Tonight’s sky of new research

Latest νs from the Earliest Galaxies: Probing neutrino self-interactions with JWST

Ranjini Mondol, Priyank Parashari, Anirban Das+2 more

• High Energy Physics - Phenomenology

AstronomerThe authors combine JWST high-redshift UV luminosity function measurements with Planck CMB data to constrain beyond-the-Standard-Model neutrino self-interactions. Such interactions could delay neutrino free streaming and produce scale-dependent changes in the matter power spectrum; high-redshift galaxies provide sensitivity to small-scale structure. The combined data yield 95% confidence upper limits on log10(G_eff/MeV^-2) of approximately -2.75 if only one neutrino flavor interacts and approximately -3.41 if all three interact. Both limits are stronger than those from Planck alone. These are model-dependent constraints, not a detection of self-interactions, and demonstrate the complementary sensitivity of high-redshift UV luminosity functions to weaker interaction strengths.

PublicCould neutrinos interact with one another in ways beyond established particle physics? Such interactions could change how matter gathered into structures in the early Universe. The researchers tested this possibility by combining measurements of the ultraviolet brightness distribution of distant galaxies from the James Webb Space Telescope with Planck measurements of the cosmic microwave background. They obtained tighter upper limits on the proposed interaction strength than Planck data alone provide. The limits depend on whether one or all three neutrino types participate. The study does not establish that these interactions occur; it shows how observations of early galaxies can help constrain them alongside laboratory experiments.

Young explorerScientists wonder whether tiny particles called neutrinos can affect one another in a new way. If they can, they might change how matter gathered to make galaxies long ago. Scientists used measurements of faraway galaxies and old light from the Universe to check this idea. They did not show that the new interaction happens, but they narrowed down how strong it could be.

Breaking dark degeneracies in k-essence models with redshift-space distortions

Rebecca Briffa, Lehel Csillag, Erik Jensko

AstronomerThis study finds that redshift-space distortion growth-rate measurements help break parameter degeneracies in dynamical dark energy models when combined with Pantheon+ supernovae and DESI DR2 BAO expansion-history data. The analysis considers ghost and dilatonic ghost condensate k-essence models, whose effective pressureless-matter phase can produce degeneracies with the matter density parameter. It restricts solutions to those without ghosts or gradient instabilities and explicitly checks the validity of the quasi-static approximation given the models’ small scalar sound speeds. The authors present the combined growth, background, and stability analysis as an efficient way to constrain these models and discuss matter-clustering constraints in relation to recent S8 discrepancies, without reporting a resolution of those discrepancies in the abstract.

PublicDifferent dark energy models can predict similar expansion histories, making them hard to distinguish. This is especially challenging when dark energy temporarily behaves like pressureless matter. The researchers find that adding measurements of how cosmic structure grows helps separate the models’ parameters from the amount of matter in the universe. They demonstrate this for two dark energy models, combining growth measurements with supernova and galaxy-distance data while excluding unstable solutions. They also check an approximation used in their calculations. The work improves constraints on these models; it does not establish that either model describes dark energy. The authors also discuss disagreements about how strongly matter clusters, but the abstract does not claim to resolve them.

Young explorerScientists are trying to understand a mystery called dark energy. Different ideas about it can make the universe grow in similar ways, so telling them apart is tricky. The scientists studied two ideas using clues about both how the universe expands and how matter gathers into clumps. Using both kinds of clues helped them narrow down the possibilities. They also checked that their calculations made sense, but they have not shown that either idea is the right one.

Viable Phantom Crossing in Softly Broken Shift Symmetric Gravity

Rodrigo Calderon, Eric V. Linder

AstronomerThe authors present a viable fit to current cosmological data using a Horndeski modified-gravity model with softly broken shift symmetry (SBSS). The model crosses the phantom divide, w = -1, at z ≈ 0.5 and improves the fit to baryon acoustic oscillations, supernova distances, and cosmic microwave background power spectra relative to w0waCDM by Δχ² ≈ -3, with the same number of effective parameters. They describe the theory as healthy, requiring neither a cosmological constant nor a potential, and substantially protected against high-energy quantum loop corrections. The reported fit supports viability, rather than establishing modified gravity as the explanation for cosmic acceleration.

PublicThe researchers tested an alternative theory of gravity as an explanation for the universe’s accelerating expansion. It fits measurements of cosmic distances and patterns in the cosmic microwave background better than the comparison model, using the same effective number of adjustable parameters. In this theory, a quantity describing the acceleration crosses a boundary called the phantom divide; that crossing is a feature of the model, not a separately established observation. The theory uses neither a cosmological constant nor a potential, and the authors report substantial protection against certain quantum corrections. Its fit to the data does not prove that it is the correct explanation.

Young explorerThe universe is getting bigger faster and faster. Scientists tried a new math idea about gravity to explain this, and it matched measurements better than another idea they compared it with. That makes it an idea worth studying, but it does not mean they know it is right.

Algebraic classification of single-field inflationary dynamics

Jinn-Ouk Gong, Wei-Chen Lin

AstronomerThis theoretical study classifies canonical single-field inflation using an exact depressed cubic for the inflaton velocity. Its roots distinguish a branch-swap boundary from the limiting boundary of downhill motion, where ultra-slow-roll dynamics naturally emerge. Independently, conservation of the momentum conjugate to the comoving curvature perturbation in the long-wavelength limit yields a criterion for growth or decay of the gauge-invariant difference between comoving and uniform-density curvature perturbations. The authors combine these criteria into a dynamical chart expressed through Hubble and potential slow-roll parameters, illustrating it with constant-roll inflation and simple toy models. The emphasis is on regimes traversed by trajectories and their implications for primordial perturbations, rather than fixed model categories; no observational test is reported.

PublicThe authors develop a mathematical map of possible behavior during inflation, a proposed period of rapid expansion in the early universe. Within a theory driven by a single field, an exact equation separates different types of motion and distinguishes a switch between mathematical solution branches from the limit of downhill motion, where an ultra-slow-roll phase arises. A separate calculation determines whether the difference between two descriptions of early-universe ripples grows or shrinks on very large scales. Combining these tools produces a chart that tracks how an inflationary history can pass through different regimes, rather than giving each model one permanent label. The work is theoretical and illustrated with simple models, not established by observations.

Young explorerScientists made a math map for an idea about how the universe might have grown very fast when it was young. The map helps them follow how the thing driving that growth could change its motion, including becoming very slow. It also helps them study tiny ripples during that time. They tried the map on simple math examples; they did not show that the real universe followed it.

Confirming HSC strong lens candidates with DESI Spectroscopy. II. Analysis of 80 galaxy-scale systems with lens redshifts above 0.8

Shen Li, Yiping Shu, Lin Nie

• Astrophysics of Galaxies

AstronomerCosmological simulations predict substantially different evolution of the total-mass density slope at z > 0.8, largely because of differing implementations of galaxy-evolution physics, but measurements in this regime remain sparse. Following an earlier report of 84 candidate strong lenses above this redshift, the authors model the 80 galaxy-scale candidates. They classify 71 as secure lenses with clear features reproduced by the models, five as probable, three as possible, and one as a non-lens given the current imaging. The analysis nearly triples the known galaxy-scale strong-lens sample at z_lens > 0.8. It establishes a sample for statistical studies of high-redshift total-mass structure and future discrimination among simulation prescriptions; it does not yet report measurements of density-slope evolution or favor a particular prescription.

PublicGalaxies can bend light from objects behind them, producing strong gravitational lensing that can help researchers study how mass is distributed. The team examined 80 candidate galaxy-scale lenses at redshifts above 0.8 and classified 71 as secure, five as probable, and three as possible lenses. One candidate lacked reliable lensing features in the available images and was classified as a non-lens. This work nearly triples the number of known galaxy-scale lenses in that redshift range. The expanded sample could help test computer simulations that disagree about how galaxies’ mass distributions change over time, but those tests are an opportunity opened by this study, not a result already established.

Young explorerA galaxy can act a little like a magnifying glass, bending light from something behind it. The scientists checked pictures of 80 faraway galaxies that might do this. They found clear signs in 71, while eight others were less certain and one did not show reliable signs. This bigger collection could help scientists learn how the stuff inside galaxies is spread out and check their computer ideas about how galaxies change.

Probing the Seed Effect of Supermassive Primordial Black Holes with Weak Gravitational Lensing

Lei Zu, Kazunori Kohri

• High Energy Astrophysical Phenomena
• High Energy Physics - Phenomenology

AstronomerThis study constrains supermassive primordial black holes (PBHs) as a dark-matter component through their modeled seed effect, distinct from the Poisson effect of their discrete distribution. PBHs accrete surrounding dark matter into dense spikes, forming dressed PBHs that enhance the matter power spectrum, especially on small scales. A halo-model treatment considers optimistic and conservative accretion prescriptions with different contributions to the 1-halo term. Markov Chain Monte Carlo analysis of DES Y3 weak-lensing measurements yields upper bounds on the PBH dark-matter fraction that tighten with increasing PBH mass. The optimistic prescription gives stronger bounds, excluding f_PBH ≳ 10^-4 for M_PBH ≳ 10^10 solar masses; these limits depend on the assumed accretion model. Separately, forecasts using mock LSST weak-lensing data suggest that constraints could improve by approximately two orders of magnitude. The analysis constrains the proposed PBH population rather than reporting a detection.

PublicThe researchers investigated whether enormous black holes formed in the early universe could account for some dark matter. In their models, these black holes pull surrounding dark matter into dense concentrations, strengthening the clustering of matter on small scales. They compared two assumptions about how efficiently this happens with Dark Energy Survey Year 3 measurements of weak gravitational lensing, the slight distortion of distant images by gravity. The resulting limits become tighter for more massive black holes. Under the more efficient growth assumption, black holes of roughly 10 billion solar masses or more cannot make up roughly one ten-thousandth or more of dark matter. The less efficient model gives weaker limits, so the conclusion depends on how dark matter gathers around the black holes. This is not a detection of primordial black holes. A separate forecast using simulated data suggests that Rubin Observatory's LSST could improve the limits by about a factor of 100.

Young explorerThe scientists asked whether some invisible matter in space could be huge black holes left over from when the universe was very young. Their models say these black holes could pull invisible matter into thick clumps around them. The team used measurements of how gravity bends light to work out how many such black holes might be allowed. They did not discover these black holes, and their answer depends on how strongly the black holes gather matter. They also tried pretend measurements for a future sky survey, which suggest it could make the limits much tighter.

