Tonight’s sky of new research

Beyond Point Photo-z Estimates: Normalizing Flows for Tomographic N(z) Reconstruction with DESI DR1

Zhuo Chen, Antoine Rocher, Kwan Chuen Chan+1 more

AstronomerThis study tests conditional normalizing flows (NFs) for photometric-redshift estimation and tomographic N(z) reconstruction against random forest (RF) and quantile random forest (QRF) models, using DESI DR1 galaxy and quasar spectroscopy with Legacy Surveys DR10 photometry. Models are trained on 1.1 million sources and tested on 2.0 million sources in a non-overlapping sky region over 0 < z_spec < 4.5. NF point estimates have the lowest scatter and outlier fraction below z_spec = 1.6 and outperform both baselines on all three reported metrics above that redshift. Distribution-level tests show that stacked NF posterior PDFs reconstruct N(z) more accurately than QRF, especially at high redshift. For z_median > 2.5, NF yields an absolute mean-redshift bias of 0.060 ± 0.031 versus 0.318 for QRF, and probability overlap of 0.905 ± 0.008 versus 0.787. Redshift-dependent post-hoc PDF calibration derived from held-out validation data produces absolute mean-redshift biases of 0.0016–0.0019 in four bins spanning 0.2 < z_median < 1.0; their central values fall below the reference benchmark 0.002(1+z). Calibration reduces the highest-redshift-bin bias to 0.016 ± 0.011. These empirical tests support the potential of NF PDFs for weak-lensing redshift-distribution calibration, but transfer across galaxy populations remains a challenge.

PublicTo use weak gravitational lensing to study cosmology, astronomers need accurate estimates of how galaxies are distributed in redshift. This study compares a machine-learning method called a conditional normalizing flow with two random-forest methods, using galaxy and quasar observations. The researchers trained the models on 1.1 million sources and tested them on 2.0 million sources in a separate patch of sky. The normalizing-flow method performed better on several measures of individual redshift estimates and reconstructed the overall redshift distributions more accurately than the quantile random forest, particularly at high redshift. An additional correction, developed using a separate validation sample, reduced errors in the average redshift. In four lower-redshift groups, the central estimates of those errors fell below a reference accuracy benchmark, while uncertainty remains in the reported results. The findings show promise for this approach, but the authors caution that applying models to different galaxy populations remains difficult.

Young explorerAstronomers need to work out how far away many galaxies are. They tested computer helpers that use clues from light to estimate something called redshift. One helper was better than the others at several parts of the job, especially for high-redshift objects. Giving it an extra correction helped it estimate the average redshift more accurately. It still makes mistakes, and using it with different groups of galaxies can be tricky.

A multiprobe ΛCDM consistency analysis with gravitational-wave standard sirens

T. M. C. Abbott, M. Aguena, F. Andrade-Oliveira+44 more

AstronomerThe authors present what they describe as the first multiprobe assessment of ΛCDM tensions incorporating gravitational-wave standard sirens. They combine LVK GWTC-5.0 sirens with DES Year 6 weak lensing and galaxy clustering, BAO, and type Ia supernovae, together with DESI BAO, and compare the results with primary CMB measurements from Planck, ACT, and SPT. The analysis uses homogeneous priors and normalizing flows to combine probes. Adding sirens to the DES 3×2pt analysis improves constraints in the Ωm–S8 plane by approximately 30% and constrains H0 to 6.2%. The combined low-redshift probes yield S8 = 0.793 ± 0.010, Ωm = 0.308 (+0.007, −0.006), and H0 = 69.4 (+4.1, −4.4) km s−1 Mpc−1. Despite the added information, the S8 discrepancy and H0 tension relative to the CMB remain essentially unchanged at current GW sensitivity. The authors interpret this as demonstrating the readiness of standard sirens for joint analyses with forthcoming surveys, rather than as resolving the tensions.

PublicThis study adds gravitational-wave distance measurements, called standard sirens, to several established ways of testing the standard model of cosmology. The researchers combine them with measurements of galaxies, gravitational lensing, supernovae, and cosmic distance scales, then compare the results with measurements of the early universe's leftover light. Adding the gravitational-wave data tightens the galaxy-and-lensing constraints on matter density and clustering by about 30%. The combined nearby-universe data give an expansion rate of 69.4 kilometers per second per megaparsec, with an uncertainty of roughly 4 in either direction. However, at today's gravitational-wave sensitivity, the disagreements with early-universe measurements about expansion and matter clustering remain essentially unchanged. The authors see the work as showing that gravitational-wave measurements are ready to contribute alongside other cosmological observations, not as a solution to those disagreements.

Young explorerScientists have different ways to learn how the universe is growing and how its matter is spread out. Those ways do not always give quite the same answer. In this study, scientists added clues from tiny ripples in space to clues from galaxies and light. The new clues helped make some answers more precise, but they did not settle the disagreements. The scientists think these ripples will be useful clues to include in future studies, too.

How tightly can PBH abundance information constrain scalar-induced gravitational waves?

Boliang Yu, Ruixin Zhou, Zi-Yu Tang

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

AstronomerThis theoretical study tests whether precise synthetic PBH abundances over a finite stellar-mass interval, an exact total abundance, and external population bounds uniquely constrain scalar-induced gravitational waves. For Gaussian perturbations and a fixed QCD formation prescription, two smooth, symmetric lognormal primordial spectra satisfy the same abundance constraints yet produce nonproportional leading-order SIGW spectra: their window-averaged predictions differ by about 20% in a lower nanohertz window and nearly a factor of 60 in an adjacent higher-frequency window. Peak position and width compensate with amplitude in the abundance calculation, while the higher window is dominated by scalar-mode pairs with both wavenumbers above the primordial peak. Local finite-width components give still larger fixed-frequency contrasts under both QCD and stochastic peak-curvature formation prescriptions. In a separately generated population, mass information covering most of the abundance reduces the higher-window contrast but does not eliminate the unequal window responses. Joint PBH-SIGW inference therefore needs to propagate compatible primordial spectral shapes rather than attach a single tensor template to an abundance fit; these are synthetic tests, not observational detections.

PublicKnowing how many primordial black holes exist at different masses may not uniquely predict the gravitational waves associated with their formation. Using synthetic black-hole population information rather than observations, the researchers constructed two patterns of early-universe fluctuations that meet the same abundance constraints but predict differently shaped gravitational-wave signals. Under their Gaussian-fluctuation and fixed formation assumptions, the predictions differ by about 20% in one nanohertz frequency range and nearly a factor of 60 in a neighboring, higher-frequency range. Changing only the overall signal strength cannot account for that difference. A separate synthetic example shows that knowing the mass distribution across most of the population reduces, but does not remove, the ambiguity. The study argues that analyses combining primordial black holes and gravitational waves should retain multiple compatible patterns of early fluctuations instead of assuming one wave signal follows from a successful abundance fit.

Young explorerScientists used pretend information about black holes that might have formed when the universe was very young. They found that two different patterns of tiny early bumps could fit the same black-hole information but predict very different ripples in space. Learning more about the black holes helped in another pretend example, but it did not make the ripple predictions match. This was a calculation, not a discovery of those black holes or ripples. It shows why scientists need to check more than one possible pattern.

Cuscuton Fifth Force: Implications of Non-Dynamical Scalars for Structure Growth

Adam Smith, Ilaria Andrei, Maria Mylova+1 more

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

AstronomerThis theoretical study derives the background and linear perturbation equations for effective cuscuton cosmology with matter minimally coupled in the Jordan frame and conformally coupled in the Einstein frame. Although the cuscuton obeys a constraint and has no propagating scalar degree of freedom, its algebraic response mediates a fifth force. The conformal factor also changes Einstein-frame particle masses and matter-perturbation friction, linking the force's strength and sign to background evolution rather than an independent coupling. A power-law model family admits tracking and sign-switching solutions; in the latter, the effective cuscuton density evolves from negative during matter domination to positive and cosmological-constant-like today. Modified CLASS calculations, including particle-mass effects on recombination, illustrate CMB temperature and linear matter power spectra for benchmarks without fitting data. In the strongest benchmarks, the sub-horizon effective gravitational coupling changes by about one percent, less than the accompanying matter-power and acoustic-scale changes. For sign-switching solutions, the coupling change is negative over most of cosmic history, demonstrating theoretical weakening rather than strengthening of gravitational attraction.

PublicThe researchers explore a theoretical way to modify gravity using a field called the cuscuton. Unlike a field that carries traveling disturbances, the cuscuton follows a constraint, yet the calculations show that it can still produce an additional force. That force is tied to how the universe evolves, rather than having an independently adjustable strength. Some models let the cuscuton's effective energy density change from negative earlier in cosmic history to positive today, when it behaves somewhat like a cosmological constant. Computer calculations predict changes in the cosmic microwave background and in how matter clusters. In the strongest examples studied, the effective strength of gravity on scales smaller than the cosmic horizon changes by about one percent, while other predicted effects are larger. In the sign-switching models, gravity is weakened over most of cosmic history. These are theoretical predictions for selected models, not results established by fitting observations.

Young explorerScientists used math and computers to explore an idea about gravity, the pull that brings things together. Their idea includes something called a cuscuton. It cannot send traveling ripples of its own, but the math says it could still change gravity's pull. In some versions, it makes that pull a little weaker for much of the universe's history. It could also change how matter gathers into clumps. The scientists have not shown that this is what the real universe does; they worked out what their idea would predict.

Bayesian and frequentist constraints on dark energy parameterizations using non-CMB data

Shubham Barua, Ansh Chandrakar, Shantanu Desai

AstronomerMotivated by DESI BAO+CMB evidence for dynamical dark energy and BAO–CMB tension within ΛCDM, this study uses only non-CMB data: DESI BAO DR2, DES-Dovekie SNe Ia, GRBs and RSD. Bayesian and frequentist analyses compare TQD, AT, CPL and GEDE with ΛCDM. GRBs add marginal constraining power, whereas SNe substantially tighten constraints. The fitted CPL equation of state crosses the phantom boundary w = −1 near z ≈ 0.5; TQD and AT improve the best-fit χ² without phantom crossing. With SNe included, TQD receives moderate Bayes-factor support and positive AIC/DIC support. AIC/DIC also positively favor CPL and AT, but the Bayes factor weakly favors ΛCDM over CPL and is inconclusive for AT, consistent with a prior-volume Occam penalty. GEDE with dark-energy density restricted to be suppressed at high redshift is disfavored by all three metrics. Support for dynamical dark energy therefore remains dependent on parameterization, dataset and comparison metric.

PublicThe researchers ask whether dark energy changes over cosmic history rather than remaining constant. To avoid a reported tension between galaxy-distance and cosmic microwave background data under the constant-dark-energy model, they analyze measurements from supernovae, galaxy distances, gamma-ray bursts and the growth of cosmic structure, without using the microwave background. They compare four mathematical descriptions of changing dark energy. Supernovae sharpen the constraints considerably, while the gamma-ray bursts add little. One description, CPL, fits a crossing of the so-called phantom boundary near redshift 0.5, but two other descriptions improve the fit without crossing it. When supernovae are included, one of these, TQD, is favored over constant dark energy by all three comparison methods, although the support is not decisive. For other descriptions, the methods disagree or favor constant dark energy. A fourth description, GEDE, is disfavored in the restricted form tested. The study does not establish that dark energy changes: the preference depends on the data, mathematical description and statistical test.

Young explorerScientists are trying to learn whether dark energy, which helps the universe expand faster, stays the same or changes as the universe grows. They used clues from space to compare different math stories about it. Exploding stars gave especially helpful clues, while bursts of gamma rays added only a little. Some changing-dark-energy stories matched the clues better than the stay-the-same story, but different ways of judging the stories did not always agree. So the scientists still cannot say for sure that dark energy changes.

foraois: Fast, Flexible Extended Press-Schechter Merger Trees with a General First-Crossing Solver

C. Power, S. Balu

AstronomerThe authors present foraois, an open-source Python framework for generating Monte Carlo dark matter halo merger trees in the excursion-set picture. Its modular design separates the linear density field, halo-collapse physics, and tree construction, allowing combinations of cosmologies, collapse prescriptions, and algorithms. It implements the Parkinson, Cole, and Helly semi-empirical correction to the EPS progenitor distribution and the Zhang and Hui numerical Markovian first-crossing solution. For the default real-space top-hat window, the latter approximates the correlated-walk problem. The framework accepts linear matter power spectra for cold, warm, and fuzzy dark matter, allows extensions to alternative collapse barriers, and supports constrained histories using the Nadler et al. Brownian-bridge construction. The authors report extensive validation and scaling tests and illustrate coupling to a lightweight semi-analytical galaxy-formation model; these are computational developments rather than observational findings.

PublicThe authors introduce foraois, a free, open-source Python tool for generating possible histories of how dark matter halos assemble through mergers. These histories are computer-generated models, not observations of actual halos. The software separates the ingredients describing matter fluctuations, halo collapse, and merger-history construction, making it easier to combine different assumptions. It can accept inputs for cold, warm, or fuzzy dark matter and offers two ways to generate merger histories. One uses an empirically fitted correction; the other solves a mathematical equation that, with the default settings, only approximates the more complicated problem. The authors report extensive testing of the software and its computational scaling, and demonstrate how it can be linked to a simplified model of galaxy formation.

Young explorerThe researchers made a computer tool called foraois that draws pretend family trees for dark matter halos, the clumps of dark matter studied in astronomy. The trees show possible ways smaller clumps could join to make bigger ones. They are made-up possibilities based on scientific rules, not pictures of what really happened. Scientists can change the rules and try different kinds of dark matter. Some of the math uses shortcuts, so the trees are not exact. The researchers tested the tool and showed an example of using it with a simple computer model of how galaxies form.

The nucleon is not a hard sphere: screening fifth forces with Skyrmions

Philippe Brax, Clare Burrage, Adam Moss

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study revisits nucleon screening in laboratory searches for chameleon and symmetron fifth forces. Instead of a uniform sphere, it models a nucleon with a constant-density core and an r^-6 pion tail, also considering exponential truncation at the physical pion mass. Analytic screening charges for the sphere and untruncated profile, supplemented by numerical solutions for the truncated profile, show that the dilute outer tail remains unscreened. In the strong-screening regime, this yields a power-law charge enhancement for the r^-6 tail and a weaker, logarithmic enhancement for the exponential tail. Reinterpreting published analyses with these profiles extends nucleon-sourced exclusions further into strong coupling; these are model-dependent revisions of existing constraints, not detections. At μ = 1 keV, neutron-interferometry symmetron constraints reach maximal self-couplings 1.4 orders of magnitude higher than with a uniform-sphere neutron, or 3.0 orders in the chiral limit. At the dark-energy scale, the hydrogen 1s–2s chameleon bound reaches couplings 1.8 orders of magnitude weaker than with a uniform-sphere proton, or 2.4 orders in the chiral limit, overtaking the muonium bound.

PublicLaboratory searches for hypothetical extra forces often treat protons and neutrons as balls of uniform density. This study instead calculates what happens if each has a dense center surrounded by a thinning outer region, including a version whose outer density falls off more rapidly to account for the physical pion mass. In these models, the dilute outskirts can continue to contribute to the extra force even when the dense center is screened, or suppressed. Applying the calculations to published experiments strengthens the inferred limits on chameleon and symmetron forces compared with the uniform-ball assumption. The more rapidly fading outer region gives a smaller improvement than the extended tail. These are theoretical, model-dependent updates to existing experimental limits, not a discovery of a new force.

Young explorerScientists are looking for a possible extra push or pull in nature. When doing the math, they often pretend that protons and neutrons are tiny balls that are equally packed everywhere. This study tried balls with packed centers and wispy edges instead. In their calculations, the wispy edges could help an extra force show through when the center could not. That changes what earlier tests can tell us, but it does not mean the extra force has been found.

Thirty years of primordial deuterium abundances: A provenance-aware statistical reanalysis

Richard de Grijs, Giuseppe Bono

AstronomerThis provenance-aware audit assembles 957 published primordial D/H values from 247 publications spanning 1994–2026, tracing observational entries to physical absorbers wherever possible. Of 795 observational entries, 80.1% reuse individual or compilation values, while only 11.4% are new determinations of individual systems. The database identifies 52 distinct absorbers, but eight systems contribute 62.0% of identifiable absorber mentions; an inverse Herfindahl–Hirschman measure indicates an effective representation of 16.28 equally represented absorbers. The modern consensus, 10^5(D/H) ≈ 2.5, remains robust under alternative absorber-level treatments and removal of the eight dominant systems. Its apparent precision, however, is more sensitive to repeated representation than publication counts suggest. The authors also identify a coordinated shift in compilations around 2013–2014 toward more selective, homogeneous analyses, even as older individual values continued to circulate. The central abundance is robust, but literature entries should not be treated as statistically independent measurements.

PublicPrimordial deuterium, a form of hydrogen, provides a precise observational test of how elements formed in the Big Bang. This study examines the published evidence rather than reporting new measurements. The authors assembled 957 published abundance values and, where possible, traced them back to the absorbing systems used to measure them. Most observational entries reused earlier values, and just eight systems accounted for 62% of identifiable system mentions. Even after excluding those eight, the modern consensus remained about 2.5 deuterium atoms per 100,000 hydrogen atoms. The main caution concerns precision: many published numbers draw on the same underlying observations, so counting them as separate evidence can make the abundance appear more precisely established than the literature's independence warrants.

Young explorerScientists study a special kind of hydrogen to check their ideas about the very early universe. These researchers looked through many science papers and found that lots of them used the same measurements again. It is like many children repeating an answer from the same few clues, instead of each finding a new clue. The usual answer stayed about the same even when the researchers left out the most often repeated sources. But hearing the same clues many times does not make the answer as certain as finding lots of different clues would.

Recovering Missing Degrees of Freedom in Simulation-Trained Field-Level Generative Models

Masato Shirasaki, Shiro Ikeda

• Machine Learning

AstronomerThis simulation-based study addresses variance shrinkage in generative models for cosmological field-level inference: finite training sets can lead models to underrepresent realization-to-realization variability. The authors interpret this shrinkage as a diagnostic of missing effective degrees of freedom and introduce physics-informed latent corrections to a continuous normalizing flow. They report recovery of a substantial fraction, but not all, of the missing variability without additional training simulations. In a weak-lensing inference application, posterior analysis shows that the latent directions are used during inference and act as effective nuisance parameters, absorbing part of the training–target distribution mismatch. The reported improvement in robustness to out-of-distribution shifts is a modeling result, not an observational finding.

PublicComputer models trained on simulated universes can miss some of the natural variation between one simulated universe and another, especially when their training examples are limited. The researchers interpret this lack of variety as a sign that the model is missing some effective flexibility. They add physics-guided hidden adjustments and report that these recover a substantial share of the missing variation without requiring more training simulations. In a test involving weak gravitational lensing, the adjustments help the model handle differences between its training examples and the cases it is asked to analyze. The study demonstrates improved robustness in simulation-based inference, rather than a new observation of the universe, and the adjustments do not remove all of the mismatch.

Young explorerImagine teaching a computer to make pretend pictures of the universe. If it learns from too few examples, its pictures may be too much alike. The researchers gave the computer extra hidden controls, guided by physics, so it could make more of the variety it had missed without needing more practice examples. In their test, the controls also helped when the computer faced examples different from its practice ones. They helped with part of the problem, not all of it. This was a test with computer-made universes, not a new discovery in the sky.

Targeting the future of spectroscopic galaxy surveys -- A cosmological study case with the Wide-field Spectroscopic Telescope

Constantin Payerne, Antoine Rocher, Aurélien Verdier+22 more

AstronomerThis study develops target-selection strategies and an optimisation framework for the proposed 12-metre Wide-field Spectroscopic Telescope (WST), expected to operate in the 2040s. Using deep multi-band photometry, including CLAUDS and HSC COSMOS-field data, it revisits established galaxy and quasar selections at z<1.6 to depths achievable in the WST era. It also introduces MagMax, a magnitude-limited sample using three-dimensional colour-colour star–galaxy separation, and Lyman-break dropout samples extending selection to z>2. Fisher-matrix forecasts assess the potential constraints of a WST-like survey on BAO distance parameters, growth rate, evolving dark energy, local-type primordial non-Gaussianity and summed neutrino mass; these are forecasts, not measurements. The principal outcome is a framework linking instrumental capabilities and observing time to cosmological constraining power, rather than simply extrapolating current survey recipes.

PublicFuture spectroscopic surveys aim to collect spectra of hundreds of millions of galaxies and quasars to study the Universe across larger distances and volumes. This paper explores how to choose targets for the Wide-field Spectroscopic Telescope, a proposed 12-metre facility expected to operate in the 2040s. Using existing deep images taken in several wavelength bands, the researchers adapt established selection methods and develop additional samples, including one extending to galaxies at redshifts above 2. They then use mathematical forecasts to explore how a survey like this could constrain cosmic expansion, the growth of structure, dark energy, conditions in the early Universe and neutrino masses. These are estimates of future capabilities, not new measurements of those quantities. The main contribution is a planning framework that connects telescope capabilities and observing time with the scientific precision a survey could achieve.

Young explorerScientists want to use a big telescope that is still being planned to study light from lots of faraway galaxies. First, they need to decide which galaxies to look at. This study uses pictures of the sky to work out ways to choose them. It also uses maths to estimate what the future telescope might teach us about how the Universe grows and changes. The telescope has not made these measurements yet. The study helps scientists plan how to use its time well.

DBI Softens Stiff-Phase Gravitational-Wave Spectra

Samuel Sánchez López, Eemeli Tomberg, Juan C. Bueno Sánchez

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

AstronomerThis theoretical study examines the present-day primordial gravitational-wave energy-density spectrum for an inflationary scalar field with a Dirac–Born–Infeld (DBI) kinetic term and a runaway potential. During the subsequent kinetically dominated era, the DBI structure lowers the equation-of-state parameter relative to canonical kination, w = 1, softening the spectrum’s blue tilt. Meanwhile, the field’s energy density redshifts more slowly, delaying radiation domination and extending the stiff phase. The authors find that these competing effects can make the predicted signal potentially accessible to future experiments in cases where the canonical counterpart would remain out of reach. Numerical evolution of the background and perturbations from inflation to radiation domination identifies viable parameter space consistent with cosmic microwave background and Big Bang Nucleosynthesis constraints. These are model predictions, not a gravitational-wave detection.

PublicThe researchers modeled how an unusual form of an inflation-driving field could change gravitational waves left over from the early universe. Compared with a standard version of the field, their model makes the predicted wave spectrum rise less steeply toward higher frequencies, but also prolongs the era before radiation dominates the universe. Together, these effects could put a signal within reach of future experiments when the standard model’s signal would be too difficult to detect. Numerical calculations followed the universe from inflation until radiation domination and found model settings compatible with constraints from the cosmic microwave background and the formation of light elements in the early universe. The study predicts a possible signal; it does not report an observation of these waves.

Young explorerThe scientists used math and computers to imagine how tiny ripples in space from the very early universe might look today. They tried a different rule for how something that helped the universe grow would behave afterward. That rule changed the ripples and made one early part of the universe’s story last longer. Their calculations suggest that future experiments might be able to notice the ripples in some cases. They have not found those ripples yet.

Multiprobe strategies for Kinematic Lensing with the Roman Space Telescope High Latitude Wide Area Survey

Yu-Hsiu Huang, Jiachuan Xu, Tim Eifler+6 more

AstronomerSimulated analyses forecast the cosmological performance of Roman kinematic lensing (KL) for the latest HLWAS design, whose Medium Tier provides overlapping photometry and spectroscopy over 2,300 square degrees. KL uses galaxy kinematics to control shape noise, the dominant statistical limitation of traditional weak lensing (WL). The analyses explore early Deep and Medium Tier data, survey roll angles, comparisons with WL, and a joint KL, galaxy-clustering, and galaxy–galaxy-lensing analysis, considering photometric uncertainties, shear calibration bias, galaxy bias, and baryonic feedback. KL alone yields a forecast dark-energy figure of merit of 22.54, more than twice that of the corresponding WL analysis. The multiprobe forecast reaches 34.58 for the full survey, even with conservative clustering and galaxy–galaxy-lensing scale cuts. The planned four passes at approximately 0, 10, 170, and 180 degrees are near optimal for KL in these simulations. These are forecasts, not observational constraints.

PublicSimulations suggest that Roman’s planned survey could improve studies of dark energy by combining measurements of galaxy images with information about how galaxies move. This technique, called kinematic lensing, helps control the uncertainty caused by galaxies having different intrinsic shapes, which limits conventional weak-lensing studies. The latest survey design includes overlapping imaging and spectroscopy across 2,300 square degrees. In the simulations, kinematic lensing more than doubles a dark-energy performance measure compared with the corresponding conventional analysis. Combining it with galaxy clustering and lensing around galaxies improves the forecast further. The study considers several sources of systematic uncertainty and finds that the planned four viewing orientations are nearly optimal for this technique. These results describe expected performance, not measurements from Roman observations.

Young explorerGalaxies have different shapes, so it can be hard to tell how much gravity has stretched their pictures. Scientists used computer pretend versions of a planned Roman survey to test a trick: look at the galaxies’ movements as well as their pictures. In these tests, the trick could help scientists learn more about mysterious dark energy. Adding other clues about galaxies helped even more. These are computer predictions, not discoveries from real Roman pictures yet.

Baryonic feedback and intrinsic alignments in profile: a frequentist view of DES Y3 cosmic shear

Anoma Ganguly, Elisabeth Krause, Tanvi Karwal+1 more

AstronomerThis analysis compares profile likelihoods and marginal Bayesian posteriors for DES Y3 cosmic shear using the DES Y3+KiDS-1000 Hybrid model to assess prior-volume effects. For shear alone, the global profile best fit and posterior mean agree in S8, but a strong S8–baryonic-feedback degeneracy leaves the upper 1-sigma limit on S8 set by the assumed feedback range. External CMB information on parameters other than Omega_m and S8 breaks this degeneracy, suppresses prior-volume effects, and brings profiles and posteriors into agreement. With that information included, small-scale shear favors moderate feedback consistent with hydrodynamical simulations calibrated to observed gas fractions. Relative to NLA, unconstrained additional TATT parameters shift and broaden the S8 profile; adding DES Y3 shear ratios mitigates this degeneracy and brings profile likelihoods and marginal posteriors into close agreement.

PublicThe study asks how much conclusions from DES Y3 cosmic shear measurements reflect the data, rather than assumptions used in the analysis. Comparing two statistical approaches, the researchers find that the inferred strength of matter clustering, called S8, is difficult to separate from the modeled effects of ordinary matter on cosmic structure. With shear measurements alone, the upper end of its one-sigma range depends on the allowed range of those effects. Adding cosmic microwave background information about other model parameters reduces this ambiguity and makes the two statistical approaches agree more closely. In that combined analysis, small-scale shear favors moderate effects from ordinary matter, consistent with simulations calibrated against observed gas fractions. A more flexible model of galaxy alignments weakens the S8 constraints, but adding DES Y3 shear-ratio measurements helps resolve that ambiguity.

Young explorerScientists used measurements of space to learn how clumpy its matter is. But different choices in their calculations could explain the same measurements, so the answer was not as clear as it first looked. Extra information from the cosmic microwave background helped two ways of checking the answer agree more closely. The study shows that scientists need to check which parts of an answer come from measurements and which parts depend on their starting assumptions.

Toward the one- and two-loop EFTofLSS for Simons Observatory CMB lensing

Evan Saraivanov, Henrique Rubira, Vivian Miranda

AstronomerThis Fisher forecast tests one- and two-loop EFTofLSS models in a joint Simons Observatory temperature, polarization, and CMB lensing likelihood, using noiseless data vectors spanning different baryonic feedback scenarios. A single additional parameter, derived by principal-component analysis of the EFTofLSS counterterms and closely aligned with the effective AGN heating temperature, provides good fits across the scenarios considered. Both loop orders reduce cosmological parameter biases with only a small loss of marginalized precision at fixed scale cuts. The one-loop model remains unbiased over a scale range similar to the dark-matter-only model, whereas the two-loop model extends to smaller scales and handles feedback variations more robustly. At each model's smallest usable scales consistent with unbiased estimates, the two-loop model forecasts tighter constraints than the dark-matter-only model. These are forecast results, not measurements from observed data.

PublicMatter can bend the light left over from the early universe, allowing astronomers to study how matter clusters. But the effects of ordinary matter, including feedback associated with active galactic nuclei, can complicate that picture. This study forecasts how two versions of a mathematical model could account for those effects in a combined analysis of Simons Observatory measurements. In tests using noiseless modeled data, one extra adjustable parameter was enough to fit the feedback scenarios examined and reduce systematic errors in inferred cosmological parameters, with only a small loss of precision when comparing the same scales. The more detailed, two-loop version could reliably include smaller scales. When each model used its own smallest reliable scales, that version gave tighter forecast constraints than a model that treats clustering as dark matter alone. These are predictions of an analysis method's performance, not results from actual observations.

Young explorerLight from long ago gets bent as it travels past matter in space. Scientists want to use those bends to learn about the universe, but ordinary stuff in space can make the answer tricky. They tested two math recipes with pretend data. Adding one extra adjustment helped both recipes avoid wrong answers in the cases they tried. The more detailed recipe could use smaller details and gave more precise answers than a recipe that left out the effects of ordinary stuff. This was a practice test, not a discovery made by looking at the real sky.

Detection of the Galaxy--Galaxy--Temperature Skewed Bispectrum

I. J. Keja, D. Karagiannis, W. R. Coulton+1 more

AstronomerThe authors report the first measurement of the galaxy–galaxy–temperature skewed bispectrum, cross-correlating squared, filtered unWISE galaxy overdensity with Planck maps at 100, 143, 217, and 353 GHz. Detections are highly significant in all four channels, with frequency dependence revealing both tSZ and CIB contributions. With galaxy occupation fixed, halo-model fits to galaxy–temperature cross-spectra favor higher integrated pressure and peak star-formation efficiency than fits to the skewed bispectrum. Comparisons using component-separated Planck tSZ and CIB maps indicate that the discrepancy is not confined to frequency-map fits. An inadequately modeled mass dependence of gas pressure is one possible interpretation, not an established explanation. The result motivates more flexible pressure, CIB-emission, and galaxy-occupation models. By upweighting massive halos hosting many galaxy pairs, the statistic supplies complementary information beyond two-point statistics at comparable computational cost.

PublicResearchers report the first measurement of a statistic that links pairs of galaxies to temperature patterns in Planck sky maps. They detect the signal strongly at four observing frequencies; its frequency dependence reveals contributions from hot gas and dust emission. Their model does not give consistent answers across two ways of analyzing the data: with the assumed distribution of galaxies among dark-matter halos held fixed, the simpler galaxy–temperature comparison favors higher gas pressure and peak star-formation efficiency than the new statistic does. Checks with maps designed to separate hot-gas and dust signals indicate that this mismatch is not limited to the original frequency maps. The cause remains uncertain; one possibility is that the model misses how gas-pressure profiles vary with halo mass. Because the new statistic gives extra weight to massive halos containing many galaxy pairs, it offers a complementary way to test these models without substantially greater computational cost.

Young explorerScientists tried a new way to compare where pairs of galaxies are with warmer and cooler patches in maps of the sky. They found a clear signal with signs of hot gas and dust. But their model gave different answers when they looked at the maps in two different ways. That might mean the model needs a better description of the gas around galaxies, but they do not know yet. The new method pays extra attention to big groups with lots of galaxy pairs, helping scientists check ideas about what is out there.

Mercury (Hg): a relativistic N-body simulation for Horndeski gravity

Ahmad Nouri-Zonoz, Farbod Hassani, Julian Adamek+2 more

• General Relativity and Quantum Cosmology
• Computational Physics

AstronomerMercury is a relativistic particle-mesh N-body code implementing the general linear Horndeski alpha-basis, extending earlier k-essence and kinetic gravity braiding implementations. It evolves the additional scalar degree of freedom and its effective stress–energy alongside nonlinear matter and metric fields, allowing structure formation to source scalar evolution and feed back on gravitational potentials. An interface with hi_class supports phenomenological alpha-function parametrisations and covariant theories, demonstrated with nKGB, Cubic Galileon and Brans–Dicke models. The authors validate linear evolution against hi_class and recover expected nonlinear k-essence and KGB limits. For the luminal models studied, a running effective Planck mass produces gravitational slip through scalar anisotropic stress, changes vector and tensor friction terms, and alters the normalisation and scale dependence of the effective dark-energy density contrast and its power spectrum. These are computational findings, not observational detections. The framework is an intermediate step toward nonlinear Horndeski simulations; incorporating nonlinear scalar self-interactions and screening remains future work.

PublicThe authors present Mercury, a computer program for simulating cosmic structure in a family of gravity theories called Horndeski gravity. These theories include an extra scalar field that interacts with matter and gravity. Mercury follows how growing structures affect this field and how it changes the simulated gravitational fields in return. Tests agree with another program where linear calculations apply and reproduce expected behaviour in previously implemented cases. In the models studied, changes over time in a quantity called the effective Planck mass alter the simulated gravitational fields and the predicted pattern of effective dark-energy density variations. These are simulation results, not observations establishing that these theories describe our Universe. More work is needed to include nonlinear interactions of the scalar field and screening effects.

Young explorerScientists made a computer program called Mercury to explore different rules for gravity as things gather together in space. The program also follows an extra field that can change gravity in these models. It passed checks against another program and earlier calculations. This does not show that real space follows these rules, and some more complicated effects still need to be added.

On the Role of Gravity in Supercooled Phase Transitions

Filippo Cutrona, Alberto Salvio

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

AstronomerThis theoretical study examines gravity in supercooled first-order phase transitions associated with radiative symmetry breaking. The authors develop a model-independent treatment valid when an explicitly identified, model-computable quantity is sufficiently small. Spacetime curvature eventually becomes relevant for transitions that would fail to complete if gravity were neglected. Including dimensionless non-minimal couplings, they find that gravity can either enlarge or shrink the parameter region permitting completion, depending on those couplings. They derive gravitational-wave consequences potentially testable with current and future detectors and explore, rather than establish, whether such transitions could explain the background detected by pulsar timing arrays. They also estimate the number of e-folds spent with the order-parameter field trapped in the false vacuum. The motivating scenarios can produce gravitational waves and, if supercooling persists long enough, primordial black holes.

PublicThe early universe may have undergone sudden changes of state after remaining in an old state below the usual transition temperature, a process called supercooling. This theoretical study asks how gravity affects such changes in a class of particle-physics theories. The calculations indicate that spacetime curvature eventually matters when a transition would otherwise fail to finish. Depending on how the field responsible for the transition couples to gravity, gravity can make completion possible across a wider or narrower range of model settings. The approach is valid only when a quantity calculated for the chosen model is sufficiently small. The researchers also calculate possible gravitational-wave signatures and consider whether these transitions could explain the background detected by pulsar timing arrays; they do not establish that explanation. They estimate how much the universe expands while the field remains trapped in its old state.

Young explorerThe very young universe might have changed its state, a little like water turning into ice. But it could have stayed stuck in its old state for a while. Scientists used math to ask how gravity could help that change finish or make finishing harder. Their answer depends on how gravity and the changing field interact, and their math works only under certain conditions. They also explored whether such changes could make ripples in space like ones astronomers have detected. That is a possible explanation, not something they have proved.

Stars Can Quench Superradiance Around Supermassive Black Holes

Yu Cheng, Andrea Caputo, Giovanni Maria Tomaselli+1 more

• High Energy Physics - Phenomenology
• Astrophysics of Galaxies

AstronomerThis theoretical study quantifies environmental depletion of light-scalar clouds around rotating black holes, focusing on bound-free transitions induced by orbiting stars and compact objects. For gravitational interactions alone, the calculated superradiant growth rate almost always exceeds the environmental dissipation rate. However, the rates are sufficiently close that including bound-bound transitions could reverse this conclusion. Environmental dissipation also exceeds losses through gravitational-wave emission, making stellar environments relevant to indirect searches. Quadratic scalar couplings to nucleons and electromagnetism can greatly enhance dissipation and prevent cloud formation. The work emphasizes environmental effects in superradiance studies around intermediate and supermassive black holes; it does not report an observational detection.

PublicTheoretical calculations explore whether nearby stars and compact objects could stop clouds of hypothetical light particles from growing around spinning black holes. Such clouds can grow through a process called superradiance, but their surroundings can drain their energy. For the gravitational interactions studied, cloud growth almost always wins, although another type of transition not yet included could change that conclusion. The surroundings also drain energy faster than gravitational waves do, so they matter when planning indirect searches for these clouds. If the particles have the additional interactions with nuclear matter and electromagnetism considered here, energy loss can become strong enough to prevent a cloud from forming. These are theoretical findings, not observations of particle clouds.

Young explorerScientists used calculations to study whether tiny, hypothetical particles could gather into a cloud around a spinning black hole. Nearby stars could take energy away from the cloud. In most of the cases they worked out, the cloud could grow faster than the stars drained it. But they still need to include another effect that might change the answer. If the particles interact with ordinary matter and light in certain ways, the cloud might not grow at all. The scientists did not see one of these clouds; they worked out what could happen.

Exothermic Higgs portal: from LUX-ZEPLIN recoil to Gamma Rays

Subhojit Roy, Jure Zupan

• High Energy Physics - Phenomenology
• High Energy Astrophysical Phenomena

AstronomerThe authors propose a minimal thermal-relic interpretation of the recently reported LUX-ZEPLIN nuclear-recoil candidate, not a confirmed dark matter detection. A single complex scalar added to the Standard Model splits into two nearly degenerate real scalars through mass terms and Higgs-portal interactions. With masses near 100 GeV and a splitting of a few hundred keV, the heavier state is cosmologically long-lived and the states have comparable relic abundances. Fixing the off-diagonal Higgs coupling by the relic abundance gives an expected event count of order one for the LZ exposure through exothermic down-scattering, without requiring the high-velocity tail needed in endothermic scenarios. Predicted complementary signatures include a broad sub-MeV photon continuum from the heavier state's two-photon decay, potentially probed by INTEGRAL/SPI and COSI, and a GeV-scale annihilation continuum extending to roughly 100 GeV, probed by Fermi-LAT dwarf-galaxy observations. The scenario satisfies current CMB constraints and strongly suppresses annihilation of dark matter captured in the Sun. Different nuclear targets and next-generation experiments could test its correlated scattering, decay, and annihilation predictions.

PublicA recently reported signal in the LUX-ZEPLIN experiment is a possible nuclear recoil, not proof of dark matter. This paper proposes an explanation involving two closely related dark matter particles that interact through the Higgs. In the model, the slightly heavier particle can become the lighter one while striking an atomic nucleus, releasing energy. For particle masses around 100 GeV, the calculation predicts roughly one event in the reported experimental exposure. The model also predicts that both types of particle survive from the early universe in similar amounts. It could be tested using detectors with different target materials and searches for light produced by particle decays and annihilations. Existing cosmic microwave background limits allow the scenario, but the proposed explanation remains to be tested.

Young explorerAn experiment reported a possible tiny bump in an atom's middle. Scientists suggest that an unseen particle might have made it by changing into a slightly lighter kind and giving the atom a push. Their idea could fit the possible bump, but that does not mean it is right. Other experiments could look for more bumps and light that the idea predicts.

Nonlinear gauge maps and the structure of Goldstone loops in canonical inflation

Cheng-Jun Fang, Zong-Kuan Guo

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

AstronomerThis theoretical study clarifies the nonlinear relation between spatially flat scalar and Goldstone descriptions of canonical single-field inflation. An exact clock map reorganizes potential interactions into derivative Goldstone interactions, while a change of slicing connects their dilation symmetry to its comoving realization. For the one-loop Goldstone two-point function in the decoupling limit, identities from the general mode equation show that apparently independent loop contributions combine, with non-boundary parts canceling after the associated counterterms are included. No explicit mode-function solution is needed for this reduction. The leading adiabatic long-mode response becomes a total derivative in loop momentum, but requires an additional regularization prescription.

PublicThis theoretical paper examines two mathematical descriptions of inflation, an early period of cosmic expansion. The authors establish an exact translation between the descriptions, showing how interactions written one way become interactions involving rates of change in the other. They then calculate a quantum correction within a simplifying limit and show that several apparently separate contributions cancel in their non-boundary parts when the required correction terms are included. This simplification does not require explicitly solving the equations for individual modes. A remaining expression describing the response to a long-wavelength disturbance still needs an additional mathematical prescription to handle it. These are mathematical findings, not observational results.

Young explorerScientists use different kinds of math to describe how the universe grew very quickly when it was young. This paper shows how to translate between two of those math descriptions. In a calculation with simplifying rules, some pieces cancel each other when all the needed terms are included. But one part still needs an extra math rule to handle it. The scientists worked this out with math, rather than by watching the sky.

KiDS-1000 cosmic shear reanalysis using MetaCalibration

Mijin Yoon, Henk Hoekstra, Shun-Sheng Li+10 more

AstronomerThe authors reanalyse Kilo-Degree Survey cosmic shear data using MetaCalibration rather than the lensfit pipeline used previously, testing whether shear-estimation biases explain the mild tension with Planck. In multi-band SKiLLS image simulations designed to match KiDS, MetaCalibration reduces multiplicative bias, particularly at the highest redshifts. The absolute value of the multiplicative bias m is below 0.017 in every tomographic bin, with negligible additive bias and negligible calibration sensitivity to key galaxy properties. Applied to the survey data, the pipeline yields S8, defined as sigma8 times the square root of Omega_m divided by 0.3, of 0.789 with lower and upper uncertainties of 0.024 and 0.020. This is consistent with the previous KiDS-1000 lensfit result of 0.776, whose lower uncertainties were 0.027 statistical and 0.003 systematic, and upper uncertainties were 0.029 statistical and 0.002 systematic. Higher effective source density improves constraining power by about 28%. The Planck discrepancy remains at a similar level, 1.8 standard deviations; the authors interpret this persistence as evidence that shear measurements are not its cause.

PublicSome studies of the subtle distortion of galaxy images have found a mild disagreement with Planck measurements of the cosmic microwave background. The researchers revisited Kilo-Degree Survey data with an alternative method for measuring galaxy shapes. Tests on simulated images matched to the survey showed smaller calibration biases, especially for the most distant galaxies, and little sensitivity to key galaxy properties. Using the real survey data, the new method gave S8, the cosmological parameter being compared, a value of 0.789 with a lower uncertainty of 0.024 and an upper uncertainty of 0.020, consistent with the earlier survey result. A higher effective density of usable galaxies improved the constraining power by about 28%. However, the mild disagreement with Planck remained at 1.8 standard deviations. The authors conclude that the shear measurements do not explain it; this is an interpretation of the comparison, not a discovery of what does cause the difference.

Young explorerScientists measured tiny changes in the shapes of faraway galaxies. Their answer was a little different from an answer found by studying a very old glow in space. They checked a different shape-measuring method using pretend pictures, then used it on real galaxy pictures. The new method worked better in the tests, but the real pictures still gave nearly the same answer as before. The scientists think the way they measured the shapes is not why the two answers differ a little.

Wide Area VISTA Extragalactic Survey (WAVES): Redshift-limited selection of targets for the Wide survey using decision-tree classification

G. Kaur, M. Bilicki, S. Bellstedt+11 more

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

AstronomerThe authors present an XGB classifier for WAVES-Wide target selection, assigning probabilities that photometric galaxies lie below z=0.2 rather than estimating individual redshifts. It is trained and tested on spectroscopy overlapping the WAVES fields, using nine-band VST+VISTA photometry. Tests at the fiducial selection limits and neighboring redshift and magnitude thresholds yield purity and completeness of roughly 90–95%, depending on the test set. Performance degrades near the selection boundaries and on DESI-selected test sets not used in training, so the survey’s 95% completeness requirement should not be treated as uniformly achieved. Applying the classifier to 8.6 million photometric galaxies yields about 1.2 million target candidates, or 1 million with P_XGB(z≤0.2)>0.72. These are candidate selections, not newly measured redshifts; 4MOST will measure the true redshifts.

PublicResearchers have tested a machine-learning method to help choose galaxies for WAVES-Wide, a survey that will use 4MOST to measure galaxy redshifts. Instead of estimating each galaxy’s redshift individually, the method uses measurements in nine light bands to assign a probability that it falls below the survey’s redshift cutoff of 0.2. Tests using galaxies with known redshifts achieved about 90–95% purity and completeness: most selected galaxies met the criteria, and most qualifying galaxies were recovered. Performance was worse near the selection boundaries and on a separately selected test sample not used for training. Applied to a catalog of 8.6 million galaxies, the method produced about 1.2 million candidates, reduced to 1 million with a stricter probability cut. Their membership still needs confirmation through redshift measurements.

Young explorerScientists want to choose galaxies for a big space survey. They taught a computer to look at galaxy pictures taken in different kinds of light and pick galaxies likely to fit their list. They checked it using galaxies they already knew about, and it usually chose well, but it made more mistakes with some tricky galaxies. It picked about a million possible galaxies with a stricter rule. A telescope still needs to check which ones really belong on the list.

Probing cosmic anisotropy with galaxy clusters and supernovae

Shubham Barua, Sujit K. Dalui, Shantanu Desai

AstronomerThe authors test directional variation in H0 using hemisphere decomposition with ΛCDM and Padé-(2,1) cosmography, combining galaxy-cluster X-ray scaling relations with PantheonPlus Type Ia supernovae. They examine five supernova redshift selections extending to z = 0.5, with lower limits of 0.015, 0.03, 0.05, 0.1, and 0.2. The combined cluster sample is consistent with statistical isotropy, while supernovae alone show an approximately 2.5σ anisotropy preference in the lowest-redshift selection that weakens as low-redshift objects are removed. Joint constraints depend on the treatment of the H0–MB and H0–k degeneracies, where k normalizes the cluster scaling relation: the low-redshift preference persists with Cepheid-host calibration, whereas fixing k yields results consistent with isotropy. The analysis therefore provides no compelling evidence for statistically significant anisotropy in local expansion and emphasizes calibration and degeneracy dependence.

PublicThe study asks whether the nearby universe expands at different rates in different directions. The authors compare estimates from Type Ia supernovae and galaxy clusters using two mathematical descriptions of cosmic expansion. The cluster data are consistent with expansion having no preferred direction. Supernovae alone show a modest hint of a directional difference, about 2.5 sigma, in the sample that includes the nearest supernovae; that hint weakens as nearby objects are excluded. When the two kinds of data are combined, the answer depends on how their brightness and X-ray scaling relations are calibrated and how linked parameters are handled. The hint remains with Cepheid-host calibration, but the combined results are consistent with no preferred direction when the cluster scaling normalization is fixed. Overall, the study finds no compelling evidence that local expansion differs by direction.

Young explorerScientists asked whether space around us is stretching faster in one direction than another. They studied exploding stars and groups of galaxies. The galaxy groups did not show a clear favorite direction. The stars gave a small hint, but it became weaker when the nearest ones were left out. When scientists put the clues together, the answer also depended on how they set up their measuring rules. So they did not find strong evidence that space nearby stretches differently in different directions.

Hunting Dark Matter with the Einstein Telescope

A.J. Iovino, M. Maggiore, N. Muttoni+1 more

• General Relativity and Quantum Cosmology

AstronomerThe abstract proposes that strongly clustered primordial black holes could evade constraints associated with evaporation of low-mass objects, including cosmic microwave background distortion bounds, if their haloes collapse into heavier black holes. These heavier black holes could constitute all of the universe’s dark matter. The scenario predicts a flat stochastic gravitational-wave background that the authors describe as detectable by the Einstein Telescope; no observational detection is reported.

PublicVery light black holes formed in the early universe would evaporate, and observations strongly limit their possible abundance. The authors propose that, if these black holes formed in tightly packed groups, the groups could collapse into heavier black holes that might account for all dark matter. They predict that this process would produce a background of gravitational waves detectable by the Einstein Telescope. This is a proposed explanation, not a reported discovery.

Young explorerVery tiny black holes can slowly disappear. The scientists suggest that a tightly packed group of them might collapse into a bigger black hole. Those bigger black holes might explain all the invisible stuff called dark matter. The idea also predicts tiny ripples in space that a detector called the Einstein Telescope could spot, but the scientists are not saying they have found them.

Mass-Varying Neutrinos from an Inverse Symmetron

Mainak Baidya, Øyvind Christiansen, Vitor da Fonseca+2 more

AstronomerNeutrinos are constrained as relativistic species at high redshift, as massive components that suppress clustering at low redshift, and through laboratory measurements. Motivated by galaxy-survey mass bounds approaching or extending into negative values, this theoretical study explores a neutrino–dark-energy coupling that makes neutrino mass evolve. An inverse phase transition breaks, rather than restores, symmetry as neutrinos become nonrelativistic. The authors find that late-time decoupling switches off the fifth force and prevents excessive growth of neutrino perturbations, eliminating instabilities in the linear regime. The model can mimic a lower neutrino mass in galaxy surveys while producing additional suppression of the matter power spectrum. An early-dark-energy component near recombination could potentially address the Hubble tension; this remains a possibility, not an established resolution.

PublicGalaxy surveys favor surprisingly low neutrino masses, with inferred bounds even approaching negative values. This motivates exploring alternatives to the usual cosmological description, not concluding that neutrinos actually have negative mass. The study examines a model in which neutrinos interact with dark energy and their masses change as the universe evolves. In the model, a change in symmetry and a later shutdown of an extra force prevent neutrino clumping from growing excessively in the linear regime studied. The model could make galaxy surveys infer a lower neutrino mass and further reduce matter clustering. The authors also suggest that an early contribution from dark energy might help explain the disagreement over the universe’s expansion rate, but they do not establish that it does.

Young explorerNeutrinos are tiny particles in the universe. Scientists are exploring an idea in which their masses change as the universe grows older. In their model, an extra pull between neutrinos turns off, stopping their clumps from growing too much in the way studied. This might help explain some puzzling clues about the universe, but scientists have not shown that nature really works this way.

Predicting Primordial Non-Gaussianity Measurements in the CSST Spectroscopic Survey

Jiangnan Duan, Yan Gong, Qi Xiong+6 more

AstronomerThis simulation-based study forecasts constraints on local-type primordial non-Gaussianity from the upcoming CSST spectroscopic galaxy survey; it does not report observational measurements. Jiutian N-body simulations provide mock emission-line galaxy catalogs at z = 0.3, 0.6, and 0.9, incorporating expected redshift uncertainties and emission-line signal-to-noise selection. The redshift-space power-spectrum and bispectrum framework models redshift-space distortions, scale-dependent bias, and nonlinear effects. For the PNG-bias parameter p = 0.55, the recovered constraints are f_NL = -4 ± 43 from the power spectrum alone and 3 ± 41 when adding the bispectrum, an uncertainty reduction of approximately 5%. For p = 1, the corresponding constraints are -3 ± 86 and 54 with upper and lower uncertainties of +70 and -80. These mock-based results illustrate CSST's potential to probe inflation, while showing that the constraints depend on the assumed PNG-bias parameter and that the bispectrum provides a modest improvement for p = 0.55.

PublicResearchers used simulated galaxy catalogs to estimate how well the upcoming Chinese Space-station Survey Telescope could test ideas about the very early Universe and inflation. They studied whether galaxy clustering could reveal primordial non-Gaussianity, a departure from a Gaussian pattern in the Universe's initial fluctuations. Their forecasts include expected survey selection effects and uncertainties in galaxy redshifts. For one assumed relationship between galaxies and the primordial signal, adding a three-point clustering statistic to the two-point analysis reduced the uncertainty by about 5%. A different assumption produced substantially broader constraints. These are forecasts from simulated surveys, not a detection of primordial non-Gaussianity in real observations.

Young explorerScientists made pretend maps of galaxies on a computer to practice for a future space telescope. They want to see whether the way galaxies are grouped can give clues about how the Universe began. In one version of their test, looking at groups of three galaxies as well as pairs made their answer a little less uncertain. The answer also depended on the rules they used in their model. This is practice with pretend galaxies, not a discovery from the telescope.

CMB Lensing Reconstruction Using Two Years of Temperature Data from the SPT-3G Summer Survey

K. Levy, S. Raghunathan, F. Guidi+91 more

AstronomerThe authors present the first CMB lensing-potential reconstruction from the SPT-3G Summer survey, using two years of temperature data across three fields totaling approximately 2640 square degrees. The joint analysis measures a lensing amplitude of A = 1.014 ± 0.053 relative to the fiducial Planck 2018 ΛCDM cosmology over 50 < L < 2000, consistent with that reference amplitude. These early results suggest potential gains in signal-to-noise from combining the Summer, Main, and Wide fields over approximately 10,000 square degrees; those gains are not demonstrated here.

PublicResearchers used two years of SPT-3G Summer survey data to reconstruct how gravity bends the cosmic microwave background, the ancient light seen across the sky. Their analysis covers three patches totaling about 2640 square degrees. The measured strength of this bending is 1.014 ± 0.053 times the value expected in their reference cosmological model, so it agrees with that expectation within the reported uncertainty. Combining these observations with other SPT-3G survey regions could make the signal clearer, but that larger combined result is not reported here.

Young explorerGravity can bend very old light as it travels through space. Scientists studied that light in three patches of the sky to work out how it had been bent. The amount they found was close to what their model expected, though the measurement is not exact. They think studying more sky could help them see the bending more clearly.

High resolution Lyman-α forest constraints on dark matter-neutrino scattering

Markus R. Mosbech, Olga Garcia-Gallego, Vid Iršič+2 more

• High Energy Physics - Phenomenology

AstronomerHigh-resolution Lyman-alpha forest data constrain dark matter–neutrino interactions through an emulator trained on full hydrodynamical simulations spanning interaction strengths and thermal histories. A Markov chain Monte Carlo analysis gives u_{νχ} ≤ 1.5 × 10^-8 at 95% confidence, reported as the strongest direct bound to date. Within this analysis, the results exclude previously reported hints of nonzero interactions. The authors also find that mapping warm dark matter constraints onto this model overestimates the constraining power.

PublicThe researchers used high-resolution Lyman-alpha forest observations to test models in which dark matter interacts with neutrinos. They compared the data with predictions built from simulations covering different interaction strengths and thermal histories. Their analysis places an upper limit on the interaction strength, rather than detecting an interaction, and rules out the strengths suggested by earlier hints. The authors report this as the strongest direct limit so far. They also find that borrowing limits from warm dark matter models would make the restrictions on this interaction appear stronger than their analysis supports.

Young explorerScientists checked whether dark matter and something called neutrinos could affect each other. They compared observations with computer models and worked out how strong that effect could be. They did not find an effect; instead, they set a limit on it. Their answer does not support earlier clues that there might be an effect. They also found that a shortcut for working out the limit would make it too strict.

Selection effects in correlated observations with application to distance-ladder observations

Will J. Percival

AstronomerThe authors derive a Bayesian likelihood for truncated selection in correlated observables and apply it to recent distance-ladder H0 measurements. They test residual Cepheid selection corrections that depend on photometric uncertainties and can be constrained jointly with H0. Evidence for nonzero corrections in calibrator galaxies is mild, at 1.3–2.3 sigma depending on the distance prior. Adding one parameter for an unknown Cepheid selection cutoff in SN Ia hosts lowers the recovered H0 by 1.4 km/s/Mpc. Further SN Ia selection corrections lower it by 0.2 km/s/Mpc, while replacing a prior uniform in distance modulus with an equal-volume distance prior lowers it by 1.0 km/s/Mpc. Together, these modeling choices substantially reduce the inferred tension with CMB measurements, although the evidence for residual Cepheid selection effects remains weak.

PublicHow astronomers choose which objects to study can bias their estimate of the universe’s expansion rate, even when selection uses a different measurement from the one being analyzed, if the two measurements are related. This study develops a statistical method to account for that problem and applies it to measurements using Cepheid stars and Type Ia supernovae. The data provide only mild evidence for overlooked selection effects in the Cepheid samples. Nevertheless, allowing for an unknown Cepheid selection threshold lowers the estimated expansion rate by 1.4 kilometers per second per megaparsec. Additional supernova selection corrections and a different assumption about galaxy distances lower it further. Together, these changes substantially reduce the disagreement with estimates from the cosmic microwave background, but they do not establish that selection bias explains the disagreement.

