHs, the authors search for broad-line AGNs in 117 spectroscopically confirmed massive galaxies at z~3–5 using deep JWST imaging and spectroscopic surveys. They identify 20 moderate-luminosity AGNs with a mean black hole-to-stellar mass ratio of approximately 0.1%, consistent with the local value. Reconstructing these ratios back to z~6, rather than directly observing that earlier population, leads them to infer that a substantial, previously overlooked population with normal mass ratios existed within the first billion years. Together with previously reported overmassive SMBHs, these findings suggest diverse early formation and growth pathways. Comparable ratios in star-forming and quiescent hosts also suggest that massive-galaxy quiescence does not necessarily require an overmassive SMBH, contrary to common theoretical expectations.

PublicSearches of the early Universe tend to spot unusually bright, massive black holes more easily than black holes with masses more typical for their host galaxies. To reduce this bias, researchers examined 117 massive galaxies using deep James Webb Space Telescope images and spectroscopic surveys. They identified 20 actively growing black holes whose masses average about 0.1% of their galaxies’ stellar masses, similar to the nearby-Universe ratio. By reconstructing how those ratios may have evolved, the team infers that many black holes with ordinary proportions already existed within the Universe’s first billion years; this is not a direct observation of that earlier population. The results suggest multiple routes for early black hole growth. Similar ratios in galaxies with ongoing and little star formation also suggest that an unusually massive black hole is not always needed for a massive galaxy to become quiet.

Young explorerA galaxy is a huge family of stars, and it can have a giant black hole in its middle. Very bright black holes are easier to find, so we might miss others. Scientists found 20 growing black holes in faraway galaxies. On average, their size compared with the mass of their galaxy’s stars was much like what we see nearby. Looking backward with calculations, the scientists think many such black holes were around even earlier. That is a clue, not something they saw directly.

From ASTRID to BRAHMA -- The role of overmassive black holes in little red dots in cosmological simulations

Patrick LaChance, Aklant Kumar Bhowmick, Rupert A.C. Croft+8 more

AstronomerThe authors test whether overmassive black holes in a BRAHMA cosmological hydrodynamic simulation at z ∼ 4–8 can explain JWST Little Red Dots (LRDs), using mock observations that combine dust-attenuated galaxy emission with AGN templates. A model in which unresolved dense gas surrounds the AGN and produces a strong Balmer break yields substantially more LRD-like systems than a standard low-redshift AGN model. Matching the observed abundance, Φ ∼ 2 × 10^-4 Mpc^-3, requires assuming that all AGN occupy this gas-enshrouded phase, implying a duty cycle approaching unity that current theoretical models do not predict. JWST constraints on the high-redshift black hole mass function suggest that a deficit of low-mass black hole LRDs, with M_BH ≲ 10^7 solar masses, in BRAHMA may contribute to this tension. With the same gas-enshrouded prescription, ASTRID, which lacks overmassive black holes, underproduces LRDs by at least about two orders of magnitude. The simulations therefore favor overmassive black holes as contributors to, rather than the sole explanation for, the observed LRD population.

PublicCould unusually massive black holes explain the compact objects called Little Red Dots seen by JWST? Researchers tested this idea by making simulated JWST observations of galaxies and their active black holes. Their models produced many more Little Red Dot look-alikes when dense gas surrounded the active black holes than when they used a standard model of their light. However, matching the observed abundance required every active black hole to be in this gas-covered state—an exceptionally high fraction that current theories do not predict. A shortage of simulated Little Red Dots containing lower-mass black holes may help explain that difficulty. A second simulation without unusually massive black holes produced at least roughly 100 times too few Little Red Dots, even with the dense gas model. The authors conclude that unusually massive black holes may explain some Little Red Dots, but are unlikely to explain the whole population.

Young explorerJWST sees little red dots in space. Scientists used computer-made galaxies to ask whether unusually big black holes, with glowing material around them, could help explain the dots. Their pretend pictures made more dots when thick gas wrapped around the glowing centers. But to make enough dots, every active black hole in the model had to have that gas wrapping. Scientists think that is unlikely. So these big black holes might explain some of the red dots, but probably not all of them.

The Kinematically Hot, Extremely Metal-Poor C-19 Stellar Stream in DESI DR2

Nasser Mohammed, Joseph Y. Tang, Ting S. Li+47 more

AstronomerThe authors characterize C-19 with a mixture model that jointly uses proper motions, radial velocities, and metallicities to distinguish stream members from the Milky Way halo background. Using DESI spectroscopy, they identify 47 confirmed members, including 41 newly identified stars and 6 previously reported members. They measure a velocity dispersion of 7.8 (+1.5/−1.3) km/s and a mean metallicity of [Fe/H] = −3.36 (+0.12/−0.10), and identify a new spur feature. These observations reinforce the characterization of C-19 as a kinematically hot, extremely metal-poor stream. Its globular-cluster-like abundance patterns contrast with a velocity dispersion difficult to reconcile with a conventional, purely baryonic disrupting globular cluster; the abstract does not establish an alternative progenitor model. Application to additional DESI streams and population-level comparisons with simulations are planned, not reported results.

PublicC-19 is a trail of stars whose chemical makeup resembles that of a globular cluster, a tightly packed group of stars. Yet the spread in its stars’ velocities is unusually large for a conventional cluster being pulled apart by a galaxy’s gravity. Using spectra from the Dark Energy Spectroscopic Instrument and a statistical method that combines stellar motions and chemical information, researchers identify 47 confirmed members of C-19, including 41 newly recognized members. They measure a velocity spread of about 7.8 kilometres per second and confirm that the stream is extremely poor in iron compared with the Sun. They also find a previously unrecognized feature called a spur. The findings support earlier descriptions of C-19 as an unusually high-velocity-spread, metal-poor stream, but do not settle how it formed. Comparisons of larger stream samples with simulations are planned for future work.

Young explorerA galaxy’s gravity can pull a bunch of stars apart into a long trail. Scientists studied a trail called C-19 and found 41 stars they had not known belonged to it before, bringing their confirmed count to 47. These stars have very little iron, and their speeds differ more than scientists would expect from an ordinary tight bunch of stars being pulled apart. The team also spotted an extra feature called a spur. They still do not know exactly how this puzzling star trail formed.

Supermassive stars with embedded stellar black hole cores: dense assembling star clusters as faint multiple Little Red Dot systems

Antti Rantala

AstronomerDirect simulations of assembling star clusters, including stellar evolution and post-Newtonian black hole dynamics, suggest that runaway stellar collisions can produce extremely massive or supermassive stars in environments with half-mass surface densities ≳10^6 solar masses per square parsec. Rapid mass segregation and relaxation within these stars’ spheres of influence can bring stellar black holes of ≲60 solar masses into strong interactions with them, potentially embedding the black holes in their gaseous layers. The authors propose that this quasi-star-like phase is a natural outcome in the densest clusters. It may last 10–100 times longer than the supermassive star’s lifetime, extending growth through stellar collisions; capture of multiple black holes could also produce embedded gravitational-wave sources. Assembly-region sizes of about 100 parsecs, quasi-star masses ≳10^4 solar masses, and proximity to young, massive blue star-forming clumps are consistent with JWST’s faint multiple little red dots, but this consistency does not establish their identity.

PublicComputer simulations explore how crowded young star clusters might create enormous stars through repeated stellar collisions. In the densest simulated environments, smaller black holes may move toward these stars and become buried inside their gas, forming objects resembling proposed “quasi-stars.” The authors suggest this stage could last 10–100 times longer than the lifetime of a supermassive star, allowing more growth through collisions with other stars. If several black holes are captured, they could also form sources of gravitational waves inside the gas. The predicted masses, surrounding region sizes, and nearby young blue star-forming clumps are consistent with some faint groups of “little red dots” discovered by the James Webb Space Telescope. This is a possible explanation, not a confirmed identification.

Young explorerThe scientists used computers to imagine a very crowded group of stars. Their models suggest that stars can bump together and build a giant star. A black hole might then get tucked inside the giant star’s gas. The scientists think this could help explain some little red dots a telescope has seen far away, but they do not yet know if those dots really are hiding black holes this way.

No Blue without Red: Evolutionary Properties of Super-Early Galaxies

A. Ferrara, G. Rodighiero, S. Carniani+3 more

AstronomerJWST observations reveal diverse UV properties among luminous galaxies at z > 10, from extremely blue, dust-poor systems to a smaller reddened population. The authors apply the Attenuation-Free Model (AFM) to 17 galaxies with suitable size constraints drawn from a spectroscopically confirmed sample of 32. In this framework, radiation-driven outflows move dust to large radii, reducing effective attenuation. The analysis infers halo masses around log(M/M_sun) = 10.7, star formation efficiencies of 0.01–0.05, and frequent super-Eddington conditions that drive outflows. The authors propose, rather than establish observationally, an evolutionary sequence from an obscured “Red Monster” phase to a UV-bright “Blue Monster” phase, interpreting EGS-z11-R0 at z = 11.45 as a candidate obscured-stage system. Compact sources with effective radii below 150 pc challenge AFM; AGN-dominated emission is suggested speculatively. Future JWST and ALMA observations are needed to test the model predictions.

PublicJWST has found very early galaxies whose ultraviolet light looks surprisingly different: many are extremely blue and contain little dust, while a smaller group looks much redder. Researchers studied 17 galaxies using a model in which radiation pushes dusty material away from a galaxy’s center, allowing more ultraviolet light to escape. Their model-based analysis suggests that these galaxies inhabit massive dark matter halos and can generate powerful outflows. They propose that some red, dust-obscured galaxies may become bright blue galaxies as those outflows clear their centers; this sequence has not yet been established by observations. They interpret the red galaxy EGS-z11-R0 within this picture, but very compact galaxies are harder for the model to explain. The suggestion that active galactic nuclei dominate those compact sources remains speculative. Further JWST and ALMA observations are needed to test these ideas.

Young explorerJWST has seen galaxies from very long ago. Some look blue, and some look redder. Scientists tried a model to explain why: light might push dusty material away from a galaxy’s middle, making it easier to see the blue light inside. They think a dusty red galaxy might turn into a bright blue one this way, but they have not proved that it happens. Their idea also has trouble explaining some very tiny galaxies. More telescope observations will help check it.

Reconstructing the Globular Cluster Initial Mass Function from Present-day Globular Cluster Systems

Elizabeth Moreno-Hilario, Hui Li, Luis A. Martinez-Medina

AstronomerThe observed present-day globular cluster mass function has a nearly universal turnover near 2 × 10^5 solar masses. To investigate its origins, the authors reconstruct the high-mass regime of the initial mass function by reversing estimated dynamical mass loss, without imposing an initial functional form. Their environment-dependent mass-loss model is calibrated against direct N-body simulations in time-dependent tidal fields. Applied to galaxies with halo masses of approximately 10^9–10^12 solar masses, the analysis combines individually measured cluster masses with statistical samples constructed from observed global properties. The recovered initial distributions shift toward higher masses and exhibit high-mass power-law behavior. Inferred slopes correlate strongly with host halo mass, becoming steeper in more massive hosts. These model-based reconstructions suggest that the initial high-mass slope depends on galactic properties; they are not direct observations of the initial populations and do not establish which competing explanation produces the near-universal turnover.

PublicAcross many kinds of galaxies, the present-day distribution of globular cluster masses peaks near 200,000 times the Sun’s mass. Researchers investigated what these clusters’ original mass distributions might have looked like by estimating how much mass they lost over time. Their reconstruction uses a model calibrated with computer simulations, alongside individual cluster measurements and statistical samples based on galaxy observations. The inferred original distributions extend toward higher masses and show a pattern: more massive galaxy halos have steeper declines in the numbers of clusters at the high-mass end. This suggests that a galaxy’s properties influence its clusters’ starting mass distribution. The original masses are inferred, not directly observed, and the study does not settle why the present-day peak is so similar across galaxies.

Young explorerGalaxies have big groups of stars called globular clusters. These groups can lose mass over time. Scientists used observations and a computer-tested model to work backward and estimate how massive the groups were at the start. Their estimates suggest that different galaxies started with different mixes of cluster masses, but they cannot watch that beginning directly.

A Consistent Comparison of Intracluster Light Assembly in Simulations I. Redshift Evolution and Progenitor Galaxies

Harley J. Brown, Garreth Martin, Frazer R. Pearce+5 more

AstronomerThis simulation study compares intracluster light (ICL) assembly in cluster-mass haloes (M178c ≈ 10^14–10^15 solar masses) across Horizon-AGN, TNG100, The Three Hundred Gizmo-Simba 7K, and Hydrangea using a homogenized ICL identification framework. The fiducial definition yields broadly consistent z ≈ 0 ICL stellar mass fractions of about 0.1–0.2 and no significant evolution in the mean fraction along cluster progenitors back to z ≳ 2. Both the absolute fraction and whether it declines toward higher redshift or remains constant depend strongly on how ICL is separated from the central galaxy; no significant inter-simulation discrepancies emerge under consistent identification methods. Tracing present-day ICL stars to their progenitors shows that lower-mass satellites generally contribute slightly more relative to their stellar mass, but the infalling satellite mass function primarily determines the dominant contributors. Most satellite-sourced ICL stars are therefore expected to come from galaxies with infall stellar masses above roughly 10^10 solar masses, largely in the 10^10.5–10^11.5 solar-mass range.

PublicGalaxy clusters contain a diffuse glow from stars stripped out of satellite galaxies or cast out during galaxy mergers. Researchers studied how this intracluster light builds up in four computer simulations. When they used the same rules to identify it, the simulations agreed broadly: under their preferred definition, this component accounts for about 10–20% of the cluster stellar mass at the present epoch, with no significant average change when tracing the clusters' ancestors into the past. But the boundary between this diffuse light and the central galaxy matters greatly: changing that definition changes both the estimated fraction and whether it appears to evolve over time. Although smaller satellite galaxies generally contribute slightly more in proportion to their mass, the simulations suggest that most satellite-sourced intracluster stars come from more massive galaxies because the mix of incoming galaxy masses controls the overall contribution. These are simulation findings, not direct observational measurements.

Young explorerA galaxy is a huge group of stars. When galaxies tug on each other or join together, some stars get pulled out and make a faint glow between galaxies. Scientists used four computer pretend-universes to study this glow. When they counted the stars the same way, the pretend-universes gave similar answers. But it is hard to decide where the big galaxy in the middle ends and the faint glow begins, so different counting rules can change the story. The computers suggest that most of the glow's stars pulled from smaller companion galaxies came from the bigger companions, even though little ones gave up slightly more for their size.

pop-cosmos: Galaxy size evolution across structural and star-formation classifications in COSMOS-Web

Madalina N. Tudorache, Hiranya V. Peiris, Stephen Thorp+7 more

• Cosmology and Nongalactic Astrophysics

AstronomerCombining pop-cosmos stellar-mass and sSFR estimates with COSMOS-Web sizes and morphologies yields 99,369 galaxies for studying size–mass and size–redshift relations. Classification by sSFR versus morphology produces quantitatively different slopes, intercepts, and intrinsic-scatter behaviour. Intrinsic scatter depends on structural morphology but not on sSFR, providing a constraint on the galaxy–halo connection. Both quiescent and bulge-dominated size–mass relations exhibit double-power-law breaks, at stellar masses of approximately 10^10.7 and 10^11.1 solar masses, respectively. The authors interpret these different pivots as evidence that quenching and structural transformation occur on different timescales. Morphology-dependent trends are recoverable only with space-based imaging in this analysis. The quiescent pivot coincides with the peak infrared-torus AGN bolometric luminosity fraction in transitioning galaxies; the bulge-dominated pivot is linked to the halo mass scale of peak AGN-driven baryonic redistribution. These coincidences may trace an interval over which AGN feedback strengthens from quenching onset to structural transformation, rather than establishing that causal sequence.

PublicA study of 99,369 galaxies finds that the relationship between a galaxy’s size, stellar mass and cosmic era depends on how galaxies are grouped. Sorting them by how actively they form stars gives different results from sorting them by structure, such as how prominent their central bulges are. The spread in galaxy sizes around these relationships depends on structure, but not on relative star-forming activity. Galaxies with little star formation and galaxies dominated by a central bulge both show a change in their size–mass relationship, but at different masses. The authors interpret this as a sign that stopping star formation and changing structure happen on different timescales. They also identify coincidences with mass scales associated with active galactic nuclei, suggesting—but not proving—that feedback from these nuclei could connect the two changes. The structural trends required space-based images to recover.

Young explorerGalaxies are big groups of stars. Scientists studied nearly 100,000 of them to see how their sizes compare. They found that sorting galaxies by their shapes gives a different picture from sorting them by how quickly they make new stars. Their results suggest that a galaxy may stop making many new stars and change its shape at different times. Busy centers inside galaxies might help connect those changes, but the scientists have not shown that for sure. They needed pictures taken from space to find the shape-related patterns.

Mapping Dust Attenuation at Kiloparsec Scales. III. The 2175Å Bump

Ruonan Guo, Cheng Li, Tao Jing+3 more

AstronomerCombining Swift/UVOT+MaNGA with 2MASS Ks imaging, this observational study maps the 2175 Å attenuation bump on kiloparsec scales in nearby galaxies. A UV-to-near-IR estimator measures 2487 high-continuum-S/N spaxels, while an NUV-only estimator measures 7934; their absolute bump estimates agree well in overlapping regions. Separating star-forming and non-star-forming regions, the authors find the strongest bumps at low Hα surface brightness per unit stellar mass, particularly in non-star-forming regions, where this quantity is not an sSFR tracer. Bump strength decreases with Hα equivalent width and increases with Dn4000 and stellar age. Metallicity, inclination, galactocentric radius, AV, and optical attenuation-curve slope are secondary predictors. Absolute NUV bump amplitude increases with both Hα and stellar-mass surface density, unlike normalized strengths k_bump and B. The authors interpret this distinction as a partial dust-column dependence of absolute amplitude, with normalized measures better tracing effective bump prominence. The correlations support, but do not establish, local radiation-field processing of the bump carriers.

PublicResearchers mapped a feature near the ultraviolet wavelength of 2175 angstroms, where dust dims galaxy light more strongly than at neighboring wavelengths. Using observations of nearby galaxies, they found good agreement between two methods for measuring the feature's absolute strength. Stronger features tend to occur in regions with older stars and weaker hydrogen emission per unit stellar mass, especially outside star-forming regions. In those regions, that emission ratio should not be treated as a measure of star formation per unit stellar mass. The study also distinguishes the feature's total size from its prominence relative to the broader dust-dimming pattern: the total size partly tracks the amount of dust. These observed relationships support the idea that local radiation changes the material responsible for the feature, but they do not prove that explanation.

Young explorerDust in galaxies dims starlight, and it dims one kind of ultraviolet light extra strongly. Scientists mapped this extra dimming in nearby galaxies. It tended to stand out more in places with older stars. They think light nearby may change the dust material that makes this special dimming, but the maps do not prove that yet.

Evolution of Binaries Under Stochastic Perturbations

Andrea Caputo, Giovanni Maria Tomaselli, Chris Hamilton

• Solar and Stellar Astrophysics
• High Energy Physics - Phenomenology

AstronomerThis theoretical study develops a general Fokker-Planck framework for the stochastic evolution of Keplerian binaries, with an algorithm for deriving drift and diffusion coefficients for arbitrary orbital variables from perturbation statistics. For adiabatic tides, white-noise tides, and impulsive encounters with a third body of arbitrary density profile, the authors derive coefficients for all six orbital elements, evolution timescales, and analytic steady-state distributions. Extensions include orientation evolution, the full tensor structure of tidal correlators, extended perturbers, and exact impulsive-encounter geometry; the latter yields a slightly sub-thermal steady-state eccentricity distribution. The equations are presented for application to binaries perturbed by dark matter subhaloes, ultralight dark matter, and the interstellar medium. These are mathematical results and potential applications to population data, not reported observational detections.

PublicThe researchers developed a mathematical toolkit to describe how random disturbances gradually change the orbits of two objects circling each other. They worked out how orbital shape, size, and orientation evolve under three kinds of disturbance: slowly varying tidal forces, tidal forces modeled as white noise, and sudden encounters with another object. Accounting precisely for the geometry of sudden encounters produces a predicted long-term distribution of orbital shapes that differs slightly from a standard theoretical distribution. The framework can be applied to studies of disturbances from dark matter structures, ultralight dark matter, and material between stars. The paper presents theoretical calculations, not measurements showing that these effects have been observed.

Young explorerImagine two space objects going around each other while things nearby give them little tugs or sudden nudges. Scientists made math rules to work out how those nudges could change the pair’s path and the way it points. These are calculations about what could happen, not a report that scientists watched it happen.

Outflows in a super-Eddington quasar drive clumpy circumgalactic medium and extended Hα nebulae at z ≳6

Lucas Tortora, Tiago Costa, Debora Sijacki+1 more

AstronomerThe discovery of billion-solar-mass black holes at z ≳ 6 motivates simulations of rapid early growth and its feedback signatures. This study uses zoom-in simulations of a massive protocluster at z ~ 6, comparing the fiducial FABLE model with variants allowing earlier black hole seeding and mildly super-Eddington accretion. In the simulations, the central quasar is Compton-thick for most of its evolution because of its compact host's ISM. Sufficiently strong feedback triggers a blow-out that opens ionizing escape channels and exposes the central engine. Metal-enriched outflows reshape the CGM, producing cold, fast neutral clumps and increasing the halo's neutral-hydrogen covering fraction. Radiative transfer calculations with a new ray-tracing code predict Hα nebulae whose size and luminosity increase with feedback strength and decrease with obscuration. These are model-derived signatures for comparison with observations, not reported observational detections.

PublicBlack holes more than a billion times the Sun's mass have been discovered in the early Universe, raising questions about how they grew so quickly and affected their galaxies. The researchers simulated a young, massive grouping of galaxies, testing models that let black holes begin growing earlier and take in matter somewhat faster. In the simulations, gas in the central black hole's compact galaxy hides its bright surroundings for most of its history. When energy released by the growing black hole becomes strong enough, it clears paths through that gas. The resulting outflows carry chemically enriched material into the surrounding halo and produce cold, fast-moving clumps of neutral hydrogen. Calculations also predict extended clouds glowing in hydrogen's Hα light: stronger feedback makes these nebulae larger and brighter, while greater obscuration makes them smaller and fainter. These predictions offer ways to test the models against observations.

Young explorerSome black holes grew very big when the Universe was young. Scientists made computer models to explore how this could happen and what it might do to nearby gas. In their models, gas hides the bright area around a growing black hole. Later, energy from that area can push gas away and open gaps for light to escape. Farther out, the moving gas makes cold clumps, and some gas glows. The models suggest that stronger pushes make the glowing clouds bigger and brighter. Scientists can look for these clues in the sky to check their ideas.

Variations in the 3.3 μm Polycyclic Aromatic Hydrocarbon Feature Across Nearby Galaxies Driven by Metallicity and Radiation Field Spectrum

Hannah B. Koziol, Karin Sandstrom, Dalya Baron+29 more

AstronomerUsing JWST/NIRCam imaging of nearby galaxies, the authors present an empirical method to isolate PAH-correlated F335M emission through continuum subtraction with F300M and F360M. The slope in F335M/F300M versus F360M/F300M color space depends on local ISM properties, most strongly on specific star formation rate. Weaker features within these bands appear suppressed relative to the main 3.3 μm feature in actively star-forming regions. Both 3.3/7.7 and 3.3/11.3 μm ratios decrease with increasing metallicity, which the authors interpret as evidence for smaller PAH populations at low metallicity. Comparisons with optical ionized-gas line ratios and dust models indicate that radiation-field spectral variations also influence these ratios. The findings support inhibited-growth formation scenarios, rather than establishing a unique explanation, and highlight the need to account for both local radiation fields and gas-phase metallicity when interpreting PAH band ratios.

PublicResearchers used James Webb Space Telescope images of nearby galaxies to study infrared light from molecules called polycyclic aromatic hydrocarbons, or PAHs. They developed a method to separate emission associated with these molecules from the underlying background light. The observed emission patterns vary with local conditions, especially the rate of star formation relative to stellar mass. Comparisons between infrared features suggest changes in the molecules’ sizes, electrical charges, and heating. The authors interpret one trend as indicating smaller PAHs where the gas contains fewer heavy elements, consistent with scenarios in which their growth is inhibited. However, the spectrum of the surrounding radiation also affects the signals, so the infrared ratios cannot be interpreted as simple measures of molecular properties alone.

Young explorerScientists used the Webb telescope to study light from tiny molecules in nearby galaxies. They worked out a way to separate that light from other light around it. The molecules’ light looks different in different places. The scientists think some differences may mean the molecules are smaller, but the light shining on them matters too. They need to consider both to understand what they see.

Energy Partitioning in Dust-catalyzed H₂ and HD Formation Revealed by Molecular Simulations Considering Nuclear Quantum Effects

Xiaolong Yang, Lile Wang, Di Li+1 more

AstronomerThis computational study uses ring-polymer molecular dynamics with a machine-learning force field to model H2 and HD formation on graphene at 25, 50 and 100 K. It focuses on chemisorbed-H recombination, previously identified as the dominant low-temperature pathway on bare graphitic surfaces when nuclear quantum effects are included. Desorbing molecules retain approximately 84–87% of the effective released energy, with weak dependence on velocity-initialization temperature under the sampling protocol used. Rovibrational motion dominates the retained energy at 25 K, while center-of-mass translation becomes increasingly important at 100 K. H2 and HD have similar total retention but modest differences in internal partitioning; effective joint rovibrational distributions show a modest positive association between vibrational and rotational excitation. Separate, purely radiative cascade calculations predict formation-pumping spectra in the optically thin, collision-free limit. From 25 to 100 K, the rovibrational share of emitted energy falls from approximately 43% to 28% for H2 and 41% to 28% for HD, while the strongest lines remain in similar wavelength regions. These are model results for graphene, not astronomical detections.

PublicWhen hydrogen atoms join on interstellar dust, the released energy can enter either the surface or the newly formed molecule. Researchers simulated this process on graphene at three very low temperatures, studying ordinary molecular hydrogen and a version containing a heavier hydrogen isotope. In these simulations, departing molecules carried away about 84–87% of the effective released energy. At the lowest temperature, most of that retained energy went into molecular vibration and rotation; motion of the whole molecule became more important at the highest temperature. The two molecular types retained similar amounts overall. Calculations of their subsequent light emission predicted a declining share of emitted energy from combined vibrational and rotational transitions as temperature increased. Those light predictions assume no collisions and that emitted light escapes freely. The findings describe a modeled surface process, rather than observations of molecules in space.

Young explorerTwo hydrogen atoms can join together on a very cold surface and then fly away as a molecule. Scientists used a computer to study this on graphene, a sheet of carbon. In their model, the new molecule took most of the released energy with it. That energy made it wiggle, spin and move away. The scientists also calculated the light it could give off afterward, assuming nothing bumped into it and the light could escape. They did not watch this happen in space.

Improved constraints on the Milky Way potential using the M68 stream and DESI spectroscopic data

Carles G. Palau, Wenting Wang, Jiaxin Han+41 more

AstronomerThe authors select 96 stars in the M68 (NGC 4590/Fjörm) stream by combining Gaia DR3 astrometry, DESI radial velocities, and DESI Legacy Surveys photometry. Covering the full observed stream section, this is the largest M68 stream selection with measured radial velocities to date. The observed stream is wider than expected from N-body simulations, and stars farthest from its centre appear correlated in radial velocity, suggesting that their stripping cannot be explained in a static, axisymmetric Galactic potential. Tests on an N-body mock sample indicate that the stream’s path close to and nearly parallel to the Galactic disc enables constraints on disc mass and halo axis ratio. Fitting 44 stars consistent with stripping from M68, together with Milky Way rotation-curve measurements, yields M_d = (5.34 ± 0.57) × 10^10 solar masses and an oblate halo with q_h = 0.83 (+0.06/−0.05). A stream-track fit gives a heliocentric distance to M68 of 10.55 ± 0.09 kpc.

PublicResearchers combined measurements from Gaia and the DESI surveys to select 96 stars in the stellar stream associated with the globular cluster M68. This is the largest selection of stars in this stream with measured speeds toward or away from us. The stream is wider than computer simulations predict, and stars farthest from its centre seem to share a pattern in those speeds. The authors interpret this as evidence that these stars could not have been pulled from the cluster in a gravitational field that stays unchanged over time and is symmetric around the Galaxy’s rotation axis. Simulated data showed that the stream could help measure the Milky Way’s mass distribution. Using 44 stars consistent with having been pulled from M68, alongside measurements of Galactic rotation, the researchers estimate the disc’s mass at 53.4 ± 5.7 billion solar masses and infer a flattened dark matter halo, with an axis ratio of 0.83 (+0.06/−0.05). They also estimate M68’s distance from the Sun as 10.55 ± 0.09 kiloparsecs.

Young explorerA group of stars called M68 has a long trail of stars. Scientists picked out 96 stars in the trail and studied how they move. The trail looks wider than their computer models expected, and some stars near its edges seem to move in a related way. That is a clue that a simple picture of our galaxy’s gravity may not explain the whole trail. Using 44 stars that fit their model, plus other measurements, the scientists estimated how much mass is in our galaxy’s disc. Their work also suggests that the galaxy’s dark matter halo is a little squashed rather than round.

A posteriori correction of Gaia CRF proper motions using conditional probability and zero-parallax prior

Valeri V. Makarov

AstronomerThe study conditions Gaia celestial reference frame proper motions on a zero-parallax prior, assuming a Gaussian covariance model for each source. Applied to 1.2 million Gaia DR3 CRF objects, the conditioned estimates have a tighter distribution around zero and an approximately 15% lower outlier rate. Positions could, in principle, also gain formal precision. A vector spherical harmonic fit through degree 4 to a filtered quasar subset at redshifts 1–1.5 yields a 3-sigma change in the estimated magnitude of the solar system barycenter’s Galactocentric acceleration. This application depends on the unknown stochastic component of the global parallax field; the shift demonstrates sensitivity to the conditioning method, not a physical change in acceleration.

PublicResearchers tested a statistical way to refine Gaia’s measurements of the apparent motions of extremely distant objects. The method assumes that these objects have zero parallax—the apparent shift associated with viewing them from different points in Earth’s orbit—and uses a particular model of measurement uncertainties. For 1.2 million objects, the revised motions cluster more closely around zero, with about 15% fewer outliers. Applying the revised data to a selected group of quasars also shifted the estimated acceleration of our solar system toward the Galactic center by three times the statistical uncertainty. That shift shows how the estimate depends on the method, rather than showing that the acceleration itself changed. The interpretation remains dependent on an unknown random component in Gaia’s overall parallax pattern.

Young explorerGaia watches very faraway things in space and measures how they seem to move. Researchers tried a new way to tidy up those measurements, assuming the things are so far away that Earth’s trip around the Sun does not make them seem to shift. The new numbers were more closely grouped around no motion, and fewer looked unusual. The method also changed an estimate of how our solar system speeds up toward the middle of our galaxy. That does not mean our solar system suddenly moved differently: it shows that how we work with measurements can change an answer, and some uncertainty remains.

Super-Eddington Accretion and Early-Stage Feedback in Ton S180

Pierpaolo Condò, Giacomo Venturi, Eleonora Parlanti+15 more

• High Energy Astrophysical Phenomena

AstronomerVLT-MUSE optical integral-field spectroscopy of the nearby NLSy1 Ton S180 separates unresolved nuclear emission from kiloparsec-scale host emission through spectral modeling and custom PSF subtraction. Single-epoch and stellar-dispersion mass estimates span log(M_BH/M_sun) = 6.5–7.7, implying dimensionless mass accretion rates of 4.1–980 given the observed luminosity. The host exhibits a circumnuclear ring, an elongated inner structure consistent with a bar, and rotation-dominated gas and stellar kinematics; simple inflow models do not significantly improve the velocity-field fit. A resolved ionized outflow extends about 2 kpc westward, with maximum blueshifted velocity around 340 km/s and an estimated mass outflow rate of approximately 4.2 × 10^-4 solar masses/year. The unresolved nuclear outflow is faster and more substantial, reaching about 1140 km/s and exceeding 1.5 solar masses/year. This contrast could indicate weak coupling of the ionized nuclear outflow to galactic scales or distinct episodes of AGN activity. The observations support rapid black hole growth but weak host-scale ionized feedback, with the detected ionized outflow confined to the inner few kiloparsecs.

PublicAstronomers used VLT-MUSE observations to study the rapidly growing central black hole in the nearby galaxy Ton S180 and the motions of gas and stars around it. Estimates of the black hole’s mass vary widely, but together with its observed brightness they indicate an extreme rate of feeding. The galaxy has a ring around its center and an elongated feature that may be a bar. Its gas and stars mainly rotate; simple models including inward gas flow do not significantly improve the match to the observed motions. The team detected ionized gas flowing outward about 2 kiloparsecs west of the center. This extended flow carries far less mass and moves more slowly than the outflow detected in the unresolved central region. The difference may mean that the central outflow transfers little of its influence to ionized gas farther out, or that the two flows trace different periods of black hole activity. Despite rapid black hole growth, the detected ionized outflow is weak on the scale of the host galaxy.

Young explorerA galaxy called Ton S180 has a giant black hole in its middle that is growing quickly as it takes in material. Astronomers watched how gas and stars move around it. Most move around the center, and some gas flows away. The gas flowing away very close to the middle is faster and carries much more material than the flow seen farther out. Scientists are not sure why. Maybe the inner flow does not push the farther-away gas very well, or maybe the flows started at different times.

Dark matter haloes from dwarf to massive galaxies: no systematic inner-density tension with ΛCDM hydrodynamical simulations

Pavel E. Mancera Piña, Justin I. Read, Jorge Sarrato-Alós+1 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe authors analyse inner dark matter profiles in a curated sample of 48 gas-rich galaxies and 8 gas-poor Milky Way satellites spanning six orders of magnitude in stellar mass. They infer substantial scatter in core sizes and coreness, with both cuspy and cored haloes across a broad stellar-mass range. Core formation is energetically consistent with stellar feedback at supernova energy coupling efficiencies of roughly 0.1–1%, although this does not establish feedback as the cause. Comparisons with NIHAO, FIRE-2, and EDGE show broad agreement in inner dark matter densities and logarithmic slopes; residual differences include steep slopes in some massive simulated galaxies and differences in stellar-to-halo mass relations. A previously developed rotation-curve diversity diagnostic finds no extreme discrepancies in this curated sample, with such discrepancies largely attributed to uncertain kinematics or baryonic mass distributions. Within the analysis's scope, the authors find no systematic inner-density tension with current ΛCDM hydrodynamical simulations, substantially alleviating rather than definitively resolving the cusp-core and rotation-curve diversity problems.

PublicSome galaxies appear to have dark matter spread relatively evenly through their centres, rather than sharply concentrated as predicted by cold dark matter models without interactions or galaxy-formation effects. Galaxies also show a wider variety of rotation patterns than simulations have traditionally reproduced. This study examines 48 gas-rich galaxies and 8 gas-poor satellite galaxies of the Milky Way, finding a broad mix of centrally concentrated and more evenly distributed dark matter. Their inferred inner dark matter distributions broadly agree with modern simulations that include gas and galaxy-formation processes, though some differences remain. The energy needed to produce the less concentrated centres could come from a small fraction, about 0.1–1%, of supernova energy, but this energy estimate does not prove that supernovae created them. The authors find no systematic disagreement for their carefully selected sample and suggest that the most extreme reported discrepancies largely reflect uncertainties in galaxy motions or ordinary matter distributions. The findings ease these challenges to cold dark matter within the study's scope, rather than settling them for all galaxies.

Young explorerGalaxies contain invisible stuff called dark matter. Scientists studied 56 galaxies to work out how tightly that stuff gathers in their middles. Some seemed tightly packed, while others seemed more spread out. Computer-made galaxies mostly showed the same kinds of patterns, though they did not match everything. Exploding stars might have enough energy to help spread the dark matter out, but this study does not prove that they did. These galaxies make an old puzzle look less troublesome, but they do not answer it for every galaxy.

A sub-100 pc view at z 5 of a multiply imaged massive quiescent galaxy

Richard Pan, Danilo Marchesini, Joseph F. V. Allingham+34 more

AstronomerVENUS-CLJ0152-QG1 is a massive post-starburst galaxy at z = 5.18, lensed into three images by a foreground cluster. Lensing provides approximately 70 pc physical resolution, enabling sub-kiloparsec investigation of quenching in a population otherwise difficult to resolve. The authors find a half-light radius twice that expected, a central stellar mass density three times lower than field analogs, and off-center ionized gas emission. They interpret these features as evidence suggesting quenching without compaction or an obvious active galactic nucleus, rather than a definitive determination of the quenching mechanism. The galaxy departs from unlensed high-redshift examples and offers a resolved test case for simulations struggling to reproduce rapid early star formation and its abrupt cessation.

PublicThe James Webb Space Telescope has revealed many galaxies that built up rapidly during the universe’s first billion years, but simulations struggle to explain both their rapid star formation and why it stopped so suddenly. This study examines VENUS-CLJ0152-QG1, a massive early galaxy seen after a burst of star formation. A foreground galaxy cluster bends and magnifies its light into three images, letting researchers distinguish structures about 70 parsecs across. The galaxy’s light is more spread out than expected, its central concentration of stellar mass is lower than in comparable galaxies outside clusters, and its glowing ionized gas lies off-center. These findings suggest that star formation stopped without the galaxy first becoming more compact or showing an obvious active central black hole. They do not establish exactly what caused it to stop.

Young explorerAstronomers studied a faraway galaxy that had made lots of stars and then stopped making them so quickly. A big group of galaxies in front of it acts like a magnifying glass, making three pictures of the same galaxy and helping astronomers see smaller details. Its starlight is more spread out than expected, and some glowing gas is away from the middle. These clues suggest the galaxy did not need to squeeze tightly together before it stopped making stars. The astronomers still do not know exactly why it stopped.

SCALES. I. Bridging Lensed Clump - Giant Clump Scales in Lensed Galaxies at z=1-4

Boris S. Kalita, Adélaïde Claeyssens, Luis C. Ho+11 more

AstronomerThe first SCALES paper introduces a difference-of-Gaussian decomposition separating compact, approximately 50–400 pc star-forming clumps from a roughly kiloparsec-scale extended component. The latter is explicitly a scale-separated local background absorbing noncompact light, not an identified physical object; together these components would constitute giant clumps at lower resolution. Applied to 23 moderately lensed galaxies with magnifications of approximately 2–9 and spectroscopic redshifts of 1–4, the method yields a clump stellar mass-function slope of 1.88 ± 0.04, consistent with the approximately 2 expected for hierarchical star formation and with slopes for kiloparsec-scale clumps in unlensed galaxies. The analysis finds that redshift-dependent detection bias exaggerates correlations of clump surface densities and clump-to-host mass ratio with redshift, indicating broad similarity among compact clumps over this range. Combining estimated clump masses, sizes and ages with literature gas-dispersion measurements at similar scales, the authors argue that approximately 100 pc clumps contain smaller, star-cluster-like subcomponents. Extended components and giant clumps are deferred to SCALES-II.

PublicBright star-forming patches in distant galaxies can look different depending on how finely a telescope resolves them. This study introduces a method that separates compact patches, about 50–400 parsecs across, from more spread-out light that would blend with them into giant patches in less detailed images. The spread-out light is treated as background, not as a single physical object. Studying 23 galaxies magnified by gravitational lensing at redshifts 1–4, the researchers measured how common clumps of different stellar masses are. The pattern agrees with expectations for star formation organized into structures within larger structures, and with measurements of larger-looking clumps in other surveys. They also find that changing detection limits exaggerate apparent trends with redshift: the compact clumps are broadly similar across the studied range. From estimated clump masses, sizes and ages, combined with published gas-motion measurements on comparable scales, the authors suggest that these clumps contain much smaller, star-cluster-like pieces rather than establishing this directly.

Young explorerFaraway galaxies have bright patches where new stars are being made. If we cannot see clearly enough, little patches and the light around them can blur into one big patch. The scientists used a new way to separate the little patches from the surrounding glow in pictures of 23 galaxies. They found that the little patches were mostly alike across the times they studied. Some differences looked bigger because certain patches were harder to spot. The scientists also think the patches may have even smaller groups of stars inside them, but that is an idea based on their clues, not something they showed directly.

SCALES. II. The Internal Composition of Giant Star-Forming Clumps at z = 1 - 4

Boris S. Kalita, Adélaïde Claeyssens, Luis C. Ho+11 more

AstronomerThe SCALES study analyzes JWST/NIRCam imaging of 23 lensed galaxies at z=1–4, using difference-of-Gaussian decomposition to separate approximately 50–400 pc clumps from extended components on giant-clump scales. Associating these components identifies 72 giant clumps. Above the stellar-mass completeness limit of 10^7.1 solar masses, their constituent clump masses are consistent with random sampling of the clump stellar mass function (CSMF), providing no information about the host giant clump. This is qualitatively compatible with both long-lived structures whose constituents are continually renewed and blended random clump associations; it does not distinguish these scenarios. Above a break near 10^7.5 solar masses, close to the completeness limit, the CSMF has a power-law slope of 1.88 ± 0.04. Giant clumps have a consistent slope of 1.95 ± 0.15. If the extended component consists of undetected clumps, its mass is consistent with extending the CSMF to approximately 10^5.5–10^6 solar masses. The most massive constituent’s mass fraction independently supports that range and rejects extension below 10^5 solar masses. These observations constrain internal mass distributions for which most models lack predictions.

PublicWhat looks like one giant star-forming clump in a distant galaxy can contain smaller clumps and more spread-out material. Using JWST images of 23 galaxies magnified by gravitational lensing, researchers identified 72 giant clumps and studied their internal structure. Among smaller clumps massive enough for the survey to count reliably, the masses fit random draws from a shared distribution rather than revealing properties of their particular giant-clump host. This finding fits two different explanations: giant clumps could be lasting structures with continually replaced constituents, or chance groupings seen blended together. The observations do not settle which explanation is right. Smaller clumps and giant clumps also show similar patterns in how common different masses are. The internal mass budget is consistent with that pattern continuing to lower, unseen clump masses, but limits how far it can extend; this is an inference, not a detection of those clumps.

Young explorerA big bright patch where stars are being born can have smaller patches inside it. Scientists used a space telescope to look inside big patches in faraway galaxies. The smaller patches had a mix of sizes by mass that looked like picking randomly from the same bag. Scientists still cannot tell whether the big patches stay together while smaller ones come and go, or whether separate patches just look bunched together.

GroArnold: A Framework for Constructing Action-based Models for Triaxial Galaxies and Dark Matter Halos

Jian-Yu Gu, Xiao-Bo Dong, Shi-Yan Zhong+1 more

AstronomerThe authors present GroArnold, a modular, publicly available framework for constructing analytical action-based distribution functions, f(J), for axisymmetric and triaxial galaxies and dark matter halos. It combines N-body initial-condition generation, simulation, angle–action estimation, and distribution-function fitting. Its Nbody-TACT module extends TACT’s triaxial Stäckel Fudge method to estimate actions directly from N-body gravitational potentials. The workflow aims to obtain distribution functions approximating dynamically stable, physically consistent states for user-specified density profiles and kinematics. Comparisons of the fitted functions’ predicted spatial and velocity distributions with the input N-body snapshots show reasonably accurate agreement; the abstract gives no quantitative accuracy or stability bounds. This is a computational modeling study, not an observational result.

PublicGroArnold is a new, publicly available computer framework for building mathematical descriptions of how matter is distributed and moves in galaxies and dark matter halos. It can model both systems symmetric around an axis and more complex shapes with three unequal axes. The framework links simulations of many interacting particles with methods that estimate their orbital properties and fit mathematical formulas. The goal is to describe systems that remain dynamically stable and physically consistent. In tests, the formulas reproduced the simulated particles’ spatial and velocity distributions reasonably accurately, although the abstract gives no numerical measure of that accuracy. These comparisons concern computer models rather than observations of real galaxies.