Comment on the recent claims of H0 measurements with the ZTF DR2 SN Ia sample (arXiv:2610.36051)

Mickael Rigault, Brodie Popovic, Ariel Goobar+17 more

AstronomerThis abstract challenges the calibration basis of the H0 determination by Karchev et al. (2026), which combines ZTF SN Ia DR2 with SH0ES calibrator SNe Ia to anchor absolute luminosities. ZTF DR2 contains roughly 3,000 SNe Ia observed with a single telescope, but its absolute photometric calibration has not yet reached the precision required for cosmological inference. The authors state that the relative photometric zeropoint offset between the two samples is unknown, fully degenerate with H0, and not determinable from publicly available data. They argue that the corrections applied by Karchev et al. do not resolve this global offset, leaving the reported H0 determination unsupported by the available calibration information. A fully calibrated dataset is being prepared, not presented here.

PublicThe authors argue that a reported measurement of the Universe’s expansion rate is not supported by the available brightness calibration. That measurement combined about 3,000 exploding stars from the ZTF survey with supernovae from SH0ES used to establish their true brightness. But an unknown difference between the two samples’ brightness scales can mimic a change in the inferred expansion rate. According to the abstract, public data cannot establish this difference, and the corrections used in the reported analysis do not fix it. The authors are working toward a fully calibrated ZTF dataset; this abstract does not provide a new expansion-rate measurement.

Young explorerAstronomers used exploding stars to try to find out how fast the Universe is growing. But they combined two groups of stars without knowing whether both groups’ brightness was measured on the same scale. That mismatch could change the answer. The authors say the information available is not enough to support the reported answer, and the fixes already tried do not solve this problem. They are working to get the brightness measurements ready for this kind of study.

GradFlex: a Gradient-Based Method for Weak Lensing Flexion Measurement

Jiarui Sun, Jun Zhang, Toshifumi Futamase

AstronomerThe authors introduce GradFlex, a method for estimating flexion, the second-order gravitational-lensing distortion that probes small-scale mass structure and complements cosmic shear. Using surface-brightness conservation, they relate pre- and post-lensing brightness-gradient fields and derive estimators from ensemble-averaged spin statistics, without assuming a specific point-spread-function model or galaxy morphology. Numerical tests spanning diverse galaxy morphologies and multiple noise realizations support its reliability under realistic observing conditions; the abstract reports no observational detection. Combining GradFlex with shear could improve constraints on cluster density profiles and studies of substructure, but these applications remain prospective.

PublicGravity distorts the apparent shapes of distant galaxies, offering clues to how mass is distributed. A subtle distortion called flexion can reveal smaller-scale structure, but it is difficult to separate from galaxies’ own shapes and measurement noise. The proposed GradFlex method uses patterns in how galaxy brightness changes across an image, without assuming a particular galaxy shape or model for how the imaging system blurs the light. Tests on simulated galaxies with varied shapes and noise support the method’s reliability, rather than demonstrating a detection in real observations. Used alongside other lensing measurements, it could help map the mass profiles and smaller structures of galaxy clusters in greater detail.

Young explorerGravity can bend light and make faraway galaxies look a little bent, too. Scientists made a new way to look for tiny bends by studying how the light gets brighter or dimmer across a galaxy’s picture. They tried it on computer-made galaxy pictures with different shapes and messy speckles, and the tests suggest it works well. They have not shown it working on real galaxy pictures here. One day, it could help us learn where the mass is inside big groups of galaxies.

Multi-Probe Cosmological Constraints on Clustering DBI Dark Energy Scenario

Samit Ganguly, Surhud More, Goutam Manna+3 more

• General Relativity and Quantum Cosmology

AstronomerThe authors constrain a clustering tachyonic Dirac–Born–Infeld (DBI) dark energy model using a multifluid treatment of background evolution and linear perturbations, with nested sampling applied to Planck 2018 compressed CMB distance priors, DESI DR2 BAO, cosmic chronometers, growth data, and three supernova compilations. Standard cosmological parameters remain consistent with ΛCDM within 2σ; DBI favours slightly lower H0 and higher present-day matter density. Bayesian evidence moderately favours DBI with Pantheon+ (Δln Z ≈ 3.4), but is inconclusive with DES-SN5YR and Union3 (≈ 0.6–0.7). Within the model, the field thaws, dark energy perturbations remain orders of magnitude below matter perturbations, and S8 rises by only about 0.5σ relative to ΛCDM. Four diagnostics indicate evolving dark energy in the analysis, while early dark energy is negligible and the thermal history is preserved. These findings do not establish evolving dark energy observationally: support depends on the supernova compilation, and the model's wφ ≥ −1 restriction prevents it from reproducing the DESI DR2 preference for an effective equation of state crossing −1.

PublicThis study tests a model in which dark energy—the component associated with the universe's accelerating expansion—can change over time and develop small density variations. The researchers compare its predictions with several kinds of cosmological observations, including supernovae, cosmic expansion measurements, and the growth of structure. Its fitted standard cosmological parameters remain broadly consistent with those of the usual cosmological-constant model. One supernova collection gives moderate statistical support for the alternative, while two others give inconclusive support. The analysis points toward changing dark energy within this model, not a definitive discovery that dark energy changes. The model leaves the early thermal history essentially unchanged, and its dark energy density variations remain much smaller than matter's. An important limitation is that it cannot reproduce the DESI DR2 preference for dark energy's effective equation of state to cross a particular boundary, w = −1.

Young explorerScientists are testing an idea about dark energy, which is linked to space expanding faster and faster. In this idea, dark energy can slowly change and have tiny uneven patches. They checked the idea against observations of the universe. One set of star-explosion observations gave it some support, but two other sets could not clearly choose between it and the usual idea. That means scientists have not proved it is right. It also cannot make one kind of change that some observations seem to prefer.

The box within the Universe: anisotropies in periodic cosmological simulations I. Dark-matter-only simulations

Gábor Rácz, Till Sawala

AstronomerThis study quantifies geometry-induced gravitational anisotropy in cubic periodic cosmological simulations, where the Green function is not fully rotationally invariant. The authors analyse 498 dark-matter-only N-body simulations evolved to z=0, with box sizes of 6.25–100 Mpc at fixed mass and force resolution. Diagnostics include the matter power spectrum, halo abundance, merger histories, shapes and alignments, and filament orientations. They find box-aligned, orientation-dependent signatures extending to scales much smaller than the box size, which can systematically shift field-level and halo-level statistics. The results identify periodic-box anisotropy as a non-negligible systematic in small simulation volumes. The authors highlight its relevance to volumes commonly used in hydrodynamical simulations, although the simulations analysed here contain dark matter only.

PublicComputer simulations often represent the Universe with a repeating cube: anything leaving one side reappears on the opposite side. This setup helps mimic an unlimited universe, but the cube’s geometry makes simulated gravity slightly direction-dependent. In 498 simulations containing only dark matter, the researchers found patterns aligned with the cube that reached scales much smaller than the cube itself and could shift statistical descriptions of cosmic structure and dark matter halos. The findings flag a source of systematic error in small simulation volumes. The authors also note its relevance to the small volumes often used in simulations that include gas, though those were not tested here.

Young explorerScientists make pretend universes on computers to learn how things gather together. They often use a box where leaving one side brings you back through the other. But the box’s shape can make gravity pull a little differently in different directions. In their computer tests with dark matter, the scientists found that this could change the patterns that formed, even patterns much smaller than the box. It is a reason to be careful when learning about the real Universe from small computer boxes.

Joint analysis of the Macquart relation and the dispersion measure power spectrum: cross-covariance and redshift self-calibration

Amy Wayland, Robert Reischke

AstronomerThis theoretical and simulation-based study derives the cross-covariance between the host-identified FRB DM–redshift (Macquart) relation and the full-catalogue DM angular power spectrum within the halo model. The covariance is a super-sample effect: only an individual DM's monopole correlates with the power spectrum, implying an exact, model-independent bound on the correlation coefficient. Validation with log-normal forward simulations of 10,000 FRBs finds per-cent-level correlations between individual DMs and bandpowers. Omitting the cross-covariance changes the width of the chi-squared distribution by only 0.8%, supporting effective independence for wide-area surveys. In a joint forecast including LSST-like weak lensing, adding the Macquart relation tightens physical baryon-density constraints by 32% and mean host-DM constraints by a factor of 4.1, but improves baryonification constraints by only about 5%, indirectly through the host contribution. The study also demonstrates unbiased parameter inference when the redshift distribution of host-unidentified FRBs is reconstructed by inverting DMs using the jointly fitted mean relation. Accuracy of that relation remains important: a 20% error can bias power-spectrum bands by up to 2 sigma for 500,000 FRBs. These are calculations, simulation tests and forecasts, not reported observational measurements.

PublicFast radio bursts can reveal ionised ordinary matter between galaxies because that matter delays different radio frequencies by different amounts. This study asks whether two ways of analysing those delays—comparing them with known burst redshifts and measuring their patterns across the sky—share enough information that combining them requires special care. Calculations checked with simulated catalogues find only a small statistical overlap, allowing the two methods to be treated as effectively independent for wide-area surveys. A forecast combining them with an LSST-like survey of weak gravitational lensing predicts that adding the delay–redshift relation would tighten constraints on ordinary-matter density by 32% and on the average delay contributed by bursts' host galaxies by a factor of 4.1. The predicted improvement in parameters describing how ordinary matter is redistributed is much smaller, about 5%. The researchers also show how bursts without identified host galaxies could have their redshift distribution reconstructed using a jointly fitted average relation. That relation must be accurate: in a catalogue of 500,000 bursts, a 20% error could shift the predicted sky-pattern measurements by up to twice their statistical uncertainty in individual bands. These findings come from modelling and forecasts rather than a new observational survey.

Young explorerQuick flashes of radio waves from space can help scientists learn about matter between galaxies. Scientists can study how the waves are slowed down in two ways: by comparing flashes whose redshifts are known, or by looking for patterns across the sky. Using maths and pretend flashes in a computer, the researchers found that these two ways mostly give separate clues, so they can be used together. Their predictions suggest this could help measure how much ordinary matter the universe has. They also tested a way to work out how the flashes are spread out in distance when their home galaxies are unknown. But that needs a good rule connecting the waves' delays to distance: a wrong rule can give a wrong picture. These are computer tests and predictions, not new measurements of real flashes.