Young explorerAstronomers use stars and exploding stars to work out how fast the universe is growing. But which ones they pick to study can change the answer. These researchers tried a way to account for that. Their calculation gave a slower growth rate, closer to an answer from another method. There are only small hints that the picking problem is really there, so this is not a sure fix.

Forecast for the detectability of patchy hydrogen reionization in WEAVE-QSO measurements of the Lyman-α forest power spectrum at redshift z ≥4

Ke Ma, James S. Bolton, Vid Iršič+9 more

AstronomerThis study forecasts, rather than reports, a detection of patchy hydrogen reionization in the WEAVE-QSO one-dimensional Lyα forest power spectrum. Mock spectra generated from the Sherwood-relics simulations for z = 4.0, 4.2, 4.4, and 4.6 show enhanced large-scale power near k ≈ 10⁻³ s km⁻¹ from relic ionization and temperature fluctuations. The covariance forecast accounts for sample size, spectral resolution, noise subtraction, continuum placement, metal contamination, and damping wings from high-column-density absorbers. Bayesian parameter inference using this forecast predicts a detection significance of approximately 4.5σ, suggesting that forthcoming WEAVE-QSO measurements could detect and characterize this relic imprint at z ≥ 4, under the modeled survey and simulation assumptions.

PublicResearchers predict that the forthcoming WEAVE-QSO survey could reveal traces of a time when hydrogen in the universe became ionized unevenly, in patches. They used simulations to create mock spectra showing hydrogen absorption in quasar light, known as the Lyman-alpha forest. In these simulations, lingering differences in temperature and ionization strengthen large-scale patterns in the absorption. After accounting for several sources of measurement uncertainty and contamination, their analysis forecasts a detection significance of about 4.5 sigma. This is a prediction based on simulations and a modeled survey, not a detection in observed data.

Young explorerLong ago, hydrogen gas in space changed, but not everywhere at once. Scientists used computer models to see whether light from faraway objects might still carry clues about those patchy changes. Their pretend observations suggest that an upcoming sky survey could spot the clues, even with things that make them hard to see. They have not found them in real observations yet.

Cosmography with DESI-DR1 Cosmic Chronometers: Direct H(z) measurements from Luminous Red Galaxy ages

Carlos A. Álvarez, Marcos M. Cueli, Balakrishna S. Haridasu+6 more

• Astrophysics of Galaxies

AstronomerUsing DESI’s redshift measurements for almost 3 million luminous red galaxies as a starting point, the authors derive cosmic-chronometer constraints on H(z) over 0.3 < z < 1.2. Spectroscopic cuts suppress star-forming contamination, and stacked spectra provide stable, high-S/N measurements of Lick indices, which are fitted with a theoretical stellar-population model to estimate ages. The resulting age–redshift relations are analyzed through both pivotal-redshift cosmography and the original discrete chronometer method. The cosmographic posteriors for H, deceleration, and jerk at the pivot are compatible with currently considered cosmologies; the authors provide a MAP H(z) estimate, median confidence-region array, and covariance matrix. Exploiting the age–redshift distributions of different velocity-dispersion groups also yields two independent local estimates. The reddest chronometer envelope gives H(z ≈ 0.61) = 88.5 with statistical uncertainties of +6.7/−12.6 and a systematic uncertainty of ±8.1 km s−1 Mpc−1. These are age-model-based observational constraints; systematic uncertainties in both approaches are assessed through an analysis of methodological choices in data treatment.

PublicResearchers used galaxy observations from DESI to estimate how fast the Universe was expanding at different stages of its history. They selected galaxies with little ongoing star formation and combined their spectra to obtain clearer signals. Comparing those signals with theoretical models of stellar populations supplied galaxy-age estimates, whose changes with redshift act as a cosmic clock. Two analysis approaches produced expansion-rate constraints. One direct estimate, at a redshift of about 0.61, is 88.5 kilometres per second per megaparsec, with statistical uncertainties of +6.7/−12.6 and an additional systematic uncertainty of ±8.1. A broader fit is compatible with currently considered cosmologies, rather than uniquely establishing one. The results depend on the age modelling and data-treatment choices, whose systematic effects the researchers assessed.

Young explorerScientists studied light from galaxies to work out how fast the Universe has been growing. They used models to estimate how old the galaxies’ stars were, a bit like reading a clock. Comparing these clocks helped them measure the growth. The answers are not exact, because reading such faraway clocks is tricky.

Assembly bias from nuisance to probe II: Salvaging linear clustering from DESI and SDSS data

Nelson Padilla, Dante Paz, Iván Lacerna

• Astrophysics of Galaxies

AstronomerUsing colour-selected DESI BGS and SDSS MGS samples, the authors test whether galactic conformity and compensated correlation statistics recover the linear matter correlation-function shape below the scales where ordinary clustering becomes nonlinear. DESI conformity monopoles, projected conformity, and compensated correlations track this shape to substantially smaller separations than ordinary colour-selected clustering. Agreement is clearest in dense DESI samples with central-primary selection, but selection dependence varies with scale and statistic. Projected conformity more closely resembles the unprojected linear matter correlation function than its projected counterpart, consistent with a response concentrated at small line-of-sight separations. The conformity quadrupole is strongly suppressed, as expected from cancellation of leading Kaiser terms. SDSS exhibits similar but noisier behaviour; MTNG, FLAMINGO, and MDPL2-SAG simulations reproduce the main trends with model-dependent amplitudes. The findings suggest suppression of nonlinear contributions while preserving linear matter information, but residual nonlinear effects need calibration before precision cosmological use.

PublicGalaxies cluster in complicated ways, making it difficult to extract the simpler pattern predicted for matter by linear theory. This study tests whether comparisons involving galaxy colours and combinations of clustering measurements can reduce those complications. In DESI observations, these measurements follow the predicted matter-pattern shape down to smaller galaxy separations than ordinary colour-based clustering measurements do. The agreement is strongest for dense samples with a particular selection of central galaxies, though the effect of sample selection depends on the measurement and scale. SDSS observations show similar but less clear behaviour. Computer simulations reproduce the main trends, but differ in their strengths. The results suggest a useful way to recover information about matter from galaxy clustering, not yet a precision-ready tool: remaining nonlinear effects must first be calibrated.

Young explorerGalaxies make patterns in space, but those patterns can be messy. Scientists tried comparing groups of galaxies in special ways to make a simpler pattern easier to see. In their observations, this worked better than the usual way, even for galaxies closer together. Computer pretend-universes showed similar patterns too. But some messiness remains, so scientists need to check the method more carefully before using it for very exact answers.

A derived evolution of dark energy from cosmic inhomogeneity confronted with baryon acoustic oscillations and type Ia supernovae

Jacky David Yang, Hans-Otto Carmesin

AstronomerThe volume dynamics of space framework incorporates matter inhomogeneity directly into expansion dynamics, predicting redshift-dependent effective Hubble and dark-energy parameters from Planck parameters alone. Its derived H(z) has the form of flat ΛCDM with a variable dark-energy density that grows by 31% toward the present, w(0) = -1.21 tending to -1 at high redshift, and a predicted present age of 13.52 Gyr, 0.30 Gyr below the homogeneous limit. Tests against DESI DR2 BAO and Pantheon+ supernovae leave H0, the sound horizon, and supernova absolute magnitude free, probing only the expansion-history shape. The prediction is disfavored relative to ΛCDM by Δχ² = 65 with one fewer parameter. Freeing the matter density reduces the penalty to 42, but BAO and supernovae separately require incompatible matter densities, 0.35 and 0.54. Their combination gives σ8 < 0.14 at 95% confidence, versus the Planck value of 0.81 used in the derivation; the heterogeneous model fits best in its homogeneous, flat-ΛCDM limit. At the leading order currently evaluated, this contribution cannot resolve the Hubble tension and produces dark-energy evolution opposite to that favored by current distance data.

PublicCould an uneven distribution of matter explain disagreements about how fast the universe expands? This study tests a framework in which that unevenness directly changes cosmic expansion. Using Planck parameters, the framework predicts that dark-energy density grows toward the present and that the universe is 13.52 billion years old; these are model predictions, not new measurements. The authors compare the predicted expansion pattern with DESI DR2 galaxy-distance information and Pantheon+ exploding-star data, while allowing the overall expansion calibration to vary. The framework fits substantially worse than the standard model with constant dark-energy density. The two datasets can each accommodate it only by requiring incompatible amounts of matter, and their combined best fit removes the proposed unevenness contribution. In the leading-order calculation tested here, the mechanism cannot explain the Hubble tension—the disagreement over the universe’s expansion rate—and changes dark energy in the opposite direction to what current distance data favor.

Young explorerThe universe is getting bigger, and its matter is spread out unevenly. Scientists tested an idea that this unevenness might help explain why measurements disagree about how fast the universe grows. They compared what the idea says should happen with clues from galaxies and exploding stars. The idea did not fit those clues as well as the usual explanation. In the version they tested, unevenness did not solve the puzzle.

Raising the Optical Depth to Reionization with Dark Matter Decay

Yu-Ning Wang, Paulo Montero-Camacho, Ziwei Wang+2 more

AstronomerThe authors test whether electromagnetic energy injection from dark matter decay through χ → e⁺e⁻ can reconcile the higher reionization optical depth preferred by DESI DR2 BAO relative to CMB inferences, approximately 0.09 versus 0.06 from large-scale CMB polarization. They derive the optical depth self-consistently using a simulation-calibrated, asymmetric Gompertzian model of astrophysical reionization plus decay-induced ionization, jointly fitting ACT+Planck CMB anisotropies, CMB lensing, BAO, and quasar damping-wing data. For a 1 GeV particle and a flat decay-rate prior, the marginalized mean optical depth increases from 0.064 to 0.072 without a significant fit improvement; log-uniform prior reweighting reduces the mean, demonstrating prior sensitivity. The modeled increase comes mainly from an extended ionization tail during the cosmic dark ages, not earlier astrophysical reionization. Across masses of 2 MeV–7 GeV, the 68% credible intervals remain below approximately 0.08, a previously identified benchmark for reducing both the neutrino-mass tension and ΛCDM exclusion below 2σ. The lifetime constraints complement photon, cosmic-ray, and gas-heating bounds and are competitive with previous CMB limits, but the posterior-favored optical-depth increase does not substantially alleviate the CMB–BAO discrepancy.

PublicMeasurements of large-scale cosmic structure from DESI and inferences from the cosmic microwave background do not fully agree. One way to express this mismatch is through the optical depth: a measure of how much ancient light scattered off free electrons as it crossed the universe. The researchers tested whether dark matter decaying into electrons and positrons could free enough additional electrons to ease the disagreement. They combined several astronomical datasets with a model of how cosmic gas became ionized. For one tested dark matter mass, allowing decay raised the average inferred optical depth from 0.064 to 0.072, but did not significantly improve the fit to the data. The size of that shift also depended on the assumed prior distribution for the decay rate. In the model, most extra scattering comes from a prolonged period of weak ionization during the cosmic dark ages, rather than an earlier start to astrophysical reionization. Across the tested masses, the favored increase remained too small to substantially resolve the mismatch. The study constrains dark matter lifetimes; it does not establish that dark matter decays.

Young explorerVery old light has traveled across space to reach us. Along the way, tiny particles called free electrons can scatter it. Different clues about the universe seem to disagree about how much scattering happened. The scientists tested an idea: maybe some invisible dark matter breaks apart and helps free more electrons. In their model, this made the old light scatter a little more, but not enough to fix the disagreement. How much it helped also depended on assumptions in their calculations. They did not discover that dark matter really breaks apart.

Perturbative Kähler Moduli Inflation

Mishaal Hai, Ahmed Rakin Kamal, Noshin Ferdous Shamma+1 more

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

AstronomerThe authors construct two classes of inflationary models in type IIB string theory compactified on a Calabi–Yau, with a blow-up Kähler modulus as the inflaton. They describe a procedure using perturbative corrections to stabilize multiple Kähler moduli. For two moduli, they explicitly construct potentials within the Kähler cone satisfying effective-field-theory and cosmological constraints. Moduli redefinition yields V(φ) = V₀(1 + C₁φ^(2/3)), compatible with CMB data and predicting r ≲ 10⁻². The loop blow-up class has V(φ) = V₀(1 + C₂φ^(-2/3)), also compatible with CMB data, with r ≲ 10⁻⁸. The latter differs from the original loop blow-up proposal in its stabilization mechanism and resulting tensor-to-scalar ratio. These are theoretical constructions, not observational detections of either model.

PublicThe study develops two string-theory models for inflation, a proposed period of rapid expansion in the early universe. Both link inflation to a quantity describing the geometry of compact extra dimensions. The authors describe how to stabilize several such geometric quantities and explicitly build two models involving two of them. Both are compatible with measurements of the cosmic microwave background, the universe’s ancient background light, but predict different upper limits on the relative strength of primordial gravitational waves: about one hundredth in the first model and one hundred-millionth in the second. Agreement with existing data does not establish that either model describes the real universe.

Young explorerScientists made two math ideas for how the universe might have grown very fast when it was very young. Both fit what we see in very old light from space. They predict different amounts of tiny ripples in space, but we do not know whether either idea is right.

Assessing the robustness of amortized simulation-based inference to transient noise in gravitational-wave ringdowns

Song-Tao Liu, Tian-Yang Sun, Yu-Xin Wang+4 more

• General Relativity and Quantum Cosmology
• Instrumentation and Methods for Astrophysics
• High Energy Physics - Phenomenology

AstronomerThe authors propose amortized simulation-based inference for gravitational-wave ringdown parameters, using a neural posterior estimator trained across the prior range. In the reported tests, the network achieves valid confidence coverage and produces posteriors consistent with established Markov-chain methods at moderate signal-to-noise ratios. At higher signal-to-noise ratios, posterior locations remain consistent, but the amplitude posterior is broader. Inference is orders of magnitude faster. Tests with injected transient noise show that estimation bias depends strongly on glitch timing, particularly when contamination overlaps the early, high-amplitude signal. These results validate the framework under the tested conditions, rather than establishing robustness to all realistic noise or incomplete signal models.

PublicAfter a black hole merger, the fading gravitational-wave signal, called ringdown, can reveal the resulting black hole’s mass and spin. This study proposes a neural-network method trained using simulations to estimate ringdown properties much faster than an established statistical approach. In the tests, its uncertainty estimates had valid statistical coverage, and its results agreed with the comparison method for moderately strong signals. For stronger signals, the estimates remained centered in similar places, but the network gave a wider range of possible signal amplitudes. Brief bursts of noise could bias the estimates, especially when they overlapped the loud beginning of the ringdown. The method was orders of magnitude faster, but its reliability has been demonstrated only under the conditions tested.

Young explorerWhen black holes join together, they make ripples in space that fade away. Scientists trained a computer using pretend signals to help work out what those fading ripples mean. In their tests, it was much faster than another method and often gave similar answers. For stronger signals, it was less sure about how big the ripples were. A sudden bit of noise could also make its answer wrong, especially near the loud beginning. It looks useful, but these tests do not show that it will work with every kind of noise.

Stability analysis and double critical phenomenon in the Einstein-Maxwell-scalar theory

Zi-Qiang Zhao, Mei-Ling Yan, Zhang-Yu Nie+2 more

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

AstronomerThis theoretical study examines a holographic superfluid model with self-interactions proportional to lambda times the fourth power of the absolute value of psi and tau times its sixth power, plus a non-minimal coupling given by the exponential of alpha times the square of the absolute value of psi. The thermodynamic and dynamical stability analyses give consistent assessments. For fixed negative lambda and fixed alpha, increasing tau shrinks the first-order transition region to a critical point and then takes the model into a supercritical region. Varying alpha can yield no critical point or a double-critical pattern: increasing alpha first takes the system into the supercritical region and then back into the first-order transition region. The authors report this single-parameter-driven double-critical phenomenon as a first for holographic superfluid models and interpret it as a nonmonotonic interplay between non-minimal coupling and higher-order interactions. These are model findings, not observational results.

PublicA theoretical study explores how a mathematical model of a superfluid changes between different states. Two ways of assessing stability—one based on thermodynamics and the other on dynamics—agree. With other specified settings held fixed, strengthening one interaction reduces the region of abrupt transitions until it ends at a critical point, beyond which the model enters a supercritical region. Changing a separate coupling parameter can produce cases with no critical point or a more unusual pattern: the model enters the supercritical region and then returns to the region of abrupt transitions as that same parameter continues to increase. The authors report this double-critical behavior for the first time in holographic superfluid models, interpreting it as a complex interaction between the model's couplings. The study does not report observations of a physical superfluid.

Young explorerScientists studied a special kind of liquid using a math model, not by watching a real liquid. The model has settings like knobs. Turning one knob can make sudden changes between states stop at a special point. Another knob can make the model leave the place where sudden changes happen and then come back, even while the knob keeps turning the same way. The scientists say this returning pattern is new for this kind of model.

Relativistic and Newtonian Proca Stars: A Tale of Two Limits

Alberto Diez-Tejedor, Carlos Herdeiro, Claudio Lazarte+4 more

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

AstronomerThis theoretical study compares a representative set of static Einstein-Proca solitons in the Newtonian limit, where the field frequency approaches the particle mass, with solutions of the effective spin-1 Schrödinger-Poisson system. The vector field and enhanced nonrelativistic U(3) symmetry make the correspondence nontrivial. The authors identify ℓ=0 electric Proca stars with radially polarized hedgehog configurations and ℓ=1 electric Proca stars with linearly polarized configurations. They clarify aspects of the ground state and resolve apparent discrepancies in morphology and stability between the two descriptions. They conclude that the nonrelativistic regime supports a richer spectrum of stable equilibria than the relativistic theory, including stable excited states. These are theoretical findings, not observational detections.

PublicThe researchers compare two mathematical descriptions of Proca stars, theoretical objects made from a vector field bound by gravity. One description uses Einstein’s theory; the other is an approximation appropriate to the Newtonian limit. Because a vector field has direction, matching the objects between these descriptions requires care. The study connects configurations with field directions pointing radially to one class of Proca stars, and configurations with a common polarization direction to another. It also resolves apparent disagreements about their shapes and stability. The authors conclude that the Newtonian description allows a wider variety of stable configurations, including excited states. The work concerns theoretical solutions, not stars observed in the sky.

Young explorerScientists used math to study unusual pretend stars, not stars they have seen in the sky. They compared a complicated set of rules with a simpler set that should work in a certain limit. Their star models have little directions, like arrows, that can point outward or line up. The scientists worked out how these patterns match between the two sets of rules. They found that the simpler rules allow more kinds of stars to stay steady, including some that are not in their lowest-energy state.

Galaxy cluster thermodynamics at z=1.7: Resolved tSZ and X-ray analysis of CL J0459.6-4946

J. van Marrewijk, L. Di Mascolo, S. Ueda+23 more

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena

AstronomerA resolved analysis of ACT/SPT-CL J0459.6-4946 at z = 1.7 combines new ALMA Band 1 and 3 thermal Sunyaev–Zeldovich observations with archival X-ray data. The inferred ICM entropy is flat and relatively high, approximately 200 keV cm² out to 0.3 r500,c, while the temperature declines outward from a hot core with Te ≃ 14 keV. The effective line-of-sight depth is (0.75 ± 0.05) r500,c, and the clumpiness factor within r500,c is 1.17 ± 0.05. The authors suggest that the dynamically active cluster is still thermalising its ICM. They find a hydrostatic mass bias relative to weak lensing of b = 0.27, with asymmetric uncertainties of +0.32 and −0.67; this is consistent with that interpretation but is weakly constrained. A southern low-entropy, high-density region appears in X-rays but not in the Compton-y map, indicating pressure equilibrium. The authors interpret it as a sloshing cold front and report it as the first such detection at high redshift. This case demonstrates the potential of approximately three hours of ALMA observations combined with 122 ks of X-ray exposure to characterise high-redshift ICM thermodynamics and motivates larger samples.

PublicAstronomers combined new ALMA observations with existing X-ray data to study the hot gas in a distant galaxy cluster at redshift 1.7. They found a very hot centre, with gas temperatures falling farther out, and a broad inner region with relatively high, nearly uniform entropy, a measure of the gas’s thermodynamic state. The researchers suggest that the cluster’s gas is still settling and converting motion into heat. A comparison of two mass estimates is consistent with this picture, but its uncertainty is large. South of the centre, a dense, lower-entropy patch appears in X-rays without a corresponding pressure feature in the ALMA-derived map. The team interprets this as a boundary made by cooler gas sloshing through the cluster, reporting the first such detection at high redshift. The study shows how combined ALMA and X-ray observations can investigate the gas in young, distant clusters.

Young explorerA galaxy cluster is a big group of galaxies with very hot gas between them. Scientists used two kinds of observations to study one far away. They found that its gas is hottest in the middle and cooler farther out. They also spotted a patch of denser gas. They think this patch is part of cooler gas sloshing around, like water moving in a bowl. The cluster’s gas may still be settling down.

Developing Environments: Formation and Quenching at Cosmic Noon Traced by the Large-scale Distribution of Gas and Galaxies

Amir H. Khoram, Sirio Belli, Trevor Mendel+15 more

AstronomerThis observational study examines environmental trends in massive-galaxy formation and quenching at 1.7 < z < 3.5 using 139 Blue Jay JWST/NIRSpec galaxies and 57 DAWN archival prism spectra in COSMOS. Joint spectro-photometric Prospector fits provide galaxy properties and histories, while COSMOS-Web galaxy counts and LATIS Lyα tomography independently trace galaxy density and intergalactic neutral hydrogen. In massive quiescent galaxies, the inferred formation-to-quenching interval increases with density. AGN and Na D outflows are confined to galaxy overdensity δ# < 0.5 and enhanced Lyα absorption δHI > 1, mostly occurring together in massive quiescent systems. About 65% of the sample follows a correlation between the environmental tracers. Two contrasting regions depart from it: a galaxy-rich, neutral-gas-poor Hyperion protocluster core contains earlier-forming quiescent galaxies without significant AGN activity or outflows, whereas a galaxy-poor, neutral-gas-rich region within 60 comoving Mpc of the densest cores hosts rapidly quenched galaxies with frequent AGN and outflows. Full gas ionization in the former and still-assembling massive halos in the latter are interpretations, not established results. The findings emphasize the complementary information supplied by galaxy counts and cool-gas mapping.

PublicWhy galaxies stop making stars may depend on their surroundings, but counting nearby galaxies does not tell the whole story. Researchers studied massive galaxies in the early Universe, combining galaxy counts with maps of cool hydrogen gas and using spectra to reconstruct their histories. Among galaxies that had stopped forming stars, the time between formation and shutdown was longer in denser environments. Two contrasting neighborhoods stood out. A galaxy-packed core of the Hyperion protocluster had little neutral hydrogen; its inactive galaxies formed earlier and showed no significant activity from central black holes or gas outflows. Another region had fewer galaxies but abundant neutral hydrogen, with rapidly shut-down galaxies frequently showing black-hole activity and outflows. The researchers suggest that gas in the crowded core may be ionized, while the second region may still be assembling. These interpretations remain uncertain, and the observations do not establish what caused star formation to stop.

Young explorerGalaxies are huge groups of stars, and some stop making new stars. Scientists looked at faraway galaxies and the gas around them to learn why. One crowded neighborhood had galaxies that formed earlier. Another, less crowded neighborhood had lots of cool gas and galaxies that stopped making stars quickly. Scientists think these neighborhoods may be growing differently, but they are not sure. Counting galaxies alone does not tell the whole story.

EMBER: A Little Red Dot Candidate at z(spec)=10.36 in the Seed Black Hole Era

Takumi S. Tanaka, Hollis B. Akins, John D. Silverman+58 more

AstronomerJWST/NIRSpec spectroscopy from EMBER places the highest-redshift known little red dot (LRD) candidate at z_spec = 10.361 (+0.003/−0.002), constrained by a prominent Lyα break and multiple tentative emission lines. C IV and [O III] λ4363 have reported signal-to-noise ratios of 3.9 and 3.6. Its extreme F444W−F770W color of 1.82 ± 0.10 and V-shaped continuum turning over near the Balmer limit support the LRD classification. A possible iron complex and a possibly high [O III] λ4363/Hγ ratio favor, but do not establish, an AGN-like interpretation. Tentative Lyα emission may indicate enhanced transmission at z ≈ 10. The source extends observations of candidate black-hole growth into the seed-formation era; upcoming MIRI spectroscopy is intended to clarify its physical nature.

PublicAstronomers using the James Webb Space Telescope have measured a redshift of about 10.36 for a candidate belonging to the newly discovered population called little red dots, placing it in the very early universe. Its colors and the shape of its light spectrum support that classification. Little red dots may host rapidly growing black holes, and this source has possible spectral features consistent with that interpretation, but its nature is not yet established. Several emission features are tentative, including one that could suggest that some hydrogen light escaped more easily through the early universe. Planned follow-up spectroscopy will help determine what powers the source.

Young explorerAstronomers used the James Webb Space Telescope to study a tiny-looking red dot whose light comes from very early in the universe. The light has clues that it belongs to a group called little red dots. It might be powered by a growing black hole, but the scientists are not sure yet. They plan to look more closely to learn what makes it shine.

MARTA: A "little" black hole hidden in a clumpy, metal-poor galaxy at z 3.8

Mirko Curti, Bianca Moreschini, Elisa Cataldi+20 more

AstronomerCombined JWST/NIRSpec, HST/JWST imaging, and archival VLT/MUSE observations identify a low-mass black hole candidate in the clumpy galaxy MARTA 3887 at z=3.7694. Broad Hα has luminosity 2.35×10^41 erg s−1 and FWHM 1270 (+260/−250) km s−1, without comparably broad [O III]. If this emission arises in a broad-line region, virial calibrations imply log(MBH/M☉)=6.52 (+0.18/−0.23) and an Eddington ratio of 0.07, rising to 0.38 with alternative calibrations. The host contains at least three compact clumps and has log(M★/M☉)=8.16 (+0.09/−0.10). Assuming stellar photoionization dominates the narrow lines, its gas has 12+log(O/H)=7.68±0.04, approximately 0.10 solar metallicity. The inferred black-hole-to-stellar mass ratio of 2.3% is about two dex above the extrapolated local relation, suggesting black-hole growth outpaced assembly of the observed host. A 100-solar-mass seed beginning growth only 92 Myr ago would require a lifetime-mean Eddington ratio near 5.7; earlier growth or a more massive seed could permit sub-Eddington mean accretion. Extended Lyα spans approximately 6.5–6.9 proper kpc, is redshifted by 64 (+10/−8) km s−1, and has a provisional escape fraction near 0.44. Together with the Mg II doublet and [O III]/[O II] ratios, these observations motivate joint studies of black-hole growth, stellar assembly, and ionizing-photon escape.

PublicAstronomers have identified a possible growing black hole in MARTA 3887, a distant galaxy made of at least three compact clumps. They detected a broad component of hydrogen emission without a similarly broad oxygen component. If the hydrogen signal comes from gas near a black hole, it implies a black hole about three million times the Sun’s mass. Its inferred mass is unusually large compared with the galaxy’s stellar mass, suggesting that black-hole growth may have outpaced the buildup of the observed host. This interpretation does not establish how the black hole formed. A small starting black hole given only the last 92 million years to grow would need exceptionally rapid average feeding; an earlier start or a larger initial black hole could ease that requirement. The observations also reveal extended hydrogen emission and other spectral clues that make this galaxy useful for investigating how radiation escapes alongside galaxy and black-hole growth.

Young explorerScientists looked at a faraway galaxy made of little clumps of stars. Its light has a clue that a black hole might be feeding there, but they are not sure yet. If it is a black hole, it seems unusually big compared with the galaxy’s stars. Scientists want to learn how it grew and how light gets out of the galaxy.

A Supermagnified Little Red Dot with a Resolved Host

Jon Judež, Roberta Tripodi, Nicholas S. Martis+24 more

AstronomerJWST observations of the gravitationally lensed little red dot “Best Friend” establish a spectroscopic redshift of 8.297 ± 0.002. Its magnification of 36 (+8/−12), the highest reported for an LRD to date, enables resolution of the host and constrains the central engine to less than 7 pc. The central spectrum favors black hole activity over a dense stellar cluster, but the cluster interpretation is not excluded. No broad lines are detected, possibly because of limited signal-to-noise and spectral resolution. A stellar-cluster interpretation would imply a stellar surface-density lower limit of >1.25 (+0.4/−0.3) × 10^6 solar masses per square parsec, roughly two orders of magnitude above typical high-redshift clusters. Spatially resolved NIRCam photometry and NIRSpec/PRISM spectroscopy yield a host stellar mass of log(M_star/M_sun) = 7.3 (+0.2/−0.8). The observations illustrate how lensing can reveal LRD morphology while leaving the nature of the central engine uncertain.

PublicJWST has observed an extremely compact early-universe source nicknamed “Best Friend,” belonging to a puzzling class called little red dots. Gravitational lensing magnifies it by about 36 times—the largest magnification yet reported for this class—allowing researchers to distinguish its host galaxy’s structure and a central source smaller than 7 parsecs. The central spectrum is better explained by black hole activity than by a tightly packed star cluster, but the star-cluster explanation remains possible. Broad spectral lines were not detected, potentially because the data lack sufficient sensitivity and spectral resolution. If the center is a star cluster, its stellar surface density would have to be roughly 100 times greater than that of typical clusters in the early universe.

Young explorerA space telescope called JWST looked at a tiny red dot nicknamed “Best Friend” from long ago. Gravity helped make it look bigger, like a magnifying glass, so scientists could see more of its shape and its tiny, bright middle. They think a black hole may be making the middle shine, but they are not sure. It might instead be a very tightly packed bunch of stars.

Dust-induced reversal of the optical wavelength dependence of spiral-arm pitch angles

Eric E. Martínez-García, Rosa A. González-Lópezlira, Ivânio Puerari+1 more

• Cosmology and Nongalactic Astrophysics

AstronomerClassical density-wave theory predicts a blue-to-red age–colour gradient across spiral arms following shock-induced star formation, whereas wavelength-dependent pitch-angle observations sometimes suggest a red-to-blue colour jump. This study investigates dust attenuation of post-shock stellar emission and gas and stellar streamline motions. It finds that relatively high optical depths, τ̂V ≳ 0.2, can reverse the relative locations of flux maxima in different bands, producing an apparent red-to-blue sequence relative to the shock. Streamline motions also keep post-shock populations near the arms longer than circular-orbit models, altering the light distribution. These findings offer a possible reconciliation: an apparent red-to-blue jump need not contradict density-wave theory, because dust can modify emission from populations with an intrinsic blue-to-red age–colour gradient.

PublicA traditional explanation of spiral arms predicts that stars formed after gas passes through a shock should create a blue-to-red colour sequence across an arm. Some observations instead suggest the reverse. This study explores how dust and the paths followed by gas and stars could affect that appearance. The analysis finds that sufficiently strong dust attenuation can shift where different colours of light appear brightest, creating an apparent red-to-blue sequence. It also finds that non-circular paths keep stars near the arms longer than a circular-orbit model would. The reversed colour pattern therefore does not necessarily disprove the traditional explanation: it could be the appearance of the expected stellar populations after dust alters their light.

Young explorerA galaxy’s spiral arms can look like colourful ribbons. One idea says that new stars should make a pattern going from blue to red, but sometimes astronomers see signs of the opposite. This study finds that dust could change which parts look brightest, making the colour pattern seem backward. It also finds that the paths stars follow can keep them near an arm longer. So a backward-looking pattern does not have to mean the original idea is wrong.

The MAGPI Survey: the evolution of galaxy spin-filament alignments since z 0.3

Stefania Barsanti, Andrew J. Battisti, Sabine Bellstedt+20 more

AstronomerMAGPI measurements at 0.20<z<0.42 use resolved stellar and ionised-gas kinematics to reconstruct 3D spin axes, with filaments identified from a stellar-mass-matched, constant-number-density population drawn from GAMA, the MAGPI Redshift Survey and DESI. At z~0.3, the statistical spin–filament alignment changes from preferentially parallel at low stellar mass to preferentially perpendicular at high mass. The transition occurs at log(M*,t/Msun)~10.8, approximately 0.6 dex above the SAMI value at z~0.05; bootstrap analysis gives 99.5% confidence that the MAGPI transition mass is higher. At fixed stellar mass, MAGPI galaxies show stronger parallel alignments than SAMI galaxies, suggesting evolution over the past ~3 Gyr. Relative to a stellar-mass-matched SAMI sample, MAGPI also shows stronger filament alignment for ionised gas than for stars. The authors interpret this as stronger gas coupling to large-scale structure, consistent with coherent gas accretion remaining efficient at higher stellar masses. At z~0, the transition occurs at lower mass and gas and stellar alignments are similar; cumulative mergers and secular evolution are proposed explanations, rather than directly established causes.

PublicGalaxies lie along enormous cosmic strands called filaments. Using the MAGPI Survey, researchers measured how galaxies’ spin axes point relative to these strands about 3 billion years ago. Lower-mass galaxies tended to spin with their axes along the strands, while higher-mass galaxies tended to have axes across them. These are statistical preferences, not rules for every galaxy. Compared with the later-universe SAMI sample, the switch between these tendencies occurred at a higher stellar mass in MAGPI, with 99.5% confidence that the transition mass is higher. At the same stellar mass, MAGPI galaxies also showed a stronger preference for parallel alignment. Their ionised gas was more closely aligned with filaments than their stars, a distinction less evident in the nearby comparison sample. The findings suggest that galaxy spins and their connection to cosmic filaments have changed over time. Continued gas supply along filaments, galaxy mergers and gradual internal changes are offered as explanations, not proven causes.

Young explorerGalaxies are huge groups of stars and gas, and many sit along giant strands in space. Scientists looked at how galaxies spin compared with those strands. In a view of the universe from long ago, smaller galaxies more often had their spinning poles pointing along the strands, while bigger galaxies more often had them pointing across. Not every galaxy followed this pattern. Comparing these galaxies with ones from a later time suggests the pattern has changed. The gas and stars also pointed differently in the older view. Scientists think flowing gas and galaxies joining together might help explain the changes, but they have not proved why they happened.

Euclid Quick Data Release (Q1). Mass-to-light ratio of elliptical galaxies: constraints from strong lensing

Euclid Collaboration, A. Sonnenfeld, A. Nersesian+97 more

AstronomerUsing strong gravitational lensing data from Euclid Q1, the authors constrain the total mass M5 within an aperture of 5 h^-1 kpc in 95 elliptical galaxy lenses. Reproducible sample selection allows correction for selection effects. At z = 0.5 and an r-band luminosity of 10^10.7 L_sun h^-2, the mean log10(M5 h/M_sun) is 11.30 ± 0.02. M5 scales with luminosity as L^β, with β = 0.71 ± 0.07, and decreases with increasing redshift at fixed luminosity. Interpreting these population correlations under merger-driven growth and passive stellar evolution implies increasing M5 with time for individual galaxies; this is conditional on that evolutionary scenario, not a direct measurement of individual growth. The measurements provide a benchmark for models of total mass distributions on 5 h^-1 kpc scales.

PublicResearchers used the bending of background light by 95 elliptical galaxies in Euclid’s first Quick Data Release to estimate the total mass within a specified inner region, rather than across each whole galaxy. They accounted for biases introduced by how the galaxies were selected. More luminous galaxies tend to contain more mass in this region, but the mass rises less rapidly than the luminosity. At the same luminosity, galaxies seen at higher redshift, corresponding to earlier cosmic times, have less mass in that region. If galaxies grow through mergers while their stars age without new star formation, these patterns imply that individual galaxies gain mass in their inner regions over time. That growth is an interpretation based on those assumptions, rather than something directly tracked. The findings can test models of galaxy structure and evolution.

Young explorerA galaxy’s gravity can bend light coming from behind it. Scientists used that bent light to work out how much stuff is inside the inner parts of 95 galaxies. Brighter galaxies usually had more stuff there. Among galaxies with the same brightness, those seen further back in time had less stuff in their inner parts. If galaxies grow by joining together while their stars grow older, this could mean their inner parts gain more stuff over time. The scientists did not watch one galaxy grow; they compared different galaxies.

The L1157 filament as traced in HNCO by the LMT

A. I. Gómez-Ruiz, C. Codella, O. S. Rojas-García+9 more

AstronomerThe authors mapped HNCO emission across the blue lobe of the chemically active L1157 outflow using the Large Millimeter Telescope and its SEQUOIA array. Observations of the 87.925 GHz transition covered a 3 × 3 arcmin region centered on the L1157-B1 shock. HNCO was detected both in the outflow and along an approximately 0.3 pc structure identified as the natal filament of the protostellar system. The authors interpret HNCO as a tracer of dense filamentary gas and its presence in cold, quiescent material as evidence that precursors of complex chemistry are already present before protostellar heating or shocks. The observations also demonstrate the LMT's ability to map weak, extended molecular emission.

PublicAstronomers used the Large Millimeter Telescope to map isocyanic acid, a molecule involved in forming more complex chemicals, around the young stellar system L1157. They detected it both in an outflow of gas and in a cold filament about 0.3 parsecs long, identified as the material from which the system formed. The researchers interpret this finding as evidence that ingredients for complex chemistry can be present before a forming star heats or shocks its surroundings. This is a detection of a chemical precursor, not evidence of life. The study also shows that the telescope can map faint molecular signals spread over extended regions.

Young explorerAstronomers used a telescope to find a molecule in gas near a baby star. They found it in gas flowing away and in a long, cold strand of gas where the star was born. This molecule can help make more complicated molecules. Finding it in the cold gas suggests that some chemical ingredients are there even before the baby star warms or jolts the gas. It does not mean they found living things.

Modeling CO Line Luminosity with FIRE simulations: II. Comparison With Observations, CO Luminosity Functions and Redshift Evolution

Doğa Tolgay, J. Richard Bond, Norman W. Murray+3 more

AstronomerThe study predicts CO(1-0) and CO(2-1) luminosities for FIRE-2 galaxies at z=0, 1, 2 and 3, post-processed with SKIRT radiative transfer and CLOUDY line-emission calculations. At z=0, the predictions reproduce the observed mean and scatter of the SFR–CO(1-0) relation for massive star-forming galaxies and low-metallicity dwarfs, as well as the observed superlinear CO(1-0)–metallicity slope. At z=1, predicted CO(2-1) luminosities extend substantially below observations; the authors suggest that limited survey sensitivity likely explains this difference. At fixed SFR, predicted CO(1-0) luminosity declines by roughly a factor of ten per unit increase in redshift. The authors attribute this primarily to declining metallicity, since simulated galaxies with comparable SFR and metallicity have similar CO(1-0) luminosities across redshifts. At fixed stellar mass, no redshift dependence is predicted. Agreement where observations provide robust detections supports, but does not observationally validate, extrapolation into unobserved regimes and potential use in predictive CO intensity-mapping models.

PublicResearchers used simulated galaxies to predict the brightness of two emission lines from carbon monoxide gas, then compared those predictions with existing observations. For present-day galaxies, the calculations reproduce measured relationships between carbon monoxide brightness, star formation and the abundance of heavier elements. For galaxies at redshift 1, the simulations include much fainter emission than observations show; the authors suggest current surveys may miss these faint galaxies. Among simulated galaxies forming stars at the same rate, carbon monoxide emission becomes fainter at higher redshift, likely because heavier elements are less abundant. This trend disappears when galaxies are compared at the same stellar mass. The agreement with available observations suggests these predictions could help model future carbon monoxide mapping experiments, although predictions for unobserved galaxies remain untested.

Young explorerScientists made pretend galaxies on computers to predict how brightly a gas called carbon monoxide would glow. Some predictions matched what astronomers see in real galaxies. The computers also predicted galaxies too faint for today's surveys to easily see. Those faint galaxies still need to be checked with observations.

EMU/GAMA: Understanding the link between dust geometry and star formation rate in galaxies

U. T. Ahmed, A. M. Hopkins, B. Farley+10 more

AstronomerUsing EMU Early Science observations at 887.5 MHz in the GAMA G23 field together with GAMA data, the authors investigate how dust affects Halpha-based star formation rates. Balmer-decrement corrections can miss optically thick regions from which Halpha cannot escape, so the ratio of radio-derived to Balmer-decrement-corrected Halpha SFRs serves as a probe of this obscuration. They find systematic dependencies of L_radio/L_Halpha on the Balmer decrement and dust mass, and combine these quantities in a dust-geometry parameter, H_dust. The resulting Halpha SFR estimator accounts for optically thick dust and yields estimates consistent with conventional SFR indicators. The approach is presented as a demonstration of a more physically complete dust model, not a replacement for standard corrections.

PublicDust can hide the light astronomers use to estimate how quickly galaxies form stars. A standard correction compares hydrogen emission lines, but it can miss regions so dusty that their Halpha light never escapes. The researchers compared radio and Halpha measurements of galaxies and found systematic links between their luminosity ratio and two dust measures: the hydrogen-line comparison and total dust mass. Combining these measures in a model of how dust is arranged, they developed an Halpha-based star formation estimate that accounts for heavily hidden regions and agrees with conventional indicators. They present the model as a way to include dust effects that standard methods may overlook, rather than as a replacement for those methods.

Young explorerDust can hide the light from places where stars are being born. Scientists compared radio signals with a special kind of light from galaxies to learn about this hiding dust. They combined two clues about the dust to help estimate how quickly stars are forming. Their estimates agreed with other usual ways of checking. This is a way to help with hidden light, not a plan to throw the old methods away.

Introducing Aurora: A New Black Hole Seeding Model With Explicit Environmental Coupling

Harry George Chittenden, Darren Croton, Karl Glazebrook+1 more

• Cosmology and Nongalactic Astrophysics

AstronomerAurora is an environment-dependent black hole seeding module for the Mimic semi-analytic framework. Motivated by evidence linking early quiescent galaxies and overmassive black holes to dense environments, it assigns a continuous seed-mass spectrum using halo mass, local overdensity, and the radial skewness of surrounding haloes. It requires only halo masses and positions, allowing use with dark-matter-only simulations. Calibrated against Sage on the Millennium merger trees, the model attributes 29 per cent of all black hole mass formed by z=0 to seeds. It produces a seed-dominated growth pathway in galaxies assembled rapidly in dense, asymmetric environments, distinct from the accretion-dominated majority. Environment-dependent seeding increases the quiescent fraction of seeded galaxies in massive haloes at z≈3.1 by up to 70 per cent, with an excess in overdense regions and a deficit in voids. Scrambling seeding environments while retaining the seed-mass spectrum removes this gradient. The two environmental couplings produce separable signatures and broaden galaxy–black hole mass-relation scatter while preserving the stellar–halo mass relation and other Sage summary statistics. These are model findings; applications at gigaparsec scales and higher resolution are discussed as future work.

PublicThis study introduces Aurora, a computer-model prescription in which the starting masses of black holes depend on their surroundings rather than being fixed. It is motivated by evidence that unusually massive black holes and early galaxies that have stopped forming stars assemble in crowded regions. In the model, black hole seeds supply 29 per cent of the black hole mass formed by the present day. Most black holes grow mainly by taking in matter, but some systems assemble chiefly from seeds in rapidly forming galaxies in dense, uneven surroundings. The model also produces more galaxies that have stopped forming stars in crowded regions and fewer in sparse regions. Shuffling the environments assigned to seeds removes that pattern. These are modeling results, not direct measurements of how real black holes began.

Young explorerScientists made a computer model of how black holes might begin and grow. They let the starting black holes have different sizes depending on how crowded their space neighborhood is. In the model, some big black holes grow mostly by bringing many little starting ones together, while most grow mainly by taking in more stuff. This is a possible story to study, not proof of what happened in space.

Witnessing pre-processing at intermediate redshift: observational evidence of infalling groups onto a merging galaxy cluster

D. Hernández-Lang, D. Pallero, A. Ivleva+12 more

AstronomerMUSE spectroscopy and HST imaging reveal interaction signatures and ongoing star formation in five high-velocity galaxies assigned to two candidate infalling groups in the merging cluster SPT-CL J0307-6225 at z=0.579. Group 1 is a morphologically disturbed interacting pair bound to the cluster, with at least one dusty starburst. Group 2 is a compact triplet offset by approximately four cluster velocity dispersions; two members share an [O II] envelope, and its dominant e(b) starburst has elevated ionised-gas velocity dispersion. Both starbursts have SFRs within the scatter of the field star-forming main sequence, consistent with modest interaction-triggered bursts rather than unusually high SFRs. Magneticum analogues of close pairs at Group 2's phase-space position occur among approximately 1% of comparable-mass cluster galaxies; the authors interpret this as allowing a bound-group scenario, not establishing it. The resolved interaction signatures support group-scale pre-processing, but do not conclusively separate it from merger-related effects. Such interactions may contribute to enhanced star formation in merging clusters.

PublicThe researchers studied five galaxies in two possible incoming groups near a merging galaxy cluster. Images and spectroscopy show that galaxies in both groups are interacting while still forming stars. One group is a disturbed pair gravitationally bound to the cluster. The other is a compact trio moving at an unusually high speed relative to the cluster; two of its galaxies share a surrounding region of glowing oxygen gas. Although two galaxies are classified as starbursts, their star-formation rates remain within the range seen among ordinary star-forming galaxies. This is consistent with modest bursts caused by interactions. Computer simulations suggest that the fast-moving trio could be gravitationally bound, but do not prove that it is. The findings support the idea that interactions within small groups can change galaxies before they join a cluster. However, separating these changes from effects of the cluster merger remains difficult.

Young explorerGalaxies are huge families of stars. Scientists looked at five galaxies in two little groups near a much bigger gathering. They saw signs that the galaxies were tugging on one another while making new stars. Those tugs might help them make stars before joining the bigger gathering. But scientists are not sure how much comes from the little groups and how much comes from the bigger gathering coming together.

Dynamically defined bulges reveal that early-type galaxies with compact bulges host more massive black holes

Hanjing Shi, Ling Zhu, Sabine Thater+4 more

AstronomerThe authors revisit the black hole mass–bulge mass relation in 30 nearby early-type galaxies with accurately measured black hole masses and wide-field integral-field spectroscopy. Schwarzschild orbit-superposition models provide a uniform dynamical bulge definition: stellar orbits within 3 kpc with circularity λ_z < 0.7, with λ_z < 0.2 considered as an alternative. Reconstructed bulge densities yield masses, sizes, and surface-density slopes. The λ_z < 0.7 bulge masses are systematically consistent with photometric estimates, while the scatter about the black hole mass–bulge mass fit decreases modestly from 0.56 to 0.47. At fixed bulge mass, smaller bulges or those with steeper density slopes host more massive black holes; eight overmassive-black-hole outliers have ultra-compact bulges. Adding bulge size or density slope brings these outliers into agreement and reduces the sample scatter to approximately 0.3. The authors interpret the observed compactness trend as evidence that merger history changes the relation, rather than directly measuring that evolution.

PublicA study of 30 nearby early-type galaxies finds that the mass of a central black hole is linked not only to the mass of the galaxy’s central stellar bulge, but also to how tightly those stars are packed. The researchers used observations and models of stellar orbits to define and measure bulges consistently. Among galaxies with similar bulge masses, those with more compact bulges tend to have heavier black holes. Eight galaxies with unusually massive black holes also have extremely compact bulges. Including compactness makes the relationship tighter and accounts for those exceptions within this sample. The authors interpret the pattern as a record of past galaxy mergers, although the study does not directly observe the relationship changing through merger histories.

Young explorerGalaxies are huge groups of stars, and these galaxies have black holes in their centers. Scientists studied 30 galaxies using observations and models of how stars move. When their middle groups of stars had about the same total mass, the ones packed more tightly tended to have heavier black holes. The scientists think past collisions between galaxies may explain the pattern, but they did not watch that happen.

Physically Motivated Stellar Populations for Galaxies at Cosmic Dawn with a Temperature-Dependent IMF

Gibson B. Bowling, Charles L. Steinhardt, Lachlan J. Hobart+15 more

• Cosmology and Nongalactic Astrophysics

AstronomerJWST observations have identified galaxies at z>12 and added constraints at z>8, with some inferred stellar masses difficult to reconcile with ΛCDM when estimated using models not calibrated for the high-redshift Universe. The authors introduce SSPT, a simple stellar population library with a temperature-dependent stellar initial mass function, and implement it in CIGALE. In a high-redshift configuration requiring young stellar populations, SSPT yields stellar masses approximately 0.3–0.5 dex below comparable CIGALE analyses using locally calibrated models, and nearly 2 dex below analyses using other codes and weaker age constraints. These are model-dependent mass estimates, not direct mass measurements; the larger difference also involves changes in code and age constraints. The results suggest that early star-forming galaxies need not be in tension with ΛCDM and that formation from virialized halos remains a reasonable hypothesis. The library and its CIGALE implementation are publicly released.

PublicThe James Webb Space Telescope has found galaxies from very early in the Universe whose estimated masses in stars have seemed hard to explain within the standard cosmological model. But those estimates depend on models of their stars, often calibrated for the nearby Universe. The authors introduce a publicly available model that lets the relative numbers of stars born at different masses depend on temperature. When configured to require young stellar populations, it gives substantially lower stellar-mass estimates than earlier approaches. The size of the reduction depends on the models, software, and age restrictions being compared. These estimates suggest that the early galaxies may fit standard cosmology after all, rather than proving that the cosmological model must change.

Young explorerA space telescope found galaxies from when the Universe was very young. Scientists thought they might have much more stuff in stars than expected. A new way to model their stars, assuming the stars are young, gives smaller estimates. That could help these galaxies fit our picture of how the Universe works.

An Unusually Clumpy Ultra-Diffuse Galaxy in the Coma Cluster: A Missing Link for Globular Cluster Formation?

Yimeng Tang, Aaron J. Romanowsky, Nobuhiro Okabe+1 more

AstronomerDeep Keck Cosmic Web Imager integral-field spectroscopy and Subaru Hyper Suprime-Cam imaging reveal about 10 luminous star-forming clumps in Coma-B122, a star-forming ultra-diffuse galaxy on the Coma cluster outskirts. The clumps contribute roughly 25% of its luminosity and 7% of its stellar mass, have typical masses of about one million solar masses, and occupy a ring roughly 2 kpc from the center. Full-spectrum fitting indicates that about 12.5% of the diffuse body's stellar mass formed during an extended episode of enhanced star formation over the past roughly 300 Myr, during which all the clumps assembled. Asymmetric diffuse light and an asymmetric H I velocity profile provide evidence for weak ram-pressure stripping; ordered stellar and ionized-gas rotation, the cold gas fraction, and phase-space position are consistent with early infall. Spatial variations in clump star formation histories and gas-phase abundances suggest that stripping-driven inflow of metal-poor gas may have triggered and sustained the recent activity. B122 could offer a present-day view of globular-cluster-system assembly during cluster infall, but whether its clumps can survive as globular clusters remains uncertain. Higher-resolution observations and more analogs are needed.

PublicAstronomers studying Coma-B122, a diffuse galaxy on the outskirts of the Coma galaxy cluster, found about 10 bright clumps where stars are forming. Arranged in a ring roughly 2 kiloparsecs from the galaxy's center, these clumps supply about a quarter of its light but only about 7% of its stellar mass. Analysis of the starlight indicates that all the clumps assembled during an extended period of increased star formation over the past roughly 300 million years. The galaxy's uneven light distribution and hydrogen-gas motions show signs of weak gas stripping as it moves through the cluster environment. Other properties are consistent with the galaxy being early in its fall into the cluster. The researchers suggest that this interaction may also have driven gas relatively poor in heavier elements inward, helping fuel the recent star formation. The clumps might reveal how diffuse galaxies build systems of globular star clusters, but it is not yet clear whether they can survive to become such clusters.

Young explorerScientists found a faint galaxy with about 10 bright bunches of new stars arranged in a ring. They think the galaxy is just starting to fall into a big group of galaxies. There are clues that some gas is being pushed away, and the scientists think this may also help move other gas inward to make new stars. The bright bunches might someday become long-lasting groups of stars, but nobody knows yet whether they will stay together.

Simulating winds in the Galactic centre. II. Observational biases on HI clouds and a multi-wavelength comparison

N. Peschken, E.M. Di Teodoro, M. Hanasz+3 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors forward-model a supernova-driven, multiphase magnetohydrodynamical outflow, generating mock HI observations matched to Green Bank Telescope Galactic-centre surveys and analysing them like the real data. In the mock observations, beam smearing enlarges, rounds and dilutes clouds, while noise removes faint clouds and low-density outskirts. Together with foreground disk confusion, these effects hide more than 80% of simulated clouds, reaching 95% in more quiescent phases. Detected clouds appear less massive, turbulent and elongated, with column densities underestimated by a factor of two; only velocities are reliably recovered. After these observational effects are included, the simulation broadly matches the observed HI properties and sky distribution, but lacks clouds with velocities above 250 km/s and Galactic latitudes above 10 degrees. Mock UV absorption gives warm-ionized columns at the low end of observations, and soft X-ray emission measures are too low above 10 degrees. The authors infer that the true cloud population is more numerous, massive, turbulent and elongated than observed; a stronger recent starburst or additional feedback may be needed to explain the remaining discrepancies.

PublicFast-moving hydrogen clouds above the Milky Way’s centre provide evidence for a wind flowing out of that region. This study asks how telescope limitations affect what astronomers infer about those clouds. The researchers simulated a wind powered by exploding stars, then made artificial observations resembling existing radio surveys. In those mock observations, limited resolution, noise and overlapping gas emission hid more than 80% of the clouds and distorted the properties of those still visible. Cloud speeds were recovered reliably, but other properties were not. The simulated observations broadly resembled the real surveys, although they lacked the fastest clouds and those farthest above the Galactic plane in the sky. Comparisons using ultraviolet absorption and X-ray emission also showed shortcomings. The authors suggest that the real cloud population is larger and more massive than it appears, and that explaining all the observations may require a stronger recent burst of star formation or another source of energy.

Young explorerThere are fast-moving clouds of gas above the middle of our galaxy. Scientists made a computer model of a wind pushed by exploding stars. Then they pretended to look at its clouds with a telescope like the real one. Most model clouds became too hard to see, and the visible ones looked different. The model matched many things in the real sky, but not everything. The scientists think many real clouds may be hidden, and the wind might need a stronger push than their model gives it.

Chemical abundances of a Galactic Centre ejecta discovered in DESI

Manuel Cavieres, Darío González Picos, Rogelio Albarracín+9 more

• High Energy Astrophysical Phenomena
• Solar and Stellar Astrophysics

AstronomerHigh-resolution Magellan/MIKE optical spectroscopy of DESI-312, a bound hypervelocity-star candidate in the halo, yields [Fe/H] = +0.2 ± 0.1. Its super-solar metallicity, kinematics, and updated isochrone age of 7.4–11.3 Gyr strengthen the interpretation of Galactic Centre formation and Hills-mechanism ejection by Sgr A*, rather than membership in an accreted, radially orbiting halo population. Korg and Turbospectrum analyses provide abundance ratios for 22 elements, supplemented by an independent line-by-line NLTE lithium analysis. Because DESI-312 is near the main sequence, its C, N, and O abundances are unaltered by dredge-up; the authors identify these, to their knowledge, as the first such measurements of unevolved Galactic Centre material. Its abundance pattern overlaps nuclear star cluster, nuclear stellar disc, and inner-bulge sequences. Its [Na/Fe] = +0.16 with uncertainties of +0.03/−0.04 is more modest than in nuclear star cluster giants of comparable metallicity. Chemistry therefore cannot uniquely identify its progenitor population, although the authors favour the nuclear star cluster on demographic and kinematic grounds. Comparisons with WINERED-HVS1 and S0-6/S10 tentatively suggest multiple progenitor populations for the S-star cluster. DESI-312 demonstrates the potential of ejected dwarfs as optical probes complementary to infrared spectroscopy of central giants.