Young explorerScientists made a computer tool called GroArnold to help describe pretend galaxies and the invisible matter around them. It moves lots of pretend particles and makes math rules to describe where they are and how they move. When the scientists checked the rules against their computer galaxies, the rules matched fairly well, but not perfectly. They want the tool to help build galaxy models that stay steady over time. These tests used computer galaxies, not real ones in the sky.

The MAGE Project: Size Evolution and Disk Formation in Massive Galaxies at Cosmic Dawn

Zhiyuan Yao, Avishai Dekel, Romain Teyssier+5 more

AstronomerThe MAGE suite comprises eleven RAMSES cosmological zoom-in simulations with approximately 10 pc resolution, evolved to z ≃ 9, targeting galaxies with stellar masses of approximately 2 × 10^8–3 × 10^10 solar masses. Stellar half-mass radius rises steeply with stellar mass at low masses, turns over near 5 × 10^9 solar masses, and shows weak redshift evolution. Intrinsic UV sizes overlap the compact end of observed distributions, including compact strong-line systems, but do not reproduce the more extended population at z > 9; dust, PSF-limited measurements, and the simulated overdense environments may contribute to this mismatch. Above approximately 5 × 10^8 solar masses, stars dominate the mass within the half-mass radius and central circular speeds exceed a characteristic stellar-feedback scale. Increasing outflow retention is consistent with galaxy-scale gas recycling that sustains central gas supply and a compaction-like buildup. The size turnover coincides with rapidly increasing rotational support, reaching v/σ ≃ 1.5–3 in star-forming gas and stars younger than 10 Myr, as central circular speeds exceed halo virial speeds. Subsequent low central gas fractions, declining central star formation, and younger outskirts suggest, rather than establish, the onset of inside-out quenching.

PublicEleven computer simulations explore how galaxies grew and developed rotating disks in the early universe. In the simulations, galaxy size initially increases strongly with stellar mass, but this trend turns over at higher masses. The simulated galaxies match some of the most compact observed galaxies, but not the more extended ones at similarly early times. Dust, limits on measuring small sizes, and the unusually dense environments modeled could help explain this difference. The simulations suggest that increasingly strong central gravity keeps more expelled gas within galaxies, supplying further central growth. Near the size turnover, rotation becomes more important in star-forming gas and very young stars. Later changes hint that star formation begins fading in the centers before the outskirts, although this interpretation is not established.

Young explorerScientists used computers to make pretend galaxies and see how they grow. In these models, gravity keeps more gas from escaping, helping stars build up in the middle. Gas and very young stars also start moving more like a spinning disk. Later, fewer stars form in the middle, while the outer parts look younger. That is a clue, not proof, about how galaxies change. The models match some small galaxies we see, but miss the bigger-looking ones.

An Extra-nuclear Water Maser in NGC 1106 Likely Driven By An AGN Shock: Implications for Maser-based Black Hole Mass Measurements

Macon Magno, Emmanuel Momjian, Krista L. Smith+4 more

• High Energy Astrophysical Phenomena

AstronomerVLA A-configuration observations at 22 GHz with 0.13-arcsecond resolution localize water maser emission in the Seyfert 2 galaxy NGC 1106 to a compact region approximately 1 kpc from the nucleus. The maser line is offset by 541 km/s from the host systemic velocity, while the nuclear continuum shows a 352 pc extended structure. Comparison with earlier 1-arcsecond observations places the maser near the boundary of a radio extension aligned with the jet axis. Its position, velocity offset, flux density, and alignment, considered alongside Galactic and extragalactic comparison masers, are consistent with an origin at the AGN outflow–ISM interface, rather than establishing that origin definitively. The authors caution that unresolved high-velocity maser features attributed to accretion disks may include contributions from kpc-scale shocks, with implications for black hole mass measurements when disk geometry is ambiguous.

PublicHigh-resolution radio observations of the galaxy NGC 1106 locate a compact source of amplified radio emission from water molecules about 1,000 parsecs from the galaxy’s center. Its radio line indicates a velocity offset of 541 kilometers per second relative to the galaxy’s overall motion. The source lies near the edge of a radio extension aligned with a jet from the active galactic nucleus. Its location and other properties suggest that the emission comes from where an outflow from the nucleus encounters gas in the galaxy, although this interpretation is not definitive. The finding matters because astronomers use some water signals to estimate black hole masses: observations that cannot distinguish separate emitting regions could mistake signals from distant shocks for signals from a disk around the black hole.

Young explorerAstronomers used a radio telescope to find a tiny patch of water molecules sending out a strong radio signal in a galaxy. The patch is far from the galaxy’s center. They think a stream of material coming from the center may be bumping into gas there and helping make the signal, but they are not sure. This matters because scientists sometimes use water signals to work out how heavy a black hole is. They need to check where the signals come from so they do not mix up different places.

What sets the star-formation rate in the Milky Way? I. A multi-scale view of the star-formation rate

Patrick Hennebelle, Paolo Suin, Georges Abboudeh+15 more

AstronomerNumerical simulations with large-scale turbulent forcing connect kiloparsec-scale Galactic conditions to star-forming clumps, using adaptive zooming down to 0.03 pc under conditions typical of the solar neighbourhood. For column densities and velocity dispersions consistent with Galactic values, the simulated star-formation rate is close to that inferred for the Milky Way. Relative to an estimate based on pure free-fall collapse, turbulent support across multiple scales suppresses the rate by more than an order of magnitude. The authors report good overall agreement with observations across spatial scales, with clump-catalogue comparisons addressed in a companion paper. They suggest that stellar feedback, including ionizing radiation and protostellar outflows, likely supplies a further reduction by a factor of 3–10. The results support an interpretation in which turbulence, together with feedback, limits star-formation efficiency to a few percent; the additional feedback reduction is presented as likely rather than as an established simulation result.

PublicWhy does the Milky Way turn gas into stars relatively slowly? This study uses computer simulations to connect large-scale conditions in the Galaxy with small gas clumps where stars form. With gas conditions resembling those in our Galaxy, the simulations produce a star-formation rate close to the rate inferred for the Milky Way. Turbulent gas motions slow star formation by more than tenfold compared with an estimate in which gravity makes the gas collapse freely. The authors report broad agreement with observations and suggest that radiation and outflows from stars likely slow the process further. Their interpretation is that turbulence and these effects from stars together keep star-formation efficiency at only a few percent.

Young explorerStars form when gas gathers into tight clumps. Scientists made a computer model of this happening in our galaxy. In the model, swirling gas helped stop the clumps from squeezing together too quickly, so stars formed much more slowly than if gravity acted without that support. The model made stars at about the pace estimated for our galaxy. The scientists think light and gas flowing out from stars probably slow things down even more.

The Role of Star Formation and Morphology in the Mass-Metallicity Relation of Galaxies at Cosmic Noon

Farhanul Hasan, Marc Rafelski, Kalina V. Nedkova+26 more

AstronomerUsing JWST/NIRISS slitless spectroscopy of more than 1,000 galaxies at 1.7<z<3.5 across over 85 square arcminutes in PASSAGE and OutThere, the study examines the dependence of the gas-phase mass–metallicity relation (MZR) on star formation and morphology. Metallicities are inferred through a Bayesian combination of strong-line ratios calibrated against JWST direct auroral-line measurements; ancillary HST and JWST imaging constrains stellar masses, SFRs, and morphology. Mass-stacked spectra constrain the MZR over approximately log(M*/M☉)=6.5–11. A second-order polynomial describes the relation well, with a steep low-mass slope and metallicities below 10% solar at log(M*/M☉)<7.5. Further stacking provides strong evidence for a fundamental metallicity relation: below log(M*/M☉)=9.5, lower-SFR galaxies are more metal-rich at fixed stellar mass. In this mass regime, larger galaxies and those with lower SFR surface densities, bulges, and/or spiral features are also significantly more metal-rich than their respective counterparts. The authors interpret these dependencies as evidence for variations in the baryon cycle: recent metal-poor accretion may dilute metallicity and drive concentrated star formation, while structurally developed galaxies may retain enriched gas. This physical explanation is suggested by the correlations, not directly established by them.

PublicA study of more than 1,000 galaxies in the early universe finds that the chemical richness of their gas depends not only on stellar mass, but also on star formation and structure. Researchers combined JWST spectra in groups to measure these patterns, using Hubble and JWST images to estimate galaxy properties. The lowest-mass galaxies had gas metallicities below one-tenth of the Sun’s. Among galaxies below about three billion solar masses in stars, those forming stars more slowly were more metal-rich than equally massive galaxies forming stars faster. Larger galaxies, galaxies with less concentrated star formation, and those with central bulges or spiral features were also more metal-rich than their respective counterparts. The authors suggest that incoming metal-poor gas could both dilute a galaxy’s gas and fuel concentrated star formation, while more developed structures retain enriched gas. The observations support these relationships, but do not directly prove that explanation.

Young explorerScientists studied light from more than a thousand faraway galaxies, which are huge groups of stars. They found that galaxies with the same amount of stars can have different amounts of metals in their gas. Among the less massive galaxies, those making stars more slowly had more metals. Shape and size mattered too. The scientists think fresh gas coming in might explain some of these differences, but they have not shown that for sure.

Seeing Unseen Gravitational Wave Inspirals at the Galactic Center

Pau Amaro Seoane, Qimin Song, Shao-Dong Zhao+14 more

• Astrophysics of Galaxies
• General Relativity and Quantum Cosmology

AstronomerThe authors propose using secular torques on the highly eccentric S-star S301 to probe an expected population of extremely large mass-ratio inspirals (X-MRIs) near the Galactic Center. Discrete encounters with the stellar-mass black hole cusp create stochastic velocity changes that smooth-potential orbital fits can misidentify as secular precession, biasing traditional X-MRI mass estimates. Their Wavelet Transform Modulus Maxima methodology characterizes local Hölder regularity to separate encounter-induced discontinuities from continuous X-MRI torques, with claimed sensitivity even when instantaneous accelerations fall below instrumental noise. An analytical argument indicates sensitivity to interior X-MRIs while finding dynamical decoupling from the exterior cusp's secular influence. Combining precision astrometry and radial-velocity projections, the authors forecast detectability of as few as two X-MRIs over five to nine years. This is a proposed detection strategy and analytical detectability claim, not a reported observation of X-MRIs.

PublicThe researchers propose searching for unseen objects spiraling toward the Milky Way's central supermassive black hole by tracking their gravitational influence on the star S301. A major obstacle is that encounters with smaller black holes can jolt the star's motion. Standard orbit-fitting methods can blur these jolts into a gradual change that resembles the signal being sought. The proposed analysis instead distinguishes abrupt changes from a smoother gravitational influence. The authors predict that precise measurements of the star's position and motion toward or away from us could reveal as few as two inspiraling objects within five to nine years. They do not report detecting such objects.

Young explorerScientists want to watch a star near the giant black hole in the middle of our galaxy. Hidden objects might gently change how the star moves, but other black holes can give it little tugs that confuse the clues. The scientists have a new way to try to tell those clues apart. They think years of watching could reveal hidden objects, but they have not found them this way yet.

Thinner Disks Struggle to Launch Jets: GRMHD Simulations of Magnetic Field Generation and Transport

Jonatan Jacquemin-Ide, Mitchell C. Begelman, Henrik Latter+2 more

AstronomerMotivated by the observed association between jets and geometrically thicker accretion states in X-ray binaries, this study uses 3D GRMHD simulations with h/r=0.1–0.3 and an initially toroidal magnetic field with plasma beta=5. In these simulations, MRI-driven non-axisymmetric shearing waves generate large-scale poloidal fields, supplemented by axisymmetric induction through channel-like stretching. Thinner disks develop weaker mean fields, weaker MRI-mediated angular-momentum transport, and accretion slower than the standard v_acc proportional to (h/r)^2 scaling predicts. Magnetic-flux transport remains comparable in speed to accretion, so weaker field generation and slower transport jointly suppress black-hole flux accumulation. The h/r=0.1 disk yields an electromagnetic jet efficiency of about 1%, whereas the thickest disk reaches a magnetically arrested disk (MAD) state and an efficiency of at least 100%. Only the h/r approximately 0.3 disk reaches MAD during the simulations, at about 20,000 r_g/c; the roughly 100 million r_g/c accumulation time for h/r=0.1 is an estimate based on measured flux distributions and transport velocities, not a simulated MAD transition. The results connect disk thickness to flux accumulation and suggest a strong dependence of jet-emergence timescales on disk geometry in transient accreting systems.

PublicSome black holes feeding on surrounding gas launch fast jets, while others do not. Observations of X-ray binaries associate jets with thicker disks of gas. To explore why, researchers simulated disks of different thicknesses around black holes. In the simulations, thinner disks generated weaker large-scale magnetic fields and moved gas inward more slowly. Together, these effects greatly reduced how quickly magnetic flux built up at the black hole. The thickest simulated disk accumulated enough flux to enter a magnetically arrested state and produced a much more efficient jet than the thinnest disk. Only the thickest disk reached that state during the simulations; the researchers estimate that the thinnest would require a far longer time. These simulation results suggest that disk thickness helps determine both whether strong jets develop and how long they take to emerge, rather than establishing that behavior observationally.

Young explorerSome black holes have spinning disks of gas around them and send out jets. Scientists used computer models to ask why thicker disks might help make jets. In their models, thicker disks built up stronger magnetic fields near the black hole and made stronger jets. Thinner disks built up those fields much more slowly. The scientists think a thin disk might need much longer to get ready, but their computer experiment did not run long enough to see that happen.

Extreme eccentricity in double neutron stars without exotic physics

Thomas M. Tauris

• Solar and Stellar Astrophysics

AstronomerThe recently reported double neutron star PSR J0653+0443 has a record orbital eccentricity of e=0.9924. The authors show that standard binary-supernova physics—instantaneous mass loss producing Blaauw recoil, together with natal kicks—can generate e>0.99 from both compact and wide pre-supernova orbits without exotic conditions. Three families of kinematic solutions reproduce the observed orbit across a range of kick velocities and progenitor configurations. Physically motivated priors based on neutron-star spin and pre-supernova mass transfer restrict the viable progenitor family and support the authors’ conclusion that the system is not exceptionally rare. These are formation-model inferences rather than a direct measurement of the natal kick; future proper-motion measurements are expected to tightly constrain its magnitude.

PublicThe recently reported pair of neutron stars PSR J0653+0443 follows a record-setting, extremely elongated orbit, with an eccentricity of 0.9924. The authors’ calculations suggest that this orbit does not require an unusual formation mechanism: mass suddenly lost in a supernova, combined with a kick imparted to the newborn neutron star, can produce such an extreme orbit. Three groups of possible formation histories fit the observed orbit. Assumptions informed by neutron-star spin and earlier mass transfer between the stars narrow those possibilities and suggest the system is not exceptionally rare. The kick has not been directly established; future measurements of the pair’s motion across the sky should help pin down its strength.

Young explorerAstronomers found two neutron stars that go around each other on a very stretched-out path. Neutron stars are what can be left after stars explode. The researchers’ calculations show that losing material in an explosion and getting a shove could make a path like this, without anything extra-strange happening. They still do not know exactly how big the shove was. Watching how the pair moves across the sky could help them find out.

The MARTINI platform II. Tracing r-process nucleosynthesis in neutron star mergers with long-lived remnants

Eleonora Loffredo, Diego Vescovi, Albino Perego+2 more

AstronomerThe authors publicly release tracer trajectories and nucleosynthesis yields for eight general-relativistic BNS merger simulations forming long-lived neutron star remnants. The models use M1 neutrino transport, DD2 and SFHo equations of state, and varied total masses and mass ratios; dynamical and wind ejecta tracers are post-processed with WinNet to 1 Gyr. At 1 day, He, Ni, Sr, and Y production is similar across models and is enhanced primarily by neutrino-irradiated disc winds. Heavy-nucleus yields vary by more than an order of magnitude, with unequal-mass systems yielding the most because of their more neutron-rich ejecta. Higher He yields than in recent M0-based studies are consistent with stronger irradiation in M1. At 1 Gyr, every model reproduces the second and third solar r-process peaks, but other abundance regions differ with ejecta electron-fraction distributions and dynamical versus wind contributions. Two equal-mass models closely match the solar pattern. These are simulation-derived yields, available with the trajectories on MARTINI, rather than observational measurements.

PublicComputer simulations explore how collisions between two neutron stars make elements when the collision leaves a long-lived neutron star behind. The researchers calculated element production for eight mergers, including the effects of neutrinos on material expelled from the surrounding disc. The models produce similar amounts of some lighter elements, but their heavy-element yields differ by more than a factor of ten. Collisions between stars of unequal mass produce the largest heavy-element amounts in these simulations. After following nuclear reactions and decay to one billion years, all models reproduce two major peaks in the Solar System’s rapid-neutron-capture abundance pattern, but they differ elsewhere; two equal-mass models give a close overall match. The publicly released calculations can help assess mergers’ contribution to heavy elements and interpret kilonova spectra, but they are not direct observations.

Young explorerWhen two neutron stars crash, they can make new kinds of atoms. Scientists used computers to try eight crashes that leave a neutron star lasting a long time. Their pretend crashes made different amounts of heavy atoms, especially when one star was bigger than the other. Some recipes looked much like the atom mix in our Solar System, but these were computer tests, not crashes the scientists watched.

Considering Numerical Relativity Surrogate Models for AGN Channel Merger Dynamics

Shawn Ray, Keefe Mitman, Vera Delfavero+8 more

• General Relativity and Quantum Cosmology

AstronomerThis simulation study incorporates a numerical-relativity surrogate into McFACTS to predict remnant properties when inspiralling binary black holes merge in the active galactic nucleus (AGN) channel. A fraction of observed mergers may arise in AGN, but the relevant dynamics remain uncertain. McFACTS models gas drag and dynamical interactions; the surrogate adds relativistic merger predictions that the existing treatment neglects. Compared with a simple analytic prescription, the surrogate yields significantly more accurate remnant spins and recoil velocities, substantially changing their simulated distributions and improving calculations of χ_eff and χ_p. These effects are especially important for higher-generation mergers. The authors caution against uncritical use of alternative prescriptions and outline computationally efficient models that reproduce much of the surrogate's results. These are modeling findings, not observational confirmation of an AGN origin.

PublicGravitational-wave detectors observe black holes merging, and some of these mergers may occur in active galactic nuclei, the bright central regions of active galaxies. This study improves software that simulates how such black-hole pairs form and evolve. The researchers connect the simulation to a model based on numerical relativity to better predict the merged black hole's mass, spin, and recoil speed—the speed of the kick it receives during the merger. Compared with a simple formula-based approach, the new treatment predicts spins and kicks significantly more accurately and changes their distributions in the simulations. This matters especially when a merged black hole later merges again. The authors also outline faster, simpler models that reproduce much of the more detailed model's output. The work improves simulations; it does not establish which observed mergers happened in active galactic nuclei.

Young explorerScientists use computers to explore what happens when two black holes join together. The new black hole can spin and get a kick that sends it moving. In this study, scientists used a better computer model to work out those spins and kicks. Its answers differed from those of a simpler model, which matters if the new black hole joins another one later. These answers come from computer experiments, not from watching these particular black holes.

Validating an X-ray-based method for identifying Fermi blazars

J. L. Weiss, E. J. Marchesini, I. Andruchow+1 more

• Astrophysics of Galaxies

AstronomerThe study tests a Swift-XRT-based method for selecting BL Lac candidates among unidentified Fermi sources. Of 148 initial X-ray-selected candidates, 71 had published optical spectra spatially consistent with the proposed associations and were reclassified using standard blazar criteria. In this subset, 80.28% are classified as BL Lacs and 87.32% as possible gamma-ray-emitting AGNs; four Seyfert galaxies are also identified. These findings support the selection method for the spectroscopically examined subset but do not establish all proposed gamma-ray associations. The authors suggest that blazars may constitute a substantial fraction of unidentified Fermi sources and recommend further spectroscopy and multiwavelength observations, including investigation of the possible Seyfert associations.

PublicAbout 34% of the gamma-ray sources detected by Fermi remain unidentified, partly because their locations are not precise enough to identify a clear counterpart. Researchers tested a way to find likely counterparts using X-ray observations from Swift-XRT. Starting with 148 candidates, they found suitable published optical spectra for 71 and checked their classifications. About 80% of those 71 were classified as BL Lac objects, a type of active galaxy, and about 87% as active galaxies that could emit gamma rays. Four were Seyfert galaxies, a class rarely associated with gamma-ray emission. The results support X-ray selection as a useful way to find candidates, but further observations are needed to investigate the proposed connections and the origin of any high-energy emission.

Young explorerA telescope called Fermi sees a powerful kind of light from space, but scientists do not always know which object it comes from. They tested whether X-ray pictures could help them pick the right galaxies to check. For 71 possible matches, they studied light that had been split into its different colors. Most were a kind of active galaxy they were looking for, so the method looks useful. But being a possible match does not mean a galaxy definitely made the powerful light. Scientists need more observations to check.

Search for Eccentric Neutron Star-Black Hole Binaries in Advanced LIGO's Fourth Observing Run using Effective-One-Body Waveforms

Aleyna Akyüz, Keisi Kacanja, Rahul Dhurkunde+1 more

• General Relativity and Quantum Cosmology

AstronomerThis search for eccentric neutron star–black hole (NSBH) mergers makes time-domain effective-one-body templates computationally feasible through multibanding and high-frequency ratio-filtering, reducing computational cost by approximately a factor of 20. Including apsidal precession and inter-orbit harmonics increases sensitive volume by about 25–30% for 0.2 ≤ e20 ≤ 0.28 relative to models omitting these features. The pipeline searches O4a and O4b Advanced LIGO data with 88.6 million templates, a bank fifteen times larger than in prior eccentric analyses. It recovers GW230518_125908 and GW230529_181500 with parameters consistent with zero eccentricity and finds no new events with e20 ≥ 0.05. The resulting 90% credible upper limits on local eccentric NSBH merger rate density range from 7.5 to 57 Gpc⁻³ yr⁻¹ across the search space, improving previous observational bounds by up to approximately a factor of four. At the parameters of GW200105_162426, the upper limit is 12.1 Gpc⁻³ yr⁻¹. Alternatively, treating GW200105_162426 as an eccentric detection yields an updated rate density of 6.6 with uncertainties of +6.3 and −3.8 Gpc⁻³ yr⁻¹ after accounting for the lack of subsequent O4 detections.

PublicA neutron star and a black hole spiraling together on an elongated rather than circular orbit could reveal that their pairing arose through gravitational interactions in a dynamical environment. The researchers developed a gravitational-wave search that costs about twenty times less to compute, allowing them to compare Advanced LIGO observations with 88.6 million model signals that include orbital features omitted by earlier simplified searches. They recovered two known mergers whose signals remain consistent with circular orbits, but found no new events meeting their eccentricity threshold. This does not show that eccentric mergers never happen; it tightens limits on how often they occur, by up to about a factor of four compared with previous observational bounds. A separate interpretation treats the earlier event GW200105_162426 as an eccentric merger and updates the estimated rate using the absence of further detections. That estimate depends on accepting the earlier event as eccentric.

Young explorerA neutron star and a black hole can go around each other before joining together. Scientists looked for tiny ripples from pairs moving in stretched-out loops instead of circles. They made their computer search much faster and found signals from two pairs they already knew about. Those signals did not need stretched-out paths to explain them, and the search found no new pairs with clearly stretched-out paths. That does not mean such pairs are not out there. It helps scientists work out how often they might join together.

Phase-resolved X-ray spectroscopy of the Vela pulsar with NICER observations

E. Zubieta, F. García, S. del Palacio+2 more

• High Energy Physics - Phenomenology

AstronomerThe study constrains thermal surface emission from the Vela pulsar using NICER observations between its 2019 and 2024 glitches, folded with ephemerides from high-cadence Argentine Institute of Radio Astronomy radio observations. Profiles in three energy bands and phase-resolved spectra were analyzed, with Chandra data used to assess contamination from the spatially unresolved pulsar wind nebula. The pulsar contributes less than 40–45% of the total observed flux below 0.9 keV, 3–4% at 0.9–2.0 keV, and approximately 2% above 2 keV. No measurable perturbation of the folded X-ray profile was found across the 2021 glitch. Spectra from seven pulse-phase regions are each well modeled by one or two blackbodies; this does not establish a single common spectral shape. Inferred hotspot temperatures span 0.79 ± 0.07 million K to 4.8 million K with +0.8/−0.6 million K uncertainties, and inferred radii span 0.048 km with +0.016/−0.009 km uncertainties to 3.9 km with +0.9/−0.6 km uncertainties. Luminosities range from approximately 5 × 10^30 to below 1 × 10^32 erg/s. These hotspot properties are model-based inferences rather than directly resolved surface measurements.

PublicResearchers studied X-rays from the Vela pulsar to investigate hot regions on the neutron star’s surface and look for changes associated with its 2021 glitch. They combined NICER observations using radio timing information and used a Chandra observation to estimate how much of NICER’s detected light came from the surrounding nebula rather than the pulsar. This distinction matters: the nebula supplies most of the detected X-ray emission, especially at higher energies. The repeating X-ray pattern showed no measurable disturbance from the 2021 glitch, although this does not rule out changes too small to detect. Models of heat emission fit seven portions of the pattern using one or two temperature components. The inferred hot regions have temperatures of roughly 0.8–4.8 million degrees Kelvin and radii ranging from about 48 metres to 3.9 kilometres, with uncertainties in these estimates.

Young explorerScientists looked at X-ray light from a star called Vela to learn about hot patches on its surface. A glowing cloud around the star adds lots of light, so they had to work out how much came from the star itself. They checked whether an event called a glitch in 2021 changed the star’s repeating light pattern. They could not see a change big enough to measure. Their models suggest very hot patches of different sizes, but these are estimates, not close-up pictures of the star.

Cosmic rays in galaxy halos I: the circumgalactic transport rate and a dynamically significant cosmic-ray reservoir

Roland M. Crocker, Mark R. Krumholz

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies

AstronomerFermi-LAT observations imply that most cosmic rays accelerated in normal star-forming discs escape into the circumgalactic medium (CGM), but their subsequent transport is uncertain. The authors construct a simple semi-analytic transport and loss model, constrained by Fermi-LAT limits on outer-Milky-Way cosmic-ray energy densities, the isotropic gamma-ray background (IGRB), stacked eROSITA CGM X-ray emission, and a requirement that accumulated cosmic-ray pressure not destabilize galaxy halos. Within this model, only two scenarios satisfy all constraints: rapid diffusion followed by free escape into the intergalactic medium, or halo diffusion times comparable to the Hubble time. In the slow-transport scenario, star-formation-powered cosmic rays can explain both the IGRB and the heating needed to offset CGM X-ray cooling. The model predicts that roughly half of the cosmic-ray energy injected into an L-star halo's CGM over its star-formation history remains at z approximately 0, making cosmic-ray pressure dynamically significant and yielding a non-negligible Milky Way halo contribution to the IGRB. The authors favor this scenario because it avoids invoking a second IGRB source with power and spectral shape coincidentally close to the star-forming-disc contribution; it is an interpretation, not a direct measurement of halo confinement.

PublicObservations with Fermi-LAT suggest that most cosmic rays—energetic particles accelerated in the discs of ordinary star-forming galaxies—escape into the surrounding gas. What happens next remains uncertain. The researchers built a simplified mathematical model and tested it against gamma-ray and X-ray observations, along with the requirement that cosmic-ray pressure not make galaxy halos unstable. Within their model, two possibilities work: the particles move quickly through the surrounding gas and escape into intergalactic space, or they linger for a time comparable to the age of the universe. In the long-lasting case, the model indicates that cosmic rays could explain the isotropic gamma-ray background and supply the heat needed to balance the surrounding gas's X-ray cooling. It also predicts that a typical L-star galaxy's halo would still hold roughly half the cosmic-ray energy injected into its surrounding gas over its history, enough for their pressure to matter. Our own galaxy's halo would then contribute a non-negligible share of that gamma-ray background. The authors favor this explanation because it avoids needing another background source with closely matching properties, but the observations do not uniquely establish it.

Young explorerGalaxies make very speedy little particles called cosmic rays. Observations suggest that many leave the galaxy's flat disc and enter the gas around it. Scientists made a simple math model to explore what happens next. Two ideas fit their checks: the particles might rush away, or they might stay around for a very, very long time. If they stay, they could help keep the gas hot and make some of the gamma-ray light seen across the sky. The scientists think staying is the better explanation, but they do not know for sure.

A Spectral-model-independent Diagnostic of Phase-resolved Spectral Convergence in Swift J0243.6+6124

Bo-Yan Chen, Peng-Ju Wang, Shu Zhang+9 more

AstronomerThe authors introduce δ_rms, a spectral-shape metric independent of spectral-model choice, to track phase-resolved spectral evolution in Swift J0243.6+6124. Spectra at two geometrically opposite pulse phases reproducibly converge to a mean shape difference of about 2% near 8.8 × 10^37 erg s−1, then diverge again at higher luminosities, especially at higher energies. The convergence coincides with a pulse-profile reversal, and the behavior traces transition luminosities previously identified through broadband continuum evolution, including approximately 4.5 × 10^37 erg s−1. The authors interpret these findings as possibly reflecting luminosity-dependent reweighting of broadly distributed surface-reprocessed or reflected emission and direct accretion-column emission; that physical explanation is not established. They present δ_rms as a robust diagnostic of radiation-geometry restructuring in bright accreting X-ray pulsars.

PublicA study of the Galactic X-ray pulsar Swift J0243.6+6124 compares the mix of X-ray energies seen at two opposite stages of its pulse cycle. Using a new measure that does not require choosing a particular spectral model, the researchers find that these two spectra become almost identical at a particular brightness, differing in shape by only about 2%. At higher brightnesses, they grow different again, especially at higher X-ray energies. The near-match occurs alongside a reversal in the pulse pattern, and the changes track brightness thresholds identified in earlier spectral work. One possible explanation is that increasing brightness changes the balance between X-rays reprocessed or reflected at the surface and X-rays arriving directly from the column of infalling material. The observations support investigating this explanation but do not establish it.

Young explorerScientists watched a star that sends out pulses of X-rays. They compared the kinds of X-rays they saw at two different moments in each pulse. As the star got brighter, the two views became almost the same. When it got brighter still, they became different again. The scientists think this might happen because the mix of light bouncing off the star and light coming straight from falling material changes. That is a possible explanation, not something they know for sure.

Numerical Simulations of the interaction between winds from tidal disruption event and supermassive black hole circumnuclear medium

De-Fu Bu, Yu-Heng Sheng, Liang Chen+3 more

• Astrophysics of Galaxies

AstronomerNumerical simulations examine how angle-dependent TDE winds alter radio light curves in the proposed wind–circumnuclear medium (CNM) interaction model for non-jetted TDEs. At fixed wind mass and kinetic energy, the simulated optically thin light curves depend strongly on the angular distribution of wind properties. Even slight deceleration, before the swept-up CNM mass reaches the wind mass, can affect the emission. Angular variations in deceleration produce angle-integrated light curves that differ substantially from spatially uniform wind-injection models. Depending on the CNM profile, the simulations can yield a slower rise or faster decline than analytical predictions, or replace the rising phase with a long-lasting plateau. These are modeling results, not reported observations, and indicate that wind angular structure must be considered when interpreting this emission mechanism.

PublicOne proposed explanation for radio emission from tidal disruption events without jets is that winds from the event collide with material around a supermassive black hole. This study uses computer simulations to test what happens when the wind's properties differ by direction, rather than being the same everywhere. Even with the same total wind mass and kinetic energy, the simulated radio brightness can change very differently over time. Small slowdowns matter, and winds traveling in different directions can slow down differently. Depending on how the surrounding material is distributed, the radio signal can brighten more slowly, fade faster, or stay nearly level for a long time instead of continuing to brighten. The study does not report observing these effects; it shows why directional differences in winds matter for predictions of radio emission that can escape without being substantially absorbed.

Young explorerScientists used a computer to study a wind near a giant black hole. They tested an idea that the wind makes radio waves when it bumps into nearby material. If the wind is different in different directions, parts of it slow down differently. In the computer tests, that could make the radio signal grow more slowly, fade faster, or stay about the same for a long time. What happens also depends on the material around the black hole. These are computer results, not things the scientists watched happen in space.

Migration Traps as Variability Attractors. II. Nonmonotonic X-Ray Timing Signatures of Embedded Stellar-Mass Black Holes in AGN Disks

Jing-Tong Xing, Tong Liu, Mouyuan Sun+5 more

• Astrophysics of Galaxies

AstronomerThe authors calculate how stellar-mass black holes embedded in AGN disks could alter coronal X-ray emission and disk UV variability through magnetic reconnection. In the proposed mechanism, migrating black holes accumulate near migration traps, perturb disk magnetic fields, and drive reconnection that heats the disk and injects plasma into the corona, potentially releasing stored coronal magnetic energy. Including the disk thermal response and X-ray reprocessing, the calculations predict an initial enhancement of short-timescale X-ray variability followed by suppression as the embedded population grows. Suppression begins earlier at higher disk mass accretion rates. The model attributes this behavior to increasingly overlapping active regions, which reduce the coronal magnetic energy available per event. It also predicts a shorter UV lag behind X-rays than in the model without embedded black holes. These are model results, not reported observational detections.

PublicBlack holes with masses comparable to stars may live inside the gas disks of active galactic nuclei. This study calculates how those smaller black holes could change the disks’ flickering light. The proposed process involves disturbances to magnetic fields that heat gas and launch plasma into the hot region above the disk, where it can help release more magnetic energy. In the model, a few embedded black holes can initially strengthen rapid X-ray flickering, but the flickering becomes weaker as more accumulate. Their increasingly frequent disturbances overlap, leaving less stored magnetic energy for each event. This weakening starts earlier when gas flows through the disk at a higher rate. The calculations also predict that ultraviolet changes follow X-ray changes with a shorter delay than in a model without the smaller black holes. The study offers theoretical predictions rather than observations establishing that this happens.

Young explorerScientists used a model to imagine small black holes living in a big, swirling disk of gas. The little black holes might disturb magnetic fields and make the gas give off bursts of light. In the model, the light flickers more at first. But when more little black holes gather, their bursts overlap and have less stored magnetic energy to share, so the flickering becomes weaker. Another kind of light follows the X-ray flickers sooner than it does in the model without little black holes. This is what the scientists’ calculations suggest, not something they report seeing.

Black Hole Spin Evolution in Magnetized Accretion Flows

Danat Issa, Ore Gottlieb, Jonatan Jacquemin-Ide+1 more

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerLong 3D general-relativistic magnetohydrodynamic simulations evolve black-hole mass and spin during radiatively inefficient accretion, with flows aligned or anti-aligned with the spin. Unlike earlier fixed-mass, fixed-spin estimates restricted to weak magnetic flux or magnetically arrested disks (MADs), this work derives the spin-up parameter and equilibrium spin continuously across normalized horizon magnetic flux, phi/phi_MAD. The simulated equilibrium spin decreases steeply: approximately 0.9 for weakly magnetized flows, 0.5 at phi/phi_MAD = 0.5, and 0.06 in sustained MADs. Slowly spinning black holes in weakly magnetized flows require at least their initial mass in accreted material to reach equilibrium, whereas sustained MADs spin down rapidly rotating holes after accretion of less than half that mass. Crucially, MAD conditions need not persist: black-hole growth increases the gravitational radius and enhances inflow, reducing normalized flux when magnetic-flux supply cannot keep pace. This can end the MAD state and reverse spin-down into spin-up, making final spin dependent on both flux history and accreted mass. These are simulation results for the specified accretion regime, not observational measurements. The authors also discuss implications for black-hole-powered engines and provide a subgrid prescription for galaxy-scale simulations and population studies.

PublicA black hole’s spin reflects a competition: falling material adds rotational momentum, while magnetically driven jets remove it. In three-dimensional computer simulations that let black holes grow and change spin, researchers studied flows that radiate inefficiently and rotate either with or against the black hole. They found that stronger magnetic flux leads to a much lower balance-point spin. Weakly magnetized flows approach a spin of about 0.9, while sustained magnetically arrested disks approach about 0.06. But the strongest magnetic state may not last. As a black hole grows, its magnetic-flux supply may fail to keep up, allowing it to switch from slowing down to spinning up. The simulations therefore indicate that final spin depends on both how much material the black hole swallows and its magnetic history—not just its current magnetic state. These findings come from simulations, not direct observations.

Young explorerScientists used computer models to study spinning black holes. Falling stuff can make a black hole spin faster, while jets powered by magnetic fields can slow it down. In the models, stronger magnetic fields could keep the spin much slower. But as a black hole grew, the fields might not keep up, and it could start spinning faster again. What happened depended on how much it ate and how its magnetic fields changed.

Simultaneous Real-Color Time-Domain Survey of the Coma Field with the Multi-channel Photometric Survey Telescope (Mephisto)

Yu Pan, Yuan-Pei Yang, Ye-Hao Cheng+25 more

AstronomerThe 1.6-m Mephisto survey repeatedly monitors a 20-square-degree field centered on the Coma cluster, obtaining strictly simultaneous imaging in three optical bands. During its initial six-month pilot, it detected and tracked nine new supernovae. High-cadence observations captured very early rising light curves and signals hours to days before formal discovery alerts, including for SN 2026dyr. Simultaneous early-phase colors enable instantaneous spectral energy distributions without temporal interpolation, providing constraints on early supernova evolution. The authors report that the supernova yield agrees well with theoretical forecasts based on local stellar-mass and star-formation-rate overdensities, supporting their strategy of targeting a nearby massive structure. They interpret the pilot as demonstrating survey efficiency; rapid optical localization of future multi-messenger events is a prospective application, not a reported detection.

PublicA new telescope called Mephisto repeatedly watched a patch of sky centered on the Coma galaxy cluster and detected nine new exploding stars during its first six months of survey operations. It measures three optical colors at exactly the same time, helping researchers study rapidly changing explosions without combining measurements taken at different moments. Some observations caught explosions beginning to brighten hours to days before formal discovery alerts. The number of supernovae found agreed well with predictions based on the concentration of stars and star formation in the region. The team sees these results as support for its survey strategy and a foundation for locating visible counterparts to future events detected through other kinds of cosmic signals.

Young explorerA telescope called Mephisto watched the same part of the sky again and again. In six months, it found nine new exploding stars. It could look at three colors at once, helping scientists see how the explosions changed. Some pictures caught explosions starting to brighten before their discoveries were officially announced.

Harmonic brightness oscillations point to magnetar giant flares in rare short gamma-ray bursts

Run-Chao Chen, Ore Gottlieb, Bin-Bin Zhang+5 more

AstronomerA reanalysis of the two short GRBs with reported kilohertz quasi-periodic oscillations, GRB 910711 and GRB 200415A, finds evidence for possible harmonic-like organization around a characteristic frequency scale near 360 Hz, with features extending above 4 kHz. The shared pattern, including in the confirmed magnetar giant flare GRB 200415A, involves frequency scales relevant to magnetar oscillation modes, but the physical origin of the QPOs remains uncertain. Together with temporal and spectral similarities and difficulties for merger-driven explanations, these findings favor, rather than establish, an MGF-like interpretation of GRB 910711. Such timing structure may complement spectral, temporal, and localization evidence in distinguishing MGF-like transients from merger-driven GRBs.

PublicResearchers reexamined two brief gamma-ray bursts, GRB 910711 and GRB 200415A, whose brightness had been reported to fluctuate rapidly. They found tentative evidence that the fluctuations follow a harmonic-like pattern around 360 cycles per second, with some features above 4,000 cycles per second. GRB 200415A is a confirmed giant flare from a magnetar, a highly magnetic star. Similar timing and spectral properties in the two events, and difficulties explaining them through mergers, favor a similar giant-flare origin for GRB 910711, but do not prove it. The cause of the rapid fluctuations remains uncertain. These patterns could offer another clue for telling magnetar giant flares apart from merger-driven bursts.

Young explorerScientists looked again at two short flashes of gamma rays from space. They found hints that both flashes flickered in a similar, very fast pattern. One flash is known to be a giant flare from a very magnetic star called a magnetar. The similarities make scientists think the other flash might be the same kind, rather than coming from objects merging together. They are not sure yet, and they still do not know exactly what makes the flashes flicker.

XRISM/Resolve Study of Large Scale Properties in Tycho's Supernova Remnant

Tyler E. Hanover, Mark D. Leising

AstronomerThe authors fit Resolve X-ray spectra from five public archival XRISM observations of Tycho's supernova remnant with a multi-component non-equilibrium ionization plasma model assuming spherical expansion and a uniform abundance pattern. Off-center pointings are divided into three angular-distance bins, fitted simultaneously with the central observation, with elemental abundances tied across all model components. Pseudo-spherical expansion provides a good fit in the regions observed by Resolve, although iron appears slower on the approaching side than on the receding side. A nearly uniform abundance pattern across the remnant is consistent with the data, rather than independently established by these fits.

PublicResearchers analyzed five archival observations of Tycho's supernova remnant using Resolve, an X-ray instrument aboard XRISM. They compared the X-ray spectra with a model of expanding hot gas that assumes the same relative amounts of chemical elements throughout the remnant. The observed regions are well described by roughly spherical expansion, although iron appears to move more slowly on the side approaching us than on the side moving away. The data are also consistent with a nearly uniform chemical mixture, but do not prove that the mixture is uniform everywhere.

Young explorerScientists used X-ray light to study the cloud left by an exploded star. In the parts they studied, the cloud seems to spread out much like a growing ball. But iron in the part coming toward us seems to move more slowly than iron in the part moving away. Their model also fits a cloud with nearly the same mix of ingredients throughout, though that does not mean they know every part has the same mix.

A universal relation predicts the observed reversal of a supernova chirp

Joseph R. Farah, Logan J. Prust, Hang Yu

AstronomerSN 2024afav exhibited sinusoidal light-curve modulations whose period shortened from about 39 ± 8 d at 99 d to 17 ± 5 d at 166 d. A model invoking a precessing disk accreting onto a fading newborn magnetar yields a normalization-independent relation between the modulation-period derivative and the light-curve dimming rate. Using only the published chirp and a spin-down time measured from the unmodulated light curve, this relation predicted that the chirp would halt and reverse near 150 d. Continued follow-up revealed five new modulations, with periods increasing from about 24 ± 4 d at 177 d to 38 ± 2 d at 208 d; the reported reversal time, 147 ± 3 d, agrees with the prediction. This agreement supports the model, but does not by itself establish the engine or precession mechanism. Application to future survey events could help distinguish precession mechanisms and disk physics.

PublicThe exceptionally bright stellar explosion SN 2024afav showed repeated rises and falls in brightness that initially grew closer together. Researchers modeled these pulses as the effect of a wobbling disk feeding material onto a fading magnetar, a proposed newborn stellar remnant powering the explosion. Their model linked changes in pulse spacing to how quickly the explosion faded and predicted that the pulses would stop speeding up and begin slowing down around 150 days. Follow-up observations found five new pulses and placed the reversal at 147 ± 3 days, matching the prediction. The result supports this explanation without proving it uniquely. The researchers suggest that similar observations of future explosions could help reveal how their central engines and surrounding disks work.

Young explorerAstronomers watched a very bright exploding star get brighter and dimmer in little pulses. At first, the pulses came faster and faster. They had an idea: a wobbling ring of stuff might be falling onto a tiny leftover star. Their idea predicted that the pulses would start coming farther apart after about 150 days. When they kept watching, they found five more pulses and saw the change happen close to that time. That is a good clue that their idea may be right, but it is not proof.