Scalar perturbations in two-scalar-field warm inflation

Orlando Luongo, Tommaso Mengoni, Paulo M. Sá

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study analyzes linear scalar perturbations in a two-field cosmological model intended to unify warm inflation, dark matter, and dark energy, with a noncanonical coupling between the inflaton and a second field that acts as late-time dark energy. Assuming negligible dissipation and perturbations in the dark-energy field, the authors derive gauge-ready equations incorporating inflaton quantum and thermal noise and stochastic energy transfer to radiation. Numerical Fokker–Planck calculations yield the scalar spectral index n_s and tensor-to-scalar ratio r for dissipation proportional to T^p. For p = -1, some scenarios agree with current CMB constraints in both weak and strong dissipative regimes; the explored p = 1 and p = 3 scenarios lie outside observationally supported regions. Relative to standard single-field warm inflation, this model produces a systematically larger n_s at fixed r.

PublicThe authors test a theoretical model that aims to connect the universe’s early rapid expansion with dark matter and dark energy using two interacting fields. They calculate how small disturbances would develop and compare the predictions with observations of the cosmic microwave background. Some versions agree with current observations when the dissipation strength decreases inversely with temperature, both for weak and strong dissipation. The versions explored with dissipation increasing linearly or as the cube of temperature do not agree with the observationally supported ranges. These are numerical predictions, not a detection of the proposed fields, and the calculations assume that disturbances and dissipation in the dark-energy field are negligible.

Young explorerScientists used a computer to try out a story about how the universe grew very fast long ago. Their story has two things called fields that affect each other and could help explain parts of the universe we cannot see. They worked out what tiny ripples the story would make and checked whether those ripples fit clues from very old light in space. Some versions fit the clues, and other versions they tried did not. They also left out some effects to make the calculation simpler. A story fitting the clues does not prove it is what really happened.

Enhancing Gravitational Waves from Global Strings via a First-Order Phase Transition

Yongtao Jia, Ligong Bian, Huai-Ke Guo

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

AstronomerThe authors report the first (3+1)-dimensional lattice simulations of a cosmological first-order phase transition in which true-vacuum bubbles nucleate with random phases, expand, and collide to form global strings. In the simulations, the network reaches a scaling regime, with a logarithmic-growth coefficient smaller than that found for a second-order transition. The simulated axion spectrum is used to derive the dark-matter relic abundance and a big bang nucleosynthesis dark-radiation constraint on the axion decay constant f_a and mass m_a. The gravitational-wave-to-axion emission-rate ratio is about two orders of magnitude larger than in the second-order case. The predicted gravitational-wave spectrum could be probed by pulsar timing arrays and space- and ground-based interferometers; this is a simulation-based prediction, not a reported detection.

PublicComputer simulations explore an early-universe transition in which bubbles of a new vacuum state form, grow, and collide, creating a network of string-like structures called global strings. The simulated network settles into a scaling pattern, with slower logarithmic growth than in a comparison involving a second-order transition. The researchers use the predicted spectrum of axions to calculate their contribution to dark matter and to constrain axion properties using limits on extra radiation during the formation of the first atomic nuclei. Compared with the second-order case, the ratio of energy emission rates in gravitational waves and axions is about 100 times larger. The predicted gravitational-wave signal could be tested with pulsar timing observations and space- and ground-based detectors, but no detection is reported.

Young explorerThe scientists used a computer to imagine how the very young universe might have changed. In their model, bubbles grew and bumped together, making a web of tiny string-like things. The web gave off particles called axions and ripples in space called gravitational waves. Compared with another kind of change, the model sent much more energy into ripples relative to axions. The scientists think tools that look for space ripples could test their prediction. They have not found these ripples in the real sky.

Scale-Invariant Three-Component Dark Matter and Gravitational Wave Signals

Mojtaba Hosseini, Rouzbeh Rouzbehi

• High Energy Physics - Phenomenology

AstronomerThis theoretical study considers a classically scale-invariant Standard Model extension with a hidden complex scalar S, two Dirac fermions, and a U(1)_D gauge boson. The scalar couples through the Higgs portal, and loop effects drive electroweak symmetry breaking. The authors identify parameter regions where both fermions and the gauge boson are stable, yielding three-component dark matter. After imposing the observed relic density and current direct-detection bounds, they analyze the finite-temperature effective potential. For one benchmark, they find a first-order phase transition and calculate its predicted gravitational-wave spectrum, comparing it with projected space-based interferometer sensitivities. The viable parameter space is small but potentially testable by future experiments; no dark-matter or gravitational-wave detection is reported.

PublicThe researchers explore a theoretical model in which dark matter consists of three stable types of particles in a hidden sector connected to familiar matter through the Higgs field. They identify a small range of model settings consistent with the measured cosmic dark-matter abundance and current limits from searches for dark matter. For one selected example, their calculations predict an abrupt phase transition in the early universe and the gravitational waves it would produce. They compare that prediction with the expected capabilities of future space-based detectors. Future experiments could test the model, but this study does not report discovering these particles or detecting their gravitational waves.

Young explorerScientists used math to explore an idea: the universe’s unseen dark matter might come in three kinds. They checked that their idea could fit what we already know. In one example, their math says the young universe could have changed suddenly and made ripples in space. Future experiments might help test the idea, but nobody found these three kinds of dark matter or their ripples in this study.

Can cosmic neutrinos induce a cosmic birefringence signal?

Mario Reig

• High Energy Physics - Phenomenology

AstronomerThe paper tests a proposed photon coupling to the cosmic neutrino asymmetry current as an explanation for the hinted isotropic rotation of CMB polarization. Gauge-invariant ultraviolet completions require a Kalb-Ramond field exactly dual to a massless axion. Matching the hinted signal fixes g_aγ/f_ℓ = 1/Λ_*², with Λ_* approximately 10 TeV. SU(2)_L invariance then implies an electron coupling satisfying g_aγ g_ae = m_e/Λ_*², approximately 5 × 10^-12 GeV^-1. The authors find this value excluded by the measured electron magnetic moment combined with light-shining-through-a-wall searches, and independently by stellar evolution. Conserved anomaly-free currents can evade these bounds, but then either a contact interaction among Standard Model fermions excludes the model or relic neutrinos decouple from the signal. They conclude that the proposed cosmic-neutrino mechanism cannot produce the birefringence signal; the polarization rotation itself remains a hint, not an established detection.

PublicThere are hints that the polarization, or preferred orientation, of light left over from the early universe has rotated uniformly across the sky. One proposed explanation involves cosmic neutrinos interacting with light. This theoretical study finds that making the proposal consistent with the required symmetries also introduces a massless particle called an axion and forces an interaction with electrons. The required interaction conflicts with existing laboratory measurements and searches, as well as evidence from how stars evolve. The authors examine ways to avoid those limits, but find that these either encounter another exclusion or remove the relic neutrinos' role in the signal. They conclude that this neutrino explanation does not work, rather than establishing whether the hinted rotation is real.

Young explorerLight from long ago may have had its direction of wiggle turned a little, but scientists are not sure yet. One idea says tiny particles called neutrinos caused the turn. The researchers checked what else would have to happen if that idea were right. They found it would clash with other things scientists have measured. The changes they considered either still did not work or meant the neutrinos were no longer causing the turn. So they say neutrinos cannot explain it this way.

Long lived MeV scale bound state dark matter alleviates the ⁷Li tension

Pa. Gokhula Prasad, V. Suryanarayana Mummidi

• High Energy Physics - Phenomenology

AstronomerThis theoretical study examines thermal and nonthermal Big Bang nucleosynthesis in a model of MeV-scale unstable dark-matter bound states, focusing on weak self-interactions. Long-lived bound states can alleviate the cosmological lithium-7 problem but also produce discrepancies in other light-element abundances. Including nonthermal nucleosynthesis acting on the model’s altered initial abundances can remove this tension. Within the parameter ranges explored, bound-state lifetimes of roughly 1–100 seconds can resolve the lithium-7 discrepancy, with a large parameter region remaining consistent with observational constraints on other light elements. These are model-dependent theoretical results, not evidence that such dark-matter bound states exist.

PublicThe amounts of light elements made in the early universe offer a way to test ideas about dark matter. This theoretical study considers unstable groups of dark-matter particles and how they might change those amounts. Long-lasting groups could help explain the mismatch between predicted and observed lithium-7, but initially create problems for other elements. The researchers find that including additional nuclear reactions outside the thermal process can address both issues in their model. For the conditions they explored, groups lasting about 1–100 seconds could reconcile lithium-7 while keeping other light elements consistent with observations. The study does not establish that this kind of dark matter exists.

Young explorerWhen the universe was very young, it made light kinds of matter, including lithium. Scientists’ calculations and what they see do not quite agree about the lithium. The researchers tried a math idea in which mysterious dark matter forms little groups that later break apart. In their model, extra changes to the early matter could help the lithium amount fit without spoiling the amounts of other kinds. It is an idea that works in their calculations, not something they have seen happen.

Can nₛ hint at a parity-odd sector of gravity?

Christian Dioguardi

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

AstronomerThis theoretical study examines slow-roll inflation in a projectively invariant metric-affine theory, linear in curvature and at most quadratic in distortion, with non-propagating torsion and non-metricity and a non-minimally coupled scalar. Within the ξ-attractor class, integrating out the non-dynamical distortion corrects the scalar kinetic term by f′(φ)² times a rational function of f(φ). The resulting kinetic function can have finite-field poles where the distortion equations degenerate. The authors classify these poles and derive effective-coupling conditions for orders p=2 and p=3, the maximum allowed here. Second-order poles produce α-attractors, with α set by the residue, and occur already in the parity-even sector. Third-order poles require parity-odd quadratic couplings; without them, the kinetic function separates into two terms whose poles have order at most two. For third-order pole inflation, numerical calculations with f(φ) proportional to φ² confirm r proportional to N_*^(-3/2), with tunable amplitude, and n_s approximately 1−3/(2N_*). This predicted tilt is mildly higher than the α-attractor value and lies near the center of the region preferred by the cited ACT, SPT and DESI data combination; this is not an observational detection of the model. Far from the pole, the authors also find an inverse-linear plateau attractor with n_s approximately 1−4/(3N_*) and r proportional to N_*^(-4/3), described as testable with forthcoming BICEP/Keck observations.

PublicThe researchers explore theoretical models of inflation, an early period of rapid cosmic expansion, using a generalized description of gravity coupled to a scalar field. Their calculations show that eliminating parts of the gravity model that do not evolve independently can create special points where the scalar field’s kinetic term becomes infinite. They classify these points and find that two types can lead to different inflationary predictions. The more unusual type requires terms in the theory that distinguish spatial configurations from their mirror images. Numerical calculations confirm its predicted behavior for one particular choice of the scalar-field function. Its prediction for how primordial fluctuations vary with scale falls near the center of the range favored by the cited combination of current observations, but those observations do not establish that this model describes the universe. The study also identifies another common pattern when inflation occurs far from the special points, with predictions the authors say forthcoming BICEP/Keck observations can test.