PublicA fast-moving star far from the Milky Way’s centre may carry a chemical record of that hard-to-observe region. Optical observations of DESI-312 show that it is richer in iron than the Sun. Combined with its motion and estimated age of 7.4–11.3 billion years, this supports—but does not prove—the idea that it formed near the Galaxy’s central black hole and was flung outward. Researchers measured its composition across many elements. Unlike the bright giant stars usually studied near the Galactic Centre, DESI-312 has not had its surface carbon, nitrogen, and oxygen changed by dredging up material from inside. Its chemistry nevertheless matches several central stellar populations, so it cannot reveal its birthplace uniquely. The authors favour the nuclear star cluster based on its stellar population and the star’s motion. Comparisons with two other stars also tentatively suggest that stars close to the central black hole may come from more than one population.

Young explorerA speedy star far from our galaxy’s middle might have been tossed outward by a giant black hole. Scientists studied its light to see what it is made of. Those ingredients and its motion give clues that it came from the middle, but they do not prove it. Different groups of stars there have similar ingredients, so scientists cannot yet tell exactly which group was its home.

The Stellar-Mass Dependence of Feedback-Driven Outflows in DESI DR1 Star-Forming Galaxies

Yimeng Tang, Yifei Luo, Conghao Zhou

• Cosmology and Nongalactic Astrophysics

AstronomerUsing DESI spectroscopy and COSMOS2020 photometry for approximately 1,200 star-forming galaxies at z < 0.25 spanning 7.9 < log(M★/M☉) < 11.5, the authors compare pPXF ionized-gas kinematics with recent star formation histories reconstructed through joint spectrophotometric fitting with Prospector. Mass-normalized gas velocity dispersion correlates positively with recent star formation below log(M★/M☉) ≲ 9.8, quantitatively consistent with earlier observations and FIRE-2 predictions for feedback-driven gas inflow and outflow cycles, or a breathing mode. Above approximately 9.8, the correlation rapidly weakens and becomes consistent with zero. The authors interpret this transition as a characteristic mass above which stellar feedback no longer dominates galaxy-scale gas kinematics, rather than as evidence that feedback ceases. The finding constrains the kinematic signature of the proposed cycles; future joint analyses of gas kinematics and stellar structure will test the broader galaxy response predicted by the breathing-mode scenario.

PublicStars can influence their galaxies by stirring and moving gas, helping regulate further star formation. Simulations predict that repeated gas inflows and outflows make small galaxies behave as though they are breathing: stronger recent star formation should accompany a larger spread in gas speeds after accounting for galaxy mass. Studying about 1,200 star-forming galaxies, researchers find this predicted relationship in lower-mass systems. Above a characteristic stellar mass, the relationship weakens rapidly and is consistent with no correlation. They interpret this as a transition beyond which stellar feedback no longer dominates gas motions across a galaxy, not as proof that stars stop affecting gas. The observations support the predicted motion pattern but do not directly establish the full breathing cycle; future work will test whether changes in stellar structure accompany it.

Young explorerGalaxies are huge groups of stars and gas. Stars can push gas around, and computer models suggest that gas in small galaxies can move in and out a bit like breathing. Scientists studied about 1,200 galaxies. In smaller ones, making more stars recently went along with more stirred-up gas, after allowing for differences in galaxy size by mass. In bigger ones, that link faded. This suggests stars may not be the main thing controlling gas motion in bigger galaxies. Scientists still need to check whether the galaxies really change in all the ways the breathing idea predicts.

See you again: an 80(°) NGC 5466 stellar stream and its constraints on the Galactic dark halo mass

Di Bai, Yong Yang, Jing-Kun Zhao+2 more

AstronomerA modified matched filter applied to Gaia DR3, DESI Legacy Imaging Surveys DR9, and Pan-STARRS DR2 produces a weighted stellar map supporting an approximately 80° extent for the NGC 5466 tidal stream. An apparent upward deviation of the leading tail at right ascension 180°–190° supports, but does not establish, a previously proposed dynamical perturbation by the Large Magellanic Cloud (LMC). Comparing 308 highly weighted stream-member candidates with model streams in different gravitational potentials yields posterior estimates of the solar-radius circular velocity Vc = 239.56 (+1.46/−1.44) km/s, halo density flattening q = 1.08 ± 0.07, halo scale radius rs = 12.97 (+3.02/−2.18) kpc, and total LMC mass = 9.63 (+1.89/−2.00) × 10^10 solar masses. The inferred Milky Way mass enclosed within approximately 50 kpc, the stream’s apocenter radius, is 4.59 (+0.48/−0.37) × 10^11 solar masses. These mass and halo constraints come from model comparisons using candidate, rather than confirmed, stream members.

PublicCombining three sky surveys, researchers mapped stars around the globular cluster NGC 5466. Their findings support a stellar trail stretching about 80 degrees across the sky. An apparent bend in its leading section is consistent with the idea that the Large Magellanic Cloud, a companion galaxy, has gravitationally disturbed the trail, but does not prove that explanation. The team compared 308 candidate trail stars with computer-generated stellar streams to estimate the Milky Way’s dark matter distribution and the companion galaxy’s mass. The models give a Large Magellanic Cloud mass of about 96 billion solar masses and a Milky Way mass within roughly 50 kiloparsecs of about 459 billion solar masses, both with uncertainties. These are model-based estimates, not direct mass measurements.

Young explorerA group of stars called NGC 5466 has a long trail of stars across the sky. Scientists made a map that helps show how far the trail reaches. One part seems to bend, and a nearby galaxy may have tugged on it, but they are not sure. They compared possible trail stars with computer-made trails to work out how much matter is in that nearby galaxy and in part of our Milky Way, including dark matter we cannot see. Their answers are estimates, not exact amounts.

An Empirical Temperature Relation for Chemical Abundances in AGN

Sophia R. Flury, Oli L. Dors, Rogemar A. Riffel+5 more

AstronomerUsing [N II] and [O III] auroral-line measurements, the authors report the first robust empirical t2–t3 relation for AGN narrow-line-region clouds: t2 = 1.285 t3 + 0.799, where t2 = Te([N II])/(10^4 K) and t3 = Te([O III])/(10^4 K). When only [O III] 4363 is available, this calibration produces substantial changes in direct-method 12+log(O/H) relative to other calibrations and most accurately recovers the fully direct abundances in their comparison. Comparisons of observed [N II] 6584/5755 and [O III] 5007/4363 ratios with ionization models suggest that metal cooling sets the distribution’s primary shape, while power-law density gradients, pressure stratification, and sometimes significant shock contributions account for much of its dispersion. These mechanisms are model-based interpretations rather than direct measurements. The calibration may improve characterization of AGN-photoionized gas and provide context for JWST observations at z>6; its relevance to early chemical enrichment is a prospective implication.

PublicThe researchers used faint nitrogen and oxygen emission lines to measure how temperatures in gas clouds around active galactic nuclei are related. Their new observational calibration helps estimate one gas temperature when only the oxygen temperature measurement is available. This matters because temperature estimates affect the inferred abundance of oxygen: the new calibration changes those estimates substantially compared with other calibrations and best reproduces the results obtained when both temperatures are measured. By comparing the observed light patterns with models, the authors find evidence that cooling by heavy elements shapes the overall pattern, while differences in density and pressure, along with shocks, help explain its spread. Those physical explanations depend on model comparisons. The work may help interpret future studies of chemical enrichment, including JWST observations of very distant galaxies.

Young explorerGas near the bright centers of some galaxies gives off light that helps scientists work out how hot it is. The scientists used light from nitrogen and oxygen to find a new rule connecting two gas temperatures. When one temperature is missing, the rule helps them estimate it and work out how much oxygen is there. They also compared the light with computer models to look for clues about why the gas behaves this way. Cooling, squeezing, and shocks may all matter, but those explanations are not direct measurements.

Kinematic analysis of the TNG50 Milky Way and Andromeda analogues

S. I. Denyshchenko, D. V. Odynets, V. S. Akhmetov+5 more

AstronomerThis simulation study tests local Ogorodnikov-Milne (O-M) parameters as tracers of spiral structure in four Milky Way- and Andromeda-like disc galaxies in TNG50-1 at z=0. Grid-based fits to stellar-particle velocities recover centroid velocities and velocity-gradient components describing local deformation and rotation. Features selected with the generalised Oort constants A, B, and C+K correspond only partially to stellar overdensities, with the correspondence depending on the galaxy and centroid-selection criteria; parameter uncertainties are also examined. For TNG50-456326, a galaxy-specific selection permits fits to four logarithmic spiral branches, whose morphology suggests two principal arms and two secondary branches. Comparisons with stellar- and gas-mass overdensity and radial-velocity maps explore their spatial relationships. Qualitative similarities to Milky Way morphology and kinematics motivate further study of this simulated galaxy as a possible kinematic analogue, rather than establishing it as one. The results support O-M parameters as complementary diagnostics of non-axisymmetric disc structure, with galaxy-specific selection remaining important.

PublicCan the motions of stars help reveal a galaxy’s spiral structure? Researchers tested this idea in four computer-simulated disc galaxies resembling the Milky Way or Andromeda. They mapped local patterns of stellar motion and compared them with maps showing where stars are more concentrated. Some motion features lined up with these denser regions, but the match was incomplete and depended on the galaxy and the rules used to select features. In one simulated galaxy, TNG50-456326, a tailored selection allowed the researchers to fit four spiral branches. Their shapes suggest two main arms and two secondary branches. The team also compared these structures with the gas distribution and radial motions. Qualitative similarities to the Milky Way make this simulated galaxy worth investigating further, but do not establish it as a counterpart. The study suggests that stellar-motion patterns can complement density maps when tracing spiral structure, provided the selection methods are adapted to each galaxy.

Young explorerScientists used computer-made galaxies to see whether the way stars move can help them find spiral arms. Some movement patterns matched places where stars were crowded together, but not all of them did. In one pretend galaxy, they traced four curly branches that looked like two main arms and two smaller branches. That galaxy had some patterns like our Milky Way, so the scientists want to study it more. Watching how stars move may help find the arms, but the same rules do not work equally well for every galaxy.

J-PAS: Exploring the connection between local environment and the triggering of bursty star formation in Extreme Emission Line Galaxies

Mauro González-Otero, Jose M. Vílchez, Antonio Giménez-Alcázar+45 more

AstronomerThis study tests whether nearby companions are associated with the starbursts in 917 extreme emission-line galaxies (EELGs) from approximately 30 square degrees of J-PAS internal-release data at 0.03 ≲ z ≲ 0.9. Pair probabilities use full photometric-redshift distributions, projected separations up to 200 kpc, and velocity differences up to 500 km/s; Monte Carlo simulations correct for projection and completeness effects. The inferred mean pair fraction is 0.162, with lower and upper uncertainties of 0.033 and 0.048, respectively, below the observed average for other star-forming galaxies within the adopted limits. Detected companions tend to have higher stellar masses and higher CIGALE SED-based metallicity estimates, suggesting that EELGs are often the lower-mass members of asymmetric pairs. Companions below the survey sensitivity and stellar-mass completeness limits may remain undetected. No statistically significant correlation is found between projected companion separation and the equivalent widths of [OIII] λ5007, Hβ, or Hα within these limits. The findings do not establish what triggers the starbursts.

PublicExtreme emission-line galaxies are small, low-mass galaxies forming stars intensely, with conditions resembling those in the early Universe. Researchers examined 917 of them in the J-PAS survey to test whether encounters with nearby galaxies might trigger their bursts of star formation. After using simulations to correct for chance alignments and incomplete detection, they estimated that about 16% have detectable companions—less than the observed average for other star-forming galaxies under the study’s limits. When companions are detected, they tend to be more massive and have higher estimated abundances of elements heavier than helium. The study found no statistically significant link between companion distance and three measures of emission-line strength. Smaller companions could escape detection, so these findings do not settle what causes the bursts.

Young explorerSome small galaxies are making lots of new stars. Scientists looked at 917 of them to see whether nearby galaxies might help start this busy star-making. They estimated that about 16 out of every 100 have a neighbor their survey can find. Those neighbors usually seem bigger. But some smaller neighbors might be hidden from the survey, so scientists still cannot say what starts the star-making bursts.

Decomposition of disk and jet optical emission: Case of PKS 1510-089 and PKS 0736+017

Shivangi Pandey, Suvendu Rakshit, Adarsh Kumar+3 more

• High Energy Astrophysical Phenomena

AstronomerThe authors separate thermal accretion-disk and non-thermal jet synchrotron contributions to the optical continua of the FSRQs PKS 0736+017 and PKS 1510-089 using their distinct polarization signatures. The analysis combines archival multi-epoch optical spectro-photometry and polarimetry, optical continuum and Hβ light curves from earlier reverberation-mapping campaigns, and 37 GHz radio data. For PKS 0736+017, the inferred disk fraction is 0.70 ± 0.01, and the jet-subtracted Hβ lag is 84.8 days, with uncertainties of +23.2 and −18.4 days. For PKS 1510-089, the disk fraction is reported as approximately 37.5% (f_d = 0.37 ± 0.01), with a corresponding lag of 54.4 days, with uncertainties of +4.4 and −5.4 days. These observationally inferred decompositions highlight the importance of accounting for jet contamination when using optical variability to estimate broad-line-region sizes and black hole masses; the abstract reports no black hole mass estimates.

PublicBright jets can complicate measurements of the gas around a quasar’s black hole because jet light mixes with light from the hot disk feeding the black hole. Using existing observations of two quasars, the researchers distinguished these contributions through differences in their polarization. They estimate that the disk supplies about 70% of the optical light in PKS 0736+017, but only about 37.5% in PKS 1510-089. After separating out the jet light, they infer delays between disk-light changes and the response of hydrogen-emitting gas of about 85 and 54 days, respectively, with measurement uncertainties. Such delays help estimate the size of the emitting region. The study emphasizes that separating disk and jet light matters for reliable measurements; it does not report new black hole masses.

Young explorerAround a black hole, a hot disk and a bright jet can both shine. Their light gets mixed together, making it hard to study nearby gas. Scientists used a special property of light to help tell the two kinds apart in two very bright space objects. They found that the disk made most of the light in one, but less than half in the other. After taking away the jet’s light, they estimated how long the gas took to answer changes in the disk’s light—like a light echo. Those estimates are not exact, but they help scientists work out how big the glowing gas region is.

What can strong lensing recover in edge-on disc galaxies? A mock study based on TNG50 simulations

Zheng Fang, Xiaoyue Cao, Ran Li+1 more

AstronomerThis controlled simulation study tests what imaging alone can recover for edge-on disc lenses beyond the projected Einstein-aperture mass. The authors model HST/ACS-like mock images of 35 SWELLS-like TNG50 galaxies with a five-stage PyAutoLens workflow, using a globally scaled MGE light template plus a spherical NFW halo for the final mass model. Decomposed fits succeed for 21 systems; coherent lens-light residuals prevent reliable modelling of the remaining 14. For the successful subset, NMAD scatters are 0.3% for Einstein radius and 0.7% for total aperture mass. The global projected mass-weighted slope has 10.3% scatter, compared with 11.4% for the mass-sheet-invariant reduced deflection curvature ξ and 40.7% for the local slope. Stellar and dark-matter aperture masses have scatters of 15.1% and 108.8%, respectively. A separate diagnostic using the exact input light for all 35 systems yields component-mass scatters of 0.8% and 6.3%, highlighting the importance of lens-light modelling. Under these controlled assumptions, imaging recovers Einstein-scale total mass and global radial structure more reliably than local structure or the stellar–dark-matter decomposition.

PublicResearchers used simulated images of 35 edge-on galaxies acting as gravitational lenses to test how well pictures alone can reveal their mass. Because the galaxies came from a simulation, the team could compare its estimates with the known input values. The modelling worked reliably for 21 galaxies; problems reproducing the galaxies’ light prevented reliable modelling of the other 14. Among the successful cases, the total mass inside the characteristic lensing region was recovered with very little scatter, and the broad pattern of how mass changes with distance from the centre was more reliable than its local detail. Separating the mass in stars from dark matter was much less reliable, especially for dark matter. A diagnostic test using the exact input galaxy light greatly reduced the scatter in those separate mass estimates. These are results from controlled simulations, not measurements of real galaxies, and their reliability depends on the modelling assumptions.

Young explorerScientists made pretend pictures of 35 galaxies seen from the side. They tested whether the pictures could tell them how much stuff was in each galaxy. Their method worked for 21 pictures, but it had trouble matching the galaxy light in the other 14. When it worked, it was good at finding the total amount of stuff in the area they tested. It was much harder to tell how much was stars and how much was dark matter. Giving the method the exact galaxy light helped a lot. This was a test with pretend galaxies, so real ones may be trickier.

GALACTIC CENTERS AS TRACERS OF GALAXY EVOLUTION: Zooming from galaxy large-scale properties into their central massive black holes

F. Pinna, N. Hoyer, S. Thater+14 more

AstronomerThis workshop summary reviews the debated connection between galactic nuclei and galaxy-wide evolution, bringing together work on central massive black holes, nuclear stellar structures, gas inflows and outflows, and galaxy interactions. Topics include black-hole seeding, formation and growth, active galactic nucleus feedback, and nuclear stellar structure formation. The paper summarizes discussions of numerical simulations and observational techniques, identifies open questions, and outlines observations and simulations needed to address them, including plans to exploit the Extremely Large Telescope. The abstract presents a research overview and future directions, not new measurements or a demonstrated causal connection.

PublicHow are the centers of galaxies connected to changes across entire galaxies? This paper summarizes a workshop exploring that still-debated question. Researchers discussed how massive central black holes and dense central star structures might be linked to gas moving into and out of galaxies and to interactions between galaxies. They reviewed computer simulations and observational techniques, identified unanswered questions, and planned future studies, including work with the Extremely Large Telescope. The abstract describes discussions and research plans rather than reporting a new discovery.

Young explorerGalaxies are huge groups of stars, and their middles can hold big black holes and bunches of stars. Scientists met to talk about how a galaxy’s middle might be connected to changes in the whole galaxy. They discussed ways to study this with telescopes and computer models. This paper shares their questions and plans, not a new answer.

Molecular gas in the disks and tails of ram pressure stripped Coma galaxies

Anežka Srbljanović, Pavel Jáchym, Ming Sun+8 more

AstronomerIRAM 30 m CO(1–0) and CO(2–1) observations detect molecular gas in four of five ram-pressure-stripped Coma cluster galaxies, including clear tail emission in three, extending up to approximately 50 kpc from their stellar disks. Tail molecular masses reach a few hundred million solar masses and represent up to 10–20% of the molecular gas remaining in the parent disks. Several galaxies have elevated molecular-gas-to-stellar-mass ratios relative to field scaling relations despite H I deficiency, with the enhancement persisting toward the sample’s lower-mass end. This is consistent with ram-pressure compression promoting H I-to-H2 conversion, rather than directly establishing that mechanism. Including tail molecular gas brings most total gas fractions close to those of field galaxies at similar stellar masses, supporting simultaneous gas removal and phase transformation. Tail CO is preferentially detected in Hα-bright regions, but greater scatter than in previous studies suggests contributions from both star-forming and diffuse molecular components. The authors interpret these findings as evidence that ram pressure both strips gas and promotes molecular gas formation in disks and tails, influencing short-term star formation.

PublicObservations of five galaxies in the Coma cluster reveal molecular gas in four, with clear detections in the stripped gas tails of three. These tails extend as far as about 50 kiloparsecs from the galaxies’ stellar disks and contain up to 10–20% as much molecular gas as remains in their parent disks. Several galaxies contain unusually large amounts of molecular gas relative to their stars despite being depleted in atomic hydrogen. The findings support the idea that pressure from the cluster environment both removes gas and compresses some atomic gas into molecular form. When molecular gas in the tails is counted, most galaxies have total gas fractions close to those of comparable galaxies outside clusters. Comparisons with glowing ionized gas suggest that the tails contain both star-forming and more diffuse molecular gas, so detecting molecular gas does not necessarily mean stars are forming there.

Young explorerAstronomers looked at five galaxies that are losing gas as they move through a crowded group of galaxies. They found a kind of gas that can help make stars in four galaxies, and in long tails behind three of them. The clues suggest that the push stripping gas away may also squeeze some gas into this star-making form. But finding that gas does not mean new stars are being made everywhere in the tails.

Statistical Modeling of Foreground Galactic Cirrus for Diffuse Halo Light Measurement

Qing Liu, Henk Hoekstra, Amaël Ellien

• Instrumentation and Methods for Astrophysics

AstronomerThe authors develop a statistical reconstruction of two-dimensional Galactic cirrus, combining far-infrared dust morphology with multiscale optical structure while iteratively refining the foreground, smooth diffuse-light model, and residual sky. Injection–recovery tests using Euclid VIS observations of Abell 2390 show substantial improvement in recovered stellar-halo photometry, but residual biases depend on local foreground structure and sky estimation. Applied to a prominent cirrus complex near the cluster’s brightest galaxy, the correction yields a smoother BCG-plus-intracluster-light distribution, a steeper outer light profile, and reduced contamination in the integrated light. These results support the method’s potential for diffuse-light photometry rather than establishing bias-free foreground removal.

PublicDust in the Milky Way scatters starlight, creating a faint foreground that can obscure the much dimmer glow around distant galaxies and between galaxies in clusters. The researchers developed a statistical method that combines infrared maps of dust with patterns in optical images to estimate this foreground while preserving distant diffuse light. Tests that add light signals to Euclid images of the Abell 2390 galaxy cluster and then try to recover them showed substantially improved measurements, although some errors remained and depended on nearby dust patterns and the estimated sky background. Applying the method near the cluster’s brightest galaxy produced a smoother picture of the galaxy and surrounding diffuse glow, with brightness falling more steeply in its outer regions and less foreground contamination in its total light.

Young explorerDust in our Milky Way scatters starlight, making a faint glow that can hide the soft light around faraway galaxies. The scientists made a way to estimate that dusty glow so they could better see the light behind it. They tested it by adding light to space pictures and checking how well they could find it again. It worked much better, but it was not perfect. When they used it on a picture of a group of galaxies, the light around the brightest galaxy looked smoother after the dusty glow was corrected.

A Cepheid-based Distance to the Type 1 Seyfert NGC 3783

Madison Markham, Misty C. Bentz, Laura Ferrarese+2 more

AstronomerHubble Space Telescope imaging over 15 visits yielded 1,541 unique point sources in the Type 1 Seyfert galaxy NGC 3783. Cepheid-template fits identified seven Cepheid candidates, including four classified as the strongest candidates. Fitting the strong sample’s period–luminosity relation using the Riess et al. (2019) LMC calibration, the independent Pietrzynski et al. (2019) LMC distance constraint, and a correction for potential metallicity effects gives a distance modulus of 33.118 ± 0.154 mag, or 42.03 ± 2.98 Mpc. This is formally consistent with the full-sample estimate and places NGC 3783 among the farthest galaxies with a Cepheid-based distance measurement.

PublicResearchers used repeated Hubble Space Telescope images to estimate the distance to the galaxy NGC 3783. They identified seven possible Cepheid stars, whose cycles of brightening and fading can be related to their intrinsic brightness, allowing astronomers to estimate distance. Using the four most convincing candidates, a calibration tied to the Large Magellanic Cloud, and a correction for possible effects of chemical composition, they obtained a distance of about 42 million parsecs, with an uncertainty of about 3 million parsecs. The estimate agrees within the uncertainties with the result from all seven candidates. NGC 3783 is among the most distant galaxies measured using this method.

Young explorerSome stars get brighter and dimmer in a repeating pattern. Watching that pattern can help astronomers work out how far away the stars are. Using the Hubble telescope, researchers found seven stars in a faraway galaxy that might be this special kind. They used the four they were most sure about to estimate the galaxy’s distance. The answer is not exact, but this galaxy is one of the farthest away measured with stars like these.

A Physics Informed Neural Network Approach to Decipher Environmental Confinement of Molecular Clouds in the Third Galactic Quadrant

Ashok Mondal

AstronomerSurveys of the Third Galactic Quadrant reveal molecular clouds that appear virially unbound under isolated-cloud models (alpha_vir > 2), yet are reported to be long-lived and star-forming. The authors reassess 2,091 clouds using a physics-informed neural network whose loss function incorporates the complete Eulerian Virial Theorem, including external surface pressure. The model infers a Galactic pressure field decreasing with absolute vertical height and Galactocentric radius, described as consistent with Galactic flaring. With this inferred confinement, 99.9% of clouds previously classified as unbound meet the authors' pressure-confined equilibrium criterion (alpha_AI <= 2). The corrected stability parameter correlates with star formation rate in log-log space (correlation coefficient 0.64). The authors interpret this as evidence that environmental confinement regulates outer-Galaxy star formation efficiency; the equilibrium reclassification depends on the inferred pressure field, and the correlation alone does not establish causation.

PublicSome molecular clouds in the outer Milky Way form stars and are reported to last a long time, even though calculations treating them as isolated suggest they should not stay together. Researchers reassessed 2,091 clouds with an AI model constrained by physical equations that include pressure from the surroundings. The model inferred that this pressure decreases farther from the Galaxy's central plane and center. Including that inferred pressure reclassified 99.9% of the previously apparently unbound clouds as being in pressure-confined balance. The revised measure of cloud stability also correlated with star formation rate. These results support the idea that a cloud's surroundings help control star formation, but the pressure is model-inferred, and the correlation does not by itself prove that explanation.

Young explorerSome huge clouds in our galaxy make stars even though a simple calculation says they should spread apart. Scientists used a computer model to ask whether a squeeze from outside could help hold the clouds together. With the squeeze it worked out, almost all the clouds that seemed unable to stay together could be held in balance. This is a possible explanation from the model, not proof that every cloud really gets that squeeze.

VLITE Observations of the Hubble Ultra Deep Field

Emil Polisensky, Wendy Peters, Simona Giacintucci+3 more

AstronomerThe study presents 136 hr of commensal VLITE observations of the HUDF at 340 MHz. The deepest image uses 20 hr, covers 4 square degrees, and reaches 158 microJy per beam rms at the field center with an 8.8 × 3.8 arcsec beam, yielding 671 sources above 5 sigma. After incompleteness corrections based on injection-recovery simulations of a model radio continuum population, source counts recover sub-mJy star-forming galaxies at abundances consistent with comparable-frequency deep fields. Observations on 45 days across two A-configuration semesters separated by 1.3 years identify eleven variable sources at 1–100 mJy with modulation indices of 6–40%. Six have peaked spectra consistent with compact AGN. Variability amplitudes are consistent with predicted refractive interstellar scintillation along this sightline, although three sources with modulation indices above 30% likely require an intrinsic contribution. VLBA follow-up confirmed one source as a compact symmetric object, illustrating the potential—not an established population census—of low-frequency variability searches for finding young radio AGN.

PublicLow-frequency radio observations of the Hubble Ultra Deep Field produced a catalog of 671 sources. After using simulations to estimate how many sources the survey missed, the researchers found that the abundance of faint star-forming galaxies agrees with other deep radio surveys. They also identified eleven sources whose radio brightness changed on roughly year-long timescales. Six have radio spectra consistent with compact active galactic nuclei. The brightness changes are consistent with a twinkling effect caused by material between stars, although three sources probably also changed their own emission. Follow-up observations confirmed one source as a compact symmetric radio object. The findings suggest that this observing approach could help identify young radio-emitting active galactic nuclei.

Young explorerAstronomers used a radio telescope to find 671 things in space that send out radio waves. Eleven changed how bright they looked. Material between stars may make them seem to twinkle, but three probably changed their own radio signals too. A closer look confirmed that one had a small, symmetric radio structure. Looking for these changes could help astronomers find young radio sources in galaxies.

Chemical and dynamical evolution of prestellar cores, the dawn of star and planet formation

Silvia Spezzano, Elena Redaelli, Paola Caselli+8 more

AstronomerThe abstract motivates a comprehensive survey of prestellar cores rather than reporting new observations or simulations. It identifies gaps in measurements of density and velocity structure on 100–1000 au scales, gas ionisation, core lifetimes, and environmental dependence. The authors argue that a deep investigation of this stage of stellar and planetary system formation requires a large single-dish submillimetre/millimetre telescope such as AtLAST.

PublicDense gas cores before stars form are important for understanding how stars and planetary systems begin. The abstract highlights the lack of a comprehensive survey of how gas is distributed and moves within these cores on scales of 100–1000 times the Earth–Sun distance, how electrically charged the gas is, how long the cores last, and how their surroundings affect them. It argues for studying these questions with a large telescope such as AtLAST, which would observe millimetre and submillimetre radiation; it does not report new findings.

Young explorerBefore a star forms, there is a thick clump of gas. Scientists want to learn how the gas moves, how it is packed together, how long the clump lasts, and how nearby things affect it. They say a big telescope like AtLAST is needed to study these questions closely. This is about what scientists still need to learn, not new answers they have found.

Episodic Star Formation - II. The Origin of the Fundamental Metallicity Relation

Xuelun Mei, Dandan Xu, Cheng Li+2 more

AstronomerThis simulation study investigates the physical origin of the Fundamental Metallicity Relation (FMR), in which higher-SFR galaxies have lower gas-phase metallicities at fixed stellar mass. The authors trace 8,979 central star-forming galaxies selected at z=0 in TNG100 back to z=1. They find that the approximately 0.11 dex scatter in the z=0 mass-metallicity relation includes long-lived galaxy-to-galaxy differences of approximately 0.09 dex and temporal fluctuations of approximately 0.07 dex. The galaxy-to-galaxy component exhibits an SFR–metallicity anticorrelation resembling the observed FMR. Time-shift analysis and stacked rising and falling SFR phases in a refined sample reveal a sequence: the cold non-star-forming gas reservoir changes first, gas-phase metallicity changes oppositely next, and SFR changes last. The authors interpret this ordering as consistent with metal-poor gas replenishment and dilution preceding an SFR peak, followed by feedback-driven heating or removal and a transition toward enrichment as SFR declines. These simulation findings offer a physical explanation for the observed anticorrelation rather than a direct observational demonstration of that mechanism.

PublicAmong galaxies with the same mass in stars, those forming stars faster tend to have less chemically enriched gas. To investigate why, researchers followed the histories of 8,979 galaxies in the TNG100 simulation. They found that differences in gas enrichment reflect both lasting differences between galaxies and changes within individual galaxies over time. Their analysis of rising and falling star-formation phases shows a sequence: the supply of cold gas not yet forming stars increases first, the gas becomes less enriched next, and star formation then rises; declining phases show the opposite pattern. The authors interpret this as evidence consistent with incoming, less-enriched gas diluting a galaxy's gas before fueling more star formation. Later, feedback-driven heating or gas removal could accompany declining star formation and increasing enrichment. This is a simulation-based explanation for an observed galaxy pattern, not direct observational proof of the proposed process.

Young explorerAstronomers see a pattern: galaxies with the same amount of stars tend to have less enriched gas when they are making stars faster. Researchers used a computer simulation to look for a reason. In the simulated galaxies, extra cold gas arrived first, the gas became less enriched, and then more stars began to form. The researchers think the new gas may dilute the old gas, like adding water to juice, before helping make new stars. Later, heating or losing gas may help slow star-making down. This is an idea supported by their computer galaxies, not proof that real galaxies always work this way.

Boosted Physics-Informed Neural Networks for Solving Homogeneous and Non-Homogeneous Lane-Emden Type Equations

Luke Oluwaseye Joel

• Mathematical Physics
• Machine Learning
• Neural and Evolutionary Computing

AstronomerThis computational study proposes a hybrid solver for Lane-Emden-type nonlinear differential equations, which are used to model stellar structure and thermal behavior in polytropic gas spheres. A physics-informed neural network (PINN) supplies an initial prediction, followed by a post-processing stage that models its residual errors using regression methods including LightGBM, Random Forest, XGBoost, and support vector regression. The correction outputs are aggregated to refine the prediction. Comparisons with a standard PINN baseline reportedly show reduced prediction error and improved generalization. The abstract provides no numerical performance gains or details of the validation cases; these are solver-performance claims, not observational findings about stars.

PublicThe study presents a way to improve computer solutions to equations used in models of stars and gas spheres. First, a neural network estimates a solution while being trained to respect the governing physical equations. Other machine-learning methods then model errors in that estimate, and their corrections are combined. The authors report that this approach produces smaller errors and generalizes better than the neural network alone. The abstract does not say how large the improvements are or describe the individual test cases. This is a study of a calculation method, not a new observation of stars.

Young explorerScientists use math to help describe stars. In this study, they made a computer helper try to solve some of that math, then used other computer helpers to fix its mistakes. They say the helpers together made fewer mistakes than the first helper alone in their tests. They did not report finding anything new by looking at real stars.

A JWST MIRI LRS Survey of 37 Massive Star-Forming Galaxies and AGN at Cosmic Noon -- Overview and First Results

Jed McKinney, Miriam Eleazer, Alexandra Pope+17 more

AstronomerThis survey combines JWST/MIRI LRS spectra with archival Spitzer/IRS spectroscopy for 37 infrared-bright galaxies at z=0.65–2.46, including star-forming systems and dust-obscured AGN. The sample has log(L_IR/L_sun)>11.5 and log(M_*/M_sun)=10–11.5. The authors describe sample selection, data reduction, spectral extraction, and PAH measurements. JWST detects PAH emission at rest-frame 3.3–5.3 microns, Paschen and Brackett lines, and absorption from CO gas, CO2 ice, H2O ice, and aliphatic dust. The 3.3-micron PAH feature can reach 1% of the 8–1000-micron infrared luminosity and correlates tightly with dust-obscured star-formation rate. The joint analysis finds an average 11.3/3.3-micron PAH ratio three times that of local luminous infrared galaxies. The authors interpret this as evidence for larger PAH grains at z~1–2, not a direct grain-size measurement. They suggest coagulation in dense, cold gas as a possible explanation, supported by strong 3.05-micron water-ice absorption. Such conditions could reduce stellar radiative feedback because larger PAHs transfer less energy per photon to the interstellar medium.

PublicAstronomers combined new James Webb Space Telescope spectra with earlier Spitzer observations to study 37 infrared-bright galaxies. Their spectra reveal emission from polycyclic aromatic hydrocarbons, or PAHs, alongside signatures of gas, ice, and dust. One PAH feature, at 3.3 microns, can account for as much as 1% of a galaxy’s total infrared luminosity and closely tracks star formation hidden by dust. The average ratio of two PAH features is three times that found in nearby luminous infrared galaxies. The researchers interpret this difference as evidence for larger PAH grains in these distant galaxies. They suggest that grains may stick together in dense, cold gas; strong water-ice absorption supports those conditions. This explanation remains an interpretation, and the proposed larger grains could pass less energy from starlight into the surrounding material.

Young explorerScientists used two space telescopes to study light from 37 galaxies. They found clues showing tiny bits of dust, gas, and ice. One kind of light was closely linked to stars being made behind dust. Other clues suggest that some dust bits may be bigger than those in similar nearby galaxies. The scientists think tiny bits might stick together in cold, crowded gas, but they have not shown for sure that this is why.

The inner dark-matter structure of TNG50 simulated galaxies

Vicente Honorato, Antonio D. Montero-Dorta, M. Celeste Artale+1 more

• Cosmology and Nongalactic Astrophysics

AstronomerThis simulation study measures inner dark-matter density slopes in TNG50 and matched dark-matter-only counterparts at z = 0, 0.2, 0.7, and 1. Slopes are obtained from direct central power-law fits to spherically averaged density profiles, motivated by the asymptotic behaviour of generalised Navarro–Frenk–White models. In TNG50, galaxies with stellar masses approximately above 10^11 solar masses have shallow inner slopes whether centrals or satellites, whereas those approximately below 10^9 solar masses show greater profile diversity. At fixed stellar mass, low-mass satellites tend to be cuspier; the steepest slopes occur in redder systems with lower maximum circular velocities in more massive host haloes. Population-level evolution is modest: profiles steepen towards lower redshift in the hydrodynamical run, while the dark-matter-only run shows the opposite trend. Hydrodynamical profiles remain systematically steeper at all sampled redshifts. The authors also find their fiducial fitting interval to be the most suitable reference for measuring the shallowest slopes at TNG50’s resolution limit. These are simulation findings, not observational measurements.

PublicComputer simulations suggest that the way dark matter gathers near galaxy centres depends on galaxy properties and changes modestly over cosmic time. In the TNG50 simulation, galaxies with the most mass in stars have relatively shallow central dark-matter profiles, while galaxies with much less stellar mass show a wider variety. Among low-mass galaxies with similar stellar masses, satellites tend to have dark matter that rises more sharply in density towards the centre. Comparing TNG50, which includes ordinary matter and its processes, with a dark-matter-only simulation reveals different trends over time: central profiles become steeper towards the present in TNG50 but show the opposite trend without ordinary matter. TNG50 profiles are systematically steeper at every time examined. These conclusions come from simulations, and measuring the shallowest profiles requires care because the simulation has limited resolution.

Young explorerScientists used computer-made galaxies to study dark matter, an invisible kind of matter. In their computer worlds, dark matter crowded towards the middle more sharply in some galaxies than in others. Adding ordinary matter changed the patterns and how they changed over time. These are clues from computer models, not measurements of real galaxies, and the models cannot show every tiny detail.

First Light and Reionization Epoch Simulations (FLARES) XXII: UV-dust spatial offsets at the Epoch of Reionisation

Paurush Punyasheel, Aswin P. Vijayan, William J. Roper+8 more

AstronomerMotivated by observed UV–FIR offsets in high-redshift galaxies, this study analyses 6,890 FLARES galaxies with stellar masses ≳10^9 solar masses at z=5–10. SKIRT radiative-transfer post-processing produces mock JWST/NIRCam rest-frame 1500 Å and ALMA rest-frame 158 μm images at approximately 0.031 and 0.3 arcsec resolution, respectively. In these simulated observations, about 16.23% of galaxies have UV–FIR emission-peak separations ≥2.5 kpc. The authors find no correlation of offsets with stellar mass, UV/FIR luminosity, size, AGN feedback, large-scale environment, or merger history. Galaxies with significant offsets preferentially have UV slopes −2.5<β<−1.5, consistent with recent star formation and dust-obscured cores shifting the apparent UV centroid. They reach half their z=5 stellar mass about 0.1 Gyr earlier than galaxies without offsets and exhibit earlier enrichment and enhanced stellar metallicities. The authors interpret these trends as indicating a transition to outward growth at z≥6; these physical inferences come from simulations rather than direct measurements of the observed galaxies.

PublicObservations of distant galaxies show that their ultraviolet and far-infrared light can be brightest in different places. To investigate why, researchers modelled 6,890 massive galaxies from an early period of the universe and created simulated images resembling observations from JWST and ALMA. About 16% of the model galaxies had ultraviolet and far-infrared brightness peaks separated by at least 2.5 kiloparsecs. These separations did not correlate with galaxy mass, brightness, size, black-hole feedback, surroundings, or merger history in the simulations. Galaxies with large separations tended to have bluer ultraviolet light, earlier star formation and enrichment, and more metal-rich stars. The authors suggest that recent star formation and dusty central regions can shift where a galaxy appears brightest in ultraviolet light. They interpret the broader patterns as evidence of growth moving outward in these early galaxies, rather than establishing this directly from observations.

Young explorerSome very faraway galaxies look brightest in different places when we look at two kinds of light. Scientists made pretend galaxies on a computer to help find out why. In some of them, the brightest spots were far apart. The scientists think dust hiding the middle of a galaxy, together with newly forming stars, could help explain this. The computer galaxies give them clues, but they do not prove that real galaxies work exactly the same way.

The Quasar Main Sequence of Highly Accreting NLSy1 Galaxies

Alberto Domínguez, Suvendu Rakshit, Vaidehi S. Paliya+2 more

• High Energy Astrophysical Phenomena

AstronomerThe study places 18,749 DESI DR1 Narrow-Line Seyfert 1 galaxies on the optical EV1 plane using broad H-beta FWHM and Fe II strength, and compares them with a homogeneously analyzed SDSS DR17 NLSy1 sample. DESI sources occupy the extreme EV1 region, with median R4570 = 0.96 +/- 0.35, consistent with SDSS at 0.96 +/- 0.36. Single-epoch virial estimates under both tested calibrations indicate low black hole masses, with median log black hole mass approximately 6.81-6.85. The inferred super-Eddington fraction is strongly calibration dependent: about 50% in both samples with the Fe II-dependent approach, but only approximately 8-9% with the Fe II-independent calibration. A geometrically thick inner disk shielding the outer broad-line region is offered as an explanation for the strong Fe II emission under the high-accretion interpretation, not as a directly established geometry. The sample supplies low-redshift candidate super-Eddington accretors for investigating analogs of rapid early-Universe black hole growth.

PublicAstronomers analyzed the spectra of 18,749 galaxies with actively feeding black holes using DESI data and compared them with a similarly analyzed SDSS sample. These galaxies show strong emission from iron, and estimates suggest their central black holes have relatively low masses. Whether many are feeding at exceptionally high rates is less certain: one estimation method puts about half above the Eddington limit, a benchmark for accretion, while another puts only about 8-9% above it. The researchers suggest that, if the high feeding rates are correct, a thick inner disk could shield more distant gas and help explain the strong iron emission. These galaxies are therefore candidates for studying how black holes might have grown rapidly in the early Universe, rather than confirmed examples of such extreme growth.

Young explorerScientists looked at light from thousands of galaxies where black holes are taking in material. Gas near the black holes gives off light, including a strong signal from iron. The scientists think some of these black holes may be feeding very fast, but different ways of checking give very different answers about how many. One idea is that a thick ring of material blocks some light from reaching gas farther away, helping explain the iron signal. Studying these galaxies may help us understand how black holes grew long ago.

The Milky Way's Missing In-Situ Halo

Madeline Lucey, Robyn E. Sanderson, Alexander H. Riley+3 more

AstronomerThe study compares the Milky Way’s measured stellar halo density profile over galactocentric radii of 1–100 kpc with 24 Milky Way-mass galaxies in the FIRE-2 and Auriga cosmological zoom-in simulations. Simulated profiles are significantly steeper within approximately 15 kpc, and breaks are rare and uniformly weaker than the Milky Way’s prominent break at approximately 20–30 kpc. Only one of the three simulated galaxies with statistically significant breaks shows a break attributable to apocenter pile-up of an accreted merger remnant, the mechanism commonly invoked for the Milky Way’s Gaia-Enceladus/Sausage debris. In the simulations, accreted stellar halo profiles broadly agree with Milky Way measurements; the in-situ component dominates within approximately 20 kpc and drives the discrepancy. The tension could reflect observational systematics, excessive early spheroidal star formation in the simulations, or differences in underlying physics, including dark matter; the study does not establish which explanation is responsible.

PublicThe Milky Way’s diffuse halo of stars holds clues to how our galaxy grew. Measurements show a pronounced change in how rapidly the halo’s stellar density falls with distance from the Galactic center. This feature has often been attributed to stars from a past merger gathering near the farthest points of their orbits. Comparing the measurements with 24 computer-simulated galaxies, researchers find that such changes are uncommon in the simulations and never as strong as the Milky Way’s. The simulated halos also become denser toward the center more sharply than measurements indicate. Stars acquired from other galaxies broadly match the measured profile; stars formed within the simulated galaxies drive the mismatch. This raises the question of why the Milky Way does not show a comparable inner halo component. Possible explanations include biases in the measurements, too much early star formation in the simulations, or differences in the underlying physics. None is established by this comparison.

Young explorerStars spread around our galaxy can help tell the story of how it grew. Scientists compared the way those stars are spread out with 24 galaxies made in computer simulations. The real stars and the computer stars did not match. In the computer galaxies, stars born inside the galaxies made the biggest difference; stars brought in from other galaxies matched better. Scientists do not yet know why. The measurements might be misleading, the computer galaxies might make too many stars early on, or the rules used in the simulations might need changing.

A MIGHTEE robust measurement of the star formation rate-radio correlation

Charlotte L. Jackson, Matt J. Jarvis, Imogen H. Whittam+9 more

AstronomerUsing radio-detected sources in MIGHTEE COSMOS DR1, the authors fit a Bayesian hierarchical mixture model incorporating full SFR posteriors from GRAHSP. Rather than applying binary AGN-rejection cuts, the method probabilistically estimates the mean SFR–1.4 GHz luminosity relation for star-formation-dominated galaxies while accounting for their changing fractions with redshift, radio luminosity and stellar mass. The inferred relation is log10[SFR/(M_sun yr^-1)] = 0.790(log10[L_1.4/(W Hz^-1)] - 23) + 1.244(1+z)^0.122 - 0.033(log10[M_*/M_sun] - 10), with intrinsic scatter of 0.178 dex. It shows significant redshift dependence but weaker stellar-mass dependence than previous studies. Moderate evolution of the radio spectral index could explain the redshift trend; the authors attribute the weaker mass dependence to avoiding AGN-removal cuts.

PublicRadio emission can help astronomers measure how rapidly galaxies form stars without dust obscuring the view, but emission from active galactic nuclei can complicate that measurement. This study uses a statistical model of radio-detected galaxies in the MIGHTEE COSMOS DR1 catalogue, including uncertainties in their star-formation rates, instead of sorting galaxies into rigid categories and discarding possible contaminants. The inferred relationship between star formation and radio brightness changes significantly with redshift, which tracks cosmic history, but depends less strongly on galaxy stellar mass than earlier studies suggested. Changes in how star-forming galaxies emit radio waves at different frequencies could explain the redshift trend, although this is an interpretation rather than an established cause. The authors also attribute the weaker mass trend to their statistical approach.

Young explorerGalaxies make new stars and give off radio waves that can help us learn how fast they are making them. But an active center in a galaxy can add radio waves too. Scientists used a new way of studying many galaxies that allows for this extra signal instead of simply leaving some galaxies out. They found that the link between radio waves and making stars changes when we look at different times in the universe. A galaxy's mass seems to matter less than earlier studies suggested. They have an idea about why the link changes with time, but it is not yet a sure answer.

Lyman-alpha haloes in the aftermath of reionisation

Daniil Smirnov, Lutz Wisotzki, Tanya Urrutia+8 more

AstronomerUsing MUSE/VLT data matched in intrinsic surface-brightness sensitivity after accounting for cosmological dimming, this study compares low-luminosity LAEs (L_Lyα ≲ 10^42 erg s^-1) at z ≥ 6 with a z ~ 3 sample spanning similar Lyα luminosities and stellar masses. Extended Lyα emission is detected around 6 of 18 high-redshift LAEs, more than doubling the known population at z ≥ 6, versus a 40% individual detection fraction at lower redshift. Despite similar detection fractions, typical exponential halo scale lengths are three times smaller at high redshift, and Lyα line widths are about 2.5 times smaller. Stacks of individual halo nondetections reveal a highly significant halo at z ~ 3 but no detectable extended emission at z ≥ 6. The authors discuss, without establishing a cause, enhanced scattering losses in more neutral intergalactic and circumgalactic gas during reionisation, or a closer connection between halo properties and host-galaxy evolution.

PublicAstronomers compared faint galaxies in the very early universe with a similar group from a later period, using MUSE on the Very Large Telescope. They adjusted the comparison so that the observations could detect the same intrinsic faintness of extended emission despite cosmic dimming. They found glowing hydrogen haloes around 6 of 18 early galaxies, a detection rate only slightly below the later group's 40%. However, the early haloes had characteristic sizes three times smaller, and their hydrogen emission lines were about 2.5 times narrower. Combining observations of galaxies without individually detected haloes revealed a halo in the later group but none detectable in the earlier group. The cause remains uncertain: more neutral gas in and around early galaxies might scatter much of the light out of view, or the differences might be more closely tied to changes in the galaxies themselves.

Young explorerSome faraway galaxies have a faint glow around them. Astronomers found this glow around 6 of 18 galaxies seen when the universe was very young. Compared with a similar group seen later, the young galaxies had smaller glows. Putting together pictures of galaxies whose glows were too faint to see one by one revealed a glow in the later group, but not in the younger group. Scientists do not yet know why. Gas might scatter some of the light so we cannot see it, or the galaxies themselves might change as they grow.

Supernovae Ia ejecta velocities and host galaxy environments: the role of survey-selection effects

L. V. Barkhudaryan, A. A. Hakobyan, M. H. Gevorgyan+6 more

AstronomerThis study re-examines host-environment differences between high-velocity (HV) and normal-velocity (NV) Type Ia supernovae using 354 nearby, spectroscopically normal events at z ≤ 0.04: 239 NV and 115 HV. The near-maximum-light Si II λ6355 velocity distribution is well described by two Gaussian components. No statistically significant subgroup differences are found in galactocentric distance, host size, or stellar mass. Previously reported environmental trends appear only marginally in the targeted-survey subsample and largely disappear in the untargeted subsample, consistent with an important role for survey selection. These findings weaken explanations based primarily on the global host properties examined. The authors instead favor explosion asymmetries and viewing angle as substantial contributors to the velocity diversity, but do not establish this explanation or exclude local environmental and progenitor effects.

PublicWhy does material in some Type Ia supernovae appear to move faster than in others near peak brightness? Earlier studies suggested that the faster and slower groups occur in different kinds of galaxy environments. Examining 354 nearby explosions, the researchers found no statistically significant differences in their host galaxies’ stellar masses or sizes, or in the explosions’ distances from galaxy centers. Weak environmental trends appeared mainly in surveys that selected particular galaxies to monitor, suggesting that survey selection helped produce earlier apparent differences. The authors favor uneven explosions seen from different directions as an important explanation for the speed differences, but this is an interpretation, not a demonstrated cause. Conditions close to the exploding stars and differences in the stars themselves could still contribute.

Young explorerWhen some stars explode, their flying material looks faster than in other explosions. Scientists checked 354 explosions to see whether this was linked to the galaxies where they happened. They found no clear differences in the galaxies’ sizes, how much mass they have in stars, or how far the explosions were from their centers. Which galaxies earlier searches chose to watch may have made the groups look more different. The scientists think an uneven explosion might look faster from one side than another, but they have not proved that. The stars and their nearby surroundings might matter too.

The JWST Emission Line Survey (JELS): Multi-wavelength properties of Paschen line-emitters at Cosmic Noon

Malte Brinch, Edo Ibar, Luis Ossa-Fuentes+14 more

AstronomerThe study combines JWST/NIRCam narrowband selection with multiwavelength photometry to characterize 77 Pa-alpha-selected galaxies at z~1.50 and 31 Pa-beta-selected galaxies at z~2.65 in COSMOS, removing AGN through X-ray/radio matching. Paschen-line SFRs, corrected using nebular extinction inferred from EAZY Av, span 0.1–22.0 and 0.7–47.9 solar masses per year, respectively. Line SFRs exceed SED-derived SFRs for most sources, interpreted as widespread short-timescale bursts, with a weak decrease in this tendency with stellar mass. Inferred nebular attenuation correlates with mass and SFR. Weighted-median stacking yields no >3-sigma detections at wavelengths beyond MIRI. ALMA Band 4 provides the tightest median 3-sigma limits: SFR_IR <53 and <44 solar masses per year, and gas masses <10^11.2 and <10^10.6 solar masses, for the Pa-alpha and Pa-beta samples, respectively. These are upper limits, not detections of obscured star formation or gas reservoirs; deeper spectroscopy and ALMA continuum observations are needed.

PublicAstronomers studied two groups of star-forming galaxies from an era of vigorous galaxy growth, selecting 77 galaxies at redshift about 1.50 and 31 at about 2.65 using hydrogen emission seen by JWST. For most galaxies, estimates of star formation from these emission lines exceed estimates that reflect longer-term activity, suggesting recent bursts of star formation. The inferred dimming by dust also increases with galaxy mass and star-formation rate. To search for emission associated with hidden star formation, the team combined far-infrared and submillimeter measurements from multiple galaxies. This did not produce significant detections, so the study sets upper limits on dust-obscured star formation and gas mass rather than measuring them. Deeper observations are needed to establish how much star formation is hidden and how large the gas supplies are.

Young explorerScientists looked at faraway galaxies where new stars are being made. They compared two kinds of clues in the light, and most galaxies seemed to have a recent burst of star-making. Dust can hide some of that activity. Even after putting many measurements together, the scientists could not clearly see the hidden part. They could only say how much might be hiding at most. They need better observations to learn more.

Anisotropy of Satellite Galaxies-II: Spatial Segregation as the Origin of Anisotropic Satellite Quenching in Haloes and Beyond

Zhuoming Zhang, Weiguang Cui, Yun Chen+1 more

• Cosmology and Nongalactic Astrophysics

AstronomerObservations show preferential satellite quenching along central galaxies’ major axes in massive halos, whereas AGN jets tend to follow the minor axes. Using SIMBA, TNG100, EAGLE, and feedback-free SIMBA at z=0, the authors find that the simulated anisotropy primarily reflects spatial segregation: quenched satellites are more centrally concentrated and more strongly major-axis aligned, while unquenched satellites lie at larger radii and are more nearly isotropic. Persistence without stellar or AGN feedback suggests that feedback is not important for satellite quenching in this interpretation, rather than establishing that conclusion observationally. Beyond halo boundaries, the signal differs strongly between simulations and correlates with the major-axis excess of galaxies, linking it to the direction-dependent distribution of groups, clusters, and filaments. The authors propose a geometrical interpretation spanning halo and extra-halo scales.

PublicSmall satellite galaxies orbiting within massive collections of matter are observed to stop forming stars more often along the long axis of their central galaxy. Jets from active galactic nuclei tend to point along the short axis, complicating the idea that these jets explain the pattern. In four computer simulations, the researchers find that the pattern mainly reflects where different satellites live: those that have stopped forming stars cluster closer to the center and along the central galaxy’s long axis, while star-forming satellites lie farther out and are spread more evenly in direction. The pattern persists in a simulation without energy input from stars or active galactic nuclei, suggesting that such feedback may not be important for satellite quenching. Outside the main halo, the simulations disagree substantially, but the pattern tracks how galaxies are distributed along the long axis. The authors interpret this as evidence that the arrangement of surrounding groups, clusters, and filaments helps explain the larger-scale pattern.

Young explorerGalaxies are huge families of stars. Astronomers see that little galaxies near a big one are more often done making stars in one direction: along the big galaxy’s long side. Scientists used computer pretend universes to explore why. In those models, the little galaxies that stopped making stars gather closer to the middle and more along that long side. Those still making stars are farther out and spread more evenly around. The pattern stays even in a model without energy sent out by stars or active galaxy centers, so the scientists think where galaxies are may help explain the pattern. Farther away, the computer models do not all agree.

Stacked strong and weak lensing united: Improved measurement of the stellar and dark matter distributions in massive early-type galaxies at z∼0.5

Momoka Fujikawa, Masamune Oguri

• Cosmology and Nongalactic Astrophysics

AstronomerCombining stacked strong- and weak-lensing measurements, this study constrains the stellar and dark matter distributions of massive early-type galaxies at 0.4 < z < 0.6. Subaru Hyper Suprime-Cam weak-lensing measurements reach 0.013 Mpc/h and are combined with stacked enclosed projected masses from 13 strong-lens systems. Adding strong-lensing constraints improves the inferred stellar and dark matter distributions. The central dark matter profile is consistent with Navarro-Frenk-White, and the inferred stellar initial mass function is bottom-heavy. The inner total density profile is well described by a power law with slope −1.96 ± 0.07, which also reasonably explains the weak-lensing signal out to 1 Mpc/h. Assuming a single cored component, the stacked weak-lensing profile constrains the internal mass-sheet transformation parameter to λ_c = 0.978 ± 0.010. These are stacked constraints rather than separate determinations for each galaxy.

PublicResearchers studied how massive galaxies bend background light to estimate how stars and dark matter are distributed within them. They combined two types of gravitational lensing, including measurements from 13 strong-lens systems, and found that using both sharpened their estimates. The combined results are consistent with a standard model for the concentration of dark matter near galaxy centers and indicate a stellar population relatively rich in low-mass stars. The total density of stars and dark matter decreases outward approximately as the inverse square of distance from the center. This description fits the inner regions well and also reasonably explains the lensing signal farther out. The findings describe the galaxies collectively, not each galaxy individually.