The Disk Awakens: IXPE's Sequel Observation of GS 1354-64 Suggests Changing-Look Behavior in the Steep-Power-Law State

Swati Ravi, James F. Steiner, Megan Masterson+20 more

AstronomerGS 1354-64 has undergone a complete outburst after decades of failed transitions. X-ray polarimetry in the fading steep-power-law state measures a 2–8 keV polarization degree of 2.3 ± 0.2% and angle of 5 ± 3°, compared with 3.9 +0.3/−0.2% and −2 ± 2° in the earlier intermediate state: the polarization degree decreases while the angle remains consistent. The intermediate-state type-C QPO has disappeared, indicating substantial accretion-flow reconfiguration. Assuming a distance of 7 kpc, the luminosity declines from 2.5% to 1.6% of Eddington over 10.2 days, interrupted by broad hour-to-day troughs that trace two hardness–intensity tracks. Spectral modeling finds a cooler disk with smaller apparent normalization in the troughs, without requiring changes in the Compton component’s photon index or normalization. A model-independent analysis measures a steeper polarization-degree increase with energy outside the troughs, 1.5 ± 0.2%/keV, versus 0.7 +0.3/−0.5%/keV within them. The troughs’ durations and spectropolarimetric properties distinguish them from traditional short absorption dips; their interpretation as a stellar-mass analog of accretion changes associated with supermassive black hole changing-look behavior remains tentative.

PublicThe black hole X-ray binary GS 1354-64 has completed an outburst after decades in which its transitions failed to complete. As the outburst faded, researchers measured less polarization—a preferred orientation of the X-ray light—than in an earlier phase, while its orientation remained consistent. A previously detected rhythmic variation in brightness also disappeared, indicating a major change in the flow of material toward the black hole. During the overall fading, the X-rays showed several broad drops lasting hours to days. Spectral models associate these troughs with a cooler disk and a smaller apparent disk normalization, without requiring a change in the modeled component produced by Compton scattering. Polarization also increased less steeply with X-ray energy during the troughs. These events differ from the short absorption dips traditionally seen in such binaries. The researchers suggest, but do not establish, that they could be a small-scale counterpart of recurring accretion changes linked to dramatic changes in supermassive black hole systems.

Young explorerA black hole and its companion star had a big X-ray outburst. As it faded, scientists saw the X-ray light get dimmer for hours or days at a time. During those dim times, their models showed that the disk of material around the black hole was cooler. They also found changes in how the X-ray light was lined up. These long dim times looked different from the usual short dips. Scientists think they might be like changes around much bigger black holes, but they are not sure yet.

RAKI: High-Order Alternative Finite Differences for General Relativistic Magnetohydrodynamics

Rahime Matur, Beyhan Karakas, Ian Hawke+1 more

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology
• Computational Physics

AstronomerThe authors present RAKI, described as the first GRMHD code to simulate binary neutron star mergers using high-order alternative finite-difference methods with adaptive-order WENO reconstruction and a fully non-staggered, node-centred vector-potential formulation. Numerical tests achieve up to ninth-order convergence for smooth problems while capturing discontinuities. In magnetised TOV star tests, the code retains 99.2% of the initial maximum magnetic field strength over approximately 2 ms, with an order of magnitude less field loss than a reference GRMHD code at the same resolution. Binary neutron star merger simulations using fifth-order reconstruction show approximately third-order gravitational-wave phase convergence in both magnetised and unmagnetised models. The discrete no-monopole constraint is maintained to machine precision, including during mergers with moving refinement regions. These are numerical validation results, not observational findings or resolutions of magnetic amplification, magnetar formation, or jet formation; the framework is intended to improve modelling of those phenomena.

PublicResearchers have developed RAKI, a computer code for simulating merging neutron stars and the evolution of their magnetic fields. Such modelling could help scientists investigate how mergers strengthen magnetic fields and produce highly magnetic neutron stars or jets. In a simulated star test, RAKI retained 99.2% of the starting peak magnetic field strength over about two milliseconds, losing about ten times less than a comparison code at the same resolution. Merger simulations also showed that gravitational-wave calculations converged as resolution increased, while a mathematical constraint on magnetic fields remained satisfied to machine precision. These are tests of a simulation tool, not observations of real mergers or proof of how magnetars and jets form.

Young explorerScientists made a new computer program to practise what happens when two neutron stars crash together. It helps them follow the stars’ magnetic fields. In computer tests, it kept those fields from fading away by mistake better than another program did. These were pretend stars inside a computer, not real crashes being watched. The program could help scientists understand real star crashes.

The first mass peak of merging black holes from core binding energies and jet-driven explosions

Nikki Yat Ning Wang, Dmitry Shishkin, Noam Soker

• Solar and Stellar Astrophysics

AstronomerA two-parameter toy model of the jittering-jets explosion mechanism (JJEM) qualitatively reproduces the black hole mass distribution observed by LIGO-Virgo-KAGRA and quantitatively reproduces its peak near 10 solar masses. The model represents a scenario in which all massive stars explode, including those that form black holes. In the proposed mechanism, black hole formation requires high stellar binding energy, associated with initial masses ≳25 solar masses, and a rapidly rotating pre-collapse core that launches jets along a fixed axis. These polar jets inefficiently remove equatorial material, allowing a large fraction to accrete into a black hole when the binding energy is high. The model parameters are the core binding-energy threshold for black hole formation and the polar jet opening angle. The agreement is encouraging for JJEM, but does not establish its validity; future hydrodynamical simulations are needed to determine the precise black hole formation conditions and resulting masses.

PublicA simplified mathematical model offers a possible explanation for the pattern of black hole masses observed by LIGO-Virgo-KAGRA, including a peak near ten times the Sun’s mass. It uses a proposed stellar-explosion mechanism in which jets help stars explode even when they leave black holes behind. In this picture, a rapidly spinning stellar core directs jets along a fixed axis. The jets remove material less effectively around the star’s equator, so strongly bound material there can fall into the forming black hole. The model reproduces the broad shape of the observed mass distribution, but this is not proof that the mechanism works in real stars. Future simulations must establish exactly when black holes would form and how massive they would be.

Young explorerScientists made a simple model to explore how exploding stars might leave black holes behind. In their idea, sprays of material shoot out in two directions, while some other material falls into the black hole. The model matches part of the pattern astronomers see in black hole weights, but scientists still need more computer tests to check the idea.

Tidal disruption or plunge: the role of neutron star internal structure in black hole-neutron star mergers

Yatharth Chaurasiya, Ritam Mallick

AstronomerThis study models BHNS merger outcomes using a general-relativistic mass-shedding condition in Kerr spacetime. The tidal-disruption radius depends on mass ratio, BH spin, NS compactness, and the central-to-mean density ratio, η. Comparing this radius with the innermost stable circular orbit maps disruption versus plunge for two relativistic mean-field EOSs and about 10,000 agnostic EOSs spanning current NS-radius uncertainty. Compactness primarily sets the disruption threshold, but different η values can yield different outcomes at fixed compactness. A remnant-mass model based on the disruption radius and calibrated against 70 numerical-relativity simulations achieves accuracy comparable to existing fits. Applied to gravitational-wave events, the models find GW200105 and GW200115 consistent with direct plunge; the candidate BHNS event GW230529 lies near the threshold and may have undergone marginal disruption, leaving a low-mass remnant. These event outcomes are model-based interpretations, not direct observations of disruption.

PublicWhen a black hole merges with a neutron star, the star may be torn apart or plunge into the black hole without first being disrupted. This study uses a relativity-based calculation to estimate which outcome occurs. The model finds that the neutron star’s compactness is the main factor setting the dividing line, although how strongly its matter is concentrated toward the center can also change the outcome. The researchers also developed a model for the mass left over after a merger, calibrated against 70 computer simulations and about as accurate as existing formulas. Applying their models to gravitational-wave events, they find that GW200105 and GW200115 are consistent with direct plunges. GW230529, a candidate black hole–neutron star merger, is near the dividing line: the neutron star may have been only slightly torn apart, leaving little material behind. These are model-based assessments rather than direct sightings of the stars being disrupted.

Young explorerWhen a black hole meets a neutron star, it might pull the star apart, or the star might fall straight in. Scientists used calculations to work out when each could happen. They found that how tightly the star’s matter is packed matters most, but how much is packed into its middle matters too. Their calculations suggest that in two space events, the stars could have fallen straight in. In another possible event, called GW230529, the star might have been pulled apart just a little, leaving a small amount of material behind. Scientists are not sure that happened.

VERITAS Limits on Dark Matter Annihilation in the Galactic Center Halo

A. Archer, P. Bangale, J. T. Bartkoske+58 more

AstronomerAn indirect dark matter search uses VERITAS gamma-ray data from within 2° of the Galactic Center. Template-based background estimation improves sensitivity to emission extended on scales comparable to the 3.5° field of view. Exclusively large-zenith-angle observations provide increased effective area above approximately 1 TeV relative to small-zenith-angle observations. No significant gamma-ray signal is found in the search region, yielding annihilation-channel-dependent upper limits on the dark matter annihilation cross section. Under the assumptions of an Einasto density profile, a 1 TeV dark matter mass, and annihilation entirely into τ+τ−, cross sections as low as ⟨σ_ann v⟩ = 1.77 × 10^-25 cm³ s^-1 are excluded at 95% confidence.

PublicSome particle models predict that dark matter particles can annihilate one another, producing ordinary particles and potentially detectable gamma rays. Researchers searched VERITAS telescope observations within 2° of the center of our Galaxy for such emission. Their background-estimation method improves sensitivity to broadly spread-out emission, while observations made at large angles from overhead increase the telescope’s effective collecting area at energies above about 1 TeV. They found no significant gamma-ray signal in the search region. This sets limits on how strongly dark matter could annihilate, rather than proving that dark matter does not exist. For dark matter with a mass of 1 TeV, an assumed Einasto distribution, and annihilation exclusively into tau particle–antiparticle pairs, the analysis excludes annihilation cross sections as low as 1.77 × 10^-25 cm³ s^-1 at 95% confidence.

Young explorerScientists used a telescope called VERITAS to look near the middle of our galaxy for a special kind of light. Some ideas say that invisible stuff called dark matter could make this light when two of its particles meet and disappear. The scientists did not find a clear signal. That does not mean dark matter is not there, but it helps them limit how often this could happen if those ideas are right.

KM3-230213A: The Highest-Energy Cosmic Neutrino

Carla Distefano

AstronomerThis review examines KM3NeT event KM3-230213A, whose inferred parent-neutrino energy is of order 10^17 eV, and its possible astrophysical and cosmological origins. It discusses active galactic nuclei, transient sources, and cosmogenic neutrinos in light of multi-messenger constraints. Extensive follow-up has yielded no unambiguous electromagnetic counterpart, and the event remains in tension with the lack of comparable detections by other experiments. More complex source scenarios and contributions from physics beyond the Standard Model remain possibilities, not established explanations. The review also considers implications for ultra-high-energy neutrino astronomy and prospects for next-generation detectors.

PublicThe KM3NeT neutrino telescope detected an event called KM3-230213A, attributed to a neutrino with an estimated energy of roughly 10^17 electronvolts. This review explores where such an energetic particle might have come from, including active galaxies, short-lived cosmic sources, or processes that produce neutrinos as extremely energetic particles travel through the Universe. Despite extensive searches, astronomers have not identified a clear light-based signal associated with the event. Its detection is also difficult to reconcile with the absence of similar events in other experiments. The origin remains unresolved: more complicated source explanations or physics beyond the Standard Model are possibilities, not discoveries. Future detectors could help clarify the picture.

Young explorerA telescope called KM3NeT detected a tiny particle called a neutrino with an enormous amount of energy. Scientists are trying to work out where it came from. They looked for a matching flash or other light signal in space, but found no clear match. Other experiments have not seen similar events, which adds to the puzzle. This paper reviews possible explanations, but none is certain. Future detectors may help scientists learn more.

From photons to neutrinos : Advancing multi-messenger modeling with Gammapy

Justin Albinet, Lea Heckmann, Matteo Cerruti+1 more

AstronomerThe authors present a multi-wavelength and multi-messenger modeling framework within the open-source Gammapy software. It fits physical emission models directly to instrumental counts from optical through very-high-energy gamma rays, avoiding intermediate flux-point estimates. Using blazars as an initial application, they demonstrate constraints on multi-wavelength emission models and reduced fitting biases. They report a first application to leptonic blazar modeling, with sufficiently short computation times for on-the-fly fitting, and explore grid fitting for more computationally intensive emission codes. Direct joint fitting of photon and neutrino events is presented as a route to statistically sound constraints on multi-messenger source physics, not as a confirmed photon-neutrino source detection or a completed joint-analysis result.

PublicThe study introduces a software tool for testing how extreme cosmic objects produce radiation and accelerate particles. Built into the open-source program Gammapy, it compares physical models directly with telescope counts across light ranging from optical wavelengths to very-high-energy gamma rays, rather than first converting those counts into separate brightness estimates. The authors demonstrate the tool using blazars, showing that it can constrain emission models and reduce fitting biases. One type of model, involving electrons and positrons, runs quickly enough to fit directly; for slower models, they explore comparing data with a grid of model calculations. The broader goal is to fit light and neutrino detections together to better constrain source physics. The abstract does not report a confirmed source emitting both messengers.

Young explorerScientists made a new computer tool to help understand powerful things far away in space. It checks ideas by comparing them with the light that telescopes count, from ordinary light to very energetic light. They tried it on space objects called blazars and showed that it can help avoid some mistakes when choosing which ideas fit the data. They also want to use it to study light together with tiny particles called neutrinos. This study does not show that they found a blazar sending both.

A Candidate Binary Microlensing Event in the 2018 Gamma-Ray Flare of 3C 279

Yihong Yang, Jianeng Zhou, Haibin Ren+8 more

AstronomerThe April 2018 GeV flare of the flat-spectrum radio quasar 3C 279 showed sharp peaks within a broader outburst, with rapid substructure previously attributed to magnetic reconnection. Motivated by its distinctive temporal profile and resemblance to optical microlensing caustic crossings, the authors test a finite-source binary-microlensing interpretation. A joint model combining binary-lens magnification, a smooth intrinsic flare, and Gaussian-process variability reproduces the principal double-peaked structure. The adopted local solution has mass ratio q ≈ 0.098 and Einstein timescale t_E ≈ 0.327 d. Absolute lens masses and projected source size remain dependent on lens distance and relative proper motion: the geometry could represent a Galactic planetary-mass binary or an intervening stellar or substellar system. Microlensing remains a testable interpretation, not an established cause; finite-source structure could potentially constrain the compact GeV-emitting region.

PublicIn April 2018, the quasar 3C 279 produced a gamma-ray outburst with sharp brightness peaks. Earlier work attributed these rapid changes to magnetic reconnection. This study explores another possibility: a pair of objects along our line of sight could have acted as a gravitational magnifying lens. A model combining this lensing effect with the quasar’s own flare and additional variability reproduces the main two-peaked pattern. That fit does not establish that lensing caused the event. The possible lenses could be a pair of planetary-mass objects in our Galaxy or a stellar or substellar system farther along the line of sight; their masses and the inferred emitting-region size depend on the lens distance and relative motion. If supported, this interpretation could offer a way to study the quasar’s compact gamma-ray source.

Young explorerA very bright object far away had a big burst of light, with two sharp peaks in brightness. Scientists tried an idea: maybe two objects in front of it bent its light, a little like a magnifying glass. Their model can make a pattern like the two peaks, but that does not prove the idea is right. If it is right, it could help them learn how small the place making that light is.

Polarization and Burst Properties of the Repeating FRB 20240209A in a Quiescent Elliptical Host

Yong-Kun Zhang, Yi Feng, Di Li+4 more

AstronomerGreen Bank Telescope polarimetry at L band and 800 MHz detected three bursts from the repeating source FRB 20240209A, previously associated with a quiescent elliptical galaxy with a mass-weighted stellar age of approximately 11 Gyr. The brightest burst resolves into eight components drifting toward lower frequencies. The bursts have mutually consistent rotation measures, and the small extragalactic RM agrees with the low value predicted from the small host-galaxy dispersion measure. Within the brightest burst, the linear polarization fraction decreases toward lower frequencies, consistent with depolarization from an RM scatter of approximately 3.5 rad m^-2. This scatter is comparable to that of several repeaters in star-forming galaxies. The authors interpret these findings as evidence that repeaters in both old, quiescent and star-forming hosts can occupy relatively complex magneto-ionic environments, suggesting—but not establishing—multiple formation channels.

PublicAstronomers detected three brief radio flashes from the repeating source FRB 20240209A using the Green Bank Telescope. The source was previously linked to an elliptical galaxy whose stars have an average age, weighted by their mass, of about 11 billion years and which has little ongoing star formation. The brightest flash contains eight parts that shift toward lower radio frequencies. Measurements of polarization—the orientation of the radio waves—show little overall rotation attributable to material beyond our galaxy. Yet the fading of linear polarization at lower frequencies is consistent with variations in that rotation, comparable to those inferred for some repeating sources in star-forming galaxies. The findings suggest that even an old, quiet host can contain a source with a relatively complex local environment of magnetic fields and electrically charged gas. They also hint that these radio-flash sources may form in more than one way, rather than proving that they do.

Young explorerA telescope caught three quick radio flashes from something in space that flashes again and again. It has been linked to a galaxy full of very old stars, where few new stars are being made. The strongest flash had eight little parts. The radio waves carry clues about magnetic fields and gas around the flashing source. Those clues suggest its surroundings may be complicated, much like those around some flashing sources in galaxies making new stars. This hints that these mysterious flash-makers might be born in different ways, but scientists are not sure yet.

Influence of Δ resonances in hyperonic neutron stars on gravitational-wave inspiral signatures

Athira S., Vivek Baruah Thapa, Monika Sinha

• High Energy Physics - Phenomenology

AstronomerThis theoretical study examines tidal properties and inspiral gravitational-wave signatures of hyperonic neutron stars containing non-strange Δ baryons in a density-dependent relativistic mean-field model using DDME2. Varying the uncertain scalar and vector Δ–meson couplings subject to xσΔ − xωΔ = 0.2 produces substantial changes in tidal deformability and corresponding differences in waveform frequency evolution, accumulated phase, and strain amplitude. These are model predictions, not observational detections, and the waveform differences are not unique to Δ resonances. Future gravitational-wave observations may constrain the couplings within this framework, but degeneracies with alternative equations of state limit the interpretation.

PublicScientists do not yet know exactly what matter is like inside neutron stars. This theoretical study explores models that include particles called Δ baryons and varies the uncertain strength of their interactions with other matter. In the models, these changes affect how easily the stars deform under a companion’s gravity, altering the predicted gravitational waves as the stars spiral together. Future observations might help narrow down those interaction strengths. However, similar wave patterns could come from other descriptions of neutron-star matter, so they would not by themselves establish that Δ baryons are present.

Young explorerNeutron stars are very tightly packed stars, and scientists are not sure what is inside them. Researchers made models with a possible kind of tiny particle inside. Changing how those particles interact changed how much the model stars could stretch and the space ripples they would make while circling each other. Watching real ripples someday might give clues, but different insides could make similar ripples, so the clues would not be proof.

The unresolved high-mass frontier of the black hole Fundamental Plane

Ramananda Santra, Samik Mitra, Shahram Abbassi

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

AstronomerThe study recalibrates the forward Fundamental Plane linking nuclear radio luminosity, X-ray luminosity, and black hole mass using galaxies with direct dynamical mass measurements, then reassesses claims of radio excess in brightest cluster galaxies at masses above roughly 10 billion solar masses. The archival BCG sample with proxy-based masses cannot uniquely establish an excess: the inferred signal depends on mass calibration and radio-selection properties. Mock observing programs further indicate that the predictive width of existing observations makes a high-mass transition difficult to detect and localize with current samples. The data therefore offer no compelling evidence for a distinct high-mass branch, rather than ruling one out. The authors call for a substantially larger, uniformly selected direct-mass sample with matched, preferably quasi-simultaneous nuclear radio and X-ray measurements, and propose a pilot survey of several dozen systems to test whether the necessary precision is achievable.

PublicAstronomers use a relationship between a feeding black hole’s mass and its radio and X-ray brightness to compare black holes. This study asks whether that relationship changes for the most massive ones, above about 10 billion times the Sun’s mass. After recalibrating the relationship using directly measured black hole masses, the researchers find that existing data do not convincingly show the extra radio brightness previously suggested for black holes in the brightest galaxies in clusters. The apparent excess depends on how masses were estimated and how the galaxies were selected for radio observations. Simulated observing programs also suggest that current samples make any change hard to detect and pinpoint. This does not prove the relationship stays the same. The authors propose starting with a survey of several dozen galaxies with directly measured black hole masses to assess whether sufficiently precise tests are feasible.

Young explorerScientists compare how heavy feeding black holes are with how brightly they shine in radio waves and X-rays. They wondered whether the very biggest black holes follow a different pattern. They checked older information, but it did not give a clear answer: guesses about the black holes’ weights and which galaxies were picked could change the result. Pretend observing tests also showed that spotting a change would be hard with the information available. So scientists do not yet know whether the biggest black holes are different. They suggest carefully studying more galaxies to help find out.

The Conditional CMB Visibility of High-Redshift X-Ray Cavities in Galaxy clusters

Ramananda Santra, Samik Mitra

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies

AstronomerThe authors derive a criterion linking CMB-driven lepton cooling, bubble volume and enthalpy evolution to intrinsic 0.5–2 keV cavity contrast, separately from instrument-dependent recovery. Using the measured atmosphere of SPT-CL J2215−3537, their calculations find that uncooled power-law leptons with s=2.5, minimum Lorentz factors of 100–1000, and a maximum of 100,000 require 0.6–1.2% of the pressure to fill the soft X-ray deficit through inverse-Compton emission. The requirement spans 0.2–3.7% across the main tested parameter ranges; complete loss of this component lowers enthalpy by less than 3% relative to an otherwise identical adiabatic bubble at the same pressure. A low-cutoff control with minimum Lorentz factor 10 and s=3 instead requires 18.9%, highlighting the uncertain low-energy spectrum. At fixed atmosphere and spectrum, the required fraction scales as (1+z)^−4. Declining-pressure tracks cross the adopted X-ray detection threshold while the enthalpy deficit remains below 0.4%, with transition timing dependent on the assumed pressure history. These are model-based visibility criteria, not an instrument-specific demonstration of cavity recovery.

PublicA bubble in a galaxy cluster can appear as a dim patch in X-rays. This study calculates how, at high redshift, energetic particles inside a bubble can scatter light from the cosmic microwave background into X-rays, filling in that dim patch. Using the measured surroundings of one cluster, the authors find that particles carrying only a small share of the bubble’s pressure could conceal the X-ray deficit under many tested assumptions, even when their eventual loss would change the bubble’s energy content very little. However, the answer depends strongly on the poorly known population of lower-energy particles and on the surrounding gas. These calculations do not establish that a particular telescope would miss a cavity; that requires a separate instrument-specific analysis.

Young explorerImagine a bubble that looks like a dark spot in a glowing cloud. Scientists calculated that tiny, speedy particles inside it could turn old light into X-rays and help hide the dark spot. The bubble could become hard to spot without losing much energy. But the answer depends on what particles are inside.

Axion-angle dependence of the rotational and tidal properties of PNJL quark stars

Safiqul Islam, Ayan Banerjee, Javlon Rayimbaev+1 more

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study computes rotational and static tidal properties of self-bound quark stars in general relativity using an axion-extended Polyakov-loop Nambu–Jona-Lasinio EOS. With other model parameters fixed, a spatially uniform axion angle is varied from 0 to π across five sequences. Calculations include the leading-order moment of inertia, second-order spin-induced quadrupole and mass shift, and finite-surface-density contributions to the rotational mass shift and static tidal response. The static maximum mass increases from 1.68 to 1.95 solar masses but remains below the lower edge of the quoted 1σ timing interval for PSR J0740+6620. At 1.338 solar masses, the moment of inertia increases by 13% and dimensionless tidal deformability rises from 342 to 547. Adjacent-angle differences in moment of inertia exceed the tested interpolation and table-resolution sensitivities over the common mass range examined. Joint fits to the normalized moment-of-inertia–compactness and I-Love-Q relations have maximum departures of 2.7% and 0.4%, respectively, within the fitted domains. Predicted binary tidal-deformability curves fall within the estimated 90% credible region of the adopted GW170817 posterior over the examined mass-ratio ranges. These results establish angle dependence and accurate joint normalized relations within this EOS family, not observational evidence for an axion effect.

PublicResearchers used a theoretical model to explore how a hypothetical axion-related property could change stars made of quark matter. They varied a spatially uniform parameter called the axion angle while keeping the model’s other settings fixed. Across the tested range, the model stars could support more mass. At one fixed stellar mass, their resistance to changes in spin increased by 13%, and they became easier to deform through a companion’s gravity. Even so, the largest nonrotating star supported by the model remained below the lower edge of the quoted one-standard-deviation mass interval for the pulsar PSR J0740+6620. The predicted tidal responses of binary stars were compatible with the adopted uncertainty region for the gravitational-wave event GW170817 over the ranges tested, but this does not demonstrate that axions or quark stars were present. Despite changes in individual properties, shared mathematical relations described several normalized properties accurately across the five model sequences.

Young explorerScientists used math to imagine special stars made of tiny bits called quarks. They changed one setting linked to something called an axion. In their model, changing that setting let the stars hold more stuff and made them easier for another star’s gravity to stretch. Some simple rules still worked well for all five sets of pretend stars. These are answers from a model, not changes scientists watched happen in real stars.

Fermion-Boson Stars in Scalar-Tensor Gravity

Jorge Castelo Mourelle, Saeed Fakhry, Néstor Ortiz

• General Relativity and Quantum Cosmology

AstronomerNumerical models in massless Damour-Esposito-Farèse scalar-tensor gravity demonstrate spontaneous scalarization in static, spherically symmetric mixed fermion-boson stars. The components interact only gravitationally: fermions are treated as a perfect fluid and bosons as a massive, free, complex scalar field. Varying boson mass, central fermionic pressure, and central bosonic amplitude yields diverse scalarized configurations, including extended bosonic halos around fermionic matter and bosonic cores within fermionic matter. The study examines solution sequences and mass-radius surfaces and determines the critical coupling parameter for scalarization onset. These are theoretical configurations, not observational detections.

PublicComputer calculations explore hypothetical stars containing two kinds of matter, fermions and bosons, that interact only through gravity. In the alternative theory of gravity studied here, these mixed stars can undergo spontaneous scalarization, developing an additional gravitational scalar field. Depending on the model parameters, bosonic matter can form an extended halo around fermionic matter or a core inside it. The researchers also examine how stellar mass and radius vary and determine the coupling threshold at which scalarization begins. The findings concern theoretical models, not stars observed in the sky.

Young explorerScientists used computers to imagine stars made from two kinds of matter that pull on each other through gravity. In some models, one kind makes a big cloud around the other. In others, it sits in the middle. They also found that an extra gravity field can switch on under certain conditions, using a different rule for gravity. These are pretend stars made with math, not stars the scientists found in the sky.

Probing Scalar Polarization with Next-Generation Gravitational-Wave Detectors: The Roles of Detector Geometry and Source Inclination

Sk Md Adil Imam, Macarena Lagos

• General Relativity and Quantum Cosmology
• Instrumentation and Methods for Astrophysics

AstronomerUsing simulated binary neutron star signals, this study forecasts constraints on gravitational-wave scalar polarization through three PPE modified-gravity parameters: tensor amplitude α, scalar amplitude α_B, and tensor/scalar phase β. Cosmic Explorer (CE) and Einstein Telescope (ET) are each forecast to tighten all three constraints by 1–2 orders of magnitude relative to an O5 LIGO–Virgo network. ET’s triangular geometry yields approximately twice as tight an α_B constraint as a two-CE network for both a GW170817-like source and a second representative binary neutron star source. For the GW170817-like case, assuming electromagnetic observations supply the sky position and luminosity distance, an additional electromagnetic inclination prior tightens the α_B constraint by approximately 56 times relative to an isotropic inclination prior. The study also examines sensitivity to inclination priors and neutron-star equation-of-state assumptions. These are forecasts, not detections of scalar polarization, and highlight detector geometry and external electromagnetic information alongside network sensitivity.

PublicCould gravitational waves ripple in an additional way beyond the two patterns allowed by general relativity? This study uses simulated neutron-star collisions to estimate how well future detectors could test for an extra scalar pattern. Cosmic Explorer and Einstein Telescope are each predicted to constrain the three gravity parameters studied 10–100 times more tightly than an O5 LIGO–Virgo network. In two simulated source cases, Einstein Telescope’s triangular layout provides about twice as tight a limit on the scalar-wave amplitude as two Cosmic Explorer detectors. Information from light could help substantially: for a source resembling GW170817, adding information about the orbit’s tilt improves the scalar-amplitude constraint by about 56 times, provided the source’s sky position and distance are already known from electromagnetic observations. The study also considers how assumptions about neutron-star matter affect the analysis. These predictions do not establish that scalar waves exist; they show how detector layout and complementary observations could sharpen future tests.

Young explorerWhen two neutron stars whirl around each other, they make ripples in space. Scientists used pretend signals in a computer to ask whether future detectors could look for an extra kind of ripple that our usual theory of gravity does not predict. Their tests suggest that the detectors’ shape, and clues from light about where the stars are and how their orbit is tilted, could help. They have not found this extra ripple; they are working out how to search for it better.

Gravitational lensing of gravitational waves by a Kerr black hole

Jian-hua He

• General Relativity and Quantum Cosmology

AstronomerThe authors simulate GW lensing by a Kerr black hole using a (1+1)-dimensional time-domain mode-sum framework, evolving over 68,000 coupled (j,m) modes. A localized hyperboloidal foliation and static field redefinition enable efficient explicit evolution, while tetrad projections and angular transformations accommodate wave packets and binary-coalescence signals at arbitrary incidence and polarization angles. In the simulations, the Kerr black hole behaves as a diffraction-limited thick lens, focusing radiation into a forward beam. Idealized packets produce a prompt pulse with a spin-independent transverse Gaussian profile, followed by a spin-sensitive lensing coda. For binary signals, strong-field lensing substantially modifies the post-merger ringdown, but the lensed inspiral and merger are nearly identical between Kerr and Schwarzschild backgrounds, with mismatches below 2.2 × 10^-5 across the inclinations and polarizations tested. The authors conclude that Schwarzschild models offer an accurate, economical surrogate for strong-field lensing searches with current ground-based detectors; these are simulation findings, not an observational detection.

PublicComputer simulations explore how a spinning black hole bends and concentrates gravitational waves into a forward beam. For simple wave packets, the shape of the first arriving pulse does not depend on the black hole’s spin, but the trailing signal does. For waves from merging binaries, strong lensing substantially changes the final ringing signal. Yet the earlier inspiral and merger portions look almost identical when simulated with spinning and non-spinning black holes across the orientations tested. The authors therefore argue that simpler, less costly non-spinning models can help current ground-based detectors search for strong-lensing signatures. The study simulates these effects rather than reporting their detection.

Young explorerScientists used computers to see how a black hole could bend waves that ripple through space and gather them into a beam. In their pretend waves, a spinning black hole changed the trailing ripples more than the first ones. Simpler computer black holes that do not spin may help scientists look for these signs. They have not reported finding them in real waves here.

Inverse Gertsenshteǐn-Zel'dovich Effect in Time-Independent Electromagnetic Field

Rajendra Prasad Bhatt, Rudraksh Verma, R. Prasad+1 more

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study generalizes calculations of the inverse Gertsenshteǐn-Zel'dovich effect, in which gravitational waves convert into electromagnetic waves in a background electromagnetic field. The authors develop a formalism for the induced electric and magnetic field components in spatially varying, time-independent backgrounds, accommodating all six possible gravitational-wave polarization modes. They illustrate it with constant and spatially varying fields and investigate signals generated in astrophysical magnetic fields, particularly those associated with neutron stars and magnetars. The abstract reports no observational detection; applications to high-frequency gravitational-wave detector design and high-energy astrophysical electromagnetic signals remain prospective.

PublicGravitational waves can turn into electromagnetic waves when they pass through a background electromagnetic field, through a process called the inverse Gertsenshteǐn-Zel'dovich effect. This theoretical work develops a way to calculate that response when the background field varies from place to place but stays constant over time. The method covers all six possible polarization modes, or patterns of gravitational-wave distortion. The researchers apply their calculations to several examples, including magnetic fields associated with neutron stars and magnetars. They suggest that the method could help design high-frequency gravitational-wave detectors and study high-energy signals from space, but the abstract does not report a detection.

Young explorerRipples in space can turn into light waves when they travel through a magnetic field. Scientists made a new way to work out what those light waves would be like when the field is different in different places. They used their calculations to explore fields around special stars called neutron stars and magnetars. This might someday help people look for ripples in space, but this study does not report seeing them turn into light.

Evolutionary tracks and isochrones of the inverse Hall cascade

Axel Brandenburg, Vinay Kumar

• Plasma Physics

AstronomerDecaying MHD turbulence can show inverse transfer, with magnetic-energy spectral amplitude growing in the subinertial range. To investigate whether the resistive dependence of its transfer speed is linked to reconnection, the authors study a Hall cascade without solving a momentum equation and with the induction term replaced by a term corresponding to the negative MHD Lorentz force. The inverse-transfer speed remains resistivity-dependent, whereas an analogous numerical reconnection experiment shows no such dependence. This comparison suggests that the resistive dependence of inverse transfer need not arise from reconnection; it does not establish that reconnection is irrelevant in general.

PublicAs magnetic turbulence fades, magnetic energy can build up on larger scales. The speed of this transfer can depend on electrical resistivity, but it is unclear whether this happens because magnetic fields reconnect. In a simplified numerical study called a Hall cascade, the authors find that the transfer speed still depends on resistivity. A related numerical experiment on reconnection shows no such dependence. The comparison suggests that reconnection is not necessarily responsible for the transfer's sensitivity to resistivity, rather than ruling out a role for reconnection altogether.

Young explorerIn a computer experiment, the researchers studied how energy in jumbled magnetic fields can build up in bigger patterns. Changing how easily electric currents fade changed how fast this happened. But in a related computer test of magnetic fields breaking and joining again, that change did not affect the speed. This is a clue that breaking and joining may not be what makes the first process speed up or slow down.

Gravitational-Wave Echoes and Greybody Cutoff from Logarithmic Throats at a Marginal-Trapping Threshold

Jahed Abedi

• General Relativity and Quantum Cosmology
• High Energy Physics - Theory

AstronomerThis theoretical study models axial gravitational-wave propagation through long throats in static, spherically symmetric configurations approaching marginal trapping. For a nondegenerate minimum F ≃ Δ + β(r−R_M)², the proper throat length diverges as −ln Δ/√β while local curvature remains finite. With lapse N ∝ F^(s/2), s > 0 produces a cavity behind the angular-momentum barrier and an echo spacing T_echo ≃ 2Λ + δ ∝ Δ^(−s/2), with δ independent of Δ. Time-domain evolutions confirm this scaling over three decades in Δ; at s = 0, the throat instead becomes part of the barrier and no distinct echo appears. The matter-supported, four-dimensional quasi-black-hole configurations have regular centres capping near-AdS₂ throats and serve as simplified models of capped horizonless microstate geometries. Their echo delays track the inverse redshift near the throat bottom, unlike the logarithmic delay growth in thin-shell gravastars and wormholes. The barrier gives a greybody cutoff, 1−Γ ≃ exp[−(ω−f)/T], whose T depends on barrier curvature rather than any interior horizon’s surface gravity. Within this model, horizon and reflecting-throat interiors produce the same prompt signal, but the horizonless case returns transmitted waves as echoes, restoring the high-frequency reflected spectrum. These are model results, not reported observations.

PublicThe researchers use a simplified theoretical model to explore gravitational waves near objects that approach black-hole-like conditions without necessarily having a horizon. The model develops a long, narrow throat even though local spacetime curvature stays finite. For certain choices of how clocks slow down along the throat, waves can enter, reflect from the capped interior, and emerge as delayed echoes. Computer evolutions confirm the predicted growth of the echo delay across the tested range; another model choice produces no distinct echo. The delay is governed by the strong slowing of clocks near the throat’s bottom and grows differently from delays in the thin-shell gravastar and wormhole models discussed. In this model, the first outgoing signal cannot distinguish a horizon from a reflecting throat. Later echoes can return wave components that initially passed through the surrounding barrier. The study reports theoretical and computational findings, not detected echoes from astronomical objects.

Young explorerScientists used a computer model to study ripples in space near something almost like a black hole. In some versions, the ripples travel down a long passage, bounce back, and come out as echoes. A deeper passage makes the wait longer. Another version makes no clear echo. These are results from a model, not echoes scientists have heard from space.

Multi-Generational Black Hole Population Analysis with an Astrophysically Informed Mass Function

Yannick Ulrich, Djuna Croon, Jeremy Sakstein+1 more

• Cosmology and Nongalactic Astrophysics
• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerThe authors analyze LIGO/Virgo/KAGRA GWTC-3 black hole population statistics with a parametric mass function derived from simulations of pulsational pair-instability supernovae (PPISN), separating stellar-collapse remnants from black holes formed in prior mergers. The model is favored over powerlaw+peak with a Bayes factor of 9.7 ± 0.1. Within this framework, the inferred lower edge of the upper black hole mass gap is 84.05 solar masses, with reported uncertainties of −12.88 and +17.19 solar masses. This provides evidence against identifying the previously detected 35-solar-mass Gaussian peak with the predicted PPISN pile-up. Including spin yields near-zero normalized spins for stellar remnants and generally larger spins for higher-generation black holes, consistent with stellar-structure and merger predictions. Combining the mass function with the spectral siren method gives H₀ = 36.19 km/s/Mpc, with reported uncertainties of −10.91 and +17.50 km/s/Mpc; the authors discuss possible explanations for this low value. These are population inferences within the adopted astrophysical model, with future data expected to improve precision.

PublicResearchers used a gravitational-wave catalog to study how black holes form, comparing the data with a model informed by simulations of massive stars. Their model distinguishes black holes born from collapsing stars from those built through earlier black hole mergers, and it fits the catalog better than a commonly used alternative. The analysis places the beginning of a predicted shortage of black holes at about 84 times the Sun’s mass, though with substantial uncertainty. It also suggests that a previously identified concentration near 35 solar masses is not the buildup expected just below that shortage. In this model, black holes born from stars spin very slowly, while those formed through earlier mergers tend to spin faster. The researchers also use the modeled mass distribution to estimate the universe’s expansion rate, obtaining a low and uncertain value. These conclusions depend on interpreting the catalog through the model; more data should sharpen the measurements.

Young explorerSome black holes are born when big stars collapse. Others grow when black holes join together. Scientists studied tiny ripples in space from black holes joining, using a model based on computer simulations of stars to help understand them. Their model worked better than another model they tested. It suggests that black holes born from stars hardly spin, while ones made by earlier black hole joins tend to spin faster. They also used the model to estimate how fast the universe is growing. These are clues, not answers known for sure, and more observations should help.

A Possible Mass Ratio and Spin-Orbit Misalignment Correlation for Mergers of Binary Black Holes in Nuclear Star Clusters

Yubo Su

AstronomerThe origin of LVK binary black hole mergers remains unresolved. A moderate preference for spin alignment with orbital normals and an apparent anti-correlation between effective spin, χ_eff, and mass ratio would seem to challenge purely dynamical formation channels lacking a preferred orientation. This paper presents a dynamical route with analytically predictable spin distributions: a stellar binary undergoes two phases of stable mass transfer to form a BBH, which is subsequently driven to merge by gravitational perturbations from a distant massive object, such as a supermassive black hole. In this scenario, χ_eff may be anti-correlated with mass ratio. However, the proposed mechanism operates only within a modest parameter-space region and predicts substantially tighter correlations than those seen in GWTC-4.0 systems. Suggested extensions could broaden its applicability, but these remain avenues for future work rather than established results.

PublicHow merging black hole pairs form is still uncertain. Their spins offer clues: observations suggest some preference for alignment with their orbits and a possible relationship between spin and the ratio of the black holes’ masses. The authors propose a route in which two stars exchange material in two stable stages before becoming black holes. Gravity from a distant massive object could then drive the pair to merge. Their calculations show that this route could produce the suggested spin–mass-ratio relationship. But it currently works only under a limited range of conditions and predicts a much tighter relationship than the observations show. Whether extensions of the idea can better account for the observations remains an open question.

Young explorerScientists are trying to learn why pairs of black holes come together. They have an idea: two stars share material before becoming black holes, and a faraway, very heavy object pulls on the pair and helps them meet. The idea predicts a link between how the black holes spin and how their sizes compare. But the real pairs do not follow the prediction as neatly, so the idea still needs more work.

Probing Axion-Photon Mixing with High-Resolution X-ray Spectroscopy

Yu Zhou, Jiejia Liu, Volodymyr Takhistov+1 more

• Cosmology and Nongalactic Astrophysics
• High Energy Physics - Phenomenology

AstronomerThis simulation-based study forecasts sensitivity to ultralight axion-like particles (ALPs) through energy-dependent spectral modulations induced by photon–ALP conversion in magnetized plasmas. It considers background AGNs behind clusters, central AGNs within cluster halos, and Galactic X-ray binaries, assessing prospects for XRISM, Athena, and Arcus. For typical magnetic-field configurations, the simulations predict that 320 ks with XRISM or 8 ks with Athena on NGC 1275 could probe g_aγ ~ 5 × 10^-13 GeV^-1 for m_a ≲ 10^-12 eV, beyond the current best limit. These are projected sensitivities, not detections or measured constraints; the study assesses their dependence on magnetic-field modeling, photon statistics, and spectral binning.

PublicHypothetical particles called axion-like particles could convert into and out of light as it travels through magnetic fields in space, leaving energy-dependent patterns in an X-ray spectrum. This study uses simulations, rather than reporting a detection, to forecast how well XRISM, Athena, and Arcus could search for those patterns in bright cosmic sources. For the active galaxy NGC 1275 in the Perseus Cluster, the simulations suggest that a 320,000-second XRISM observation or an 8,000-second Athena observation could test weaker particle–light interactions than the current best limit, for sufficiently low particle masses. The forecast depends on the assumed magnetic fields, the number of photons collected, and how the spectra are divided into energy intervals.

Young explorerScientists wonder whether tiny particles we have not found could turn into light and back again while traveling through magnetic places in space. That might leave a little pattern in X-rays from bright things far away. The scientists used computer models to work out how X-ray telescopes could look for that pattern. The models suggest these searches could be very powerful, but they do not show that the particles have been found.

Numerical Modeling of Relativistic Effects in Synchrotron-Emitting Shocks

Ross Ferguson, Ben Margalit

AstronomerThe authors present a publicly available numerical full-volume radiative-transfer model for synchrotron-emitting shocks of arbitrary velocity, accounting for all special-relativistic effects. Comparisons with commonly used approximate models indicate that the full-volume treatment is generally necessary for shock proper-velocities (Γβ)sh ≳ 0.1; approximate models can err by an order of magnitude or more in trans-relativistic shocks. These are model-comparison findings, not new observational measurements. They suggest possible biases in physical properties inferred for some FBOTs, jetted TDEs, and other relativistic explosions using approximate analytic treatments, but do not establish such biases for individual sources.

PublicMany cosmic explosions produce synchrotron radiation, but calculating how that light reaches us becomes complicated when their shock waves move fast enough for relativity to matter. The researchers introduce publicly available software that calculates this radiation throughout the emitting volume while accounting for relativistic effects. Comparing calculations, they find that commonly used shortcuts can give answers wrong by a factor of ten or more for shocks in the transition toward relativistic speeds. This raises the possibility that some properties previously estimated for certain cosmic explosions are biased; the study does not demonstrate that any particular observed explosion has been mischaracterized.

Young explorerWhen a big explosion happens in space, a fast-moving wave can make light. Scientists often use shortcuts to work out how much light we should see. This team made a new computer tool that follows the light more carefully. When they compared the calculations, they found that the shortcuts can be very wrong for very fast waves. The new tool may help scientists understand some space explosions better, but it does not show that their guesses about any one explosion were wrong.