Young explorerScientists used math to study how the universe might have grown very quickly when it was very young. They tried different rules for gravity and found that some rules make the growing universe behave in similar ways. One possibility fits a pattern favored by the sky measurements they discuss, but that does not mean it really happened that way. They also found another possibility that future sky measurements could help check.

Torsion talks only to spin: the CMB temperature as a test of energy exchange in Einstein-Cartan cosmology

Fernando Izaurieta, Samuel Lepe, Cristian Quinzacara

• General Relativity and Quantum Cosmology

AstronomerThe study tests how torsion-related energy exchange is assigned among matter sectors using CMB temperature measurements. In Einstein-Cartan theory, sector-specific Noether identities make energy-momentum nonconservation proportional to that sector’s spin, leaving minimally coupled photons conserved. By contrast, a metric-affine cosmology fitted to DESI DR2 assigns exchange universally, giving photons almost one-third additional energy. Assuming the photons retain a blackbody spectrum, as FIRAS requires for sources governed by local conditions, this prescription predicts temperatures below T0(1+z) by 7% at z≈0.9 and 8.5% at z≳3, without a free parameter. Toward PKS 1830−211, the measured temperature is 5.08±0.10 K at z=0.886, versus 4.78 K predicted. Combined with CO absorbers, these measurements favor standard scaling by Δχ²=13; 18 Planck cluster bins yield χ²=50.8 for the model versus 15.5 for standard scaling. Under the same interpretation, predicted changes to the primary anisotropies’ spectral shape are also excluded by Planck. Assigning the spin to dark matter instead restores standard T(z), while changing H(z) by less than 10⁻⁴ below z=3 at the fitted parameters.

PublicMeasurements of the universe’s background radiation test a particular way of sharing energy between cosmic geometry and matter. A cosmological model fitted to DESI DR2 data assumes that every component, including light, receives energy. If the light keeps its observed blackbody spectrum, this model predicts that the background was cooler in the past than the standard temperature law says. Absorption toward PKS 1830−211 gives 5.08±0.10 kelvin, compared with the model’s prediction of 4.78 kelvin. Other absorption and galaxy-cluster measurements also favor the standard law. The authors argue that, in Einstein-Cartan theory, energy exchange instead depends on each component’s spin, so minimally coupled light receives none. A scenario in which dark matter carries the spin restores the standard temperature law and barely changes the predicted expansion rate at the fitted settings. The findings challenge the universal-sharing prescription, not every cosmology involving torsion.

Young explorerSpace is filled with a faint glow left over from the early universe. Scientists measured how warm that glow was long ago. One idea says that space gives extra energy to everything, including light. But that idea predicts a past glow colder than the measurements show. A different version, where invisible dark matter carries the spin involved instead of light receiving the energy, keeps the usual temperature rule. The measurements favor that usual rule.

Searching for axion-like particles with SPHEREx

Marco Regis, Marco Taoso, Jorge Terol Calvo

• High Energy Physics - Phenomenology

AstronomerThis study assesses the prospective sensitivity of the upcoming near-infrared telescope SPHEREx to axion-like particles (ALPs) decaying into two photons. Assuming dark matter consists of ALPs, the authors analyze expected signals from the dark matter halos of dwarf spheroidal galaxies, the Large Magellanic Cloud, and the Milky Way. They project that SPHEREx could significantly improve existing limits on the axion–photon coupling for ALP masses of 0.5–3 eV. This is a sensitivity forecast, not a reported detection.

PublicThe researchers explore whether the upcoming near-infrared telescope SPHEREx could search for hypothetical axion-like particles by looking for the light released when one decays into two photons. Their analysis assumes these particles make up dark matter and considers signals from dark matter surrounding the Milky Way, the Large Magellanic Cloud, and small galaxies called dwarf spheroidals. They predict that SPHEREx could substantially tighten current limits on how strongly these particles interact with light, for particle masses of 0.5–3 electronvolts. The study does not report finding the particles.

Young explorerScientists wonder if the invisible stuff called dark matter is made of tiny particles that can turn into two little bits of light. They studied whether a future telescope called SPHEREx could look for that light around our galaxy and some other galaxies. If dark matter really is made of these particles, the telescope might help scientists narrow down what they could be like. They have not found the particles in this study.

Are magnetic fields in cosmic voids primordial?

Deepen Lark, Ruth Durrer, Jennifer Schober

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

AstronomerThe authors propose a late-Universe contribution to cosmic-void magnetism from galactic magnetic dipoles spreading through the conducting intergalactic medium by turbulent magnetic diffusion. Galaxies within voids shorten the required propagation distance to a few Mpc, a scale bracketed by current turbulent-diffusivity estimates. If diffusion reaches sufficiently far, randomly oriented dipoles are predicted to produce volume-filling fields with a white-noise spectrum and amplitudes well above lower bounds inferred from the absence of GeV halos around TeV blazars. Evidence for void fields remains debated, and sufficient propagation is a condition of the proposal, not an established result. This potential astrophysical background could explain void fields without primordial magnetogenesis and must be considered before interpreting them as primordial relics; its predicted white-noise spectrum offers an observational discriminator.

PublicWhether magnetic fields exist in the vast spaces called cosmic voids, and where they come from, remains unsettled. The authors propose that magnetic fields from galaxies could spread into these spaces through turbulent diffusion in the gas between galaxies. Galaxies living inside voids would reduce how far the fields need to travel. If that spreading reaches far enough, the combined fields could fill voids and exceed the minimum strengths inferred from certain gamma-ray observations, although that observational evidence is debated. The proposal could explain void magnetism without fields left over from the early Universe. It also predicts a distinctive pattern in how magnetic strength is distributed across spatial scales, called a white-noise spectrum, that could help distinguish this explanation.

Young explorerSpace has huge, mostly empty places. Scientists are not sure whether these places have magnetic fields or where those fields might come from. This paper suggests that galaxies could share their magnetic fields with the space around them, as swirling gas helps the fields spread. If they spread far enough, fields from many galaxies could fill the empty places. That might mean the fields did not have to come from the very early Universe. This is an idea to check, not something scientists have shown happened.

Dark Energy Crosses the Line: Quantifying and Testing the Evidence for Phantom Crossing

Emre Özülker, Eleonora Di Valentino, William Giarè

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

AstronomerUsing the CPL parametrization, w(a) = w0 + (1 - a)wa, the authors confirm that combinations of recent CMB, BAO, and Type Ia supernova datasets disfavor LambdaCDM at approximately 3 sigma or more and favor phantom-divide crossing. This preference persists when DESI BAO measurements are replaced by SH0ES H0 measurements, despite the known tension between these probes when combined with CMB data. The inferred evolution runs from an early phantom-like phase to a late quintessence-like phase, with the crossing redshift depending on the dataset combination. Within these analyses, absence of a crossing is excluded at 3.1–5.2 sigma. To test whether crossing is an artifact of CPL's linear form, the authors introduce two modified CPL models that prohibit crossing and phenomenologically represent thawing and freezing scalar-field behavior. Only the freezing phantom-like alternative performs comparably to standard CPL, and only in a few cases. Standard CPL gives the best fit for every dataset combination considered. These comparisons support a data preference for crossing, but the conclusion remains tied to the datasets and parametrizations tested.

PublicThe researchers ask whether dark energy's behavior changes over cosmic history in a way that crosses a boundary called the phantom divide. Their analysis combines measurements of the cosmic microwave background, BAO, and Type Ia supernovae. With a commonly used mathematical description called CPL, the data favor a transition from phantom-like behavior earlier to quintessence-like behavior later, rather than the standard LambdaCDM model. The preference persists when DESI BAO data are replaced with SH0ES measurements of the present expansion rate, although these measurements are known to be in tension when combined with the microwave-background data. The researchers also test two versions of CPL that forbid crossing. Neither consistently matches standard CPL's fit, though one comes close in a few cases. This supports crossing as a feature preferred by the data, rather than merely an artifact of CPL's form, but does not establish it independently of the models and datasets tested.

Young explorerScientists are studying whether something called dark energy has changed as the universe has grown older. They compared different math stories with measurements of the universe. The story where dark energy changes from one kind of behavior to another matched best in all the groups of measurements they tested. Stories that did not allow that change usually matched less well. That is a clue, not proof that the change really happened.

Constraints on Compact Dark Matter Population from Micro-lensing Effect of Gravitational Wave for the third-generation gravitational Wave Detector

Xin-Yi Lin, Xi-Jing Wang, Huan Zhou+1 more

AstronomerThe authors develop a framework combining simulated gravitational-wave microlensing in the Einstein Telescope frequency band with hierarchical Bayesian inference to infer the population properties of extragalactic compact dark matter, including candidates such as primordial black holes. Assuming a power-law mass function, they forecast that several microlensed events among 10^4 binary black-hole coalescences could constrain the compact-dark-matter abundance at the approximately 10^-3 level. This is a simulation-based forecast, not an observational constraint, and suggests a complementary test of compact-dark-matter scenarios with future gravitational-wave observations.

PublicIf some dark matter consists of compact objects such as primordial black holes, their gravity could leave distinctive distortions in gravitational waves from merging black holes. The researchers simulate this effect for the future Einstein Telescope and develop a statistical method to estimate the abundance and mass distribution of these objects. Assuming a particular mathematical form for their mass distribution, they forecast that just several distorted signals among 10,000 mergers could probe compact objects making up roughly 0.1% of dark matter. This is a prediction from simulations, not a detection of dark matter.

Young explorerWhen two black holes join together, they make ripples in space. If some invisible matter is packed into small, heavy objects, those objects could change the ripples as they travel past. Scientists made pretend signals on computers to study how a future detector might spot those changes. This could help them learn about invisible matter, but they have not found it this way yet.

Clustering redshift distribution calibration of weak lensing surveys using the DESI-DR1 spectroscopic dataset

R. Ruggeri, C. Blake, J. Aguilar+63 more

AstronomerThe authors apply clustering-based redshift calibration to weak-lensing source samples from DES, KiDS, and HSC, cross-correlating their overlapping tomographic bins with DESI-DR1 BGS, LRG, and ELG samples over 0.1 < z < 1.6. Realistic mock catalogues test sensitivity to fitting scale, reference-sample selection, and source-galaxy bias evolution. A simulation-calibrated source-bias correction uses conservative priors inflated by a factor of two to accommodate modelling uncertainty. Magnification contributions are explicitly modelled and marginalised over; these become non-negligible at z ≳ 1 given the depth of the DESI ELG sample. The resulting bias-weighted redshift distributions agree within uncertainties with previously published self-organising-map calibrations in every survey and tomographic bin. The authors interpret this agreement as support for DESI-enabled clustering redshifts as a robust, independent complement to existing calibration methods, with the potential to reduce a dominant systematic uncertainty in weak-lensing cosmology.