Young explorerBig galaxies can bend light coming from behind them. Scientists combined these bent-light clues from many galaxies to work out where their stars and invisible dark matter are. Their results suggest that the galaxies have lots of small stars and that their centers are more crowded with matter than their outer parts. Using two kinds of light-bending clues together helped them get a clearer picture, but it is a shared picture of the galaxies, not a separate map of each one.

A Little Red Dot emerging from a nitrogen-rich UV-luminous galaxy with Very Massive Stars

Alberto Torralba, Jorryt Matthee, Rui Marques-Chaves+13 more

AstronomerJWST/NIRSpec medium-resolution spectroscopy of COLA1, a UV-luminous galaxy at z=6.6 (M_UV=-21.3), reveals a blue UV continuum, strong NIV] emission, stellar P Cygni profiles, and broad HeII. Stellar population models including very massive stars, with an upper mass limit of 300 solar masses, are statistically preferred; the best fit has a stellar mass of approximately 10^8 solar masses and an age of 2.4 ± 0.8 Myr. A redder rest-optical continuum and broad Balmer lines with Balmer absorption resemble Little Red Dot (LRD) spectra. Evolving the best-fit population predicts 1–2 magnitudes of UV fading in about 5 Myr, potentially producing a typical V-shaped LRD spectrum. The inferred abundance ratios are log10(N/O)=-0.07 ± 0.05 and log10(C/O)=-0.64 ± 0.11, giving log10(N/C)=+0.58 ± 0.12. Density-sensitive nitrogen and carbon doublets require distinct zones with electron densities above approximately 10^6.5 and below approximately 10^3.5 per cubic centimeter, respectively. For the dense zone, the estimated log10(N/C)>1.3 at 2-sigma requires extreme enrichment mechanisms; proposed possibilities include rapidly rotating stars above 100 solar masses, tidal disruption events, or supermassive stars. Runaway stellar collisions seeding an intermediate-mass black hole are a speculative explanation for LRD formation, not an established result.

PublicJWST observations of the distant galaxy COLA1 reveal an unusual combination: bright ultraviolet light, strong nitrogen enrichment, and features resembling the compact sources called Little Red Dots. Models that include stars more than 100 times the Sun’s mass fit the ultraviolet spectrum better than those without them. The best-fitting stellar population is only about 2.4 million years old, although that age depends on the modeling. Spectral lines indicate both very dense and much less dense gas, with particularly extreme nitrogen enrichment inferred in the dense region. The galaxy’s redder visible-light spectrum already resembles Little Red Dots. Models predict that its ultraviolet light could fade substantially in about five million years, making the overall spectrum look more typical of that population. Several mechanisms might explain the unusual chemistry. The authors also speculate that collisions among massive stars could have seeded a black hole, but the observations do not establish that scenario.

Young explorerScientists used the JWST telescope to study a faraway galaxy called COLA1. Its light shows lots of nitrogen compared with oxygen and carbon. Comparing the light with computer models suggests that it has some very big, very young stars. The models say its ultraviolet light could fade as those stars grow older. The scientists also wonder whether crashing stars helped make a black hole there, but that is an idea, not something they have shown.

Sub-sonic compressible magnetohydrodynamic turbulence I. Alfvénic and fast-magnetosonic injection, amplitude dependence, and compressibility effects

Eleonora Puzzoni, Silvio Sergio Cerri, Dimitri Laveder+2 more

• Plasma Physics
• High Energy Astrophysical Phenomena

AstronomerUsing 1024^3 PLUTO simulations of decaying, subsonic, compressible ideal-MHD turbulence, the authors investigate sensitivity to initial mode content, fluctuation amplitude, and plasma beta. Fully developed density fluctuations are insensitive to whether the initial perturbations are Alfvénic or fast-magnetosonic. Fast-mode injection undergoes rapid early shock dissipation before decaying at a rate comparable to the Alfvénic case; fast-mode contributions remain relevant in developed turbulence only for exclusively fast-mode injection. At delta B/B0 > 1, spectra are nearly isotropic and Kolmogorov-like for Alfvénic injection or Iroshnikov–Kraichnan-like for fast-mode injection. At delta B/B0 much less than 1, Alfvénic and mixed-wave initial conditions yield strong anisotropy, with perpendicular and parallel spectra proportional to k_perp^(-5/3) and k_z^(-2), respectively, steepening at beta much greater than 1. Weak fast-mode injection instead produces a shock-populated state with a nearly isotropic k^(-2) spectrum. Magnetic-field curvature and mirror structures depend strongly on amplitude and beta, and the predicted -2.5 power-law scaling appears only at large amplitude and high beta. These are simulation findings relevant to Galactic cosmic-ray transport, not measurements of transport itself; effects on cosmic-ray diffusion and field-line random walk are deferred to Paper II.

PublicComputer simulations explore how turbulence in magnetized gas could influence the movement of cosmic rays through our Galaxy. The researchers find that the strength and type of the starting disturbances, together with a gas property called plasma beta, can strongly change the resulting turbulence and magnetic-field structure. Strong disturbances produce nearly direction-independent turbulence, while weak disturbances can produce strongly direction-dependent patterns or a state containing shocks, depending on how they begin. Yet the amount of density variation in developed turbulence is similar for the two main starting wave types. These results come from simulations, not observations, and this paper does not determine how much cosmic-ray travel changes; that question is reserved for a follow-up study.

Young explorerScientists used a computer to make pretend space gas with magnetic fields and stir it in different ways. They found that big and small wiggles can make different patterns, and the kind of wiggle they start with matters too. These patterns might change how tiny, speedy particles travel through our galaxy, but this study has not worked out that part yet.

Hidden Neutrino Active Galaxy Candidates: Prospects for Catalog and Stacking Searches with IceCube, IceCube-Gen2, and KM3NeT

Mainak Mukhopadhyay, Jose Alonso Carpio, Heer Patel+2 more

• Astrophysics of Galaxies
• High Energy Physics - Phenomenology

AstronomerThe authors assemble X-HiNAC, a theory-guided sample of 28 intrinsically X-ray-bright, jet-quiet AGN candidates for hidden high-energy neutrino sources, using Swift/BAT and BASS surveys plus dedicated NuSTAR observations and spectral analyses. They compile intrinsic X-ray fluxes, spectral properties, luminosity distances, and black hole masses for neutrino searches. The selection is intended to remain model independent conditional on neutrino flux being proportional to intrinsic X-ray flux. Using a magnetically powered corona model, they assess individual-source and stacking prospects with IceCube-Gen2 and KM3NeT. Under favorable model assumptions, stacking the remaining sources while excluding NGC 1068 could yield a 5-sigma detection in approximately 5–15 years at current and upcoming neutrino observatories; this is a forecast, not a reported detection. Systematic uncertainties, especially black hole mass estimates that can differ by up to an order of magnitude between measurement techniques, substantially affect the predicted emission.

PublicThe researchers compiled 28 X-ray-bright active galaxies without prominent jets as candidates for sources of high-energy neutrinos. They combined X-ray surveys with dedicated observations to characterize these galaxies and guide neutrino searches. The list relies on the assumption that stronger intrinsic X-ray emission corresponds to stronger neutrino emission. A model in which magnetic energy powers a corona around the central black hole suggests that combining signals from multiple candidates, excluding NGC 1068, could produce a detection meeting the 5-sigma statistical threshold in about 5–15 years under favorable assumptions. This is a prediction, not a new neutrino detection. The forecast is sensitive to uncertain galaxy properties: different ways of estimating black hole masses can give answers differing by a factor of ten. Better mass measurements and X-ray observations would help refine the predictions.

Young explorerScientists made a list of 28 bright galaxy centers that might send out tiny particles called neutrinos. They used X-ray light to help choose where to look. A model suggests that looking for signals from several galaxies together might reveal the particles after about 5 to 15 years, if the model’s hopeful assumptions are right. They have not reported finding those signals here. They also need better measurements of the galaxies’ giant black holes to make their guesses more reliable.

Lightest and heaviest nuclei as keys to the origin of ultrahigh energy cosmic rays

Anna M. Suliga, Glennys R. Farrar

• High Energy Physics - Experiment
• High Energy Physics - Phenomenology

AstronomerThe authors report that Pierre Auger Observatory spectrum and composition data support two predicted light-element UHECR populations at a significance of at least 7.2 sigma. In the binary neutron star merger interpretation, one population is accelerated directly in jets, while the other consists of photodisintegration products of heavy nuclei accelerated in the bulk outflow. Their rigidity cutoffs, with R = E/Ze, agree with prior estimates. The data also favor 5–10% of UHECRs originating as r-process nuclei. The authors interpret these findings as strong evidence for a merger origin, rather than direct identification of individual sources, and discuss UHECRs and ultrahigh-energy neutrinos as probes of otherwise inaccessible merger physics.

PublicThe origin of the most energetic cosmic-ray particles remains uncertain. This study reports strong evidence pointing to collisions between neutron stars. The researchers find that Pierre Auger Observatory data support two groups of light-element particles predicted by this explanation: particles accelerated directly in jets, and fragments of heavier nuclei broken apart by light. They report statistical support of at least 7.2 sigma for the two groups, with energy-per-charge limits matching earlier estimates. The data also favor 5–10% of these cosmic rays starting as nuclei made through rapid neutron capture, another clue supporting neutron star mergers. These findings support the merger explanation but do not directly trace individual particles to a particular collision.

Young explorerTiny bits of matter zoom through space with enormous energy, and scientists want to know where they come from. One idea is that they come from two neutron stars crashing together. Scientists looked at measurements and found strong signs of two groups of tiny bits, just as this idea predicted. Some could have been sped up directly, while others could be pieces of bigger bits broken apart by light. This is a strong clue that neutron star crashes make these speedy particles, but it does not prove where every particle came from.

Intranight optical monitoring of eight quasars with superluminal jets and low optical polarization: Probing the mechanism of rapid flux variability

Krishan Chand, Gopal-Krishna, Ashutosh Tomar+3 more

• Astrophysics of Galaxies

AstronomerThe study tests the relative diagnostic importance of optical polarization and relativistic beaming for intranight optical variability (INOV) in eight low-synchrotron-peaked FSRQs with optical polarization below 3% and apparent jet speeds of 5–31c. Twenty new monitoring sessions, each lasting at least three hours, are combined with 19 literature sessions. For strong INOV, defined by amplitude greater than 5%, the duty cycle is zero with the standard F_eta test and approximately 7% with the enhanced F-test. High-polarization quasars show a duty cycle around 30% even with F_eta. Despite the strong Doppler boosting inferred from the apparent jet speeds, strong INOV is rare in this low-polarization sample. The authors interpret this contrast as compelling evidence that optical polarization is the primary diagnostic of INOV, with relativistic beaming playing a supportive role; the measured duty cycle remains test-dependent.

PublicWhat better signals whether a quasar will change brightness strongly within a single night: the polarization of its light or the brightness boost associated with its fast jet? Researchers studied eight quasars whose optical light had low polarization but whose observed jet motions suggested strong boosting. Across 39 monitoring sessions, brightness changes larger than 5% were rare: the estimated fraction of sessions showing them was zero with one statistical test and about 7% with a more sensitive test. The comparison figure for highly polarized quasars was about 30%, even with the first test. The authors conclude that polarization is the stronger indicator of rapid variability, while jet boosting has a supporting role. This is an interpretation of the observed contrast, not proof of what causes the brightness changes.

Young explorerScientists watched eight very bright things in space called quasars. They have fast jets, but their light waves were not very lined up—a property called low polarization. The scientists looked for big changes in brightness during a night and found that these were rare. Quasars with more lined-up light show those changes more often. The scientists think the way the light lines up is a better clue to these quick changes than the brightening linked to a fast jet. It is a clue, not a final answer about why the light changes.

Probing the geometry and outflows of the accreting millisecond pulsar SAX J1808.4-3658 with multi-band polarimetry

M. C. Baglio, G. Illiano, A. Papitto+13 more

AstronomerVLT/FORS2 R- and I-band polarimetry of SAXJ1808.4-3658 during its 2025 outburst, coordinated with IXPE observations, detects optical linear polarisation at every epoch, with P approximately 0.3–1.5% and position angles approximately 8–48°. The mean optical angle is offset by approximately 16–24° from the persistent X-ray polarisation angle, which pulse-profile modelling identifies as tracing the spin axis. Optical angle swings of up to approximately 40° within minutes disfavour disc scattering. Colour-magnitude behaviour and the polarisation dependence on a red excess attributed to the jet favour a jet origin during the main outburst, consistent with contemporaneous radio detections. The mean optical angle agrees with that in the previous outburst; the offset could arise near a wide jet base whose Doppler-boosted side dominates. At the onset of reflaring, the optical polarisation degree peaks and its angle aligns with IXPE, although the disc likely dominates the optical flux. Possible explanations include a fading-jet polarisation flare, outflow scattering, and synchrotron emission at the disc–magnetosphere boundary, with the last tentatively favoured.

PublicAstronomers measured the preferred orientation of light waves from the accreting X-ray pulsar SAXJ1808.4-3658 during its 2025 outburst, combining optical observations with X-ray polarimetry. The optical light was weakly but significantly polarised at every observing epoch. Its average orientation differed from the X-ray orientation, which modelling links to the star’s spin axis, and swung by as much as about 40 degrees within minutes. These rapid changes argue against scattering in the disc as the main explanation. Together with the source’s colour changes and radio detections, the observations instead favour optical emission from a jet during the main outburst. A broad jet base could explain the angular offset, but this remains an interpretation. When renewed brightenings began, the optical polarisation was strongest and aligned with the X-ray orientation. The cause of this later behaviour is uncertain: the authors tentatively favour emission where the disc meets the star’s magnetic region, while also considering a fading jet or scattering in an outflow.

Young explorerAstronomers watched light from a spinning star that was taking in material and getting brighter. They measured which way the light waves lined up. That direction changed quickly—within minutes. The clues suggest that much of this special light came from a stream of material shooting away from the star, rather than light bouncing off the disc around it. Later, when the star started brightening again, the light lined up differently. The scientists are not sure why. One idea is that it came from where the disc meets the star’s magnetic region.

The Valence and Inner Shell Ionization Properties of Sr I - III by Non-Thermal Electrons in Kilonovae

Steven Bromley, Luke Shingles, Evan Garbe+5 more

• Solar and Stellar Astrophysics
• Atomic Physics

AstronomerStrontium identified in AT2017gfo showed spectral evolution indicative of a rapidly changing ionization balance, motivating improved atomic data for interpreting later-time spectra. Using the Flexible Atomic Code, the authors calculate valence- and inner-shell ionization cross sections for Sr I, Sr II, and Sr III. They recover complex structures resembling those in published Sr I and Sr II measurements, likely associated with excitation autoionization. For Sr III, which lacks measurements, the calculations suggest negligible excitation-autoionization contributions. The cross sections are incorporated into Spencer-Fano non-thermal electron degradation models coupled to an ionization-balance solver, with excitation autoionization treated as excitation plus Auger-electron production. Level- and configuration-average calculations yield ion fractions agreeing within 5–20%. In the models, omitting final-charge-state-resolved branching ratios for inner-shell ionization and successive Auger cascades substantially changes the ionization balance. The calculated cross sections will be made available on Zenodo.

PublicStrontium was identified in the light from the kilonova AT2017gfo, and its changing spectral signature indicated rapid changes in how many electrons its atoms had lost. To help interpret later observations, researchers calculated how electrons produced by radioactive beta decay can knock electrons out of strontium. Their calculations reproduce complex features similar to those in laboratory measurements for neutral and singly ionized strontium. For doubly ionized strontium, where no measurements are available, they predict little contribution from a process in which excitation leads to electron ejection. The team then used the new atomic data in models that track energetic electrons and strontium's electrical charge states. Two levels of computational detail gave charge-state fractions agreeing within 5–20%. The models also show that accounting for cascades that eject several electrons can substantially affect the predicted charge balance. These are atomic calculations and modeling results, not new measurements of the kilonova.

Young explorerScientists found signs of a kind of atom called strontium in the light from a bright space event. Those signs changed as the atoms lost or gained tiny parts called electrons. The researchers used computers to work out how fast-moving electrons could knock other electrons out of strontium atoms. Some of their answers looked like patterns already measured in experiments, but one kind of strontium atom has not been measured yet. Their models showed that it matters when one knock starts a chain that lets several electrons escape. This work could help scientists understand the changing light from the space event.

CHIME All-sky Multiday Pulsar Stacking Search (CHAMPSS): Power Spectrum Injections and Survey Sensitivity

Reynier Squillace, Lars Künkel, Robert Main+8 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors present artificial pulsar-signal injection into Fourier power spectra as a computationally inexpensive alternative to time-series injection for the CHIME All-sky Multiday Pulsar Stack Search (CHAMPSS). The injection cost is negligible relative to the search pipeline overhead. Injection tests indicate that CHAMPSS is most sensitive to pulsars with frequencies of roughly 0.1–100 Hz and fluxes above 1 mJy. Sensitivity depends only weakly overall on dispersion measure, duty cycle, and sky coordinates, although the parameters exhibit complex, non-monotonic interactions. The authors interpret the results as suggesting that frequency-dependent noise, especially red noise, and sampling limitations at higher frequencies are the dominant extrinsic limitations on sensitivity. These are injection-based characterizations of survey biases, not reports of newly detected pulsars.

PublicThe researchers tested how well the CHAMPSS radio survey can find pulsars by adding artificial pulsar signals to a frequency-based representation of the survey data. This approach requires negligible computing effort compared with running the search itself and avoids the expense of adding signals directly to the time series. The tests indicate that the survey is most sensitive to pulsars with signal frequencies of about 0.1–100 hertz and radio fluxes above 1 millijansky. Other tested properties have a weaker overall effect, but interact in complicated ways. The results suggest that noise, particularly at low frequencies, and limits on how rapidly the data are sampled are the main external obstacles to detecting pulsars. The study tests the survey's capabilities rather than announcing new pulsar discoveries.

Young explorerPulsars send out radio pulses that scientists try to find in telescope data. This team added pretend pulsar signals to the CHAMPSS survey's data in a way that takes very little extra computer work. They used these pretend signals to check which kinds of pulses the search finds most easily. The tests suggest that unwanted noise and how often the telescope records the signal can make some pulses harder to find. This was a test of the search, not a discovery of new pulsars.

A temporally clustered gravitational wave pair and a Type IIb supernova

Sheng Yang, Ting-Wan Chen, Weichangfeng Guo+22 more

AstronomerThe authors report two marginal GW candidates, S190910d and S190910h, separated by 7.1 hours, whose three-dimensional localizations overlap the position and distance of the rapidly evolving Type IIb supernova SN 2019rsq. Their temporal separation and localization overlap yield a pairwise null probability of 7.6 × 10^-5 in a Monte Carlo test; this is not a probability for the supernova association, which alone is not statistically rare. Independent re-analyses recover both candidates as signal-like. Under a common-origin hypothesis, S190910h is consistent with source-frame component masses near 2.5 and 1.3 solar masses, while S190910d favors approximately 34 and 3 solar masses, with an observed amplitude compatible with the supernova distance. The supernova light curve is consistent with collapse near the GW activity. A fragmenting collapsar disk is proposed as a plausible framework for the masses, hour-scale delays, and supernova properties, not an established explanation. The suggested association raises, but does not demonstrate, the possibility of multiple compact-object mergers accompanying one stellar collapse.

PublicResearchers report two possible gravitational-wave signals 7.1 hours apart whose estimated locations and distances overlap those of supernova SN 2019rsq. The signals remain marginal candidates, although independent analyses also find them signal-like. Their combination of timing and location overlap is unusual in the authors’ statistical test, but the supernova coincidence by itself is not statistically rare. The supernova’s changing brightness is consistent with a star collapsing around the time of the signals. The authors suggest that a disk breaking into pieces around a collapsing star might explain multiple mergers within hours, rather than long after the collapse. Neither the shared origin nor this explanation is established.

Young explorerScientists found two possible tiny ripples in space, about seven hours apart. They might have come from the same place as an exploding star, but scientists are not sure. One idea is that a disk around the collapsing star broke into pieces that joined together and made ripples. That is a possible explanation, not something they have proved.

A Unified Mass-Loading Model for ASKAP J1745-5051: Linking Long-Period Radio Transients to Magnetic Cataclysmic Variables

Yejing Zhan, Fa-Yin Wang

AstronomerASKAP J1745-5051 exhibits LPT-like radio pulses recurring approximately every 82 minutes, magnetic accretion, and X-ray modulation at a consistent period. The authors propose a unified mass-loading framework in which a dense Roche-lobe-overflow stream supplies the accretion curtain and near-white-dwarf X-ray sources, while a tenuous donor wind populates magnetic flux tubes at densities of (1–4) × 10^7 cm^-3, meeting the local density requirement for electron-cyclotron maser emission. A fiducial geometry places the X-ray maximum near orbital phase 0.886 and the radio-visibility window at phases 0.22–0.33, consistent with the primary observed pulse window. In the model, geometrical modulation and curtain absorption yield stronger soft-band than hard-band X-ray variability. Long-term phase-connected radio monitoring with simultaneous X-ray observations could test the interpretation through recurring radio phase changes and correlated changes in X-ray modulation. J1745 may be an evolved magnetic cataclysmic variable near the orbital-period minimum, potentially extending the proposed connection between detached binary LPTs and accreting systems to a late evolutionary stage.

PublicASKAP J1745-5051 is a white dwarf binary that produces radio pulses about every 82 minutes and X-ray variations with a matching period. This combination poses a puzzle: gas flowing onto the white dwarf can be dense, but the proposed radio-emission mechanism needs much thinner gas. The researchers propose that two gas supplies coexist: a dense stream feeds the accretion flow and X-ray sources, while a thin wind from the companion supplies magnetic pathways where radio emission could arise. One example geometry gives a radio viewing window consistent with the main observed pulse window and explains how geometry and absorption could make lower-energy X-rays vary more strongly than higher-energy X-rays. This is an interpretation to be tested, not a confirmed picture. Long-term radio monitoring alongside X-ray observations could check it. The system may be a late-stage accreting binary near its minimum orbital period.

Young explorerTwo stars travel around each other, and one is a white dwarf. We see radio flashes from their system about every 82 minutes, and its X-rays change on a matching schedule. Scientists think thick and thin streams of gas might share the space around the stars. The thick gas could help make the X-rays, while the thin gas could let radio flashes form. Their model lets us see the flashes at times that fit the main flashes already spotted. They need to keep watching in radio and X-rays to find out whether this idea is right.

Probing the nature of Galactic microquasars with diffuse gamma rays and neutrinos: low-mass versus high-mass X-ray binaries

Pei-Pei Zhang, Wei Liu, Zong-Kang Zeng+2 more

AstronomerSub-PeV gamma-ray observations provide strong evidence for a Galactic origin of cosmic rays near the knee, while observations disfavor most supernova remnants as PeV accelerators. Microquasars are candidate PeVatrons and potentially dominant contributors, but their population’s spatial distribution remains uncertain. This study compares low-mass and high-mass X-ray binary distributions using very-high-energy diffuse gamma rays and neutrinos. The predicted gamma-ray longitude profiles differ substantially: an LMXB-dominated distribution produces stronger concentration toward the Galactic center. The authors also find that the HMXB distribution cannot account for the latest Galactic diffuse-neutrino observations. These findings do not establish microquasar dominance. Higher-precision diffuse-flux measurements with LHAASO, HAWC, IceCube, and KM3NeT could determine the population’s spatial distribution and test its role in the knee’s origin.

PublicMicroquasars are possible sources of extremely energetic cosmic rays in our Galaxy, but whether they dominate that supply remains uncertain. This study asks whether their distribution is better represented by binary systems with lower-mass or higher-mass companion stars. The authors predict different patterns of diffuse gamma-ray emission across the Galaxy for the two possibilities. The lower-mass-companion distribution would concentrate the emission more strongly toward the Galactic center. They also find that the higher-mass-companion distribution cannot explain the latest observations of diffuse Galactic neutrinos. More precise gamma-ray and neutrino measurements could help identify where the microquasar population lies and test whether it supplies cosmic rays near the energy range called the knee.

Young explorerScientists wonder whether objects called microquasars give tiny space particles a very big boost. They compared ideas in which these objects have lighter or heavier companion stars. The lighter-star idea predicts more high-energy light toward the middle of our galaxy. The heavier-star pattern does not explain the latest observations of tiny particles called neutrinos. Better measurements could help test these ideas; scientists have not proved microquasars are the main source.

Extreme Hard X-ray Variability in the TeV Blazar Mrk 421: Insights from NuSTAR Observations

Gopal Bhatta, Eshaan Bhatta

AstronomerSpectral and timing analyses of 27 NuSTAR observations of the TeV blazar Mrk 421 from 2012–2024 probe hard X-ray variability on long-term and intra-day timescales. The flux varies by up to a factor of 200 over the decade, including a tenfold rise within 15 days during a flare. A lognormal flux distribution and linear RMS–flux relation suggest multiplicative variability. A log-parabolic model best describes most spectra, with a strong linear anti-correlation between photon index and curvature. Synchrotron peak energy correlates positively with flux, alongside a subtle harder-when-brighter trend. The authors interpret these findings as consistent with standard blazar emission models and supportive of particle acceleration by shocks or magnetic reconnection in the relativistic jet, without establishing which mechanism dominates.

PublicUsing 27 NuSTAR observations collected from 2012 to 2024, researchers studied changes in the high-energy X-rays from the blazar Mrk 421. Its X-ray brightness varied by as much as a factor of 200 over the decade and rose tenfold within 15 days during one flare. The statistical pattern of these changes suggests that the variations multiply together rather than simply add up. Most observations were best described by a smoothly curved X-ray spectrum. As the source brightened, its synchrotron emission peak shifted to higher energies, with a subtle tendency toward a greater share of higher-energy X-rays. The findings are consistent with particles gaining energy through shock fronts or rearranging magnetic fields in its fast-moving jet, but do not establish which process is responsible.

Young explorerScientists watched X-rays from a space object called Mrk 421. In their observations, it sometimes shone much brighter and sometimes much dimmer. During one bright burst, it became ten times brighter in 15 days! When it was brighter, its X-ray light also tended to be a little more energetic. The scientists think tiny particles in its fast-moving jet may get a boost from shocks or changing magnetic fields, but they have not shown which one does it.

Angular Momentum Transport across Accretion States around a rapidly spinning black hole

Rohan Raha, Koushik Chatterjee

AstronomerHigh-resolution three-dimensional GRMHD simulations around a rapidly rotating black hole (a = 0.998) compare angular-momentum transport in SANE, intermediate-flux, and magnetically arrested disk (MAD) states. In SANE and intermediate states, outward stresses do not overcome inward angular-momentum advection, leaving the net flux inward. In MAD, ordered Maxwell stresses regulate the disk and drive winds, while a Blandford-Znajek jet supplies a distinct, approximately constant outward angular-momentum flux extracted from the black hole; the total flux is outward. Magnetic-flux eruptions perturb both channels: an equatorial current sheet extends beyond the ergosphere, expelled magnetically dominated bubbles enter the polar region, and the jet becomes asymmetric. Its tilt more than doubles, while its opening angle widens before contracting below its pre-eruption value. Eruptions suppress horizon accretion, briefly reverse angular-momentum flux through the jet surface, and reorganize disk Maxwell stresses. Turbulent stress recovers toward its saturated MAD level as horizon-threading flux rebuilds. Simulated eruption durations and inter-variable lags of approximately 40–90 r_g/c scale to milliseconds for stellar-mass black holes and tens of minutes for Sgr A*. These simulation results distinguish disk-regulating magnetic torques from black-hole-sourced jet transport; they are not observational measurements.

PublicComputer simulations explore how gas and magnetic fields move angular momentum around a rapidly spinning black hole. This transport matters because gas must shed angular momentum to fall inward. In the simulations with weaker magnetic flux, inward transport outweighs outward transport overall. In the most strongly magnetized, magnetically arrested state, organized magnetic fields regulate the disk and drive winds, while a jet carries angular momentum extracted from the black hole, making the total transport outward. Eruptions of magnetic flux temporarily disrupt this arrangement: less gas enters the black hole, the jet becomes lopsided and more tilted, and its opening first widens and then narrows. Angular-momentum transport through the jet surface briefly reverses. The modeled eruption durations and delays between changes scale to milliseconds for stellar-mass black holes and tens of minutes for the Milky Way's central black hole, Sgr A*. These are simulation findings, not observed eruptions, and the relative importance of the different transport mechanisms remains uncertain.

Young explorerScientists used a computer to study gas swirling around a fast-spinning black hole. In their strongest-magnet model, magnetic fields help move some of the swirling motion outward, and a jet carries some away from the black hole. Sometimes the magnetic fields burst outward. Then less gas falls in, and the jet leans more and changes shape. This happened in the computer model; it was not something the scientists watched in the sky.

Effects of Competing Reactions on ⁵⁹Cu and ⁶³Ga on Abundance Distributions in Type I X-Ray Bursts

Yinwen Guan, Ertao Li, Zhihong Li+9 more

• Nuclear Theory

AstronomerIn K04 one-zone post-processing simulations of X-ray bursts, the authors combine four sets of Monte Carlo calculations using STARLIB rates and temperature-dependent uncertainties with XGBoost classification, SHAP analysis, and reaction-flow analysis. They identify competing (p,α) and (p,γ) channels on copper-59 and gallium-63 as the primary drivers of secondary abundance peaks outside the central 68% confidence interval in all 44 isotopes examined. Fixing both reaction pairs at their median rates reduces the fractions of samples in secondary-peak regions by 96–100%, while leaving the central 68% interval bounds largely unchanged for most mass numbers. The copper-59 pair has the larger effect. Reaction-flow analysis attributes these features to enhanced recycling, reduced supply to heavier isotopes, and faster proton consumption; earlier proton exhaustion further suppresses subsequent captures. The resulting shifts in production–destruction balance generate high- or low-abundance secondary peaks beyond the Ni–Cu and Zn–Ga cycles. These model results motivate improved nuclear-physics constraints on copper-59(p,γ)zinc-60 and both competing gallium-63 channels; they are not observational measurements of burst ashes.

PublicThe elements left behind by X-ray bursts affect how a neutron star’s crust transports heat and undergoes heating and cooling. This study uses computer simulations, rather than observations, to investigate why uncertain nuclear reaction rates sometimes produce separate peaks in predictions of the leftover elements. The researchers trace these peaks mainly to competing reactions involving copper-59 and gallium-63, with copper-59 having the stronger influence. In the model, recycling material through reaction cycles reduces the amount reaching heavier elements and uses up protons sooner, changing which elements accumulate. Holding these reaction rates at their middle values nearly eliminates the extra peaks without greatly changing the central range of predictions for most mass numbers. The study identifies specific reactions needing better nuclear-physics constraints to improve predictions.

Young explorerA neutron star can have a burst that leaves behind different kinds of tiny building blocks. Scientists used a computer model to explore what might be left over. Two sets of reactions acted like forks in a road: changing the paths could leave much more or much less of some building blocks. The scientists want to learn more about those reactions so their predictions can get better. They did not measure the leftovers from a real burst.

The Birth of Plasmoids: Weibel-Driven Secondary Tearing and its Suppression in Relativistic Reconnection

Matthew Goodbred, Anatoly Spitkovsky

• Plasma Physics

AstronomerTracking newborn plasmoids in 2D particle-in-cell simulations of pair-plasma reconnection with magnetizations 0.1 ≤ σ₀ ≤ 1000, the authors identify a current-filamentation/Weibel instability driven by counter-streaming, out-of-plane current carriers near primary x-lines as the seeding mechanism. Measured growth rates are about 0.1 times the background plasma frequency, consistent with linear theory evaluated using the simulated distributions. Away from an x-line, inflowing plasma increases the number of current carriers and reduces their drift. The instability shuts off when that drift becomes comparable to the momentum spread along the outflow, at a distance ℓ_iso proportional to σ₀. These simulation results account for the onset of plasmoid-dominated relativistic reconnection and predict suppressed plasmoid formation beyond roughly ℓ_iso from primary x-lines, even in the ultra-relativistic regime. Particle acceleration, variability, and coherent radio emission attributed to plasmoids may consequently occupy smaller regions than previously assumed; these implications are not observational detections.

PublicMagnetic reconnection rearranges magnetic fields in plasma and can produce structures called magnetic islands. In two-dimensional computer simulations of plasma made of electrons and positrons, researchers traced the birth of these islands to an instability caused by particles carrying electric current in opposite directions near key reconnection sites. The simulated instability grew at rates consistent with a theoretical calculation. Farther from those sites, incoming plasma supplies more particles to carry the current, slowing their directed motion until the instability stops. The simulations indicate that stronger magnetization lets the island-forming region extend farther, but predict that island formation is still suppressed beyond a limited distance, even under extremely relativistic conditions. If this picture applies more broadly, particle acceleration, brightness variations, and coherent radio emission linked to magnetic islands may come from smaller regions than previously assumed. The study is based on simulations, not direct astronomical observations.

Young explorerScientists used a computer to study how tiny particles and magnetic fields can make little magnetic islands. In their flat, two-dimensional model, particles moving in opposite directions started a growing disturbance that made the islands. Farther from where this began, more particles shared the job of carrying electric current, and the island-making disturbance stopped. The model suggests that islands may form only in certain places, not everywhere. Scientists still need to find out how well this picture fits real space.

Magnetized Accretion Flows with Low Angular Momentum Around Supermassive Black Holes

Razieh Ranjbar

AstronomerThis theoretical study examines slowly rotating black-hole accretion using a steady, height-integrated transonic model with radial mass loss and a radial magnetic-field prescription informed by previous simulations. Comparing hydrodynamic and magnetized Bondi-like and disk-like solutions, the authors find that magnetic pressure, tension, and torque substantially modify the sonic radius, angular momentum, and mass accretion rate reaching the black hole. Sufficiently strong fields produce magnetically dominated inner flows with plasma beta below unity and strongly sub-Keplerian rotation; magnetic stresses can drive transitions to lower angular momentum. Outflows can also significantly reshape disk-like solutions. Separate 2D simulations of magnetized Bondi and torus accretion qualitatively reproduce the modeled radial structure and magnetically dominated, sub-Keplerian character, rather than establishing quantitative agreement or observational confirmation.

PublicThe researchers use mathematical models and computer simulations to study how large-scale magnetic fields affect slowly rotating gas falling toward black holes. In their models, magnetic forces change where the inward flow passes the speed of sound, how much rotation the gas retains, and how much gas reaches the black hole. With sufficiently strong fields, magnetic pressure outweighs gas pressure near the black hole, and the gas rotates much more slowly than expected for a circular orbit supported by rotation alone. Gas flowing outward can also substantially change the structure of disk-like inflows. Two-dimensional simulations reproduce the broad features of the mathematical solutions, but these are theoretical findings, not observations of actual black holes.

Young explorerThe scientists used math and computer experiments to explore gas falling toward a black hole. They found that magnetic forces can change how the gas falls and spins, and how much reaches the black hole. When those forces are strong enough, the gas near the black hole spins much more slowly. Some gas can also flow outward and change the shape of the gas falling in. These are results from models, not things the scientists watched happen around a real black hole.

Angle-dependent emission from evolving accretion layers

Shahram Abbassi, Fahimeh Habibi

AstronomerGrey, special-relativistic similarity solutions quantify how atmospheric evolution alters the emergent angular radiation field even at constant integrated optical column. The model is an irradiated, internally heated, expanding plane-parallel layer, with the full angular field determining the source function and acceleration of a pressureless flow in prompt radiative balance. Evolving solutions are compared with frozen transport calculations on identical density and velocity profiles, either fixing the source or allowing it to relax. Heating drives a transition from limb darkening to limb brightening, while the temporal correction to angular contrast reverses sign with optical column. For an upper-boundary speed of 0.04c, injection speed of 0.06c, and heating four times the reference incident flux, the intensity ratio at direction cosines 0.1 and 1 is 18.8 per cent above the frozen fixed-source result at τ₀=0.15 and 2.53 per cent below it at τ₀=0.55. Source relaxation preserves the reversal. The corresponding direct photon flight times are one third and three per cent of the flow age for oblique and normal directions, respectively. These theoretical solutions provide a local benchmark for evolving disc atmospheres and reprocessing layers, not a system-specific prediction; applications require additional thermal, spectral, and geometrical physics.

PublicA theoretical study shows that an expanding atmosphere can change how bright it looks from different directions even when its total optical thickness stays constant. The researchers calculated how light travels through a simplified, heated layer while the layer evolves, then compared this with calculations that hold the atmosphere frozen in time. Heating can make shallow viewing directions brighter rather than dimmer than a straight-on view. The additional effect of evolution can either strengthen or weaken this brightness contrast, depending on the layer’s optical thickness; allowing the model’s light source to readjust does not remove that reversal. These are results from an idealized mathematical model, not observations of a particular object. They offer a benchmark for studying atmospheres above accretion discs and layers that absorb and re-emit radiation, but applying them to a real system requires more complete physics.

Young explorerImagine light traveling through a warm layer that is spreading out. Scientists used a simple math model to compare light moving through the changing layer with light moving through a layer held still. In the model, the changing layer could look brighter or dimmer from the side compared with looking straight through it. Which way the difference went depended on how hard it was for light to pass through the layer. This was a math study, not something seen in a real space object, and real objects would need a more detailed model.

A Massive and Eccentric Binary Millisecond Pulsar in the Globular Cluster M10

Yujie Wang, Zhongli Zhang, Zhichen Pan+4 more

AstronomerFAST timing of the millisecond pulsar PSR J1657-0406A in M10 yields an orbital period of approximately 37 days and eccentricity of approximately 0.12. The measured periastron advance is 0.00090 ± 0.00013 degrees per year, implying a total system mass of 2.5 ± 0.6 solar masses if general relativity accurately describes the orbital motion. No optical counterpart was detected within the positional uncertainty, disfavoring a main-sequence companion. Based on possible formation channels for the eccentric orbit, the authors favor a helium white dwarf companion, but cannot exclude a massive white dwarf or neutron star.

PublicObservations with the FAST radio telescope show that the rapidly spinning pulsar PSR J1657-0406A, in the star cluster M10, has a companion in an elongated orbit lasting about 37 days. Astronomers measured a slow rotation of the orbit's orientation. If general relativity correctly describes the motion, this implies that the two objects together have about 2.5 times the Sun's mass, with an uncertainty of about 0.6 solar masses. No optical counterpart was detected at the pulsar's location, making an ordinary main-sequence star an unlikely companion. Considering how the elongated orbit could have formed, the researchers favor a helium white dwarf, though a massive white dwarf or a neutron star remains possible.

Young explorerA spinning star in a group of stars called M10 sends out radio flashes. Scientists used a radio telescope to learn that it travels with another object, going around each other about every 37 days on a path that is not quite a circle. They did not see the companion in ordinary light. They think it is probably a small leftover star called a helium white dwarf, but they are not sure: it could be a different kind of leftover star.

A magnetically heated slim disc-corona model for tidal disruption events

Wei Chen, Chris Done, Erlin Qiao+2 more

AstronomerThe authors develop a super-Eddington slim-disc model in which magnetic reconnection channels accretion power into a hot Comptonizing corona, and test it against the X-ray TDE AT2021ehb. The brightest spectra are broadly reproduced with M_BH ~ 10^6–10^7 solar masses and dimensionless accretion rate ~1, but matching the observed rapid, large changes in coronal contribution requires variable magnetic coupling to the disc. Such coronal variability resembles transient XRB outbursts rather than comparably luminous AGNs, suggesting a possible association with rapidly evolving, non-steady accretion. As the inferred accretion rate falls to ~0.01, the spectrum hardens but remains at photon index Gamma ≳ 2, unlike AGNs and XRBs at comparable luminosities. The detailed evolution therefore matches neither class; the authors interpret this as likely reflecting the highly variable nature of TDE accretion.

PublicResearchers studied how a disc of material feeding a black hole exchanges energy with a hot surrounding region called a corona during the tidal disruption event AT2021ehb. Their model uses magnetic reconnection to transfer energy from the disc to the corona and broadly matches the brightest observed X-ray spectra. However, reproducing the corona’s rapid, substantial changes requires the strength of that magnetic connection to vary. Similar variability occurs in outbursts from stellar-mass black-hole systems, but not in similarly luminous active galactic nuclei. As AT2021ehb faded, its X-ray spectrum shifted toward higher energies, though not as far as either comparison group at similar luminosities. The authors suggest that a rapidly changing flow of material may explain its distinctive behavior, rather than finding an exact match to either group.

Young explorerScientists watched X-rays from an event near a black hole called AT2021ehb. The light changed quickly. They made a model in which magnets move energy from swirling material into a very hot cloud. The model roughly matched the brightest X-rays, but it needed the magnetic link to change to explain the quick changes in the cloud’s light. As the event faded, its light changed differently from the other black-hole systems they compared it with. The scientists think the swirling material may have been changing very quickly, but that explanation is not certain.

Gravitational-Wave Signal from a Short GRB Relativistic MHD Jet

Or Zuriel, Dmitry D. Ofengeim, Omer Bromberg+2 more

• General Relativity and Quantum Cosmology

AstronomerThe authors compute gravitational waves from a relativistic MHD simulation of a short gamma-ray burst jet with parameters corresponding to GRB 170817A, directly integrating the retarded solution of the linearized Einstein equations. Separating baryonic and electromagnetic contributions links waveform features to simulated engine dynamics. The predicted signal is memory-like, with h(f) proportional to 1/f at low frequencies and a knee near 0.5 Hz set by the injection time, corresponding to the burst duration. An early peak is attributed to magnetic field lines opening and ejecta receiving an equatorial kick at jet onset. The signal is strongest far from the jet axis. The simulated radiated GW energy is about 10^42 erg, approximately 10^-9 of the jet energy. Its scaling as jet energy squared divided by the shortest variability timescale makes this a lower-limit estimate. Sensitivity comparisons suggest marginal detectability of GW170817-like events with DECIGO out to 10 Mpc and the Einstein Telescope out to 1 Mpc. These are predictions, not detections. The simulation used smooth injected Poynting flux; millisecond engine variability, predicted by some models but not demonstrated here, would substantially increase GW energy and detectability.

PublicA computer simulation explores how the jet powering a short gamma-ray burst could produce gravitational waves: ripples in spacetime. The model uses parameters corresponding to GRB 170817A, but the calculated signal is not an observed detection. An early peak in the predicted waves is linked to magnetic field lines opening and material being kicked sideways as the jet begins. Such a signal could reveal activity hidden deep inside the burst’s engine. The waves are strongest when viewed well away from the jet’s direction, but carry only about one-billionth of the jet’s energy in this simulation. Comparisons with detector sensitivities suggest that similar events might be marginally detectable by DECIGO within 10 megaparsecs or the Einstein Telescope within 1 megaparsec. The simulated energy input was smooth; rapid engine fluctuations proposed in some models could make the waves much stronger and easier to detect.

Young explorerScientists used a computer to pretend to make a powerful jet that shoots out during a short flash in space. In their model, magnetic fields spread open and give nearby material a sideways push. This makes tiny ripples in space that might tell us what is happening inside the hidden jet-making engine. The scientists calculated these ripples; they did not see them. If the engine flickers very quickly, the ripples could be stronger, but this model did not test that.

Self-lensing of electromagnetic counterparts to extreme mass ratio inspirals

Ruwen Zhou, Zhen Pan

AstronomerUsing forward ray tracing in Kerr spacetime, the study models self-lensing of electromagnetic flares produced when an inclined extreme mass ratio inspiral shocks gas at accretion-disk crossings. Far-side flares can be strongly magnified while near-side flares remain almost unmagnified, yielding strong–weak alternation despite identical intrinsic emission. In the model, Lense–Thirring precession shifts crossing azimuths and produces long-term amplitude envelopes whose spacing could constrain the precession period; it can also increase cumulative geometric lensing probability over longer observing windows. Keplerian motion of disk-co-rotating hotspots can produce time-dependent magnification within flares, generating shoulders or double peaks and changing effective widths. The authors propose, rather than observationally establish, a spectral discriminator: self-lensing can amplify later, cooler emission into a softer secondary peak, whereas delayed images from a static external lens repeat the same intrinsic spectral evolution.

PublicComputer modeling explores how a supermassive black hole could change repeated flashes from a much smaller object crossing its surrounding disk of gas. The crossings can shock the gas and produce flares. The black hole’s gravity can magnify flashes from behind it much more than flashes from the near side, making otherwise identical flashes alternate between bright and faint. A gradual turning of the orbit caused by the black hole’s rotation can create longer-term brightness patterns that could help reveal how quickly the orbit turns. Motion of glowing regions within the disk can also reshape individual flashes, sometimes giving them two peaks. The researchers propose using changes in the light’s spectrum to distinguish this effect from lensing by a separate, static object: the black hole’s own lensing can emphasize later, cooler light, while the separate lens would repeat the same sequence of spectral changes. These are modeling results and a proposed test, not reported observations.

Young explorerThe researchers used a computer to explore flashes near a giant black hole. A much smaller object can make flashes when it passes through a disk of gas. The black hole can act a little like a magnifying glass, making flashes behind it look brighter than flashes in front. Moving glowing spots can even make one flash look like it has two bumps. The researchers also suggest that looking at how the light changes could help tell what made it look that way. These are ideas explored with a computer, not flashes they report seeing.

Mass and angular momentum assessement of the neutron star XTEJ 1807-294 using X-ray triplets

Radostina P. Tasheva, Ivan Z. Stefanov

• Solar and Stellar Astrophysics
• General Relativity and Quantum Cosmology

AstronomerThe X-ray power-density spectrum of the accreting millisecond pulsar XTEJ 1807-294 contains several simultaneously observed QPO triplets, each comprising lower and upper kHz QPOs and a low-frequency QPO. The authors use these triplets to estimate the neutron star’s mass and specific angular momentum, propagating errors to obtain parameter intervals. They repeat the calculations with several kHz QPO models and suggest that consistency among bounds inferred from different triplets may help assess model viability. The abstract reports neither numerical parameter estimates nor a preferred model.

PublicX-ray observations of the neutron star XTEJ 1807-294 show several sets of three nearly repeating brightness variations occurring together: two rapid variations and one slower variation. The researchers use these patterns to estimate the star’s mass and its angular momentum per unit mass, including uncertainty ranges. They repeat the analysis with different models for the rapid variations. Agreement between estimates from different sets of patterns could help judge which models are viable, but the abstract gives no numerical estimates or preferred explanation.

Young explorerScientists see X-rays from a star called XTEJ 1807-294 flicker in three almost-repeating patterns at once: two fast ones and one slower one. They use these patterns to work out how much matter the star has and learn about its spinning, allowing for uncertainty. They try different explanations for the fast flickers. If different groups of flickers give matching answers, that could help them judge the explanations, but this summary does not say which works best.

Hidden by Exponential Screening: The Invisibility of the Dymnikova Black Hole de Sitter Core to Accretion Observables

Orhan Donmez, Sushant G. Ghosh, Farruh Atamurotov+1 more

• General Relativity and Quantum Cosmology

AstronomerGeneral-relativistic hydrodynamic simulations of Bondi–Hoyle–Lyttleton accretion test whether a Dymnikova black hole’s regular de Sitter core affects the flow despite exponential screening of the metric correction. Six models span critical lengths of 0.1–1.1M, reaching 97% of the extremal value, with identical gas parameters and resolution. In the most strongly corrected model, the gravitational acceleration differs by 12% at the inner boundary, but the response is local: the innermost post-shock density falls by 10% and the quiet-phase accretion rate by 0.12%, with no effect beyond about 2.7M. Once the shock-cone instability saturates, even metric differences of roughly 10^-10 lead to decorrelated flows, motivating comparisons of independent-realization ensembles. Ensemble-averaged accretion rates are independent of critical length within 0.8% at 2σ; variability amplitude, cone angle, and stagnation radius remain within realization scatter, propagation lags agree within 1.6%, and no power spectrum shows a detectable core signature. These simulation results support the authors’ interpretation that timing probes the shock-cone mechanism rather than the regular core in this setup, while emphasizing that apparent inter-model flow differences require ensemble-based statistical validation.

PublicCould gas falling toward a black hole reveal whether its center is a singularity or a smooth core? This study investigates that question with computer simulations, not telescope observations. The researchers simulated gas accretion onto six versions of a black-hole model with a smooth core. Even the strongest modification changed the gas mainly very close to the hole. After accounting for the unpredictable evolution of the gas flow by comparing groups of independent simulations, the average rate of gas falling in agreed within 0.8%, and the tested variability patterns showed no detectable core signature. The authors conclude that, for the simulated conditions, timing measurements would reveal the behavior of the gas’s shock cone rather than distinguish the smooth core from a conventional Schwarzschild black hole. The work also shows why differences between individual simulations should not automatically be interpreted as physical effects.

Young explorerScientists used computers to imagine gas falling toward black holes. They asked whether changing a black hole’s very middle from a sharp mathematical point to a smooth center would change how the gas moves. In their computer tests, the gas changed a little very close to the hole, but its bigger patterns looked much the same. The gas also moved in hard-to-predict ways, so the scientists had to repeat their tests to compare them fairly. These tests did not find a clear clue in the gas’s changing rhythm that could reveal the smooth center.

Two Fast Radio Burst Candidates Detected in the RATAN-600 Blind Survey

S.A. Trushkin, D.O. Kudryavtsev, P.G. Tsybulev+1 more

• Astrophysics of Galaxies

AstronomerA blind RATAN-600 Western Sector survey covering about 1500 square degrees at 4400–5000 MHz detected two single dispersed pulses, which the authors interpret as rare high-frequency FRBs. Their respective widths are about 6.7 and 15.6 ms, flux densities about 0.8 and 1.7 Jy, and estimated dispersion measures 200 ± 20 and 266 ± 10 pc cm^-3. Final SNRs were 8–9 after additional optimal filtering. Subtracting estimated Milky Way dispersion and adopting DM_IGM = 1000z gives approximate redshifts of 0.09 and 0.13; these are dispersion-based estimates, not direct redshift measurements. The estimated isotropic energies are 10^40 and 2 × 10^40 erg, respectively. Pulse detection used machine learning with a neural network trained on synthetic FRB profiles.

PublicA radio survey with the RATAN-600 telescope detected two brief pulses that the researchers interpret as rare fast radio bursts seen at high radio frequencies. The pulses lasted about 6.7 and 15.6 milliseconds and were found in a survey covering roughly 1500 square degrees of sky. The team used a neural network trained on artificial burst profiles to help detect single pulses, with final signal-to-noise ratios of 8–9 after extra filtering. By estimating how much the pulses were dispersed during their journey and subtracting the Milky Way’s estimated contribution, the researchers inferred approximate redshifts of 0.09 and 0.13. These values, and the bursts’ estimated energies, depend on the adopted relationship between dispersion and redshift rather than direct redshift measurements.

Young explorerA big radio telescope caught two very quick flashes of radio waves from space. Each lasted much less than a second. The scientists think they are a kind of space flash called a fast radio burst. A computer trained with pretend flashes helped them look for real ones. The scientists also used clues in the waves to estimate how far away the flashes might be, but those distances are not known for sure.

X-ray Variability of Mrk 421 in 2025 January: A Ten-Day XPoSat XSPECT Campaign with Contemporaneous NICER Coverage

Sikandar Akbar, Zahir Shah, Zahoor Malik+3 more

AstronomerTen days of XPoSat/XSPECT observations of the high-synchrotron-peaked blazar Mrk 421, with contemporaneous NICER data, reveal substantial X-ray variability and spectral hardening with brightness. The 0.8–15 keV fractional variability is 19.6 ± 0.3%, with 26 Bayesian-block flux states spanning a factor of 2.3. The best-constrained flare has rise and decay e-folding times of about 3 h and 30 h. For typical jet parameters, electron cooling is faster than the decay, suggesting gradually weakening acceleration rather than directly tracing cooling. Two lognormal components best describe the count-rate distribution, consistent with multiplicative variability; the power spectrum has a red-noise slope of about 1.7 over 25 min–10 d. XSPECT and NICER count rates correlate across eight matched epochs (r = 0.941). Day- and flux-resolved log-parabola fits show hardening with brightness: in flux-resolved XSPECT spectra, the 1 keV photon index falls from 2.24 to 1.96 and the synchrotron peak shifts from about 0.66 to 1.06 keV, with no significant curvature change (β ≈ 0.7). Power-law fits to bright Bayesian blocks at the same count rate yield photon-index differences up to 6.4σ, demonstrating that count rate alone does not determine spectral state.

PublicResearchers followed the blazar Mrk 421 in X-rays for ten days using XPoSat/XSPECT and contemporaneous NICER observations. They identified 26 brightness states spanning a factor of 2.3. The clearest flare brightened quickly and faded much more slowly, with characteristic times of about three hours and thirty hours. Assuming typical conditions in the jet, the X-ray-emitting electrons should lose energy faster than that fading, so the researchers suggest that the process accelerating them gradually weakened. The X-ray spectrum generally shifted toward higher energies as the source brightened, and its synchrotron peak moved to higher energy without a significant change in spectral curvature. However, intervals with the same measured count rate could have clearly different spectra: brightness alone does not fully describe the source’s X-ray behavior.

Young explorerScientists watched X-rays from a space object called Mrk 421 for ten days. Its brightness went up and down. One clear burst got bright quickly and faded much more slowly. When the object was brighter, its X-rays usually had more energy. But sometimes it was equally bright at two different times and still gave off a different mix of X-ray energies. The scientists think the slow fading may mean that the push giving tiny particles their energy was getting weaker.

A Multi-messenger Study of the Cygnus bubble

Abhijit Roy, Giovanni Morlino, C Rishi+3 more

• High Energy Physics - Phenomenology

AstronomerThe study jointly models the measured ultra-high-energy gamma-ray spectrum and spatial morphology of the Cygnus bubble within a cluster-wind termination-shock acceleration framework. It derives constraints on maximum particle energy, acceleration efficiency, magnetic-field strength, and shock geometry, and assesses compatibility with a hadronic emission scenario. A refined target-gas distribution is used to calculate expected hadronic gamma-ray and neutrino fluxes and evaluate the statistical significance of a potential neutrino signal for current and near-future observatories. The abstract supplies no numerical constraints or detection significances and does not establish a hadronic origin or report a neutrino detection. The implications concern young massive clusters as potential Galactic PeVatrons and contributors to diffuse high-energy emission.

PublicResearchers use measurements of extremely energetic gamma rays from the Cygnus bubble to investigate whether winds from a cluster of massive stars can accelerate particles to very high energies. By modeling both the gamma rays' energies and their distribution across the region, they constrain conditions where the winds encounter termination shocks. They also refine a model of the surrounding gas to estimate gamma rays and neutrinos that energetic particles could produce through collisions with that gas. The study evaluates how significant a possible neutrino signal might be in present and upcoming observatories; it does not report a neutrino detection or confirm that particle collisions explain the gamma rays.

Young explorerA group of big stars blows strong winds into space. Scientists think places where those winds slow down suddenly might make tiny particles go very fast. They studied very energetic light from a space bubble called Cygnus to learn what those places could be like. They also worked out how many tiny particles called neutrinos might come from the bubble. That is a prediction, not a report that they found those neutrinos.

A GeV PWN Candidate in the PSR J1135--6055/G293.8+0.6 Field

Liancheng Zhou, Yunlu Gong, Jun Fang+1 more

AstronomerA Fermi-LAT analysis of PSR J1135–6055 and the composite SNR G293.8+0.6 finds a point-like excess over 20 GeV–1 TeV with TS = 26.30 and photon index Γ = 1.63 ± 0.33. The best-fit position is consistent with the pulsar within the 95% statistical localization region; neither uniform-disk nor Gaussian spatial models are favored, so there is no evidence for significant extension. MeerKAT observations of a bright central plerion within the faint shell, together with Chandra detection of a compact nebula around the pulsar, establish a PWN in the remnant. A one-zone leptonic model plus an independent jet component reproduces the multiwavelength observations, with the GeV emission attributed mainly to inverse-Compton scattering by relativistic electrons and positrons. The positional agreement and broadband interpretation support classification of the LAT source as a GeV PWN candidate, not a confirmed association.