Probing Extragalactic Ultralight Axion Dark Matter with Decade-Long Blazar Optical Polarimetry of 1ES 1959+650

Qiu-Ju Huang, Bao Wang, Jun-Jie Wei+1 more

• Cosmology and Nongalactic Astrophysics
• High Energy Physics - Phenomenology

AstronomerThe authors report the first search for ALP-induced periodic polarization-angle oscillations in 10 years of optical polarimetry of the blazar 1ES 1959+650. A Lomb–Scargle periodogram combined with Monte Carlo analysis finds no statistically significant periodicity. Across ALP masses of approximately 1.4×10^-23–5.2×10^-20 eV, the inferred upper limits on g_aγ range from 1.3×10^-13 to 6.0×10^-10 GeV^-1 under the adopted central host-galaxy dark-matter density assumption, and from 2.5×10^-13 to 6.2×10^-13 GeV^-1 under a soliton-core density assumption. These density-dependent constraints surpass those from Very Long Baseline Array jet polarimetry and European Pulsar Timing Array polarimetric data, and are competitive with long-term timing constraints from PSR J0437-4715 in the same mass window. The null result supports long-term blazar polarimetry as a complementary extragalactic probe, rather than constituting an ALP detection.

PublicResearchers searched 10 years of observations of the blazar 1ES 1959+650 for a possible sign of dark matter. Hypothetical particles called axions or axion-like particles could make the polarization direction of its light swing back and forth periodically. No statistically convincing repeating pattern was found. Instead, the team used the absence of a signal to limit how strongly these particles could interact with light over a range of possible particle masses. The limits depend on assumptions about the dark-matter density in the blazar’s host galaxy, so they do not rule out these particles altogether. The study shows that long-term polarization monitoring can complement other searches for axion-like dark matter.

Young explorerScientists think some of the universe’s invisible matter might be made of tiny particles that could make light’s pointing direction wiggle in a repeating way. They checked ten years of light from a faraway object called a blazar, but found no clear repeating wiggle. That does not mean the particles are not there. It helps scientists narrow down how strongly these possible particles could affect light, depending on how much invisible matter they think is nearby.

Why Stellar Sequences Turn Over: Fixed Points, Instability, and Equation-of-State Universality

Isaac Legred, Nicolas Yunes

• General Relativity and Quantum Cosmology
• Nuclear Theory

AstronomerThis theoretical study recasts stellar structure as a dynamical system. In an appropriate representation of the Tolman-Oppenheimer-Volkoff equations, a relativistic fixed point is directly associated with the mass-radius turnover and the maximum mass of stellar sequences. The resulting effective dimensional reduction near the onset of instability explains several relations that are insensitive to the equation of state and predicts additional ones. In the weakly relativistic limit, the authors identify a complementary universal structure at maximum mass, termed the compressible limit, and derive distinct maximum-mass relations in the Newtonian and post-Newtonian regimes. Combining these theoretical results with current astrophysical constraints, they infer that J0740+6620 is unlikely to be close to the TOV maximum mass unless the equation of state has a strong first-order phase transition at densities just above the pulsar’s central density.

PublicThe researchers use a new mathematical description to explain why sequences of model stars reach a maximum mass. In their relativistic equations, a special mathematical point is linked to where the mass-radius curve turns over. Near this limit, the models effectively depend on fewer independent quantities, helping explain why some relationships remain similar despite differences in the assumed properties of stellar matter. The study also predicts new relationships and derives separate maximum-mass relationships for models where relativistic effects are weak or absent. These are theoretical results, not new observations. Combined with existing astronomical constraints, they suggest that the pulsar J0740+6620 is probably not close to the relativistic maximum mass, unless its matter undergoes a strong, abrupt phase change at densities just above the density at its center.

Young explorerScientists used math to study how stars reach a biggest possible mass in their models. They found a special pattern that helps explain why different star models can follow similar rules. Their calculations also suggest that a real star called J0740+6620 probably is not close to that limit, unless the stuff inside it changes very suddenly when squeezed a little more than at its center.

Finite temperature effects on g-modes of inviscid neutron stars

David Morales-Zapien, Prashanth Jaikumar, Thomas Klähn

• Solar and Stellar Astrophysics
• Nuclear Theory

AstronomerThis theoretical study examines thermal effects on secular, composition-driven core g-modes in inviscid neutron stars. Using a chiral SU(2) flavor sigma model to construct isentropic temperature profiles, the authors find that the temperature dependence of the global core g-mode frequency is governed by the nuclear symmetry-energy slope parameter L. Depending on L, a warm star's mode frequency can be either higher or lower than its cold counterpart's. The calculations highlight the interplay between thermal effects and composition gradients and suggest that g-mode observations could constrain the density dependence of the symmetry energy; no observational constraint is reported.

PublicA theoretical study explores how temperature changes a type of internal vibration in neutron stars that arises from differences in their core composition. The model finds that warming a star can either raise or lower the vibration's frequency, depending on a parameter describing how nuclear symmetry energy changes with density. The results suggest that observing these vibrations could help researchers understand matter inside neutron stars, but the study does not report such an observation.

Young explorerNeutron stars can wiggle inside. Scientists used a model to explore how being warmer changes one kind of wiggle. They found that it could get faster or slower, depending on how the stuff inside the star behaves. If scientists can observe these wiggles, they might learn more about what is inside these stars.

Characterizing the Scale Height and Filamentary Structure of Radiatively Cooled MADs

Akshay Singh, Damien Begue, Asaf Pe'er

AstronomerGR-MHD simulations examine radiative cooling in magnetically arrested disks around a non-spinning black hole, spanning accretion rates of 10^-7 to 10^-4 of the Eddington mass accretion rate and including synchrotron and bremsstrahlung losses. Accumulated magnetic flux regulates inner-disk accretion through discrete, interchange-driven filaments. Analytical and numerical results identify a transition accretion rate above which cooling outpaces heating, with heating assumed to arise from local coupling to the magnetic field. Above this transition, reduced thermal pressure produces substantially thinner, denser filaments and higher radiative efficiency than at lower accretion rates. The authors find that conventional disk scale-height measures become misleading in this regime and introduce an alternative based on the polar position of the density maximum to better characterize the filamentary structure. These are simulation and analytical findings, not observational measurements.

PublicComputer simulations explore how losing heat changes gas flowing toward a non-spinning black hole when strong magnetic fields regulate the flow. In the models, gas near the black hole moves in separate filaments rather than forming a smooth disk. Above a threshold rate of gas supply, cooling overtakes heating under the researchers’ assumed heating mechanism. The filaments then become much thinner and denser, and the flow releases a larger fraction of its accreted energy as radiation. The researchers also find that usual measures of disk thickness can misrepresent this structure, so they introduce a different measure based on where the gas density peaks. The findings come from models, not direct observations.

Young explorerScientists used a computer to study gas moving toward a black hole. In their model, strong magnetic fields make the gas move in separate little streams. When gas flows in fast enough, the streams lose heat faster than they gain it and become thinner and more tightly packed. The scientists also suggest a better way to describe the shape of these streams. This happened in a computer model, not in a picture of a real black hole.

Spectra and Ionization Efficiencies of Charged Decay Particles in Kilonova Ejecta

L.N. Van den Berg, K. Hotokezaka

AstronomerThis theoretical study self-consistently calculates ionization cross sections, stopping powers, thermalization histories, and degradation spectra for alpha particles and fission fragments in expanding kilonova ejecta. It includes bound- and free-electron interactions, fragment charge evolution, and adiabatic losses, using continuous slowing-down and Spencer–Fano treatments. Across the compositions and ionization states considered, the calculated work per ion pair is remarkably similar for beta electrons, alpha particles, and fission fragments; heavy-element ions show nearly identical normalized ionization efficiencies across decay products. The authors attribute this robustness to shared collision physics governing ionization and energy loss. The calculations imply that late-time ejecta ionization depends only weakly on the dominant radioactive decay channel, even when alpha decay and fission dominate heating; this is a theoretical implication, not an observational finding.

PublicRadioactive particles help strip electrons from atoms in the expanding material of a kilonova, shaping the light it emits at late times. This study calculates how alpha particles and fragments from nuclear fission lose energy and cause ionization. For the materials and electrical charge states examined, the energy spent per freed electron is surprisingly similar for these particles and for electrons produced by beta decay. The authors explain that the same collision physics controls both electron removal and energy loss. Their calculations suggest that which type of radioactive decay supplies most of the heat has only a weak effect on the material’s late-time ionization state. The study does not report an observational test of that prediction.

Young explorerIn a kilonova, tiny bits from radioactive material bump into atoms and can knock out their electrons. Scientists calculated what happens when different kinds of tiny bits do this. For the materials they studied, the energy used to knock out one electron was almost the same for each kind. That suggests changing which kind supplies most of the heat may not change very much how many electrons get knocked out later on. This idea comes from calculations, not from watching it happen.

TDEs on FIRE: Illuminating the Cosmic Evolution of Tidal Disruption Rates

Rudrani Kar Chowdhury, Lixin Dai, Janet N.Y. Chang+1 more

AstronomerUsing FIRE-2 cosmological zoom-in simulations, the authors calculate per-galaxy tidal disruption rates over z=1–10 for intermediate-mass through supermassive black holes. The simulated mean rate rises from early epochs to a peak of approximately 4 × 10^-4 galaxy^-1 yr^-1 near z=2.5, then declines to approximately 10^-5 galaxy^-1 yr^-1 at z=1. Rates correlate strongly with host star formation rate and central stellar density throughout the modeled redshift range. Qualitative trends with black hole and galaxy mass resemble those in the local universe, suggesting, rather than establishing, similar black hole–galaxy scaling across cosmic time. Simulated satellite galaxies have comparably high rates and contribute an increasingly large fraction at high redshift, indicating potential for probing intermediate-mass black holes and early galaxy assembly. These are simulation-based findings; comparisons with next-generation observations remain future work.

PublicTidal disruption events occur when a black hole tears a star apart. Their frequency in the distant, early universe remains largely unexplored. Using computer simulations rather than new observations, researchers estimated how often these events occur in galaxies across a broad span of cosmic history. The average simulated rate rises to a peak near redshift 2.5, at roughly four events per 10,000 years per galaxy, then falls to about one per 100,000 years per galaxy at redshift 1. Galaxies with more star formation and denser central populations of stars tend to have higher rates. Smaller companion galaxies also show comparably high rates in the simulations and account for a growing share of events at earlier times. The authors suggest these events could help study intermediate-mass black holes and early galaxy assembly, but future observations are needed to test the simulated trends.

Young explorerA black hole can pull so hard on a star that the star gets torn apart. Scientists used computer-made galaxies to explore how often this might have happened long ago. In their computer models, it became more common for a while, then less common. It also happened more often in galaxies making more new stars and in galaxies with stars packed closely together in the middle. Smaller galaxies near bigger ones could be important too. These are clues from computer models, not things the scientists watched happen in faraway galaxies.

Synchrotron Emission from Cooled Particle Distributions

Ross Ferguson, Ben Margalit

AstronomerThis theoretical modeling work derives analytic fitting functions for synchrotron emission and absorption coefficients that account for cooling of initially power-law or thermal electron distributions. Radiative losses and adiabatic expansion redistribute electrons in energy, modifying both emission and absorption. The authors extend local treatments previously handled numerically, reporting accurate expressions with greater computational efficiency than earlier numerical approaches. The functions are intended for synchrotron afterglow modeling of sources including GRBs, LFBOTs, and jetted TDEs; the abstract reports no observational application or quantitative accuracy benchmarks.

PublicElectrons that produce synchrotron radiation lose energy by emitting radiation and as their surroundings expand. These losses change the electrons’ energy distribution and therefore how they emit and absorb light. This study develops mathematical formulas that account for those changes for two starting distributions of electron energies. The authors report that the formulas are accurate and faster to compute than earlier numerical methods. They could help model the afterglows of gamma-ray bursts and other cosmic transients, but the abstract does not report tests against observations.

Young explorerTiny particles called electrons can make light while losing energy. As they lose energy, the way they make and soak up light changes. Scientists made new math shortcuts to describe this for two starting groups of electrons. They say the shortcuts work well and are faster than older calculations. These shortcuts could help scientists understand light that lingers after big events in space; this study is about the math, not a new sighting.

Black hole spin-mass correlation and vector resonant relaxation in gaseous star clusters: the origin of GW231123?

Zacharias Roupas

• Astrophysics of Galaxies

AstronomerThe proposed cluster-formation channel links stellar black hole masses and spins through accretion of residual gas and predicts a tendency for spins to be anti-aligned with orbital angular momentum in the cluster. The authors find that GW231123 lies on the predicted high-mass, high-spin plateau, with positive Bayesian evidence relative to the LVK prior. Vector resonant relaxation equilibrium is also favored over the isotropic LVK prior for the relative spin-tilt distribution. The joint Bayes factor provides strong evidence for the favored cluster models in these comparisons; the event is consistent with, rather than definitive proof of, the proposed channel.

PublicThe authors propose that black holes growing by swallowing leftover gas in a forming star cluster develop a connection between their masses and how fast they spin. Their model also predicts a tendency for the spins to point opposite to the direction of orbital motion in the cluster. They find that the gravitational-wave event GW231123 fits the model's predicted high-mass, fast-spinning regime. A model describing how gravitational interactions redistribute orbital directions also better matches the relative spin directions than the collaboration's starting assumption of randomly oriented spins. Together, the statistical comparisons strongly favor the selected cluster models over those starting assumptions, but do not establish that this is how the event formed.

Young explorerThe scientists have an idea: black holes can eat gas while a group of stars is forming, and growing bigger can be linked to spinning faster. A space ripple called GW231123 fits the big, fast-spinning black holes their idea predicts. The way the spins point also helps their idea fit. These clues support the idea, but do not prove it is right.

Quasi-steady flavor configuration of multi-energy neutrino ensembles

Manuel Goimil-García, Irene Tamborra

• High Energy Physics - Phenomenology

AstronomerThe authors present semi-analytic approximations to the quasi-steady outcomes of slow and fast neutrino flavor conversion in quasi-homogeneous systems with periodic boundary conditions. Motivated by the inability of state-of-the-art hydrodynamic simulations to include neutrino quantum kinetics, the work addresses the need for subgrid treatments of neutrino self-interactions. The authors report excellent agreement with multi-angle, multi-energy solutions of the neutrino kinetic equations over a wide range of representative neutrino and antineutrino distributions, independently of the neutrino mass ordering. This is a comparison with kinetic calculations in the specified idealized setting, not an observational result or a demonstration in full supernova hydrodynamics.

PublicNeutrinos can change between different types, or flavors, and these changes strongly affect how collapsing stars explode and what signals they emit. Current hydrodynamic simulations cannot include the full quantum calculations needed to describe this behavior. The authors develop simplified mathematical approximations for the nearly steady outcomes of both slow and fast flavor changes. They report very close agreement with more detailed neutrino calculations for a broad range of representative neutrino and antineutrino distributions, regardless of the ordering of neutrino masses. The tests use idealized, nearly uniform systems with repeating boundaries; they do not establish how well the approximations work in a full exploding-star simulation.

Young explorerWhen a star collapses, tiny particles called neutrinos can change from one kind into another. Those changes help shape the explosion, but they are very hard for computer models to follow. The researchers made a simpler math recipe and found that it matched more detailed calculations very well in the cases they tested. Those tests used a simplified setup, not a whole exploding star.

Observable Signatures of Supernova Shock Breakout in Confined Circumstellar Medium

Wun-Yi Chen, Ke-Jung Chen, Keiichi Maeda+1 more

AstronomerThe authors present the first two-dimensional multigroup radiation-hydrodynamic simulations of shock breakout from red supergiants embedded in confined circumstellar medium (CSM) produced shortly before core collapse. In these simulations, escaping radiation creates a precursor that modifies shock dynamics, drives multidimensional mixing in radiating layers, and changes the emerging CSM emission. For the explored CSM models, predicted bolometric peaks are approximately 1–3 × 10^44 erg s−1, with durations of approximately 4–35 hours, controlled by CSM mass and confinement radius. The calculations predict pronounced extreme-ultraviolet emission, including photons with energies ≥54.4 eV capable of sustaining flash-ionized He II and powering strong He II λ4686 recombination emission. The study identifies potential dense-CSM breakout diagnostics and assesses detectability with Einstein Probe and ULTRASAT; these are model predictions, not reported detections.

PublicComputer simulations explore the first burst of light as an explosion’s shock emerges from a red supergiant star surrounded by nearby gas shed shortly before its collapse. In the models, light runs ahead of the shock, changes its motion, and stirs the surrounding gas, altering the radiation that escapes. For the gas configurations studied, the bright episodes last roughly 4–35 hours, with their brightness and duration depending on how much gas surrounds the star and how far it extends. The calculations also predict strong extreme-ultraviolet radiation that could make helium produce a distinctive emission line. The researchers assess whether Einstein Probe and ULTRASAT could detect signs of these events, but the abstract reports predictions rather than observations.

Young explorerScientists used computers to imagine a huge star exploding inside a blanket of gas. In their pretend explosions, light races ahead of the blast and pushes and stirs the gas. Changing the gas blanket changes how bright the flash is and how long it lasts. The scientists worked out signs that space telescopes might look for. They have not reported seeing these flashes in this study.

Spontaneous wandering of the magnetic axis in pulsars: 3D magneto-thermal simulations and the imprint on braking indices

Clara Dehman, Daniele Viganò

AstronomerBraking-index measurements for hundreds of pulsars, subject to observational caveats, show n<3 at early ages, n>3 at middle ages, and increasingly large, fluctuating values at greater characteristic ages. Long-term 3D magneto-thermal simulations explore how initial magnetic structure, from dipole-dominated to tangled and small-scale-dominated configurations, affects the dipolar field, obliquity, and braking index alongside alignment. In small-scale-dominated models with weak dipolar components, redistribution continuously feeds the dipolar mode, which can grow or decay depending on the initial spectrum, producing n<3 or n>3. Obliquity can vary on timescales as short as order kiloyears. These spontaneous changes often dominate the alignment torque contribution and can account for large n−3 of either sign at characteristic ages of roughly 100,000 years or more, unlike the dipole-dominated models. Quantitative agreement with measurements and structured timing residuals may still require short-term magnetospheric or superfluid-driven torque variations; comparison with observed timing properties remains future work.

PublicMeasurements of hundreds of pulsars—spinning neutron stars—suggest that the way their rotation slows changes with age, although the observations have caveats. This study uses three-dimensional computer simulations to test whether complex magnetic fields inside the stars could help explain that pattern. In models where most magnetic structure is concentrated on small scales, it continually feeds the large-scale dipole field, which can strengthen or weaken. The dipole's orientation can also change over timescales as short as a few thousand years. Together, these simulated changes could explain large departures in either direction from the reference braking index of 3 for pulsars with characteristic ages of about 100,000 years or more; models starting with dipole-dominated fields do not account for those departures. This is not yet a complete quantitative explanation: shorter-term changes involving the magnetosphere or the star's superfluid may also be needed, and further comparisons with observations are planned.

Young explorerPulsars are spinning stars, and astronomers see that they slow down in different ways as they get older. Scientists made computer models to see whether tangled magnetism inside them could help explain this. In the models, little magnetic patterns can feed a bigger pattern, making it stronger or weaker and changing where it points. That could explain some of the surprising ways older pulsars slow down. But the models do not explain every detail yet, and other changes in and around the stars may matter too.

A Coherent Search for New Galactic Magnetars using Fermi/GBM and follow-up Swift/BAT: 7 Candidates and a Large Burst Catalog

Ariel Perera, Barak Zackay, Tejaswi Venumadhav

AstronomerThe study combines short, soft triggers from a coherent Fermi/GBM detection pipeline spanning 2013–2025 with targeted searches of archival Swift/BAT images to identify magnetar activity. A statistical association framework uses BAT detections to obtain arcminute localizations for GBM bursts, while spatio-temporal clustering links poorly localized bursts to common sources. The methods identify 1,720 magnetar bursts: 1,170 are confidently associated with 11 known magnetars, while 550 remain unassigned. Seven candidate new magnetars are identified through three complementary discovery channels, but are not confirmed discoveries. The catalog comprises the associated bursts, reaches the lowest fluences observed by GBM, and includes spectral and temporal analyses. X-ray follow-up of the candidates could reveal previously unidentified Galactic magnetars.

PublicMagnetars are rare neutron stars with extreme magnetic fields; only about 30 are known in our Galaxy. Their brief X-ray and gamma-ray flashes can reveal their activity, but tracing a flash to its source is difficult. Researchers combined Fermi/GBM observations from 2013–2025, which cover a wide area of sky but locate bursts imprecisely, with archived Swift/BAT images, which can pinpoint sources more accurately over a smaller area. They identified 1,720 magnetar bursts, confidently linking 1,170 to 11 known magnetars and leaving 550 without a specific source. They also identified seven possible new magnetars, not yet confirmed. Their catalog contains the bursts linked to known sources, including very faint flashes, and examines their spectra and timing. Further X-ray observations could help establish whether the candidates are previously unknown magnetars.

Young explorerSome tiny stars have very strong magnets and send out quick flashes of light that our eyes cannot see. Scientists used two space telescopes together: one watches a big patch of sky, and the other can show more clearly where a flash came from. They found many flashes and matched lots of them to stars they already knew, but could not tell which stars made the rest. They also found seven clues to possible new magnetic stars. They need to look again to find out whether those really are new ones.

Extending the Pulsar radio population through Quantum Vacuum Cherenkov Emission

Tales A. O. Gomes, Sergei V. Bulanov, Jaziel G. Coelho+3 more

AstronomerRadio pulsars observed within and below the conventional P–P-dot death valley challenge polar-cap pair cascades powered by curvature radiation (CR) and resonant inverse Compton scattering (RICS). This theoretical study identifies vacuum-polarization-enabled Cherenkov radiation as a complementary pair-creation channel within the vacuum-gap model. The authors find sufficiently short acceleration lengths and photon mean free paths for rapid electron–positron conversion, including regimes where conventional channels are strongly suppressed. The resulting model death lines partially overlap with and extend beyond the CR and RICS death valleys, expanding the predicted parameter space for radio-emitting neutron stars. The mechanism offers a possible basis for coherent emission from long-period sources, rather than a direct observational detection of the process, and motivates future tests of nonlinear QED with facilities such as the Square Kilometre Array.

PublicSome neutron stars emit radio signals even where standard theories suggest that the particle production needed to support those signals should fail. This study proposes an additional route: in a strong field, quantum effects can allow Cherenkov light to be produced in a vacuum and then convert into electron–positron pairs. Within the researchers’ model, this process happens quickly enough to operate even when the usual mechanisms are strongly weakened. Their calculations therefore expand the range of neutron stars that could plausibly emit radio waves, including some with long rotation periods. This is a theoretical explanation, not a direct observation of the proposed process; future radio facilities such as the Square Kilometre Array could help test it.

Young explorerSome spinning stars send out radio signals even when scientists’ usual ideas say they should be quiet. Researchers have worked out another possible way for these stars to make pairs of tiny particles using light and strong fields in empty space. Those particles might help explain the surprising radio signals. The idea works in their model, but scientists have not directly seen this process happening in the stars.

Widespread steep X-ray spectra of luminous z=5.85-7.64 quasars and their implications for future X-ray surveys

A. Tortosa, L. Zappacosta, E. Piconcelli+51 more

• Astrophysics of Galaxies

AstronomerThe study tests whether steep X-ray spectra in luminous reionization-era quasars are associated specifically with efficient long-term SMBH growth. It analyses 28 QSOs at z = 5.85–7.64, with 26 included in correlation tests, extending HYPERION mainly toward lower growth efficiencies. Black hole masses and growth indicators were re-derived homogeneously, incorporating recent JWST spectroscopy. No statistically significant correlation is found between coronal spectral parameters and black hole growth indicators. The luminous quasars systematically exhibit steep X-ray continua, with high photon indices and/or low high-energy cutoffs, consistent with cold coronae. A connection to rapid accretion remains a possible interpretation, not an established result. If such spectra are common among early AGN, reduced count rates at fixed intrinsic luminosity could affect future survey detectability and population censuses.

PublicResearchers examined X-ray observations of 28 luminous quasars from the early universe to ask whether their unusual X-ray spectra are tied to how efficiently their enormous black holes grew. Using 26 objects for correlation tests, they found no statistically significant relationship between the X-ray properties and measures of black hole growth. The quasars consistently showed spectra compatible with relatively cool X-ray-emitting regions near the black holes. Rapid feeding could help explain this, but that connection is not established. If these spectra are widespread among early active black holes, future X-ray surveys could detect fewer of them than otherwise expected at the same intrinsic luminosity, potentially affecting estimates of their abundance.

Young explorerScientists studied X-ray light from very bright objects powered by huge black holes when the universe was young. They found clues that the places making this light were fairly cool, but no clear link to how efficiently the black holes had grown. If many early black holes shine this way, future searches might miss some.

Discovery of Hidden Extragalactic Pulsars in the Parkes Archival Data

Rahul Sengar, Laila Vleeschower, Matthew Bailes+3 more

AstronomerReprocessing the original Parkes Multibeam Magellanic Cloud surveys with high-harmonic folding of candidates near the noise floor yielded six previously undetected radio pulsars. Five are in the LMC, bringing its known radio-pulsar population to 49; one has a 3.8 s spin period, the longest known in either Magellanic Cloud. The sixth lies toward the SMC but is associated with the Milky Way foreground. Four discoveries exhibit scintillation; one shows clear nulling, while others show possible nulling. Luminosity-function and duty-cycle analyses of the current Magellanic Cloud sample are consistent with Galactic canonical pulsars. Population-synthesis simulations suggest that deeper surveys could detect many more Magellanic Cloud pulsars, including up to a handful of millisecond pulsars, conditional on the adopted upper limits for their parent populations. The discoveries demonstrate the value of archival reanalysis for survey completeness.

PublicAstronomers found six previously undetected pulsars—spinning neutron stars that produce radio pulses—by searching old Parkes survey data again for very faint signals. Five belong to the Large Magellanic Cloud, a satellite galaxy of the Milky Way, raising its known radio-pulsar count to 49. One turns once every 3.8 seconds, making it the slowest known pulsar in either Magellanic Cloud. The sixth appears in the direction of the Small Magellanic Cloud but belongs to our own galaxy. Four show scintillation, or fluctuations in signal strength; one clearly has gaps in its detectable pulses, and others may do so. The brightness distribution and the fraction of each rotation occupied by a pulse are consistent with those of ordinary Milky Way pulsars. Simulations suggest deeper searches could find many more, perhaps including a handful of very fast millisecond pulsars, but that forecast depends on assumptions about how many exist.

Young explorerScientists looked again at old telescope recordings and found six spinning stars whose radio signals had been missed. These stars are called pulsars, and their signals reach us like blinking lighthouse beams. Five are in a nearby galaxy called the Large Magellanic Cloud, and one is in our own Milky Way. One takes 3.8 seconds to spin around—the slowest pulsar known in the two Magellanic Clouds. Scientists also used computer models to explore what better searches might find. The models suggest there could be many more pulsars to discover, perhaps even a few very speedy ones, but those have not been found by this work.

Time-domain metric reconstruction for hyperbolic scattering

Oliver Long, Leor Barack

• General Relativity and Quantum Cosmology

AstronomerThis methodological study develops a time-domain approach toward numerical self-force calculations for unbound scattering orbits, extending a Hertz-potential reconstruction strategy previously pursued only for bound orbits. The authors derive closed-form jump conditions for each multipole mode of the scalar-like Hertz potential along arbitrary geodesics in Schwarzschild spacetime and numerically implement the method for a scattering orbit. The potential satisfies the Teukolsky equation and provides the basis for reconstructing the metric perturbation. Such calculations could ultimately constrain scattering angles order by order in a small mass ratio without a weak-field approximation, informing effective-one-body and other semi-analytical descriptions of binary dynamics. This paper stops at calculating the Hertz potential: neither the self-force nor its effects on the scattering orbit are calculated.

PublicThe paper develops a computational technique toward studying how two objects deflect one another during a close gravitational flyby when one is much less massive than the other. Such calculations could help improve models of binary motion in general relativity without assuming gravity is weak. The authors derive mathematical conditions needed for their method and demonstrate a numerical calculation for a flyby in Schwarzschild spacetime. Their calculation produces an intermediate mathematical quantity used to describe a disturbance in spacetime, not yet the gravitational self-force or its effect on the flyby. Those physical calculations are left for future work; this is a methods study, not an observational finding.

Young explorerImagine a small object zooming past a much heavier one, with gravity bending its path. Scientists are building a computer method to work out that bend more carefully. In this paper, they worked out and tested one mathematical piece the method needs. They have not yet used it to calculate the extra gravitational effect on the small object's path. That is a job for later.

Self-force in hyperbolic black hole encounters

Oliver Long

• General Relativity and Quantum Cosmology

AstronomerThis theoretical and numerical study develops self-force methods for hyperbolic two-body scattering, expanding in a small mass ratio without requiring a weak-field approximation. The authors derive the first-order conservative self-force correction to the scattering angle and demonstrate agreement with recent post-Minkowskian results. Their numerical approach reconstructs the metric perturbation from a Hertz potential satisfying an inhomogeneous, mode-decomposed Teukolsky equation, with closed-form worldline jump conditions derived for arbitrary geodesic orbits in Schwarzschild spacetime. A 1+1-dimensional scalar-field code provides conservative scalar self-force corrections to the scattering angle. Direct Teukolsky evolution suffers numerical instabilities as numerical error seeds unphysical homogeneous solutions at the horizon and null infinity; a transformation to a Regge-Wheeler-like field resolves this issue. The authors present a full numerical implementation for circular and scattering orbits in Schwarzschild. These methods could inform effective-one-body and other descriptions of relativistic binary dynamics; the reported results are calculations, not observations.

PublicThe study develops ways to calculate how gravity bends the paths of two bodies that pass one another rather than remain in orbit together. It assumes that one body is much less massive than the other, but does not require gravity to be weak. The researchers derive a correction to the deflection angle that accounts for the smaller body's influence on its own motion through the gravitational field, focusing on the part of the interaction that conserves energy. They find agreement with recent theoretical calculations. They also build numerical tools, first calculating a related scalar-field version of the problem. A gravitational-field calculation initially becomes unstable because numerical errors excite unwanted mathematical solutions; changing the mathematical variables resolves that problem. The resulting method is implemented for circular and passing trajectories around a nonrotating black hole. This is theoretical and computational work, not an astronomical observation, and it may help improve models of two-body motion in general relativity.

Young explorerImagine a tiny object zooming past a much heavier one. Gravity bends its path, and the tiny object also makes a small change to the gravity around it. The scientists worked out how that small change affects the turn. They assumed one object was much lighter, but gravity did not have to be weak. They also made computer tools to study these paths. When tiny computer mistakes made one calculation go wrong, they changed the math to fix the problem. They tested ideas with calculations, not by watching objects in space.

Revisiting predictions for cosmic-ray antinucleon fluxes from Galactic Dark Matter

Lorenzo Stefanuto, Mattia Di Mauro, Fiorenza Donato+3 more

• High Energy Physics - Phenomenology

AstronomerThe study predicts cosmic-ray antiproton, antideuteron, and antihelium fluxes from secondary production and Galactic dark matter annihilation, using production spectra, nuclear coalescence, and Galactic propagation models. AMS-02 antiproton measurements constrain the annihilation cross-section under the BIG and QUAINT propagation scenarios. The authors project that future GAPS sub-GV antiproton measurements could tighten these limits by up to an order of magnitude for dark matter masses below roughly 50 GeV; this is a sensitivity forecast, not an achieved constraint. GAPS has completed its first Antarctic flight. For heavier antinuclei, detection prospects are evaluated only for scenarios consistent with AMS-02 antiproton data and depend strongly on the experiment, propagation model, and hadronization tuning. The analysis emphasizes complementary antinuclei channels and low-energy measurements for constraining light dark matter, rather than reporting a dark matter detection.

PublicAntimatter particles in cosmic rays can form when fast-moving atomic nuclei collide with atoms between stars. Dark matter annihilation might provide another source, but this study does not report its detection. The researchers predict the amounts of several antimatter particles and use AMS-02 antiproton measurements to limit how strongly dark matter could annihilate. They forecast that future low-energy antiproton data from GAPS, which has completed its first Antarctic balloon flight, could make those limits up to ten times tighter for dark matter particles lighter than about 50 GeV. Prospects for detecting heavier antimatter nuclei vary substantially with the experiment and assumptions about particle production and travel through the Galaxy.

Young explorerTiny bits of antimatter fly through space. Some come from ordinary crashes between particles. Scientists wonder whether mysterious dark matter could make some too. They used space measurements to work out how much dark matter might contribute, but did not find it. They predict that a balloon experiment could help check more carefully. What it might find depends on how the particles are made and move through space.

Pole Skipping, Avoided Crossing, and Resonant Excitation in Kerr Quasinormal Modes near Algebraically Special Frequencies

Kei-ichiro Kubota, Hayato Motohashi

• General Relativity and Quantum Cosmology
• Statistical Mechanics
• High Energy Physics - Theory

AstronomerThis theoretical analysis addresses anomalous Kerr quasinormal-mode behavior near algebraically special frequencies: apparent bifurcation, disappearance, and a nonsmooth connection to the Schwarzschild limit. By tracking poles and zeros of Green-function building blocks across Riemann sheets, the authors identify the apparent bifurcation as an avoided crossing accompanied by resonant excitation. They attribute disappearance to pole skipping, in which a Matsubara-mode zero cancels a quasinormal-mode pole, and present these mechanisms as resolving the long-standing anomalies.

PublicA mathematical study explains puzzling behavior in calculations of how rotating black holes ring. Some ringing patterns appeared to split or disappear, and their connection to the nonrotating case was not smooth. By following features of the mathematical functions describing these patterns, the researchers find that the apparent splitting comes from patterns approaching but avoiding a crossing, accompanied by resonant excitation. The disappearance results from a mathematical cancellation—not a black hole vanishing. These are theoretical findings, not observations of black holes.

Young explorerScientists use math to study how spinning black holes can ring, a little like bells. Some ringing patterns seemed to split or vanish in their calculations. The new work explains that patterns can come close without crossing, and that one part of the math can cancel another. It is the ringing pattern in the math that disappears, not the black hole.

A double debris disc around a white dwarf sculpted by two planetary bodies

Nicola Pietro Gentile Fusillo, Felipe Lagos-Vilches, Boris T. Gänsicke+2 more

• Earth and Planetary Astrophysics

AstronomerWD J132800.85-145019.95 is a newly discovered white-dwarf gas-disc system with quadruple-peaked emission lines, unlike the double-peaked profiles of the 21 previously known systems. The authors attribute the emission to two separate gaseous rings spanning 0.14–0.34 and 0.54–1.93 solar radii. They propose that two distinct planetary bodies, ranging from a few kilometres across to Pluto-sized, produce this structure; these bodies are not reported as detected. Gas production in white-dwarf debris discs remains debated, and the stable double-disc structure challenges current formation and evolution models.

PublicAstronomers have discovered an unusual arrangement of gas around the white dwarf WD J132800.85-145019.95. Its emission lines have four peaks rather than the two seen in previously known gas-disc systems. The researchers attribute this pattern to two separate rings of gas. They suggest that two planetary bodies, with possible sizes ranging from a few kilometres to the size of Pluto, could explain the structure, but the bodies themselves have not been detected. The stable pair of rings poses a new challenge for explanations of how debris discs form and change around white dwarfs.

Young explorerAstronomers found something unusual around a star remnant called a white dwarf. The light from gas around it makes four bumps in their measurements instead of the usual two. They say the gas forms two separate rings. They think two rocky objects might help explain the rings, but they have not seen those objects. Scientists still have work to do to understand how the rings formed and stay there.

Machine learning applications in the heliosphere

Vishal Upendran, Banafsheh Ferdousi

• Machine Learning
• Space Physics

AstronomerThis chapter presents a framework for applying machine learning to space weather, treating processes from the Sun to their ground-level impacts as coupled systems that can also be studied separately. Each system is described by a state vector S specifying its physical variables, with observables represented by operators O[S]. Machine-learning algorithms are cast as learned operators for inference, propagation, and emulation. The chapter discusses how this formalism can support physical understanding and accelerate operational forecasting-model development; the abstract reports no observational findings or quantitative forecast-performance tests.

PublicSpace weather concerns how processes on the Sun affect conditions near Earth. This chapter describes a way to organize those processes as connected systems, while allowing each system to be studied separately. It explains how machine learning can act as a set of tools for inferring a system’s state, predicting how it changes, and emulating its behavior. The aim is to improve understanding and help develop practical forecasting models, rather than to report a newly observed event or a measured improvement in forecast accuracy.

Young explorerThings happening on the Sun can affect the space around Earth and even reach down to the ground. This chapter explains a way to study the connected parts of that story using computers that learn from examples. The goal is to help scientists understand what is happening and make forecasts. It does not report a test showing how much better those forecasts are.

Probabilistic Stellar Mass and Radius Estimation with Bayesian Hierarchical Stacking

Maxence Lamirel, Andrés Moya, Roberto J. López-Sastre+1 more

• Earth and Planetary Astrophysics
• Instrumentation and Methods for Astrophysics

AstronomerThe authors develop Bayesian hierarchical stacking (BHS) to predict stellar masses and radii from commonly available observables, combining Bayesian additive regression trees, a two-process heteroscedastic sparse Gaussian process, and a hierarchical Bayesian neural network. The framework propagates measurement uncertainties, accounts for correlated inputs, and incorporates model variance into predictive distributions. On a held-out test set, mean absolute relative differences (MARDs) are 3.5% for mass and 2.1% for radius, outperforming empirical relations and standard machine-learning baselines. For 44 Kepler LEGACY stars, BHS masses differ from BASTA estimates by 4.8% MARD, versus 8.5% for empirical relations. Across about 2400 exoplanet hosts, mass and radius predictions each differ from literature values by 2.7% MARD; these comparisons establish agreement with other estimates, not direct measurement accuracy. Residuals show mild underestimation for cool dwarfs, consistent with sparse training coverage, and positive offsets near the main-sequence turn-off that may reflect catalogue isochrone priors. Scatter in Delta log g relative to g = GM/R² is three times lower than for literature values, indicating improved internal consistency.

PublicUnderstanding planets around other stars requires knowing their stars’ masses and sizes, but most host stars lack direct measurements of these properties. This study combines three statistical learning models to estimate them from commonly available observations while accounting for measurement uncertainty and differences among models. On a separate test set, the method achieved average relative differences of 3.5% for mass and 2.1% for radius, performing better than the comparison methods. For about 2400 planet-hosting stars, its estimates differed from published values by 2.7% on average for both properties. Agreement with published estimates does not by itself establish the true masses and sizes. The predictions also showed better consistency with the physical relationship linking mass, radius, and surface gravity. Some discrepancies remain: the method slightly underestimates properties of cool dwarf stars, and offsets for stars nearing the end of their main-sequence lives may partly reflect assumptions in existing catalogues.

Young explorerTo learn about a planet, scientists need to know how heavy and how big its star is. The researchers made three computer helpers work together to estimate those things from observations. Their team did better in tests than the other methods they tried. But these are still estimates, not direct measurements, and the helpers have more trouble with some kinds of stars.

Evolutionary Demographics of Molecular Ice Mantles in Young Stars with SPHEREx

J. Serna, S. P. Matt, M. McClure+2 more

AstronomerA search of SPHEREx spectra for 20,292 young stellar objects aged <20 Myr from the Gaia-based Kounkel & Covey (2019) kinematic catalog identifies 746 H2O ice candidates using laboratory absorption templates, including 131 high-confidence H2O+CO2 detections and 22 with corroborating CO absorption. The H2O+CO2 detection rate falls by roughly an order of magnitude between ages ≲3 Myr and ~5 Myr. Candidates preferentially occupy high-extinction sightlines (A_G ≳2.5 mag) and exhibit embedded SED morphologies. These associations are consistent with envelope dispersal and photodesorption reducing detectable ice mantles during early pre-main-sequence evolution, but do not establish those mechanisms. The catalog supplies a homogeneous demographic baseline and prioritized targets for JWST follow-up.

PublicResearchers searched SPHEREx spectra of 20,292 young stars for the light-absorption patterns of frozen water, carbon dioxide, and carbon monoxide. They found 746 possible water-ice sources, including 131 high-confidence detections of both water and carbon dioxide ice; 22 also show supporting carbon monoxide absorption. The rate of detecting water and carbon dioxide ice together is about ten times lower around stars aged roughly five million years than around those aged three million years or younger. Ice candidates are concentrated along heavily obscured lines of sight and around stars whose light patterns indicate that they remain embedded in surrounding material. The findings suggest that dispersing envelopes and light-driven removal of ice may reduce detectable ice during stars’ first few million years, but do not prove that explanation. The catalog also identifies promising targets for closer study with JWST.

Young explorerScientists looked at light from many young stars for clues of ice. They found hundreds of possible places with frozen water, and some also had other kinds of ice. They spotted water and carbon dioxide ice together less often near older stars than near younger ones. Maybe the stars lose their dusty blankets, or light helps remove the ice, as they grow. The scientists still need to check why this happens.

Tayler Instability and Its Saturation in Rotating Stars

Valentin Skoutnev, Andrei Beloborodov

• High Energy Astrophysical Phenomena
• Fluid Dynamics

AstronomerGlobal simulations test the recently completed linear theory of the Tayler instability and investigate nonlinear saturation in stably stratified, rotating stellar regions. They confirm overstable magnetostrophic and inertial waves with similar magnetostrophic growth timescales but different oscillation frequencies. Magnetostrophic waves saturate at δB/B ∼ 1, dissipate the toroidal field on magnetostrophic timescales, and efficiently regenerate axisymmetric poloidal fields through nonlinear coupling. Inertial waves instead saturate at δB/B ≪ 1, erode the toroidal field much more slowly, and do not efficiently regenerate poloidal fields. The authors interpret these simulation results as indicating that the Tayler-Spruit dynamo can operate only through the magnetostrophic branch, potentially following Spruit’s 2002 steady-state scenario and ruling out Fuller’s 2019 small-amplitude saturation scenario. Implications for angular momentum transport and field amplification in evolving stars and nascent neutron stars are discussed; these are simulation findings, not stellar observations.

PublicComputer simulations explore how an instability in magnetic fields wrapped around a rotating star might help sustain its magnetism and redistribute its rotation. The simulations confirm two kinds of growing magnetic waves, but find very different outcomes. One kind, called magnetostrophic waves, grows to large strength, rapidly dissipates the wrapped field, and efficiently rebuilds another component of the field needed for the proposed magnetic dynamo cycle. The other kind, inertial waves, remains weak, wears down the wrapped field much more slowly, and does not efficiently rebuild that component. The authors conclude that only the magnetostrophic waves can support this proposed dynamo. Their results favor one earlier picture of how the dynamo might settle into a steady state and argue against a competing weak-wave picture. These conclusions come from simulations rather than direct observations of stars.

Young explorerA spinning star can have invisible magnetic loops inside it. Scientists used a computer to see what happens when those loops wobble. They found two kinds of wobble: one becomes strong and helps make new magnetic loops, while the other stays small and does not help much. The strong wobble might help keep the star’s magnetism going. This is what happened in their computer model, not something they watched inside a real star.

Asteroseismic properties of young pulsators in the Perseus Molecular Cloud. Discovery of period-spacing patterns in HD 281229

Saakshi Wadhwa, Dario J. Fritzewski, Gang Li+1 more

AstronomerUsing Gaia-based membership catalogues and TESS full-frame photometry, the authors searched for young intermediate-mass pulsators in the Perseus Molecular Cloud. Lomb–Scargle analysis and iterative pre-whitening identified eight pressure-mode pulsators and two objects with possible gravity-mode pulsations among 148 membership-selected targets. Including the previously known δ Sct star V705 Per brought the analysed sample to 149. The authors estimated νmax for confirmed pressure-mode pulsators and searched gravity-mode candidates for period-spacing patterns. In HD 281229, simultaneous fits to detected dipole and quadrupole period-spacing patterns using the traditional approximation of rotation yielded Π₀ = 4776 ± 400 s and a near-core rotation frequency of 1.317 ± 0.05 d⁻¹. They report HD 281229 as the youngest star known to date with a detected and modelled period-spacing pattern. These model-dependent constraints demonstrate the potential of gravity-mode asteroseismology to investigate very young stellar interiors and rotation, while the broader gravity-mode classifications remain tentative.