PublicThis study checks how galaxies in three weak-lensing surveys are distributed in redshift, an important source of uncertainty when using these surveys to study the universe. The researchers compare patterns in the galaxies’ positions with those of galaxies whose redshifts were measured by DESI. They use simulated galaxy catalogues to test the method and estimate corrections for how galaxies cluster, allowing extra uncertainty in those corrections. They also account for magnification effects, which become important in the higher-redshift part of their analysis. Their estimates agree, within uncertainties, with earlier calibrations made using a different technique. The findings support this approach as an independent cross-check that could help reduce uncertainty; they do not establish the redshift distributions exactly.

Young explorerAstronomers want to know how far away groups of galaxies are. They compared patterns in galaxy maps with patterns for galaxies whose distances they know better. They also used pretend galaxy maps on computers to check their method. Their answers matched earlier estimates as closely as the uncertainties allowed. This is a helpful extra check, not a perfect answer.

Searching for Cosmological Collider in the Planck CMB Data II: collider templates and Modal analysis

Petar Suman, Dong-Gang Wang, Wuhyun Sohn+2 more

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

AstronomerThe authors search Planck CMB data for primordial non-Gaussianity associated with massive-particle exchange during inflation. They construct simplified cosmological-collider templates covering broad ranges of mass, spin, and sound speed, and propose orthogonalizing them against the tightly constrained equilateral and orthogonal single-field PNG shapes to reduce degeneracies. A parameter scan using the Modal bispectrum estimator yields a maximum significance of 2.35 sigma, after accounting for the look-elsewhere effect, for an orthogonalized massive spin-0 exchange template. This is not a convincing detection. Cross-validation with CMB-BEST gives consistent results for benchmark templates. The authors argue that orthogonalization offers an optimized strategy for future searches in the current low-signal-to-noise regime.

PublicResearchers searched Planck observations of the cosmic microwave background for patterns that could reveal massive particles present during inflation, an early period of cosmic expansion. They built models of possible signals and developed a way to separate them from other early-universe patterns that can look similar. The strongest match had a significance of 2.35 sigma after allowing for the many possibilities searched, so it is not convincing evidence for such particles. A second analysis method produced consistent results for selected test models. The authors suggest that their signal-separation approach could improve future searches.

Young explorerScientists looked at very old light from the universe, searching for patterns that might be clues to heavy particles from long ago. They made pattern guides and tried a new way to tell similar patterns apart. They found a small hint, but it was not strong enough to say the particles were really there. Another way of checking agreed on some test patterns. They think their new method could help with future searches.

Spectral Hierarchy of the Cosmic Web

Francisco-Shu Kitaura, Francesco Sinigaglia

• Computer Vision and Pattern Recognition

AstronomerThe authors introduce a spectral hierarchy of cosmic-web classifiers by applying scale-weighting kernels to the density field before second-derivative, eigenvalue-based classification. The framework unifies potential/tidal and curvature-based definitions and extends to higher-derivative levels that emphasize smaller-scale structure. Its operators connect web environments to ingredients in renormalised bias and effective descriptions of large-scale structure. In AbacusSummit simulations, the authors encode void, sheet, filament and knot labels as an ordered web-contrast field and cross-correlate it with halos on a coarse mesh with spacing approximately 5.5 h^-1 Mpc. They report significant tracer-relevant information from very large scales to the mesh Nyquist limit, with more local hierarchy levels dominating toward nonlinear scales. The findings are simulation-based and resolution-limited; the authors identify fast mock-galaxy production, field-level modelling and studies of environment-dependent clustering and assembly bias as applications.

PublicThe cosmic web can be classified into empty regions, sheets, filaments and dense knots. This study introduces a unified way to make those classifications while giving different weight to large- and small-scale structure. The researchers tested the method in computer simulations, measuring how the classifications relate to the locations of dark-matter halos. They found useful information across the scales accessible to their analysis, with methods emphasizing more local structure contributing most toward smaller, nonlinear scales. These are simulation findings, not observations, and the smallest scales tested were limited by the calculation’s grid. The authors suggest the framework could help build simulated galaxy maps and study how cosmic surroundings relate to clustering.

Young explorerImagine a pretend universe on a computer, with empty places, flat sheets, long threads and crowded clumps. Scientists made a new way to sort these shapes by paying attention to bigger or smaller patterns. In their computer tests, the different ways of sorting helped describe where clumps of matter were. They think this could help make pretend galaxy maps.

Lensing in the Blue III: Weak Lensing Shape Catalogs of 30 Merging Galaxy Clusters

Sayan Saha, Jacqueline E. McCleary, Spencer W. Everett+39 more

• Instrumentation and Methods for Astrophysics

AstronomerSuperBIT presents a weak-lensing dataset covering 30 galaxy clusters observed during its 45-night balloon flight in April–May 2023. Operating above 98% of Earth's atmosphere, the telescope achieved near-diffraction-limited imaging. The analysis uses metacalibration to obtain calibrated galaxy shapes in cluster and calibration fields, with diagnostics of PSF-model residuals, their lensing impact, and correlations between galaxy shapes and galaxy or PSF properties. Parallel image simulations incorporating measured flight PSFs, observed sky backgrounds, and detector noise yield a multiplicative shear bias of (1.54 ± 6.00)%, consistent with zero within the quoted uncertainty; this bias estimate comes from simulations, not a direct measurement of cluster shear bias.

PublicDuring a 45-night balloon flight in April–May 2023, SuperBIT photographed 30 galaxy clusters from above 98% of Earth's atmosphere, producing exceptionally sharp images. The dataset is designed to measure weak gravitational lensing: the subtle distortion of background galaxy shapes by gravity. The team calibrated galaxy shapes and checked whether telescope image blurring or other measured properties could distort the lensing signal. In simulated images built to reflect actual flight conditions, the analysis showed a systematic scaling error of 1.54%, with an uncertainty of ±6.00 percentage points. That simulation result is compatible with no such error, but the uncertainty leaves room for one.

Young explorerA telescope called SuperBIT rode high in the sky on a balloon and took pictures of 30 groups of galaxies. Gravity can bend light and make faraway galaxies look a little stretched. The scientists carefully checked the galaxy shapes and the blur in the pictures. They also made pretend pictures like the real ones to test their measuring method. Those tests did not show a clear mistake in how strongly the method measured the stretching, but they could not rule one out.

Estimates of the Dynamic Characteristics of Binary Systems for Traversable Wormholes Search

I. A. Moiseev, O. S. Sazhina

AstronomerThis study simulates the detectability of traversable wormholes in non-accreting wide binaries and the Galactic center; it does not report an observed wormhole. The model joins two asymptotically flat Schwarzschild spacetimes, leaves the detailed throat geometry unspecified, and matches monopole perturbations across the throat in the short-throat approximation. A massive body on an elliptical orbit on the opposite side perturbs the motion of a companion star on our side. For a supermassive black-hole wormhole candidate, the perturbing acceleration is compared with stochastic gravitational forcing from surrounding stars. In dormant wide binaries, the authors examine radial-velocity signatures, possible distinctions from triple systems, and limitations imposed by subtracting a Keplerian orbit. Under the adopted model and observational sampling, simulated perturbations are detectable at 1.5 km/s measurement accuracy for every observation span considered. At 5 km/s accuracy, the non-parametric analysis becomes statistically significant after approximately 17 years of simulated observations. Spectral and non-parametric methods reduce the required accumulation time relative to matched filtering alone. These detectability claims remain conditional on the model assumptions and sampling.

PublicCould a hypothetical wormhole reveal itself through a star’s motion? This paper explores that possibility with simulations, not an actual detection. In the model, a massive object orbiting on the far side of a wormhole gravitationally disturbs a star on our side. The researchers examine whether those disturbances could be recognized in wide pairs of objects that are not accreting matter, and consider competing gravitational disturbances from stars near the Galactic center. For the simulated wide binaries, velocity measurements accurate to 1.5 km/s reveal the modeled signal over every observing duration tested. With a less precise accuracy of 5 km/s, one statistical method needs about 17 years of simulated observations. The authors also discuss confusion with three-object systems and limitations from removing the star’s ordinary orbital motion. These findings depend on the assumed wormhole model and observing schedule.

Young explorerImagine a wormhole as a pretend tunnel through space. The scientists asked whether something moving on the far side could tug on a star on our side and make its motion change. They tried this in computer experiments, not by finding a real wormhole. In their model, careful measurements could spot the change, but less careful measurements could take many years. Other things can tug on stars too, so a changing motion would need careful checking.

Cosmological discrete self-similarity in primordial black hole formation

Luis E. Padilla, Tomohiro Harada, Ethan Milligan+1 more

• General Relativity and Quantum Cosmology

AstronomerFully relativistic simulations of near-critical massless scalar-field collapse in an expanding Friedmann-Lemaître-Robertson-Walker universe exhibit discrete self-similarity, with log-periodic oscillations in the primordial black hole mass-scaling relation. This establishes a simulation-based proof of principle that discrete self-similarity survives in a cosmological background. Scalar-field kination contrasts with radiation-fluid collapse, which exhibits continuous self-similarity. The authors illustrate corresponding log-periodic modulations in a PBH mass spectrum; these may survive if formation is dominated by a sufficiently narrow range of scales. The results suggest that PBHs could encode the matter sector and cosmic dynamical state at horizon re-entry, not only primordial perturbation amplitudes; no observational detection is reported.

PublicComputer simulations suggest that black holes forming in the early, expanding Universe could preserve clues about the conditions that created them. In simulations of a collapsing massless scalar field, the researchers found a repeating pattern in how black hole mass changes near the threshold for formation. This pattern repeats at intervals on a logarithmic scale and differs from the behavior of collapsing radiation. An illustrative calculation shows how it could leave a pattern in the distribution of primordial black hole masses. That pattern might persist if formation mainly occurred over a sufficiently narrow range of scales. This is a theoretical possibility supported by simulations, not a pattern detected in real black holes.

Young explorerScientists used computers to pretend they were watching tiny black holes form when the Universe was very young and growing. In their pretend universe, they found a repeating pattern in how big the black holes became. A pattern like this might help tell us what the young Universe was like, but it may not last in every situation. Scientists have not seen it in real black holes.