PublicRadio and X-ray observations establish that a nebula powered by the pulsar PSR J1135–6055 lies inside the supernova remnant G293.8+0.6. Using the Fermi Large Area Telescope, researchers also find a high-energy gamma-ray excess whose position agrees with the pulsar within the statistical uncertainty. The gamma-ray source appears point-like, with no significant evidence that it is spread out. A model that includes energetic electrons and positrons, plus a separate jet component, reproduces the observations across different wavelengths. In that model, most of the GeV gamma rays arise when these particles boost lower-energy light to higher energies. The researchers therefore identify the gamma-ray source as a candidate pulsar wind nebula; its connection to the known nebula is not yet confirmed.

Young explorerAstronomers found a cloud around a spinning star inside the remains of an exploded star. They also found very energetic light coming from about the same place. The light looks like a tiny dot, and they cannot tell that it spreads out. Their model suggests that speedy little particles could give other light a big energy boost. The cloud might be making the energetic light, but the astronomers are not sure yet.

Milliarcsecond-scale jet reorientations in GRS 1915+105 pointing towards a warped accretion disc

L.I. de Regt, P. Atri, S.E. Motta+3 more

AstronomerFour VLBA and EVN epochs in 2019–2021 probe milliarcsecond-scale jet morphology in GRS 1915+105 during its early X-ray-obscured phase. Relative to the pre-obscuration mean jet position angle of 142° ± 7°, the authors measure a maximum offset of 57° ± 8°, the largest yet reported for this system. The epochs span compact and flaring sources with large offsets, an extended jet closer to the earlier axis, and a non-detection. No measurable position-angle changes occur within individual eight-hour epochs, ruling out rapid Lense–Thirring precession of the inner disc as the direct driver of the reorientation. The timescales, geometry, and apparent association with X-ray obscuration instead favour a radiation-driven warped accretion disc, but this remains an interpretation and the absorbing material's nature is unknown.

PublicAfter more than 26 years of bright X-ray emission, the black hole binary GRS 1915+105 became faint in X-rays in 2018 while staying bright in radio waves. Observations suggest that material of unknown nature is blocking the X-rays. High-resolution radio observations at four times between 2019 and 2021 found varied jet behaviour, including a jet direction as much as 57° ± 8° away from its earlier orientation. The absence of measurable direction changes during individual eight-hour observations rules out one proposed direct cause: rapid precession of the inner disc caused by the black hole's rotation. The authors instead favour a disc warped by radiation, which could help explain both the jet's changing direction and the persistent X-ray blockage; that explanation is not yet established.

Young explorerA black hole and its companion star used to shine brightly in X-rays, a kind of light our eyes cannot see. Then they looked much dimmer, perhaps because something was blocking that light. Astronomers used radio telescopes to look at a jet of material shooting away from near the black hole and found it pointing in different directions at different times. They think the disc of material around the black hole may be bent, which could help explain both the changing jet direction and the blocked light. They do not know for sure yet.

Detectability of an orbital-angular-momentum-based gravitational wave detector

Haorong Wu, Xilong Fan

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

AstronomerThis theoretical detectability study develops a balanced readout and evaluates the noise budget of a proposed orbital-angular-momentum (OAM) gravitational-wave detector from 1 mHz to 100 Hz. For a symmetric OAM superposition, GW-induced transitions contribute differentially, whereas laser-intensity and mode-impurity crosstalk contribute in common mode, allowing their suppression by balanced detection. The budget also includes laser-phase and shot noise. Under a fixed beam-waist constraint, shorter arms allow a larger paraxial parameter and lower equivalent angular-noise strain. For an assumed 4 m arm, 160 round trips, paraxial parameter 0.1, 10 kW incident beam-splitter power, and 1064 nm wavelength, representative noise spectra give predicted SNRs of 24.7 and 239 at imbalance parameters of 10^-3 and 10^-5, respectively, for an equal-mass binary black hole with source-frame component masses of 10^4 solar masses at z = 1. The latter case approaches the shot-noise limit. These are model-based sensitivity estimates, not demonstrated detections, and emphasize compact optics and strong common-mode rejection.

PublicThe researchers assess a proposed way to detect gravitational waves using changes in light’s orbital angular momentum, a property associated with its spatial structure. Their calculations show how a balanced comparison of light signals could preserve the gravitational-wave effect while suppressing shared disturbances from laser brightness and imperfect light modes. They estimate performance across frequencies from 1 millihertz to 100 hertz for a compact design with 4-metre arms and repeated light round trips. Using assumed noise levels and a model signal from two black holes, each with a source-frame mass of 10,000 Suns, at redshift 1, they predict signal-to-noise ratios of 24.7 or 239, depending on how well the readout is balanced. The better-balanced case approaches the limit set by the quantum noise of light. This is a proposed detector and a calculated performance assessment, not an actual gravitational-wave detection; its promise depends strongly on suppressing shared noise.

Young explorerScientists have an idea for using light with a twist to look for tiny ripples in space. They worked out how to compare two light signals so that some unwanted wiggles cancel out, while the ripple’s signal stays. Their calculations suggest that a small setup could work well if the two signals are balanced very carefully. They have not caught a space ripple with this detector yet; this study is about how well the idea might work.

Proposal for the resolution of the disagreement between DAMA and other Underground Dark Matter Experiments

C. D. Froggatt, H.B.Nielsen

• High Energy Physics - Phenomenology

AstronomerThe authors propose an explanation for the discrepancy between DAMA/LIBRA’s reported several-standard-deviation signal, interpreted as dark matter, and the absence of a comparable signal in xenon-based searches and the NaI(Tl) experiments ANAIS and COSINE-100. They hypothesize that dark matter becomes excited while traversing the mountain overburden. Because DAMA is described as roughly twice as deep as ANAIS and COSINE-100, they argue that its longer transit path would produce more excited particles. They further assume predominantly electron emission to evade xenon experiments’ strong nuclear-recoil limits. A recent single LUX/ZEPLIN event is tentatively attributed to a small additional nucleus-emission rate. These are proposed mechanisms and interpretations, not an established dark-matter detection or a demonstrated resolution of the discrepancy.

PublicUnderground searches for dark matter do not agree: DAMA/LIBRA reports a signal interpreted as dark matter, but other experiments do not see a comparable signal. The authors suggest that dark matter might gain internal energy while passing through the mountain above a detector. In their proposal, DAMA’s greater depth gives the particles more time to become energized. They also assume that these particles mainly emit electrons, making them difficult to detect through the nuclear-recoil searches emphasized here for xenon experiments. They suggest that one recent LUX/ZEPLIN event could involve a rarer emission of a nucleus. This is a possible explanation, not proof that dark matter has been found or that the experiments’ disagreement has been solved.

Young explorerScientists have put special detectors underground to look for something called dark matter. One detector sees a hint that others do not. These scientists have an idea: maybe dark matter picks up energy as it travels through a mountain, so a deeper detector gets more of the energized kind. They also guess it mostly sends out tiny particles called electrons. This is an idea to explain the different hints, not something they have shown is true.

From Kination to Detection: Scotogenic Scalar Dark Matter

Eung Jin Chun, Ranjeet Kumar, Sanjoy Mandal+1 more

• High Energy Physics - Phenomenology

AstronomerThis theoretical study investigates scalar dark matter in the scotogenic model with an early kination-dominated epoch. The enhanced expansion rate produces earlier freeze-out and a larger relic abundance, allowing viable dark matter masses of approximately 200 GeV to 1 TeV while reducing reliance on co-annihilation with a nearly degenerate singlet fermion. Current indirect searches strongly constrain the 100–200 GeV region. Much of the surviving parameter space could be tested by CTA and next-generation direct detection experiments. The viable spectra also predict complementary collider signatures—missing transverse energy, displaced leptons, and disappearing charged tracks—with potential tests at the HL-LHC and future lepton colliders. These are model-dependent possibilities, not reported dark matter detections.

PublicThe researchers explore a theoretical dark matter model in which the early universe passed through a phase called kination, with a faster expansion rate. In their calculation, dark matter stopped interacting efficiently sooner, leaving more of it behind. This allows viable dark matter particle masses from about 200 GeV to 1 TeV and reduces the need for help from another particle with almost the same mass. Existing searches for indirect signs of dark matter already strongly restrict masses of 100–200 GeV in this model. Future searches with CTA and next-generation direct detection experiments could test much of the remaining possibilities. Particle colliders could provide additional tests through missing energy, leptons appearing away from the collision point, or charged tracks that disappear. The study proposes testable possibilities rather than reporting a discovery.

Young explorerScientists used a model to ask what might happen to dark matter if the universe grew faster when it was very young. In their model, more dark matter was left over. Searches have already made some versions of this idea hard to fit, but other versions are still possible. Future experiments could look for clues, like energy that seems to be missing or tiny particle trails that disappear. This is an idea to test, not a discovery of dark matter.

Higher-Order Symmetry Energy Effects on the Properties of Neutron Stars

Zijing Zhou, Xuhao Wu, Shishao Bao+3 more

• Nuclear Theory

AstronomerThis theoretical study isolates the effects of symmetry-energy curvature K_sym using controlled families of relativistic mean-field parametrizations based on TM1 and IUFSU, holding the symmetry energy J and its slope L fixed at saturation density. Within these families, increasing K_sym lowers the symmetry energy above saturation density and reduces the proton fraction in beta-equilibrated matter, yet produces a stiffer equation of state and a higher sound speed. The maximum neutron-star mass changes only weakly, while the radius of a 1.4-solar-mass star depends nearly linearly on K_sym. These are model findings, not observational measurements.

PublicThe researchers used theoretical models to explore how one feature of nuclear matter affects neutron stars. They varied a parameter describing how the energy associated with the neutron–proton imbalance bends as density changes, while keeping two related properties fixed at a reference density. In these models, increasing that parameter lowers this energy contribution and the proton share at higher densities, yet makes the matter more resistant to compression and allows sound to travel faster. The largest supported neutron-star mass changes little, while the radius of a 1.4-solar-mass star follows an almost straight-line relationship with the parameter. The abstract does not report observations testing these predictions.

Young explorerScientists used math models to study the tightly packed stuff inside neutron stars. They changed one setting while keeping two others the same. In their models, turning that setting up made the star stuff harder to squeeze and made sound move faster through it. The heaviest star the models could hold up changed only a little, but the size of a star with a chosen mass changed in a regular way. These are answers from models, not measurements of real stars.

Symmetry energy effect on hot nuclear matter and proto-neutron stars

Xuhao Wu, Peng-Cheng Chu, Min Ju+1 more

• Nuclear Theory

AstronomerThis theoretical study uses a relativistic mean-field equation of state to examine how nuclear symmetry energy affects proto-neutron stars. It investigates thermal and bulk properties under isothermal and isentropic assumptions with fixed lepton fractions, and explores heating and cooling stages for different entropy and lepton-fraction combinations. The calculated finite-temperature polytropic index is negatively correlated with the maximum PNS mass supported by the EOS. Increasing the symmetry-energy slope L produces larger PNS radii, although this dependence weakens at higher lepton fractions in the isentropic case. These model results indicate that symmetry energy and its density dependence influence PNS structure and evolution; they are not observational measurements.

PublicResearchers used a theoretical model to study how the properties of dense nuclear matter affect hot, young neutron stars as they heat and cool. They focused on symmetry energy, which describes how nuclear matter responds to an imbalance between neutrons and protons. In their calculations, a larger value of L, a parameter describing how symmetry energy changes with density, led to a larger stellar radius. Under the assumption of constant entropy, this effect weakened when the lepton fraction was higher. They also found that a calculated measure of the matter's pressure response was linked to the greatest stellar mass the model could support: higher values went with lower maximum masses. These are model-based findings under specified thermal and composition assumptions, rather than observations of stars.

Young explorerScientists used a math model to study hot, young neutron stars. They changed a rule about how the tiny particles inside behave. In the model, changing this rule one way made the stars wider, but how much wider depended on what was inside them. The scientists also studied the stars as they heated up and cooled down. These answers come from a model, not from measuring real stars.

Detecting Muons with a Siemens Biograph Vision Quadra

Lorenzo Mercolli, William M. Steinberger

• Medical Physics
• Instrumentation and Detectors

AstronomerThe study demonstrates atmospheric-muon detection with a clinical long axial field-of-view PET scanner during a blank scan without a radioactive source, using a prototype mode that records all single-crystal interactions. Muon energy deposits exceed the recorded energy range, preventing identification by energy discrimination. Instead, time-of-flight information selects pairs of high-energy crystal interactions across the gantry consistent with downward-going ultrarelativistic particles. Random pairings cannot be rejected event by event. The muon interpretation therefore rests on the measured angular distribution: comparison with a Monte Carlo simulation incorporating the expected muon angular distribution, scanner geometry, and event-selection bias shows that the crossing-event population is consistent with atmospheric muons.

PublicResearchers used a clinical PET scanner to detect atmospheric muons, particles that pass through the scanner, during a scan with no radioactive source. A prototype recording feature captured individual interactions in the scanner's crystals. The muons deposited too much energy for the scanner's recorded energy range, so energy alone could not identify them. Instead, the team selected pairs of signals whose positions and timing matched a very fast particle traveling downward across the scanner. Some pairs could still be chance coincidences, and these could not be ruled out individually. Comparing the distribution of crossing directions with a computer simulation that accounted for the scanner's shape and selection method showed that the measured events were consistent with atmospheric muons.

Young explorerTiny particles called muons come down through the air. Scientists used a hospital scanner to look for them, without putting any radioactive material inside. They looked for two little signals in different places, timed as if a very fast particle had passed through. Some signals could match just by chance, so they could not be sure about each pair. But the directions of many pairs matched a computer model of muons passing through the scanner. That helped show the scanner was detecting muons.

Signatures of quark matter from neutron star mass-radius curve

Tuhin Malik, Milena Albino, Pedro Sanson+1 more

• Nuclear Theory

AstronomerAn analysis of more than 250,000 theoretical mass–radius curves, using five hadronic relativistic mean-field models and four quark-matter descriptions, identifies possible signatures of quark matter in neutron stars. Within this model set, a radius maximum above 1.7 solar masses strongly favors quark matter. A second proposed diagnostic is X = [R(2.0) − R(1.6)] − [R(1.6) − R(1.4)] > −0.2 km, with masses in solar units. Most hyperonic sequences have radius maxima around 1.5 solar masses and maximum-mass compactness below 0.27. Nucleonic sequences that exhibit a radius maximum peak below 1.3 solar masses and have maximum-mass compactness above 0.26. These are model-derived diagnostics, not observational detections of quark matter.

PublicResearchers studied more than 250,000 theoretical relationships between neutron-star mass and radius to look for clues to quark matter inside these stars. In their models, a peak in radius occurring above 1.7 times the Sun’s mass strongly favors a quark-matter interior. They also propose a test that compares radii at three specified masses. Models containing hyperons or only nucleons tend to show different patterns in where the radius peaks and how compact the most massive stars are. These findings suggest ways to interpret mass and radius measurements; they do not report an observed detection of quark matter.

Young explorerScientists used computer models to study how big neutron stars could be at different masses. They found that certain patterns might be clues that a star has tiny things called quarks inside. Other kinds of insides made different patterns in the models. These are clues from models, not proof that scientists have found quark matter inside a real star.

Cloudy black-hole configurations of the composed Einstein-Yang-Mills-Higgs field theory: Analytic treatment

Shahar Hod

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

AstronomerThis analytical study examines magnetically charged Reissner–Nordström black holes supporting spatially regular linearized Yang–Mills–Higgs fields. These bound-state configurations mark the onset of non-Abelian hair formation in Einstein–Yang–Mills–Higgs theory. The paper derives a compact expression for the discrete resonance spectrum of μ = m_w r_+, where m_w is the Higgs-generated Yang–Mills field mass and r_+ is the horizon radius, in the small-mass, weakly magnetized regime 1 ≪ r_+ ≪ m_w^−1. For excited resonances, the adjacent-value ratio asymptotically approaches the k-independent value μ_(k+1)/μ_k = exp(−2π/√3). These are analytical results for linearized field configurations in a specified theory and regime, not observations of black-hole hair.

PublicIn a particular theory combining gravity with other fields, black holes can possess extra surrounding field structure called “hair.” This paper uses mathematical analysis to study the onset of that structure around magnetically charged black holes. It derives a formula for the allowed values of a quantity combining the black hole’s horizon size with the mass associated with the surrounding field. Within the small-mass, weakly magnetized regime studied, successive values for highly excited configurations approach a fixed ratio, forming a repeating mathematical pattern. The findings concern theoretical, weak-field configurations, not observed clouds or a detection of black-hole hair.

Young explorerScientists used math to study whether a black hole could have something like a cloud around it—not a fluffy cloud, but a special field. In their model, these clouds fit only at certain settings. They found that the settings follow a shrinking pattern. This is a result from math, not a cloud they saw in the sky.

Spectral instability of charged scalar quasinormal modes and superradiance: Stabilizing the unstable

Kyriakos Destounis

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

AstronomerThis theoretical study tests whether strong quasinormal-mode sensitivity to potential perturbations translates into strong changes in superradiant scattering for massless charged scalar fields on Reissner–Nordström and Reissner–Nordström–de Sitter backgrounds. A localized positive potential bump, small in mass-scaled height, is moved outward from the light ring while preserving the original radiative boundary conditions. In the asymptotically flat case, mode migration and successive overtakings bring even the least-damped positive-frequency mode into the superradiant frequency regime without making it grow. Real-frequency amplification changes only weakly, with no pronounced narrow resonance. In selected de Sitter configurations, the bump instead stabilizes an initially growing monopole mode. After stabilization, peak superradiant amplification can still exceed both its unperturbed value and a gain of 100%, falling below 100% only at more distant bump locations. Thus, a prescribed positive perturbation can suppress modal growth without altering the superradiant frequency bounds or immediately suppressing peak scattering amplification.

PublicBlack holes can amplify certain waves, allowing those waves to extract energy. This theoretical study asks whether small changes that strongly shift a black hole’s characteristic wave frequencies also strongly change that amplification. The researchers modeled massless charged waves and added a small, localized bump to the potential governing their propagation. In the model without a cosmological constant, some characteristic frequencies moved into the range where amplification is possible, but the associated vibrations still faded. Wave amplification itself changed only slightly. In selected models with a positive cosmological constant, the bump stopped an initially growing vibration. Yet the peak amplification could remain stronger than before the change, with a gain above 100%. These calculations show that stopping a growing vibration need not immediately stop strong energy extraction; they are not observations of actual black holes.

Young explorerScientists used math to study waves near black holes. They added a little bump to the rules that guide the waves. In some of their models, the bump made a wave that was growing bigger start fading instead. But the black hole could still give lots of energy to waves passing by. So making a growing wave settle down did not always stop other waves from getting a boost. This was a math study, not something watched in space.

Entropy-based classification of core-collapse supernova gravitational waves for nuclear equation-of-state inference

Aknur Sakan, Nurzhan Ussipov, Y. Sultan Abylkairov+6 more

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

AstronomerThe study tests an entropy-based machine-learning framework for classifying core-collapse supernova gravitational-wave signals associated with different nuclear equations of state. Signal decomposition, feature extraction, and feature selection yield a compact representation evaluated with several classifiers, including tests with detector noise. The authors report accurate waveform classification and better performance than raw-data classification under noisy conditions, but the abstract provides no numerical performance metrics or noise levels. The results support the potential of complexity-based features for efficient, interpretable waveform analysis; they do not establish an equation-of-state measurement from an observed supernova.

PublicWhen a star’s core collapses, its gravitational waves can carry clues about how extremely dense matter behaves. This study tests whether machine learning can distinguish waveforms linked to different models of that matter. Rather than using the raw signals directly, the researchers extract a small set of features that describe their complexity. They report accurate classification and better performance with detector noise than when using raw data, although the abstract gives no numerical accuracy. This is a test of an analysis method, not a reported measurement of dense matter from an observed supernova.

Young explorerWhen a star’s middle falls inward, it can make ripples in space. Those ripples may hold clues about the tightly packed stuff inside. Researchers tested a computer method that looks for patterns in ripples linked to different ideas about that stuff. They say it sorted the patterns well, even with extra noise mixed in, and did better than using the ripples without first picking out useful clues. This tests a way to study stars; it does not mean they have found out what is inside a real exploding star.

Measuring the Neutron-Star Moment of Inertia using Nonlinear Orbital Variations from Lense-Thirring Precession

Emmanuel Fonseca

• General Relativity and Quantum Cosmology

AstronomerThe study demonstrates that the pulsar-timing signature of Lense–Thirring (LT) precession develops nonlinear orbital variations over a sufficiently long baseline for arbitrary orbital orientation. If detected, these variations could constrain the pulsar’s moment of inertia without independent measurements of orbital geometry or distance, avoiding difficulties in separating linear LT variations from distance-dependent effects of other mechanisms. Simulations indicate detectability for suitable combinations of timing precision and orbital geometry. For PSR J1757−1854, the simulations predict detectable nonlinear LT signatures and a moment-of-inertia constraint potentially as precise as 10% by 2040, even without distance information; these are forecasts, not reported detections.

PublicA pulsar’s moment of inertia describes how its mass is distributed and how strongly it resists changes in rotation. This study explores measuring it through Lense–Thirring precession, an effect that changes the orbit of a pulsar in a binary system. The authors show that, over enough time, this effect produces orbital changes that do not follow a simple straight-line trend. If detected by timing the pulsar’s radio signals, these changes could reveal its moment of inertia without separate measurements of its distance or orbital orientation. Simulations suggest the method could work with suitable timing precision and orbital orientation. For PSR J1757−1854, they forecast a measurement potentially as precise as 10% by 2040, even without knowing its distance. This is a simulated prediction, not a measurement already achieved.

Young explorerA pulsar is a star that sends out radio pulses we can time like clock ticks. When it travels around a companion, a twisting effect called Lense–Thirring precession can slowly change its path. Scientists used computer pretend-play to see whether timing those pulses for long enough could help them learn how the star’s mass is spread inside, even without knowing how far away it is. Their simulations suggest this might work for a pulsar called PSR J1757−1854 by 2040. They have not measured it this way yet.

Constraining high-energy neutrinos from tidal disruption events with IceCube high-energy starting events

Mainak Mukhopadhyay, Patrick Wusinich, Kohta Murase

• High Energy Physics - Phenomenology

AstronomerThe authors perform a maximum-likelihood search for spatial and temporal correlations between IceCube’s 12.5-year high-energy starting-event (HESE) dataset and 89 selected tidal disruption events (TDEs), proposed sources of TeV–PeV neutrinos. No significant correlation is found; the data are consistent with the background-only hypothesis. They use this null result to constrain the intrinsic jet fraction, f_jet, and isotropic-equivalent cosmic-ray energy, E_CR. Despite limited statistics, they obtain E_CR ≲ 3 × 10^53 erg for f_jet ≳ 0.6 at more than 90% confidence. They also discuss theoretical implications and limits on the all-sky diffuse neutrino flux from TDEs. Additional electromagnetic TDE data and neutrino observations from IceCube and KM3NeT could strengthen these constraints.

PublicTidal disruption events have been proposed as sources of very energetic particles called neutrinos. Researchers compared a selected sample of 89 such events with 12.5 years of IceCube neutrino data, looking for matches in both direction and time. They found no statistically significant connection: the apparent matches are consistent with background coincidences. This does not rule out tidal disruption events as neutrino sources, but it limits combinations of how often these events contain jets and how much energy they put into cosmic rays. For example, if at least roughly 60% contain intrinsic jets, the analysis constrains their isotropic-equivalent cosmic-ray energy to about 3 × 10^53 erg or less, at more than 90% confidence. More observations could tighten these limits.

Young explorerScientists wondered whether space events called tidal disruption events send out tiny particles called neutrinos. They checked whether the particles came from the same places and at the same times as 89 of these events. They did not find a clear match beyond what chance could explain. That does not mean these events never make neutrinos. More watching could help scientists learn whether they do.

UV and Optical Signatures of Late-time Disk Instabilities in Tidal Disruption Events

Daichi Tsuna, V. Ashley Villar, Anthony L. Piro+1 more

AstronomerThe authors model UV/optical emission from late-time thermal instabilities in TDE accretion disks, with accretion power reprocessed by an optically thick outflow following brief super-Eddington episodes. For a typical TDE around a 10^6-solar-mass black hole, the model predicts days-long flares with near-UV luminosities of 10^42–10^43 erg s^-1 and optical luminosities of 10^41–10^42 erg s^-1. Such events could be detectable to redshift approximately 0.1 by ULTRASAT, Vera C. Rubin Observatory, and Argus Array. A search of existing nearby TDEs in Zwicky Transient Facility data yields upper limits of 1–2 flares per year per TDE, depending on outflow mass, rather than a measured flare rate. Future joint UV/optical and radio monitoring could test both the disk-instability scenario and its proposed connection to late-time radio emission.

PublicWhen a star is torn apart by a supermassive black hole, its debris can form a disk around the black hole. This study models possible brief episodes of unusually rapid feeding long after the initial disruption. In the model, an opaque outflow absorbs and re-emits energy from the feeding process, producing ultraviolet-bright flashes lasting days, with accompanying visible light. These are predictions, not reported detections. A search using existing Zwicky Transient Facility observations of nearby stellar disruptions instead sets upper limits of about one to two flashes per year for each event, depending on the assumed amount of outflowing material. Future surveys could detect such flashes out to a redshift of about 0.1. Watching in ultraviolet, visible light, and radio together could test whether these episodes also explain the late radio emission seen in these events.

Young explorerWhen a giant black hole tears a star apart, the pieces can swirl around it. The scientists used a model to ask whether the swirling pieces might later make quick flashes of light. Their model says each flash could last a few days and shine mostly in ultraviolet light, which our eyes cannot see. They also looked through older telescope observations, but did not report finding these flashes. Future telescopes might spot them and help test whether this idea is right.

Eccentricity Distribution for Dynamical Gravitational-Wave Merger Channels in The Pinhole Regime

Mor Rozner, Teagan A.Clarke, Isobel M. Romero-Shaw+1 more

• General Relativity and Quantum Cosmology

AstronomerThe authors argue that various dynamical black hole merger channels should yield a common eccentricity distribution in the high-eccentricity limit at gravitational-wave frequencies relevant to LIGO/Virgo/KAGRA. They attribute this expectation to the large separation of scales between the gravitational-wave regime needed to produce eccentric mergers in this band and the astrophysical formation environment. Their analytical solution agrees exceptionally well with numerical studies. This is a theoretical finding, not an observational measurement, with implications for modeling and searches for eccentric gravitational-wave sources.

PublicBlack hole pairs can be brought together through different dynamical processes. This study predicts that, among pairs with very elongated orbits, those different routes should produce the same pattern of orbital elongations at gravitational-wave frequencies relevant to LIGO, Virgo, and KAGRA. The authors link this similarity to a large difference in scale between the environments where the pairs form and the regime where gravitational waves drive their eccentric mergers. Their mathematical solution closely matches numerical studies; the abstract does not report an observed population confirming the prediction. The work could inform models and searches for these signals.

Young explorerTwo black holes can go around each other on a very stretched-out path before joining together. The researchers think that different ways of bringing them together could lead to the same pattern of very stretched-out paths when their space ripples reach the frequencies scientists search for. Their math matches computer studies very well, but this is a prediction, not something they have shown by watching real black hole pairs.

HESS J1832-085: evidence for a new gamma-ray binary candidate

Agnibha De Sarkar, Tanuman Ghosh

AstronomerArchival multiwavelength analyses support a gamma-ray binary interpretation of the point-like TeV source HESS J1832-085, which still lacks a confirmed counterpart. A potential X-ray counterpart has a hard, absorbed spectrum and moderate variability. Analysis of approximately 17.3 years of Fermi-LAT data at 1–300 GeV identifies a tentative excess spatially consistent with the TeV source and proposed X-ray counterpart. UKIDSS and 2MASS images also reveal a candidate stellar counterpart close to the X-ray position. An illustrative binary radiative model broadly reproduces the X-ray and TeV emission but cannot explain the tentative GeV excess. The source remains a promising candidate rather than a confirmed gamma-ray binary; dedicated multiwavelength follow-up is needed.

PublicAstronomers have found clues that HESS J1832-085, a source of very high-energy gamma rays, may be a gamma-ray-emitting binary system. Archival observations reveal a possible X-ray counterpart whose brightness varies moderately, a tentative signal at lower gamma-ray energies, and a nearby star that could be associated with the source. These possible connections are not confirmed. A model of emission from a binary system broadly matches the X-ray and highest-energy gamma-ray emission, but does not explain the tentative lower-energy gamma-ray signal. Further observations across different kinds of light are needed to establish what the source is.

Young explorerAstronomers are trying to find out what makes a bright spot in a kind of light our eyes cannot see. They found clues in other kinds of light and a nearby star that might belong with the spot. They think it could be two objects going around each other, but they are not sure. Their model explains some of the light, but not all of a possible extra signal. They need more observations to check their idea.

Neutrino and electromagnetic signatures from Superluminous Supernovae: a case study for SN 2017egm

Mainak Mukhopadhyay, Shigeo S. Kimura, Indrek Vurm+1 more

• High Energy Physics - Phenomenology

AstronomerThe authors model multi-wavelength and multi-messenger emission from superluminous supernovae under the hypothesis that a newborn millisecond magnetar supplies their power; the actual energy source remains uncertain. Their coupled magnetar–wind–nebula–ejecta calculation self-consistently evaluates wind and nebular pair multiplicities and the bulk wind Lorentz factor that governs electron–positron injection into the nebula. They compute thermal and non-thermal electromagnetic emission and neutrino signatures. For SN 2017egm, the nearest observed SLSN, the predicted high-energy gamma-ray emission matches the reported Fermi LAT detection. Taking SN 2017egm as a canonical SLSN, they forecast that stacking a population of SLSNe in the Vera C. Rubin Observatory era with upcoming neutrino observatories could yield a 3-sigma neutrino detection within a decade of operation; this is a detection prospect, not an observed neutrino signal.

PublicSuperluminous supernovae are rare stellar explosions that shine about 10–100 times brighter than ordinary ones, but their power source is still uncertain. This study explores whether a newly born, strongly magnetic star spinning once every few milliseconds could supply that energy. The researchers model how the star, its wind, the surrounding nebula and the expanding explosion debris evolve and produce light and neutrinos. Their predicted high-energy gamma rays for SN 2017egm, the nearest observed superluminous supernova, match a recent detection by the Fermi LAT instrument. That agreement does not establish the proposed power source. Using this explosion as a representative example, they predict that combining signals from many such explosions could allow future neutrino observatories to reach a 3-sigma detection within a decade during the Vera C. Rubin Observatory era. No neutrino detection is reported here.

Young explorerSome exploding stars shine much brighter than most, and scientists do not yet know what gives them so much energy. One idea is that a tiny, very magnetic star spinning very fast inside the explosion acts like a power supply. Scientists made a model of this idea. For one explosion, the model’s prediction matched a kind of light that a space instrument had seen, but that does not prove the idea is right. The model also suggests that future detectors might find tiny particles called neutrinos by adding together clues from many explosions over about ten years. They have not found those particles from these explosions yet.

Deep Optical Follow-up Observations to IceCube Cosmic Neutrinos: a case for IC230724A with Subaru/HSC and prospects with Rubin/LSST

Shigeo S. Kimura, Masaomi Tanaka, Seiji Toshikage+8 more

AstronomerThe authors report Subaru/HSC optical follow-up of the well-localized neutrino alert IceCube 230724A, reaching 25.5 mag. A dedicated blind analysis, including extensive evaluation of background and true-positive rates, found no tidal disruption event (TDE) candidate in the region of interest. This non-detection does not establish whether TDEs are major cosmic high-energy neutrino sources. Looking ahead, the authors forecast that Rubin/LSST coverage of the error regions of 10 neutrino events could constrain the TDE contribution to the cosmic high-energy neutrino background to approximately 60% or less for non-detection, or 30% or more for detection.

PublicThe main sources of the high-energy neutrinos detected by IceCube remain uncertain. Researchers used Subaru/HSC to search deeply in visible light around the reported location of one neutrino event, IceCube 230724A. They found no candidate tidal disruption event (TDE), a possible type of neutrino source, after an analysis designed to assess chance signals and the likelihood of finding real ones. This does not rule out TDEs as important sources. The authors predict that if Rubin/LSST observes the possible source regions of 10 neutrino events, it could limit the TDE share of the cosmic high-energy neutrino background to roughly 60% or less if none are detected, or indicate a share of roughly 30% or more if detections are made. Those are forecasts, not current measurements.

Young explorerIceCube catches tiny particles called neutrinos from space, but scientists are still trying to learn where many of them come from. They used a telescope to look where one neutrino might have come from. They did not find the kind of space event they were looking for. That does not mean those events never send us neutrinos. The scientists think a future telescope survey could help them learn more by checking the possible homes of 10 neutrinos.

Accreting stellar-mass black holes

Greg Marcel, Bailey Tetarenko, Adam Ingram+3 more

AstronomerThis review synthesizes progress on accreting stellar-mass black holes through continuum spectra, timing, emission lines, and X-ray polarization. It describes how disk–corona–jet interactions underlie spectral and timing behavior, with quasi-periodic oscillations and broadband noise probing inner-flow dynamics. Multi-wavelength emission lines diagnose disk structure, outflows, and reprocessing, while relativistic iron K reflection probes the inner disk. Polarization studies suggest a hard-state corona extended perpendicular to the jet axis; soft-state observations remain poorly understood and do not yet match simple theoretical expectations. The origins of state transitions, magnetic fields’ role in outflows and accretion geometry, and the disk-instability–jet connection remain open questions, motivating further multi-wavelength, timing, and polarimetric studies.

PublicStellar-mass black holes feeding on surrounding matter can change dramatically in brightness and spectrum and produce jets. This review brings together research on what their light reveals about the surrounding disk, a region called the corona, and the jets. Changes in brightness and emission lines help researchers investigate the flow of matter, including regions close to the black hole. Polarization—the orientation of light’s oscillations—suggests that in the hard spectral state, the corona extends perpendicular to the jet. In the soft state, however, polarization observations do not yet fit simple theoretical expectations. Why these systems switch states, how magnetic fields influence the flow, and how disk instabilities connect to jet launching remain unresolved. The review calls for further observations using several complementary methods.

Young explorerWhen a black hole pulls in nearby stuff, the stuff around it can shine, flicker, and sometimes shoot out in jets. This review gathers what scientists have learned by studying that light. The light gives clues about where the stuff is and how it moves. Some clues suggest how a region near the black hole is shaped, but other clues still puzzle scientists. They want to watch in more ways to learn why the light changes and how the jets begin.

A Collapsar-Disk Origin for GW190814

Vishal Baibhav, Brian D. Metzger, Lam Hui

• General Relativity and Quantum Cosmology

AstronomerGW190814 involved a 23-solar-mass black hole and a 2.6-solar-mass compact object, an extreme mass ratio difficult to reproduce through standard isolated-binary or dynamical channels. The authors explore a collapsar-disk origin: gravitational fragmentation in a neutrino-cooled disk could produce neutron stars or low-mass black holes that subsequently merge with the central black hole. This scenario predicts a preceding stripped-envelope supernova. They identify the Type Ib supernova candidate SN2019npv, within the GW190814 credible volume approximately 60 days before coalescence, as a possible precursor, not an established association. They show that three-body interactions among disk fragments can place compact objects on wide orbits, allowing merger delays of weeks to months; the observed interval is too long for a conventional kilonova counterpart. GW190814 was not expected to produce detectable tidal-disruption-powered emission, but future delayed mergers in this channel could power luminous transients through reprocessed kilonova heating or collisions between merger and supernova ejecta. Conditional on identifying SN2019npv as the electromagnetic counterpart, the bright-standard-siren inference is H0 = 71.1 (+9.3, −7.5) km s⁻¹ Mpc⁻¹.

PublicGW190814 was a merger between a black hole with 23 times the Sun’s mass and a compact object with 2.6 times its mass. Explaining such unequal partners is challenging. This study proposes that the smaller object formed when a disk around a newly formed black hole broke into dense fragments. Interactions between fragments could delay a merger by weeks or months. A candidate supernova, SN2019npv, occurred about 60 days earlier within the region of space allowed by the gravitational-wave observation, making it a possible precursor—but the connection is not established. The proposed mechanism could explain that delay, which is too long for a conventional kilonova counterpart. The authors also predict that some future mergers formed this way could produce bright flashes. If the supernova and GW190814 truly belong together, their association would allow an estimate of the Universe’s expansion rate.

Young explorerScientists detected a black hole merging with a much smaller, very dense object. They wonder whether the little object formed from a disk of material around the black hole, then went around it for a while before falling in. A possible exploding star was seen about two months earlier in the same broad part of space. It might be connected to the merger, but scientists do not know yet.

Hamiltonian variational reconstruction of the 3D magnetic geometry of relativistic jets

Fabio Buffoli

AstronomerThe authors introduce H-MOG, a variational reconstruction of a jet’s 3D magnetic geometry from its width W(z) and linear polarization p(z), and establish which field properties these observables constrain. Tests use synthetic jets and ten GRMHD simulations spanning magnetically arrested and standard accretion flows at five spins, rather than observations of real jets. For a side-on jet, W and p are exactly invariant under field reversal and sky-plane reflection, producing a four-fold degeneracy that includes opposite helical handedness. Geometry is recovered within this degeneracy, with reported mean cosine alignment of approximately 0.94–1.00 for synthetic jets and 0.76–0.98 for the GRMHD library; the mirror choice is inherited from initialization. A rotation-measure constraint determines the toroidal sign but not the poloidal sign, regardless of resolution. A spin-based prior fails because spin does not determine poloidal polarity. Internal Faraday rotation can distinguish all four configurations, but does so only weakly in ray-traced GRMHD images. Thus width and linear polarization alone leave field sense and handedness undetermined. For a side-on jet, determining the poloidal sense requires information beyond rotation measure, such as field-line rotation sense, departure from a 90-degree viewing angle, or circular polarization.

PublicCan a jet’s image reveal which way its magnetic field points? This study introduces H-MOG, a method for reconstructing magnetic structure from a jet’s width and the linear polarization of its light. Tests on artificial jets and computer simulations show that it can recover the field’s geometry, but with an important ambiguity: a jet viewed from the side looks the same under these measurements if all magnetic arrows are reversed or the structure is mirrored. The method therefore cannot, from those measurements alone, determine the arrows’ directions or the handedness of the magnetic spiral. An additional measurement called rotation measure resolves only part of the ambiguity, and using the simulated system’s spin does not supply the missing direction. Faraday rotation within the jet can theoretically distinguish all four possibilities, but the differences were weak in simulated images. These are simulation-based findings, not a demonstrated reconstruction of a real jet.

Young explorerImagine a space jet with an invisible, twisty magnetic ribbon inside. Scientists made a way to work out its shape using pretend jets on computers. But there is a catch: turning all the ribbon’s arrows around, or making a mirror copy, can leave the same clues. Extra clues might help tell them apart, but some were very faint in the computer pictures.

Cosmogenic photon fluxes at ultra-high energies

Marcus Niechciol, Chiara Jane Papior, Markus Risse

AstronomerThis modeling study evaluates cosmogenic photon yields and fluxes across ultra-high-energy cosmic-ray injection and source scenarios, whose predicted fluxes can differ by orders of magnitude. For photons above 10^18 eV, the calculated yield is largest for proton-emitting sources at roughly 15 Mpc. Protons yield more photons than heavier nuclei at the same total energy, but the difference decreases with source distance. The authors consider mixed-composition scenarios previously found to reasonably describe Pierre Auger Observatory data, alongside pure-proton and pure-iron benchmarks for comparatively high and low fluxes. Mixed-composition scenarios without injected protons predict fluxes more than 1.5 orders of magnitude below current experimental limits. A substantial proton fraction at the highest energies could bring the photon flux within reach, while current photon limits already constrain certain pure-proton parameter combinations.

PublicExtremely energetic cosmic rays produce photons as they travel through space. This study calculates how much of that light different kinds of cosmic-ray sources could produce; it does not report a detection. The predicted amount can vary by orders of magnitude with the particles emitted, their energies and the source distance. For photons above the energy threshold studied, proton-emitting sources about 15 megaparsecs away give the largest calculated yield. Protons produce more photons than heavier atomic nuclei of the same total energy, though this difference shrinks for more distant sources. Models with a mixture of nuclei but no protons at emission predict photon fluxes well below current experimental limits. If protons make up a substantial share of the highest-energy cosmic rays, the photons might be detectable. Existing limits already restrict some models in which sources emit only protons.

Young explorerVery speedy particles traveling through space can make light. Scientists calculated how much light different kinds of these particles might make. Their answers depend on what the particles are and how far they travel. Some ideas predict too little light for today's searches to find. If there are plenty of particles called protons among the speediest ones, the light might be easier to find. The study did not find this light; it worked out what scientists might look for.

Core-Collapse Supernova detections from Einstein Telescope within the Milky Way

I.F. Giudice, A.L. De Santis, M.T. Botticella+6 more

AstronomerThis simulation study forecasts gravitational-wave detectability for core-collapse supernovae with the Einstein Telescope (ET), alone and in networks including next-generation detectors such as Cosmic Explorer. It combines GWFish, waveform catalogs from state-of-the-art 3D simulations, and TRILEGAL stellar populations to model dependence on progenitor mass, source position, and detector configuration. For PNS-driven explosions, the predicted ET detection horizons range from about 20 to more than 100 kpc at 90% confidence, depending on progenitor mass and waveform; favorable network cases reach about 170 kpc. A representative 15-solar-mass progenitor yields a horizon of about 100 kpc for ET's 2L configuration, implying essentially complete Milky Way coverage and partial coverage of the Magellanic Clouds under the modeled assumptions. These are detectability forecasts, not reported gravitational-wave detections.

PublicComputer simulations suggest that the future Einstein Telescope could detect gravitational waves from collapsing-star explosions throughout much or all of our galaxy, depending on the star and the signal it produces. The study combines simulated explosions with models of stellar populations and detector arrangements. Its estimated detection reach ranges from about 20 to more than 100 kiloparsecs for the Einstein Telescope alone, extending to about 170 kiloparsecs in the most favorable detector-network cases. For one representative star with 15 times the Sun's mass, a particular telescope configuration could cover essentially the entire Milky Way and part of the neighboring Magellanic Clouds. These predictions describe future detection capabilities, not signals already observed.

Young explorerWhen a big star collapses and explodes, it can make tiny ripples in space. Scientists used computers to explore whether a future detector called the Einstein Telescope could notice those ripples. Their models suggest it might hear some explosions across our galaxy, and working with other detectors could help it reach farther. How far depends on the star and its ripples. This is a prediction from computer models, not an explosion the telescope has already heard.

The imprint of individual neutron star spins on ejecta, r-process nucleosynthesis, and kilonovae in binary neutron star mergers

Beyhan Karakas, Rahime Matur, David Radice+2 more

• General Relativity and Quantum Cosmology

AstronomerThis numerical study tests how individual neutron-star spins affect ejecta, r-process yields and kilonova emission, including comparisons at fixed total mass, mass ratio and effective spin, which controls the leading-order GW spin dependence. The simulations cover three total-mass regimes using the finite-temperature, composition-dependent SFHo equation of state with neutrino emission and absorption. At 2.55 solar masses and zero effective spin, individual-spin changes produce a roughly 45-fold range in dynamical ejecta mass, more than two orders of magnitude in absolute A≥140 yield, and lanthanide-to-light-r-process mass ratios from about 2 to 70. Prompt-collapse models at 4.10 solar masses show heavy-element yield differences exceeding four orders of magnitude at zero effective spin. Predicted kilonova peak brightnesses differ by up to about 0.9 mag. At an assumed distance of 40 Mpc, all three zero-effective-spin pairs remain above the adopted detection depths at common epochs for every viewing angle, with same-epoch colour differences up to about 1.5 mag. Colour differences persist when secular ejecta are replaced by an identical parametric disc outflow, supporting an important dynamical-ejecta contribution rather than disc mass differences as the primary driver. Neutrino absorption brightens the model kilonovae and shifts peak-associated colours blueward. These simulation-based electromagnetic signatures could help resolve individual-spin degeneracies in GW signals; they are not observational detections.

PublicThe leading part of a gravitational-wave signal from two merging neutron stars mainly reveals a combined measure of their spins, making the stars' separate spins hard to distinguish. This study uses computer simulations to show that different individual spins can nevertheless produce very different amounts of expelled matter and heavy elements, even when the combined spin measure is unchanged. In one set of models, the expelled mass varies by about a factor of 45. The predicted kilonova light also changes in brightness and colour. Tests using the same model for matter flowing out of the surrounding disc suggest that matter thrown out during the merger makes an important contribution to the colour differences. Absorption of neutrinos makes the predicted light brighter and bluer near its peak. These are simulation results, not observations: they suggest that combining a kilonova's light with gravitational-wave information could help reveal each star's spin. Predictions of detectability depend on the assumed distance and detection limits.

Young explorerWhen two neutron stars crash together, they can throw out matter and make a glow. The stars also spin. Scientists used computer models to try different spins. Even when the spins looked the same when combined, the models could throw out very different amounts of matter and make different colours of light. That light might help scientists work out how each star was spinning. This is a prediction from computers, not something this study saw in the sky.

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 death valley in the period–period-derivative diagram challenge polar-cap pair cascades powered by curvature radiation (CR) and resonant inverse Compton scattering (RICS). The authors identify quantum-vacuum Cherenkov radiation, enabled by strong-field QED vacuum polarization, as a complementary pair-production channel within the vacuum gap model. Their model finds sufficiently short acceleration lengths for photon emission and subsequent photon mean free paths to permit rapid electron–positron production, including regimes where CR and RICS are strongly suppressed. The resulting theoretical death lines partially overlap with and extend beyond the conventional death valleys, expanding the modeled parameter space for radio-active neutron stars. This offers a possible physical basis for coherent radio emission from long-period neutron stars previously considered inactive, rather than an observational detection of the mechanism. Future facilities such as the Square Kilometre Array could provide opportunities to test this nonlinear-QED interpretation.

PublicSome neutron stars send out radio pulses even though standard theories place them in a region where the particle production needed to support radio emission should be ineffective. This study explores an additional route: in an extremely strong magnetic field, quantum effects change how the vacuum behaves, allowing Cherenkov radiation that can then produce pairs of electrons and positrons. Within the authors’ model, this process happens over short enough distances to supply pairs even where the usual mechanisms are strongly weakened. The calculations therefore expand the range of neutron stars that could sustain radio emission, potentially explaining some slowly rotating radio sources. This is a theoretical explanation, not a detection of the proposed process; future radio facilities such as the Square Kilometre Array could help test it.

Young explorerSome spinning stars send us radio flashes even when our usual ideas say they should be quiet. Scientists worked out another way these stars might make tiny particles that help them send radio signals. Near a star with a very strong magnetic field, even empty space can act in a surprising way, letting light turn into pairs of tiny particles. Their calculations suggest this could help some slowly spinning stars keep flashing. Scientists have not yet seen this particular process happening in those stars.

A concordance model of neutron star kicks

Cheyanne Shariat, Kareem El-Badry, Smadar Naoz

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerCombining orbital properties and birth rates of Gaia neutron-star (NS) and Be+NS binaries with velocity constraints from young isolated pulsars, the authors infer a shared bimodal natal-kick distribution compatible with all three populations. The low-kick component is lognormal, with a median speed of 6.5 km/s and quoted uncertainties of −2.7/+5.9 km/s; the high-kick component is consistent with the young-pulsar distribution, peaking near 200 km/s. In the model, low kicks account for about 10% of NS births but produce most Gaia NS binaries and roughly half of Be+NS binaries. Predicted systemic recoil velocities also agree with observed kinematics of these binaries and NS low-mass X-ray binaries. Gaia NS formation histories remain unknown, but the inferred kick law favors progenitors containing intermediate-mass stripped stars and approximately one-solar-mass companions in au-scale orbits. The model predicts about 300 such progenitor binaries in the Milky Way, 40 in the LMC, and 30 in the SMC today. For hierarchical triples, the calculated fractions retaining their tertiary after the supernova are 2–10% for Gaia NS triples and 3–23% for Be+NS triples. These are model-based inferences and predictions, supporting—but not establishing uniquely—a common kick law in which large kicks dominate births while low kicks are disproportionately represented among surviving binaries.

PublicNeutron stars receive a kick when they are born in supernova explosions, potentially disrupting their partnerships with other stars. Researchers combined information about two populations of neutron-star binaries with speeds inferred for young isolated pulsars. They found that one model with two groups of kick speeds can explain all three populations: a small group with gentle kicks, having a median speed of about 6.5 kilometres per second, and a larger group whose speed distribution peaks near 200 kilometres per second. The model assigns only about one in ten neutron-star births to the gentle-kick group, yet those stars account for most surviving Gaia neutron-star binaries and roughly half of Be+neutron-star binaries. Its predictions also match observed motions of several types of neutron-star binaries. The origins of Gaia neutron-star binaries remain uncertain; the authors favor a particular kind of stripped-star progenitor and predict hundreds of these precursor systems in the Milky Way. Those progenitors are a model prediction, not a newly observed population.

Young explorerWhen a neutron star is born in an exploding star, it gets a push. A big push can separate it from a star buddy. Scientists compared information about neutron stars with buddies and ones on their own. Their model suggests that most get big pushes, while a few get gentle ones. The gently pushed stars are more likely to keep their buddies. This model fits the information they studied, but scientists still do not know exactly how some of these star pairs began.

Probing Cosmic-Ray-Boosted and Supernova-Sourced Sub-GeV Dark Matter with Paleo-Detectors

Xiaoyong Chu, Yue-Lin Sming Tsai, Mei-Wen Yang

• High Energy Physics - Phenomenology

AstronomerThis study projects the sensitivity of olivine paleo-detectors to sub-GeV dark matter accelerated by cosmic-ray scattering or produced thermally in core-collapse supernovae. Such (semi-)relativistic particles could generate nuclear recoils above keV thresholds, leaving tracks accumulated over geological timescales. For a 100 g·Gyr exposure, the authors compute track-length distributions and use an Asimov dataset, including neutrino, uranium-chain neutron, and thorium-recoil backgrounds, to derive projected 95% confidence-level sensitivity to the dark matter–nucleon cross section for masses from a few MeV to hundreds of MeV. The projections reach parameter regions beyond current and near-future dark matter and neutrino experiments. In particular, cumulative exposure to Galactic supernova dark matter fluxes is projected to improve sensitivity by a few orders of magnitude relative to conventional experiments. These are sensitivity forecasts, not a dark matter detection.

PublicAncient minerals could act as long-running dark matter detectors by preserving tiny damage tracks left when particles strike atomic nuclei. Lightweight dark matter moving at ordinary speeds in our galaxy is difficult to detect, but collisions with high-energy cosmic rays could speed it up, and exploding stars could produce fast dark matter. The researchers calculated how these particles might leave tracks in olivine, accounting for other sources of similar signals. Their forecasts suggest that minerals recording events over geological times could test possibilities beyond the reach of current and planned experiments. Accumulating signals from many Galactic supernovae could improve sensitivity by factors of thousands in some cases. The study predicts what such detectors might detect; it does not report finding dark matter.

Young explorerScientists wonder if invisible stuff called dark matter could leave tiny marks inside very old rocks. Fast particles in space could give it a push, and exploding stars might make fast dark matter too. The rocks could keep those marks for a very long time. The scientists worked out what the marks might look like and how to tell them apart from other marks. They think old rocks could help us search, but they have not found dark matter this way.

Solar axions from nuclear transitions

Tanmoy Kumar, Newton Nath

• High Energy Physics - Phenomenology
• Solar and Stellar Astrophysics
• Nuclear Theory

AstronomerThe study investigates possible 14.4 keV and 9.4 keV solar axion and axion-like particle emission from M1 nuclear transitions in iron-57 and krypton-83, respectively, using quiet-Sun soft X-ray data from the Solar X-ray Monitor aboard India's Chandrayaan-2 lunar mission. Although the effective axion–nucleon couplings differ only slightly between the two nuclei, the corresponding predicted fluxes differ by nearly three orders of magnitude. The resulting iron-based constraints are more than one order of magnitude stronger than the krypton-based constraints, both on the absolute value of the product of the effective axion–nucleon and axion–photon couplings and on the axion–photon coupling alone as a function of axion mass. The abstract reports constraints, not an axion detection.

PublicResearchers used soft X-ray observations of the quiet Sun from India's Chandrayaan-2 lunar mission to investigate hypothetical particles called axions and axion-like particles. These could be produced by nuclear transitions in iron-57 at 14.4 keV and krypton-83 at 9.4 keV. Although their effective interactions with nuclear particles differ only slightly, the expected particle fluxes differ by nearly a factor of 1,000. The iron analysis therefore gives limits more than ten times stronger than the krypton analysis on the combined interaction strengths with nuclear particles and light, and on the interaction with light alone across particle masses. These are limits on possible particles, not a reported discovery.

Young explorerScientists used an X-ray watcher on India's Chandrayaan-2 Moon mission to study the quiet Sun. They looked for clues about tiny particles called axions that might exist. Iron-57 in the Sun could make them with an energy of 14.4 keV, and krypton-83 could make them with 9.4 keV. The study says the amounts expected from these two kinds of atoms differ by almost 1,000 times, even though one measure of how strongly they interact is nearly the same. Iron gave rules more than ten times tighter about how strongly these possible particles could interact with light and the tiny pieces inside atoms. The scientists report limits on what might be there, not that they found these particles.

SPLIT: Loosely-coherent inference of long-inspiral gravitational-wave sources for robustness against modeling and data outliers

Shubham Kejriwal

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

AstronomerThe authors introduce a segmented Bayesian inference framework for LISA EMRIs and IMRIs, whose months-to-years signals make fully phase-coherent analyses vulnerable to accumulated waveform errors. Implemented in SPLIT, a GPU-accelerated Python package, the method analyzes short blocks coherently and combines their posteriors using loosely coherent phase information. In a simulated signal injection incorporating environmental effects, a fully coherent vacuum-GR analysis produces a maximum one-dimensional systematic bias of approximately 4.8 sigma, whereas the segmented approach limits such biases to approximately 0.5 sigma or less. This simulation demonstrates reduced parameter bias at the cost of some optimal signal-to-noise ratio; it is not a result from observed LISA data.

PublicThe future LISA space observatory is expected to detect gravitational waves from inspiraling systems with very unequal masses, tracking their signals for months or years. Small errors in models of these long signals can build up and distort estimates of the systems' properties. The researchers developed software called SPLIT that analyzes shorter sections separately, then combines them without requiring an exact match to the wave's timing throughout the entire signal. In a simulated signal that included environmental effects, this method reduced the largest reported parameter bias from about 4.8 times the statistical uncertainty to about half that uncertainty or less, compared with a conventional analysis that assumed a vacuum. The improvement comes with some loss of signal-to-noise ratio, and has not yet been demonstrated on actual LISA observations.

Young explorerScientists are getting ready to study tiny ripples in space that a future space detector called LISA will hear. A ripple can last a very long time, and small mistakes in matching its pattern can add up. The scientists made a computer tool that studies short pieces and then puts the clues together. In a computer-made test ripple, this gave less misleading answers than trying to match the whole ripple at once, though it lost a little signal strength. This was a practice test, not a ripple LISA has really heard.