PublicResearchers used TESS measurements of changing starlight to search for pulsating young stars in the Perseus Molecular Cloud. Among 148 selected stars, they found eight with pressure-driven pulsations and two showing possible gravity-driven pulsations. They also studied a previously known pulsating star, bringing the total examined to 149. One star, HD 281229, showed a pattern in its pulsation periods that the team could model to estimate how fast its inner region rotates and constrain its internal properties. The authors describe it as the youngest star yet known with such a detected and modelled pattern. The findings show how stellar pulsations can help reveal the interiors of very young stars, although some pulsation identifications remain uncertain and the inferred internal properties depend on modelling.

Young explorerYoung stars can change how brightly they shine as they wobble. Scientists watched many young stars and found several with these tiny changes. For one star, called HD 281229, they found a special pattern in the wobbles. They used a model to work out how fast the star might spin deep inside. Some of the other stars’ wobbles still need checking.

The Ubiquity of White-Light Flares on the Sun

Shuanghong Li, Yongliang Song, Kun Wang+3 more

AstronomerUsing a newly developed white-light flare (WLF) identification method and SDO/HMI photospheric observations, the authors examine 1,951 B-, C-, and M-class flares from 769 low-activity active regions, each with fewer than 10 flares, during January 2011–May 2025. They identify 1,012 WLFs, an occurrence rate of 51.9%, with rates increasing from 36.9% for B-class to 56.9% for C-class and 85.2% for M-class flares. Occurrence is also highly correlated with active-region sunspot number. White-light kernels show diverse properties, evolution, and relationships with GOES soft X-ray flux and its time derivative. The authors interpret these observations as strong evidence that WLFs are common, including among B-class flares; the selected sample and incomplete detection do not establish that every solar flare produces white-light emission.

PublicSolar flares can brighten in visible light, but scientists have debated whether this is rare or simply difficult for telescopes to detect. Applying a new detection method to SDO/HMI observations from January 2011 to May 2025, researchers identified visible-light brightening in 1,012 of 1,951 flares studied—51.9%. The fraction rose with flare class, from 36.9% for B-class flares to 85.2% for M-class flares, and was strongly linked to the number of sunspots in the source region. The bright patches within these flares also behaved in varied ways. These observations suggest that visible-light flares are common, even among relatively weak B-class events. They do not show that all flares brighten in visible light, and the study focused on regions producing fewer than 10 flares.

Young explorerThe Sun sometimes has bursts called flares. Scientists looked for little patches that got brighter in light we can see. Using a new way to search telescope pictures, they found these patches in about half of the flares they studied—even in many small flares. Bigger flares were more likely to have them. This suggests the bright patches are common, but it does not mean every flare has them.

Understanding the origin of silver in metal-poor stars based on the non-local thermodynamic equilibrium analysis of Ag I lines

Lyudmila Mashonkina, Tatyana Sitnova, Svetlana A. Yakovleva+1 more

• Astrophysics of Galaxies

AstronomerThe authors derive Ag abundances using NLTE Ag I line formation, a literature-based model atom incorporating recent inelastic Ag I + H I collision data, high-resolution spectra, and synthetic spectra calculated with one-dimensional atmospheres. Two treatments of hydrogen collisions yield solar NLTE abundances of log epsilon(Ag) = 1.15 and 1.10. They report the first NLTE Ag abundances for 41 stars spanning -2.74 <= [Fe/H] <= -0.56. Corrections for Ag I 3382 Å reach 0.92 dex in giants and 0.51 dex in dwarfs. The inferred abundances show enhanced [Ag/Fe] and a Galactic trend resembling [Eu/Fe]. Ag/Eu, Ag/Ba, and Ag/Sr ratios in the r-II stars CS22892-052 and CS31082-001 agree closely with the Prantzos et al. (2020) r-process model; stars with -1.6 < [Fe/H] <= -0.56 have near-solar [Ag/Eu]. The authors interpret these results as main r-process dominance throughout the sampled metallicity range, with a main s-process contribution no greater than 20% above [Fe/H] = -1.6. These conclusions rest on the adopted atmospheric and line-formation modelling.

PublicResearchers used high-resolution starlight spectra and improved calculations to estimate how much silver is present in the Sun and 41 stars with less iron than the Sun. Their calculations account for departures from local thermodynamic equilibrium, which affect how silver produces spectral lines. The resulting abundance corrections are larger in giant stars than in dwarfs. In the sample, silver is enhanced relative to iron and follows a pattern similar to europium. Ratios involving silver in two stars also agree closely with a published model of the r-process, a neutron-capture production process. The authors interpret the findings as evidence that the main r-process dominated silver production across the range studied. They infer that the main s-process supplied no more than 20% in the higher-metallicity part of that range; this is a model-based conclusion, not a direct observation of silver being made.

Young explorerStars have silver in them! Scientists studied light from the Sun and 41 other stars, using improved calculations to work out how much silver they contain. The patterns suggest that one way of making silver, called the r-process, made most of it in the stars studied. They did not watch the silver being made.

Atmospheric Parameter Determination of RR Lyrae Stars With Mephisto Multi-band Photometry

Xingzhu Zou, Maosheng Xiang, Tanda Li+18 more

• Astrophysics of Galaxies

AstronomerThe authors present a framework for jointly inferring phase-resolved Teff, log g, and [Fe/H] from Mephisto multi-epoch ugriz photometry with an additional v band. A supervised neural-network forward model trained on theoretical stellar-atmosphere colors reproduces those synthetic colors to 0.01 per cent; this is model-reproduction precision, not demonstrated observational accuracy. Applied to six RRab and four RRc stars in three globular clusters, the method yields typical per-phase uncertainties of approximately 62 K, 0.10 dex, and 0.16 dex in Teff, log g, and [Fe/H], respectively. Combining measurements across the pulsation cycle reduces the typical formal uncertainty in final [Fe/H] estimates to about 0.03 dex. Sensitivity analysis identifies complementary constraints: u-v is robustly sensitive to log g, v-g informs [Fe/H], and all five adjacent-band colors inform Teff. The results support the method’s potential for building large RR Lyrae benchmark samples; application to Cepheids is not demonstrated here.

PublicResearchers tested a way to estimate the temperature, surface gravity, and iron abundance of pulsating stars by measuring their colors repeatedly as they brighten and dim. Their method uses a neural network trained on colors calculated from theoretical stellar-atmosphere models, then applies it to observations from Mephisto. The test covered ten RR Lyrae stars in three globular clusters. Typical reported temperature uncertainties at individual stages of a pulsation were about 62 degrees kelvin. Combining repeated observations also reduced the formal uncertainty in iron abundance, although that statistical precision does not by itself establish the method’s overall accuracy. Different color combinations help constrain different stellar properties. The authors see this approach as an efficient route to large samples of reference stars for studying stellar pulsations and the Milky Way.

Young explorerSome stars get brighter and dimmer again and again. Scientists watched the colors of ten of these stars and used a computer trained on model star colors to estimate how hot they are, how strong gravity is at their surfaces, and how much iron they contain. Looking many times helped make the iron estimates less uncertain. The scientists hope this method will help them study many more stars.

J060242.22+332452.7: hierarchical triple system with inner eclipsing contact binary

Mikhail Kovalev

AstronomerThe author reports the discovery of the hierarchical triple J060242.22+332452.7, comprising an inner contact binary and a third star. The binary shows eclipse timing variations attributed to the light-travel-time effect, while LAMOST medium-resolution spectra reveal radial-velocity changes of the tertiary. A joint ETV–RV fit yields an outer period of 1866 ± 6 days and eccentricity of 0.40 ± 0.05. The inclination-dependent mass quantities are M_AB sin³(i₃) = 2.02 ± 0.22 solar masses and M_C sin³(i₃) = 0.86 ± 0.08 solar masses, rather than independently determined true masses. An astrometric orbit is expected in the next Gaia data release but is not reported here as a detection.

PublicThe study reports a three-star system called J060242.22+332452.7. Two stars form a close, touching pair, while a third follows a wider orbit around them. Changes in the timing of the pair’s eclipses are attributed to changes in how far their light must travel as the pair moves through the wider orbit. Spectra from LAMOST also show changes in the third star’s motion toward or away from us. Combining these observations gives a wider orbital period of 1866 ± 6 days and an eccentricity of 0.40 ± 0.05, indicating an elongated orbit. The inferred masses remain dependent on the orbit’s unknown tilt. The author expects the next Gaia data release to reveal the system’s orbital motion across the sky; that is a prediction, not a result reported in this study.

Young explorerAn astronomer found three stars in a group. Two are so close that they touch, and a third travels around the pair. The close stars take turns blocking each other’s light. Those dimmings arrive a little early or late, which the astronomer explains as their light having a shorter or longer trip to us. Changes in the third star’s light also help show how it moves. Together, these clues suggest that the wider trip takes about five years. The astronomer thinks a future Gaia release will show this motion across the sky, but that has not been shown here yet.

Episodic Plasma Flows and Coronal Brightenings in an Arch Filament System Observed with SUNRISE III

Sergio Javier González Manrique, Juan Carlos Trelles Arjona, Christoph Kuckein+43 more

AstronomerHigh-resolution Sunrise III TuMag and SCIP observations, combined with SDO data, track an arch filament system (AFS) in an emerging flux region continuously for nearly four hours. Mg I b₂ line-of-sight velocities show three episodic flow events, with footpoint downflows reaching approximately 17 km s⁻¹ and enhanced upflows near loop tops. This pattern is consistent with emergence and draining, although the strongest upflows and downflows occur nearly simultaneously. AIA 304 and 171 Å observations show transient EUV brightenings in the surrounding emerging system, but their temporal correspondence with enhanced flows is not systematic. Multiline spectropolarimetric inversions infer temperatures of approximately 4000–10,000 K and smoothly varying magnetic inclination along a representative loop. Non-force-free-field extrapolations supply the large-scale magnetic context. The observations establish complex spatial and temporal evolution, not a direct causal connection between local flow enhancements and EUV brightenings.

PublicResearchers used Sunrise III and the Solar Dynamics Observatory to follow a system of arch-shaped solar filaments in a region where magnetic fields were emerging, continuously for nearly four hours. They identified three episodes of plasma flow, with upward motion near the arch tops and downward motion at their bases reaching about 17 kilometres per second along the viewing direction. This is consistent with material rising and then draining, but the strongest upward and downward motions happened almost simultaneously. Brief brightenings in extreme-ultraviolet light appeared in the surrounding region. Some coincided with stronger flows and others did not, so the observations do not establish that the flows caused the brightenings. Analysis of the light also inferred temperatures of roughly 4000–10,000 kelvin and a gradual change in magnetic-field direction along one representative arch.

Young explorerScientists watched arches of hot gas on the Sun for almost four hours. They saw three bursts of movement: gas went up near the tops and down near the bottoms. The fastest upward and downward movements happened at almost the same time. Nearby, they also saw little flashes in a kind of light our eyes cannot see. Some flashes happened when the gas moved more strongly, but others did not. So the scientists cannot say that the moving gas made the flashes.

Infrared spectroscopy of the longest-period Galactic Mira variables from Palomar Gattini-IR: Identification of a candidate thermally pulsing Super-Asymptotic Giant Branch star

Ming To Suen, Kishalay De, Sam Rose+13 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerIRTF/SpeX spectroscopy of 13 Galactic Mira variables with periods ≳1000 days, selected from Palomar Gattini-IR, finds 12 with properties consistent with massive O-rich AGB stars. The exception, IRAS 19552+3142, has P ≈1060 days, ΔJ ≳2 mag, C₂ and CO bands indicating C/O ≳1, and archival mid-infrared SiC emission near 11.3 μm. Its confirmed carbon-rich chemistry makes it the longest-period C-rich Galactic Mira known. Such chemistry is difficult to reconcile with standard massive AGB evolution, in which hot-bottom burning maintains an O-rich surface. Dredge-out during super-AGB evolution is proposed as a possible explanation, not an established identification. Its M[4.5] ≲−10 mag, [3.6]−[4.5] ≳2.0 mag, and mass-loss rate ≳10⁻⁴ solar masses per year resemble extreme AGB progenitors of intermediate-luminosity red transients and a chemically peculiar super-AGB candidate in the Small Magellanic Cloud. It may therefore be a thermally pulsing Galactic super-AGB star; improved models and long-baseline infrared searches are needed.

PublicAstronomers studied 13 dusty stars in the Milky Way whose brightness cycles last roughly 1,000 days or longer. Twelve show properties consistent with massive, aging stars with oxygen-rich chemistry. One, IRAS 19552+3142, instead has carbon-rich chemistry, making it the longest-period carbon-rich Mira variable known in our galaxy. That is puzzling because standard models predict that massive stars at this stage should remain oxygen-rich at their surfaces. One possible explanation is that this star belongs to a class called super-AGB stars, with episodes that bring carbon-rich material to the surface. Its high brightness, red infrared color, and rapid loss of material support comparisons with other unusual aging stars, but do not confirm that explanation. The researchers call for better theoretical predictions and infrared searches spanning long periods to understand these rare, dust-hidden stars.

Young explorerSome old stars slowly get brighter and dimmer, and dust can hide them from view. Astronomers studied 13 of these stars using infrared light, which helps them look through the dust. One star was especially surprising: they found signs of carbon-rich material where the usual ideas about stars like it would suggest oxygen-rich material. Perhaps it is a rare kind of old star that brings carbon from inside up to its surface. That is a possible explanation, but the astronomers do not know for sure yet.

Rotation and outburst-like brightenings in ZZ Ceti stars observed by TESS

Zs. Bognár, Á. Sódor

AstronomerAn analysis of 120 s and 20 s TESS photometry through Sector 96 searched known ZZ Ceti stars for rotationally split pulsation multiplets and outburst-like brightenings. Automated selection with visual validation yielded accepted triplet candidates in 11 stars, including three first-time triplet detections, implying rotation periods of approximately 8–94 h. These periods are broadly consistent with the dispersion reported in previous studies. Light-curve inspection retained 19 outburst-like events in 11 stars, but pixel-level diagnostics suggest that most arise from foreground asteroid contamination. TIC 219442838, TIC 307908863, and TIC 630426257 remain candidate stellar outbursters. None is in the accepted triplet-rotation sample, so these samples do not establish a connection between outburst activity and rotation.

PublicResearchers searched TESS brightness measurements of pulsating white dwarf stars for clues to how fast they spin and whether they undergo sudden brightenings. In 11 stars, they identified candidate groups of three pulsation frequencies that imply rotation periods of about 8 to 94 hours; three of these triplet detections were reported for the first time. They also found 19 apparent brightening events in 11 stars, but detailed checks suggest that most were caused by foreground asteroids rather than changes in the stars themselves. Three stars remain possible outburst sources. None belongs to the group with rotation estimates from accepted triplets, so the findings do not establish a link between spinning and outbursts.

Young explorerSome small stars pulse, making their light change in a repeating way. Scientists looked at these patterns with a space telescope called TESS and found clues to how fast 11 stars spin. They also looked for sudden flashes of extra light. Most of those flashes were probably caused by asteroids passing in front of the telescope’s view, not by the stars. Three stars might really have brightened suddenly, but scientists are not sure yet. These were not the same stars with the spin clues, so this search did not show whether spinning and sudden brightening are connected.

The Bochum Survey of the Southern Galactic Disk: IV. Multi-Band Photometry

Julia Blex, Dominik J. Bomans, Kerstin Weis+7 more

• Astrophysics of Galaxies

AstronomerThe Southern Galactic Disk Survey presents a matched multi-band photometric and light-curve catalogue for almost 21.7 million Gaia DR3 sources, including 113,449 identified variables. Monitoring covered 268 fields across a 6-degree-wide stripe of the southern Galactic disk from September 2010 to September 2019, with 21–407 simultaneous r′ and i′ observations per field and supplementary U, B, V, and z′ coverage. Comparison with the Gavras et al. (2023) literature cross-match catalogue and VSX indicates that approximately 40% of the variable sources lack a variability-type classification. The GDS catalogues, available through GAVO, contain light curves for all these sources and may support further classification.

PublicA nine-year survey of a strip of the southern Milky Way has brought together brightness measurements in several colour bands for almost 21.7 million sources. The catalogue identifies 113,449 sources whose brightness changes over time. Comparisons with existing records indicate that about 40% of these variable sources have not yet been classified by the kind of brightness changes they show. Their brightness histories are available through the German Astrophysical Virtual Observatory and could help researchers classify them.

Young explorerAstronomers watched a long strip of our galaxy for nine years, checking how bright things looked. They made a huge list and found more than 113,000 things whose brightness changes. For about four out of every ten of those, they do not yet have a label for the kind of change. They have shared the brightness records so scientists can help sort them into groups.

A morpho-kinematic view of the Necklace nebula

E. Santamaría, J.A. Toalá, L. Sabin+2 more

• Astrophysics of Galaxies

AstronomerSpatially resolved spectroscopy and SHAPE 3D modeling constrain the morphology and kinematics of the Necklace Nebula’s disrupted equatorial ring and bipolar outflows. Comparisons of observed and synthetic images and position–velocity diagrams yield a best-fitting model that reproduces the main features, confirming a ring tilt of about 60° from the sky plane and placing the outflows at 46° to the line of sight. The inferred slight misalignment may indicate a distinct ejection event rather than outflows that simply extend the ring. Possible explanations include precession, a temporal change in the dominant mass-loss geometry, or magnetic-field misalignment. Given the close binary nucleus and established post-common-envelope status, the results support, but do not establish, binary shaping even before the common-envelope phase.

PublicResearchers combined observations of gas motions with a three-dimensional computer model to study the Necklace Nebula, which has a broken ring and outflows extending in opposite directions. Their best-fitting model reproduces its main appearance and motions but indicates that the ring and outflows are not quite aligned. This could mean they formed in separate episodes of gas ejection, although the study does not establish that explanation. Possible causes include a changing ejection direction, a change in how gas was lost, or a misaligned magnetic field. The nebula has two closely orbiting central stars, and the findings support the idea that their interaction helped shape it even before the stars shared a common envelope of gas.

Young explorerThe Necklace Nebula has a broken ring of gas and gas flowing out in two opposite directions. Scientists watched how the gas moves and made a computer model to help work out its shape. The model suggests that the ring and the flows do not line up quite right. They might have been sent out at different times, but scientists are not sure. Two stars close together in the middle may have helped shape the gas.

Mg II Signatures of Frequency Dependent Wave Propagation in Magnetic Elements

Deborah Baker, David M. Long, Marco Stangalini+4 more

AstronomerThe study links photospheric magnetic-element oscillations to chromospheric Mg II h + k spectral states. Horizontal velocity power spectra derived from SDO/HMI magnetic-element tracking are compared with IRIS profiles classified by k-means into morphology-based (SHAPE) and intensity-based (ABS) groups. Some SHAPE clusters show enhanced 4–6 mHz power, occasionally exceeding power in the photospheric p-mode band. ABS clusters show a monotonic increase in the relative high-frequency contribution with emission strength and magnetic flux. These observed associations suggest that magnetic structuring regulates kink-wave energy transmission and conversion into chromospheric signatures, but they do not directly establish those mechanisms.

PublicResearchers compared the sideways motions of magnetic patches at the Sun’s visible surface with ultraviolet light from the chromosphere above. They found that certain spectral shapes were associated with stronger high-frequency motions. Separately, groups with brighter emission and greater magnetic flux showed a steadily larger high-frequency share of the motion. The findings suggest that the Sun’s magnetic structure helps control how wave energy travels upward and appears in chromospheric light. The study identifies relationships, however, rather than directly proving how that energy is transferred or converted.

Young explorerThe Sun has little magnetic patches that wiggle. Scientists found that faster wiggles went along with certain patterns of light from a layer above them. Brighter groups with stronger magnetism also had a bigger share of fast wiggles. This gives clues about how energy moves, but does not prove exactly how.

A Low-Dimensional Chemical Representation of High-Resolution Stellar Disk Spectra: Residual Abundance Signatures

Sarah E. Aquilina, Melissa K. Ness, Sven Buder

• Astrophysics of Galaxies

AstronomerUsing HARPS spectra of low-alpha disk stars at R = 115,000 and SNR > 100, the authors test low-dimensional spectral reconstruction with The Cannon, conditioned on five stellar parameters and three abundance labels, [Ti/H], [Y/H], and [Nd/H], derived with Korg. On unseen test stars, the model achieves a median flux-residual amplitude of 0.3%; deviations in 15 absorption features of unlabelled elements are typically below 0.7%. Residuals of about 1% correspond to abundance differences of 0.01–0.05 dex. Degrading the spectra to R = 28,000 lowers the median residual to 0.2% by redistributing residual signal over the instrumental line profile, rather than resolving more chemical information. The publicly available model reproduces features from 29 elements to sub-percent precision over -1.13 < [M/H] < 0.29. These tests support a low-dimensional description of the dominant chemical variation in this stellar population, while weaker information remains in the residuals. The authors argue that R ~ 100,000 and SNR > 100 are essential for resolving this additional structure and offer the model as a benchmark for current surveys and upcoming facilities.

PublicThe chemical elements in stars leave absorption features in their spectra, but many of those chemical signatures vary together. This study tested whether a model using a small set of stellar properties and the abundances of just three elements could reproduce high-quality spectra of low-alpha stars in the Milky Way’s disk. For stars not used in training, the model reproduced the spectra with a median mismatch of 0.3%, including features from elements whose abundances were not supplied to it. Small remaining mismatches still contain additional chemical information. When the researchers reduced the spectra’s resolution, the median mismatch fell to 0.2% because the remaining signals were spread out, not because more chemical detail was recovered. The results show that a compact model captures most, but not all, of the chemical variation in these stars. The authors argue that very sharp, low-noise spectra are needed to reveal the weaker details; their public model provides a benchmark for evaluating what stellar surveys can recover.

Young explorerA star’s light has little dark marks that give clues about what the star is made of. The researchers taught a computer to copy these marks using only a few clues about each star. It made very close copies, even for stars it had not practised on. But tiny differences were left over, and those can hold more clues about the star’s ingredients. Blurring the light made the differences look smaller, but also hid some detail. The researchers say very clear views are needed to find those extra clues.

Insights into the Kinematic Evolution of Filament-Induced Jets: Coupling of Interchange and Flare Reconnection

Zehao Tang, Xiaoli Yan, Zhike Xue+3 more

AstronomerThe study analyzes the complete evolution of an SDO-observed solar jet associated with a B-class flare and identifies two distinct kinematic stages. Stage-dependent signatures occur in magnetic morphology, the Hα profile, jet speed and height, X-ray flux, the loop-top source, and temperature. The authors interpret this coordinated evolution as a transition from interchange reconnection to flare reconnection and propose a coupled physical picture that unifies the diagnostics. The event offers insight into filament-induced jets, while the broader question of jet triggering remains unresolved.

PublicResearchers followed a jet erupting in the Sun’s atmosphere alongside a B-class solar flare, using observations from the Solar Dynamics Observatory. They found two distinct stages, with differences in the jet’s speed and height, temperature, light signatures, and magnetic structure. They interpret these changes as evidence that two kinds of magnetic reconnection—processes that rearrange magnetic fields—acted in sequence. This explanation may help clarify how filament-induced solar jets develop, but it does not settle the general question of what triggers solar jets.

Young explorerScientists watched a jet of hot material shoot out in the Sun’s atmosphere. It changed in two steps. They think the Sun’s magnetic fields rearranged in two different ways to help make those steps happen. They are still working out what starts jets like this.

The Pointing Error Due To Laser Propagation in Space Plasma for TianQin Gravitational Wave Detection

S.W. Zhou, W. Su, S.Y. Zhou+2 more

• High Energy Astrophysical Phenomena
• Instrumentation and Methods for Astrophysics
• General Relativity and Quantum Cosmology
• Space Physics

AstronomerThis simulation study assesses plasma-induced pointing errors in TianQin’s planned inter-satellite laser links. A magnetohydrodynamic model supplies plasma distributions for different orbital orientations, and fourth-order Runge–Kutta ray tracing follows laser propagation over one TianQin orbital cycle, with solar-wind dynamic pressure close to its 23-year average. The calculated deflection angles are of order 10^-20 rad, with pointing eccentricities on picometer scales, well below the mission’s requirements. These modeled results indicate negligible plasma-induced pointing noise under moderate space-weather conditions; they do not establish performance during more extreme conditions.

PublicTianQin is a planned space observatory that will use laser links between satellites to detect gravitational waves. This study uses computer simulations to test whether unevenly distributed charged gas in space could bend the lasers enough to disrupt their pointing. Under modeled moderate space-weather conditions, the predicted bending and pointing shifts are far smaller than the mission’s limits. The findings are encouraging for TianQin, but they are simulation results rather than measurements and do not establish what happens during extreme space weather.

Young explorerTianQin is a planned space project that will use lasers between satellites to look for tiny ripples in space. Scientists used a computer model to ask whether gas in space might bend the laser beams and make them point the wrong way. In their model of moderate space weather, the beams moved far too little to cause a pointing problem. This is a helpful prediction, not a test with real satellites, and it does not tell us what would happen in a big space storm.

Energy-Dependent Hard X-Ray QPP Modulation in M- and X-Class Solar Flares Observed by Aditya-L1/HEL1OS

Sachin Rajkapoor Kanaujiya, Ram Ajor Maurya, Valery M. Nakariakov

AstronomerThe study compares the energy dependence of hard X-ray quasi-periodic pulsation modulation depths in 18 M-class flares and a previously studied X-class sample, using four HEL1OS channels spanning 8–20 keV. The earlier catalogue identified statistically significant pulsations in 25 of 34 X-class events with sufficient data quality; measurement availability in the present comparison varies by channel. Modulation depth increases from approximately 2.3% at 8–11 keV to 13.2% at 17–20 keV for M-class flares, versus approximately 1.0% to 3.1% for X-class flares. The steeper increase in the M-class sample is the principal observational contrast, but a systematic statistical assessment is still needed to determine whether the energy-dependent modulation-depth distributions differ. These observations provide constraints for models of QPP generation and energetic-electron emission rather than establishing a generation mechanism.

PublicSolar flares can produce nearly repeating pulses of X-rays. This study used HEL1OS observations to compare how pronounced those pulses are at different X-ray energies in two flare classes. In both groups, the pulses became larger relative to the overall emission at higher energies. Across the measured energy range, this relative pulse size rose from about 2.3% to 13.2% in the M-class sample, compared with about 1.0% to 3.1% in the more powerful X-class sample. The stronger rise in the M-class sample is an observed pattern, but further statistical testing is needed to establish how the two groups' pulse-size distributions differ. The findings may help researchers test explanations for how flares release energy and produce energetic electrons.

Young explorerBig bursts on the Sun can send out X-rays that brighten and fade in an almost repeating beat. Scientists studied two groups of these bursts. In higher-energy X-rays, the beats stood out more against the rest of the glow, especially in the group of less powerful bursts. Scientists still need to check the numbers more carefully to learn how different the two groups really are.

Recent advances in numerical modeling of solar inertial modes

Yuto Bekki, Laurent Gizon

AstronomerThis review surveys hydrodynamic modeling of solar inertial modes, low-frequency global oscillations restored by the Coriolis force and detected through long-term observations of horizontal surface flows. Linear eigenmode analyses have helped identify and classify observed mode families. Numerical models indicate that their sensitivity to differential rotation and fluid properties could constrain poorly known deep-convection-zone parameters, including turbulent viscosity and superadiabaticity. Amplitudes of linearly stable modes can be estimated from stochastic forcing, while unstable-mode amplitudes require nonlinear modeling. The review also considers possible heat and angular-momentum transport by large-amplitude modes, without establishing those roles as observational results. Magnetohydrodynamic effects are outside its scope.

PublicLong-term measurements of sideways flows on the Sun’s surface have revealed slow, large-scale oscillations shaped by the Sun’s rotation. This review explains how computer models of fluid motion help researchers identify these oscillations and explore what they might reveal about the Sun’s hidden interior. The models suggest that the oscillations could help constrain how turbulent flows behave and how conditions vary deep in the region where convection carries heat. Estimating their strengths requires different methods depending on whether the oscillations naturally decay or grow. Large oscillations might also help move heat and redistribute rotational motion, but these possible roles remain uncertain. The review does not address magnetic effects.

Young explorerScientists have seen slow, giant wiggles in the Sun by watching flows across its surface. The Sun’s spinning helps make these wiggles happen. This review explains how scientists use computers to understand them and learn what they might tell us about deep inside the Sun. The wiggles might help move heat and change how the Sun’s material spins, but scientists are still figuring that out. The computer studies discussed here leave out magnetism.

Analysis of Multi-Wavelength Data for 30 Galactic Emission-Line Stars with Dusty Envelopes

A.Zh.Naurzbayeva, A.S.Miroshnichenko, N.Sh.Alimgazinova+17 more

AstronomerA search for the B[e] phenomenon targeted 30 stars selected by optical brightness, optical color, and large near-infrared color indices. Spectroscopy confirmed previously detected emission lines in 11 stars and detected them for the first time in four others. Optical–infrared SEDs were compared with theoretical SEDs, and fundamental parameters were estimated using fits corrected for interstellar and circumstellar extinction together with Gaia DR3 distances. The study reevaluated 14 objects previously classified as pre-main-sequence stars. It identified the B[e] phenomenon in 16 objects, most with observed properties resembling FS CMa stars or binary systems with predominantly hot circumstellar dust. IRAS 06237+0020 and IRAS 19156-0935 have properties consistent with early-stage proto-planetary nebulae, rather than definitive classifications. The nature and evolutionary status of 11 sample objects remain uncertain.

PublicResearchers examined 30 stars selected for their visible and infrared colors and brightnesses, looking for a distinctive behavior called the B[e] phenomenon. Their spectra confirmed previously known emission lines in 11 stars and revealed such lines for the first time in four others. Overall, 16 objects showed the B[e] phenomenon, and most resemble a small known group of stars or binary systems associated with predominantly hot surrounding dust. Comparing the stars’ visible and infrared light with theoretical models, while accounting for dust extinction and measured distances, helped estimate their properties and reassess earlier classifications. Two objects have properties consistent with an early proto-planetary-nebula stage, but this is not a firm identification. The nature and evolutionary stage of 11 objects remain unresolved.

Young explorerScientists looked closely at the light from 30 stars. They found a special pattern in the light of 16 of them. Most of those look like members of a small group of stars, or pairs of stars, with hot dust around them. The scientists also compared the light with model pictures to learn more about the stars. They still do not know for sure what kind of objects 11 of them are or what stage of life they are in.

Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. IV. Heavy Element Enhanced Stars

Yangming Lin, Haining Li, Wako Aoki+7 more

• Astrophysics of Galaxies

AstronomerA homogeneous abundance analysis of 82 heavy-element-enhanced, metal-poor stars from the LAMOST/Subaru sample finds systematic [X/Eu] differences between r-I and r-II stars. Together with distinct dynamical properties, these differences suggest that r-II stars likely formed in low-mass dwarf galaxies with little contamination from other nucleosynthetic channels. The extremely metal-poor r-II star J1158+0734 has [Fe/H] = -2.93 and [Zn/Fe] = +0.67; the authors favor yields from a high-energy, massive core-collapse supernova as the explanation for its Zn enhancement. Dispersion in the surface abundances of s-process-enhanced stars is consistent with enrichment by AGB progenitors with diverse properties. J2256+0215 has unusually low carbon, [C/Fe] = +0.08, and a 12C/13C ratio of 2.33, providing evidence for additional evolutionary mixing. Three identified r+s stars show abundance patterns indicating contributions from both processes. The authors also propose, rather than establish as a validated diagnostic, identifying CEMP-r+s stars using -0.2 ≤ [La/Nd] ≤ 0.2 and -0.5 ≤ [Eu/Nd] ≤ 0.0.

PublicResearchers analyzed 82 stars that contain little iron but are enriched in heavier elements. Differences in chemical composition and motion between two groups suggest that the more strongly enriched r-II stars likely formed in small dwarf galaxies, where fewer other element-making processes altered their chemical makeup. One star has unusually abundant zinc, which the researchers interpret as material produced by a high-energy explosion of a massive star. Other stars show varied chemical patterns consistent with enrichment from stars in the asymptotic giant branch stage of evolution. A star with little carbon and an unusually low ratio of two carbon isotopes provides evidence for additional mixing during its evolution. Three stars show contributions from both rapid and slow neutron-capture processes, which build heavy elements. The team also proposes chemical criteria for recognizing carbon-enhanced stars with contributions from both processes; these criteria are a proposed identification tool, not an established result.

Young explorerScientists studied the ingredients in 82 stars. Different stars had different mixes, giving clues about where their ingredients came from. One star had extra zinc that may have come from a powerful exploding star. Another showed clues that its material had been mixed around as it changed. The scientists also suggested a new way to spot stars with ingredients made in two different ways.

Nine new eclipsing accreting ultracompact white dwarf binaries from the Zwicky Transient Facility

J. van Roestel, M. J. Green, T. L. S. Wong+19 more

AstronomerA box least-squares search of ZTF light curves for Gaia-selected candidates and ZTF-selected dwarf novae identified nine new eclipsing accreting ultracompact white dwarf binaries, increasing the published sample from 21 to 30. The study also re-analyses four previously reported systems and presents Keck I/LRIS identification spectra for nine systems. All 13 show eclipses directly in survey photometry, with orbital periods of 26.0–65.0 min and median ZTF g magnitudes of 18.7–21.5. Ten are consistent with AM CVn classifications, and two are likely helium cataclysmic variables, one possibly hosting a high-state disc. ZTF J2116+2446 shows hydrogen lines but no detected helium, making it the shortest-period UCB with that spectral signature; a white dwarf–brown dwarf origin is proposed, not established. High-speed eclipse modelling to obtain model-independent component masses and radii is deferred to future work. Those measurements, particularly for the three hydrogen-rich systems, are intended to test proposed formation channels, including the evolved cataclysmic-variable channel.

PublicAstronomers have discovered nine tightly orbiting pairs in which a white dwarf draws material from a companion and the stars periodically eclipse one another. The discoveries raise the published tally of these eclipsing, accreting ultracompact systems from 21 to 30. Together with four previously known pairs re-examined here, they complete an orbit every 26 to 65 minutes. Most appear to belong to a hydrogen-free class called AM CVn binaries. One unusual system shows hydrogen in its spectrum but no detected helium; the researchers suggest it might have developed from a white dwarf paired with a brown dwarf, although that history is uncertain. The eclipses offer a way to measure the stars’ masses and sizes and test ideas about how such pairs form. Those detailed measurements are planned for future work, not reported here.

Young explorerScientists found nine new pairs of stars that race around each other. In each pair, a small star called a white dwarf takes material from its partner. We see the pairs get dimmer when one star passes in front of the other. These hiding games could help scientists work out how heavy and how big the stars are. That measuring work is still to come.

Six New Eclipsing AM CVn Binaries from the Zwicky Transient Facility

Aaron Householder, Kevin B. Burdge, Yapeng Zhang+16 more

AstronomerA GPU-accelerated Box Least Squares search of ZTF photometry discovered six eclipsing AM CVn binaries with orbital periods of 39.3–59.9 minutes. Keck I/LRIS spectra of all six show helium emission and no detectable hydrogen, confirming their classification. These discoveries increase the known deeply eclipsing sample from 11 to 17: in these systems, the accreting white dwarf dominates the optical light and is eclipsed by the cool donor. Future high-speed photometry is expected to yield mass ratios, inclinations, and fractional radii of both components, enabling tests of formation models and tighter constraints on long-term evolution; those measurements are not presented here.

PublicAstronomers discovered six tightly orbiting pairs of stars in which a white dwarf draws helium from a cooler companion. Each pair completes an orbit in 39.3 to 59.9 minutes, and the companion periodically passes in front of the white dwarf, blocking its light. The systems were found by searching Zwicky Transient Facility brightness measurements. Spectra taken with the Keck I telescope show helium emission but no detectable hydrogen, confirming that all six belong to the AM CVn class. The discoveries raise the known number of deeply eclipsing systems of this kind from 11 to 17. Future rapid brightness measurements are expected to reveal their relative masses, orbital tilts, and sizes relative to their separation, helping researchers test how these pairs form and evolve.

Young explorerAstronomers found six new pairs of stars that race around each other, taking about 39 to 60 minutes to go around once. In each pair, a small star called a white dwarf takes helium gas from its cooler partner. That partner sometimes moves in front of the white dwarf and hides its light, like a tiny eclipse. The stars’ light showed helium but no hydrogen that the astronomers could detect. Watching these eclipses more closely in the future could help scientists learn more about the stars and how they change over time.

Extension and validation of the ZPEKTR code for determining the inclination angles of Be stars

Daniela Turis-Gallo, Michel Curé, Ronaldo. S. Levenhagen+2 more

AstronomerThis study evaluates ZPEKTR’s recovery of rotation rates and inclinations for classical Be stars, accounting for rotational oblateness and gravity darkening. Noise-injection tests on synthetic spectra found reliable rotation-rate recovery across the tested inclinations, with inclination recovery improving at faster rotation and becoming reliable at V/Vc ≥ 0.46 within the tested parameter space. The authors fitted He I 4388, 4471, and 6678 Å profiles by Q minimisation to derive stellar and rotational parameters for 21 classical Be stars observed with archival BeSOS/PUCHEROS spectra and new LCO/NRES observations. The inferred inclinations agree closely with independent interferometric measurements, with R² = 0.985. These tests and observational comparisons support ZPEKTR as a promising spectroscopic alternative for constraining inclinations and rotation, particularly in sufficiently rapid rotators.

PublicRapidly spinning classical Be stars are flattened and have uneven surface brightness, so their spectra depend partly on the angle from which we see them. Researchers tested the ZPEKTR computer code on simulated spectra with added noise to see how well it could recover spin rates and viewing angles. Spin rates were recovered reliably across the viewing angles tested, while viewing angles were more reliable for faster-spinning stars. In these tests, reliable angle estimates required rotation at least 46% of the critical speed. The team also analysed spectra of 21 real Be stars; their estimated viewing angles closely matched independent measurements made using interferometry. The results suggest that spectroscopy could offer a practical way to study the orientations and rotation of larger samples of these stars.

Young explorerSome stars spin so fast that they become a little squashed, and some parts of their surface shine more brightly than others. Scientists used a computer program to work out how fast these stars spin and which way they tilt toward us. First, they tried it on pretend starlight with extra fuzz added. It worked better at finding the tilt when the pretend stars spun faster. Then they studied light from 21 real stars. Their tilt answers closely matched another way of checking, which is a promising sign that the program can help us learn about fast-spinning stars.

The δ Scuti instability strip and period-luminosity relation as seen by TESS and Gaia DR3

Daniel Hey, Simon Murphy, Timothy R. Bedding+8 more

• Astrophysics of Galaxies

AstronomerA nearly all-sky survey of 1,526,218 A- and F-type stars in and around the δ Scuti instability strip uses TESS 10-minute cadence data to resolve their pulsation spectra. Homogeneous stellar parameters come from Gaia DR3 parallaxes and archival photometry, with temperatures agreeing with interferometry to within about 300 K. A Positive–Unlabelled classifier identifies 156,706 δ Scuti pulsators, which rotate significantly faster on average than non-variable A-type stars. In the effective-temperature–luminosity plane, the pulsator fraction peaks at 30% for the full sample and reaches 80% in the brightest magnitude bins, indicating that detection sensitivity explains much, but not all, of the strip’s apparent impurity. The period–luminosity relation agrees with previous determinations and is recast as a scale-invariant period–density relation linked directly to the pulsation constant. The secondary ridge is interpreted as probably combining several overtone modes. Stars nearest the fundamental ridge have systematically lower rotational velocities and occupy a distinct part of the strip. A cross-match with a Gaia open-cluster catalog finds a correlation between mean pulsation frequency and cluster age, suggesting, rather than establishing, an ensemble age indicator for young stellar populations.

PublicUsing TESS observations taken every 10 minutes, researchers surveyed more than 1.5 million stars in and around the range of temperatures and luminosities where δ Scuti pulsations are expected. Their classifier identified 156,706 of these pulsating stars, which on average rotate faster than non-variable A-type stars. The fraction detected as pulsators peaks at 30% across the full sample but reaches 80% among the brightest stars. This suggests that many pulsations are missed in fainter stars, although limited sensitivity does not fully explain why some stars in the expected range show no detected pulsations. The study confirms an earlier relationship between pulsation period and luminosity and expresses it in terms of stellar density. A secondary pattern probably reflects a mixture of several higher-order vibration modes. Stars closest to the main, fundamental-mode pattern rotate more slowly and occupy a distinct part of the expected pulsation region. Among stars associated with open clusters, average pulsation frequency correlates with cluster age. That finding suggests a possible new way to estimate the ages of young groups of stars, but the method is not yet established.

Young explorerSome stars vibrate a little like ringing bells. Researchers used a space telescope called TESS to look at more than a million stars and picked out over 150,000 of one kind of vibrating star. These stars usually spin faster than some stars that do not show changes. The team could spot vibrations more often in bright stars, so some faint stars may be vibrating without us noticing. They also found a clue that how fast stars vibrate is linked to the age of the star group they belong to. Maybe one day those vibrations could help tell how old young groups of stars are, but that idea still needs checking.

Thermodynamic and structural properties of the thin atmosphere of a white dwarf

Riccardo Fantoni

• General Relativity and Quantum Cosmology

AstronomerThe study uses path integral Monte Carlo calculations to determine thermodynamic and structural properties of Coulomb plasma (jellium) in a white dwarf’s thin atmosphere, within a general-relativistic description of the star. The abstract reports no specific property values or observational comparisons.

PublicResearchers use computer calculations to study the physical behavior and arrangement of charged particles in a white dwarf star’s thin atmosphere. Their model includes Einstein’s description of gravity. The abstract does not give specific findings from the calculations.

Young explorerScientists use computers to study tiny charged particles in the thin layer around a star called a white dwarf. They include the star’s gravity to help work out how those particles behave.

Looking for Companionship: Radial Velocity Follow-Up of Lithium-Rich Giants with ESPRESSO

Maryum Sayeed, Andrew R. Casey, Benjamin T. Montet+4 more

• Earth and Planetary Astrophysics

AstronomerHigh-resolution ESPRESSO spectra of 58 Li-rich red giants, analyzed with The Joker Monte Carlo sampler, yield ten candidate companion systems: a detected fraction of 17%, consistent with the 16% expected for normal red giants under comparable ESPRESSO cadence and precision using APOGEE DR16. All candidates have A(Li) = 1.5–2.7 dex and log g = 2–3 dex; none have A(Li) > 2.7 dex. Inferred minimum companion masses comprise three planetary-mass objects at approximately 7–11 Jupiter masses, one brown dwarf at approximately 19 Jupiter masses, and six stellar-mass objects at 0.08–0.98 solar masses. The reported significant difference in companion fraction across A(Li) ≈ 2.7 dex suggests, but does not establish, at least two enrichment pathways. Proposed mechanisms for low-to-moderate lithium include planet engulfment, mass transfer, and tidal spin-up enabling the Cameron–Fowler mechanism; higher-lithium giants may instead reflect mergers or prior engulfment. Longer baselines and dedicated follow-up are needed to confirm orbital parameters and distinguish these explanations.