Probing the matter-dominated expansion with multi-redshift Lyman-α BAO from DESI DR2

Hiram K. Herrera-Alcantar, Julien Guy, Alma X. Gonzalez-Morales+60 more

AstronomerThis analysis splits the DESI DR2 Lyα forest auto-correlation and forest–quasar cross-correlation into three bins at effective redshifts 2.13, 2.40, and 2.81. BAO precision is approximately 2.0–2.5% per bin radially and transversely, and 1.1–1.2% isotropically. Pipeline tests on 400 synthetic datasets yield unbiased BAO recovery and well-calibrated uncertainties. Across the redshift range, D_V/r_d rises from 30.26±0.39 to 32.22±0.47, D_M/D_H rises from 3.96±0.15 to 5.63 with uncertainties of +0.22/−0.24, and D_H/r_d falls from 9.40±0.20 to 7.22±0.17. The inferred expansion evolution, H(z)∝(1+z)^n with n=1.34±0.16, is consistent with ΛCDM and expected matter-dominated scaling. The clustering-evolution exponents are γ_α=3.05±0.16 for forest bias, γ_β=−0.97±0.26 for the RSD parameter, and γ_Q=1.56±0.23 for quasar bias; the latter agrees with independent quasar clustering measurements. Combined with DESI DR2 galaxy and quasar BAO, the three-bin results give constraints consistent with the single-bin analysis in flat ΛCDM and w₀wₐCDM, while improving curvature constraints by approximately 12% in ΛCDM+Ω_K.

PublicResearchers used patterns in the absorption of quasar light—the Lyman-alpha forest—in DESI’s second data release to measure cosmic expansion at three different redshifts. The patterns contain a characteristic scale called baryon acoustic oscillations, which helps measure cosmic distances. Splitting the data into three groups allowed the team to trace changes in expansion rather than obtain one combined measurement. Their isotropic BAO measurements have roughly 1.1–1.2% precision per group, and the inferred expansion history agrees, within the uncertainties, with the standard ΛCDM cosmological model and the expected behavior when matter dominates cosmic expansion. Tests on 400 simulated datasets found no systematic offset in the recovered BAO measurements and supported the reported uncertainties. The analysis also measured how the clustering of the absorbing material and quasars changes with redshift. When combined with other DESI galaxy and quasar BAO measurements, the results remain consistent with the earlier single-group analysis and tighten constraints on spatial curvature by about 12% in a ΛCDM model that allows curvature.

Young explorerScientists looked at patterns in light from very faraway objects called quasars. Some of that light was absorbed on its way to us. The patterns help scientists measure how the universe stretches. By sorting the patterns into three groups, they could study that stretching at three times in the universe’s past. What they found fits, within the measurement uncertainties, a common picture of how the universe grows. They also practiced their measuring method on 400 pretend sets of data, and those tests showed that it worked as expected.

Primordial black holes forming during kination: the trapped, the overdense, and the void

Cristian Joana

AstronomerNonlinear numerical-relativity simulations investigate PBH formation in a single-field model evolving from slow roll through transient ultra-slow roll into kination. The simulations track initially sub-Hubble field fluctuations through the non-attractor transition, determine their super-Hubble curvature profiles, and evolve their subsequent re-entry during kination. Among the initial configurations explored, three outcomes occur: a patch trapped in inflation, a positive-curvature overdensity, and a negative-curvature void bounded by an overdense shell. Each can form a PBH through a different mechanism. Collapse thresholds measured for one selected overdense profile and one selected void profile, and compared with sinc-profile thresholds, show that neither central curvature nor peak linear compaction alone supplies a profile- or channel-independent collapse criterion. The authors conclude that PBH abundance calculations in non-attractor models must use distributions of complete profiles and treat the three channels separately.

PublicComputer simulations explore how primordial black holes could form from fluctuations in the very early universe, in a model with a brief phase of unusually slow field evolution followed by a phase called kination. For the starting conditions tested, the simulations produce three kinds of regions: one that remains caught in inflation, one with an overdense center, and one with a central void surrounded by a denser shell. All three can potentially produce black holes, but through different mechanisms. Tests of one selected overdense shape and one selected void shape, compared with a reference shape, show that neither of two single-number measures reliably determines collapse across different shapes and formation routes. The authors argue that predicting how many primordial black holes this class of models produces requires accounting for the full shapes of the regions and considering each route separately. These are simulation findings, not observations of primordial black holes.

Young explorerScientists used computers to explore how black holes might have formed when the universe was very young. In the cases they tried, they found three kinds of places: one that kept stretching very fast, one with extra stuff in the middle, and one with a more empty middle and extra stuff around it. Each kind could make a black hole in a different way. Their tests suggest that the whole shape matters, not just one number about the middle. This happened in computer models; it is not something they saw in the sky.

Probing the baryonic--dark matter connection in galaxy clusters using X-rays with gated recurrent unit neural networks

Asif Iqbal, Subhabrata Majumdar, Weiguang Cui+3 more

AstronomerThe authors introduce a gated recurrent unit (GRU) framework that predicts three-dimensional galaxy-cluster mass profiles from spherically averaged intracluster gas profiles, treating radius as a sequence and accommodating different radial samplings. Training and validation on hydrodynamical simulations from The Three Hundred Project yield unbiased predictions with typical 1σ scatter of about 5% over most of the cluster region, outperforming hydrostatic equilibrium (HSE) estimates in those tests. The model supplies radius-dependent uncertainties and is reported to be robust to variations in data quality and cluster morphology. Joint training on GIZMO-SIMBA and GADGET-X enables generalisation across those two simulation suites. Enclosed gas mass is the dominant predictor, supplemented by pressure and temperature. Applied to XMM-Newton observations, GRU masses closely agree with HSE estimates for the lower-mass REXCESS sample but exceed HSE masses systematically for the higher-mass X-COP sample. The latter offset is consistent with hydrostatic mass bias, rather than an independent demonstration of the GRU masses’ accuracy on real clusters. Extension to Sunyaev-Zel’dovich and optical data is proposed, not demonstrated.

PublicMeasuring the masses of galaxy clusters helps researchers study the universe, but standard methods that assume the clusters’ hot gas is in hydrostatic balance can be biased, especially in disturbed clusters. This study trains a deep-learning model to estimate how mass is distributed with distance from a cluster’s centre using profiles of its hot gas. In computer simulations, the model’s predictions show no systematic offset and have a typical spread of about 5% over most of the cluster region, improving on the standard method in those tests. When applied to X-ray observations from XMM-Newton, the model agrees closely with standard estimates for the lower-mass REXCESS sample but gives systematically higher masses for the higher-mass X-COP sample. That difference is consistent with the standard method underestimating mass, but does not independently establish which estimates are correct. Using other kinds of observations is a possible future extension.

Young explorerGalaxy clusters are huge groups of galaxies with hot gas around them. Scientists taught a computer to use patterns in that gas to guess how much matter is inside different parts of a cluster. It did well on computer-made clusters. Then they tried it on real clusters seen in X-rays. For one group, its guesses were close to those from an older method. For another group of heavier clusters, it guessed more matter than the older method did. That might mean the older method misses some matter, but the difference alone does not prove the new guesses are right.

Single Frequency CMB Foreground Removal with Inter-scale Machine Learning

Helen Shao, Fiona McCarthy, Blake D. Sherwin+2 more

AstronomerThis simulation study presents signal-preserving machine-learning foreground removal that exploits correlations across angular scales to clean CMB B-mode polarization, a probe of inflation. CNNs trained on DustFilaments reconstruct large-scale dust foregrounds (ell < 200) from small-scale inputs (ell > 200). At a single frequency, the residual foreground-power fraction is approximately 0.704 for B-only inputs and 0.376 with temperature and E-mode inputs, both worse than spatial ILC using Simons-Observatory-like frequencies. A hybrid network combining multi-frequency and inter-scale information reduces these fractions to 4.71 × 10^-4 and 3.62 × 10^-4, respectively, while retaining ILC's signal-preserving property. Its residual power is approximately seven times lower than ILC and two to three times lower than a frequency-only network, demonstrating complementary information across scales and frequencies in these simulations. These gains are established only for DustFilaments; generalization across simulations remains a key challenge.

PublicDust in our Galaxy obscures a polarization pattern in the cosmic microwave background that could help scientists study the universe's earliest moments. In simulated sky maps, researchers trained machine-learning networks to use small-scale dust patterns to estimate and remove larger-scale contamination. Using just one observing frequency was less effective than an established method that combines several frequencies. But combining information across both frequencies and angular scales left about seven times less dust-contamination power than that established method, while preserving the desired primordial signal. This is a promising simulation result, not a demonstrated improvement on real sky observations: the gains have been shown only with the DustFilaments simulations, and working reliably across different simulations remains a major challenge.

Young explorerScientists want to study very old light from space, but dust in our galaxy gets in the way. They taught a computer to look at little dust patterns to help clean up bigger ones in pretend sky pictures. The computer did best when it also used pictures made at different frequencies, and its method keeps the light scientists want to study. But it has only worked this well with one kind of pretend sky so far. Scientists still need to find out whether it works well with other kinds.

Optical Signatures of Sgr A* and M87* with Dark Matter Halos

Noraiz Tahir, Muhammad Ali Paracha, Mubasher Jamil

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study calculates photon spheres, shadows, weak- and strong-lensing observables, and caustic structures for Sgr A* and M87* with cold-dark-matter and cored scalar-field-dark-matter halo profiles. Comparisons with EHT shadow diameters place all tested models within 1.2 sigma of the measurements, with small differences in fit quality, Δχ² ≲ 1.2. The shadow comparison therefore does not clearly discriminate between the models. The calculated lensing topology differs between the two objects: Sgr A* retains tangential and radial critical curves, whereas M87* may retain only tangential critical curves, attributed to its larger mass. This is a proposed signature for future observations, not an observed topological difference.

PublicThe Event Horizon Telescope has imaged the shadows of the supermassive black holes Sgr A* and M87*. This study calculates how two possible distributions of dark matter around them would affect their shadows and the bending of light. All tested models agree closely with the measured shadow sizes, so this comparison does not clearly favor one model. The calculations also suggest that the two black holes could produce different patterns of extreme light bending: one type of pattern present around Sgr A* might be absent around the more massive M87*. Future observations could look for that predicted difference; it has not been established by these measurements.

Young explorerScientists have pictures of dark shadows around two black holes. They used math to ask how invisible stuff called dark matter might change those shadows and bend light nearby. Both ideas they tried made shadow sizes close to the ones in the pictures, so the pictures do not clearly pick a winner. Their math also says the two black holes might bend light in different patterns. Scientists could look for those patterns in the future.