Ultra-High-Energy Cosmic Ray Boosted Relic Neutrinos

Jiajie Zhang, Jiajun Liao

• High Energy Physics - Phenomenology

AstronomerThis study models the diffuse flux of relic neutrinos boosted by ultra-high-energy cosmic rays through Standard Model neutral-current interactions. It includes elastic neutrino–nucleon scattering, coherent and incoherent neutrino–nucleus scattering, baryon-resonance production, and deep inelastic scattering, using mixed-composition UHECR spectra from PriNCe and the H3a and H4a Hillas models with SFR, QSO, and GRB source evolution. The calculations predict an energy-dependent channel hierarchy: coherent scattering dominates the low-energy flux for heavy nuclei; elastic nucleon and incoherent nuclear scattering become important as individual nucleons are resolved; resonances contribute non-negligibly at high energies; and deep inelastic scattering appears only at the highest energies, most visibly for H4a. Current IceCube and Pierre Auger Observatory data are used to derive upper limits on the cosmic neutrino background overdensity, rather than establish a detection. Reliable signal predictions require joint treatment of scattering channels, cosmic-ray composition, source evolution, and the neutrino mass spectrum.

PublicExtremely energetic cosmic rays could transfer energy to relic neutrinos in the cosmic neutrino background, offering an indirect way to study that background. The researchers calculated the resulting neutrino signal using several models of cosmic rays and their sources, and included multiple ways that neutrinos can interact with protons, neutrons, and atomic nuclei. Their calculations predict that different interactions matter at different neutrino energies: interactions with whole nuclei dominate at lower energies for heavy cosmic-ray nuclei, while interactions that resolve their constituents become important at higher energies. Using existing IceCube and Pierre Auger Observatory data, the team placed upper limits on how concentrated the relic neutrino background could be; this is not a reported detection of the boosted background. The predicted signal depends on cosmic-ray composition, how sources evolve over time, neutrino masses, and which interactions are included.

Young explorerSpace has tiny particles called neutrinos left over from long ago. Very speedy particles called cosmic rays could bump into them and give them more energy. Scientists calculated how this might happen. Their calculations say that different kinds of bumps matter at different energies. They also used information from two observatories to work out limits on how crowded those old neutrinos could be. They did not report finding this special signal.

A VLT/CRIRES+ study of helium 1.083μm absorption features towards the inner Orion Nebula

Thomas J. Haworth, Mark McCaughrean, Mario van den Ancker+3 more

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies

AstronomerJWST/NIRCam F115W imaging revealed previously unknown dark features in the inner Orion Nebula, initially attributed to absorption or suppressed emission in the He I 1.083 μm triplet. VLT/CRIRES+ high-resolution spectroscopy of selected targets confirms a reduction in triplet flux that is fairly uniform across the line. In the nebula’s blister geometry, a dense, bright ionised layer lies on the far side, near the Orion A molecular cloud, with lower-density gas elsewhere. A simple radiative-transfer model explains the dark features through absorption of emission from this dense layer by intermediate-density helium in front of it. Clumps, globules, and winds from objects such as proplyds are suggested absorbing structures, rather than individually established identifications.

PublicImages from the James Webb Space Telescope revealed previously unknown dark features in the inner Orion Nebula. Follow-up observations with the Very Large Telescope confirm that selected features are darker because they contain less light from a particular helium signal, at a wavelength of 1.083 micrometres. The reduction is fairly even across that spectral signal. To explain this, the researchers used a simple model in which helium gas in front of a bright, dense layer of the nebula absorbs some of its light. The absorbing gas could be in clumps, small clouds, or winds from objects such as proplyds; the model does not establish which structure accounts for each feature.

Young explorerAstronomers found new dark patches in pictures of a big cloud in space called the Orion Nebula. They looked more closely at some patches and found less of a special kind of light made by helium gas. Their simple model suggests that helium gas in front of a bright part of the cloud blocks some of that light, making dark shapes. The gas might be in little clouds or blowing winds, but they have not shown which makes each shape.

Slowly rotating white dwarfs in f (R, T ) = R + 2λT gravity: structure and stationary tidal response

Edson Otoniel, Jonathan A. Rebouças, P. H. R. S. Moraes

• High Energy Astrophysical Phenomena

AstronomerThis theoretical study calculates cold carbon fluid white-dwarf equilibria and stationary tidal responses in f(R,T)=R+2λT gravity through second order in uniform rotation. Comparisons hold baryon number fixed, and aligned electric quadrupolar tidal perturbations also conserve angular momentum. Over the common mass range, negative coupling produces larger radii and dimensional tidal deformabilities. For the baryon sequence studied, at 40% of each model’s Kepler reference frequency, background readjustment supplies 95.8–97.5% of the rotational enhancement; the explicitly mixed rotational–tidal contribution is positive and numerically resolved but subdominant. Relative to each coupling’s static model, the enhancement falls from 107.4% in general relativity to 14.2% at the most negative coupling, despite the latter’s larger absolute deformability. The authors attribute this to less relative background expansion and a different Love-number variation. These are model calculations, not observational measurements.

PublicThe researchers calculated how spinning white dwarfs made of cold carbon would respond to tidal stretching under a modified theory of gravity. In their models, a negative value of the theory’s coupling parameter makes the stars larger and more easily deformed by tides. Yet a star that is easier to deform overall need not receive a larger proportional boost from spinning. At 40% of each model’s reference spin frequency, rotation increases tidal deformability by 107.4% in general relativity but only 14.2% for the most negative coupling studied, each compared with its own nonspinning model. Most of the increase comes from rotation changing the star’s underlying structure, rather than from the explicit interaction between rotation and tides. These findings are theoretical and apply to the models and sequence examined, not to observed stars.

Young explorerScientists used math to imagine how spinning white dwarf stars could change shape when gravity tugs on them. They tried a different rule for gravity, and some pretend stars became bigger and easier to stretch. But spinning did not always make those stars much stretchier than they already were. Most of the extra stretchiness came from spinning changing the star’s shape and structure. This was a math study, not something scientists watched a real star do.

Double White Dwarfs with Circumbinary Disks: Evolution, Population Properties, and Gravitational Wave Signatures

Wenwu Ma, Zhenwei Li, Dylan Hebrail+5 more

AstronomerSome observed eclipsing double white dwarfs (DWDs) have eccentricities of order 10^-3 or larger, despite the expectation of negligible eccentricity from isolated binary evolution. This study models interaction with a circumbinary disk assumed to form from a recent common-envelope ejection. The authors report the first inclusion of this interaction in DWD population synthesis and use the models to constrain disk mass and lifetime. The models predict a relationship between the DWD eccentricity and orbital-period distributions that future observations could test. Disk interaction can shrink orbits and excite eccentricity, potentially extending the time a system is individually resolvable by a future space-based gravitational-wave detector. The results suggest including this interaction when modeling Galactic DWD gravitational-wave sources and their stochastic foreground; the disk origin and its role in the observed eccentricities remain model assumptions and interpretations rather than established observations.

PublicPairs of white dwarfs, the compact remnants of stars, are expected to follow nearly circular orbits when they evolve as isolated pairs. Yet observations show that some eclipsing pairs have slightly stretched orbits. This study explores a possible explanation: a disk of material surrounding both stars, assumed to be left over from a recent episode in which the pair expelled a shared gaseous envelope. Population models predict a link between orbital shape and orbital period that future observations could check. In the models, the disk can tighten the orbit and make it less circular, potentially allowing a future space-based gravitational-wave detector to distinguish the pair's signal for longer. These findings support including disks in predictions of gravitational-wave signals from white-dwarf pairs, but do not establish that disks caused the observed orbital shapes.

Young explorerSome pairs of tiny, very dense stars go around each other in paths that are a little stretched instead of perfectly round. Scientists used computer models to explore whether a ring of leftover material around both stars could help explain this. In the models, the ring can pull the stars closer and make their paths more stretched. That might also help a future space machine pick out their ripples in space for longer. Scientists still need more observations to test the idea.

Tracking the evolution of sub-Neptunes. I. Gyrochronology of planet hosting stars

Alessandro C. Lanzafame, Vincenzo Drago, Nino Greco+3 more

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies

AstronomerThis first paper in a series establishes a homogeneous stellar-age framework for studying sub-Neptune evolution. The authors compiled rotation periods and stellar parameters for 4,639 confirmed exoplanet hosts and obtained gyrochronological constraints for 2,204. Ages were inferred with a two-zone rotational-evolution model and Bayesian analysis using rotation periods, dereddened Gaia BP-RP colours, and literature masses as Gaussian priors. Well-constrained ages have typical formal uncertainties of 10–15%, substantially more precise than isochrone fitting generally provides for unevolved main-sequence stars. Inferred masses agree with the literature priors, and model effective temperatures are consistent with independent determinations. However, the rotational tracks extend to the terminal-age main sequence beyond the empirical calibration range, so ages beyond the open-cluster calibration remain model-dependent. The catalogue, publicly available through CDS, enables future investigation of sub-Neptune evolution and the emergence of the radius valley; this abstract does not report findings on those evolutionary questions.

PublicA star’s age helps researchers reconstruct the history of its planets, but ages are difficult to determine for stars still in the main part of their lives. This study collected rotation periods and other information for 4,639 stars known to host planets. By combining those data with a model of how stellar rotation evolves, the researchers obtained age constraints for 2,204 stars. The best-constrained estimates have formal uncertainties typically around 10–15%, though that precision does not remove uncertainty in the model itself. In particular, ages outside the range tested against star clusters remain model-dependent. The publicly available catalogue is intended to support future studies of how planets smaller than Neptune change over time, rather than reporting those changes here.

Young explorerIt is hard to tell how old a star is. Scientists used how stars spin, other clues, and a computer model to estimate ages for many stars that have planets. Some ages are more uncertain because the model has not been checked across the whole age range. These estimates can help scientists study how planets change as they grow older.

A JWST/NIRSpec Catalog of Low-Mass Candidates toward NGC 2024 from Multi-component Spectral Modeling

Haomiao Huang, Shu Wang, Xiaodian Chen+2 more

AstronomerMulti-component modeling of JWST/NIRSpec PRISM spectra toward NGC 2024 yields adopted fits for 78 sources, separating photospheric emission, dust and ice extinction, and optional thermal emission. Most spectra favor additional large-H2O-ice opacity relative to a small-grain baseline; a smaller subset requires gray opacity, potentially from large refractory grains. Some spectra also require thermal emission to reproduce the long-wavelength continuum. Fitted parameters and the adopted distance yield radii and bolometric luminosities, while comparison with evolutionary models provides mass estimates and a classification of 46 candidate members, 27 background sources, and five uncertain sources. Candidate members have lower fitted surface gravities than likely background stars. Of the candidates, 23 lie above the youngest available isochrones, plausibly reflecting extreme youth and uncertainties in evolutionary-model initial conditions. The catalog offers a uniform characterization of this sample and a framework for modeling other obscured star-forming regions.

PublicResearchers modeled James Webb Space Telescope spectra of 78 objects toward the dusty star-forming region NGC 2024. Their approach separates light from the objects themselves from the effects of obscuring dust and ice and, where needed, surrounding heat-emitting material. Most spectra are better explained when the model includes extra absorption by large water-ice grains. A smaller group needs additional, relatively wavelength-independent dimming, which might come from large grains of other materials. Using the fitted properties, the region's distance, and models of how young objects evolve, the team estimated sizes, luminosities, and masses. They identified 46 candidate members of the region, classified 27 sources as background objects, and left five uncertain. Half of the candidate members lie above the youngest available model tracks, possibly because the cluster is very young and the models' starting conditions are uncertain. These are model-based characterizations, not definitive membership or age measurements.

Young explorerA dusty cloud can hide baby stars and other small space objects. Scientists studied light from 78 objects in the direction of a place called NGC 2024 using the James Webb Space Telescope. They used computer models to help untangle the objects' own light from the effects of dust, ice, and warm material around them. Most light patterns fit better when the models included bigger bits of water ice. The team thinks 46 objects may belong to this star nursery, 27 are behind it, and five are still hard to place. Some possible nursery members do not match even the youngest models well. They might be very young, but the models are uncertain too.

The upper main sequence in h and chi Persei

A. Marco, I. Negueruela, N. Castro+1 more

AstronomerSpectroscopy of around 80 stars in h and chi Persei and NGC 663, combined with Gaia astrometry, constrains massive-star evolutionary pathways and the role of binary interaction. Atmospheric parameters were derived for almost 60 upper-main-sequence stars of type B2 V and earlier, with broad agreement between two independent automated procedures. The authors locate the cluster turn-offs between B1 V and B1.5–2 IV, distinguishing them from a population of B1–B1.5 giants near the terminal-age main sequence that includes a high fraction of Be stars. Most stars are consistent with single-star evolutionary models at a common age within each cluster. Some B-type supergiants are exceptionally luminous relative to other cluster members; their cluster-like kinematics and stellar parameters suggest, but do not establish, a merger origin. Lower-luminosity B-type supergiants appear consistent with the wider population. Kinematics indicate that most Be stars have not been dynamically perturbed by a supernova. Be stars below the turn-off likely formed through case A mass transfer, while those above it show no other characteristic marking a distinct evolutionary population.

PublicThe study examines how interactions between paired stars may shape the lives of massive stars in three young clusters: h Persei, chi Persei, and NGC 663. The researchers analyzed spectra of around 80 stars and combined them with Gaia measurements of stellar positions and motions. Most stars fit models of stars evolving without interaction at a shared age within each cluster. A few unusually bright blue supergiants stand out, however. Their motions and stellar properties suggest that they may have formed when two stars merged, although this is an interpretation rather than a confirmed history. The motions of most Be stars indicate that they have not been disturbed by a supernova explosion. The authors suggest that less massive Be stars below the clusters’ evolutionary turn-off likely gained material from a companion. More massive Be stars above that turn-off show no other sign of belonging to a separate evolutionary population.

Young explorerSome stars have a partner, and the two can change each other as they grow older. Scientists studied stars in three big groups. Most looked as expected for stars growing without a partner’s help. A few were much brighter than the others. They might have formed when two stars joined together, but scientists are not sure. Some other stars probably got extra material from a partner.

The light curve modeling of eclipsing cataclysmic variables: from period bouncers to nova-likes

Sergey Zharikov

• High Energy Astrophysical Phenomena

AstronomerThis paper describes the concepts and implementation of CVlab V2.0, a code for simulating light curves of close binary systems with accretion-disk structures. It discusses the code’s assumptions, limitations, applications, and prospects for further development. The abstract reports no observational findings or specific simulation results.

PublicThe paper describes CVlab V2.0, a computer program that simulates how the brightness of two closely paired stars changes over time when the system includes a disk of accumulating material. It explains how the program works, its assumptions and limitations, its uses, and possible future improvements. The abstract does not report new observations or particular simulation outcomes.

Young explorerThis paper explains a computer program that pretends to watch two stars close together, with a disk of material in the pair. It works out how their light might change over time. The author explains how the program works, what it can and cannot do, and how it might be improved. These are computer models, not new pictures of real stars.

A potential observational test to disentangle the companion of binary millisecond pulsar PSR J1928+1815

Wen-Cong Chen

• High Energy Astrophysical Phenomena

AstronomerPSR J1928+1815 is a binary millisecond pulsar with reported regular radio eclipses. A helium-star companion has been proposed as the most likely explanation, but a white dwarf remains possible, and uncertain interstellar extinction complicates optical and near-infrared identification. Using the measured mass function and eclipse-inferred inclination, the authors calculate a gravitational-radiation orbital-period derivative of −(6.8–9.6) × 10^−13 s s^−1 for a 1.4-solar-mass white dwarf. They propose that a measured derivative exceeding −9.6 × 10^−13 s s^−1 would identify a helium companion above 1.4 solar masses. Their helium-star models also include tidal transfer of orbital angular momentum into stellar spin as the companion expands, adding to the orbital decay from gravitational radiation. For helium-star masses of 1.0–1.6 solar masses, the predicted derivative is −(4.9–13.5) × 10^−13 s s^−1; the authors suggest tides could particularly help confirm a 1.35–1.5-solar-mass helium star. Assuming a helium companion, they constrain the maximum evaporation efficiency associated with the pulsar's spin-down luminosity to 0.006. These calculations offer a proposed diagnostic, not a confirmed companion identification.

PublicThe rapidly spinning pulsar PSR J1928+1815 has regular interruptions in its radio signal, but the identity of its companion remains uncertain. A helium star is considered the most likely companion, although a white dwarf has not been ruled out. Dust between us and the system makes identification using visible and near-infrared light difficult. The researchers propose another test: measuring how the pair's orbital period changes. Their calculations predict orbital shrinkage from gravitational radiation and, for an expanding helium star, an additional tidal effect that transfers energy of motion associated with the orbit's angular momentum into the star's rotation. This tidal contribution could help distinguish a helium companion from a white dwarf. The predicted changes depend on the companion's mass and nature; the abstract does not report a measurement that settles its identity. Assuming a helium companion, the study also limits how efficiently the pulsar's lost rotational energy can drive evaporation.

Young explorerA tiny spinning star sends out radio flashes, but we sometimes stop receiving them as it travels around with another star. Scientists think its partner may be a helium star, but it could be a different kind called a white dwarf. Dust makes the partner hard to see. The scientists calculated how the time the stars take to go around each other might change. Measuring that change could help tell which kind of partner is there, but they do not know for sure yet.

Current Sheets and Magnetic Reconnection statistics by Solar Orbiter at few to tens of Ion Inertial Lengths II: Conditions for Reconnection, and Current Sheet Planarity

Inmaculada F. Albert, Sergio Toledo-Redondo, Víctor Montagud-Camps+6 more

• Earth and Planetary Astrophysics
• Space Physics

AstronomerThis statistical study uses 103 hours of Solar Orbiter in-situ ion data sampled at 4 Hz between July 2020 and September 2022, mainly in slow and Alfvénic solar wind. An automatic algorithm identifies current sheets with thicknesses from approximately one to 86.4 ion inertial lengths and classifies them as Alfvénic or reconnecting. Sheet orientations are consistent with an isotropic distribution, and the median ratio of reconnection jet speed to theoretical outflow speed is 0.71. The authors find no diamagnetic-drift suppression in the cataloged sheets, attributing this to symmetric upstream conditions. They find that flow shear in the reconnection direction suppresses reconnection and is consistently greater in Alfvénic than reconnecting sheets. Guide-field-direction shear is too small to suppress reconnection in the ion-scale solar-wind sheets studied.

PublicUsing 103 hours of Solar Orbiter measurements, researchers studied thin boundaries called current sheets in the solar wind, where magnetic fields can rearrange through magnetic reconnection and drive jets of gas. The boundaries showed no preferred orientation within the statistical findings. The median ratio of measured reconnection jet speed to theoretical outflow speed was 0.71; this is a speed comparison, not a measure of energy-conversion efficiency. The study finds that differences in flow velocity across a boundary can suppress reconnection when directed along the reconnection flow. Such differences were greater in sheets classified as Alfvénic than in reconnecting sheets. Flow differences along another magnetic-field direction were too small to suppress reconnection. A separate proposed suppression mechanism involving diamagnetic drift had no effect in this sample, which the authors attribute to similar conditions on the two sides of the boundaries.

Young explorerThe Sun sends a stream of very hot gas into space. Scientists used a spacecraft to study thin places in that stream where magnetic fields can change how they connect and send gas rushing out. They found that differences in how the gas moves on either side can stop this change when they point one way. Differences pointing another way were too small to stop it in the places they studied.

An all-sky catalogue of Be transition stars from WISE and Gaia

Qi Jia, Mingjie Jian, Gang Li+2 more

• Astrophysics of Galaxies

AstronomerUsing Gaia DR3 astrometry and multi-epoch WISE/NEOWISE-R mid-infrared photometry, the authors compile an all-sky catalogue of 3,300 classical Be transition stars, including 2,743 newly identified objects, from 4.2 million candidate OBA stars. Selection uses correlated W1 magnitude and W1−W2 colour variability tracing circumstellar disk formation and dissipation. Measured median outburst and decay durations are 459 and 478 days, respectively, consistent with earlier WISE measurements and compatible with viscous decretion disk evolution timescales, rather than a unique confirmation of that framework. TESS photometry for 3,017 targets yields 63 eclipsing systems: 33 Algol-type, 17 Beta Lyrae-type, and 13 W Ursae Majoris-type. Two sources with multi-epoch LAMOST spectra show candidate radial-velocity shifts exceeding 20 km/s, but their line-profile behaviour suggests that outburst-related changes may contribute to the apparent shifts; these are not unambiguous evidence of orbital motion. The catalogue enables future statistical studies of outbursts, disk evolution, and binarity.

PublicResearchers have assembled an all-sky catalogue of 3,300 stars that switch between quiet B-star phases and active Be-star phases associated with surrounding disks of gas. Of these, 2,743 are newly identified. The team searched 4.2 million candidate stars using Gaia data and repeated infrared observations from WISE and NEOWISE-R, looking for linked changes in brightness and colour that trace disks forming and dissipating. The measured outburst and fading phases have median durations of 459 and 478 days. These long timescales fit expectations from a model of disk evolution, but do not uniquely establish that model. TESS observations of 3,017 targets revealed 63 eclipsing binary systems containing these changing stars. Spectra of two sources also show possible velocity shifts, but changes in the shapes of spectral lines during outbursts may help produce those signals, so they are not clear evidence of orbital motion. The catalogue offers a foundation for studying how these disks change and how that activity relates to stellar companions.

Young explorerSome stars have a disk of gas around them that can grow and fade away. Scientists watched how stars changed in brightness and colour and made a list of 3,300 stars going through these changes. For the measured bursts and fading times, the middle values were each a little longer than a year. They also found 63 pairs of stars where one passes in front of the other and blocks some light. Two stars showed hints of changing speed, but the hints might come partly from changes in their gas, so scientists cannot use those hints alone to be sure they are moving around a partner.

Solar Ephemeral Regions Hales and Joys laws

Anu Sreedevi, Bibhuti Kumar Jha, Bidya Binay Karak+1 more

AstronomerUsing Helioseismic and Magnetic Imager full-disc line-of-sight magnetograms, the study tracks the emergence and decay of ephemeral regions (ERs) and quantifies their magnetic flux and morphology. The ER flux distribution is log-normal, and the estimated total unsigned flux emergence rate is about 1.45 × 10^22 Mx/day. ERs are distributed almost uniformly across the solar disc, with a substantial fraction emerging outside the activity belts. Tilt-angle statistics show weak adherence to Hale’s polarity law. The authors interpret these mixed signatures as suggesting that most ERs are associated with the global solar dynamo, while the remainder most likely originate from a small-scale dynamo. This attribution is an interpretation of the statistics rather than a direct identification of each region’s origin. The findings connect ER and active-region scales and constrain how magnetic flux emerges and is structured.

PublicThe Sun produces small magnetic regions with two opposite poles, as well as larger active regions and sunspots. Researchers used magnetic images to follow these short-lived regions as they appeared and faded. They found them spread almost evenly across the Sun’s visible disc, with many appearing outside the usual activity bands. Their pole orientations showed only a weak tendency to follow Hale’s polarity law, a pattern associated with solar magnetism. The authors interpret the combined evidence as suggesting that most of these small regions are linked to the Sun’s large-scale magnetic-field-generating process, while others probably arise from a smaller-scale process. The observations support this explanation statistically, but do not establish the origin of each individual region.

Young explorerThe Sun has little magnetic patches with two opposite ends. Scientists watched these patches appear and fade. They found them spread almost everywhere across the Sun’s face, and their directions followed a pattern only a little bit. The scientists think most patches may be connected to the way the whole Sun makes magnetism, while others may come from smaller magnetic activity. They do not know for sure how each patch was made.

The colors of protoplanetary disks - Impact of nonspherical dust particles on the polarized and total intensity colors

Maxime Roumesy, Jie Ma, Ryo Tazaki+2 more

• Earth and Planetary Astrophysics

AstronomerUsing MCFOST synthetic visible-to-near-infrared scattered-light images in total and polarized intensity, the authors investigate disk colors for compact spheres, irregular particles, and compact and fractal aggregates. For aggregates larger than the wavelength, color depends on monomer size but weakly on aggregate size, especially at low fractal dimension. Polarized color is more sensitive to dust properties than total-intensity color because it combines the wavelength dependence of scattering and polarization degree. Effective medium theory is reliable only for compact aggregates with small monomers; effective albedo helps predict colors, but radiative transfer is required to account for multiple scattering. Within the models considered, HD 100546's red optical-to-near-infrared colors exclude compact grains and organic-rich compositions, while remaining consistent with compact or fractal amorphous-carbon aggregates containing large monomers. Combining colors with polarized scattering phase functions is proposed as a promising way to reduce dust-model degeneracies, with broader application still needed.

PublicDust in planet-forming disks is difficult to identify because different kinds of particles can scatter light in similar ways. This study used computer-generated images to test how dust changes a disk's color from visible to near-infrared light. In the simulations, the size of the smaller particles making up a dust clump mattered more for color than the clump's overall size when the clump was larger than the light's wavelength. Colors measured in polarized light were more sensitive to dust properties than ordinary brightness colors. Comparing the models with the red colors of HD 100546 favored certain carbon-based dust clumps with large building blocks and ruled out compact grains and organic-rich compositions among the options tested. The authors suggest combining colors with measurements of how polarized scattering varies with angle to distinguish dust models more reliably; this remains a promising approach rather than a unique identification of the dust.

Young explorerDust around a young star can help make planets, but we do not know exactly what that dust is like. Scientists made pretend pictures on a computer to see how different dust would change the colors. For big dust clumps, the little pieces inside often mattered more than the whole clump's size. One real disk's reddish colors fit some carbon dust clumps in their tests, but that does not prove exactly what is there. Looking at colors in more ways could help solve the puzzle.

Small-Scale Magnetic Fields of Hyades M Dwarfs: Evolution with Age from the Pleiades to Field Stars

Fábio Wanderley, Katia Cunha, Oleg Kochukhov+9 more

AstronomerZeeman-broadening analysis of magnetically sensitive APOGEE lines yields mean small-scale magnetic fields of 0.7–4.3 kG for 18 Hyades M dwarfs. Comparison with previous Pleiades and exoplanet-hosting field-star samples gives mean fields of 2965 ± 632 G, 1925 ± 1028 G, and 573 ± 272 G for the Pleiades, Hyades, and field samples, respectively. The authors interpret these distributions as reflecting age differences: the Pleiades stars are predominantly magnetically saturated, the roughly 500-million-year-older Hyades sample spans saturated and unsaturated regimes, and the field stars are consistently unsaturated. A combined field-strength–Rossby-number relation yields saturation thresholds of Ro = 0.145 and mean field strength 2452 G. Cooler Hyades stars tend to have stronger fields at a common age; this trend is less apparent in the other samples, attributed to age spread among field stars and saturation in the Pleiades. Isochrone comparisons indicate positive correlations of field strength with radius inflation and photospheric spot coverage. Stronger fields also correlate with greater Hα equivalent-width excess and higher X-ray-to-bolometric luminosity ratios; these correlations do not by themselves establish causation.

PublicResearchers used the magnetic broadening of spectral lines to estimate magnetic fields on 18 small, cool stars in the Hyades cluster. Their fields range from 0.7 to 4.3 kilogauss. Compared with earlier studies, the younger Pleiades stars generally have stronger fields, while stars outside these clusters that host planets have much weaker fields. The authors interpret these differences as reflecting stellar aging. Combining the samples, they identify a saturation level beyond which field strength levels off in its relationship with Rossby number, a measure used to compare stellar rotation with internal convection. Within the Hyades, cooler stars tend to have stronger fields. Stronger fields also go together with greater surface spot coverage, larger radii relative to stellar-model expectations, and stronger atmospheric activity measured using hydrogen emission and X-rays. These are observed associations, not proof that magnetic fields cause all of these differences.

Young explorerStars can have magnetic fields, a bit like magnets. Scientists studied the light from 18 small stars in a group called the Hyades to work out how strong their magnetism is. Compared with stars studied before, a younger group usually has stronger magnetism. The scientists think age helps explain the difference. In the Hyades group, cooler stars tend to be more magnetic. Stars with stronger magnetism also tend to have more spots and more active outer layers, but finding these things together does not prove that one causes the other.

Revealing the dusty shell of the semi-regular variable V CVn

Yanko Nikolov, Nicolaus Steenken, Richard Ignace+8 more

AstronomerA multi-technique campaign spanning six pulsation cycles of the semi-regular variable V CVn in 2020–2025 combined high-cadence photopolarimetry, spectropolarimetry, and first CHARA interferometry in 2024–2025. Optical linear polarization reached 6% during the 2023–2025 cycles, while its anticorrelation with brightness and the decades-long position-angle stability near 100 ± 20 degrees persisted. Interferometry resolved the photosphere but detected no large-scale asymmetries, such as bow shocks or isolated scattering arcs, within the scales and sensitivities probed. The authors consequently exclude earlier ISM-interaction and static-reflection-cloud models as the primary polarization drivers. They instead propose a circumstellar disk or flattened envelope, analogous to L2 Puppis, whose geometry might be shaped or maintained by ISM ram pressure associated with the star's high proper motion. Transient dust clumps, interpreted as likely linked to long-secondary-period-driven episodes of enhanced mass loss, could explain the variable polarization within this stable geometry; neither the disk nor this causal mechanism is established by the reported observations.

PublicThe variable star V CVn changes how strongly its light is polarized—aligned in a particular direction—but that direction has stayed roughly steady for decades. Observations covering six stellar pulsation cycles from 2020 to 2025 found polarization peaks as high as 6%, with stronger polarization still tending to occur when the star was fainter. Interferometric observations distinguished the star's visible surface but found no large, uneven surrounding structures within the size range and sensitivity tested. The authors argue against earlier explanations involving a bow shock or fixed reflecting clouds as the main cause. Instead, they propose a disk or flattened cloud of material around the star, with temporary dust clumps producing the polarization changes. They suggest that pressure from gas the star moves through could help maintain the flattened shape, and that a longer cycle of stellar variability may trigger episodes of material loss that form the clumps. These are proposed explanations, not confirmed detections of a disk or proof of how the dust forms.

Young explorerV CVn is a star whose light has a special pattern, a little like light passing through sunglasses. The pattern gets stronger and weaker, but keeps pointing nearly the same way. Scientists watched the star and found that the pattern tended to be stronger when the star looked dimmer. They think dust around the star might make a flat shape, with little clumps that come and go. That could explain the changing light, but they have not yet shown that this dusty shape is really there.

Evidence of flare and coronal mass ejection-driven shock acceleration of relativistic protons on 21 November 2024

M. Jarry, A. Papaioannou, G. Vasalos+9 more

AstronomerThe 21 November 2024 far-side flare in AR 13892, accompanied by enhanced hard X-rays at Solar Orbiter and a CME moving at 1436 km/s along the limb, produced a widespread SEP event with proton energies above 100 MeV at Earth, STEREO-A and Solar Orbiter. Combining multi-spacecraft particle data, velocity dispersion analysis, 3D shock reconstruction and magnetic connectivity modelling, the study finds inferred solar release times consistent with an early flare-accelerated population at all three observers. SEP abundances independently show flare-related signatures. The inferred early release at STEREO-A is immediately followed by connection to an efficient CME-driven shock; reconstruction of the type II radio source supports Earth's connection to an efficient shock region several minutes later. Within the adopted models, Solar Orbiter's release precedes connection to the reconstructed shock front, disfavouring that connected shock as the source of its earliest particles. STEREO-A and Solar Orbiter nevertheless show similar spectral evolution, while the near-Earth spectrum reaches relativistic energies and has a high-energy rollover. The analysis supports multiple acceleration processes whose contributions differ among observers, rather than a uniform acceleration history.

PublicA solar eruption on the Sun's far side on 21 November 2024 sent high-energy particles across a wide region, reaching Earth and the STEREO-A and Solar Orbiter spacecraft. The eruption included a flare and a fast-moving cloud of solar material that drove a shock. Researchers used particle measurements, radio observations and computer models to investigate which process gave the particles their energy. Their timing analysis is consistent with an early contribution from the flare at all three locations, and the particles' chemical abundances also show signs of flare-related acceleration. Modelling indicates that STEREO-A became magnetically connected to an effective particle-accelerating shock immediately after the early release, with Earth connecting several minutes later. At Solar Orbiter, the earliest inferred release came before the modelled shock connection, making that shock connection an unlikely explanation for the first particles there. The findings suggest that both flare-related and shock-related processes contributed, but not in the same way everywhere; the detailed timing interpretation depends on the models used.

Young explorerA big eruption happened on the far side of the Sun. Tiny bits of matter moving very fast reached Earth and two spacecraft far apart in space. Scientists studied the bits to work out what sped them up. Their clues suggest that a sudden flash called a flare gave some bits an early push. A shock made by a rushing cloud from the Sun may have helped speed up others. The scientists' models suggest that the pushes were not the same everywhere, and they are still working out exactly how they happened.

SHAPE: Solar Heliospherical Analysis and Prediction of Eruptions A machine learning approach to solar flare forecasting

S. Kadakol, P. Deshmukh, A. B. Bendre

AstronomerSHAPE is a two-phase deep-learning forecasting pipeline using GOES XRS soft X-ray observations rather than sunspot proxies. For monthly flare counts aggregated annually, it combines a cycle-shape curve anchored to published solar-cycle minima with a compact GRU and Monte Carlo dropout for residual variability. Training on the NOAA GOES Flare Report for 1995–2020 and validation on 2021–2025 yield a mean absolute error of 204 flares per year, with the 2024 maximum underestimated. A shared-trunk, dual-head LSTM uses 12-day windows of five intensity features to predict the next day's strongest C-, M- or X-class flare, with optional active-region physics-score blending and a threshold favouring M-or-above recall. A 100-day chronological backtest gives M+ true skill and Heidke skill scores of 0.351 and 0.335, a Brier skill score of 0.163 relative to climatology, and an expected calibration error of 0.023. Persistence is competitive on both skill scores, indicating that much short-term predictability reflects autocorrelation rather than learned structure. These tests support compact, rapidly trainable forecasting models, but do not establish reliable operational prediction of rare, destructive flares.

PublicResearchers tested SHAPE, an artificial-intelligence system that uses direct measurements of the Sun's soft X-rays, rather than sunspot counts, to forecast solar flares. One part predicts monthly flare numbers and adds them into yearly totals. Tested on 2021–2025 after training on earlier records, its average absolute error was 204 flares per year, and it predicted too few during the 2024 peak in solar activity. A second part uses the previous 12 days of measurements to predict the next day's strongest flare category. In a 100-day test, it improved on a forecast based on long-term event frequencies, but simply using the previous day's flare category was competitive on two key measures. Much of the apparent short-term predictability therefore comes from conditions persisting from one day to the next. The compact models are quick to train on standard computers, but dependable warnings for the rarest, most destructive flares remain an unsolved problem.

Young explorerThe Sun sometimes gives off big bursts called flares. Scientists made a computer helper that looks at X-rays from the Sun to guess how many flares will happen and how strong tomorrow's biggest flare might be. In their tests, it made useful guesses, but it guessed too few flares during a very busy time. For tomorrow's flare, a simple guess that tomorrow will be like today did about as well on some tests. The helper is not yet a sure way to warn us about the biggest bursts.

Solar Wind Turbulence Spectra and Correlation Scale from 4 to 50 r(☉): STEREO and PUNCH Observations

F. Pecora, G. Nisticò, R. Chhiber+21 more

• Plasma Physics
• Space Physics

AstronomerRemote-sensing brightness observations from STEREO/COR2 at 4–9 solar radii and the first science-ready PUNCH/WFI images at 21–50 solar radii probe the radial evolution of density-fluctuation power spectra and correlation scales. Line-of-sight integration systematically steepens spectral exponents by about −0.5 across all resolved scales: nominal energy-containing and inertial-range spectra of k^-1 and k^-5/3 appear as k^-1.5 and k^-2.1, respectively, consistent with previous synthetic-image simulations. The correlation scale increases with heliocentric distance across the sampled ranges, in agreement with earlier theoretical models and observations closer to the Sun.

PublicImages from STEREO and the first science-ready images from PUNCH show how density variations in the solar wind change with distance from the Sun. The observations cover two regions, 4–9 and 21–50 times the Sun’s radius, and show that the characteristic size over which density variations remain related grows farther outward. Looking through overlapping material along the line of sight also changes the apparent pattern of turbulence across different sizes, making its measured spectrum steeper. This viewing effect agrees with earlier simulated images, while the growing characteristic size agrees with previous models and observations nearer the Sun.

Young explorerThe Sun sends a wind of tiny particles into space. Scientists used pictures to study uneven patches in this wind and found that their typical size gets bigger farther from the Sun. But the pictures look through many patches at once, which changes how the patterns appear.

Stellar wind variability in OB stars and its effect on mass-loss determinations

Raman K. Prinja

• Astrophysics of Galaxies

AstronomerThis review examines variability in OB-star winds, primarily through UV spectroscopy, and studies using it to infer large-scale velocity and density structures. The structures appear spatially coherent and rooted in the stellar photospheres. Evidence indicates that they can be optically thick to resonance-line radiation and sufficiently dense to modulate wind-generated X-ray flux. Their effects on wind-line formation complicate precise mass-loss determinations. Millimetre and radio continuum observations are highlighted as a future route to constraining the radial stratification of wind clumping and improving empirical mass-loss estimates, rather than as an already demonstrated solution.

PublicNearly all stars of the OB class show signs that their outflowing gas changes over time. This review brings together studies, mainly using ultraviolet light, suggesting that these winds contain large, coherent structures apparently connected to the stars’ visible surfaces. Evidence suggests the structures can be opaque to certain ultraviolet spectral lines and dense enough to change the amount of wind-produced X-rays that escapes. They also complicate estimates of how much material the stars lose. Observations at millimetre and radio wavelengths are proposed as a way to map how wind clumping changes with distance from a star and eventually obtain more reliable estimates.

Young explorerThese stars blow gas into space, and their winds keep changing. Scientists have studied the light and found clues that the gas forms big patches that seem connected to the stars’ surfaces. These patches can block some kinds of light, making it harder to tell how much gas a star is losing. Scientists hope that looking at other kinds of light, called millimetre and radio waves, will help them understand the patches better.

Episodic Protostellar Outflows: A Proper Motion Study in Serpens South

Simran Kaur, Adele L. Plunkett, Zhi-Yun Li+5 more

• Astrophysics of Galaxies

AstronomerThe first proper-motion study of the collimated, episodic molecular outflow from the Class 0 protostar CARMA-7 in the central hub of Serpens South compares sub-arcsecond ALMA observations from 2017 and 2021. Knots traced in 12CO J = 3-2 and SiO J = 8-7 show proper motions of 10–40 mas/yr, corresponding to 30–90 km/s. The flow is predominantly blueshifted to the south and redshifted to the north, with radial velocities reaching at least 25 km/s. Combining radial velocities and proper motions yields inferred lobe inclinations of approximately 60–80 degrees to the line of sight. The knot motions constrain the ejection history and refine the inferred morphology, with reported ejection timescales of roughly 10–120 years.

PublicAstronomers tracked clumps of gas expelled by CARMA-7, a very young star in the Serpens South star-forming region. Comparing ALMA telescope observations from 2017 and 2021 revealed the clumps moving across the sky at speeds corresponding to about 30–90 kilometers per second. The narrow outflow contains distinct clumps associated with separate ejection episodes. Gas to the south mostly moves toward us, while gas to the north mostly moves away. Combining these motions with the sideways movement, the researchers infer that the outflow lies about 60–80 degrees from our viewing direction. They also estimate that the ejections occurred roughly 10–120 years ago, helping reconstruct the young star’s recent activity.

Young explorerA baby star called CARMA-7 is sending out clumps of gas in a narrow stream. Astronomers compared telescope pictures taken four years apart and saw that the clumps had moved. The gas on one side mostly comes toward us, and the gas on the other side mostly goes away. The moving clumps suggest that the star sent out gas in separate bursts, roughly 10 to 120 years ago.

R-process nuclei in the rare-earth region above N=126 in Relativistic Hartree-Bogoliubov theory: A preponderance of shape-coexistence in nuclei

M.M. Sharma

• Nuclear Theory

AstronomerThis theoretical study examines neutron-rich even-even nuclei with Z=58–72 beyond N=126, relevant to the r-process abundance peak near A≈195, using deformed relativistic Hartree–Bogoliubov calculations with NL-SV1, SVI-2, and NL3. In the extreme r-process-path region, SVI-2 binding energies agree closely with the HFB-24 mass formula; this is a model comparison, not an experimental validation. All three models predict widespread coexistence of well-deformed prolate and oblate configurations between N=126 and N=184, with increasing neutron number driving a smooth change from prolate to oblate ground states through near-degeneracy. The calculations predict that deformation beginning at N≥130 enhances stability in many chains with Z>60, shifting the expected neutron drip line substantially toward more neutron-rich nuclei, especially at higher Z. Implications for r-process nucleosynthesis are discussed, but the abstract reports no quantified abundance changes.

PublicCalculations suggest that the shapes of very neutron-rich atomic nuclei could affect how heavy elements form through rapid neutron capture. The researchers compared three theoretical models for nuclei relevant to a prominent peak in the predicted distribution of elements made by this process. All three predict that many of these nuclei can have two competing shapes: elongated or flattened, with very similar energies. Adding neutrons can change which shape is favored. The calculations also suggest that changes in shape make many nuclei more stable, potentially allowing them to hold more neutrons before reaching the predicted limit of neutron binding. These are theoretical predictions rather than laboratory observations; the abstract discusses possible consequences for element formation without giving numerical changes in element abundances.

Young explorerAn atom has a tiny middle called a nucleus. Scientists used calculations to study nuclei with lots of neutrons, which are little parts inside them. Their calculations suggest that some nuclei could be stretched out or squashed flat, with either shape almost equally easy to have. Adding more neutrons could change which shape they prefer. Changing shape might also help some nuclei hold extra neutrons. This could matter for how heavy elements are made, but these ideas come from calculations, not from watching the nuclei do it.

Forecasting the Ambient Solar Wind With a Physics-Informed Learned Inner Boundary: Part I-Differentiable Inverse Reconstruction From Solar Images

Enrico Camporeale, Andong Hu, Prateek Mayank+1 more

• Space Physics

AstronomerThe study infers an effective, unobserved solar-wind boundary speed at 21.5 solar radii by training a solar-observation-to-boundary map through a differentiable, reduced transport solver extending to near L1. Screening 42 candidate features identifies coronal-hole area, proximity to the ecliptic, and darkness as most informative. The reference model also uses their recent history, GONG potential-field expansion factors, and wind speed one rotation earlier. In five-fold chronological cross-validation across solar cycle 24, reconstruction achieves an ROC area of 0.879 for speeds above 600 km/s, compared with 0.802 for 27-day recurrence and 0.850 for screened-feature linear regression. It underrepresents variability, with a predicted-to-observed standard-deviation ratio of 0.81, and its tail-weighted loss introduces a +26 km/s bias. Factorial tests attribute the improvement primarily to training through speed-dependent propagation; stream interaction contributes little, and linear or physically parameterized maps match the neural network. About 57% of hourly speed variance remains undetermined by these inputs, with similar residual errors across model classes, supporting more informative inputs rather than greater model flexibility. These are reconstruction results; forecasting and probabilistic prediction are deferred to Parts II and III.

PublicSpacecraft near Earth measure the solar wind only after it has traveled and changed. This study works backward to estimate an effective wind speed closer to the Sun, where that speed is not directly observed. It links solar images and magnetic measurements to near-Earth measurements through a simplified model of the wind’s journey. The size, location, and darkness of coronal holes were especially informative. Tests using successive periods of solar cycle 24 showed better identification of fast wind than either repeating conditions from 27 days earlier or using a basic statistical comparison model. However, the reconstruction tended to give speeds that were too high on average and showed less variation than the observations. Accounting for how travel depends on wind speed mattered more than using a neural network: simpler models performed equally well when trained through that transport calculation. The inputs left about 57% of hourly speed variation unexplained, suggesting that better information matters more than a more complicated model. Forecasting is reserved for later papers.

Young explorerThe Sun sends out a wind through space. Scientists can measure it near Earth, but they cannot directly see its speed at the closer place studied here. They used pictures of the Sun and a computer model to work backward and estimate that speed. Letting faster wind travel faster helped. A simpler computer model did as well as a more complicated one, but both still missed lots of changes in the wind.

Radial Evolution of a CIR: Observations From a Nearly Radially Aligned Event Between Parker Solar Probe and STEREO-A

R. C. Allen, G. C. Ho, G. M. Mason+31 more

• Space Physics

AstronomerOn September 19, 2019, Parker Solar Probe at approximately 0.5 au and STEREO-A at approximately 1 au observed the same corotating interaction region (CIR) while nearly radially aligned, enabling a comparison of its radial evolution with minimal temporal and longitudinal differences. Bulk plasma and magnetic field signatures evolved consistently with previous observations. Suprathermal ion enhancements, however, covered a broader longitudinal range at Parker Solar Probe, though at much lower intensities than at STEREO-A. The authors interpret this broader extent as largely resulting from magnetic field-line topology between the compressed slow solar wind upstream and the high-speed stream following the CIR, highlighting the importance of large-scale magnetic connectivity.

PublicTwo nearly aligned spacecraft observed the same corotating interaction region—a structure in the solar wind—at different distances from the Sun on September 19, 2019. Parker Solar Probe was about half as far from the Sun as STEREO-A, allowing researchers to compare how the region changed as it traveled outward. The solar-wind plasma and magnetic field changed in familiar ways, but the enhanced population of unusually energetic ions extended across a wider range of longitudes at the closer spacecraft, even though its intensity was much lower there. The researchers suggest that the arrangement of magnetic field lines largely explains this difference, rather than establishing that explanation as certain.

Young explorerTwo spacecraft, one closer to the Sun and one farther away, watched the same busy patch in the wind blowing from the Sun. Nearer the Sun, they found extra speedy particles spread over a wider area, but the extra particles were much less plentiful there. The scientists think the way magnetic lines bend and connect helps explain the difference.

Comparison of models for dynamical structures of solar plasma

S. N. Artekha

• Plasma Physics
• Space Physics

AstronomerThis theoretical study develops axisymmetric plasma models motivated by convective instability under the Schwarzschild criterion and excess thermal or magnetic energy. A superadiabatic temperature gradient allows overheated plasma to rise. The authors construct analytical solutions for an ideal-hydrodynamic model of initial structure formation, consider differential rotation in a refined growth-stage model, and use a full Navier–Stokes MHD model to follow rotating structures through their development. With velocities adjusted to boundary conditions, the models share converging radial flow near the base, outward flow near the top, and maximum vertical velocity at the center of the axis. In the model, a stationary axisymmetric ambient magnetic field and its gradients have little influence on the structure and velocity field. Applications to solar structures, including jets, are discussed; the abstract reports theoretical results, not observational validation.

PublicThe researchers use mathematical models to explore how rising, rotating structures could form in plasma, the hot material found in the Sun. Their proposed starting point is overheated plasma rising because of an unstable temperature gradient. They examine models of increasing complexity, from the earliest rise to the development of a rotating structure. The models produce similar flow patterns: material moves inward near the bottom, rises fastest at the center of the axis, and spreads outward near the top. A steady, symmetric surrounding magnetic field has little effect in their calculations. The authors discuss possible applications to solar structures such as jets, but do not report observations confirming the models.

Young explorerScientists used math to explore how very hot material might rise and spin on the Sun. In their models, the material moves inward at the bottom, rises fastest in the middle, and spreads out near the top. These are ideas worked out with math, not things this study watched happen on the Sun.

Differential velocity cumulative distribution (DVCD): an efficient statistical method for binary-star analysis in large stellar catalogues using radial velocities

Luo Feng, Zhao YongHeng, Liu Chao

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

AstronomerThe study proposes and implements the Differential Velocity Cumulative Distribution (DVCD) algorithm for statistical characterization of binary stars using radial-velocity data. The authors report improved accuracy and computational efficiency relative to existing approaches, with computation times reduced by factors of 10^-4 to 10^-5 under comparable conditions. Applied to APOGEE DR16 red giants divided into 16 subsets by log g and M/H, DVCD yields an inferred binary fraction that decreases with decreasing surface gravity and increasing metallicity. These trends provide constraints on binary evolution, while the reported efficiency suggests potential for large-scale statistical analyses.

PublicResearchers developed a method called DVCD to study how common paired stars are, using measurements of stellar motion toward or away from us. They report that it is more accurate and much faster than existing approaches under comparable conditions. Applying it to red giant stars in the APOGEE DR16 dataset, they inferred that pairs are less common among stars with weaker surface gravity and higher abundances of elements heavier than helium. These patterns could help researchers understand how stellar pairs evolve; they do not by themselves establish what causes the trends.

Young explorerSome stars have a partner star. Scientists made a new way to look for clues about these pairs by studying how stars move toward us and away from us. They say their way works faster and more accurately than older ways. Among the giant stars they studied, pairs seemed less common when the stars had weaker gravity at their surfaces or more heavy ingredients. This may help scientists learn how star pairs change.

Generative Learner for Distributional Causal Effects

Maria Nareklishvili, Nicholas Polson, Vadim Sokolov

• Astrophysics of Galaxies
• Artificial Intelligence

AstronomerThe authors propose a generative neural-network learner to estimate conditional average treatment effects and characterize their distribution. Three jointly fitted subnetworks estimate propensity scores, baseline-outcome conditional quantiles, and conditional quantile treatment effects; integrating the latter yields the conditional average effect. Under classical causal assumptions in the Neyman–Rubin framework, the authors report average out-of-sample mean-squared-error reductions of 5.4%–93.5% relative to generalized random forests, double machine learning, and generative adversarial networks across experimental designs. For an empirical application, they express the Stefan–Boltzmann law as a unidirectional causal model and analyze publicly available stellar data. The estimated effects satisfy the law's implied restrictions, demonstrating consistency with those restrictions rather than independently establishing the causal assumptions.

PublicThe researchers propose a neural-network method for estimating how an intervention affects an outcome, including how those effects vary with the characteristics of the cases being studied. Under standard assumptions needed for causal analysis, they report lower prediction errors than three competing methods across the experimental designs considered. They also apply the method to public data about stars, using a one-way cause-and-effect model based on the Stefan–Boltzmann law. The estimated effects obey the constraints implied by that law. This agreement is a consistency check, not proof that the method's causal assumptions are correct.

Young explorerThe researchers made a new computer helper to work out what might change when something else changes. They tried it on information about stars, using a science rule called the Stefan–Boltzmann law. Its answers fit what that rule allows. That is a good check, but it does not prove the helper has every cause and effect right.

New axion bounds derived from the 100-parsec Gaia DR3 white dwarf luminosity function

Martín L. Alberino, Marcelo M. Miller Bertolami, María E. Camisassa+2 more

• High Energy Astrophysical Phenomena
• High Energy Physics - Phenomenology

AstronomerThe authors compare the white dwarf luminosity function of the 100-parsec Gaia DR3 sample with Monte Carlo population-synthesis predictions incorporating observational errors, white dwarf models with axion-induced cooling, and updated axion bremsstrahlung rates. For the brightest objects, M_Bol < 10, the chi-squared statistic is largely insensitive to the assumed stellar formation rate, usually the dominant modeling uncertainty. The analysis disfavors a sizable additional cooling contribution and yields an axion-electron coupling limit of g_ae < 1.68 × 10^-13 at 95% confidence, rather than an axion detection. Earlier studies found mildly improved fits for 0.7 × 10^-13 < g_ae < 2.1 × 10^-13; the authors attribute the difference to previous simplifying assumptions and the improved Gaia sample.

PublicHypothetical particles called axions could carry energy out of white dwarf stars, making them cool faster. The researchers compared the distribution of white dwarf brightnesses in a Gaia DR3 sample within 100 parsecs with simulated star populations, including models with extra cooling from axions and realistic measurement errors. For the brightest white dwarfs, the comparison depended little on the assumed history of star formation, a major source of uncertainty. The analysis disfavors a large extra cooling effect and places a 95% confidence upper limit of 1.68 × 10^-13 on the strength of the axion-electron interaction; it does not detect axions. Unlike some earlier studies, it does not favor sizable extra cooling. The authors interpret the difference as arising from better observations and fewer simplifying modeling assumptions.

Young explorerWhite dwarf stars are hot stars that are cooling down. Scientists wondered if tiny particles called axions, which we do not know exist, might help them lose heat faster. They compared how bright real white dwarfs are with computer-made groups of stars, some with extra cooling from axions. The comparison did not favor lots of extra cooling. It helped scientists set a limit on how strongly axions could interact with tiny parts of matter called electrons, but it did not show that axions are real.

Accretion Rates and Thermohaline Convection in Polluted White Dwarfs

J. R. Fuentes, Matias Castro-Tapia, Jim Fuller+1 more

• Earth and Planetary Astrophysics
• Fluid Dynamics

AstronomerThe authors develop a time-dependent model of thermohaline mixing in polluted white dwarfs, treating transport as a propagating front coupled to surface heavy-element abundance rather than as enhanced diffusion. Hydrodynamical simulations support a composition gradient slightly above marginal thermohaline stability. Analytic solutions predict that mixed-layer depth h and surface abundance X_surf both initially scale as t^(1/2), transitioning to h ∝ t^(4/27) and X_surf ∝ t^(10/27). Without gravitational settling, the front does not reach steady state; including settling yields an equilibrium surface abundance proportional to the accretion rate raised to 30/43. For G 29–38, the model reproduces the observed heavy-element abundance with accretion rates of approximately 1–2 × 10^10 g/s, comparable to previous stellar-evolution calculations but about an order of magnitude above the X-ray estimate. The authors suggest partially suppressed boundary-layer X-ray luminosity as a possible explanation, not an established result. They also provide a prescription for inferring accretion rates from surface abundances and stellar parameters.

PublicHeavy elements in the atmospheres of polluted white dwarfs offer clues to the makeup of disrupted planetary material. Reading those clues requires understanding how incoming debris mixes into the star. This study develops a model in which the mixing advances inward as a moving front, supported by fluid simulations. The model predicts how the mixing depth and surface abundance change over time; including the gravitational sinking of heavy elements allows the surface abundance to reach equilibrium. For the white dwarf G 29–38, matching the observed abundance requires about 10–20 billion grams of incoming material per second. That agrees with earlier stellar models but is roughly ten times the estimate from X-rays. The authors suggest that the accreting region might emit less X-ray light than expected, but this explanation remains uncertain. Their model also offers a way to estimate debris arrival rates for other polluted white dwarfs.

Young explorerBits of broken planets can fall onto a small star called a white dwarf. The bits mix into the star, so scientists need to understand that mixing to learn what the planets were made of. The researchers made a computer model in which the mixed part grows deeper over time. For one star, their model needs much more falling material than an estimate from its X-ray light suggests. Maybe the falling material makes less X-ray light than expected, but the scientists do not yet know.

High-Resolution Modelling of Coronae and Winds in Solar-type Stars with Varying Rotation Rates II. Stellar Winds

Yue-Hong Chen, Julián D. Alvarado-Gómez, Xin Cheng+6 more

AstronomerObservations suggest a link between steady-wind mass loss and coronal X-ray activity, but the two primarily probe large-scale open and small-scale closed magnetic fields, respectively. Using SWMF–AWSoM with convective dynamo-generated magnetic maps and solar magnetograms, the authors model Alfvén-wave-heated winds for four solar-type stars and the Sun, spanning rotation rates of 1.0–23.3 times solar and field strengths of 6.0–1200 G. Faster rotation in these models produces more tightly wound spirals, larger Alfvén surfaces, higher terminal wind speeds, and harsher wind-pressure environments for exoplanets. Estimated mass- and angular-momentum-loss rates differ systematically from Zeeman-Doppler Imaging-based predictions. Building on the X-ray-corona modelling in Paper I, the authors report a self-consistent model relation in which mass-loss rate scales with surface X-ray flux with a power-law index of approximately 0.67. The effective Alfvénic lever arm scales with open-flux magnetisation with an index of approximately 0.35. Modelled wind pressures at several super-Earth orbits provide inputs for habitable-zone space-weather assessments, rather than direct measurements of planetary conditions.