PublicWhy do some red giant stars contain unusually large amounts of lithium? Researchers studied spectra of 58 lithium-rich red giants and identified ten candidate systems with companions. This 17% detection rate is consistent with the 16% expected for ordinary red giants observed with similar timing and precision, rather than showing an overall excess of companions. The inferred minimum companion masses range from planetary to stellar. Crucially, all ten candidates belong to the less lithium-rich part of the sample; none were found among stars with the highest lithium levels. The authors interpret this difference as evidence suggesting more than one way to enrich a star with lithium. Possible explanations include swallowing a planet, receiving material from another star, or interactions that promote lithium production. Stars with the most lithium might have merged with or already swallowed companions. These explanations remain unconfirmed, and longer-term observations are needed to establish the orbits and test the possibilities.

Young explorerSome big, old stars have a surprising amount of a material called lithium. Scientists looked at 58 of these stars and found signs that ten might have something going around them. None of those ten had the very highest lithium amounts. Maybe different stars get extra lithium in different ways, such as swallowing a planet or joining with another star. Scientists need to watch longer to check these ideas.

Spectral properties of mesoscale fluctuations in interplanetary coronal mass ejections

Anna-Sofia Jylhä, Simon Good, Emilia Kilpua

• Plasma Physics
• Space Physics

AstronomerWavelet analysis of 142 ICME intervals with clear flux-rope signatures at 1 au reveals a typically present, spectrally narrow mesoscale 1/f range between the large-scale flux rope and smaller-scale turbulence. At spacecraft-frame frequencies of 10^-4–10^-3 Hz, corresponding to approximately 2.8 hours–17 minutes, spectra are significantly shallower than at adjacent scales, with a mean slope near -1. Relatively high cross-helicity magnitudes and low compressibility suggest substantial Alfvénicity, while residual energy is more negative than in the smaller-scale turbulence. Classification using mesoscale slope uncertainties separates smoother power-law spectra, with a balanced cross-helicity distribution, from less common bumpy spectra, with predominantly antisunward cross helicity. Similarly analyzed slow-wind intervals show comparable properties. The findings characterize observed fluctuations in the selected flux-rope intervals rather than establishing their physical origin.

PublicLarge clouds of solar material traveling through space can contain both broad magnetic twists and smaller, turbulent magnetic changes. Researchers examined measurements from 142 passages through clouds with clear magnetic twists, at roughly Earth's distance from the Sun. Between the large and small scales, they found a distinct pattern in changes lasting about 17 minutes to 2.8 hours: magnetic fluctuation power decreased with frequency more slowly than at neighboring scales, approximately following a 1/f pattern. The fluctuations also had properties suggesting an Alfvénic, wave-like character, although this does not establish their origin. Most spectra were relatively smooth, while a smaller group was bumpier and showed a stronger preference for disturbances traveling away from the Sun. Slow solar wind showed similar properties, so the pattern was not unique to these clouds.

Young explorerThe Sun sends big clouds into space that carry twisted magnetic fields. Scientists studied how those fields changed. Between the big twists and the tiny, jumbled changes, they often found a special in-between pattern. They found a similar pattern in a slower stream of material from the Sun, too. These clues help describe the magnetic changes, but do not yet tell us what makes them.

Horizontal Magnetic Fields Dominate the Weak Field Quiet Sun in Sunrise III Observations. Evidence from Traditional and Transformer-Based Inversions

Ryan J. Campbell, Carlos Quintero Noda, Manuel Collados+32 more

AstronomerSCIP observations constrain quiet-Sun magnetic topology using two inversion methods: transformer-based SINN, trained exclusively on synthetic Stokes profiles from a radiative magnetohydrodynamic simulation, and independent DeSIRe inversions. Linear polarisation exceeds 4σ in 34.6% of the field of view, extending the detected population beyond typical short-integration Hinode observations. Populations selected by circular-polarisation amplitude show strong horizontal dominance for weak fields and a more balanced topology for strong fields. At log τ = −1, median horizontal and unsigned line-of-sight components in the weak-field population are 63 and 7 G with DeSIRe and 60 and 6.5 G with SINN, giving ratios near nine. Agreement between the methods supports horizontal dominance in the weak-field population of this dataset, while the broader prevalence of quiet-Sun field orientations remains debated because weak linear-polarisation signals make inferences sensitive to data quality and inversion methodology.

PublicResearchers used SCIP observations to investigate how magnetic fields are oriented in a quiet region of the Sun. Two different methods for interpreting the light’s polarisation agreed that the weaker fields in this dataset have a much stronger sideways component than vertical component, while stronger fields have a more even balance. For the weaker-field population, the inferred sideways component was about nine times the component along our line of sight. One analysis method was trained entirely on simulated signals, but both methods were applied to actual observations. Detectable linear polarisation covered 34.6% of the observed area. The agreement strengthens the interpretation for this dataset; it does not settle the wider debate, because these faint signals are sensitive to observation quality and analysis choices.

Young explorerThe Sun has magnetic fields that can point in different directions. Scientists studied light from a quiet patch of the Sun to work out which way they point. Two different ways of checking gave the same main answer: the weaker fields mostly pointed sideways along the Sun’s surface, rather than up and down. The stronger fields had a more even mix. The clues in the light are faint, so this tells us about the patch they studied, not every quiet place on the Sun.

Revisiting Sub-Neptune Population Synthesis: The Role of Core Luminosity in Boil-off, Photoevaporation, and the Radius Distribution

Yao Tang, Jonathan J. Fortney, Natalie Batalha+1 more

AstronomerThe observed bimodal radius distribution of close-in small planets motivates this population-synthesis study using SEAMIST, which self-consistently couples photoevaporation and core-powered mass loss while accounting for envelope metallicity. In the simulations, envelopes with 50–100 times solar metallicity provide a good match to the observed population. Boil-off generally dominates atmospheric loss, while photoevaporation typically removes at most 3 wt% of the envelope mass. Core luminosity supplies approximately 10–20% of the thermal energy available for envelope re-equilibration during boil-off, enhancing mass loss by only about 0.4 wt% in absolute terms. Core heating has a larger effect during the longer photoevaporation phase but little influence on the long-term radius distribution. The authors therefore interpret core-powered mass loss as a modification of atmospheric escape through its lower-boundary conditions rather than a distinct mechanism. In their best-fit model, the radiative atmosphere contributes approximately 20% of the total optical radius, highlighting the need for improved modeling of this atmospheric region.

PublicSmall planets orbiting close to their stars are observed to fall into two main size groups. This study uses computer models to investigate how losing atmosphere might produce that pattern. The simulations match the observed population well when planetary envelopes have 50–100 times the Sun’s abundance of heavier elements. In these models, a process called boil-off generally removes more atmosphere than photoevaporation. Heat from a planet’s core changes atmospheric escape but has little effect on the eventual distribution of planet sizes. The authors therefore argue that core heating modifies atmospheric escape rather than powering a separate escape mechanism. Their best-fitting model also assigns about one-fifth of a planet’s apparent optical radius to its radiative atmosphere, making better atmosphere modeling an important next step.

Young explorerAstronomers see two main size groups among small planets close to their stars. The researchers made computer models to explore why. In their models, planets lose some of their blankets of gas. Heat from deep inside changes how gas escapes, but hardly changes the final pattern of planet sizes. The models also suggest that understanding the outer gas better could help explain how big these planets look.

Searching for Circumplanetary Dust in the Cavity of the AB Aurigae Disk with ALMA

Lillian Jiang, Brendan P. Bowler, Ya-lin Wu+1 more

AstronomerALMA Band 7 observations of AB Aurigae at 0.88 mm achieve approximately 30 mas resolution and 20 μJy/beam rms, searching for circumplanetary material around proposed protoplanets in the transition-disk cavity. The continuum recovers an asymmetric dust ring peaking near 140 au and compact stellar-position emission, but no point source at AB Aur b or the other candidate locations, with a 3σ limit of 60 μJy. Assuming optically thin emission and a dust temperature of 40 K, this implies a dust-mass upper limit of approximately 0.0059 Earth masses, comparable to the circumplanetary disk around PDS 70 c. Carbon monoxide emission fills the continuum cavity and shows inner spirals and ordered rotation; gas at AB Aur b connects smoothly to the ambient disk without a localized excess or obvious kinematic deviation. These nondetections do not establish whether the debated candidates are planets. If they are accreting, their circumplanetary material must have low dust mass, small size, optically thick dust, or few large millimeter-emitting grains.

PublicAstronomers used ALMA to search for dusty material around possible forming planets near the young star AB Aurigae. They detected a lopsided dust ring and emission at the star, but no compact millimeter-wavelength source at any proposed planet location, including the debated AB Aur b. If the dust is at 40 kelvin and its emission can pass through without being substantially absorbed, the observations limit its mass around a candidate to about 0.0059 Earth masses. Gas fills the gap inside the dust ring, displaying spirals and rotation, but shows no localized brightening or obvious unusual motion at AB Aur b. The results do not settle whether these candidates are planets. If they are gathering material, their surrounding dust must be low in mass, confined to a small region, opaque at the observed wavelength, or lacking large grains that emit at millimeter wavelengths.

Young explorerA young star called AB Aurigae has a ring of dust around it. Scientists looked for dust around places where baby planets might be growing, but they did not spot any little dust sources there. They also saw gas inside the ring, but it did not move in an obviously different way where one possible planet might be. This does not mean there are no baby planets. If they are growing there, the dust around them could be very scarce, tucked into a tiny space, too thick to see through, or missing the bigger grains the scientists were looking for.

Young Planets around Young Accreting Stars: II. Circumplanetary Disk Formation and Accretion

Arturo Cevallos Soto, Zhaohuan Zhu

AstronomerGlobal 3-D ideal-MHD simulations examine planets with planet-to-star mass ratio q = 0.01, approximately 10 Jupiter masses, at 0.45, 0.9, and 1.8 times the stellar magnetospheric truncation radius. The innermost planet develops no persistent bound structure: its high velocity relative to the magnetosphere reduces the effective Bondi radius below the planetary size. The outermost planet forms a stable, coplanar circumplanetary disk, with nearly Keplerian rotation inside approximately 0.25 Hill radii and meridional circulation driven by high-latitude inflow and midplane decretion. Hill-sphere inflow is comparable to previous Hill-based hydrodynamic estimates. Near the truncation radius, the middle planet instead forms a persistent polar circumplanetary disk whose angular-momentum vector lies parallel to the protoplanetary disk midplane. Effective Bondi-radius and thermal-mass criteria identify conditions for circumplanetary disk formation. Estimated inflow accretion rates imply mass-doubling times of at least approximately 10 Myr because of the low disk surface density, suggesting limited late-stage growth before disk dispersal. These are simulation results and inferred growth times, not observational findings.

PublicComputer simulations explore how very large young planets gather gas near a star whose magnetic field channels gas onto it. The researchers place planets at three distances spanning the inner, low-density cavity and the surrounding planet-forming disk. The outermost planet develops a stable gas disk aligned with the larger disk, while the planet near the cavity boundary develops a disk oriented at right angles to it. The innermost planet cannot maintain a bound gas structure because it moves too quickly relative to the magnetically controlled gas for its gravity to hold that gas close. Gas continually circulates through the outermost planet's disk rather than simply settling into it. Estimated gas inflow rates suggest that doubling these planets' masses would take at least about 10 million years. The authors therefore suggest that such planets gain relatively little additional mass before the surrounding disk disperses. These findings come from simulations, not direct observations.

Young explorerThe researchers used a computer to imagine giant baby planets near a young star. In their model, gas made a little spinning disk around one planet. Around another, the little disk stood sideways compared with the big disk around the star. A planet closer to the star moved too fast through the gas to keep a lasting gas disk. The researchers think these giant planets may grow only a little more before the gas around the star goes away. This is what their computer model suggests, not something they watched happen in the sky.

NSF-DOE Vera C. Rubin Observatory's First View of the Neptune Trojan L5 (Trailing) Cloud: Two New Long-Term Stable Trojans

Megan E. Schwamb, Pedro H. Bernardinelli, Kathryn Volk+12 more

AstronomerA preliminary search of Rubin Observatory’s commissioning-phase Science Validation survey identified two confirmed, long-term stable Neptune L5 Trojans, 2025 MH348 and 2025 NN80, doubling the known L5 sample, plus one candidate, 2025 MD138. Neptune Trojans occupy the 1:1 mean-motion resonance, librating about L4 or L5, 60° ahead of or behind Neptune. Discovery of L5 members had been hindered for more than 15 years by the cloud’s projected overlap with the crowded Galactic plane and center; in 2025 it moved sufficiently away from the plane to overlap the survey footprint. The authors characterize the objects’ physical and dynamical properties, describe the confirmed stable members as primordial, and compare the L5 sample with L4. They also present the first characterization of objects discovered by Rubin’s moving-object pipelines with an LSST-like cadence, providing a blueprint for LSST-era analyses.

PublicRubin Observatory has found two confirmed small bodies that share Neptune’s orbital period while traveling in a group about 60 degrees behind the planet. Named 2025 MH348 and 2025 NN80, they double the known population of this trailing group of Neptune Trojans. A third object, 2025 MD138, remains a candidate. For more than 15 years, the group appeared against the crowded stars of the Milky Way’s plane and center, making discoveries difficult. In 2025, it moved far enough from that backdrop to fall within Rubin’s commissioning survey coverage. The researchers describe the two confirmed objects as long-term stable, primordial members and study their physical characteristics and orbits, comparing them with the Trojan group ahead of Neptune. The work also demonstrates how discoveries from Rubin’s moving-object search software can be characterized using observations spaced like those planned for LSST.

Young explorerNeptune travels around the Sun with little space objects that follow along behind it. Scientists found two more of these objects in pictures from Rubin Observatory, doubling the number known in that trailing group. They also found another that might belong, but they are not sure yet. The group used to hide against a very crowded background of stars, which made it hard to spot. Now it has moved away from that busy background. The scientists say the two confirmed objects can stay in their places for a very long time.

Nongravitational Motion of 3I/ATLAS Far from the Sun: Robust Detection, Weak Constraints on the Activity Law

Małgorzata Królikowska, Federico Spada, Luke Dones

• Astrophysics of Galaxies

AstronomerAn orbit-fitting analysis of 3I/ATLAS tests whether astrometry can identify the heliocentric dependence of nongravitational acceleration. The observations cover heliocentric distances greater than 3.49 au before perihelion and 2.67 au afterward. A purely gravitational orbit adequately describes the distant pre-perihelion data, but yields significantly non-Gaussian residuals for the distant post-perihelion data. Combining both sets clearly reveals nongravitational acceleration through reduced residual rms and removal of systematic temporal trends. However, standard water-ice, more volatile, and extreme volatile activity prescriptions give statistically comparable fits despite markedly different distance dependences. The astrometry therefore constrains the presence of nongravitational acceleration much better than its heliocentric dependence or physical origin.

PublicMeasurements of the interstellar object 3I/ATLAS show that gravity alone cannot fully explain its motion when observations from before and after its closest approach to the Sun are analyzed together. The earlier, distant observations fit a gravity-only orbit well, while the later, distant observations show discrepancies. Adding an acceleration beyond gravity improves the combined fit and removes systematic patterns in the errors. But the measurements do not reveal a unique cause: models based on water ice and on more easily vaporized ices fit about equally well, even though they predict very different changes in activity with distance from the Sun. Detecting the extra acceleration is therefore more secure than explaining what produces it.

Young explorerScientists watched a visitor from outside our solar system called 3I/ATLAS. When they put together measurements from before and after it passed closest to the Sun, its path showed an extra push that gravity alone could not explain. They tried different ideas about ice turning into gas to explain the push, but several ideas matched the measurements about equally well. They can tell the extra push is there much better than they can tell what causes it.

Coupled evolution of Earth's H2-rich proto-atmosphere and oxidized magma ocean: Efficient H₂O production through dissolved H2 transport and atmospheric buffering of the magma ocean redox state

Tatsuya Yoshida, Kirara Arima, Naoki Terada+2 more

AstronomerThis modeling study examines chemical coupling between a potentially H2-rich early terrestrial atmosphere and an oxidized magma ocean. The coupled atmosphere–interior evolution model includes boundary-layer diffusion, melt redox reactions, oxide and H2O partitioning among phases, atmospheric control of cooling, and removal to the core of metallic iron produced by Fe2+ disproportionation. In the model, more frequent boundary-layer renewal by buoyant overturn of dense, surface-cooled melt enhances atmospheric H2 uptake and subsequent H2O production. Chemical equilibration can occur within approximately 10^4 years if the magma ocean is sufficiently deep and hot to reach the lower mantle. Atmospheric redox exchange buffers the redox changes associated with solidification, preventing extreme oxidation or reduction of the coupled system. The results suggest, rather than observationally establish, that this coupling could have contributed to Earth's early water inventory while preserving a reducing, H2-rich atmosphere.

PublicA computer model explores how early Earth's atmosphere might have interacted with a global ocean of molten rock. Giant impacts likely created such magma oceans, but their chemical connection to a possible hydrogen-rich atmosphere remains uncertain. In the model, surface cooling makes dense molten rock sink, renewing the contact region between air and rock. More frequent renewal helps hydrogen enter the molten rock and react to form water. If the magma ocean reaches deep enough into Earth's lower mantle and is sufficiently hot, the model finds that the atmosphere and molten rock can reach chemical balance within about 10,000 years. Their interaction also limits extreme chemical changes as the rock solidifies. These findings suggest a possible contribution to Earth's early water supply while its atmosphere remained rich in hydrogen; they do not demonstrate that this history actually occurred.

Young explorerLong ago, Earth may have had a giant sea of melted rock with hydrogen gas above it. Scientists made a computer model to explore what could happen when the gas and melted rock mixed and reacted. In the model, melted rock cooled at the top and sank, helping more gas enter the rock and make water. This might have helped give young Earth some of its water while leaving lots of hydrogen in the air. It is a possible story, not something the scientists watched happen.

2026 ED138: A Large Trans-Neptunian Object in Early Rubin Observatory Data, and How Many More May Remain

Matthew J. Holman, Mario Jurić, Kevin J. Napier+19 more

• Instrumentation and Methods for Astrophysics

Astronomer2026 ED138 is a newly discovered, independently validated TNO identified in Rubin Observatory data with the pointdexter linking code. Its absolute magnitude, H_V=3.19, places it among the ten intrinsically brightest known TNOs; its inferred diameter is 612–1530 km for assumed geometric albedos of 0.25–0.04, making it a dwarf-planet candidate rather than a confirmed dwarf planet. Archival DECam detections extend the observational arc to 3789 days. Its barycentric orbit has a=43.09 au, e=0.139, and inclination 24.4°, placing it at the edge of Neptune’s 12:7 mean-motion resonance, like Haumea, but its g−r=0.63 color is too red for membership in Haumea’s collisional family. Its apparent i-band magnitude of approximately 19.4 makes spectroscopy, light curves, and detailed HST and JWST observations feasible, not reported results. The authors attribute previous non-detection to its far-southern location near the crowded Galactic plane. Recovery statistics for known TNOs with H_V<4 suggest roughly three additional such objects, probably more, remain undiscovered away from the plane; further objects are considered likely within 10° of the plane, where no search has yet reached this depth.

PublicAstronomers report discovering and independently confirming 2026 ED138, a large object beyond Neptune, in Vera C. Rubin Observatory data. Older images extend its observed history to more than ten years. It ranks among the ten intrinsically brightest known objects in this distant population and is a dwarf-planet candidate. Its estimated diameter ranges from 612 to 1530 kilometers because its surface reflectivity is uncertain. Its orbit lies near the edge of a repeating orbital relationship with Neptune, much like Haumea’s, but its redder color rules out membership in the family of fragments associated with Haumea. It is bright enough for future detailed observations with ground-based telescopes, Hubble, and James Webb. The authors say earlier surveys missed it because it lies far south near the crowded band of the Milky Way. Their recovery of other known bright objects suggests that roughly three more, and probably more, await discovery away from that band, with additional objects likely hidden closer to it; these are estimates, not new detections.

Young explorerAstronomers found a big object far beyond Neptune and checked that the discovery was real. It is called 2026 ED138. Old pictures show that telescopes had seen it for more than ten years without anyone recognizing it. It might be a dwarf planet, but that is not certain yet. Scientists also do not know exactly how big it is, because they do not know how much light its surface reflects. It was hard to spot among lots of stars. The team thinks more big objects may still be hiding, but they have not found those yet.

Reconciling Giant Impacts with the Radius Valley: The Role of Silicate-Hydrogen Miscibility for Sub-Neptunes

Eva Zlimen, Hilke E. Schlichting, James G. Rogers

AstronomerThis modeling study revisits giant-impact-driven atmospheric escape with silicate–hydrogen miscibility coupling planetary interiors and envelopes. Unlike chemically inert models, which previously found complete atmospheric loss from sub-Neptunes struck by impactors one-tenth their mass, miscible models can yield substantially less escape. The reduction reflects higher envelope mean molecular weight, interior hydrogen sequestration, and modified compositional gradients. Hydrogen subsequently exsolves into the envelope as the planet cools; more massive planets cool more slowly and retain interior hydrogen longer. Atmospheric retention therefore depends more strongly on planet mass than impact energy, provided the impact does not gravitationally unbind the planet. In these models, planets above roughly 4.50 Earth masses with hydrogen mass fractions greater than 5% typically retain atmospheres at the several-percent level after an impact, whereas planets below roughly 3.30 Earth masses are almost entirely stripped. The results suggest, rather than establish observationally, that super-Earths and sub-Neptunes could arise from one rocky-interior population even if giant impacts were common after disk dispersal.

PublicGiant collisions may not remove a planet’s atmosphere as easily as earlier models suggested. In this study’s models, hydrogen can mix with the rocky interior rather than remain entirely in the atmosphere, leaving less gas exposed to escape after an impact. Changes in atmospheric composition also help reduce gas loss. As the planet cools, hydrogen comes back out into the atmosphere. More massive planets cool more slowly and keep hydrogen inside longer, so they generally retain more atmosphere, unless the collision is powerful enough to gravitationally break the planet apart. Lower-mass planets are more readily stripped. These calculations suggest that relatively bare super-Earths and gas-enveloped sub-Neptunes could develop from the same starting population of rocky-interior planets, even with frequent giant collisions; they are not direct observations of that history.

Young explorerCan a planet keep its blanket of gas after a huge crash? Scientists used models to explore this. Some hydrogen can mix into the rocky inside, leaving less gas outside to be lost. As the planet cools, that hydrogen can come back out. Bigger planets may keep more gas, while smaller ones may lose almost all of it. This is a possible story, not something the scientists watched happen.

Update on the Orbital Motion of Encke's Periodic Comet: Nongravitational Deceleration Gradually Gaining

Zdenek Sekanina

AstronomerIndependent nongravitational orbit computations by S. Nakano and D. Farnocchia suggest that Encke's comet has continued its previously reported transition from nongravitational acceleration to deceleration, with the deceleration increasing in magnitude. Their A_2 values agree with one another and with the author's earlier values. The author critically assesses conflicting Minor Planet Center solutions that imply a return toward acceleration; the trend is therefore not supported by all computations. Observation counts used in orbital solutions rose exponentially following CCD adoption, unlike after photography became common five or six decades earlier, and show dips during both World Wars. Recent observations spanning the entire orbit required redefining the effective epochs assigned to the nongravitational parameters.

PublicNew calculations suggest that the extra effect on Encke's comet's motion, beyond gravity, is increasingly acting to slow it rather than speed it up. Two independent sets of calculations agree with each other and with the author's earlier work, but conflicting calculations from the Minor Planet Center suggest a return toward speeding up. The author questions those conflicting results. The paper also finds that the number of observations used to calculate the orbit grew exponentially after CCD cameras were introduced, with dips in observing activity during both World Wars. Because recent observations cover the comet's whole orbit, the times associated with the calculated extra effects needed to be redefined.

Young explorerScientists are working out how a comet called Encke moves. Two sets of calculations suggest that an extra slowing effect, beyond gravity, is getting stronger. But another set suggests something different, so the calculations do not all agree. Scientists have now watched the comet all along its path, helping them study how it moves.

Optical clock network tracks tidal variations of the gravity potential

Kilian Stahl, Ingo Nosske, Chetan Vishwakarma+41 more

• Instrumentation and Methods for Astrophysics
• Atomic Physics

AstronomerA European network of optical clocks connected by phase-stabilized fibre links has measured time-varying gravitational potential differences through relativistic clock-rate shifts. Two geographical configurations, each with an approximately 800 km baseline, sampled different combinations of diurnal and semidiurnal tidal components; one used a transportable optical clock as a remote sensor. The measured shifts tracked tidal variations, resolving the predicted signal within one day and agreeing with model predictions. Celestial tidal potentials and Earth's response produce clock-rate changes of several parts in 10^17. The observations extend chronometric levelling from static to dynamic potential differences and demonstrate the importance of time-dependent relativistic corrections in frequency metrology. Monitoring non-tidal potential variations associated with deformation or mass redistribution remains a prospect for networks with improved stability and availability, not a demonstrated result here.

PublicGravity changes how quickly clocks tick. Researchers compared extremely precise optical clocks across Europe, connected by specially stabilized fibre links, to measure how differences in gravity's effect on time change as tides vary. They used two arrangements spanning about 800 kilometres each, including one with a transportable clock. The measured changes followed the predicted tidal pattern, with the signal distinguishable within one day of measurement. This extends earlier clock-based measurements that mainly focused on steady gravity differences. More stable and more consistently available clock networks might eventually monitor other changes in gravity caused by ground deformation or shifting mass in geologically or volcanically active regions, but this study demonstrated tidal measurements rather than those future applications.

Young explorerGravity can make clocks tick a tiny bit faster or slower. Scientists connected very precise clocks far apart in Europe and compared their ticking. As the Moon and Sun helped make tides, the clocks changed their ticking in the way scientists expected. They could pick out that tiny change within one day. In the future, even better clock networks might help notice changes when the ground moves or material shifts around, but that is not what they tested here.

Seven Years of TESS Precovery Observations of the Dwarf-planet Candidate 2026 ED₁₃₈

Te Han, Jeroen Audenaert, Daniel Muthukrishna+2 more

• Instrumentation and Methods for Astrophysics

Astronomer2026 ED138, a trans-Neptunian object announced in October 2026 as Rubin Observatory's first discovered dwarf-planet candidate, is recovered in five month-long TESS sectors spanning 2019–2026, four predating discovery. The authors subtract Gaia DR3 stars using TGLC, remove static residuals with a running median, and stack images along the predicted trajectory. They report detections of 5–21 sigma per sector and 34 sigma combined. TESS astrometry alone confirms the JPL orbit. The measured brightness is consistent with, rather than an independent demonstration of, the expected 0.08 mag fading from increasing distance and changing phase angle; dwarf-planet status remains a candidacy.

PublicAstronomers recovered the distant solar-system object 2026 ED138 in five sets of TESS images taken between 2019 and 2026, including four taken before its discovery. Announced in October 2026, it was the first dwarf-planet candidate discovered by the Vera C. Rubin Observatory, not a confirmed dwarf planet. To reveal it in crowded images, the researchers removed starlight and other lingering background features, then combined images along its predicted path. They detected it in all five sets. Its positions in the TESS images independently confirm the JPL orbit, and its brightness agrees with the slight fading expected as its distance and viewing angle changed.

Young explorerAstronomers found a faraway object called 2026 ED138 in old pictures from a space telescope named TESS. Most of those pictures were taken before anyone discovered it! They cleaned away the light of stars and put pictures together to spot the faint object. The pictures confirm its path around the Sun. Its brightness also fits the small fading they expected as it moved farther away and we saw it from a different angle. It might be a dwarf planet, but that is not certain.

The dark surface of (163693) Atira and implications for inner-Earth asteroid origins

Bryce T. Bolin, Carl Ingebretsen, Robert Jedicke+8 more

AstronomerAtira's radar-derived diameter of 4.9 km and absolute magnitude H_V ≈ 16.4 imply a very low geometric albedo, p_V ≈ 0.02. ARC 3.5-m/ARCTIC photometry gives a* = −0.05 ± 0.03 and a g-to-i spectral slope of 3.4 ± 0.9% per 100 nm. The reflectance favors a provisional X-type classification; the low albedo additionally supports a Tholen P-type interpretation. NEOMOD3 assigns approximately 66% probability to delivery through inner Main Belt channels and 26% to central and outer Main Belt channels. Its albedo-category probabilities for Atira are 0.07 ± 0.02 below p_V = 0.1, 0.64 ± 0.04 for 0.1 ≤ p_V < 0.3, and 0.29 ± 0.04 at p_V ≥ 0.3. Thus, Atira's inferred low albedo is an uncommon outcome under the model. Across 38 inner-Earth objects, inner Main Belt delivery generally dominates and intermediate albedo is favored for 33. Dark inner Main Belt material or more distant primitive populations remain compatible origins, not established source identifications. Further characterization is needed to test modeled compositional diversity.

PublicThe asteroid Atira appears much darker than the most likely surface category assigned to it by a population model. Its radar-measured width of 4.9 kilometers, combined with its brightness, implies a very low reflectivity. New color measurements favor a tentative X-type classification; together with the dark surface, they support a more specific P-type interpretation. The NEOMOD3 model assigns only about a 7% probability to Atira's low-reflectivity category and about a 66% probability that it arrived through routes from the inner Main Belt. These are model estimates, not a directly observed history. Among 38 inner-Earth asteroids, the model favors intermediate reflectivity for 33. Atira could represent dark material delivered from the inner Main Belt or from more distant primitive populations; further studies will test how well the model captures this variety.

Young explorerAtira is a space rock that goes around the Sun inside Earth's path. Scientists used its size and brightness to work out that it is very dark. A computer model says a rock like Atira would more likely be less dark. The model also suggests where it might have come from, but that is not certain. Studying more space rocks will help scientists check their ideas.

TEMPEST - A modular Python-based thermophysical model for rough, irregularly-shaped airless bodies

D. G. Lyster, C. J. A. Howett

• Instrumentation and Methods for Astrophysics

AstronomerTEMPEST is a modular, open-source Python model of diurnal thermal evolution on irregular, airless bodies. It treats non-Lambertian multiple scattering with arbitrary bidirectional reflectance distribution functions and represents sub-facet roughness using sphere-section geometry. It provides explicit one-dimensional periodic conduction and semi-implicit Crank-Nicolson solvers, with support for alternative thermal solvers. Precomputed scattering tables and parallelisation support calculations from thousands to more than 100,000 facets. The authors report good agreement with Thermprojrs in one dimension, Sorli's Binary Thermophysical Model in three dimensions, and Lunar Reconnaissance Orbiter thermal data, without quantifying agreement in the abstract. A simulation using a high-resolution shape model of 25143 Itokawa highlights the importance of self-shadowing and mutual radiative heating for local temperatures. TEMPEST has already supported analyses of Lucy, Galileo, and ground-based data; use with upcoming mission datasets is a prospective capability.

PublicTEMPEST is a new, freely available computer model for calculating how surface temperatures change over a day on irregularly shaped worlds without atmospheres. It accounts for rough ground, different ways surfaces reflect light, shadows, and heat exchanged between nearby parts of a surface. The authors report that its calculations agree well with two existing models and with thermal measurements from the Lunar Reconnaissance Orbiter, although the abstract gives no numerical measure of that agreement. In a simulation of the asteroid Itokawa, shadows and heat radiated between surface areas strongly influenced local temperatures. The tool has already been used to analyse spacecraft and ground-based observations and could also support future mission datasets.

Young explorerScientists made a computer tool called TEMPEST to work out how warm or cold places get on rocky worlds with no air. It includes shadows, bumpy ground, and heat that one patch sends to another. Its answers matched other computer tools and Moon measurements well, the scientists report. A computer test of an asteroid showed that shadows and nearby warm patches matter for its temperature.

Mapping Stellar Obliquity Across Space and Time

Lauren I. Biddle, Brendan P. Bowler

AstronomerThe study compares stellar and orbital inclinations for 114 single Sun-like stars across four samples spanning different ages and orbital separations. Minimum misalignment rates are 33% (+7/−6 percentage points) for 49 protoplanetary disk systems, 21% (+9/−7) for 24 debris disk systems, 23% (+10/−8) for 21 warm Jupiter systems, and 20% (+9/−8) for 20 hot Jupiter systems. All rates agree within 1σ, and the minimum-obliquity distributions show no significant variation with orbital separation or system age. These findings suggest, but do not establish, that obliquities are largely set during formation. Later inclination evolution could instead be infrequent, small, or concentrated in unexamined regimes, including close stellar companions, hot host stars, small planets, and long-period giant planets.

PublicA star’s spin can be tilted relative to the paths of its planets or the disk around it. Researchers compared these orientations in 114 single stars similar to the Sun, studying systems with planet-forming disks, debris disks, or giant planets on different-sized orbits. The minimum fractions showing misalignment ranged from about 20% to 33%, but the differences were not statistically significant. The study also found no significant change in the minimum tilts with system age or orbital distance. This suggests that much of the tilt may be established when systems form, rather than developing later. It does not rule out later changes that are uncommon, small, or occur in types of systems outside this study.

Young explorerA star spins like a top, and planets travel around it. Sometimes the star’s spin is tilted compared with the planets’ paths or the disk around the star. Scientists looked at 114 stars like our Sun. They did not find a clear difference in the tilts when they compared younger and older systems, or things closer to and farther from the star. Maybe these tilts mostly start when stars and planets are born. But some tilts could still change later, and this study did not check every kind of system.

Magma Buoyancy Couples Lunar Mantle Convection and Magmatism: Long-Lasting Mare Volcanism and Radius Change in a 3-D Regional Model

Ken'yo U, Masanori Kameyama, Takatoshi Yanagisawa+2 more

• Geophysics

AstronomerA 3-D regional spherical-shell mantle convection model with magmatism explores the Moon’s observed volcanic and radius-change histories. In the simulations, internal heating produces a basal partially molten layer within the first several hundred million years. Finger-like magma ascents develop into partially molten plumes, sustained by magma buoyancy and additional decompression melting. Magma delivery to the mantle top peaks 4–3.5 billion years ago, coinciding with maximum melting-driven radial expansion; both subsequently decline as the mantle cools and solidifies. Thermally softened conduits left by earlier plumes allow repeated ascent at fixed locations for billions of years, with recycling of uppermost-mantle magmatic products also triggering renewed ascent. The authors attribute conduit stability to the 3-D geometry. The model offers a mechanism for prolonged localized volcanism and quantitatively accounts for early expansion followed by contraction. Matching the observed history requires an initially hot but mostly solid mantle with a dense basal layer.

PublicResearchers used a three-dimensional computer model to investigate why volcanic activity on the Moon lasted billions of years in localized areas, and why the Moon first expanded and later contracted. In the simulation, heating creates a partly melted layer deep inside the Moon. Rising magma develops into plumes that generate more melt as they ascend. The modeled magma supply peaks between 4 and 3.5 billion years ago, matching the observed volcanic peak, while melting also drives expansion. As the interior cools, magma supply and expansion decline. Earlier plumes leave warm, softened pathways that later plumes repeatedly follow, helping sustain localized activity. The model provides a possible explanation, rather than a direct observation of the Moon’s interior. Matching the observed history requires a starting mantle that was hot but mostly solid, with a dense layer at its base.

Young explorerThe Moon had volcanoes long ago. Scientists made a computer model to explore how they could keep going in the same places for a very long time. In the model, melted rock rises and leaves warm paths that more melted rock can follow later. Melting also helps the Moon grow a little before it cools and shrinks. This is a possible explanation, not something scientists watched happening inside the Moon.

Breccia and basalt classification of thin sections of Apollo rocks with deep learning

Freja Thoresen, Aidan Cowley, Romeo Haak+4 more

• Instrumentation and Methods for Astrophysics
• Machine Learning

AstronomerThe study presents a machine-learning framework for classifying lunar rock thin sections using Apollo petrographic images acquired in plane-polarized, cross-polarized, and reflected light at varying magnifications. Contrastive learning fine-tunes a pretrained Inception-ResNet-v2 network with the SimCLR loss to extract image features. A binary classifier trained through transfer learning achieves a reported accuracy of 98.44% (±1.47) in distinguishing breccias from basalts. This result concerns thin-section image classification; assisting astronauts with in-situ sample selection is a proposed application, not a demonstrated capability.

PublicResearchers developed a computer method to distinguish two types of Moon rock, breccias and basalts, using images of thin rock slices from the Apollo missions. They adapted an existing image-analysis network to learn useful features, then trained a classifier that achieved a reported accuracy of 98.44% (±1.47). The longer-term aim is to help astronauts choose scientifically valuable samples on future lunar missions. The reported result is for thin-section images, not a demonstration of astronauts using the tool on the Moon.

Young explorerScientists taught a computer to look at pictures of very thin slices of Moon rocks brought back by Apollo astronauts. It learned to tell two kinds of rock apart and got the answer right almost every time in the study. The scientists hope tools like this could help astronauts choose rocks to bring home someday, but they have not shown that this tool can do that on the Moon.

The Atacama Cosmology Telescope: Release of A databaSe of millimeTeR ObservatioNs of Asteroids Using acT (ASTRONAUT)

Ricco C. Venterea, John Orlowski-Scherer, Nicholas Battaglia+8 more

• Instrumentation and Methods for Astrophysics

AstronomerASTRONAUT is a public database of asteroid millimeter-wave flux measurements collected by the Atacama Cosmology Telescope from 2017 to 2021 in bands centered near 90, 150, and 220 GHz. Hosted in an Amazon S3 bucket, it provides observation times, normalized fluxes, and associated uncertainties for 170 asteroids with signal-to-noise ratios above 5 in at least one frequency band in the stacked, co-added maps. This selection threshold refers to the combined maps, not necessarily individual observations. The authors demonstrate light-curve generation and provide a reference Jupyter notebook, with the container and notebook publicly available through GitHub.

PublicThe authors present ASTRONAUT, a public collection of measurements of asteroid brightness at millimeter wavelengths. The Atacama Cosmology Telescope collected the observations between 2017 and 2021 in three frequency bands. The database contains observation times, scaled brightness measurements, and their uncertainties for 170 asteroids selected for sufficiently strong signals in combined observations. The paper gives an example of using the data to track brightness over time, along with a notebook explaining how to access the cloud-hosted collection. This is a data release and usage guide, rather than a report of a new physical conclusion about asteroids.

Young explorerA telescope measured how bright some space rocks looked in a kind of light our eyes cannot see. Scientists shared measurements for 170 of these rocks so other people can use them. They also shared instructions showing how to make a chart of a rock’s brightness over time. The measurements are not perfectly exact.

Saturn's Evolutionary History and Seismology: Survival of Deep Stably Stratified Regions in Evolutionary Models of Saturn Consistent with Ring Seismology

Yubo Su, Janosz W. Dewberry, Roberto Tejada Arevalo+2 more

AstronomerThis study explores initial conditions for Saturn evolution models that, after 4.56 Gyr, yield structures with oscillation frequencies consistent with those inferred from ring seismology. Restricting the models to interiors without compact rocky cores, the authors obtain good simultaneous agreement with most observed planetary properties, at the level of current evolutionary models, and key observed oscillation frequencies. Preliminary results suggest a moderately less extended stably stratified region, approximately 0.4–0.5 Saturn radii, than previously inferred. They also tentatively suggest that the deep helium gradients inferred in earlier static structural models may not be necessary to reproduce the seismic data.

PublicOscillations detected through Saturn’s rings provide clues to the planet’s hidden interior. The researchers tested computer models of Saturn’s evolution over 4.56 billion years, considering only models without a compact rocky core. Their models agree well with most observed properties of Saturn and with key oscillation frequencies, within the capabilities of current evolutionary models. The preliminary results suggest that an interior region resistant to mixing may extend less far than previously thought, to roughly 40–50% of Saturn’s radius. They also tentatively suggest that the deep changes in helium abundance inferred by earlier models may not be needed to explain the ring-based observations. These are modeling inferences, not direct measurements of Saturn’s interior.

Young explorerSaturn’s rings show clues about how the planet wiggles, helping scientists guess what is hidden inside. Scientists made computer versions of Saturn and let them grow old to see which ones matched those clues. They only tried versions without a small, tightly packed rocky center. Some matched many things we observe about Saturn. These early results hint that a layer inside Saturn where material does not mix easily might be smaller than scientists thought. Big changes in how much helium gas is deep inside might not be needed either. Scientists are not sure yet.

Detection and characterization of the temperate super-earth Gliese 48 b

G.Conzo, M.Moriconi, S.A.Corrêa Jr

AstronomerA re-analysis of CARMENES and decade-long HIRES radial velocities identifies Gliese 48 b around a magnetically active M3.5V dwarf with a 51.5-day rotation period. The planet has P = 39.6299 ± 0.29 days and M sin i = 8.11 ± 1.63 Earth masses; its composition is undetermined. The authors attribute the signal to a planet based on coherence over 15 years and achromaticity between visible and near-infrared channels. TESS photometry shows no transit at the orbital period. Injection-and-recovery tests indicate that a hypothetical 1287 ppm transit corresponding to a minimum radius of 1.69 Earth radii would be detectable at SPNR > 7, supporting the reported high-confidence exclusion of a transiting geometry and inclination constraint i < 89.3 degrees; this is not a radius measurement. With incident flux about 0.889 times Earth's, the planet lies near the inner edge of the Conservative Habitable Zone and within the Optimistic Habitable Zone. This placement motivates astrobiological interest but does not establish habitable surface conditions.

PublicAstronomers report a planet orbiting the active red dwarf Gliese 48 every 39.6 days, with a minimum mass about eight times Earth's. They identify it through changes in the star's measured motion: the signal persists over 15 years and agrees between visible and near-infrared observations, supporting a planetary explanation. TESS observations found no dip in starlight from the planet crossing the star. Tests with an artificial transit signal suggest that a crossing planet at the minimum size considered would have been detected, so the authors conclude with high confidence that the orbit does not produce transits. The planet receives about 89% as much stellar energy as Earth and falls within one definition of the habitable zone, near the inner edge of a more conservative definition. Its composition remains unknown, and the habitable-zone designation does not show that it actually supports life or habitable conditions.

Young explorerAstronomers found signs of a planet going around a small red star called Gliese 48. One trip around its star takes about 40 days. They found it by watching the star wobble, not by seeing the planet itself. They did not see the planet pass in front of the star, and tests suggest they would have noticed such a crossing. The planet gets a little less energy from its star than Earth gets from the Sun. That makes it interesting to study, but we do not know what it is made of or whether anything could live there.

TransitNet: A Compact Attention-Augmented Deep Learning Framework for Low-SNR Transit Blind Searches

Xingchen Yan, Jian Ge, Qingtian Liu+3 more

• Instrumentation and Methods for Astrophysics
• Artificial Intelligence
• Machine Learning

AstronomerTransitNet is a compact, attention-augmented deep-learning framework for low-SNR blind transit searches, accompanied by a unified dataset, benchmarking, and threshold-calibration framework. On recovery benchmarks using unseen Kepler targets, it achieves 95.2% accuracy at SNR 6–8, with ROC-AUC 0.974 and PR-AP 0.982, outperforming TLS and BLS. For injected Earth-size and sub-Earth-size transits, recovery is 93.0%, versus 63.1% for TLS and 60.0% for BLS. Its estimated transit windows fully cover 97.4% of injected transits in an independent evaluation set. In real Kepler observations, it recovers all 34 selected confirmed planets, with a mean absolute midpoint error of 1.24 hours. The approximately 1.5 MB model yields inference speed-ups of about 12–25 times over CPU-TLS and 4–5 times over CPU-BLS. These results establish performance in the tested regime; extension to longer-period Earth-size searches is motivated, not demonstrated.

PublicThe researchers present TransitNet, a small artificial-intelligence model designed to find faint dips in starlight caused by planets passing in front of their stars. In tests with artificially added signals representing Earth-size and smaller planets, it recovered 93.0%, compared with 63.1% and 60.0% for two comparison methods. In real Kepler observations, it also recovered all 34 previously confirmed planets selected for testing; these were not new discoveries. The model estimates when each crossing occurs, with an average absolute timing error of 1.24 hours for those confirmed planets. It also ran faster than the CPU-based comparison methods. The results support its usefulness under the tested conditions, but searches for Earth-size planets with longer orbital periods remain a future extension.