Filament-Arm Node Systems (FANS): A new probe of the winding and chirality of the cosmic web

Pedro da Silveira Ferreira, Renyue Cen

AstronomerThe authors define Filament-Arm Node Systems (FANS), multiple cosmic-web filament arms connected to a common node, as an object-based probe of cosmic chirality on characteristic scales of about 60 Mpc/h. They measure spirality as winding amplitude and handedness as its clockwise or counter-clockwise sign, and introduce an axis-conditioned estimator for the projected signature of a coherent three-dimensional axial handedness pattern. In two distinct SDSS filament reconstructions, significance tests using sign-flip nulls and 27 controlled construction-parameter variations reveal no significant handedness preference, globally or around a preferred axis. These constraints are consistent with parity symmetry expected in standard LCDM, rather than proof of symmetry. Comparing the lowest- and highest-redshift bins within 0.1<z<0.6, they find decreasing spirality with cosmic time, including within individual arm-multiplicity classes. Gravitational straightening of filament arms is a possible interpretation. FANS provide a baseline for future parity tests with larger filament samples.

PublicThe cosmic web contains long filaments that meet at junctions. This study defines systems of several filaments joined at one junction and measures how strongly their arms wind around it and whether they wind clockwise or counter-clockwise. Using two reconstructions from SDSS data, the researchers find no statistically significant preference for either direction, including when searching for a preferred axis. This is consistent with the mirror symmetry expected in the standard cosmological model, but does not prove that symmetry is exact. Comparing earlier and later cosmic epochs, they also find that the arms become less wound over time, even when grouping systems by their number of arms. Gravity straightening the filaments is a possible explanation, not an established cause. The method offers a starting point for future tests with larger surveys.

Young explorerHuge strands in space meet at places like roads meeting at a crossing. Scientists looked at how these strands curl around their meeting places. They did not find clear evidence that the strands prefer curling one way rather than the other. They also found that the strands look less curled at later times in the universe. Gravity might be helping to straighten them, but the scientists are not sure that is why.

Lensing in the Blue IV: The First Weak Gravitational Lensing Maps from the Stratosphere

Sayan Saha, Maya Amit, Jacqueline E. McCleary+42 more

AstronomerSuperBIT’s April 2023 science flight obtained imaging of 30 galaxy clusters. This work presents the first weak-lensing convergence maps from those observations for six selected clusters. Background galaxies are selected using three-band photometry and a color-color method, and their calibrated shapes are used to reconstruct convergence through Kaiser–Squires inversion. The convergence signal-to-noise maps are compared with red-sequence cluster-member number-density maps as independent mass tracers; the abstract does not quantify their agreement. The results demonstrate the first successful weak-lensing signal reconstruction from imaging by a sub-orbital astronomical observatory.

PublicThe balloon-borne SuperBIT telescope imaged 30 galaxy clusters during its April 2023 science flight. Researchers used six of those clusters to make maps tracing their mass through weak gravitational lensing: the subtle distortion of background galaxies’ apparent shapes. They used images in three color bands to help distinguish background galaxies from foreground ones, then compared the lensing maps with maps of cluster-member galaxy concentrations. The abstract does not specify how closely the maps agree. This is the first successful reconstruction of a weak-lensing signal using images from a sub-orbital astronomical observatory.

Young explorerA telescope carried by a balloon took pictures of big groups of galaxies. The groups’ gravity slightly changes how galaxies behind them look. Scientists used those tiny changes to draw maps showing where matter is in six groups. They also compared these with maps of where the groups’ galaxies gather. This was the first time scientists made this kind of gravity map using pictures from a telescope flying below orbit.

When, Why, and How CMB Compression Fails

Davide Pedrotti, William Giarè, Hanyu Cheng+1 more

AstronomerThis study tests the validity of CMB likelihood compression calibrated in ΛCDM by comparing parameter constraints from data combinations using the full Planck-CMB likelihood with those using its compressed counterpart across several beyond-ΛCDM models. Compression remains accurate for the late-time dark-energy extensions studied when they preserve the dark-matter background evolution and introduce no significant additional perturbative effects. Modified dark-matter evolution, however, breaks the mapping between present-day matter density and matter density at CMB-relevant epochs, invalidating compressed constraints even for exclusively late-time modifications. In the affected cases, compression can shift posterior centers, induce strongly anisotropic deformations, reorder principal modes, and mix and rotate eigendirections. These distortions yield incorrect marginalized parameter constraints, with discrepancies approaching an order of magnitude in some cases studied. The findings concern the reliability of the inference method, not observational evidence for any particular new-physics model.

PublicResearchers tested whether a compact summary of cosmic microwave background data can safely replace the full statistical analysis when investigating alternatives to the standard cosmological model. Comparing analyses based on the full Planck likelihood with a summary calibrated to the standard model, they found that the shortcut worked for the late-time dark-energy models studied, provided those models preserved dark matter’s background evolution and added no significant effects on fluctuations. It failed for models that changed how dark matter evolves, even when the changes occurred only late in cosmic history. Such changes disrupt the link between today’s matter density and the density at times relevant to the microwave background. The shortcut could then shift and reshape the inferred ranges of cosmological parameters, with discrepancies approaching a factor of ten in some cases. This is a warning about how to test new theories, not a discovery that dark matter actually evolves in these ways.

Young explorerScientists use an old glow in space to learn about the universe. They checked whether using a short summary of that glow gives the same answers as using the fuller information. For some ideas about how the universe changes, the shortcut worked well. But for ideas in which dark matter changes differently over time, the shortcut could give very different answers. The study does not show that dark matter really changes that way. It shows that scientists must be careful about when they use the shortcut.

pbhalo: computing primordial black hole and minihalo populations from a single primordial perturbation spectrum

Bogdan A. Rudenko

AstronomerThe authors present pbhalo, an open-source Python package linking PBH and dark matter minihalo calculations to a single primordial curvature power spectrum in a specified cosmology. Enhanced small-scale power can produce PBHs during radiation domination and minihalos, including ultracompact minihalos, from the same modes during matter domination. The package computes the PBH mass function, halo mass function and UCMH abundance, and jointly applies observational constraints on PBH abundance and the spectrum. Components are validated against colossus, pbhstat and published results; lognormal peaks illustrate the joint constraints. This is a computational framework, not a reported detection of these populations. The code is MIT-licensed.

PublicThe paper introduces pbhalo, a freely available Python tool for calculating how stronger small-scale variations in the early universe could produce both primordial black holes and small clumps of dark matter. In this picture, the black holes form earlier, when radiation dominates the universe, while the dark matter clumps form later, when matter dominates. Starting from one description of those early variations, the tool calculates the numbers and masses of these objects and applies limits from observations. Its components were checked against other software and published results, and the authors demonstrate combined limits using a particular peak shape for the early variations. The paper presents a calculation tool, not evidence that these objects have been found.

Young explorerTiny uneven spots in the baby universe might have helped make black holes early on and little bunches of dark matter later. The scientists made a free computer tool to work out how many of these things might form and how heavy they might be. They checked parts of the tool against other calculations. They did not report finding these things in the sky.

Inflation, Cosmic Perturbations and Non-Gaussianities

Yi Wang

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

AstronomerThis theoretical review covers inflationary perturbations at linear and nonlinear orders. It also surveys a variety of inflation models, emphasizing their signatures in cosmic perturbations. The abstract reports no observational findings or tests of these models.

PublicThis paper reviews theories of cosmic inflation and the disturbances associated with it. It covers both simpler, linear descriptions and nonlinear descriptions, and discusses how different inflation models could leave different patterns in cosmic disturbances. It is a review of theory, not a report of new observations.

Young explorerThis paper looks at ideas about how the universe may have grown very quickly and what little ripples might go with that growth. It explains different ways to describe the ripples and how different ideas about the growth might make different patterns. It reviews ideas rather than reporting something newly seen.

Quintessential Inflation in Light of ACT DR6

Sayantan Choudhury, Swapnil Kumar Singh, Satish Kumar Sahoo

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

AstronomerThis theoretical study examines a generalized-exponential quintessential-inflation potential in light of ACT DR6 scalar-tilt constraints. The potential slow-roll hierarchy is derived through fourth order and checked against numerical scalar and tensor mode calculations. For n=15 and λ=10⁻⁹ at 60 remaining e-folds, the numerical predictions are n_s≈0.96396, r≈7.71×10⁻⁵, and a negative running of running of order 10⁻⁵. Using the exact Hubble-flow endpoint, the full inflationary field excursion exceeds M_Pl, although the ten-e-fold observable interval is much smaller. A phenomenological radiation-injection family is evolved through kination, radiation domination, and matter domination, with leading-order gravitational-wave transfer spectra and an integrated radiation-density test. Adding a shallow exponential term permits a calibrated late-time quintessence phase, whose homogeneous equation of state and expansion are evaluated numerically. These are model calculations, not detections; the resulting map of inflation, reheating, gravitational-wave, and dark-energy requirements depends on the assumed transfer treatment and thermal history.

PublicThe researchers use mathematical and numerical calculations to examine a model linking the universe’s early rapid expansion with a later dark-energy phase. They assess its early-universe predictions in light of ACT DR6 measurements and follow possible histories for how radiation is introduced after inflation. They also calculate predicted gravitational-wave spectra. Adding a shallow extra term to the model allows a late-time dark-energy phase whose expansion behavior they calculate numerically. The work maps the requirements for these different stages to fit within the same framework; it does not establish that this model describes the real universe. Its conclusions depend in part on assumptions about the universe’s thermal history and the evolution of gravitational waves.

Young explorerScientists used math and computers to explore an idea about how the universe could grow very fast when it was young and speed up again much later. They worked out what the idea would predict and considered different ways the universe might have changed in between. This is a study of what could happen, not proof that it did happen, and the answers depend on some choices in their model.

Baryogenesis and EDMs in the 2HDM with a Complex Singlet

Björn Garbrecht, Edward Wang

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

AstronomerThe authors present the first joint analysis of Higgsogenesis and electric dipole moments (EDMs) in a model with two Higgs doublets, a complex scalar, and a Majorana fermion. In the proposed mechanism, scalar decays generate an asymmetry between the Higgs doublets, Standard Model processes partly transfer it to fermions, Majorana-mediated interactions generate B−L, and weak sphalerons partially convert B−L into a baryon asymmetry. Their numerical analysis finds viable baryogenesis with singlet masses as low as 10^5 GeV through resonant enhancement. Some parameter choices also yield large electron and neutron EDM contributions. These are model results, not detections: the scenario links baryogenesis and Higgs-sector CP violation to potential EDM signals through out-of-equilibrium decays, without requiring a first-order electroweak phase transition.