PublicObservations hint that low-mass stars with stronger X-ray activity also lose mass differently through their steady winds, but interpreting the link is difficult: winds mainly follow magnetic fields that extend outward, while X-rays trace heating in smaller magnetic loops. The researchers simulated winds from four Sun-like stars and the Sun. In their models, faster-spinning stars produce faster winds, more tightly wound magnetic spirals, and greater wind pressure on orbiting planets. Combining these calculations with their earlier modelling of X-ray-emitting stellar atmospheres, they find that wind mass loss increases with surface X-ray output according to a power law with an exponent of about 0.67. They also estimate how winds remove stellar angular momentum and the wind pressures at several super-Earth orbits. These are modelling results, not direct measurements of those winds or evidence that the planets are habitable; they offer a physical basis for assessing space weather around other stars.

Young explorerStars like our Sun blow winds into space. They also have magnetic fields: some stretch far out, while others make little loops where hot gas gives off X-rays. Scientists made computer models of the Sun and four similar stars to explore how these things fit together. In the models, stars that spin faster blow faster winds that push harder on nearby planets. The models also link brighter X-rays with more material blowing away. These are computer predictions, not winds the scientists directly measured, and they do not tell us whether those planets can support life.

The variable mass-loss in low-mass red giant stars: Chromospheric motion across stellar evolution in 47 Tuc

Ian Baeza, L. Monaco, H. Frelijj+8 more

• Astrophysics of Galaxies

AstronomerTemporal FLAMES/GIRAFFE spectroscopy of red giants in NGC 104 (47 Tuc) uses Hα to characterize chromospheric variability relevant to poorly understood mass loss. At separations of about four days and longer, stars with log(L/L☉) ≳ 2.4 show Hα variations whose average magnitude and range increase with luminosity, alongside systematic core blueshifts indicative of outflows and deeper cores indicating greater chromospheric optical depth. Detectable profile variability has a characteristic timescale of approximately one day, with a flat luminosity dependence. Shorter-timescale variations remain consistent with statistical uncertainties, although a possible increase toward dimmer stars is reported. The trends correlate similarly with luminosity and effective temperature; no additional correlation with cluster sub-populations or significant AGB–RGB differences is found. Outflow trends resemble previous observations spanning a wide metallicity range. The physical interpretation remains open: changing Hα sensitivity to winds, an atmospheric transition associated with heating efficiency, or continued chromospheric expansion with geometrically dominated Hα formation could explain the observations.

PublicRepeated observations of red giant stars in the cluster 47 Tuc reveal changes in their chromospheres, atmospheric regions thought to help drive stellar mass loss. The researchers tracked H-alpha, a spectral feature produced by hydrogen, and found that changes typically become detectable over about a day. Across intervals of roughly four days or more, brighter giants above a luminosity threshold generally showed larger and more varied changes. Their spectra also showed signs of outward-moving gas and greater chromospheric opacity. Shorter-term changes were not clearly distinguishable from statistical uncertainty. These observations do not establish what drives the atmospheric changes or mass loss: the researchers discuss several possibilities, including changes in atmospheric heating, expansion, or how sensitively H-alpha traces stellar winds.

Young explorerBig, old stars can lose some of their gas into space. Scientists watched light from stars in a group called 47 Tuc to learn about their changing outer layers. They could usually spot changes after about a day. Over several days, brighter stars tended to show bigger changes, and their light gave clues that gas was moving outward. Scientists still do not know exactly why this happens.

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

AstronomerThe authors report WD J132800.85-145019.95, a white-dwarf gas-disc system with quadruple-peaked emission lines, unlike the double-peaked profiles of the 21 previously known gas discs. They 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, with sizes ranging from a few kilometres to Pluto-sized, produce this structure; these bodies are not reported as directly detected. Gas production in white-dwarf debris discs remains debated, although it has been linked to an embedded surviving planetesimal in at least one other system. The stable two-disc configuration challenges current models of debris-disc formation and evolution.

PublicAstronomers have discovered an unusual arrangement of gas around the white dwarf WD J132800.85-145019.95, the remnant of a star. Previously known gas discs around white dwarfs show two peaks in their emitted spectral lines; this system shows four. The researchers attribute those four peaks to two separate gas rings. They suggest that two surviving planetary bodies, potentially ranging from a few kilometres across to the size of Pluto, could explain the structure, but they have not reported directly detecting those bodies. How such discs produce gas remains uncertain, and this stable pair of rings poses a challenge for existing explanations of how planetary debris evolves around white dwarfs.

Young explorerScientists found something unusual around a leftover star called a white dwarf: its light shows signs of two rings of gas. They think two rocky objects might help explain the rings, but they have not seen those objects directly. The rings give scientists a new puzzle about what happens to planets and their broken pieces after a star grows old.

Nine new eclipsing accreting ultracompact white dwarf binaries from the Zwicky Transient Facility

J. van Roestel, M. J. Green, T. L. S. Wong+21 more

AstronomerA box least-squares search of ZTF light curves for Gaia-selected candidates and ZTF-selected dwarf novae yielded nine new eclipsing accreting ultracompact white dwarf binaries, increasing the published sample from 21 to 30. The study also re-analyses four systems reported by Khalil et al. (2024). 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; Keck/LRIS identification spectra were obtained for nine systems. Ten systems are consistent with classical AM CVn binaries, 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 distinction; a white dwarf–brown dwarf origin is suggested, not established. Future high-speed eclipse modelling is intended to provide essentially stellar-model-independent component masses and radii, including for the three hydrogen-rich systems relevant to testing the evolved cataclysmic-variable formation channel; those measurements are not presented here.

PublicAstronomers report nine newly discovered eclipsing systems in which a white dwarf gains material from a closely orbiting companion, raising the published total of such ultracompact systems from 21 to 30. They also revisit four previously reported systems. All 13 show eclipses in Zwicky Transient Facility brightness records and complete an orbit every 26 to 65 minutes. Most appear consistent with a hydrogen-free, helium-transferring class called AM CVn binaries, while two are likely members of a related class called helium cataclysmic variables. One unusual system, ZTF J2116+2446, shows hydrogen but no detected helium in its spectrum; the researchers suggest it may have developed from a white dwarf paired with a brown dwarf. Because these systems eclipse, future rapid brightness measurements can reveal the stars’ masses and sizes with little dependence on stellar models, helping test how these close pairs formed. Those measurements remain future work.

Young explorerSome stars travel in very close pairs, with one small, dense star called a white dwarf taking material from its partner. Astronomers found nine more pairs that briefly get dimmer when one passes in front of the other. They also looked again at four pairs found before. Each pair goes around in just 26 to 65 minutes! Watching these dips more closely could help scientists work out how heavy and how big the stars are, and learn how the pairs came to be. That part is still to come.

First-principles calculations of far-wing absorption in He-broadened CO₂ infrared spectra

Ha Tran, Emile Ducreux

• Instrumentation and Methods for Astrophysics

AstronomerThis theoretical and modeling study predicts the far-wing absorption of He-broadened CO2 across 200–1000 K for exoplanet opacity calculations. Requantized classical molecular dynamics predictions for the 4.3 micrometer band agree closely with available room-temperature experimental data. The authors then use predictions and measurements to parameterize an impact energy-corrected sudden model, reporting accurate reproduction of far-wing absorption in several infrared regions over the modeled temperature range. They derive temperature-dependent chi-factor corrections to represent the sub-Lorentzian far wings of major CO2 infrared bands. Experimental agreement is explicitly established at room temperature, not throughout the full temperature range. Existing JWST detections of the 4.3 micrometer CO2 band motivate this work; the study does not report new exoplanet observations.

PublicUnderstanding a planet’s atmosphere requires knowing how its gases absorb light. This study models how helium affects carbon dioxide absorption, including the weaker absorption far from the centers of its main infrared bands. Computer simulations agree closely with available laboratory measurements at room temperature. The researchers use simulations and measurements to build a model spanning 200–1000 K and derive temperature-dependent corrections for calculating atmospheric absorption. These corrections describe weaker far-wing absorption than a standard Lorentzian profile would predict. The work could support interpretation of exoplanet spectra, including the carbon dioxide feature already seen by JWST, but it does not report new planet observations or experimental tests across the entire temperature range.

Young explorerScientists study the light that gases soak up to learn about faraway planets. Here, they used computers to work out how helium changes the light absorbed by carbon dioxide. Their calculations closely matched laboratory tests at room temperature. They also made predictions for colder and hotter gases to help scientists understand planet atmospheres. They did not observe any new planets in this study.

HD 210058 b and BD+37 4838 b: A precessing eccentric hot Jupiter and a misaligned substellar companion around two A-type stars

Z. Balkóová, J. Žák, M. Skarka+8 more

AstronomerUsing TESS photometry and HARPS-N transit spectroscopy, the authors modeled Doppler shadows to measure sky-projected spin-orbit angles for two companions to rapidly rotating stars. They confirm HD 210058b (TOI-1355b) as a 10-Jupiter-mass hot Jupiter on a slightly misaligned orbit, with lambda = -32 degrees (+4/-6). Archival photometry shows changing inclination and impact parameter, interpreted as nodal precession with an approximately 860-year period; this interpretation predicts only about six more years of observable transits. BD+37 4838b (TOI-1414b) orbits a hybrid gamma Doradus–delta Scuti pulsator and has lambda = 56.9 degrees (+1.4/-2.3). Its mass could not be reliably recovered: the reported upper limit of approximately 24.3 Jupiter masses establishes its substellar nature but leaves its planetary classification unresolved. These angles describe projected geometry, not the full three-dimensional spin-orbit alignment.

PublicThe researchers studied two companions passing in front of fast-spinning stars, using brightness measurements and changes in the stars' spectra to work out how the companions' orbits line up with their stars' rotation as seen from Earth. They confirmed that HD 210058b is a hot giant planet with about ten times Jupiter's mass, following a somewhat tilted orbit. Its changing transit path suggests that the orbit slowly swivels, with an estimated cycle of 860 years. Under that interpretation, its transits should remain visible for only about six more years. The other companion, BD+37 4838b, also follows a tilted orbit. Its mass remains uncertain: the researchers report only an upper limit of about 24.3 Jupiter masses. They establish that it is substellar, but cannot yet settle whether it is a planet.

Young explorerStars spin, and planets travel around them. Those motions do not always line up neatly. Scientists watched two objects pass in front of spinning stars and found that their paths look tilted. One object is definitely a big, hot planet. The other is too small to be a star, but the scientists still do not know whether it is a planet. The big planet's path also seems to be slowly turning. If that explanation is right, in about six years it will stop passing in front of its star from our point of view, even though it will still be going around the star.

Gravitational Capture of Large Interstellar Planetesimals by Collapsing Prestellar Cores

Richard Anderson, Kedron Silsbee

• Solar and Stellar Astrophysics

AstronomerThis theoretical study uses one-dimensional prestellar-core collapse models to estimate the volume from which a changing gravitational potential can capture free-floating planetesimals. Combining these calculations with assumed planetesimal size distributions and velocity dispersions, the authors estimate the largest typically captured body and total captured solid mass for populations originating in either the stellar birth cluster or the Galaxy. Predictions depend strongly on collapse details: the largest captured bodies have diameters of 2.8–6.4 km for the Galactic population and 70–1200 km for the modeled birth-cluster environment, with assumed velocity dispersions spanning 0.7–8.5 km/s. Total captured solid mass does not exceed 0.07 Earth masses in any modeled case. The authors argue that this mass is probably insignificant overall, but propose that the largest captured bodies could grow through disk-pebble accretion, potentially accelerating planet formation or enabling it where local planetesimal formation is difficult. These are model predictions and proposed implications, not observed captures or demonstrated planet growth.

PublicCould a forming star capture wandering rocky bodies and use them as seeds for planets? This study explores that possibility with simplified models of a collapsing cloud. The calculations predict that the cloud’s changing gravity can capture planetesimals, with the outcome strongly dependent on how the collapse proceeds and on the assumed population of wandering objects. Bodies from the star’s birth cluster could provide much larger seeds than those from the wider Galaxy. In every modeled case, the total captured material amounts to no more than 0.07 times Earth’s mass. The authors suggest that, although this adds little material overall, the largest captured bodies might grow into planets by collecting pebbles in the surrounding disk. Such growth could help planet formation, but the study does not establish that it actually happens.

Young explorerA star begins inside a cloud that squeezes together. Scientists used computer models to explore whether its changing gravity could catch wandering space rocks. Their models suggest it could. The biggest caught rocks might collect little pebbles and grow into planets, but the scientists have not shown that this really happens.

Two Isolated Microlensing Events Near the Upper Shore of Einstein Desert

Qiyue Qian, Weicheng Zang, Yoon-Hyun Ryu+67 more

• Solar and Stellar Astrophysics

AstronomerThe study reports observations and analyses of two microlensing events possibly produced by isolated giant planets or brown dwarfs near the upper boundary of the Einstein desert, a deficit at angular Einstein radii of 9–26 microarcseconds. MOA-2021-BLG-145 has an angular Einstein radius of 23.1 ± 2.0 microarcseconds, just inside the interval, while KMT-2026-BLG-0357 has 36.5 ± 3.7 microarcseconds, above it. Subsequent detections within the originally empty interval mean that its detailed structure requires a larger sample. Bound planetary events show no corresponding deficit, suggesting, but not establishing, a connection to the formation or evolution of isolated objects. Some free-floating planets may lie above the desert; direct lens-mass measurements are needed for a fuller understanding of that population.

PublicAstronomers have found relatively few isolated objects that bend a background star’s light on a particular angular scale, a gap called the Einstein desert. This study analyzes two microlensing events—temporary magnifications caused by gravity bending light—that may be due to isolated giant planets or brown dwarfs. One falls just inside the gap’s upper edge, and the other lies above it. The gap was originally empty, but later detections show it is not completely barren, and more events are needed to map it. Planets bound to stars show no matching gap, suggesting that the difference could reflect how isolated objects form or evolve. The objects’ identities remain uncertain, and direct mass measurements are needed to better understand the free-floating planet population.

Young explorerAn object in space can bend light from a star behind it and make the star look brighter for a little while. Scientists studied two times this happened. The objects doing the bending might be big planets traveling alone or objects called brown dwarfs, but scientists are not sure. One event is near the edge of a range where scientists have seen very few events, and the other is outside that range. This quiet patch is not completely empty. Scientists need to find more events and measure the objects’ masses to understand it better.

Cometary dust activity as a proxy for refractory organic material release

Serhii Borysenko

AstronomerThe study assesses Afρ as a comparative, first-order proxy for refractory-organic release using published photometry of 27 active small bodies spanning several dynamical classes. Representative near-perihelion, phase-corrected A(0)fρ values range from a few centimetres to approximately 10^4 cm, with substantial within-class dispersion indicating that orbital classification alone does not determine dust activity. Direct dust-composition measurements, including the high refractory-organic fraction measured for 67P/Churyumov-Gerasimenko, support interpreting dust activity as an indirect indicator of potential organic-material release. The proposed proxy is not a direct measurement of organic release: uncertainties in grain-size distribution, density, porosity, velocity, and optical properties preclude a universal conversion from Afρ to dust mass-loss rate.

PublicDust from comets can carry carbon-rich organic material that resists vaporization. This study brings together published observations of 27 active small bodies to ask whether a standard measure of dust activity, called Afρ, could help compare their potential release of that material. The reported dust-activity values span more than a thousandfold, and objects in the same orbital group can differ greatly. Measurements of comet dust composition support the idea that dust activity could be an indirect clue to organic-material release, but the study proposes this use rather than establishing a direct measurement. Because dust grains differ in size, density, structure, speed, and how they interact with light, there is no universal way to turn Afρ into the mass of dust released per unit time.

Young explorerComets can let out dust that carries carbon-rich stuff. Researchers looked at earlier observations of 27 small space objects and found that some had much more dust activity than others. Even objects with similar paths around the Sun could be very different. The researchers suggest that a dust-activity number might help compare how much carbon-rich stuff the objects could let out. But it cannot tell us exactly how much, because dust grains can be different sizes, move at different speeds, and reflect light differently.

exoALMA XXV: A Statistical Analysis of Gaseous Substructure in Low-Inclination Disks

Richard Teague, Sean M. Andrews, Jaehan Bae+15 more

AstronomerSecond-order structure functions of velocity and temperature perturbations in four low-inclination exoALMA disks reveal correlated structure relative to data-derived, noise-only nulls. Radial correlation lengths are beam-limited in all four, excluding non-axisymmetric structure on radial scales larger than approximately 1.5 pressure scale heights. Three disks have resolved azimuthal elongation by factors of 1.6–2.3, consistent with small-scale perturbations sheared by Keplerian rotation. The authors introduce a modal power spectrum and winding contrast to quantify azimuthal periodicity and radial phase variation without tracing spiral crests. Three disks show significantly wound velocity residuals, but only MWC 758 has disk-wide coherent winding shared by the temperature field. Its trailing m=1 temperature pattern is consistent with illumination of a warp; its small-scale, sheared velocity structure could redistribute angular momentum. These interpretations are not established mechanisms. The statistics extend quantitative winding measurements to flocculent structure lacking parameterizable spiral arms.

PublicThe researchers measured patterns in gas motion and temperature in four planet-forming disks, comparing them with noise-only tests built from the observations. All four contain correlated patterns. Their radial extent is unresolved, with the observations ruling out non-axisymmetric structure broader than about 1.5 local pressure scale heights in that direction. In three disks, the patterns are resolved along the direction around the star and are elongated, as expected if orbital rotation stretches small disturbances. Two new statistical measures also reveal winding in the gas-motion patterns of three disks without needing to trace a distinct spiral arm. Only MWC 758 shows coherent winding across the disk in both motion and temperature. Its temperature pattern could reflect illumination of a warped disk, while its small-scale gas motions might redistribute angular momentum; neither explanation is confirmed.

Young explorerScientists studied four disks of gas around stars where planets can form. They found patterns in how the gas moves and how warm it is, not just random fuzz in the pictures. In three disks, some patterns look stretched around the star, as moving gas might stretch them. The scientists also found a way to measure winding patterns even when there is no clear spiral to trace. In one disk, called MWC 758, the warmth and motion both make winding patterns across the disk. Light shining on a bent part of that disk might explain the warmth pattern, but the scientists are not sure.

Roughness-Dependent Radiative Effects on Dimorphos within Hera's Reach

Yixuan Wu, Kin Thong Lee, Yifei Jiao+3 more

AstronomerThis modeling study couples a rough-surface binary thermophysical model to planar spin-orbit dynamics to estimate radiative migration in the post-DART Didymos-Dimorphos system. For two Dimorphos shape models in synchronous principal-axis rotation, roughness reduces the radiative contribution to the mean orbital contraction rate during Hera's six-month investigation by 28–39% relative to smooth surfaces. With roughness included, planar-libration calculations predict centimeter-scale radiation-driven contraction and a mean orbital-phase advance of 40–85 degrees from DART to Hera's arrival. The predicted radiative phase advance during Hera's investigation is 0.7–2.0 degrees, potentially detectable against a projected 0.05-degree formal orbital-longitude uncertainty. In the modeled tumbling state, net radiative contraction is much smaller, and roughness reduces its rate by 16–18%. These are model predictions, not reported measurements. Combining refined roughness modeling with Hera's orbital, rotational, thermal, and shape observations could help constrain post-impact dissipation and rubble-pile mechanical properties, and improve binary YORP estimates used to interpret tidal response and binary evolution.

PublicAfter DART struck Dimorphos, the small asteroid's orbit around Didymos continues to evolve under several influences, including recoil from emitted radiation. This study models how uneven surfaces change that radiation-driven motion. For two modeled shapes rotating in step with their orbit, roughness reduces the predicted radiation-driven orbital contraction rate by 28–39% during Hera's planned six-month investigation. Even with roughness, the calculations predict centimeter-scale orbital shrinkage that makes Dimorphos move faster around its orbit. During Hera's investigation, the resulting shift in orbital position could be detectable given the mission's projected measurement precision, though this is not an observed result or a guaranteed detection. A modeled tumbling asteroid shows a much smaller net radiation-driven contraction. Better surface modeling, combined with Hera's measurements, could help researchers separate the processes changing the orbit and learn about the asteroids' internal mechanical properties, with relevance to planetary defense.

Young explorerDimorphos is a little space rock that goes around another space rock. After DART hit it, scientists used a computer model to explore how its path might keep changing. Radiation leaving the rock can give it a tiny push. In the model, a bumpy surface makes that push shrink the orbit less than a smooth surface does. A tumbling rock behaves differently, too. These are predictions, not changes scientists have measured in this study. The Hera mission might be able to spot the tiny change and help scientists learn what these rocks are like inside.

Mean-element Parareal: Parallel-in-Time Integration of the Solar System

Michael Hippke

• Instrumentation and Methods for Astrophysics

AstronomerThe authors introduce mean-element parareal (MEP), a parallel-in-time method, and report measured acceleration of a single 5 Gyr Solar System integration with eight planets and general relativity, at the same accuracy as the serial integrator. With a latency-optimized C kernel, the serial run takes 5.8 h; MEP takes 52 min on 64 cores or 1.8 h on 16 cores, corresponding to parallel speed-ups of 6.7 and 3.3, respectively. The 64-core run is 10.4 times faster than the previous 9.0 h single-core record. MEP's coarse propagator uses numerical first-order mean-element theory to remove short-period semi-major-axis oscillations, preventing their amplification into growing phase errors by Keplerian shear. The authors report that standard parareal with a coarse Wisdom–Holman integrator fails for planetary orbits because an inexpensive coarse integrator cannot resolve those oscillations. They describe this as, to their knowledge, the first measured multicore speed-up of a single long-term planetary integration; larger-scale parallelization remains a prospect.

PublicThe researchers report a faster way to simulate the Solar System's long-term motion by sharing one simulation across multiple computer cores. Such calculations have usually proceeded step by step, because tiny errors can grow and change the computed paths. Their method, called mean-element parareal, uses an approximate calculation that removes rapid orbital wiggles that would otherwise cause growing timing errors. In a simulation of eight planets that includes general relativity, it computed five billion years of motion in 52 minutes using 64 cores, compared with 5.8 hours using one core with their optimized code, while retaining the serial calculation's accuracy. This is a computing result, not an observation of the planets or a guarantee of their exact future paths. The authors say it is, to their knowledge, the first measured speed-up of this kind for a single long-term planetary simulation, and could enable greater parallel computing in the future.

Young explorerScientists made a faster way for computers to pretend how eight planets move around the Sun for a very, very long time. Usually, the computer must work out each step before starting the next. Their new trick lets many parts of the computer help with the same pretend journey, without losing accuracy compared with the step-by-step version. With 64 computer helpers, a journey covering five billion pretend years took 52 minutes to calculate. This was a computer test, not watching the real planets travel into the future.

Tracking the evolution of sub-Neptunes. II. The radius valley on gyrochronological ages

N. Greco, A.C. Lanzafame, I. Pagano+3 more

• Solar and Stellar Astrophysics

AstronomerUsing gyrochronological ages, the study examines 746 planets around 510 FGK hosts aged 0.1–4 Gyr, with a completeness-characterised reference sample of 581 planets around 404 hosts. A selection-conditioned mixture model accounting for stellar-age uncertainties infers that the intrinsic super-Earth fraction rises mainly during the first approximately 2 Gyr, with no significant evolution thereafter. An exponential approach-to-plateau model places 90% of that increase within 1.9 Gyr at 90% credibility. The radius valley is consistently resolved from approximately 1.5 Gyr onward, without significant changes in depth or width. A shift in its minimum from approximately 1.5 Earth radii before 2 Gyr to approximately 1.8 Earth radii at older ages, alongside a change in the super-Earth radius distribution, is only suggestive. These findings are consistent with atmospheric loss continuing for 1–2 Gyr in some planets. More massive cores completing envelope loss later is a possible interpretation of the tentative shift, but the data do not uniquely distinguish atmospheric-loss mechanisms.

PublicPlanets show a gap in sizes between super-Earths and sub-Neptunes, generally understood as a sign that some planets lose their atmospheres. This study explores when that gap develops, using 746 planets whose host stars have ages estimated from their rotation. After accounting for how readily planets are detected and confirmed, and for uncertainty in stellar ages, the researchers infer that the proportion of super-Earths grows mainly during the first roughly two billion years, with no significant change afterward. The size gap is consistently distinguishable from about 1.5 billion years onward, with no significant change in its width or depth. There are tentative hints that the gap moves toward larger planet sizes at older ages. The findings are consistent with some planets continuing to lose atmosphere for one to two billion years, but they do not establish which atmospheric-loss process is responsible.

Young explorerSome planets have thick blankets of air, and some have much less. Scientists studied planets around stars of different ages to look for clues about how those blankets change. They found signs that planets called super-Earths become more common during the first two billion years, but not much after that. This could mean some planets take a very long time to lose their air blankets. The scientists still cannot tell exactly how the air escapes.

Harmonic Angular Mapping Method for Binary Microlensing Grid Search

Kansuke Nunota

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerThe authors present a binary-lens microlensing grid-search algorithm that expands the angular dependence of precomputed magnification maps in Fourier modes. Observation-dependent weighted sums are contracted in Fourier space, allowing inverse FFTs to evaluate chi-squared across all trial source-trajectory angles without repeatedly processing individual observations. In tests on 200 Roman-like synthetic events, 166 events (83%) yielded fits within an absolute chi-squared difference of 1 from Levenberg–Marquardt fits initialized at the injected parameters. The FFT map scan averaged 5.05 minutes per event. For the same discrete search volume, Fourier angular evaluation was estimated to be approximately 900 times faster than conventional magnification-map sampling. These simulation tests support the method as an efficient way to find useful initial conditions for binary-lens light-curve modeling, rather than demonstrating equivalent performance on observed events.

PublicResearchers developed a faster way to search for models of binary-lens microlensing brightness changes. Their method reorganizes precomputed magnification maps using Fourier mathematics, so many possible paths can be checked together rather than repeatedly working through each observation. They tested it on 200 simulated events designed to resemble Roman observations, not on real observed events. For 166 events (83%), the fit-quality score, called chi-squared, differed by no more than 1 from a comparison fit started at the simulation's input parameters. The new scan took an average of 5.05 minutes per event. One part of the calculation was estimated to be approximately 900 times faster than the conventional approach when checking the same discrete set of possibilities. The method can provide useful starting points for more detailed modeling; the reported agreement did not hold for every simulated event.

Young explorerScientists made a quicker way for a computer to try explanations for how light changes in a space event called binary-lens microlensing. It uses a math shortcut to check lots of possible paths together. They tried it on 200 pretend events made by a computer, not real events seen in the sky. For 166 of them, or 83%, its answer had a matching score within 1 point of another method that was given the pretend event's starting settings. Each search took about 5.05 minutes on average. They estimated that the shortcut part was about 900 times faster than the usual way of checking the same choices, not that the whole job was that much faster. It helps find good starting guesses, but it did not match that closely every time.

A Century-Long Archival Search and Analysis of the Rubin Observatory-Discovered Dwarf Planet Candidate 2026 ED₁₃₈

Joseph Murtagh, Colin Orion Chandler, Mario Jurić+8 more

• Instrumentation and Methods for Astrophysics

Astronomer2026 ED138, discovered in early Rubin Observatory data, has HV = 3.11 ± 0.05 mag and an inferred diameter of 635–1590 km for assumed geometric albedos of 0.25–0.04. Archival observations span 89 years, including a marginal 1937 plate detection, and improve the long-term ephemeris fivefold. The authors predict 15 occultations of stars with G ≤ 16.5 mag in 2027–2030, six over populated land. Despite an approximately 87° change in viewing direction since 1954, plate photometry remains consistent with the present-day phase curve. Plate-by-plate fits exclude oblate shapes with c/a ≤ 0.6 for at least half of spin-axis orientations; combined with a present-day light-curve amplitude below approximately 0.11–0.15 mag, they exclude a Haumea-like Jacobi ellipsoid for approximately 90% of orientations. The proposed photometric period is tentative: 10.4 h, or approximately 20.7 h if double-peaked. Near-infrared colors indicate BR classification, with J−H = 0.60 ± 0.15, and show no evidence for Haumea-like 1.5 μm water-ice absorption, supporting non-membership in the Haumea family. z-band photometry limits Eris-like methane coverage to approximately 25% or less. Numerical integrations over ±1 Gyr show intermittent residence in Neptune’s 12:7 resonance for tens of megayears, but rarely permanent capture.

PublicA newly discovered object beyond Neptune, 2026 ED138, had been recorded unnoticed in older images because it lies far south and near the crowded plane of our galaxy. Researchers assembled observations spanning 89 years, although the earliest detection, from 1937, is marginal. Its brightness suggests it is among the largest known objects beyond Neptune, but its estimated diameter ranges from 635 to 1590 kilometres because its surface reflectivity is uncertain. The older positions improve predictions of its future location fivefold. The team predicts 15 passages in front of stars during 2027–2030, including six visible over populated land. Brightness measurements make some strongly flattened or elongated shapes unlikely, depending on the direction of its spin axis. A possible rotation period of 10.4 hours, or about 20.7 hours, remains tentative. Its colors support the conclusion that it is not part of the Haumea family. Computer simulations suggest it can temporarily share a repeating orbital pattern with Neptune for tens of millions of years, rather than usually remaining locked in that pattern permanently.

Young explorerAstronomers found a big, faraway object beyond Neptune, then spotted it in old pictures too. Those pictures help them work out where it will go. They think it will pass in front of some stars, briefly hiding them, but those events have not happened yet. They are still unsure how big it is and how fast it spins. Computer experiments suggest its trips around the Sun sometimes follow a repeating pattern with Neptune, but usually not forever.

Planet-gap-induced ice lines form observable dust rings in protoplanetary disks

Kan Chen, Tommy Chi Ho Lau, Paola Pinilla

AstronomerThis simulation study tests whether CO2 ice lines can generate dust rings when a hot planetary gap makes the disk midplane temperature non-monotonic. Radial jumps in the fragmentation threshold at two ice lines along the gap edges produce dust pileups and enhanced grain sizes. Predicted 13 μm images show clear double rings persisting over the simulated 10 Myr, while 1.3 mm images have only a factor-of-a-few ring-to-gap contrast, consistent with shallow rings in ALMA surveys but not establishing their origin. A uniform fragmentation threshold of 10 m/s instead produces a single high-contrast pressure-bump ring and reduces inward pebble flux by up to two orders of magnitude; a uniform 1 m/s threshold yields weak substructure and strong outer-disk depletion. The authors propose a multi-wavelength discriminator: ice-line rings remain at fixed radii from scattered light to millimetre wavelengths, whereas the dominant pressure-trap ring peaks farther inward at shorter wavelengths.

PublicComputer simulations explore whether boundaries where carbon dioxide freezes can create dust rings in disks around young stars, a possibility that remains debated. The models use a locally heated gap made by a planet, which can shift these freezing boundaries and create more than one. In one model, dust collects and grains grow at two boundaries near the gap edges. Predicted images show two clear rings at a wavelength of 13 micrometres throughout the simulated 10 million years, but much subtler rings at 1.3 millimetres. Those subtle rings resemble ones seen in ALMA surveys, though this does not prove they formed through freezing. Comparison models with different, spatially uniform resistance to grain fragmentation produce either one prominent ring at a pressure bump or only weak structure with substantial loss of outer-disk dust. The authors propose comparing images at different wavelengths: freezing-boundary rings should stay at the same distances from the star, while a pressure-trapped ring should appear closer in at shorter wavelengths.

Young explorerYoung stars can have big disks of dust around them. Scientists used computer models to ask whether places where carbon dioxide freezes could help dust gather into rings. In their model, a planet's gap has a warmer patch that changes where freezing happens. Dust gathers into two rings, which look clearer in some kinds of light than others. This is a computer prediction, not proof that real rings form this way. The scientists suggest looking in different kinds of light to help tell this idea apart from another way of gathering dust.

Cometary impacts an unlikely pathway towards the origins of life on Earth

Richard J. Anslow, Catriona H. McDonald, Amy Bonsor+2 more

AstronomerThis study reassesses cometary delivery of prebiotic feedstock at concentrations required for prebiotic chemistry, drawing on advances in impact simulations, comet–atmosphere interactions, and dynamical modelling of short-period comet origins and evolution. Although comets contain diverse volatile organics, modelling suggests substantial destruction during hypervelocity impacts. The authors infer that the rapid decline in Earth's cometary bombardment, combined with efficient destruction of fragile organics, made successful delivery exceedingly rare. This model-based conclusion challenges, rather than definitively rules out, a major cometary contribution to the origins of life on Earth.

PublicComets contain many organic molecules that could have supplied ingredients for the chemistry leading to life. But containing those ingredients is not the same as delivering them intact and concentrated enough to be useful. Drawing on simulations of impacts, interactions with the atmosphere, and models of comet histories, the researchers conclude that fragile molecules were efficiently destroyed and that comet impacts on Earth declined rapidly. They infer that successful delivery was exceedingly rare, challenging the idea that comet impacts were an important source of life's starting ingredients without proving they played no role.

Young explorerComets carry chemicals that might help life get started. But crashing into Earth can break many of those chemicals apart. Scientists used computer models to study whether enough could arrive safely. Their models suggest that, as comet crashes became less common, bringing enough unbroken ingredients was very rare. So comets may not have been big helpers in starting life on Earth.

Are habitable-zone TESS Objects of Interest really there? Period resolution from the full archive

Juan F. Pagés Navarrete

• Instrumentation and Methods for Astrophysics

AstronomerThe authors reanalyse 187 TOIs catalogued with P = 0 or P ≥ 200 d using public TESS data through Sector 107. Their flux-based approach weights period aliases using per-epoch transit likelihoods, transit duration and a geometric prior, while checking coherence, data edges, contamination and instrumental artefacts. It blindly recovers 12 published periods; in injection-recovery tests, it recovers 71% of periods constrained by a new transit, with no incorrect recoveries. The analysis resolves 28 periods and fixes eight more by exclusion. Of 28 duo-transit TOIs placed in the conservative habitable zone by catalogue periods, about two are expected to remain there, both giants, and none of the 12 planet-sized objects; resolved cases instead have hotter-orbit aliases. Conversely, the analysis recovers three published M-dwarf habitable-zone examples and validates four planets with new periods. These include TOI-2298 b, a 3.0-Earth-radius sub-Neptune with P = 146.58 d in a K dwarf’s conservative habitable zone, and TOI-6075 b, a 1.7-Earth-radius planet with P = 416.5 d, although 833 d remains possible. Alias-marginalised habitable-zone probabilities are released for the full sample.

PublicWhen TESS records only one or two passages of a planet across its star, the time it takes to complete an orbit can be unknown or misleading. That also makes estimates of its starlight exposure—and its habitable-zone label—unreliable. Rechecking 187 candidates, the researchers resolved 28 orbital periods and fixed eight more by ruling out alternatives. Among 28 two-transit candidates labelled as being in the conservative habitable zone, they estimate that only about two actually belong there, both giant planets. But incorrect or missing periods also conceal promising discoveries: the team validated four planets with newly determined periods, including a planet three times Earth’s radius in the conservative habitable zone of a K-type star. Another validated planet, TOI-6075 b, is 1.7 times Earth’s radius and has a likely 416.5-day orbit, though an 833-day orbit remains possible. A habitable-zone classification describes starlight exposure, not demonstrated habitability.

Young explorerA planet can make its star look a little dimmer when it passes in front. Seeing that happen only once or twice can make it hard to know how long the planet’s trip around the star takes. Scientists checked those guesses again. Many planets thought to get a just-right amount of starlight probably get too much instead. They also confirmed four planets with new orbit timings, including one in the just-right starlight zone. That does not tell us whether anything lives there.

White dwarf pollution in wide binaries: the role of planetary mass

Constanza Norambuena, Carolina Charalambous, Claudia Aguilera-Gómez

• Solar and Stellar Astrophysics

AstronomerAtmospheric pollution in white dwarfs is interpreted as accretion of rocky debris from remnant planetary systems. This study uses N-body simulations with time-dependent stellar evolution and a stellar companion to examine how planetary mass affects planetesimal survival and delivery in wide binaries. In the simulations, lower-mass planets perturb the reservoir less efficiently, preserving planetesimals and allowing delivery to persist into the cool white dwarf phase. Higher-mass planets deplete the reservoir earlier, preventing sustained late-stage pollution in the modeled systems. Planetary mass regulates the duration of rocky-material availability, while planetary location has only a minor effect. Simulated pollution is more frequent in binaries with lower inclinations and eccentricities; these findings are simulation results, not new observational measurements.

PublicRocky material in white dwarf atmospheres is interpreted as debris falling onto these stellar remnants from leftover planetary systems. The researchers used computer simulations to explore how a planet's mass affects this process when a distant companion star is also present. In their models, less massive planets disturb the supply of rocky debris more gently, leaving material available to fall onto the white dwarf even after it has cooled. More massive planets exhaust the supply earlier. A planet's location has a smaller effect than its mass, and pollution occurs more often in modeled binaries with lower orbital tilts and less elongated orbits. The study offers a simulation-based explanation for how rocky material can remain available late in a white dwarf's evolution, rather than reporting new observations.

Young explorerA white dwarf is a leftover star, and rocky bits can fall onto it. Scientists made computer models with a white dwarf, a planet, another star, and lots of rocky bits. In the models, lighter planets nudged the rocks more gently, so some rocks lasted longer and could fall onto the white dwarf after it cooled. Heavier planets used up the rock supply sooner. This is what happened in the computer models, not something the scientists watched happen in the sky.

HCN detection in the Kreutz sungrazing comet C/2026 A1 (MAPS) shortly before its disruption

Amélie Godard Palluet, Dominique Bockelée-Morvan, Nicolas Biver+5 more

AstronomerThis first millimetre-wavelength study of a Kreutz sungrazer observed C/2026 A1 (MAPS) with the IRAM 30-m telescope on April 1–3, 2026, at heliocentric distances of 0.10–0.23 au, immediately before perihelion and complete disintegration. The authors report the first HCN detection in this comet family, through the (3–2) transition at 265.886 GHz, and use non-LTE radiative-transfer modelling to derive molecular production rates. Two outbursts were observed, on April 1 and April 3. The second was estimated to release 0.4%–1.2% of the comet’s total mass, suggesting disruption had begun before entry into the Roche-limit region. Upper limits, rather than detections, were obtained for HNC, CS, H2CO, CO, OCS and CH3OH.

PublicAstronomers studied comet C/2026 A1 (MAPS) during the three days before its closest approach to the Sun and complete breakup. Such Sun-skimming comets can expose material from deep inside, offering clues to their overall chemical makeup. Using the IRAM 30-m telescope, the team detected hydrogen cyanide for the first time in a comet of the Kreutz family and tracked two bursts of activity. They estimate that the second burst, one day before the comet disintegrated, released 0.4%–1.2% of its total mass. This suggests the comet was already beginning to break apart before entering the Roche-limit region. Searches for six other molecules yielded only upper limits on their production rates, not confirmed detections.

Young explorerA comet flew very close to the Sun and broke apart. Astronomers watched it with a telescope during the three days before that happened. They found a gas called hydrogen cyanide and saw two bursts of activity. They think the second burst was a clue that the comet had started breaking apart before it fell to pieces.

The Giant Planet Mass Function Across Stellar Mass and Metallicity: Massive Stars Make Massive Planets

Judah Van Zandt, Brendan Bowler

• Solar and Stellar Astrophysics

AstronomerA hierarchical occurrence analysis of 719 FGKM stars in the California Legacy Survey combines radial velocities with Hipparcos-Gaia astrometry to constrain companion true masses, accounting for survey completeness and parameter uncertainties over 0.4–50 Jupiter masses and 0.1–10 AU. The reported giant-planet occurrence is 0.19 ± 0.02 planets per star overall, rising to 0.39 (+0.06/−0.05) for hosts above one solar mass and 0.30 (+0.04/−0.03) for hosts with [Fe/H] > 0. Evidence that the planet mass-function shape depends on stellar mass is moderate, at 2–3 sigma: higher-mass hosts favor higher characteristic planet masses. Across the full sample, occurrence declines above a few Jupiter masses; below about three Jupiter masses, either a plateau or a peak near one to two Jupiter masses remains consistent with the analysis. The brown dwarf desert begins at companion-to-host mass ratios of 0.013–0.02. Within core accretion, larger gas reservoirs around more massive stars or earlier core formation in metal-rich disks are proposed explanations, not demonstrated mechanisms.

PublicAn analysis of 719 stars finds that giant planets are more common around stars more massive than the Sun and around stars richer in elements heavier than helium. The researchers combined measurements of stellar motion to estimate companion masses and accounted for companions the survey could miss. They also found tentative evidence that more massive stars tend to host giant planets with higher characteristic masses; this trend is less firmly established than the difference in planet frequency. Overall, companions become less common above a few times Jupiter’s mass. The analysis cannot yet distinguish whether smaller giant planets occur at a roughly steady rate or are most common near one to two Jupiter masses. Larger supplies of gas, or earlier formation of planetary cores, could help explain the patterns, but those explanations have not been established.

Young explorerScientists studied 719 stars and found that some kinds of stars have giant planets more often than others. Stars heavier than our Sun may also have bigger giant planets, but that clue is not certain yet. One possible reason is that growing planets had more gas to collect. The scientists have not shown that this is why.

The Neptunian ridge through the lens of TESS

Amadeo Castro-González

AstronomerAn analysis of TESS occurrence posteriors for FGK main-sequence stars independently detects the Neptunian ridge previously identified with Kepler at orbital periods of approximately 3–6 days. For planets of approximately 5–8 Earth radii, its occurrence density exceeds that of the denser adjacent region by J = 2.05 (+0.52/−0.44), with 99.9% posterior support, equivalent to a one-sided 3.1σ. Leave-one-out cross-validation and Bayesian evidence strongly favour profiles peaking within the ridge over a single power law. A lognormal profile is preferred, but evidence for a narrower inner wing and more extended outer wing remains weak. The analysis also recovers the hot Jupiter pileup at approximately 10–16 Earth radii with a consistent contrast, while excluding an analogous sub-Neptune excess at approximately 2–4 Earth radii with 3.4σ posterior support. Possible ridge asymmetry is compatible with high-eccentricity migration, but does not establish that origin. More precise occurrence measurements are needed to determine the shape; PLATO's expected planet yield offers a prospective opportunity.

PublicTESS data independently confirm a concentration of Neptune-sized planets, roughly 5–8 times Earth's radius, that orbit their stars every 3–6 days. These planets occur about twice as densely in this orbital range as in the more populated of the neighbouring ranges, agreeing with earlier Kepler findings. The analysis also finds a similar concentration of larger, hot Jupiter planets, but rules out a comparable concentration of smaller sub-Neptunes with strong statistical support. Models with a peak describe the Neptune-sized population better than a simple steadily changing trend. There are hints that the peak drops more sharply toward shorter orbits than toward longer ones, but the evidence for this uneven shape is weak. Such a shape could fit the idea that planets arrive on very stretched orbits that tides later make more circular; it is not proof of that explanation. More precise measurements, potentially aided by PLATO's expected planet discoveries, are needed.

Young explorerTESS has helped scientists check where planets like to circle their stars. They found an extra bunch of planets bigger than Earth that go around their stars once every three to six days. Another planet survey, Kepler, had spotted this bunch before. Scientists also found a bunch of even bigger planets there, but not a matching bunch of smaller ones. They wonder whether some planets got there after travelling on very stretched-out paths. That is still an idea to test, and they need better measurements to learn more.

Sensitivity of the IceCube atmospheric muon rate to decadal trends in the effective atmospheric temperature

Tanvi Krishnan, Gabriela Barenboim, Carlos A. Argüelles

• High Energy Physics - Phenomenology
• High Energy Astrophysical Phenomena
• Atmospheric and Oceanic Physics

AstronomerThis feasibility study assesses whether IceCube atmospheric muon rates can constrain decadal trends in effective atmospheric temperature, a vertically weighted temperature most sensitive to the stratosphere. Atmospheric reanalysis and records of cosmic-ray, solar, and geomagnetic variability reproduce the measured seasonal muon-rate response; the study then tests its applicability to long-term changes with a different vertical temperature profile. Detector stability, rather than counting statistics, is the limiting requirement: an unmodeled rate drift of 1% per decade would mimic 2.8 K per decade, requiring stability of approximately 0.3% per decade. Snow-accumulation contributions can be constrained within this budget. For a 14-year record, atmospheric variability yields a one-sided 95% confidence-level statistical sensitivity of 1.6 K per decade. The approximately 0.9 K per decade cooling indicated by 2011–2025 atmospheric records would become distinguishable after approximately 30 years of measurement, given this sensitivity. This is a sensitivity assessment, not an IceCube detection of a decadal cooling trend.

PublicCould particles recorded by IceCube provide an independent way to track long-term temperature changes above Antarctica? This study investigates that possibility using muons, whose recorded rate responds to atmospheric temperature, especially in the stratosphere. Calculations using existing atmospheric and space-environment records reproduce IceCube’s measured seasonal response. Tracking changes over decades is harder: small changes in the detector’s recorded rate could look like temperature changes, so that rate must remain stable to about 0.3% per decade. A 14-year record has limited statistical sensitivity. The researchers estimate that the cooling of about 0.9 degrees per decade indicated by atmospheric records from 2011–2025 would become distinguishable after roughly 30 years of measurement, provided the required stability is achieved. They have not reported an independent IceCube measurement of that cooling.

Young explorerScientists want to know whether tiny particles counted by IceCube could help tell if the air high above Antarctica is getting cooler over many years. They can explain how the particle count changes with the seasons, but spotting a slow change is trickier. The counter must stay very steady so changes in the counter do not fool them. Other air records suggest cooling. The scientists estimate that about 30 years of careful counting could make that cooling clear, but they have not shown it with IceCube yet.

Solving the Mystery of the Electron Radiation Belt at Uranus: Leveraging Knowledge of Earth's Radiation Belts in a Re-Examination of Voyager 2 Observations

R. C. Allen, S. K. Vines, G. C. Ho

• Space Physics
• Instrumentation and Methods for Astrophysics

AstronomerVoyager 2 supplied the only direct measurements of Uranus’s radiation environment, establishing the picture of a weaker ion belt and a surprisingly intense electron belt. Recent reanalysis suggests that the flyby instead sampled atypical solar wind conditions during passage of a corotating interaction region. Comparing the Uranus observations with a similar event at Earth and expanding the flyby’s contextual interpretation, this study proposes that solar wind–magnetosphere interactions may have enhanced lower band chorus emissions capable of accelerating electrons to relativistic energies. This is a proposed explanation, not a confirmed detection of that acceleration mechanism at Uranus, and motivates further investigation with a Uranus orbiter.

PublicOur picture of radiation around Uranus comes from a single spacecraft visit: Voyager 2 found a weaker belt of charged atoms and a surprisingly intense belt of electrons. A recent reanalysis suggests that the visit happened during an unusual disturbance in the solar wind, rather than under typical conditions. By comparing those measurements with a similar event at Earth, the researchers suggest that the disturbance may have strengthened waves around Uranus that could accelerate electrons to speeds approaching the speed of light. The explanation remains uncertain, and the study highlights the need for a spacecraft to orbit Uranus and investigate further.

Young explorerVoyager 2 is the only spacecraft that has directly checked the tiny, fast-moving particles around Uranus. It found a surprising number of energetic electrons. Scientists now think it may have visited while an unusual gust from the Sun was passing by. By comparing that visit with something similar near Earth, they suggest the gust might have made waves that helped electrons go very fast. They do not know for sure, and they want a spacecraft to circle Uranus and learn more.

Jovian Polar Vortex Generation in a Shallow-Water Model with Quasi-Stochastic Convection

Ruan Yuhang, Fu Hao, Li Cheng+1 more

• Atmospheric and Oceanic Physics
• Fluid Dynamics

AstronomerThis modeling study investigates whether organized moist convection can help form and maintain gas-giant polar vortices. A polar gamma-plane shallow-water model uses a quasi-stochastic convective parameterization: localized impulsive mass sinks are more likely where local vorticity is cyclonic. Numerical experiments produce shielded cyclones and persistent vortex crystals reminiscent of Jupiter’s polar configuration. Stronger mesoscale feedback promotes vortex growth, shielding, and spectral organization; characteristic vortex scales depend on both the deformation radius and the convective parameterization. Simulated structures drift in either direction, with rates and directions not adequately described by a conventional Rossby-wave phase-speed estimate. A Biot–Savart diagnostic attributes competing drift contributions to predominantly counterclockwise advection from other vortices and clockwise advection from background vorticity outside the identified vortices. These results suggest a possible formation pathway involving convective feedback, rather than establishing how the observed planetary vortices formed.

PublicHow storms near Jupiter’s and Saturn’s poles form and persist remains uncertain. Researchers explored one possibility with a simplified computer model in which bursts representing convection occur more often in cyclonic regions. The simulations produced long-lasting groups of vortices resembling Jupiter’s polar arrangement. Stronger feedback between convection and the rotating flow encouraged vortex growth and more organized patterns. The simulated patterns could drift clockwise or counterclockwise: analysis found competing influences from neighboring vortices and the surrounding flow, which a conventional wave-speed estimate did not adequately describe. The study offers a possible explanation for these storm patterns, not proof that real planetary storms form this way.

Young explorerJupiter and Saturn have swirling storms near their poles. Scientists used a computer model to explore how these storms might grow and stay together. In the model, little bursts helped make groups of swirls that looked a bit like Jupiter’s storms. The groups could turn either way. This is a possible explanation, but it does not prove how the real storms formed.

Gaussian perturbation interpretability for regression techniques to understand retrieval black-boxes

Jools D. Clarke, Kai Hou Yip, Nikolaos Nikolaou

• Instrumentation and Methods for Astrophysics

AstronomerThe authors introduce Gaussian perturbation methodology to identify which spectral regions drive black-box atmospheric retrievals, using physical knowledge of spectral correlations to address limitations of perturbing individual wavelength bins. They compare the approaches using TauREx-III as a proxy black box on HST observations of HD 209458 b and JWST observations of HAT-P-26 b, then apply the method to a convolutional neural network retrieval of HAT-P-26 b. For gases constrained by the retrievals, Gaussian-perturbation importance agrees with expectations, including a degeneracy-induced reversal of the response at the core of HAT-P-26 b’s CO2 band. The analysis also indicates that the neural network learned this degeneracy. The method reveals spectral reliance not established by the forward-model physics alone; it does not independently establish the correctness of retrieved abundances.

PublicComputer models can estimate what gases are in distant planets’ atmospheres from their spectra, but it can be difficult to tell which parts of the light pattern drive an answer. This study introduces a way to test that reliance while accounting for connections between neighboring parts of a spectrum. The researchers demonstrate it with a physics-based retrieval tool using observations of two planets, then apply it to a neural network analyzing one of them, HAT-P-26 b. For gases the models could constrain, the important spectral regions matched expectations. The method also revealed that the neural network learned an ambiguity seen in the physics-based retrieval, which reverses the response within a carbon dioxide feature. This helps explain how the models reach their answers, rather than proving those answers are correct.

Young explorerScientists study patterns in light to work out what gases are around faraway planets. Computers can help, but they do not always show how they chose an answer. These researchers made a way to gently change connected parts of a light pattern and watch how the computer’s answer changes. They tried it with observations of two planets. The computers mostly paid attention to the parts scientists expected, and one computer learned a tricky pattern where different answers can look alike. This helps scientists check the computer’s thinking, but does not mean every answer is right.

A New Global Chemical Equilibrium Code: Refractory Element Signatures in Super-Earths and Sub-Neptunes

Simon Grimm, Marie-Luise Steinmeyer, Aaron Werlen+3 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors present an updated, open-source, CPU-based global chemical equilibrium framework for coupled metal-silicate-gas systems. A gradient-based optimizer reduces the chemical-network solution cost by more than two orders of magnitude. They apply it to a large synthetic planet population spanning masses, thermal states, volatile inventories, and bulk Mg-Si-Fe compositions, under the end-member assumption that hydrogen dissolution increases without bound with pressure. In these calculations, atmospheric mass fraction and atmospheric metal mass fraction are controlled primarily by atmosphere-magma interface temperature and water budget; accreted hydrogen fraction matters less because most hydrogen dissolves into the interior. For water-accreting planets, Mg/Si and Fe/Si strongly affect carbon partitioning among gas, silicate, and metal, generating large variations in atmospheric metal mass fraction and C/O. These are model results, not atmospheric detections, and their interpretation depends on the adopted hydrogen-dissolution assumption.

PublicA planet’s atmosphere can exchange chemicals with its molten interior, so understanding its air may require understanding its rocky material too. The researchers updated an open-source computer model of this exchange, making its chemical calculations more than 100 times less computationally costly, and tested it on a large set of simulated planets. In those simulations, the temperature where the atmosphere meets molten rock and the planet’s water supply mattered most for how much atmospheric mass remained and what fraction consisted of elements heavier than hydrogen and helium. The initial hydrogen supply mattered less because most hydrogen entered the interior. For planets that acquired water, the proportions of magnesium, silicon, and iron also changed where carbon ended up and altered atmospheric composition. These are simulation findings rather than observations, and they assume an extreme case in which hydrogen dissolution keeps increasing without limit as pressure rises.

Young explorerSome planets have melted rock under their air. The air and the melted rock can trade ingredients. Scientists made a faster computer model to explore how this might work. In their pretend planets, heat, water, and the ingredients in the rock helped decide what stayed in the air. Much of the hydrogen, one of the ingredients, went into the planet instead. This is what the computer model showed, not something the scientists saw happening on a real planet. The model also assumed that more and more hydrogen could dissolve inside as pressure grew, with no limit.

Extending dynamical mass measurements: probing GI as a possible origin of mm-dust spirals

V. Pezzotta, S. Facchini, A. F. Izquierdo+7 more

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerThe authors dynamically constrain the masses and scale radii of the disks around HD 97048 and WaOph 6 by fitting molecular-tracer rotation curves with a model incorporating thermal stratification and disk self-gravity. For HD 97048, they infer a stellar mass of 2.226 (+0.054/−0.049) solar masses, a disk mass of 0.300 (+0.055/−0.061) solar masses, and a scale radius of 172 (+24/−14) au. For WaOph 6, the corresponding values are 0.956 (±0.006) solar masses, 0.210 (+0.045/−0.038) solar masses, and 647 (+193/−155) au. They also determine gas-to-dust and disk-to-star mass ratios. The method is extended to embedded sources with absorption features, which require careful velocity-profile extraction to avoid bias. Omitting beam-smearing corrections can alter inferred disk masses by up to approximately 45%. Bootstrapping over disk geometry and two-dimensional thermal structure yields overall disk-mass uncertainties of approximately 20%. Across all dynamically weighed disks to date, those with millimeter-continuum dust spirals have systematically lower Toomre Q values, linking spiral morphology with lower gravitational stability without establishing a causal origin for the spirals.

PublicHow much material is available to make planets? This study estimates the masses of the disks around the stars HD 97048 and WaOph 6 by modeling how their gas rotates, accounting for both temperature differences within the disks and the disks’ own gravity. The inferred disk masses are about 0.30 and 0.21 times the Sun’s mass, respectively, with overall uncertainties of roughly 20%. The authors show that correcting for the blurring of gas motions within the observing beam is important: neglecting it can shift disk-mass estimates by as much as about 45%. Absorption features also require careful treatment. Comparing all disks weighed with this dynamical approach so far, they find that disks showing dust spirals tend to have lower values of a gravitational-stability indicator. That association does not by itself establish what caused the spirals.

Young explorerYoung stars can have big disks of gas and dust around them, with material that could make planets. Scientists studied two of these disks by watching how their gas moves. They used a model to work out how heavy the disks might be. Blurry views can make the answer wrong, so they had to correct for that, and their answers still have some uncertainty. They also found that disks with dusty spiral shapes tend to be less steady against the pull of gravity. That is a clue, but it does not prove why the spirals formed.