Young explorerWhen a planet moves in front of its star, the star can look a little dimmer. Scientists made a computer helper called TransitNet to look for these tiny dips. They tested it with pretend planet dips added to star measurements, and it found more of them than two other search methods. It also found the signals of all 34 already-known planets chosen for a test using real star measurements. That does not mean it found new planets. The scientists hope to use it to look for Earth-size planets that take longer to go around their stars, but they have not shown that yet.

Addressing Exoplanetary Degeneracies Through Geometry: Application to Asynchronously Rotating Systems

Mradumay Sadh

• Instrumentation and Methods for Astrophysics

AstronomerThis modelling study extends the geometry-based irradiance code InstellCa to InstellCa--2, computing longitude-averaged instellation at a given planetary latitude and the corresponding effective-temperature profile. It treats the planet as a three-dimensional, asynchronously rotating body, accounting for the changing stellar zenith angle and resulting diurnal cycle. Case studies of 55 Cancri e and the TRAPPIST-1 system illustrate how relative rotation and extreme stellar proximity can affect estimated effective temperatures. Asynchronous rotation of 55 Cancri e is a prior hypothesis, and its atmospheric status remains debated; the examples do not establish either rotation states or atmospheric detections. The analysis permits physically feasible Bond albedos excluded under a synchronously rotating bare-rock assumption and suggests that appropriate geometry can reduce degeneracies among modelled atmospheric states.

PublicThe study updates a computer model to calculate how much starlight reaches different latitudes on a planet and what effective temperatures that implies. It considers planets whose rotation is not synchronized with their orbit, so the star changes position in their sky and produces a day–night cycle. Using 55 Cancri e and the TRAPPIST-1 system as examples, the researchers explore how this geometry can matter for planets very close to their stars. In the model, accounting for the changing angle of starlight allows physically plausible fractions of reflected light that would be ruled out if the planet were assumed to be a synchronized, airless rock. This could help distinguish between possible atmospheric models, but it does not establish that these planets rotate asynchronously or possess atmospheres; the existence of an atmosphere on 55 Cancri e remains debated.

Young explorerThe researchers improved a computer model of how a star shines on a nearby planet. They tried planets that turn so their star moves across the sky, making day and night. Their model shows that the angle of the light can change how warm we calculate different parts of a planet to be. Getting that angle right could help scientists work out whether a planet has air around it, but this study does not prove that it does.

Resolving power of effective rheologies of planetary interiors with an application to the Moon

Yeva Gevorgyan

AstronomerThis study develops a local interpretation of equivalent homogeneous rheologies by differentiating the layered-to-homogeneous mapping at fixed geometry, varying selected layer rigidities and viscosities. A pole-residue representation of the degree-two Love number yields a physical-to-effective transfer matrix; singular values, resolution, and mode dominance diagnose which physical perturbations are distinguishable and how they map into effective parameters. In a five-layer lunar model, the full degree-two response is sensitive to seven of eight solid-layer rheological parameters. The near-null direction is inner-core rigidity, consistent with shielding by the fluid outer core. Fewer physical directions remain visible over the LLR frequency interval, where an elastic spring, an isolated dashpot, and two Voigt elements reproduce the nine-pole response to first order. Finite-perturbation tests agree with the tangent prediction within a few percent, but a nearly degenerate pair of long-timescale modes limits the approximation's validity range. These are model-based, local sensitivity results, not observational determinations of lunar layer properties.

PublicCalculating how tides deform a planet with many internal layers can be costly, so researchers often replace those layers with a simpler mathematical model. This study develops a way to connect small changes in that simpler model to changes in the stiffness and resistance to flow of individual layers. In a five-layer model of the Moon, the full calculated tidal response is sensitive to seven of eight tested material properties. Inner-core stiffness has very little influence, consistent with the surrounding liquid core shielding its effect. Over the more limited frequency range relevant to lunar laser ranging, fewer combinations of interior properties can be distinguished. A simpler spring-and-damper representation reproduces the detailed response to first order over that range. Tests with finite changes agree with the small-change prediction within a few percent, but the approximation has limits. The findings describe what the model can reveal, rather than measurements of the Moon's interior.

Young explorerImagine a pretend Moon made of layers that can bend and slowly change shape when tides tug on them. Working out what every layer does takes lots of calculating. The researchers made a simpler version using pretend springs and parts that resist motion, then checked which layer changes it could show. In their Moon model, changing the stiffness of the very middle made almost no difference, which fits with the liquid layer around it hiding its effect. The shortcut worked well for the small changes they tested, but it cannot reveal every layer detail or handle every size of change.

The EMA Justitia Probe: Terminator Frame-Based Deployment Orbit Selection and Surface Coverage Analysis

Shamil Biktimirov, Fatima Alnaqbi, Anton Ivanov

• Instrumentation and Methods for Astrophysics

AstronomerThis mission-design study evaluates imaging during the EMA probe’s proposed uncontrolled ballistic descent to (269) Justitia, rather than reporting flight observations. The concept uses near-terminator deployment geometry with continuous Sun visibility and either single-axis Sun-spin for periodic imaging or three-axis asteroid-pointing for continuous asteroid visibility. Deployment requirements account for uncertain gravity and release trajectory, main-spacecraft proximity operations, illumination, and safe operations. A selection method based on the terminator reference frame and a minimum boresight deviation margin identifies orbit-orientation families satisfying illumination and observation constraints. Reference orbits are checked through geometry analysis and trajectory propagation with a polyhedron gravity model; surface coverage is evaluated for uncontrolled tumbling, Sun-spin, and asteroid-pointing. These analyses support the concept’s feasibility and characterize expected imaging performance, without establishing actual flight performance. The approach is also proposed for future ballistic probes with similar constraints.

PublicResearchers have developed and tested a plan for the Emirates Mission to the Asteroid Belt probe to photograph the asteroid Justitia while descending toward it without controlling its flight path. The challenge is to keep sunlight available and the camera suitably aimed despite uncertainty about the asteroid’s gravity and the probe’s release trajectory. The proposed release geometry lies near the boundary between the asteroid’s day and night sides. The probe could spin with an axis pointing toward the Sun, giving periodic chances to take pictures, or control its orientation to keep the asteroid continuously in view. Computer-based trajectory and viewing analyses assess suitable release orbits and compare surface coverage under these modes and uncontrolled tumbling. The results suggest that close-up imaging is feasible under the modeled conditions; they are predictions from mission planning, not pictures or measurements obtained during a descent.

Young explorerScientists are planning how a small space probe could take pictures while falling toward a space rock called Justitia. They need sunshine to stay in view and the camera to look the right way. One plan lets the probe spin and take pictures when the rock comes into view. Another keeps the probe turned toward the rock. The team used computer models to check the plan because they are not sure exactly how the rock will pull on the probe or how the probe will be released. The tests suggest the picture-taking plan could work, but the probe has not shown this by doing it yet.

Proposed optimal targets for a Lazuli ExtraSolar Coronagraph reflected starlight exoplanet campaign

Logan A. Pearce, Ewan Douglas

• Instrumentation and Methods for Astrophysics

AstronomerThe paper proposes 27 known giant exoplanets as a potential optimal initial target list for visible reflected-light observations with the ExtraSolar Coronagraph (ESC) on the announced 3-m Lazuli Space Telescope. Reflected-light imaging can probe atmospheric composition in mature systems without the age dependence of thermal emission and can access closer separations at visible wavelengths. The proposed sample spans planetary ages and temperatures not previously explored by direct imaging. Some targets are also expected to be accessible to the Nancy Grace Roman Coronagraph and ELT-METIS thermal imager, offering complementary atmospheric characterization. The authors discuss prospective ESC science and improvements from future astrometric and radial-velocity measurements; the abstract reports target selection, not new atmospheric detections.

PublicThe authors identify 27 already-known giant planets that could be promising first targets for the announced Lazuli Space Telescope. Its ExtraSolar Coronagraph is designed to observe visible starlight reflected by giant planets, helping scientists study what their atmospheres contain. This approach can investigate mature planets and planets closer to their stars than imaging their heat allows. The proposed list covers ages and temperatures not previously explored through direct planet imaging. Some targets could also be studied with the Roman Coronagraph and the ELT-METIS heat-sensitive imager, providing complementary views of their atmospheres. These are proposed observations and scientific opportunities, not newly measured atmospheres.

Young explorerPlanets can shine by bouncing back light from their stars. Scientists picked 27 giant planets that a planned space telescope might look at this way. The light could help them learn what is in the air around those planets. Other telescopes could help study some of them, too. This is a list of planets to try looking at, not a report of what the telescope has already seen.

Identifying Scientifically Interesting Galaxies with Vision-Language Models

Yixuan Cheng, Nolan Koblischke, Jo Bovy

• Astrophysics of Galaxies

AstronomerThe study evaluates whether pretrained vision-language models can rank galaxy images by scientific interest from natural-language instructions, without labeled examples or training on the target data. In a 20,000-image Hubble Space Telescope sample containing 167 reference anomalies previously identified by machine learning and expert inspection, Gemini 3.1 Flash-Lite ranks 98.2% of those anomalies within the top approximately 2,000 images. The reported present-day inference cost is about $5.05 per 10,000 images. The search recovers known gravitational lenses, jellyfish-galaxy candidates, and galaxies with visible jets, and releases 102 high-scoring candidates for further investigation. These results support the model's practical use for prioritizing scientific relevance rather than statistical rarity in this sample; the released candidates are not presented as confirmed discoveries.

PublicThe strangest-looking galaxy pictures are not always the most scientifically useful. This study tests whether an existing AI model can use written instructions to pick out images worth astronomers' attention, without being trained on examples from the collection. Among 20,000 Hubble Space Telescope images, the model placed 98.2% of 167 previously identified unusual objects in its highest-ranked roughly 2,000 images. Its reported processing cost is about $5.05 per 10,000 images at current prices. It picked out known gravitational lenses, possible jellyfish galaxies, and galaxies with visible jets. The researchers also released 102 promising candidates for closer study, not confirmed new discoveries. The test suggests AI could help astronomers decide which images to investigate first.

Young explorerAstronomers have lots of galaxy pictures, and they want to find the ones worth a closer look—not just the ones that look the strangest. Researchers asked an AI helper to sort 20,000 pictures by how interesting they might be for science. It put almost all of the unusual objects people had already found near the top of its list. The researchers also shared 102 promising picks to check more carefully. Those picks might be interesting, but they are not confirmed new discoveries yet.

NORI: a GPU-accelerated code for simulating self-gravitating and self-interacting dark matter

Oliver Zier, Ruediger Pakmor, Xuejian Shen+4 more

AstronomerNORI is a CPU/GPU N-body code for isolated self-gravitating systems with elastic, isotropic dark-matter self-interactions sampled by a Monte Carlo method. It targets the computationally demanding gravothermal collapse of SIDM cores. Replicated particle data and Morton-ordered trees avoid MPI communication during tree walks, while a fixed evaluation order yields bitwise-identical CPU and GPU results. Sequential scattering conserves pair momentum and energy to round-off and permits multiple scatterings per particle per step. With global time-steps, NORI is several times faster on CPUs than the authors’ AREPO-2 implementation; a four-A100 GPU node is up to 60 times faster per step than a 112-core CPU node running AREPO-2. For full collapse runs, with AREPO-2 using individual time-steps, the reported speed-up is about 30 to reach central densities of 10^3–10^4 times the NFW scale density. The authors follow a halo with 10^8 particles within r200 to 10^4 times that scale density. These are simulation and performance results, not observational evidence for SIDM. Data replication limits the code to about 2 billion particles; its intended applications include isolated SIDM collapse and cluster collisions.

PublicIf dark matter particles interact with one another, a dark-matter halo can develop a central core that later collapses to much higher density. Following this possible evolution in a computer is difficult because the shrinking core requires many simulated particles and increasingly short time-steps. The researchers present NORI, a simulation program that runs on CPUs and GPUs and produces bit-for-bit matching results on both. In their tests, a node with four A100 GPUs ran individual time-steps up to 60 times faster than their comparison program, AREPO-2, running on a 112-core CPU node. The advantage was about 30-fold for a full core-collapse calculation to the reported density range, where AREPO-2 used a different time-stepping approach. NORI followed one halo containing 100 million particles within its specified outer radius as its central density reached 10,000 times a reference halo density. These results demonstrate a computational tool, not a detection of dark-matter interactions. Its need to keep copies of all particle data limits it to about 2 billion particles.

Young explorerScientists made a computer program called NORI to explore what might happen if bits of dark matter could bump into each other. In these pretend worlds, the middle of a dark-matter cloud can squeeze into a much denser clump. That gets harder for a computer to follow as the clump shrinks. NORI can do these calculations much faster than another program in the researchers’ tests. They used it to follow a cloud made of 100 million pretend particles. This helps scientists study an idea about dark matter; it does not show that real dark matter actually behaves this way.

Focal plane modal estimation of high-order wavefront drifts on coronagraphic testbeds

Saikrishna Manojkumar, Susan F. Redmond, Leonid Pogorelyuk+4 more

AstronomerThe authors present modal dark zone maintenance (MDZM), a focal-plane high-order wavefront sensing and control algorithm intended to address slow thermal and mechanical wavefront drifts relevant to HWO imaging of exo-Earths 10 orders of magnitude fainter than their host stars. An Extended Kalman Filter estimates drift in the deformable-mirror actuator basis using probe-pair images across the full focal plane, yielding mirror commands without Electric Field Conjugation or its regularization parameter. MDZM was demonstrated in simulations and on NASA JPL’s Decadal Survey Testbed; the experiments maintained normalized intensity near 3 × 10^-10 for over 36 hours and narrowed the gap to photon-derived theoretical bounds relative to DZM. Estimates of naturally occurring testbed drift suggest potential system-identification capabilities. The study also scans exposure time and drift rate on the testbed. Previous hardware demonstrations used 2.5% bandwidth; the authors additionally compare 10%-bandwidth and narrowband sensing in FALCO simulations based on the testbed. The abstract reports no outcome for that comparison, and the simulated bandwidth remains below the 20% anticipated for realistic HWO observations.

PublicDirectly photographing Earth-like planets is difficult because they can be 10 billion times fainter than their stars. Small, slowly changing distortions in a telescope’s light can spoil the dark region needed to reveal such planets. The researchers developed an algorithm that estimates these distortions from images and calculates corrections for a deformable mirror. In simulations and laboratory hardware tests, they demonstrated the method; the experiments kept normalized intensity, a measure relevant to suppressing unwanted light, near 3 × 10^-10 for more than 36 hours. The method also performed closer to a theoretical limit set by the available photons than the earlier approach. These are testbed results, not observations of planets with the future Habitable Worlds Observatory. Earlier hardware tests used a narrow range of wavelengths. The team also simulated a broader range, but the abstract gives no performance outcome for that comparison, and the simulated range is still narrower than expected for HWO observations.

Young explorerImagine trying to see a very faint little planet beside a dazzling star. Tiny changes in a telescope can let unwanted light sneak into the dark place where scientists want to look. The researchers made a computer helper that uses pictures to work out how to adjust a bendy mirror. In laboratory tests, it helped keep that place very dark for more than 36 hours. They also tried it in computer simulations. This does not mean they have taken a picture of an Earth-like planet with the future telescope. They are still testing how the helper works with a wider mix of light.

Experimental Demonstration of Double-Fourier Interferometer Imaging for Future Space-Based Far-Infrared Observatories

Jeremy P. Scott, Locke D. Spencer, Chris Benson+4 more

AstronomerThis study validates key double-Fourier interferometry techniques in a laboratory testbed operating over 0.3–2.1 THz, rather than through astronomical observations. A DFI combines spatial interferometry with Fourier transform spectroscopy to enable high-resolution broadband spectral imaging. After accounting for intensity imbalances, nonlinear phase errors, and phase-center offsets, the experiments demonstrate aperture synthesis of one- and two-dimensional targets with accurate geometry recovery. A low-pass optical filter applied to extended sources tests sensitivity to spatially dependent spectral variations. Combining independent detector-array pixels sampling different source-plane regions also demonstrates wide-field imaging. Measurements agree closely with theoretical predictions; minor discrepancies are attributed to optical aberrations and perspective effects. The authors interpret these laboratory results as evidence that DFI is a capable, mature architecture for future space-based FIR observatories, not as a demonstration of an operating space instrument.

PublicFar-infrared astronomy helps study star formation, active galactic nuclei, and systems where planets form, but limited image sharpness makes this difficult. Researchers tested a proposed instrument approach that combines spatial and spectral measurements to produce sharper images while distinguishing different wavelengths. In laboratory experiments—not observations of space—the instrument recovered target shapes, detected spectral differences across extended targets, and combined measurements from detector pixels viewing different regions to image a wider field. Results closely matched theory, with small differences attributed to optical imperfections and viewing geometry. The authors see this as support for using the technology in future space observatories.

Young explorerScientists tested a special picture-making machine in a laboratory. It uses light our eyes cannot see. It could work out the shapes of test objects and tell when different parts had different kinds of light. Its pictures mostly matched what scientists expected. They hope this kind of machine can help future space telescopes see more clearly.

Model of the instrumental polarization induced by a rotating HWP with anti-reflective sub-wavelength structures for CMB polarimetry

Ryota Takaku, Hiroaki Imada, Guillaume Patanchon+1 more

• Cosmology and Nongalactic Astrophysics

AstronomerThis computational study uses rigorous coupled-wave analysis to characterize a multilayer sapphire half-wave plate (HWP) with anti-reflective sub-wavelength structures (SWS), targeting HWP-synchronous instrumental polarization in future primordial CMB B-mode searches. Across three asymmetric SWS models, the calculations show no substantial differences in transmittance, polarization efficiency, or instrumental polarization attributable to asymmetry type. Fourth-harmonic instrumental polarization is typically of order 10^-4 in the CMB bands; mitigation is expected, not demonstrated. The authors also evaluate the response of an actually fabricated SWS geometry, whose asymmetry enhances retardance, and compare it with an idealized model of the same asymmetry type. Higher transmittance tends to accompany lower instrumental polarization in this comparison, suggesting that improving total transmission while accounting for the fabricated profile may matter more than tuning SWS asymmetry itself.

PublicFuture experiments seeking a primordial polarization pattern in the cosmic microwave background need to avoid false signals introduced by their equipment. This study calculates how a rotating sapphire optical component, called a half-wave plate, behaves when its surface has tiny anti-reflective structures. Three models with different kinds of structural asymmetry show no substantial differences attributable to the asymmetry type. The calculated false-polarization component most relevant to reconstructing the sky signal is typically about 10^-4 in the relevant frequency bands. The researchers expect it can be reduced, but do not demonstrate that reduction here. They also calculate the response of a geometry that was actually fabricated and compare it with an idealized version. Their results suggest that making the component transmit more light, with attention to its manufactured surface shape, may be more useful for reducing false polarization than adjusting the kind of asymmetry alone.

Young explorerScientists want to study a special pattern in very old light from space. A spinning sapphire piece helps them, but it can also add a tiny pretend pattern. The scientists used computer calculations to try different shapes of very small bumps on the sapphire. Changing how the bumps were uneven did not make much difference in those tests. Their calculations suggest that letting more light through might help shrink the pretend pattern more than changing the unevenness. They expect the tiny unwanted pattern can be reduced, but they have not shown that here.

Characterisation of the ILMT 4K x 4K TDI CCD imager

Gokul singh Mehra, Bhavya Ailawadhi, Talat Akhunov+10 more

AstronomerThe study measures the gain and read-out noise of the 4K×4K CCD on the 4-m International Liquid Mirror Telescope, which operates in Time Delay Integration mode because the telescope points at the zenith. Two methods use non-uniformly illuminated rising-twilight frames: one measures flux variance along rows with minimal horizontal gradients despite a strong vertical gradient; the other analyses flux-ratio variations between regions with similar background illumination. A derived linear variance–mean-flux relation yields a gain of approximately 3.9 electrons/ADU with both methods. Bias frames independently give a read-out noise of 1.55 ADU, or about 6 electrons. These measurements characterize detector performance and support accurate calibration.

PublicResearchers measured how the electronic camera on the 4-m International Liquid Mirror Telescope converts collected electric charge into image values, and how much noise is introduced when those values are read out. Because the telescope points straight overhead, its camera uses a special image-acquisition mode called Time Delay Integration. The team tested two ways to measure the camera’s response using images taken as the twilight sky brightened, despite uneven lighting across the images. Both methods found about 3.9 electrons of charge per digital image unit. Separate measurements using bias frames found read-out noise equivalent to about 6 electrons. Knowing these quantities helps researchers calibrate the camera’s images accurately.

Young explorerA telescope has a big camera that takes pictures of the sky. Scientists used pictures taken while the sky was getting brighter to check how the camera turns light into numbers. They tried two ways, and both gave about the same answer. They also measured a little extra fuzziness the camera adds when it reads a picture. These checks help scientists understand the pictures better.

PyMsOfa 2.0: A Pure-Python Implementation of the IAU Standards of Fundamental Astronomy Service

Dongjie Tan, Jianghui Ji, Jiacheng Liu

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerPyMsOfa 2.0 replaces the earlier Python wrapper around the SOFA C library with a pure-Python, NumPy-based implementation of all 247 official SOFA routines. Constants, series, and coefficients are unchanged from the SOFA sources, and routine names differ only by a pym prefix. The authors report verification of every routine against the official C release: most agree to machine precision, while the remainder meet the tolerances specified in the SOFA documentation. NumPy-array inputs support batch processing for survey pipelines and Monte Carlo simulations, without compiling an external C library; the package is reported to run identically on Linux, Windows, and macOS. An extension module includes validated models outside the official SOFA release, including IAU 2006_J2/2000A_R26 precession–nutation. Reported applications include Gaia astrometric reduction and CHES astrometric studies. The package is available through PyPI, GitHub, and Zenodo.

PublicAstronomers need dependable calculations to work out positions in the sky. This paper presents PyMsOfa 2.0, a Python implementation of all 247 routines in the International Astronomical Union’s SOFA standards library, whose official versions are released only in Fortran and C. Unlike the earlier Python package, this version does not depend on compiling an external C library and can process groups of inputs together. The authors tested every routine against the official C version: most matched to the precision of computer arithmetic, and the others stayed within SOFA’s stated accuracy limits. The package also offers validated models that are not yet included in the official SOFA release. It has been used in Gaia data processing and studies for the CHES mission. This is a software release and verification report, rather than a new astronomical discovery.

Young explorerAstronomers use computer recipes to help work out where things are in the sky. The authors made a new Python toolbox with all 247 recipes from a standard astronomy library. It can work on many sets of numbers together. They checked every recipe against the standard C version: most answers matched as closely as computer arithmetic allows, and the others were within the standard’s allowed limits. The toolbox also has some checked extra recipes that are not yet in the official set. This paper is about making and checking a tool, not finding a new star or planet.

Shock detection in meshless finite mass hydrodynamic schemes

Ludwig M. Böss, Frederik Groth, Klaus Dolag+1 more

AstronomerThe authors present initial efforts to implement a shock-finding algorithm with shock-surface reconstruction for meshless finite mass (MFM) hydrodynamics. Identifying overlapping and colliding shocks amid complex shear flows remains challenging in cosmological structure-formation simulations, and fully Lagrangian methods have historically performed less well in this respect than Eulerian or pseudo-Lagrangian approaches. The algorithm's accuracy is assessed against analytic predictions and a legacy SPH-based shock finder. Applied to cosmic structure-formation simulations, it yields improved predictions for shock energy dissipation and cosmic-ray acceleration. These are simulation-based predictions, not observational measurements; the abstract gives no quantitative accuracy or improvement estimates.

PublicShock waves help turn the energy released as cosmic structures form into heat, turbulent motion, magnetic fields, and accelerated particles. They are difficult to identify reliably in computer simulations, especially when shocks overlap or collide within complicated flows. The researchers present early work on a new method for locating shocks and reconstructing their surfaces in a particular type of simulation. They test its accuracy against mathematical predictions and an older shock-finding method, then apply it to simulations of cosmic structure formation. They report improved predictions of how shocks dissipate energy and accelerate cosmic rays, but the abstract does not say how large the improvements are. These findings concern simulations rather than direct observations.

Young explorerWhen things come together in space, they can make strong waves called shocks. These waves can heat space gas and speed up tiny particles. The scientists made a new tool to find the waves in computer models, even when the waves bump into each other. They checked the tool against math predictions and an older tool. They say it helps their models better predict what the waves do with energy and tiny particles. This is work with computer models, not something they watched happen in space.

lenscape: Fast, High-resolution Δχ² Maps of Microlensing Events

Michael Hippke

• Earth and Planetary Astrophysics

AstronomerThe author presents lenscape, an open-source Python package for accelerating Δχ² mapping over binary-lens separation s and mass ratio q in planetary microlensing analyses. Such maps identify degenerate solutions and constrain parameter uncertainties, but require light-curve optimization with finite-source magnifications at every grid point. The package uses multi-stage neighbor propagation and adaptive contour refinement to accelerate mapping and suppress local-minimum artifacts. For MOA-2022-BLG-091, it reproduces the published 50×50 map in 14 minutes and generates a 400×400 map in under two hours on a desktop computer. These reported performance results concern this event; the abstract does not establish performance across a broader sample.

PublicA new open-source Python program, lenscape, speeds up a demanding step in analyzing planetary microlensing events. Researchers compare many possible models of a star-and-planet lens, mapping how well different separations and mass ratios fit the changing brightness. These maps help reveal alternative explanations and uncertainty, but calculating them can be slow. The software passes information between neighboring models and refines selected map regions to speed the work and reduce misleading features caused by fits getting stuck. In a demonstration using MOA-2022-BLG-091, it reproduced a published 50-by-50 map in 14 minutes and made a finer 400-by-400 map in under two hours on a desktop computer. The abstract reports this demonstration, not a test across many events.

Young explorerScientists study how a star and its planet bend light to learn about them. They try lots of possible answers and make a map showing which ones fit best. A new computer program called lenscape helps make these maps faster and reduces some mistakes in the search. In one test, it remade an earlier map in 14 minutes and made a much more detailed map in less than two hours. That test shows what it did for one case, not how fast it will be every time.

UnEZ: A Fully Unsupervised Self-Templating Neural Network for Redshift and Line Strength Estimation

Asha Abd, Karl Glazebrook, Colin Jacobs

• Astrophysics of Galaxies
• Machine Learning

AstronomerUnEZ is a fully unsupervised, physics-informed neural network that estimates spectroscopic redshifts and line strengths without training templates or redshift or line-strength labels. Its encoder predicts emission- and absorption-line amplitudes and widths; a fixed deterministic decoder produces an object-specific template, redshift estimate, redshift confidence curve, and spectral model. Tested on SDSS Data Release 18 against its independently vetted redshift catalog, UnEZ achieves an outlier fraction of 0.459% and NMAD of 1.237 × 10^-4 at SNR > 10, and 3.89% and 1.471 × 10^-4, respectively, at SNR > 3. The authors report performance competitive with modern redshift algorithms and demonstrate using the predictions to construct templates for traditional methods. These results establish performance on the tested dataset; scalability to future surveys is a claimed advantage rather than a demonstrated future-survey result.

PublicUnEZ is a machine-learning system that estimates galaxy redshifts and the strengths of features in their light spectra without being trained on labeled answers or supplied template spectra. Redshift and spectral features emerge from a model guided by physics. The researchers tested it on Sloan Digital Sky Survey Data Release 18, using the survey's checked redshift catalog as an independent benchmark. For spectra with signal-to-noise ratios above 10, the reported fraction of outlying redshift estimates was 0.459%; with a lower threshold of 3, it was 3.89%. The authors report that its performance competes with modern redshift-estimation methods. They also show how its outputs can build templates for other methods. The approach is intended to help handle larger future surveys, but those future applications were not tested here.

Young explorerLight from a galaxy has a pattern, a bit like a rainbow with marks in it. Scientists made a computer program called UnEZ that uses rules from physics to learn from these patterns without being given the answers first. It estimates how much the pattern is shifted toward red and how strong its marks are. The scientists checked its guesses against a carefully checked list from a big sky survey. It did well, especially when the light patterns were clearer, but some guesses were still far off. They hope it can help study even bigger collections of galaxy light.

SuperCrude EoS: A Simple, Analytical, and Reasonably Accurate Equation of State for Astrophysical Fluid Dynamics

Paul C. Duffell, Dillon Hasenour

• High Energy Astrophysical Phenomena
• Solar and Stellar Astrophysics

AstronomerSuperCrude is a simplified equation of state for explosive astrophysics, using compact, physically motivated analytic approximations instead of interpolated data tables. Code tests show accuracy comparable to helmeos over large regions of parameter space, but effective adiabatic-index errors reach a few percent where degeneracy, gas, and radiation contributions are comparable. Temperature estimates are less accurate, with errors of tens of percent. The analytic formulation is designed to guarantee exact thermodynamic consistency. Hydrodynamic and astrophysical tests include a simulated thermonuclear white-dwarf explosion. When coupled to a stiff nuclear network, SuperCrude does not reproduce helmeos nucleosynthetic yields, motivating further improvement of its temperature accuracy.

PublicThe researchers present SuperCrude, a simplified mathematical description of how matter behaves under the extreme conditions involved in stellar explosions. It replaces detailed lookup tables with compact formulas. Computer tests show that it matches the accuracy of an existing method, helmeos, across a broad range of conditions, but not everywhere: one measure of how matter responds to compression has errors of a few percent in some regimes, while temperature errors are tens of percent. The formulas are designed to keep thermodynamic relationships exactly consistent. Tests include a simulated explosion of a white dwarf star, not an observed explosion. When paired with calculations of nuclear reactions, SuperCrude produces different amounts of newly formed elements than helmeos does, highlighting the need to improve its temperature estimates.

Young explorerScientists made a simpler set of math rules to help computers pretend that a star is exploding. The rules worked about as well as a more detailed set in many tests, but they were not as good at telling how hot the pretend star was. When the computer also worked out how the explosion makes different kinds of atoms, the two sets of rules gave different answers. The scientists want to make the temperature part better.

Flow-based neural networks for scalable high resolution imaging of VLBI observations

Lev Kats, Alexey Goldin, Andrey S. Andrianov

AstronomerThe authors use the WaveletFlow neural-network architecture to address the computational scaling of Bayesian interferometric imaging as the number of reconstructed features increases. The method increases the pixel count in the recovered image distribution and is applied to model data, archival RadioAstron observations of M87, and ALMA observations of HL Tau. The authors report individual-image fidelity comparable to CLEAN while providing more statistical information. They suggest this additional information may benefit future studies of compact sources such as active galactic nuclei; the abstract gives no quantitative performance or computational-cost comparisons.

PublicReconstructing detailed astronomical images from interferometer observations can require expensive calculations, especially when researchers want to describe the range of images consistent with the data. The authors used a neural network called WaveletFlow to increase the number of pixels in these reconstructions. They tested it on model data and existing observations of M87 and HL Tau. They report image quality comparable to the CLEAN method, but with more statistical information about the possible reconstructions. That information may help future studies of compact astronomical objects, although the abstract does not quantify the improvement or computing costs.

Young explorerScientists use telescope data to work out what things in space look like. This team tried a computer tool that can make pictures with more tiny picture dots and show different pictures that could fit the data. They tested it with made-up data and real telescope observations. They say its pictures look about as good as those from a method called CLEAN, but it gives more information about the possible pictures. They think that could help scientists study small-looking things far away in space.

The Korean Space Telescope (KST): A Dedicated Space Observatory for the Dark Universe

M. James Jee, Ho Seong Hwang, Dongwook Lim+14 more

• Cosmology and Nongalactic Astrophysics
• Earth and Planetary Astrophysics
• Astrophysics of Galaxies
• High Energy Physics - Experiment

AstronomerThe abstract presents the Korean Space Telescope (KST), a planned 1.4-meter wide-field space observatory dedicated to dark-sector studies, rather than reporting observational results. Its single instrument would combine diffraction-limited visible imaging at approximately 0.15 arcsec with simultaneous near-infrared slitless spectrophotometry. Spectral information would depend on source brightness, ranging from full R ~ 100 typing for bright sources to synthetic medium-band or broadband photometry for fainter ones, without separate NIR follow-up. A proposed 2,000 deg² Wide survey and 10 deg² cluster-targeted Deep survey would combine weak lensing, baryon acoustic oscillations, and a NIR-standardized Type Ia supernova Hubble diagram, targeting a pivot dark-energy equation-of-state uncertainty of sigma(w_p) ~ 0.03. Additional goals are to map dark matter from cluster cores to galactic substructure to test cold, warm, and self-interacting dark-matter models, and to construct a deep NIR host catalog for distance-ladder-independent H_0 inference from gravitational-wave dark sirens. The same observations would support galaxy evolution, AGN, exoplanet, and Milky Way science. KST is presented as Korea’s first dedicated astrophysics space mission, complementary to Rubin, Euclid, and Roman.

PublicThe Korean Space Telescope is a planned space observatory designed to investigate dark energy, dark matter, and the universe’s expansion. It would take sharp visible-light images while simultaneously collecting near-infrared information about each detected source, with more detailed spectral information available for brighter objects. Its proposed survey combines a broad view of the sky with deeper observations aimed at galaxy clusters. Researchers intend to combine several ways of measuring cosmic expansion and the growth of structure to test dark-energy models, and to map dark matter to compare competing explanations of its nature. A catalog of galaxies that might host gravitational-wave events would also support an independent measurement of the universe’s expansion rate. These are proposed capabilities and scientific goals, not discoveries already made. The observations would additionally serve studies of galaxies, active galactic nuclei, exoplanets, and the Milky Way, complementing other major observatories.

Young explorerScientists are planning a space telescope called KST. It would take sharp pictures of space and collect light our eyes cannot see. They hope to learn about invisible matter and the mysterious dark energy linked to how the universe expands. It would look across a big patch of sky and look more deeply at some groups of galaxies. The same pictures could help scientists study stars, galaxies, and planets around other stars. These are things the telescope is meant to do, not things it has already discovered.

Tabular Foundation Models Dramatically Outperform Bespoke Photometric Redshift Estimators

Biprateep Dey, Joshua S. Speagle

AstronomerOn a widely used photometric-redshift benchmark, tabular foundation models (TFMs) that predict full probability distributions in a single forward pass systematically outperform bespoke estimators under both representative and biased spectroscopic training regimes. Using only in-context learning with 1,000 training examples, they match or exceed baselines trained on more than 40,000 galaxies. The authors describe synthetic pretraining as providing a learned prior over regression problems. The advantage is greatest with little or no calibration data and persists when bespoke baselines receive up to 10,000 representative calibration spectra. These benchmark results support TFMs as a sample-efficient approach for future imaging-only surveys, with selection bias mitigated by including a small representative calibration sample in context; performance on those future surveys is not demonstrated here.

PublicEstimating a galaxy’s redshift, a proxy for its distance, from images usually requires examples with redshifts measured using spectra. Those examples are scarce and tend to favor bright, easily observed galaxies. In a benchmark test, researchers found that a type of pretrained AI model could estimate redshift probabilities using 1,000 examples as context, matching or beating specialized models trained on more than 40,000 galaxies. Its advantage held for both representative and biased training samples and remained even when competing models received substantial extra calibration data. The results suggest a way to make better use of limited spectroscopic data in future imaging surveys, including reducing selection bias with a small, representative calibration sample. The study tests a benchmark, not those future surveys.

Young explorerScientists want to use pictures to estimate how far away galaxies are. They help computers learn with galaxies whose distances have been checked another way, but those examples often favor the bright, easy-to-see ones. In a test, a computer model that had already practiced on made-up problems did as well as or better than special models while using far fewer galaxy examples. It also gave a range of possible answers instead of just one guess. This could help with future galaxy picture projects, though those projects have not been tested here.

Towards an Astronomical Use of New-Generation Geodetic Observations

Víctor Pérez-Díez

AstronomerThis thesis develops and applies a pipeline that converts VGOS correlator outputs into calibrated, full-polarization visibilities for astronomical imaging. It combines linear-to-circular polarization conversion, instrumental phase and amplitude calibration, and wideband global fringe fitting that accounts for dispersive ionospheric effects, followed by regularized maximum likelihood imaging. Applications to 1803+784 and five other AGN yield multi-frequency intensity and polarization images, frequency-dependent core shifts, spectral indices, and Faraday rotation properties. For 1803+784, the fitted core-shift index is k_r = 0.73 with uncertainties of +0.12 and -0.19, suggesting departures from a simple conical jet in energy equipartition. Applying reconstructed source models to geodetic observables reduces closure-delay scatter and post-fit residuals for strongly structured sources, particularly 3C418. The correction's effectiveness depends on source variability and the temporal proximity of the imaging observations.

PublicA radio telescope network designed to improve measurements of Earth's orientation and reference frames can also reveal details of active galactic nuclei. This thesis develops a method to calibrate observations from the VLBI Global Observing System (VGOS) and make images at multiple frequencies, including images of polarized radio emission. Applied to six active galactic nuclei, the method measures how the apparent core position changes with frequency, how the emission varies across frequencies, and how its polarization rotates. For the blazar 1803+784, the core-position measurements suggest that a simple conical jet model with equal energy in particles and magnetic fields may not fully describe the source. Using the reconstructed images to account for source structure also reduces scatter and residual errors in geodetic measurements, especially for 3C418. How well this works depends on changes in the source and how close in time the imaging observations are to the measurements being corrected.

Young explorerA team used a network of radio telescopes, built to help measure Earth, to make pictures of six bright centers of faraway galaxies. They made a new way to turn the telescope signals into pictures using different kinds of radio light. For one galaxy, the measurements hint that its jet is not quite like a simple model scientists use. The pictures also helped reduce some errors in measurements used to study Earth. But galaxies can change, so the pictures work better for this job when they are taken close to the same time as those measurements.

Search for Cosmic Rays in GRANDProto300

Jolan Lavoisier, Aurélien Benoit-Lévy, Kumiko Kotera+6 more

• High Energy Astrophysical Phenomena
• High Energy Physics - Experiment

AstronomerGRANDProto300 aims to validate autonomous radio detection of cosmic rays at 10^17–10^18.5 eV, enabling future study of the Galactic-to-extragalactic source transition. The array operated with 46 antennas from November 2024 through June 2025; 63 have collected data stably since July 2025. The presented search pipeline rejects temporally and spatially clustered noise and applies polarization, zenith-arrival, and expected-trigger-delay cuts. Its efficiency is evaluated using July–October 2025 data. A convolutional neural network identification layer remains under development to distinguish cosmic-ray signals from noise using signal traces. The authors present model accuracy following training on simulations and real cosmic-ray signal datasets, but the abstract gives no numerical efficiency, accuracy, or cosmic-ray detection yield.

PublicGRANDProto300 is testing whether an antenna array can autonomously identify radio signals from very energetic cosmic rays. The goal is eventually to help study the transition between cosmic rays originating within our Galaxy and those from beyond it. After operating 46 antennas from November 2024 to June 2025, the project has collected data steadily with 63 antennas since July 2025. The researchers describe a sequence of filters for removing noise and evaluate its effectiveness on July–October 2025 data. They are also developing an artificial-intelligence classifier trained with both simulated signals and real cosmic-ray signal datasets. The abstract does not provide performance figures or state how many cosmic rays the search identified.

Young explorerThis team uses special antennas to look for radio signals made by tiny, very energetic particles from space. Unwanted signals can get in the way, so the team is testing ways to sort them out. They are also teaching a computer to tell particle signals from noise, using both pretend signals made in simulations and real examples. The antennas are collecting data, but this short report does not say how many particles the search found or how well the sorting worked.

The Radio Neutrino Observatory in Greenland (RNO-G) - System Design and Instrumentation

Nils Heyer for the RNO-G Collaboration, Steven Barwick, AJ Nielsen

AstronomerThis instrumentation contribution outlines the RNO-G electronics chain, from antenna signals to recorded pulses. The observatory is designed to measure EeV cosmic neutrinos by detecting nanosecond radio flashes. New developments focus on electric melters for installing LPDA antennas in the Greenland ice sheet. The system is expected to simplify deployment and reduce positioning uncertainty to ±2 cm in x/y and ±1° in rotation. Field tests at Summit Station are reported, but the abstract gives no test outcomes establishing those positioning uncertainties.

PublicThe Radio Neutrino Observatory in Greenland is designed to detect extremely high-energy cosmic neutrinos through radio flashes lasting billionths of a second. This contribution describes how its electronics turn antenna signals into recorded pulses and introduces electric melting equipment for placing antennas in the ice. The new installation system is expected to make deployment easier and reduce uncertainty in antenna placement to ±2 centimetres horizontally and ±1 degree in rotation. The researchers report field tests at Summit Station, but the abstract does not say whether the tests achieved that precision.

Young explorerScientists in Greenland are building a way to look for tiny particles from space called neutrinos. Their antennas are meant to catch very quick radio flashes. They describe how the antennas' signals get recorded and new electric tools that melt ice to help put antennas in place. They expect these tools to make the job easier and help place the antennas more exactly. They report testing the tools in Greenland, but this short description does not tell us how well the tests worked.

Robust statistical significance for Gravitational Wave inference

Alexandre Sébastien Göttel

• General Relativity and Quantum Cosmology

AstronomerThe paper presents evidence networks that learn dataset distinguishability to infer Bayes factors for gravitational-wave model comparisons. It addresses the difficulty of calibrating Bayes factors without known noise-background distributions and the growing uncertainties and biases associated with using event-level nested-sampling outputs in population analyses. The authors report rates of up to 10^5 Bayes factors per second, enabling background distributions under different signal assumptions to estimate significance. They also demonstrate population-level inference using up to 10^4 events with no discernible bias in population quantities. These are methodological demonstrations, not reports of new astrophysical detections. The abstract highlights transient noise artifacts in at least 20% of gravitational-wave events as a concern for interpreting Bayes factors. The work lays foundations for a likelihood-free method without Gaussian, stationary-noise assumptions; it does not claim a completed demonstration of that broader capability.

PublicResearchers use Bayes factors to compare explanations for gravitational-wave signals, but these numbers can be difficult to translate into a clear measure of statistical significance. Noise can complicate their interpretation, and existing population-analysis methods can accumulate errors as more detections are included. This paper presents a machine-learning approach that calculates up to 100,000 Bayes factors per second, allowing researchers to build reference distributions for estimating significance under different signal assumptions. The authors report tests involving up to 10,000 events with no detectable systematic bias in population-level results. This is a demonstration of an analysis method, not a new discovery about gravitational-wave sources. Handling more general noise without the usual simplifying assumptions remains a direction the work lays foundations for.

Young explorerScientists study tiny wiggles in space, but unwanted noise can make them tricky to understand. This paper shows a fast computer helper that compares different explanations for the wiggles. In the authors’ tests, it could also study big groups of events without a noticeable one-way mistake in the group’s results. It is a new way to study signals, not a new space discovery, and more work is needed to handle noise more generally.

Preparation of a celestial field for precise VLBI observations of the JUICE spacecraft: a test case of the Venus flyby

Krisztina Perger, Sándor Frey, Giuseppe Cimò+11 more

AstronomerTo support PRIDE astrometry of JUICE around its August 2025 Venus gravity assist, the authors observed nine in-beam calibrator candidates and three nearby Radio Fundamental Catalog sources with the European VLBI Network at 8.4 GHz. Nodding phase-referencing observations tied source positions to nearby International Celestial Reference Frame sources through relative astrometry. Four in-beam candidates and all three catalog sources were detected and imaged, with coordinates determined at typically sub-milliarcsecond precision. None of the targeted in-beam candidates was suitable for VLBI phase referencing: they were too faint or spatially resolved. Their measured positions and flux densities could nevertheless, in principle, help verify a spacecraft detection during the Venus flyby; this is a potential use, not a demonstrated spacecraft-tracking result. The analysis also resolved milliarcsecond-scale structure in J0843+1826 and identified J0843+1814 as a young radio galaxy, likely belonging to a cluster.