M Dwarf Singles and Multis Have Dissimilar Metallicities Indicating Different Origins

Aida Behmard, Sheila Sagear, Yuxi+3 more

• Solar and Stellar Astrophysics

AstronomerUsing a homogeneous abundance sample of FGK and M dwarfs, the authors find that M dwarfs with multiple detected transiting planets are significantly more metal-poor than those with one detected transiting planet (p = 0.00079), including when restricted to planets smaller than 4 Earth radii (p = 0.0013). The difference emerges at the late-K to M dwarf transition, and metallicity decreases with increasing detected planet multiplicity among M dwarf multis. Planets in singles also have significantly higher eccentricities and shorter orbital periods than planets in multis. The authors interpret these associations as evidence for more active dynamical histories in M dwarf singles and metallicity-dependent dynamics shaping their architectures, rather than establishing causation. Whether an analogous metallicity difference exists for FGK dwarfs remains unclear. Proposed explanations include more massive FGK disks enabling such dynamics even at low metallicity, or larger disks producing less compact multiplanet systems that are often detected as singles in transit data.

PublicAmong M dwarfs, the study finds that stars with several detected planets passing in front of them contain fewer heavy elements than stars with just one detected transiting planet. This difference remains when the sample is limited to planets smaller than four Earth radii, and stars with more detected transiting planets tend to have still lower heavy-element abundances. Planets in the single-detection systems also have more elongated orbits and shorter orbital periods. The authors suggest that heavy-element abundance influences how planetary orbits evolve, with single-detection systems experiencing more dynamical activity, but this interpretation is not a demonstrated cause. It remains unclear whether the same abundance difference holds for FGK stars. The authors propose that differences in the disks where planets form could explain why. Importantly, detecting only one transiting planet does not establish that a star has only one planet.

Young explorerAstronomers studied stars called M dwarfs by watching planets pass in front of them. Stars where they spotted several planets tended to have less of the heavy kinds of material than stars where they spotted just one. The planets spotted alone also tended to follow more stretched-out paths and take less time to go around their stars. The astronomers think those planets may have had a more jumbled history, but they are not sure. And seeing just one planet does not mean there are no others hiding from view.

Correcting stellar contamination in transmission spectroscopy with contemporaneous monitoring: Application to GJ 1214 b

Ò. Porqueras-León, M. Perger, J. C. Morales+19 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors use coordinated multi-band photometry and high-resolution spectroscopy around JWST observations of GJ 1214 b to estimate stellar contamination in transmission spectra. They compare a StarSim inversion, which infers activity parameters and propagates them into corrections, with UnSPOTTER, whose neural networks learn corrections from StarSim simulations. Both frameworks agree within uncertainties and indicate low contamination at the observed stellar rotation phase. UnSPOTTER constrains inferred corrections to approximately 10–30 ppm across the JWST wavelength range, implying, rather than directly demonstrating, residuals of similar size. For a hypothetical observation near activity maximum, the predicted contamination is strongly chromatic and would affect atmospheric retrievals. The inversion supplies interpretable parameters and surface maps; UnSPOTTER marginalises over surface-configuration degeneracies and provides tighter predictions within its validated simulation domain. Extension to other active stars for scheduling forecasts and corrections remains a potential application.

PublicUneven patches on a star can distort the light used to study a planet’s atmosphere. The researchers monitored the star hosting GJ 1214 b around JWST observations and compared two ways to estimate this distortion: fitting a stellar activity model and using neural networks trained on simulated stars. Both methods indicate that the observations took place at a favourable point in the star’s rotation, with little contamination. The neural-network method estimates corrections with uncertainties of about 10–30 parts per million, suggesting remaining errors of a similar size rather than measuring them directly. The models predict that observations near the star’s most active phase would suffer wavelength-dependent distortions that affect atmospheric interpretation. Applying the approach to other active stars is a possibility, not an established result, and the neural-network predictions are validated only within the simulations tested.

Young explorerWhen a planet passes in front of its star, scientists study the light to learn about the planet’s air. But patches on the star can confuse the clues. Scientists watched one star and used two computer methods to check. Both suggest its patches caused little trouble during these observations. The computers predict more trouble at a more active time. The team hopes these methods can help with other stars too.

Hubble Space Telescope Observations of Active Asteroid (101955) Bennu

David jewitt, Max Mutchler, Yoonyoung Kim

AstronomerOSIRIS-REx measurements established Bennu as an active asteroid, but deep, high-resolution Hubble observations at its 2023 orbit-plane crossing detected no ejected material. Near-nucleus surface-brightness profiles and the absence of a measurable particle trail yield model-dependent mass-loss limits of <0.12 kg/s and <0.006 kg/s, respectively. These limits are one to two orders of magnitude below remotely measured mass-loss rates in other active asteroids, suggesting that weak activity could escape remote detection in many or most asteroids. Using a still lower mass-loss rate estimated from OSIRIS-REx data, the authors calculate a specific rate of 1e-7 kg/km²/s. Extrapolating this to the main-belt population gives an estimated dust production of 850/sqrt(r_min) kg/s, with minimum asteroid radius r_min expressed in meters. For r_min >1 m, the inferred contribution ranges from <1% to 10% of the rate required to sustain the Zodiacal cloud in steady state; this is an extrapolation, not a measured population-wide dust output.

PublicSpacecraft measurements have shown that asteroid Bennu sometimes ejects particles, but Hubble images taken in 2023 revealed no escaping material or particle trail. The observations were timed for a viewing angle favorable for spotting a trail. Depending on the model used, the images limit Bennu’s mass loss to less than 0.12 kilograms per second near the asteroid and less than 0.006 kilograms per second from the missing trail. These limits are much lower than rates measured remotely for other active asteroids, raising the possibility that many asteroids shed material too faintly for distant telescopes to detect. The researchers also extrapolated a still lower rate estimated from spacecraft data to the entire main asteroid belt. Depending on the smallest asteroid size included, their estimate for minimum radii greater than one meter amounts to less than 1% to 10% of the dust supply needed to maintain the Zodiacal cloud. That estimate is not a direct measurement of dust production across the belt.

Young explorerBennu is a space rock that sometimes tosses out tiny bits, as a visiting spacecraft discovered. Later, scientists looked with the Hubble telescope but could not see any bits or a trail. That does not mean Bennu never tosses anything out: there might be too little to see from far away. The scientists also used a spacecraft-based estimate to work out how much dust lots of asteroids might make. Their calculation suggests these asteroids could supply a small part of the dust needed to keep a big dust cloud in our solar system going, but they did not watch all those asteroids doing it.

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 magnetospheric truncation radius of a protoplanetary disk accreting onto its host star. The innermost planet develops no persistent bound structure: its high speed relative to the magnetosphere reduces its effective Bondi radius below its physical size. The outermost planet forms a stable, coplanar circumplanetary disk (CPD), with nearly Keplerian rotational support inside approximately 0.25 Hill radii. High-latitude inflow and midplane decretion drive meridional circulation and recycling; Hill-sphere inflow is comparable to previous Hill-based hydrodynamic estimates. Near the truncation radius, the middle planet forms a persistent polar CPD with its angular-momentum vector parallel to the surrounding disk midplane. The authors identify CPD formation conditions using effective Bondi radius and thermal-mass criteria. Estimated planetary inflow rates imply mass-doubling times of at least roughly 10 Myr because of low disk surface density, suggesting limited late-stage growth before disk dispersal. These are simulation findings and inferred growth constraints, not observations.

PublicComputer simulations explore whether massive young planets can hold disks of gas around themselves near a star whose magnetic field disrupts the inner part of its surrounding gas disk. The researchers model planets of about 10 Jupiter masses at three distances. The outermost planet develops a stable gas disk aligned with the larger disk, while the middle planet, near the magnetic boundary, develops a persistent disk oriented at right angles to it. The innermost planet retains no lasting bound gas structure because it moves too quickly relative to the magnetically controlled gas for its gravity to hold gas effectively. Gas continually enters and leaves the outer planet's disk rather than simply collecting there. Estimated inflow rates suggest that these planets would need at least about 10 million years to double their mass in the sparse gas, so the authors infer that little additional growth may occur before the surrounding disk disperses. These conclusions come from simulations, not direct observations.

Young explorerScientists used a computer to imagine three big, young planets near a star, where the star's magnetism moves gas around. In the model, the farthest planet got a flat gas disk around it. The middle planet got a disk tipped sideways. The closest planet moved too fast through the gas to keep a lasting gas disk. Gas flowed in and out of the farthest planet's disk. The scientists think these planets might 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.

Internal heating in rapidly rotating convection is not a shortcut to geostrophic turbulence

Justin A. Nicoski, Tobias G. Oliver, Stefano Maffei+1 more

• Fluid Dynamics
• Solar and Stellar Astrophysics

AstronomerUsing an asymptotically reduced quasi-geostrophic model, formally valid as Ek approaches zero and retaining Pr as an independent parameter, the authors test whether internal heating provides access to diffusion-free geostrophic-turbulence scalings at modest forcing. Their simulations find no shortcut: Nusselt and Reynolds numbers approach the predictions no more closely than with boundary heating, the predicted Pr^(-1/2) collapse fails over the surveyed range, and the prefactor depends on the heating profile. Their no-slip/stress-free cases track the radiatively driven simulations of Hadjerci and colleagues case by case. However, those earlier simulations cover only a narrow forcing interval near the maximum compensated Nusselt number within their GT criterion. Over the reduced model’s wider range, this quantity rises to a maximum and then drops by more than an order of magnitude, despite continued rotational constraint. The authors therefore argue that bulk transport scalings are incomplete GT diagnostics, while saturation of the interior mean temperature gradient and vertical velocity kurtosis remain reliable indicators.

PublicHeat generated inside planets and stars can drive turbulent motion. Researchers have proposed that internal heating might also make it easier to reach a predicted regime of turbulence strongly influenced by rotation. This study tests that proposal with a simplified mathematical model designed for a limiting case of strong rotational influence, rather than observations of planets or stars. The simulations find no such shortcut: heat transport and flow speeds do not match the predicted scaling laws any better than when heating comes from the boundaries. The model reproduces earlier simulations over their limited range, but a wider exploration reveals that an adjusted measure of heat transport rises and then falls sharply even while rotation continues to constrain the flow. The authors argue that heat transport alone cannot reliably identify the regime; measures of interior temperature variation and the distribution of vertical speeds provide better clues.

Young explorerHeat inside a planet or star can make its material swirl. Scientists used a computer model to ask whether heating from inside makes a special kind of spinning swirl easier to reach than heating at the edges. In their model, it did not. They also found that measuring how much heat moves is not enough to tell what kind of swirling is happening.

Contrastive Astromer: Two-Stage Contrastive Representation Learning for Astronomical Light Curve Classification

Justin Minggan Wei, Pavlos Protopapas, Guillermo Cabrera-Vives

• Computer Vision and Pattern Recognition

AstronomerContrastive Astromer adapts ASTROMER 2 light-curve representations for classification without changing the encoder architecture. Unsupervised contrastive training on single-band MACHO light curves aligns augmented views of each object; subsequent supervised contrastive training on a separate labeled Alcock sample, with an auxiliary classification loss, strengthens class discrimination. Evaluation freezes the encoder and trains a separate classifier. On 600 held-out objects, macro-F1 is 0.7943 with 500 downstream training examples per class, exceeding the authors’ reproduction of the ASTROMER 2 finetune-and-classify pipeline by 5.10 percentage points. With 20 and 100 examples per class, macro-F1 is 0.7078 and 0.7704, respectively, also above that baseline. Embedding analyses indicate improved local class consistency and global separation after supervised adaptation. These are classification results on the evaluated samples; the smaller downstream training budgets do not eliminate the labeled data used during adaptation.

PublicAstronomical surveys record many light curves—measurements of how objects’ brightness changes over time—but relatively few have reliable category labels. The researchers introduce Contrastive Astromer, which first learns to associate altered versions of the same object’s light curve, then uses a separate labeled sample to better distinguish categories. They keep the resulting representation model fixed and train a separate classifier. In a test of 600 objects, the classifier scored 0.7943 on macro-F1, a measure of classification performance, using 500 training examples per category. That was 5.10 percentage points above the researchers’ reproduction of an existing ASTROMER 2 workflow. It also outperformed that comparison with 20 or 100 classifier-training examples per category, though the earlier adaptation stage still used a separate labeled sample. Analyses suggest the method organizes light curves into more clearly separated categories.

Young explorerThings in space can get brighter and dimmer. Scientists taught a computer to sort patterns of those changes into groups. First, it practiced noticing that slightly changed versions of one pattern belonged together. Then it learned from examples that already had group names. When tested on 600 objects, it sorted them better than the older computer method the scientists used for comparison. It also did better when the final sorting lesson had fewer examples, but an earlier lesson still needed examples with names.

Wide-field search for submicrosecond optical and gamma transients as manifestation of primordial black holes evaporation with the TAIGA-HiSCORE Cherenkov array

I.I. Astapov, G.M. Beskin, P.A. Bezyazykov+71 more

• High Energy Astrophysical Phenomena
• General Relativity and Quantum Cosmology

AstronomerThe study processes two additional seasons (2022–2024) of TAIGA-HiSCORE searches for rare submicrosecond optical transients and develops a search for tightly clustered gamma-ray events above 100 TeV. The possible production of both optical pulses and gamma-ray flashes by evaporating relic black holes motivates this two-channel search within one instrument; it is not a detection of black hole evaporation. No narrow gamma-ray groups were found in search windows of 1000, 100, and 6 microseconds, yielding a reported event-rate upper limit of 10^-3 sr^-1 h^-1. The abstract also reports an updated optical-transient rate limit of 5 × 10^-4 sr^-1 h^-1 at a quoted flux of 10^-4 erg s^-1 cm^-2.

PublicResearchers used the TAIGA-HiSCORE array to search for extremely brief flashes of visible light and tightly grouped bursts of very energetic gamma rays. The paper adds two observing seasons, covering 2022–2024, to earlier optical searches and develops the gamma-ray search. Evaporating ancient black holes might produce both kinds of signal, making them a possible target rather than an established explanation. No tightly grouped gamma-ray bursts were detected, so the researchers set an upper limit on how often such events could occur. They also updated the limit on the rate of very brief optical flashes. These limits do not establish that black hole evaporation occurred.

Young explorerScientists used a special detector to look for tiny, quick flashes in the sky. Very old black holes might make flashes like these as they disappear, but that is only a possibility. The scientists did not find the bunches of high-energy flashes they searched for. Their search helps put limits on how often such flashes could happen.

Shear Mapping in Python (SMPy): Modular, Extensible, and Accessible Dark Matter Mapping

Georgios N. Vassilakis, Jacqueline E. McCleary, Maya Amit+1 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe abstract presents Shear Mapping in Python (SMPy), a standardized, documented, open-source package for reconstructing convergence maps from weak-lensing galaxy shear catalogs. Convergence is the projected surface mass density normalized by the lens-source critical surface density, so these maps trace total matter rather than dark matter alone. SMPy implements Kaiser-Squires inversion, aperture mass mapping, and the full KS+ algorithm, which corrects for missing data, field borders, and reduced shear. The authors describe the KS+ implementation as the first publicly available one to their knowledge. Initially developed for SuperBIT, SMPy is now presented as a general-purpose tool for cosmological survey data. The abstract reports software capabilities, not new observational mass measurements or quantitative performance tests.

PublicMatter can slightly distort the apparent shapes of distant galaxies by bending their light. By combining these tiny distortions across thousands of galaxies, astronomers can infer how matter is distributed, including both visible matter and dark matter. This work introduces SMPy, a free, openly available Python software package that turns galaxy-shape distortion measurements into projected mass maps. It offers three mapping methods, including one designed to correct for missing data, image-field edges, and an additional lensing effect called reduced shear. Originally developed to support the SuperBIT telescope, the package is presented as useful for wider cosmological surveys. The abstract describes the software rather than reporting a new dark-matter map or measured improvement in accuracy.

Young explorerWhen light from faraway galaxies passes near lots of matter, its path bends and the galaxies can look a tiny bit stretched. Scientists use those little stretches to make maps of where matter is, even matter we cannot see. This work introduces a computer tool called SMPy that helps make those maps in three different ways. One way can help deal with missing information and the edges of a map. The maps include both matter we can see and dark matter; this is a tool for making maps, not a report of a new discovery.

Detection and excision of radio-frequency interference in radio arrays

Vikram Ravi

AstronomerThis modeling study asks which data product best reveals a given radio-frequency interference (RFI) emitter. It includes primary-beam attenuation, near-field wavefront curvature, bandwidth smearing, and fringe tracking. Antenna-based versus array-based sensitivity depends on mean per-baseline RFI coherence: cross-correlation detection is preferred only above a threshold of (N-1)^(-1/2), for N antennas. Evaluations cover VLA A and D, MeerKAT, and DSA configurations, with five representative emitters at distances from 5 km to medium-Earth orbit. The model favors cross-correlations for stationary terrestrial emitters in compact, filled arrays, but not extended, sparse arrays. For aircraft and low- and medium-Earth-orbit satellites, rapid fringe rotation destroys coherence, favoring summed autocorrelations by one to seven orders of magnitude across the configurations considered. For RFI below single-antenna noise, no phase-unknown cross-correlation statistic outperforms the autocorrelation sum. Tied-array beams are modeled as least sensitive, seeing terrestrial emitters as a single antenna does. The author also describes real-time GPU-based autocorrelation excision for the 110-antenna DSA and outlines future-array design implications; these are not presented as observational validation of the sensitivity model.

PublicRadio interference can hide astronomical signals, but the best place to detect it may not be the combined data astronomers normally use. This study models different ways of handling signals from telescope antennas. Its calculations suggest that combining correlations between antennas helps detect stationary ground-based interference in compact arrays, but not in widely spread, sparse arrays. Moving aircraft and satellites lose the signal alignment needed for that approach; in the configurations studied, adding the antennas’ individual power measurements is predicted to be one to seven orders of magnitude more sensitive. The advantage depends on the interference retaining enough coherence between antennas, so there is no single best choice for every source. The paper also describes a real-time, graphics-processor-based interference-removal implementation for the 110-antenna Deep Synoptic Array. The sensitivity comparisons come from a model, not reported observational tests.

Young explorerRadio telescopes listen to space, but unwanted radio signals can get in the way. This scientist used a math model to ask how a group of telescope antennas could notice those signals best. The model says signals from moving airplanes and satellites are easier to spot by adding up what each antenna measures on its own. For things staying still on the ground, comparing pairs of antennas can sometimes work better. These are answers from a model, not results from watching the sky.

FiDeR: Denoising Astronomical Images at the Observational Resolution

Lei Wang, Bin Li, Lin Nie+4 more

AstronomerFiDeR reduces image noise while approximately preserving the input PSF. It applies a finite number of Richardson–Lucy iterations to a nonnegative source-plus-background image, then reconvolves using a kernel derived from a calibration point source processed with the same settings, including the background-to-source flux ratio. Comparisons with six denoisers use simulated point-source and mixed stellar–galaxy fields, plus JWST NIRCam and MIRI observations. Stellar tests retain approximately the input bright-source widths, with small residual offsets for faint sources. In the simulated mixed field, peak signal-to-noise ratios reach 46.701 and 44.850 dB at backgrounds of 10 and 20 counts per pixel; corresponding wing errors are 0.657 and 0.858 counts. Aperture-flux and shape errors are small, but BM3D achieves higher structural similarity. NIRCam results show lower core and combined-region errors; benefits in the three-exposure MIRI test are mainly in the stellar aperture and photometry. The results support substantial denoising with little measured PSF change within the tested regimes, not universal preservation. Subsequent measurements must account for residual noise correlations.

PublicAstronomical images contain noise that can obscure faint objects, but removing it can also change how stars and galaxies appear. FiDeR is a new method designed to reduce noise while keeping approximately the same image response to a point source. Tests used both simulated skies and real images from the James Webb Space Telescope. Bright simulated stars largely retained their original widths, while faint ones showed small remaining differences. The method also performed well on several measures of brightness and shape, although another method scored better on structural similarity. Improvements in the real images varied by instrument and measurement. These results are promising within the conditions tested, but remaining errors can be linked across pixels and must be included when estimating measurement uncertainties.

Young explorerPictures of stars can look grainy. Scientists tested a new way to clean them up while trying to keep stars the same size in the picture. It worked well in pretend space pictures and helped with real telescope pictures, too. But it was not perfect, especially for faint stars, so scientists still need to be careful when measuring the cleaned pictures.

Aperture Photometric Accuracy of Point-spread-function-deconvolved Astronomical Images

Shen Zhang, Lei Wang, Yachong Diao+11 more

AstronomerThe authors introduce an improved Richardson–Lucy (RL) deconvolution framework using negative backfilling (NB) and the filtered image deconvolution and noise backfilling (FiDNoBa) algorithm. Kalman low-pass prefiltering is combined with reintegration of filtered-out noise components after RL iterations to suppress artifacts while preserving flux. In simulations, the reported relative mean deviation is below 1% for isolated sources, approximately 0.37% for blended Sérsic galaxies, and approximately 5% in crowded stellar fields; the crowded-field tests also recover significantly more sources than traditional point-spread-function photometry. Tests on real JWST/NIRCam and VLT Survey Telescope OmegaCAM images demonstrate mitigation of ringing, handling of complex instrumental signatures including extended STPSF wings, and stable aperture photometry. The numerical accuracy figures come from simulations, not the observational tests.

PublicThe paper presents a method for sharpening astronomical images while keeping measurements of object brightness reliable. Standard Richardson–Lucy image sharpening can amplify noise and create artificial rings. The new approach first filters the image with a Kalman filter, then restores the filtered-out noise components after sharpening to help preserve the total light. In simulated images, the authors report brightness-measurement deviations below 1% for isolated objects, about 0.37% for overlapping model galaxies, and about 5% in crowded star fields, where the method also recovers more sources than a traditional technique. Tests on real images from JWST and the ground-based VLT Survey Telescope show reduced artificial ringing and stable brightness measurements. Those real-image tests are distinct from the simulations that provide the quoted accuracy figures.

Young explorerPictures of stars and galaxies can look blurry and speckly. The researchers made a new way to sharpen them without making so many pretend rings or changing how much light they contain. They first filter out some speckles, sharpen the picture, and then put the filtered-out speckles back to help keep the light measurements right. They tested it on made-up space pictures and real telescope pictures. In the made-up pictures, it measured brightness well and found more stars in crowded places than an older method. In the real pictures, it reduced pretend rings and kept brightness measurements steady.

From Rock Tumbling to Telescope Mirror Grinding: How Optical Perfection Emerges from Random Motion

Emmanuel Schaan

• Classical Physics
• Physics Education
• Optics

AstronomerThe paper derives a first-principles explanation, starting from Preston’s material-removal law, for how manual abrasive grinding of two glass disks produces matching spherical surfaces with accuracy of tens of nanometers. Grinding-stroke symmetries make planes and spheres generic equilibria in the theory. Small-scale irregularities decay exponentially on the grinding timescale, T_grind, whereas large-scale departures from sphericity diffuse away on T_sphere ∝ (R_mirror/R_stroke)^2 T_grind. Gravity and finite disk size destabilize planes; for sufficiently short strokes, spheres remain stable because deformation is much slower than spherization, while their curvature radius changes adiabatically. The framework also explains differences between rotary and vibratory rock tumbling, why neither produces spheres, and why sanding small flat surfaces causes rounding. These are theoretical explanations rather than newly reported experimental measurements.

PublicHow can rubbing two glass disks together with abrasive produce matching spherical curves accurate to tens of nanometers? This paper develops a theoretical explanation based on a law describing how grinding removes material. The motion smooths small bumps relatively quickly, while broader departures from a spherical shape disappear more slowly. The theory identifies both flat and spherical surfaces as possible balanced shapes, but gravity and the disks’ limited size make flatness unstable. Spherical shapes remain stable if the grinding strokes are sufficiently short, even as their curvature slowly changes. The same framework explains why rotary rock tumbling rounds edges more than vibratory tumbling, why neither makes spheres, and why sanding small flat surfaces rounds them. The abstract presents a derivation, not a new experimental test.

Young explorerIf you rub two glass disks together with gritty powder between them, they can become very smooth, matching curved shapes. The scientists used math to explain how this happens: little bumps wear away quickly, but bigger uneven parts take longer. Their explanation says that short enough rubbing strokes can keep the curved shapes steady, even while the curves slowly change. They also use the same idea to explain how rocks get rounded and why sanding a small flat thing can round it.

Deconvolved IXPE Polarization Maps of the Crab Nebula in a Maximum-a-Posteriori Framework

Keisuke Uchiyama, Mikio Morii, Toru Tamagawa

• High Energy Astrophysical Phenomena

AstronomerThe authors apply maximum a posteriori (MAP) polarization-resolved deconvolution to the first IXPE observation of the Crab Nebula in the 2–8 keV band. The method reconstructs intensity jointly in sky position and polarization angle, accounting for the instrumental response to incident direction and polarization angle. Compared with basic analysis, the reconstruction yields sharper spatial structure and a more clearly identifiable jet. In the reconstructed jet region, the magnetic-field orientation shows a statistically significant tendency to lie perpendicular to the intensity-gradient orientation. The analysis uses a simplified response with remaining systematic uncertainty, but demonstrates the method’s potential to improve the interpretability of IXPE polarization maps of nebular sources.

PublicResearchers reanalyzed the first IXPE X-ray observation of the Crab Nebula using a method that reconstructs both where the light comes from and its polarization, a property related to its orientation. Compared with the basic analysis, the reconstructed image has sharper detail and makes the nebula’s jet easier to identify. In the jet region, the analysis finds a statistically significant tendency for the magnetic field to run at right angles to the direction in which brightness changes most rapidly. The method uses a simplified model of the instrument’s response, leaving systematic uncertainty, so that limitation matters when interpreting the findings.

Young explorerScientists used a new way to make a clearer X-ray picture of a cloud in space called the Crab Nebula. It made a stream called a jet easier to see. Their picture also gives clues that the magnetic field in the jet tends to point across the direction where the picture gets brighter fastest. But their way of describing how the telescope sees the light is simplified, so the picture still has some uncertainty.

The Agentic Observer Hackathon: Autonomous Decision-making in Simulated Astronomical Surveys

Haosong Wang, Ting Tan, Yao Li+7 more

AstronomerThe Agentic Observer Hackathon evaluates autonomous survey decision systems submitted by 102 teams using held-out simulated campaigns, not on-sky operations. In a synthetic multi-object survey with prescribed exposure responses and assignment constraints, systems choose pointings, target assignments and exposure configurations while handling observing requests, instrumental faults and data loss. Leading systems combine numerical exposure planning with language models that interpret operational information and support longer-term decisions. Exploratory tests find improved fault reporting with model access in several systems, but revised scientific priorities substantially alter rankings. Reference-campaign analysis tracks target completion and identifies errors in the baseline system's inference of prescribed quality bands. The released simulator and reference strategies provide shared conditions for comparing allocation, selection and interruption recovery.

PublicHow could an automated observing system divide telescope time when priorities change or equipment fails? The Agentic Observer Hackathon explored this question in a simulated astronomical survey, evaluating systems submitted by 102 teams on campaigns set aside for testing. The systems selected where to point, which targets to observe and how to configure exposures. Leading entries combined numerical planning with language models to interpret operational information and help with longer-term choices. Exploratory tests showed better fault reporting with model access in several systems, but changing the scientific priorities substantially changed the rankings. These are simulation results, not demonstrations at a real telescope. The released simulator and example strategies offer a common testing ground for future comparisons.

Young explorerImagine a pretend telescope with lots of things to look at and only so much time. Teams made computer helpers that chose where it should look and what to do when something went wrong. Researchers tested helpers from 102 teams in this pretend world. The leading helpers mixed number planning with language tools that helped them understand messages and plan ahead. When researchers changed which science jobs mattered most, the order of the winners changed a lot. This was practice in a simulation, not a test with a real telescope.

The Transient Array Radio Telescope: An open-source all-sky imaging radio interferometer

Timothy C.A. Molteno, Max Scheel, Pat Suggate+2 more

AstronomerThe paper describes the Transient Array Radio Telescope (TART), an open-source, 24-element imaging interferometer operating at 1573–1577 MHz in L band for research and education. It covers the array layout, electronics, radios, correlator, and software architecture, including satellite-based calibration and imaging pipelines. Presented imaging results yield an estimated telescope sensitivity of approximately 52 kJy; the abstract does not specify the conditions or definition of this sensitivity estimate.

PublicThe Transient Array Radio Telescope (TART) combines signals from 24 antenna elements to make radio images. Designed for research and education, it has an open-source design. The paper explains its hardware and software, including how satellites are used to calibrate the telescope. It also presents imaging results that lead to an estimated sensitivity of about 52 kilojanskys, a measure of radio signal strength, though the abstract gives no details about the conditions behind that estimate.

Young explorerTART is a telescope that uses 24 antennas working together to make pictures from radio waves instead of light we can see. The paper explains how its parts and computer programs work, and how satellites help it get ready to make pictures. The researchers show pictures it made and use them to estimate how strong a radio signal it can detect. TART is made for both research and learning.

Characterisation Methodology for Persistence and Anti-persistence in IR Detectors for the Euclid and SVOM Space Missions

Naomie De Araujo, Aurélia Secroun, Marie Tourneur Silvain+3 more

AstronomerThe study presents a methodology for characterising persistence and anti-persistence in H2RG and ALFA infrared detectors used by Euclid and SVOM. Simultaneous charge trapping and release can distort pixel responses after illumination, biasing flux measurements and potentially producing false detections. The method combines differential ramps, Savitzky–Golay filtering and non-linearity correction. Applied to ground-characterisation data, it reveals spatial inhomogeneities, dependencies on fluence, flux, temperature and wavelength, and unexpected spectral effects in ALFA. These preliminary results validate the characterisation approach; in-flight correction models meeting mission accuracy requirements remain a future goal, not a demonstrated outcome.

PublicInfrared detectors used by the Euclid and SVOM space missions can retain effects of earlier light exposure as electrical charges become trapped and are released inside their pixels. These effects, called persistence and anti-persistence, can distort brightness measurements and potentially create false detections. Researchers present a method for measuring these distortions. Tests using ground-based detector data reveal that the effects vary across the detectors and depend on the amount and rate of incoming light, temperature and wavelength. They also reveal unexpected wavelength-related effects in ALFA detectors. The findings are preliminary and support the new method, but corrections that work during the missions and meet their accuracy needs are still a future objective.

Young explorerThe light sensors on two space missions can be affected by light they saw earlier. Tiny electrical charges get caught inside them and come out later, which can make the sensors give wrong readings. Scientists tried a new way to study this using tests done on the ground. They found that different parts of the sensors behave differently, and that light and temperature matter too. These early findings may help scientists make better corrections for the sensors in space, but those corrections are not ready yet.

Anomaly-ranked confirmation slows new-class learning

Argyro Sasli, Michael Coughlin

• Machine Learning
• Data Analysis, Statistics and Probability

AstronomerThis study tests whether anomaly-ranked examples are effective training examples for recognising a new class. Across five benchmarks spanning physics, medicine and computer vision, examples flagged by the anomaly detector are those a classifier learns first. However, in three systems, expert confirmation of the highest-ranked members yields poorer recognition than confirmation of an equal number of randomly selected members. Transferring subsequent example selection to the classifier recovers part of this loss in two systems. A paired intervention replacing nearby known classes with distant ones sharply reduces the confirmations required for recognition. Within the tested classes, these results distinguish discovery from learning a class's extent: prioritising the top anomaly ranks can make learning less efficient. The abstract reports benchmark findings, not a demonstrated outcome for an astronomical survey.

PublicSoftware that spots unusual examples can help experts identify a new category, but the most unusual examples may not be the best ones for teaching another program to recognise that category. Across five tests in physics, medicine and computer vision, the examples flagged by the anomaly detector were learned first by the classifier. Yet in three systems, training with expert-confirmed examples from the top of the anomaly ranking produced worse recognition than using the same number of randomly chosen members of the new category. Letting the classifier choose later examples partly improved recognition in two systems. A separate controlled change—replacing similar known categories with more distant ones—greatly reduced how many confirmations were needed. The findings apply to the tested categories and show that finding something new and teaching its full variety are different tasks.

Young explorerImagine a computer points to things that look unusual, and a person checks which ones belong to a new group. Those checked things help another computer learn the group. In some tests, choosing only the things at the very top of the unusual list taught it less well than picking the same number from the new group at random. Letting the learning computer choose what to check next helped a little in some tests. So, in these tests, finding a new kind of thing was not the same as choosing good examples to teach all the different ways it can look.

Nonlinear Physics and Self-Organized Criticality in Astrophysics

Markus J. Aschwanden

• Statistical Mechanics
• Solar and Stellar Astrophysics
• Chaotic Dynamics

AstronomerThis paper discusses the nonlinear physics underlying six basic definitions of self-organized criticality (SOC): phase transitions, fractal structures, power laws, SOC contingency, exponential growth, and diffusive decay. It emphasizes that SOC's definition remains ambiguous and controversial. Statistics of SOC events or avalanche processes can be inferred from event-size distributions or spatiotemporal evolution. The abstract reports no specific observations, simulations, or quantitative results.

PublicSelf-organized criticality is a scientific concept whose definition remains disputed. This paper discusses six ways of defining it, involving changes between states, fractal patterns, power-law relationships, dependence on circumstances, exponential growth, and diffusive decay. It also explains that statistics of events called avalanches can be inferred from how their sizes are distributed or how they develop across space and time. The abstract does not report a specific experiment or measurement.

Young explorerScientists do not all agree on how to define an idea called self-organized criticality. This paper talks about six ways to describe it. Scientists can study events called avalanches by looking at how big they are or how they spread and change over time. The short description does not tell us about a new experiment.

Learned Surrogates of Three-Dimensional Magnetohydrodynamic Turbulence

Semih Kacmaz, E. A. Huerta

• Machine Learning
• Fluid Dynamics
• Plasma Physics

AstronomerThe authors present what they describe as the first learned surrogates for three-dimensional resistive MHD turbulence, comparing a convolutional UNet, a shifted-window transformer and a Fourier neural operator. These autoregressive emulators are trained on decaying-turbulence simulations at 128^3 resolution, with 500 simulations at each Reynolds number of 1000, 3000 and 6000. Training proceeds from single steps to short rollouts under a common stopping rule. Over approximately one large-eddy turnover time, the UNet and transformer achieve relative velocity errors of 0.018–0.053 while retaining simulated current sheets, enstrophy, current density and energy spectra. The UNet is more accurate at Reynolds numbers 3000 and 6000; the transformer leads at 1000. On public benchmarks, the models report errors 39% below the best published model on FactFormer's isotropic-turbulence set and one-third to one-half below the best supplied baseline on The Well's compressible-MHD set. They also match a 1.3-billion-parameter pretrained foundation model over its rollout windows with 20–62 times fewer parameters. These are simulation-based tests with finite evaluation windows, not observational validation. Code, configurations, evaluation scripts and a seeded data generator are planned for release upon publication.

PublicSimulating the tangled motion of plasma and magnetic fields is computationally expensive. This study trains three kinds of artificial-intelligence model to imitate three-dimensional plasma-turbulence simulations. Over a tested interval of about one large swirling motion's turnover time, two models reproduce the simulated velocity with relative errors of 1.8–5.3% and retain several important features of the magnetic fields and fluid motion. Neither model is always best: their ranking changes with the simulated flow conditions. Tests on two public datasets also show lower errors than the comparison models, and the models match a much larger pretrained model over its tested prediction windows using far fewer parameters. These findings concern imitation of computer simulations, not measurements of real plasma, and do not establish accuracy over arbitrarily long predictions. The authors plan to release their code and data-generation tools upon publication.

Young explorerHot, electrically charged gas can swirl around with magnetic fields, and making a computer copy of that motion takes lots of work. The researchers taught computer helpers to copy how those swirls change in other computer simulations. Two helpers copied many details well for a short time, but neither was always the best. This was a test with computer-made gas, not real gas, and it does not show that the helpers can keep copying it correctly forever.

Choosing a generator for streaming Gaussian noise in gravitational-wave mock data: accuracy, cost and reproducibility

Isaac C. F. Wong

• General Relativity and Quantum Cosmology
• Data Analysis, Statistics and Probability

AstronomerThis computational comparison evaluates generators of long colored Gaussian-noise streams for mock gravitational-wave data challenges, ranking them by covariance error relative to the target over the analysis band. Errors are derived from each generator’s algebra; generated noise serves only to check implementations. With the target spectrum smoothly continued below the band, crossfading independent windows of at least 256 s achieves errors below 10^-3 for all eleven tabulated detector curves, at about 4.7 million samples per second with a few hundred bytes of state. The window needed for an error of 10^-3 ranges from 8 to 235 s, with the longest requirements on design curves containing narrow lines and some dependence on spectral tabulation. Overlap-save filtering is faster but requires tens of thousands of taps for errors of a few percent; no tested autoregressive or ARMA configuration reaches the accuracy–throughput fronts. Cutting the target at the band edge instead produces errors above one half for every method on the projected aLIGO O4 curve, and for crossfading on five additional curves. Crossfaded noise is cyclostationary: with spectral continuation, its cyclic error exceeds its stationary error only at 8 s on the aLIGO O4 and Virgo and KAGRA design curves, but remains within a factor of two of the stationary contribution on the aLIGO O3 and Virgo and KAGRA design curves. The authors recommend crossfading with detector-specific tabulated windows and smooth continuation below the band; these are noise-generation results, not detector observations.

PublicMock gravitational-wave data need long streams of artificial noise with carefully specified statistical properties. This study compares ways to create those streams, calculating how closely each method matches the intended pattern of correlations and checking the software with generated noise. Blending independently generated segments performs well when the target noise spectrum is extended smoothly below the frequency range being studied. With segments lasting at least 256 seconds, its covariance error is below 0.001 for all eleven detector noise curves considered, while producing about 4.7 million samples per second. A filtering alternative is faster but needs very long filters even for errors of a few percent; the tested autoregressive alternatives offer no best accuracy–speed trade-off. A crucial caveat is that abruptly cutting off the target spectrum at the lower frequency boundary, as current generators do by default, can cause large errors. The blending method also has statistical properties that vary periodically with time. The authors recommend it with suitably chosen segment lengths and a smooth low-frequency extension. These findings concern simulated noise, not newly observed gravitational waves.

Young explorerScientists make pretend noise to help test ways of finding gravitational waves. This study compared different ways to make that noise match a chosen pattern. Gently blending separate pieces worked well when the pattern was also extended smoothly to slower wiggles. Cutting the pattern off suddenly could make the pretend noise match badly. The blended noise is not perfect: its pattern changes a little as time goes by. The researchers recommend blending pieces of the right length and keeping the slow-wiggle pattern smooth. They tested pretend noise, not new waves from space.

Imaging the Current Distribution in Superconducting Transition-Edge Sensors with Scanning SQUID Microscopy

Samantha Walker, Austin Kaczmarek, Douglas A. Bennett+11 more

• Superconductivity
• Instrumentation and Detectors

AstronomerScanning SQUID microscopy directly probes spatial superconducting properties and transport current in two MoAu X-ray transition-edge sensor designs under voltage bias within the resistive transition. The authors identify superconducting regions through their local diamagnetic response and reconstruct current distributions from the transport current’s Oersted field. They observe bias-dependent current redistribution that tracks current-induced changes in superconducting regions. These measurements highlight mesoscale spatial structure largely neglected in existing TES models, including variations associated with device geometry and proximity effects from superconducting leads and normal-metal features, as important for device physics, operation, and design.

PublicTransition-edge sensors detect tiny temperature changes by operating where a superconductor begins to develop electrical resistance. Many models largely leave out how superconductivity and current flow vary across a sensor. Using a scanning magnetic probe, the researchers mapped superconducting regions and reconstructed current paths in two designs of molybdenum-gold X-ray sensors. They observed that changing the electrical bias rearranged the current flow alongside changes in the superconducting regions. The findings show why spatial variations within these sensors matter for understanding and designing them; the abstract does not report an improvement in detector performance.

Young explorerThese tiny X-ray detectors notice very small changes in how warm they are. Scientists used a special magnetic scanner to look inside two detector designs. They found that when they changed the electrical setting, the electricity took different paths, while the parts that could carry electricity without resistance changed too. This helps scientists understand how the detectors work.

Statistical Machine Learning for Astronomy -- A Textbook

Yuan-Sen Ting

• Machine Learning
• Applications
• Machine Learning

AstronomerThis textbook develops statistical machine learning for astronomy from a Bayesian perspective, emphasizing uncertainty quantification, assumptions, limitations, and uncertainty propagation rather than reporting new observational results. It derives methods from first principles and connects classical statistics to modern techniques. Topics include regression with measurement uncertainties, logistic regression and classification, Principal Component Analysis, clustering, sampling and Markov Chain Monte Carlo, Gaussian Processes, and neural networks. Astronomical applications and 22 companion Jupyter-notebook tutorials complement the mathematical treatment, with attention to the demands of large surveys.

PublicThis textbook explains how astronomers can use statistics and machine learning to analyze data while keeping track of uncertainty. It connects traditional statistical ideas with methods for making predictions, sorting data into categories, and finding patterns. Its Bayesian approach emphasizes understanding why a method works, when it is appropriate, and what its limits are. The book provides mathematical explanations and 22 hands-on computer tutorials using astronomical data; it is a teaching resource, not a report of a new astronomical discovery.

Young explorerThis is a book about learning from space data with math and computers. It teaches people ways to find patterns and sort things into groups, while remembering that measurements are not perfect and answers can be uncertain. It explains how the methods work and gives readers 22 computer activities to practice with space data. It teaches tools rather than announcing a new discovery.

Pixellated Posterior Sampling of Point Spread Functions in Astronomical Images

Connor Stone, Ronan Legin, Alexandre Adam+4 more

AstronomerThe authors introduce Bayesian pixel-level modeling of an upsampled PSF, combining an analytic Gaussian likelihood with a generative diffusion prior trained on HST ePSF templates. In the reported comparisons with parametric Moffat, ePSF template-based, and regularized-likelihood methods, their models achieve likelihoods higher by orders of magnitude and noise-consistent residuals while remaining visually realistic. The method also handles faint and heavily masked point sources, with broader posterior distributions reflecting greater uncertainty. The recovered pixel-level posterior is intended to propagate detailed PSF morphological uncertainty into downstream analyses relevant to weak lensing, astrometry, and photometry; the abstract does not report improvements in those downstream measurements. Posterior-sampling code is available on GitHub.

PublicA point spread function describes how a telescope spreads a point source's light across an image. This study introduces a way to estimate that pattern in finer detail while also tracking uncertainty about its shape. The method combines a statistical model of the image with a generative model trained on a library of Hubble Space Telescope light-pattern templates. In the authors' comparisons, it fits the data substantially better than several existing methods, leaving differences consistent with noise while retaining realistic-looking patterns. It can also work with faint sources or sources whose images have many pixels masked out, although the uncertainty then grows. The aim is to carry this uncertainty into later astronomical measurements, rather than treat the estimated light pattern as perfectly known.

Young explorerA telescope makes a tiny dot of light look like a little blurry shape. These researchers made a computer method to work out that shape and show which other shapes might fit too. In their tests, it matched the pictures better than the other methods they compared it with. It could still work when the light was dim or much of the picture was hidden, but then it was less sure about the shape. Knowing how unsure it is could help astronomers when they use the pictures.

LISA science ground segment conventions

Quentin Baghi, Stanislas Babak, Leor Barack+23 more

• High Energy Astrophysical Phenomena
• General Relativity and Quantum Cosmology

AstronomerThis document specifies conventions for data simulations, waveforms, and analysis pipelines within LISA’s Distributed Data Processing Centre (DDPC), and can serve as a best-practice guide for LISA publications. It covers time-to-frequency transformations, gravitational-wave source parametrization, instrumental response, time-delay interferometry, and reference-frame definitions. It is a conventions document, not a report of observational findings or simulation results.

PublicThis document provides shared rules for simulating and analyzing data for the Laser Interferometer Space Antenna (LISA). It explains conventions for describing gravitational-wave sources, representing signals in time and frequency, and accounting for the instrument’s response. Written for LISA’s Distributed Data Processing Centre, it can also guide publications about the mission. It presents analysis conventions rather than new discoveries.

Young explorerThis is a rulebook for people working on a space project called LISA. It helps them use the same ways to describe tiny ripples in space and work with pretend data on computers. It does not announce that they found anything new.

A dual-polarization whitened-template trigger for real-time radio detection of extensive air showers

Qader Dorosti, Alperen Aksoy, Ilja Bekman+7 more

AstronomerThe authors develop a compact dual-polarization radio trigger using detector-folded air-shower simulations and measured backgrounds from the Auger Engineering Radio Array. A filter combining air-shower pulse morphology with measured background statistics achieves 96% signal efficiency at a frame-equivalent background trigger rate of 3.12 kHz on an independent validation dataset, outperforming amplitude thresholding and unwhitened template matching. Tests with recordings from different times and geographically distributed stations show that transferring the unchanged filter requires threshold adaptation to recent background conditions. With 1 ms threshold updates, background rates span 35.2–41.4 kHz for a nominal 35.7 kHz target while retaining air-shower sensitivity. The architecture meets FPGA timing constraints at 200 MHz, supporting feasibility rather than demonstrating autonomous field detection.

PublicThe researchers developed a compact system to distinguish radio pulses from extensive air showers from brief bursts of radio interference. They built and tested it using simulated air-shower signals that account for the detector response, together with real radio backgrounds recorded by the Auger Engineering Radio Array. On a separate validation dataset, it identified 96% of the signal examples at a background-trigger rate of 3.12 thousand per second, outperforming two simpler methods. Tests using recordings from different stations and times showed that the same filter could be reused, but its decision threshold needed frequent adjustment as background conditions changed. Updating that threshold every millisecond kept background-trigger rates near, though not exactly at, the chosen target. The design also meets the timing requirements of a programmable chip running at 200 MHz, making autonomous detection feasible; the abstract does not report an autonomous field demonstration.

Young explorerThe researchers made a fast helper to pick out special radio blips from lots of unwanted radio noise. They tested it with pretend air-shower blips made on a computer and real noise recordings. It found most of the pretend blips and did better than two simpler ways of looking for them, but some noise still fooled it. When the noise changed, the helper needed to change how picky it was. The design can work fast enough on a special computer chip, but these tests do not yet show it finding real air showers all by itself.

Modeling the technical specifications for future multi-object spectroscopy instrumentation

Ummee Tania Ahmed, Andrew Hopkins, Simon Ellis

AstronomerThe authors investigate a proof-of-concept code that models the operation of current-generation astronomical fiber positioners, accommodating arbitrary numbers of fiber probes and targets. They systematically explore observational and instrumental parameters, including target and fiber densities, exclusion radius, and patrol radius. By simulating fiber-to-target allocation across multiple visits, the tool assesses efficiency and completeness for specified configurations. Its intended application is to inform technical requirements for future multi-object spectroscopy instruments, whether based on new techniques or extensions of existing technologies. The abstract reports no quantitative performance results or validation against operating instruments.

PublicThe study explores a prototype computer program for planning instruments that use movable optical fibers to collect light from many astronomical targets. The program models which fibers can be assigned to which targets over repeated observations, varying factors such as how crowded the targets and fibers are and how far the fibers can move or approach one another. It assesses how efficiently and completely different setups could collect the desired observations. The goal is to help guide future instrument designs; the abstract does not report measured improvements or numerical results.

Young explorerImagine a telescope with lots of little movable light collectors. A computer program plays a planning game: which collector should point at which thing in the sky, and what should it try next time? It tries different rules about how many collectors there are and how they can move. The scientists hope this will help people design future telescope tools. This is a computer test, not a report of new things found in the sky.

Feasibility of Capillary-Driven Orbital Liquid Mirror Telescopes

Janoah Dietrich, Álvaro Romero-Calvo

• Fluid Dynamics
• Space Physics

AstronomerThis modeling study assesses proposed space-based liquid mirror telescopes using axisymmetric capillary and thin-film models, rather than observations of operating space mirrors. For Sun–Earth L2 orbits, solar radiation pressure and self-gravitation dominate the modeled perturbations: equilibrium distortions exceed λ/20 above apertures of 0.86 m at 380 nm and 1.58 m at 2.5 μm. The models predict micrometeoroid disturbances self-heal in seconds to minutes, while settling after filling takes years to decades at large apertures and propulsive maneuvers violate optical tolerances within seconds to hours. These findings indicate a need for interface control in large concepts such as NASA’s 50 m FLUTE. Modeled thermocapillary actuation supports VIS/NIR apertures of 2.3/8.0 m with 100 μK temperature resolution, or 10.6/37.7 m with 10 μK resolution. Separately, parasitic Marangoni flows demand sub-mK thermal uniformity for NIR and 1–100 μK for visible operation in any capillary LMT. The authors identify surface-normal settling acceleration, outside the capillary regime, as the most promising route to apertures of tens of meters. Required accelerations range from 39 mm s⁻² for a 5 m NIR mirror to 17 m s⁻² for a 50 m visible mirror. This proposed passive approach is predicted to suppress both perturbation-induced distortions and thermal Marangoni flows; it is not demonstrated hardware performance.

PublicCould a space telescope use a reflective liquid instead of a rigid mirror? This study uses mathematical models, not an operating space telescope, to test that proposal. In the modeled Sun–Earth L2 environment, sunlight pressure and the liquid’s own gravity distort mirrors beyond the study’s optical tolerance at diameters above 0.86 meters for visible light and 1.58 meters for near-infrared light. Small impact disturbances are predicted to heal quickly, but large mirrors could take years to decades to settle after filling, and spacecraft maneuvers could quickly spoil their optical shape. Temperature-based control could help, but requires extremely fine temperature control and uniformity. The authors favor a different proposed solution for mirrors tens of meters across: applying acceleration perpendicular to the surface. Their models suggest this could passively suppress distortions and temperature-driven flows, but the approach has not been demonstrated here.

Young explorerScientists wonder if a space telescope could have a shiny liquid mirror. They used math to see how it might behave, not a real mirror in space. Their models say sunlight and gravity could spoil a big mirror’s shape. Tiny hits might heal quickly, but a newly filled big mirror could take years to settle. The scientists suggest pushing the liquid toward its surface to help keep it smooth, but that idea still needs testing.

EPIMETHEUS: Effective point spread function inferred from mosaics

Pietro Benotto, Benedetta Vulcani, Vittoria Altomonte

• Astrophysics of Galaxies

AstronomerThe authors present EPIMETHEUS, an open-source, modular Python library for constructing average effective point spread functions (ePSFs), from stellar selection through model generation. It addresses the rotational and positional alignment complexities of mosaics combining exposures from different epochs, observing conditions, and position angles, while also supporting single-orientation images. Multiple images or mosaics can be processed together when individual fields contain too few bright, unsaturated stars. Selection tools include automatic filtering by orientation and light concentration, plus visual inspection for manual exclusions, with transparent user control over the stellar sample. The release includes empirical ePSFs for standard HST and JWST filters in COSMOS, UDS, Abell 2744, and GOODS-S. The abstract provides no quantitative accuracy benchmarks.

PublicMeasuring stars' positions and brightness accurately requires knowing how a point of light is spread out in an astronomical image. Building that model is especially difficult for mosaics assembled from exposures taken at different times, in different conditions, and at different angles. The authors introduce EPIMETHEUS, free, open-source Python software that guides researchers from choosing suitable stars to building a model of this light pattern. It can use several images together when one image has too few bright stars that are not overexposed, and researchers can inspect and adjust the star selection. The team also releases models derived from observations for standard Hubble and James Webb Space Telescope filters in four named sky fields. The abstract describes the software's capabilities but does not quantify its accuracy.

Young explorerA star looks like a tiny patch of light in a telescope picture. To measure it carefully, scientists need to know the shape of that patch. This can be tricky when many pictures taken at different times and angles are joined together. The team made a computer tool called EPIMETHEUS to help scientists choose stars and work out the shape of their light patches. Scientists can check which stars the tool uses. The team also shares light-patch models made from real Hubble and James Webb telescope pictures.

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 implemented in JAX with differentiable Fresnel optics from dLUX and regularised maximum-likelihood inference, conditioned on the entire NIRCam wavefront-sensing archive. JWST currently monitors mirror-segment surfaces and alignment using pairs of defocused reference-star images every few days, analysed with a closed-source phase-retrieval package. The authors report typically reducing fit reduced chi-squared from 60–65 to 12–13 and reconstructing JWST’s wavefront history from the start of science operations to early 2026. Camino operates alongside the current STScI algorithm and enables community access and integration into science-analysis workflows. Predictive, physics-based calibration without 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 the condition and alignment of its mirror segments. The authors introduce camino, an openly available program that models these images to estimate distortions in the light reaching the telescope’s camera. Using the archive of these monitoring images, they report better agreement between their model and the images and reconstruct the telescope’s optical history from the start of science operations to early 2026. The program works alongside the existing analysis software and can be incorporated into researchers’ own analyses. The longer-term aim is to predict the needed corrections without taking dedicated reference-star observations at the same time; this has not yet been demonstrated here.

Young explorerJWST needs its mirror pieces lined up very carefully to take good pictures. Every few days, it takes blurry pictures of a star to help check them. The researchers made a new computer program that anyone can use to read those clues. They say it matches the blurry pictures better and helps trace how the telescope’s light changed over time. Someday, they hope programs like this could work out the corrections without needing special star pictures taken at the same time, but that is still a goal.

The Quantum Noise Fraction and the addressable fraction in High-Frequency Gravitational Wave Detection

Sergio Gaudio

• General Relativity and Quantum Cosmology
• Quantum Physics

AstronomerThe analysis bounds sensitivity gains from eliminating quantum-origin noise by E_max = 1/sqrt(1 − beta), where beta is its fraction of total noise power. For bosonic readout modes, beta = 1/(2n_th + 1), giving a thermal frontier k_B T ln 3 = hbar omega: at 10 mK, quantum noise dominates above 229 MHz, subject also to excess readout-chain noise. A proposed diagnostic in a multimode acoustic antenna is a one-half increase in the logarithmic slope of sqrt(S_h Q) along the odd-overtone comb, independent of how Q varies with overtone number. For this antenna, crossing the frontier sacrifices more classical sensitivity than quantum enhancement recovers. Calculations for a GHz mode of an existing bulk acoustic wave device at 10 mK give beta = 0.984 and E_max = 7.8, but intrinsic bath zero-point force noise prevents a linear readout from attaining that ceiling. At the standard quantum limit, beta = 0.992 while the addressable fraction is only 0.496, allowing a gain of 1.41 rather than the nominal ceiling of 11.0. A projected array of 10,000 devices cross-correlated for one year, with integration bandwidth equal to the linewidth, reaches 3.6 × 10^−24 Hz^−1/2. Even granting the full 7.8-fold gain, it remains a factor of 1.0 × 10^10 above the big-bang-nucleosynthesis bound; that remaining gap is classical.

PublicRemoving quantum noise cannot improve a detector indefinitely: the benefit depends on how much of its noise is quantum rather than thermal or otherwise classical. This analysis identifies a temperature–frequency boundary beyond which quantum noise dominates, although real readout electronics impose additional conditions. Crucially, quantum noise is not all removable. For one acoustic-device mode, the calculated ideal improvement is 7.8-fold, but a linear readout cannot reach it because some noise comes from the mode’s surrounding bath. Under a standard quantum-limited operating condition, the available gain is only about 1.41-fold, despite a much larger nominal ceiling. The authors also estimate the performance of 10,000 devices combined for a year; this is a projection, not a reported measurement. Even allowing the full ideal improvement, the projected sensitivity remains ten billion times above a bound from big-bang nucleosynthesis. Quantum-noise reduction alone cannot close that classical sensitivity gap.

Young explorerA very sensitive detector is like an ear trying to hear a tiny whisper through noise. The researchers worked out how much making one kind of noise quieter could help. Some of that noise cannot be removed by the kind of listening system they studied. They also calculated how many detectors might work together, but did not report doing that experiment. Even with very hopeful noise reduction, a huge gap would remain.