PublicAstronomers tested distant radio sources as possible reference markers for tracking JUICE, the spacecraft launched in 2023 and due to reach Jupiter in 2031. In preparation for its August 2025 flyby of Venus, they used the European VLBI Network to observe nine candidate markers and three sources already listed in a radio catalog. They detected four candidates and all three catalog sources, measuring their positions very precisely. However, none of the nine candidates was suitable for the intended reference role because the sources were too faint or their radio emission too spread out. The measurements might still help confirm a detection of JUICE during the flyby, but the study does not demonstrate that use. The team also identified one candidate as a young radio galaxy that probably belongs to a galaxy cluster.

Young explorerJUICE is a spacecraft traveling to Jupiter. Scientists looked for faraway things that give off radio signals, hoping to use them like signposts to help track it near Venus. They found some and measured where they were, but none of the new signposts worked well enough: their signals were too weak or too spread out. The measurements might still help scientists check that they have spotted JUICE.

Identifying narrow-band mutual coupling resonances in SKA-low stations using frequency-independent current basis functions

John Cumner, Oscar S.D. O'Hara, Quentin Gueuning+3 more

AstronomerThe study presents a method for identifying narrow-band features caused by mutual coupling in aperture-array embedded element patterns, using singular value decomposition of frequency-dependent current basis functions to construct frequency-independent bases. Demonstrations cover a three-element linear array and a full pseudo-random station of SKA log-periodic antennas. The pseudo-random station exhibits numerous current resonances, notably at 50.8 and 83.6 MHz, where coupled power on passive antennas can approach or exceed that on the excited antenna. Simulated SKA-low core delay power spectra show substantial foreground leakage obscuring the EoR window when the observing band includes resonances. For the analyzed pseudo-random SKALA4.0 station, the bands 59.2–76.2 MHz and 84.2–103.3 MHz are identified as free of current-resonance contamination, preserving the EoR window in these simulations; this is not a claim that they are free of all observational contamination.

PublicClosely packed radio antennas can affect one another electrically, creating sharp features at particular radio frequencies. These features could interfere with efforts to detect the 21-centimeter signal from the early universe using SKA-low. The researchers present a mathematical method to identify these effects and apply it to two antenna arrangements. In the larger, irregular arrangement, some resonances transfer enough power to nearby antennas to rival or exceed the power on the antenna being driven. Simulations show that including such resonances in an observing band can spread foreground interference into the region where the early-universe signal is sought. For the particular SKALA4.0 station layout studied, the analysis identifies two frequency ranges, 59.2–76.2 MHz and 84.2–103.3 MHz, without contamination from these current resonances. This does not establish that real observations in those ranges would be free of other interference.

Young explorerRadio antennas listen to signals from space. When antennas are close together, they can make electrical wiggles in one another that could hide a faint signal from long ago. Scientists made a math tool to find these troublesome wiggles. Their computer tests showed how the wiggles could get in the way, and they found two radio ranges without this particular problem in the antenna arrangement they studied. That does not mean every problem is gone.

Temporal regularization of petal modes in SCAO systems: The Soft-Limiter approach

Guido Agapito, Jueqi Lin, Carmelo Arcidiacono+3 more

AstronomerThe authors propose an MMSE Soft-Limiter to control differential piston, or petal modes, in segmented ELT pupils, which visible-light pyramid wavefront sensors sense poorly under realistic residual turbulence. The deterministic controller combines a subspace MMSE estimator based on von Kármán priors with continuous temporal regularization, acting as a leaky integrator only on relative petal degrees of freedom. In end-to-end SPECULA simulations of ELT/ANDES, it confines differential piston within one fringe across 0.6–1.2 arcsec seeing, whereas a classical integrator loses lock and wanders across multiple fringes at seeing of 1.0 arcsec or worse. The simulations indicate bounded science-band impact under severe turbulence and preservation of optimal continuous-mode correction in good seeing, without the Strehl penalty associated with Edge Actuator Coupling. The derived and verified leakage-gain condition, g ≲ g_eff/π, allows the fast loop to retain genuine physical steps up to half the wavefront-sensing wavelength with small droop. A slower phasing sensor must resolve integer-wavelength ambiguities. The operating-window boundaries cross near 1.0 arcsec seeing; beyond this, preserving physical discontinuities falls entirely to the phasing channel. These are simulation results, not an on-sky demonstration.

PublicExtremely large telescopes use segmented mirrors, and their support structures divide the incoming light into separate regions. Differences in the alignment of light waves between these regions can be difficult for the telescope’s atmospheric-correction sensor to detect, allowing errors to build up and blur images. The authors propose a lightweight controller that restrains these poorly measured differences while preserving correction of other distortions. In computer simulations of the ELT/ANDES system, the controller kept the errors within one interference cycle across the tested atmospheric conditions; a conventional controller wandered across several cycles in stronger turbulence. This is not yet a demonstration on a real telescope. The method also has an important limitation: it cannot by itself determine offsets of whole wavelengths. A slower alignment sensor must resolve those ambiguities, and under stronger turbulence that sensor must also take full responsibility for preserving genuine wavefront steps.

Young explorerA giant telescope has a mirror made of pieces. Light from the different pieces needs to line up to make a clear picture, but wobbly air can make that hard. Scientists designed a new computer helper to stop some alignment mistakes from growing. It worked in a computer test, not yet a test on the sky. It still needs a second, slower helper to sort out some mistakes, especially when the air is very wobbly.

Model-Based Retrieval of Four Years of JWST/NIRCam Wavefronts

Shrishmoy Ray, Benjamin Pope, Louis Desdoigts+8 more

AstronomerThe authors present camino, an open-source NIRCam modelling and wavefront-inference algorithm built in JAX with dLUX differentiable Fresnel optics and regularised maximum likelihood inference, conditioned on the entire NIRCam wavefront-sensing archive. JWST currently obtains pairs of defocused reference-star images every few days and uses a closed-source phase-retrieval package to infer its wavefront. The authors report that camino typically reduces the reduced chi-squared of fits to these data from 60–65 to 12–13 and reconstruct JWST’s wavefront history from the start of science operations through early 2026. The implementation operates alongside the current STScI algorithm and supports integration of wavefront estimation into science-analysis workflows. Predictive, physics-based calibration that removes the need for contemporaneous dedicated reference-star observations remains an ultimate goal, not a demonstrated outcome.

PublicJWST regularly takes deliberately out-of-focus pictures of a reference star to check how its mirror surfaces and alignment affect incoming light. The authors introduce camino, an openly available program that models these images and estimates those optical effects. Using the telescope’s archive of NIRCam wavefront-sensing data, they report substantially better image fits and reconstruct how JWST’s optical performance changed from the start of science operations through early 2026. The program works alongside the existing closed-source system and makes this kind of analysis more accessible to researchers. The longer-term aim is to predict the corrections needed for science observations without taking dedicated reference-star observations at the same time; the abstract does not report that this goal has been achieved.

Young explorerJWST looks at a star and takes blurry pictures on purpose to check how its mirrors are working. The researchers made a new computer program that other people can use, too. It matches those blurry pictures better and uses old pictures to work out how the telescope’s mirrors have behaved over time. One day, tools like this might help scientists check the telescope without taking extra star pictures each time, but they have not done that yet.

posterior-landscape: morphological feature finding in two-dimensional probability densities

Michele Mancarella, Viola De Renzis, Alessandro Agapito

• High Energy Astrophysical Phenomena
• General Relativity and Quantum Cosmology
• Data Analysis, Statistics and Probability
• Computation

AstronomerThe authors present posterior-landscape, a Python framework for characterizing morphology in two-dimensional probability densities using topological data analysis, density-ridge estimation, and scale-space image analysis. It extracts localized concentrations, valleys, ridges, and slope changes. For Bayesian reconstructions, it propagates uncertainty in feature recovery, geometry, and correspondence across posteriors. It also links two-dimensional structures to one-dimensional marginal features and quantifies correlations with other inferred parameters. The method is validated on controlled densities and demonstrated on gravitational-wave population reconstructions to identify and interpret features and assess their cosmological information. The resulting catalogues are intended to support future comparisons with predictions; the abstract reports no specific population feature or cosmological constraint.

PublicThe researchers introduce software that searches two-dimensional probability maps for patterns such as peaks, valleys, and ridges. These maps represent possible values of quantities being inferred, rather than direct pictures of objects. For Bayesian analyses, the software tracks uncertainty in whether patterns are recovered, their shapes, and how they correspond across maps. The team tested the method on controlled examples and demonstrated it on gravitational-wave population reconstructions, assessing which patterns could provide information relevant to cosmology. Its catalogues are also intended to help compare theoretical predictions with reconstructed populations in future work; no particular cosmological finding is reported in the abstract.

Young explorerImagine a map where hills show more likely answers and valleys show less likely ones. Scientists made a computer tool to find these shapes and keep track of how unsure they are about them. They tested it on practice maps and used it on maps from gravitational-wave studies. It could help them compare ideas about the universe.

Measuring Precipitable Water Vapor through Dual-Band GPS at Rubin Observatory

Anja Weyant, W. M. Wood-Vasey, Elana K. Urbach+2 more

AstronomerThe authors report the first six months of GNSS-derived precipitable water vapor (PWV) measurements at Rubin Observatory, monitored continuously since 2025 September 5. Atmospheric water vapor introduces wavelength-dependent extinction, particularly beyond 7,000 angstroms, requiring accurate per-observation transmission estimates for precision applications such as supernova cosmology. The analysis reproduced International GNSS Service results with high consistency, and the receiver was commissioned at Allegheny Observatory before relocation to Rubin. Mean PWV was 3.0 kg/m² in Southern Hemisphere spring and 5.4 kg/m² in summer. A clear daily variation, with an amplitude of 1.2–3.8 kg/m², was strongly correlated with east–west wind strength; this correlation does not establish causation. The authors conclude that their processing method achieves 0.9 kg/m² accuracy and 0.36 kg/m² precision, supporting continuous, high-temporal-resolution PWV monitoring for demanding LSST science.

PublicEven at Rubin Observatory’s dry site in the Chilean Andes, changing amounts of atmospheric water vapor absorb some of the light astronomers want to measure. The researchers used delays in navigation-satellite signals to monitor this water vapor around the clock. During the first six months, average water vapor levels were higher in summer than in spring, and there was also a clear daily cycle strongly linked to east–west wind strength. That link alone does not show that the wind causes the changes. The team reports an accuracy of 0.9 kg/m² and a precision of 0.36 kg/m² for its method. These measurements can help astronomers account for the atmosphere when making especially demanding observations, including those used to study the universe with supernovae.

Young explorerWater in the air can soak up some starlight before it reaches a telescope. Scientists at Rubin Observatory used signals from satellites to keep track of that water, day and night. They found more water in the air in summer than in spring, and the amount changed during the day too. Those daily changes were closely linked to changes in the wind, but that does not prove the wind caused them. Knowing how much water is overhead can help scientists understand the starlight they measure.

Tailoring Infra-Red Filters for Global Mapping of Enceladus' Thermal Environment

D. G. Lyster, C. J. A. Howett, N. E. Bowles+3 more

• Earth and Planetary Astrophysics

AstronomerThis initial feasibility and design study presents the proposed Enceladus Thermal Mapper (ETM), rather than new thermal observations of Enceladus. Building on instrument heritage from TechDemoSat-1, Mars Climate Sounder, and Lunar Trailblazer, ETM is intended to map surface temperatures, including winter polar temperatures as low as 45 K. The design uses a 384 × 288-pixel sensor, with a projected sampling of 80 m/pixel from a 150 km orbit around Enceladus. Such an orbit would enable continuous high-resolution thermal mapping, addressing the limited high-resolution flyby coverage obtained by Cassini from its Saturn-centric orbit. A digital model of the filter assembly was developed to optimise filters for thermal emission measurements. The intended scientific benefits are tighter constraints on global conductive heat loss, improved characterisation and context for the active South Polar Terrain, and better understanding of geological evolution and potential habitability; these remain anticipated benefits, not demonstrated observational results.

PublicResearchers describe an early design and feasibility study for the Enceladus Thermal Mapper, a proposed instrument to measure temperatures across Saturn’s icy moon Enceladus. Cassini identified the moon as an important target for studying potentially habitable environments because it has an underground ocean and active icy volcanism, but its orbit around Saturn limited detailed flyby coverage. The proposed mapper would instead orbit Enceladus, aiming for continuous, detailed temperature maps, including the extremely cold winter poles, where temperatures can fall to 45 kelvin. Its design targets 80 metres per pixel from an altitude of 150 kilometres. The team developed a digital model to help optimise filters for measuring heat emitted by the surface. If realised, the instrument could help scientists estimate how much heat escapes through the moon’s icy exterior and understand its active south polar region. This study reports instrument design work, not new temperature maps or evidence of life.

Young explorerEnceladus is an icy moon of Saturn with an ocean hidden underneath its ice. Scientists are designing a small tool that could travel around the moon and make maps showing which places are warmer or colder. They have made a computer model to help design parts of the tool, but it has not made these maps yet. The maps could help scientists learn how heat escapes from the moon and understand the active icy area near its south pole. They could also help us understand whether the moon might have conditions suitable for life, not tell us that life is there.

Energy-flux noise induced by imperfections of the Gaussian beam in the Li-Baker HFGW detector

Lin-Lin Yang, Hao Yu, Pan-Pan Wang+2 more

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study models Gaussian-beam imperfections in the Li-Baker high-frequency gravitational-wave detector as higher-order Laguerre-Gaussian (LG) modes and analytically derives their energy-flux noise-to-signal ratios. Higher-order co-polarized modes produce no tangential energy-flux noise at the optimal detection planes, phi = pi/2 or 3pi/2, whereas cross-polarized modes contribute non-negligible noise. Under representative parameters, an individual cross-polarized mode typically requires a power fraction below 10^-46 to keep noise below signal; LG_01 gives the strictest constraint, below 6.0 × 10^-49. Monte Carlo simulations suggest that the combined power fraction of multiple cross-polarized higher-order modes must remain below 10^-49. The authors propose polarization filtering to suppress these components while preserving the signal; this is theoretical noise-control guidance, not an experimental demonstration.

PublicThe paper calculates how imperfections in a laser beam could create unwanted noise in the Li-Baker detector for high-frequency gravitational waves. In the model, certain beam distortions with the same polarization as the intended beam produce no noise in the measured tangential energy flow at particular detection planes. Distortions with the other polarization, however, can overwhelm the signal unless their share of the beam's power is extraordinarily small. For the representative conditions studied, simulations involving several such distortions suggest a combined power fraction below 10^-49. The authors propose using a polarization filter to remove the troublesome components while preserving the signal, but the abstract reports calculations and simulations, not a successful experimental test.

Young explorerScientists studied a detector that uses a light beam to look for tiny ripples in space. Their calculations say some kinds of messy light could hide the signal, while other kinds would not add this noise at just the right places. They suggest using a special light filter to keep the helpful light and block the troublesome light. They have worked this out with math and computer tests, but have not shown here that the filter works in a real experiment.

Sequince: a modular sequential Monte Carlo toolkit

Michael J. Williams, Christian E. A. Chapman-Bird

• Computation
• Methodology

AstronomerThe paper introduces sequince v0.1.0, a modular Python toolkit for sequential Monte Carlo (SMC), which approximates sequences of probability distributions using weighted samples. Relevant to Bayesian inference and particle filtering, it provides composable weighting, resampling, mutation, transformation, and control steps, plus prebuilt samplers for tempered SMC, persistent sampling, and nested sampling via SMC. Core components follow the Python Array API standard and support NumPy, JAX, PyTorch, and CuPy for CPU or GPU analyses. Random-number control and checkpointing support reproducible workflows. This is a software and design description; the abstract reports no astronomical application or performance comparison.

PublicThe paper presents sequince, a Python software toolkit for a statistical approach called sequential Monte Carlo. This approach represents a series of probability distributions with collections of samples, giving some samples more weight than others. The toolkit offers reusable building blocks and ready-made sampling methods, allowing researchers to assemble different algorithms. It supports several numerical software libraries and can run analyses on CPUs or GPUs. Features for controlling random numbers and saving progress help researchers reproduce their work. The abstract describes the software's first version, rather than reporting a scientific discovery or demonstrating that it outperforms other tools.

Young explorerScientists sometimes use lots of possible answers to work out what might be true, giving some answers more importance than others. This paper introduces a computer toolkit called sequince that helps them do that. Its parts fit together like building blocks, so scientists can make different ways to explore the possibilities. It can also save their progress and help them repeat the same steps. The paper describes the toolkit, not a new discovery about space.

SPECTRUM: A Strategic Framework and Technical Blueprint for European Exascale Research Data and Compute Infrastructure

Sergio Andreozzi, Stefano Bagnasco, Florian Berberich+21 more

• Distributed, Parallel, and Cluster Computing

AstronomerThis paper summarises two SPECTRUM planning documents addressing the exabyte-scale data volumes anticipated from the HiLumi LHC, SKA Observatory and LOFAR 2.0 within the next decade, which the abstract states will exceed current infrastructure capacity. Based on shared evidence, the Technical Blueprint maps capabilities for a European compute and data continuum, consolidates gaps across high-energy physics, radio astronomy and related use cases, and recommends actions in eight technical areas. The Strategic Research, Innovation and Deployment Agenda (SRIDA) sets out thirteen priorities under four pillars, links them to investment areas and European funding instruments, and phases them against the facilities' timelines. The paper describes the documents' consultative method and expected impact; it reports a planning framework, not demonstrated infrastructure performance or astronomical findings.

PublicMajor particle-physics and radio-astronomy facilities are expected to generate exabyte-scale amounts of data within the next decade, exceeding what today's infrastructure can handle. This paper explains two SPECTRUM project documents that plan a European response. One maps computing and data capabilities, identifies gaps and recommends technical actions. The other organises research, innovation and deployment priorities, connects them to possible European funding, and lays out a schedule aligned with the facilities' timelines. These are recommendations and plans with expected benefits, not evidence that the proposed infrastructure has already been built or shown to work.

Young explorerBig science machines and radio telescopes are expected to make more information than today's computer systems can handle. A team called SPECTRUM made two plans to help Europe get ready. One says what computer help is needed, and the other sets out what to work on and when. This paper explains those plans and what the team hopes they will do. It does not say the new computer systems are already built.

On-ground calibration of the X-ray, gamma-ray, and relativistic electron detector onboard TARANIS

Yuuki Wada, Philippe Laurent, Damien Pailot+9 more

• Atmospheric and Oceanic Physics

AstronomerThe paper reports development, prelaunch validation, and calibration of XGRE, the X-ray, Gamma-ray and Relativistic Electron detector aboard TARANIS, designed to investigate lightning-associated terrestrial gamma-ray flashes and terrestrial electron beams. Each of its three sensors combined a LaBr3 crystal layer for X-ray and gamma-ray detection with two plastic-scintillator layers for electron and charged-particle discrimination. Calibration established photon energy ranges of 0.04–11.6, 0.08–11.0, and 0.08–11.3 MeV for XGRE1–3, respectively, with corresponding energy resolutions of 20.5%, 25.9%, and 28.6% FWHM at 0.662 MeV. Tests included thermal cycling and calibration with the sensors installed aboard the satellite before its launch on 17 November 2020. Calibration results validated a simulation model of XGRE and TARANIS; Monte Carlo calculations then yielded effective areas for X-rays, gamma rays, and electrons, and photon and electron responses across incident elevation and azimuth angles. These are instrument-calibration measurements and simulated responses, not reported observations of lightning-related events.

PublicResearchers developed and tested XGRE, a three-sensor detector aboard the TARANIS satellite, to study high-energy radiation and fast electrons associated with lightning. Each sensor used a crystal layer to detect X-rays and gamma rays, plus two plastic layers to help distinguish electrons and other charged particles. Before the satellite launched on 17 November 2020, laboratory tests measured the sensors’ energy coverage and how precisely they could measure photon energy. The team used those calibration measurements to validate a computer model of the detector and satellite. Simulations then calculated how effectively XGRE would detect radiation and electrons arriving from different directions. The abstract describes detector testing and simulated performance, rather than discoveries about lightning itself.

Young explorerLightning can be linked to invisible rays and very fast tiny particles. Scientists built a detector called XGRE to ride on a satellite and help study them. Before launch, they tested its three sensors to learn what they could detect and how well they measured energy. Then they used those tests to check a computer model and calculate how the detector would respond to rays and particles coming from different directions. This work was about checking the detector, not reporting what it saw near lightning.

NEXUS: Quick Release Notes

Ming-Yang Zhuang, Yue Shen, Junyao Li+6 more

• Astrophysics of Galaxies

AstronomerThis evolving document describes targeting, observing status, and Quick Data Release contents and caveats for the Deep tier of NEXUS, a JWST Cycles 3–5 Treasury survey near the North Ecliptic Pole spanning 2024–2028. The survey combines overlapping Wide (~400 square arcminutes) and Deep (~50 square arcminutes) tiers. Wide uses NIRCam/WFSS spectroscopy at 2.4–5 micrometers over three annual epochs, with six-band NIRCam imaging; its specified final spectral continuum sensitivity is S/N per pixel >3 at F444W <22.2. Deep is designed for NIRSpec MOS/PRISM spectroscopy at 0.54–5.5 micrometers of approximately 10,000 targets in total over 18 epochs at two-month cadence, with F200W and F444W imaging at each epoch. Deep observations began in May 2025. Both tiers also include parallel MIRI and additional NIRCam imaging. Regular quick releases provide Deep-tier imaging, MSA spectra, and vetted spectroscopic redshifts to support follow-up. The paper reports selected science cases, but the abstract gives no specific scientific findings.

PublicNEXUS is a James Webb Space Telescope survey near the north ecliptic pole, running during 2024–2028. It combines a wider survey with a smaller, deeper survey, collecting images and spectra—light separated by wavelength. The Deep survey is designed to observe about 10,000 targets in total across 18 observing rounds, spaced two months apart; those observations began in May 2025. Repeated visits provide observations of the same region at different times. This paper is an evolving guide to the Deep survey’s target selection, observing progress, and regularly released data, including images, spectra, and checked redshift measurements. It also explains limitations of the early releases and presents selected science examples, though the abstract does not describe specific discoveries.

Young explorerThe James Webb Space Telescope is looking at a patch of sky again and again. A project called NEXUS takes pictures and spreads light into different colors for scientists to study. One part of the project plans 18 rounds of looking, about two months apart, and started in May 2025. This paper tells scientists what the telescope has looked at, shares data they can use, and explains things they should be careful about. It does not tell us about a particular new discovery in this short description.

Operating the Fabry-Pérot systems of the European Solar Telescope in multi-aperture mode

G.B. Scharmer, M.G. Löfdahl, J. de la Cruz Rodríguez+5 more

• Solar and Stellar Astrophysics

AstronomerThe authors propose an optional multi-aperture mode for the European Solar Telescope (EST) to improve wide-field imaging before its multi-conjugate adaptive optics (MCAO) system is operational. Without MCAO, high-altitude seeing is expected to strongly suppress high-spatial-frequency signals across nearly the entire 1 arcmin science field, especially at low solar elevations and short wavelengths. Optically segmenting the 4.2 m aperture into six 1.4 m sub-apertures would reduce high-altitude wavefront errors to levels more reliably addressed by conventional ground-layer adaptive optics and image restoration, with the aim of sustaining image quality for spectropolarimetric time series. The proposed implementation uses low-cost camera-lens modifications in the three Fabry-Perot systems covering 380–860 nm, allowing rapid, independent switching between full- and multi-aperture modes. Simulations and reconstructions of simulated data demonstrate benefits, while an optical design supports feasibility; these are not on-sky performance measurements.

PublicEarth’s turbulent atmosphere can blur the fine details that the European Solar Telescope is designed to see, particularly when the Sun is low in the sky or observations use shorter wavelengths. The authors propose an optional way to divide the telescope’s light-collecting aperture into six smaller sections, making some of that atmospheric distortion easier to correct. The aim is to keep images consistently sharp across a broad view of the Sun, helping scientists follow changes over time. The design would let the telescope switch quickly between its full aperture and the divided arrangement as conditions change. Computer simulations and image processing of simulated observations support the idea, and the authors present an optical design to show it is feasible. Its potential benefits have not been demonstrated with actual telescope observations in this study; it is intended especially for the period before the telescope’s planned wide-field atmospheric correction system is operating.

Young explorerAir moving above Earth can make a telescope’s pictures of the Sun look fuzzy. Scientists suggest giving a big solar telescope a choice: use its whole opening, or split it into six smaller openings so the fuzziness is easier to fix. They hope this will help keep pictures clear while they watch the Sun change. They tried the idea with computer-made pictures and designed how it could work, but this study does not show it working on the real sky.

FARSim: a fast RF-chain-aware trigger-screening surrogate for radio detection of ultra-high-energy cosmic rays

Xin Xu, Pengfei Zhang, Fufu Yang+3 more

AstronomerFARSim is a fast, physics-informed surrogate for screening radio-array layouts and triggers for ultra-high-energy cosmic-ray air showers. It reuses a reduced library of ZHAireS footprints, combining geomagnetic and charge-excess field decomposition, energy and geomagnetic-angle scaling, geometrical projection, contour-based core sampling, and event-rate integration. Of 1999 independent validation showers, 941 met predefined radial-support and station-count requirements; these yielded a median event-level relative RMSE of 9.4% and median Pearson correlation of 0.965 for reconstructed geomagnetic lateral profiles. A time-domain extension combines predicted three-component peak fields with geometry-dependent normalized pulse templates, allowing RF-chain propagation and voltage-threshold and L1-trigger diagnostics. Evaluated at the true peak amplitude, it achieved a median vector-waveform R² of 0.986 on 2112 traces excluded from pulse-shape fitting; this metric does not establish equivalent accuracy when using predicted amplitudes. These are simulation-based validations, not observational measurements. Absolute exposure predictions and detector commissioning still require full end-to-end simulations.

PublicDesigning radio arrays to detect particle showers caused by ultra-high-energy cosmic rays requires many costly computer simulations. FARSim speeds up early design comparisons by reusing a smaller collection of detailed simulations to estimate radio signals and test trigger settings. In an independent simulated test, 941 of 1999 showers met the method’s predefined coverage and station-count requirements. For those showers, reconstructed radio-emission profiles had a median relative error of 9.4% and closely tracked the detailed simulations. The researchers also extended the method to reconstruct how electric fields change over time and to examine the resulting detector voltages. Tests on 2112 separate simulated traces showed close waveform agreement, but used the true peak amplitude rather than testing the full amplitude prediction. FARSim is intended for rapid screening of designs, not as a replacement for the complete simulations needed to predict absolute detection exposure or commission a detector.

Young explorerVery energetic particles from space can make showers of smaller particles in the air. Those showers make radio signals. Scientists built a computer shortcut called FARSim to help compare different ways of arranging radio antennas and deciding when they should notice a signal. It learns from detailed pretend showers made by another computer program. In tests, it copied many of those signals quite well, but some tests only used showers that met special rules, and one test gave it the correct signal strength. It is a quick helper, not a replacement for all the detailed computer checks.

Setting requirements on out-of-band rejection for next-generation CMB experiments. Application to the LiteBIRD instrument

L. Mousset, L. Montier, J. Aumont+15 more

AstronomerThis modeling study derives out-of-band rejection requirements for LiteBIRD’s Medium and High Frequency Telescopes, motivated by the sensitivity needed to target cosmic microwave background B-mode polarization. The method models the instrument’s optical response and spectral emission from both the sky and the instrument to propagate optical power through the telescopes. It assesses effects on the detection chain, thermal heat load, and astrophysical component separation, considering both additional static power and dynamic power variations. The derived requirements are attenuation factors in decibels for frequency subdomains, intended to guide telescope filter design. The abstract gives no numerical requirements or measured filter performance.

PublicTo reach the sensitivity needed to study a particular polarization pattern in the cosmic microwave background, LiteBIRD’s telescopes must reject radiation outside their intended frequency ranges. This study uses models of the telescopes and radiation emitted by the sky and the instruments themselves to work out how strongly that unwanted radiation must be blocked. The researchers examine its effects on the detectors, heating, and the ability to separate different sources of sky emission, including both steady unwanted power and power that changes over time. They derive frequency-dependent blocking requirements to guide filter design; the abstract does not report numerical values or tests of finished filters.

Young explorerLiteBIRD’s telescopes need to study a special pattern in light from space. But light they do not want could get in, add heat, and make the job harder. The researchers used models to work out how much of this unwanted light the telescopes’ filters should block. Their work gives rules for designing those filters, rather than showing how finished filters work.

Environmental Noise Challenges for the Einstein Telescope - A Review

Matteo Di Giovanni

• General Relativity and Quantum Cosmology

AstronomerThis review surveys ongoing environmental-noise studies for the planned Einstein Telescope (ET), including site characterization, infrastructure design, and mitigation strategies under development. ET is designed with 10–15 km interferometer arms, underground infrastructure, and cryogenic technologies to suppress thermal noise. Its intended low-frequency coverage, starting at 2 Hz, would allow observation of earlier compact-binary inspiral phases, improving early warnings and multi-messenger follow-up. Environmental disturbances from human activity, seismic motion, and infrastructure are a particular concern at 2–10 Hz. The chapter outlines challenges and proposed mitigation approaches rather than reporting demonstrated ET performance.

PublicThe planned Einstein Telescope would detect gravitational waves from merging compact objects earlier in their approach, potentially giving other observatories more warning to look for accompanying signals. Its design combines long underground detector arms with very cold technology to reduce unwanted noise. But greater sensitivity also makes disturbances from ground motion, human activity, and infrastructure an important concern, especially at low frequencies. This chapter reviews work to understand those disturbances, choose and characterize suitable sites, and develop ways to reduce interference. These are design goals and ongoing studies, not results from an operating Einstein Telescope.

Young explorerScientists are planning a giant underground machine to notice tiny ripples in space. They hope it can spot pairs of objects moving toward a crash sooner, so other telescopes have more time to look. But shaking ground and nearby human activity could get in the way. This chapter explains how scientists are studying those problems and planning ways to keep the machine quiet enough to work well.

Unified matched-filter and excess-power pipeline for gravitational-wave detector characterization

Zach Yarbrough, Olivia Godwin, Derek Davis+1 more

Astronomersgnax is an open-source, Python-native detector-characterization pipeline that combines snax-style multi-rate sine-Gaussian matched filtering and omicron-style multi-resolution Q-transforms in one streaming graph, with shared configuration, ingestion, whitening, and output formats. Reported benchmarks show a 2.8-fold reduction in per-channel Q-transform processing cost when scaling from one to 32 channels. It processes one day of 16 kHz strain in 14 minutes; four processes sharing an NVIDIA V100 process 792 auxiliary channels at 1.11 times real-time throughput. The same configuration supports offline and online operation, with approximately five-second matched-filter latency and Q-transform latency of tens of seconds. Injection tests recover 99.4% of recoverable sine-Gaussian signals, with broadband burst recovery consistent with established generators. In 24 hours of LIGO strain, total trigger counts agree with production omicron to 0.1%, and per-trigger signal-to-noise ratios agree at the percent level across frequency bands. Auxiliary-channel comparisons recover 80% of the snax loud-feature population per time bin. Validation also identifies a multiband amplitude error in production snax that inflates reported signal-to-noise ratios below 25.6 Hz by factors of sqrt(2) to 2.

PublicThe researchers present sgnax, free, open-source software for characterizing gravitational-wave detectors by flagging brief features in detector data and related monitoring channels. It brings two existing analysis methods into one system that can handle both stored and incoming data. In reported performance tests, it processed a full day of the detector's main data in 14 minutes. Tests with added artificial signals recovered 99.4% of the sine-Gaussian signals classed as recoverable—not 99.4% of all possible signals. On a day of LIGO data, its total number of flagged features closely matched an established program, although a separate monitoring-channel comparison recovered only 80% of another program's loud-feature population per time bin. The checks also uncovered an error in that other program that exaggerated the reported strength of low-frequency features. These are software-validation results, not claims of new gravitational-wave discoveries.

Young explorerScientists made a computer tool to help check machines that listen for tiny ripples in space. It quickly marks little blips in the machines' recordings. When scientists added pretend blips to test it, the tool found nearly all the ones their test counted as findable. They also found a mistake in an older tool that made some blips look stronger than they were.

DINOspec: Efficient Multimodal Alignment of Vision and Spectral Foundation Models for Astronomy

Erica Lastufka, Mariia Drozdova, Daniel Schaerer+1 more

AstronomerDINOspec tests whether independently pretrained image and spectral representations can be aligned without retraining their encoders. It connects frozen DINOv3 and pretrained AION-1 encoders through lightweight adapters and contrastive learning using 20,472 paired astronomical images and spectra. Reported F1 scores improve from 0.72 to 0.78 for galaxy morphology classification and from 0.70 to 0.74 for spectral type classification, with as few as 21 million trainable parameters. Redshift prediction shows no consistent improvement over the AION-1 baseline of R² approximately 0.9. These empirical model evaluations support lightweight alignment as a way to combine separately learned representations, but its benefits depend on the configuration and downstream task.

PublicImages show what celestial objects look like, while spectra capture complementary information from their light. The researchers developed DINOspec to connect two existing AI models, one for images and one for spectra, without retraining their core components. Using 20,472 paired images and spectra, they trained small connecting modules. In their tests, this improved classification of galaxy shapes and spectral types. It did not consistently improve redshift prediction compared with the existing spectral model. The study shows that connecting specialized astronomy AI models can help with some tasks, but does not guarantee better performance on every task.

Young explorerScientists have one computer helper that studies space pictures and another that studies light split into different colors. They built a small connection so the helpers could use what each had learned, without teaching their main parts all over again. In tests, this helped sort galaxies by shape and sort their light patterns. But it did not help with every job they tried.

Wide Field Localization Using Fixed Modulation Collimators

Steven E. Boggs

• High Energy Astrophysical Phenomena

AstronomerThe authors develop a fixed modulation-collimator architecture for continuous, wide-field localization of gamma-ray bursts at hard X-ray and soft gamma-ray energies. Each bigrid comprises two aligned periodic slit grids ahead of a non-imaging photon-counting detector. Simultaneous measurements from grid pairs at fixed phase offsets recover source phase within a triangular transmission fringe; four-phase demodulation cancels detector background and grid leakage without mechanical rotation. A cascade of progressively coarser-pitched grid stages resolves the repeated-fringe positional ambiguity, extending the two-grid vernier technique previously used for Sco X-1. The authors describe this cascade as reducing photon-count and grid-calibration requirements for fine localization over a broad field. Orthogonal cascades extend the scheme to two dimensions. This is an instrument architecture, not a reported GRB localization result; the abstract provides no measured performance or numerical localization precision.

PublicThis work presents a design for locating gamma-ray bursts, brief flashes of high-energy radiation, across a wide area of sky without moving instrument parts. Pairs of slotted screens placed ahead of simple photon counters let through different amounts of radiation depending on its arrival direction. Comparing several counters at once can reveal that direction while canceling background contributions and radiation leaking through the grids. Because a repeating screen pattern can point to several possible locations, the design combines screens with progressively wider pattern spacing to distinguish among them. Two perpendicular sets would locate a source in two dimensions. The authors present the design as a promising route to simple, inexpensive instruments that continuously watch the sky, but the abstract does not report a working instrument's measured performance.

Young explorerThe researchers have a plan for finding where a bright flash in space comes from. Their space watcher would count tiny bits of light passing through screens with rows of narrow openings. Different screens would let through different amounts, giving clues about where the flash is. More screens would help sort out clues that look alike. Nothing would need to spin. This is a design idea, not a report that the watcher has already found a space flash.

Automatic astrometric calibration of low-cost all-sky cameras

J. R. González Fernández, Laura Hermosa Muñoz, María Fernández Alonso+1 more

AstronomerThe open-source Python package ascal performs all-sky astrometric calibration using a compact fisheye model, an exact rotation for camera tilt, and automatic star matching. Initialisation requires one image plus the observing site's coordinates and observation time. Tests on nine cloud-free, moonless frames from a Raspberry Pi camera with a 1.55 mm lens used eight-frame fitting and held-out evaluation in turn, yielding a median residual of 0.70 pixels across 4,172 matches, with a reported 95% interval of 0.64–0.80 pixels. Two optional decentering parameters reduced the median to 0.60 pixels. All nine single-frame calibrations passed the quality criteria and predicted positions in other frames with a median residual of 0.77 pixels. Applying the clear-sky calibration to 73 frames with varying moonlight or cloud cover yielded a 0.62-pixel median residual for accepted matches on moonlit frames; this does not establish equivalent performance for every cloudy frame. Single-frame calibration also succeeded for all 23 additional all-sky systems tested, spanning 0.3–77 megapixels and JPEG, FITS, and camera-raw formats, with a median fit residual of 0.42 pixels. Without refitting, second-frame tests across 18 systems yielded a median residual of 0.66 pixels. These results support calibration reuse provided camera geometry remains unchanged and enough stars remain visible for reliable matching.

PublicAll-sky cameras photograph a wide expanse of sky, but their images need calibration to connect pixel locations with positions in the sky. The researchers present free, open-source software called ascal that accounts for fisheye distortion and camera tilt, then automatically matches stars. It can start from one image when the camera's location and observation time are known. Tests on nine clear, moonless images produced typical position errors smaller than one pixel, including when predicting star positions in other images. The software also calibrated images from all 23 additional camera systems tested. Tests involving moonlight found similarly small errors for accepted star matches. The results support reusing a calibration, but only while the camera geometry stays unchanged and enough stars are visible; they do not demonstrate reliable matching through all cloud conditions.

Young explorerA camera that sees lots of the sky needs help knowing where the stars are in its pictures. Scientists made a computer tool that matches stars and works out their places. It worked on pictures from many cameras. The same setup can be used again if the camera stays the same and enough stars can still be seen.

Characterization of the CSST Survey Camera CCDs: I. basic electro-optical performance

Zun Luo, Hu Zhan, Youhua Xu+8 more

AstronomerThis first paper in a series reports ground-based electro-optical characterization of all 31 flight-model CCDs for the Chinese Space-station Survey Telescope (CSST) Survey Camera. All meet or exceed the camera specifications. Measured full-well capacity is at least 80,000 electrons, with the upper limit set by the test electronics; non-linearity is below 1.4% over 7,000–70,000 electrons. Median readout noise is 3.6 electrons, and dark current is at most 0.02 electrons per pixel per second at −85 °C. The detectors show high quantum efficiency across 255–1000 nm, typical pixel response non-uniformity below 1%, and charge transfer efficiency above 99.9994% at a flat-field signal of 10,000 electrons. These laboratory measurements establish a baseline and supply inputs for image simulations and data-processing pipelines; they are not on-orbit performance measurements.

PublicLaboratory tests show that all 31 CCD light detectors built for the Chinese Space-station Survey Telescope’s Survey Camera meet or exceed its specifications. The telescope is designed for a decade-long survey using sharp images in multiple wavelength bands and spectroscopy. The tests found low electronic noise, little unwanted signal generated inside the detectors at their operating temperature of −85 °C, and high efficiency at detecting light across the survey’s wavelength range. Each detector could hold at least 80,000 electrons of signal, but the testing electronics prevented the team from measuring the full capacity. These ground-based results provide a reference for future performance checks and inputs for simulated images and data-processing software; they do not establish how the detectors perform in space.

Young explorerScientists tested 31 light-catching chips made for a space telescope’s camera. All 31 passed the camera’s tests. When kept very cold, the chips made little unwanted signal and were good at catching light. The equipment used for testing could not find the chips’ biggest possible signal because it reached its own limit first. These tests happened on the ground, not in space. They will help scientists prepare to turn the telescope’s signals into pictures.

Propulsion Systems for a Starshade Rendezvous Mission with the Habitable World Observatory

Mario Damiano, Rhonda Morgan, Michael Turmon+2 more

• Earth and Planetary Astrophysics

AstronomerEnd-to-end EXOSIMS Monte Carlo simulations assess propulsion and operational limits for a proposed starshade rendezvous mission with an HWO-like telescope at Sun–Earth L2. The models use a 60 m starshade for 500–1000 nm spectroscopy and a 35 m starshade for 250–550 nm characterization. For the 60 m design with 1000–3000 kg of initial propellant and no refueling, NEXT ion propulsion yields 9–13% more characterizations than AEPS Hall propulsion and 13–16% more than a Starlink-class Hall option, owing to its higher specific impulse. With refueling, simulated yields converge to about 120 cumulative characterizations over 10 years; propulsion choice mainly changes the number of refueling events. The 35 m AEPS design is less fuel-sensitive and primarily limited by mission duration and geometric accessibility. Raising the minimum solar keepout angle from 40° to 50° has little effect on yield, and from 50° to 65° a modest effect; above 65°, yield declines rapidly, with severe degradation near 80°. These are simulated mission outcomes, not observed planet characterizations, and distinguish fuel-limited from time- or keepout-limited operating regimes.

PublicComputer simulations explore how a proposed starshade mission could help a telescope study Earth-like planets beyond our solar system. The study compares engines, fuel supplies, refueling, and restrictions on where the telescope–starshade system can point relative to the Sun. For a 60-metre starshade operating without refueling, the NEXT ion engine produces 9–16% more planet characterizations than the two other engine options tested, depending on the comparison. With refueling, all three options reach roughly 120 cumulative characterizations over a simulated 10-year mission; this is a count of characterizations, not necessarily distinct planets. For a smaller, 35-metre starshade, mission length and access to targets matter more than fuel supply. Requiring observations to stay increasingly far from the Sun’s direction eventually sharply reduces the simulated yield. The findings could guide mission design, but they are predictions from simulations rather than results from an operating mission.

Young explorerScientists used computers to try out plans for a space telescope and a big shade that could help it study planets around other stars. They tested different engines and how much fuel to carry. For the bigger shade, one engine let it do more planet studies before its fuel ran out. If it could get more fuel in space, the engines let it do about the same amount of studying. For the smaller shade, having enough time and being able to point toward the planets mattered more than fuel. These were computer tests, not a trip that has already happened.

Excursion-set structure factor of the auroral electric field

Magnus F Ivarsen, Kaili Song, Jean-Pierre St-Maurice+1 more

• Space Physics
• Geophysics

AstronomerThe study uses coherent E-region radar echo point clouds to separate spatial structure from temporal evolution in auroral electrodynamics, an ambiguity for a spacecraft crossing. Tracking echo clusters and Fourier-transforming motion-shifted echo pairs yields a dynamic structure factor that characterizes electric-field spatial power and persistence over 5–40 km where the radar look direction is perpendicular to the geomagnetic field. The inference relies on echoes sampling the field's excursion set above the Farley–Buneman instability threshold, rather than directly mapping the entire field. Observed echo patterns move with their clusters: large-scale structures persist for tens of seconds, whereas structures below 10 km renew within seconds. Conjunctions with Swarm satellite pairs reproduce this scale dependence in field-aligned currents, supporting coherent radar as a probe of multiscale variability on Alfvénic timescales.

PublicWhen a spacecraft crosses an aurora, it can be hard to tell whether a changing electrical pattern is small or simply short-lived. This study addresses that problem by following clusters of radar echoes over time. The echoes occur only where the ionosphere's electric field exceeds an instability threshold, so they provide an indirect way to trace its changing structure. Across sizes of 5–40 kilometers, the researchers find that larger echo patterns last tens of seconds, while patterns smaller than 10 kilometers change within seconds, even after accounting for the clusters' motion. Comparisons with pairs of Swarm satellites show the same size-dependent behavior in electrical currents flowing along the magnetic field.

Young explorerNear an aurora, electricity makes changing patterns that researchers can study with radar echoes. If a spacecraft passes a pattern, it may be hard to tell whether the pattern is tiny or changes quickly. So the researchers watched groups of radar echoes move. They found that big patterns lasted longer, while smaller ones changed in just a few seconds. The radar only picks up places where the electric field is strong enough, so it does not show everything. Satellite measurements of electric currents showed a similar pattern: smaller parts changed faster.