PublicThis theoretical study explores a possible explanation for how the universe developed an imbalance between matter and antimatter, and how that explanation might be tested using electric dipole moments of electrons and neutrons. In the proposed model, decays of a new scalar particle start an imbalance involving two Higgs fields. Other particle interactions then transform it into a matter imbalance. Numerical calculations suggest the mechanism can work with new singlet-particle masses as low as 100,000 GeV because of a resonant enhancement. For some model settings, it also produces large electric dipole contributions, which describe a separation of electric charge within a particle. These are predictions from a model, not observed signals. Unlike approaches requiring a first-order electroweak phase transition, this proposal connects matter production to possible dipole signals without that extra assumption.

Young explorerScientists are exploring an idea about why the universe has more matter than antimatter. In their idea, a new kind of particle breaks apart and starts a tiny imbalance. Other particles pass it along and change it into extra matter. Their calculations suggest this could work and might also make electric charge sit a little unevenly inside electrons and neutrons. Looking for that unevenness could help test the idea, but the calculations do not show that nature really did it this way.

Classical and quantum evolution of inflationary fluctuations

Guillermo Ballesteros, Jesús Gambín Egea, Alejandro Pérez Rodríguez

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

AstronomerThis theoretical study compares inflationary correlation functions calculated with classical and quantum dynamics. Even when the correlations are matched at a particular time during inflation, they differ at its end if interactions are relevant. The discrepancy is exponentially sensitive to the number of e-folds since matching. The authors illustrate this with the tree-level bispectrum of primordial curvature fluctuations and the one-loop tensor power spectrum. They also show that classical evolution beginning at a finite time does not imply poles in the scalar bispectrum.

PublicThe researchers compare two ways of calculating patterns in tiny disturbances during inflation, an early period of rapid cosmic expansion: classical physics and quantum physics. Their calculations show that making the two descriptions agree at one moment does not guarantee agreement when inflation ends, if interactions matter. The difference is exponentially sensitive to how much expansion occurs after that moment. They demonstrate this in calculations of relationships among the disturbances, not in observations. They also show that starting the classical calculation at a finite time does not necessarily produce mathematical singularities in one of these descriptions.

Young explorerScientists used two sets of physics rules to work out patterns in tiny ripples while the very young universe stretched quickly. Even if the two answers match at one moment, they can be different later when the ripples affect one another. How much the universe stretches after that moment matters a lot. This is a finding from calculations, not something the scientists saw in the sky.

Leptogenesis with sub-electroweak-scale reheating temperature

Basabendu Barman, Arindam Basu, Debasish Borah+1 more

• High Energy Physics - Phenomenology

AstronomerThis theoretical study examines leptogenesis during post-inflationary reheating with reheating temperatures below sphaleron freeze-out. Assuming a monomial inflaton potential, it analyzes three perturbative decay channels: pairs of Standard Model-like bosons, pairs of Standard Model-like fermions, or exclusively pairs of heavy right-handed neutrinos that briefly dominate the energy density before decaying into Standard Model final states. By tracking the sphaleron interaction rate throughout reheating, the authors identify parameter regions in each scenario that reproduce the observed baryon asymmetry while satisfying existing cosmological constraints. They also discuss the potential for future primordial gravitational-wave observations to probe these scenarios; no such detection is reported.

PublicThe Universe contains more matter than antimatter. This theoretical study explores whether that imbalance could have developed while the Universe was reheating after inflation, even if the reheating temperature was below the temperature at which certain particle reactions cease to operate efficiently. The authors test three possible ways for the field driving inflation to decay, including one involving heavy neutrinos that briefly dominate the Universe’s energy density before decaying. Following the relevant reaction rates during reheating, they find model conditions that can reproduce the observed matter imbalance without conflicting with existing cosmological limits. Future observations of gravitational waves from the early Universe might test these ideas, but the study does not report observational confirmation.

Young explorerThe Universe has more matter—the stuff that makes stars and people—than antimatter. Scientists used math to explore three ways this might have happened as the very young Universe warmed up after growing very quickly. They found that each idea could make the right amount of extra matter under certain conditions. That does not mean they know which idea really happened. Someday, tiny ripples in space from long ago might help test these ideas.

Spontaneous Scoto-leptogenesis

Arghyajit Datta, Hyun Min Lee, Jun-Ho Song

• High Energy Physics - Phenomenology

AstronomerThis theoretical study proposes “Spontaneous Scoto-leptogenesis” within the dynamical minimal scotogenic model, linking neutrino masses, inert scalar dark matter, and low-scale baryogenesis. A rolling Majoron associated with spontaneous global U(1) B−L breaking generates an effective B−L chemical potential. B−L-violating right-handed-neutrino decays, inverse decays, and mediated scatterings generate an asymmetry that electroweak sphalerons convert into baryon asymmetry. The authors find that the mechanism operates in the strong-washout regime and permits a TeV-scale lightest right-handed neutrino in thermal scotogenic leptogenesis with two hierarchical right-handed neutrinos. They identify the role of the λ5 coupling in leptogenesis and in efficiently erasing the inert scalar asymmetry. They also explore Majoron production through kinetic misalignment, finding that the model can support a multicomponent dark sector containing both inert scalars and Majorons. These are model-based findings, not observational detections. Proposed complementary tests include dark matter direct detection, collider searches for inert scalars, and future searches for Majoron dark matter or dark radiation.

PublicWhy does the Universe contain more matter than antimatter, and what gives neutrinos their masses? This theoretical proposal connects those questions with the identity of dark matter. In the model, an evolving field called the Majoron helps generate a matter–antimatter imbalance through interactions involving right-handed neutrinos. The authors find that the mechanism can work with the lightest of these neutrinos at energies of a few trillion electron volts, potentially bringing the scenario within reach of direct tests. The model can also contain two dark matter components: inert scalar particles and Majorons. None of these proposed particles or mechanisms is reported as detected here. The authors suggest testing the framework through dark matter experiments, particle-collider searches, and future searches for Majorons or dark radiation.

Young explorerThe Universe has more matter than antimatter, and it also has invisible stuff called dark matter. Scientists have proposed a new idea that could help explain both, as well as the tiny masses of particles called neutrinos. Their idea uses new particles and a changing field, and dark matter could come in two kinds. This is a possible explanation, not something experiments have shown to be true.

Black Hole Seeds and Little Red Dots: Connecting Formation and Growth with a JWST Multi-Cycle Treasury Program

Fabio Pacucci, Raffaella Schneider, Harley Katz+83 more

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena

AstronomerThis white paper advocates a coordinated JWST Multi-Cycle Treasury program to constrain early black hole seeding, growth, and galaxy co-evolution, and to clarify the nature of broad-line emitters and Little Red Dots (LRDs). JWST has revealed abundant faint active galactic nuclei and compact, high-redshift LRDs, but the interpretation of LRDs as accreting massive black holes remains debated. High inferred early black hole number densities and apparent black hole mass excesses relative to stellar mass in some systems challenge simple seeding and growth scenarios; existing samples cannot disentangle seed properties from subsequent growth. The proposed program would combine grating spectroscopy, deep MIRI imaging, and repeated-field variability measurements with uniform selection extending to low black hole and host masses. The aim is to obtain self-consistent black hole mass functions, Eddington-ratio distributions, and host properties, providing complementary constraints rather than an already demonstrated solution to the origin of early massive black holes.

PublicJWST has found many faint active galactic nuclei and a population of tiny-looking, distant sources called Little Red Dots. Growing massive black holes are one leading explanation for the dots, but their true nature is still uncertain. The inferred abundance of early black holes, and indications that some are unusually massive compared with their galaxies’ stars, challenge simple accounts of how black holes began and grew. Present observations cannot clearly separate the effects of a black hole’s beginnings from its later growth. This white paper proposes a coordinated JWST observing program spanning multiple observing cycles, combining detailed spectra, deep infrared images, and repeated observations to track changes in brightness. Uniformly selected samples including lower-mass black holes and galaxies could help test competing explanations for black hole origins, growth, and their relationship with galaxy evolution. These are proposed tests, not results already obtained.

Young explorerJWST has spotted many faint places where giant black holes are feeding, and some tiny-looking red dots far away. Scientists think the dots might also hide growing black holes, but they are not sure. They also do not yet know how the first giant black holes got started or grew so big. This paper asks for a long, carefully planned set of telescope observations, including looking at the same places again to see what changes. Those new looks could give scientists better clues about the black holes and the galaxies around them, but the answers are not known yet.

The obscured nucleus of NGC3256 S. I. Anisotropic AGN near-IR radiation field traced by CO v=1-0 with JWST/NIRSpec

Miguel Pereira-Santaella, Eduardo González-Alfonso, Ismael García-Bernete+4 more

AstronomerJWST/NIRSpec observations of the deeply obscured, low-luminosity AGN in NGC 3256’s southern nucleus reveal spatially resolved CO v=1-0 emission at 4.67 micrometers extending about 300 pc along the base of its bipolar molecular outflow. The emission is excited by infrared radiation from the dusty core. Monte Carlo radiative-transfer modeling implies that the core’s spectral luminosity density near 4.7 micrometers, as seen by the outflow material, is about 2–4 times that inferred along our line of sight. This indicates an anisotropic radiation field. A flux-density decline shallower than the inverse-square law further suggests collimation, with an estimated half-opening angle of 15–20 degrees and a collimating-structure diameter of 15 ± 5 pc, slightly smaller than the obscuring envelope’s 25 ± 5 pc diameter. Together with blueshifted nuclear CO absorption tracing envelope expansion, these findings suggest that the AGN is beginning to clear its surroundings. The estimated hydrogen column density, about 10^22–10^23 cm^-2, resembles that of Type 2 AGN. However, explaining the absence of extended high-ionization emission requires a high obscuring covering factor, possibly maintained by merger-related inflows. The nucleus thus shares properties with both Type 2 AGN and compact obscured nuclei.

PublicThe southern center of the interacting galaxy system NGC 3256 contains a faint active nucleus hidden by dust, alongside a fast outflow of molecular gas. JWST detected infrared light emitted by carbon monoxide gas near the outflow’s base. By modeling how radiation from the dusty center excites this gas, researchers inferred that the outflow receives roughly two to four times more infrared light than we infer from our viewing direction. The way that light fades with distance also suggests that it is channeled into a narrow beam rather than spreading equally in all directions. Combined with evidence that the obscuring envelope is expanding, this suggests—but does not establish—that the active nucleus is beginning to clear its surroundings. Considerable obscuration remains: the authors argue that material must cover much of the nucleus to explain the lack of extended emission from highly ionized gas. Inflows associated with the galaxy interaction might help replenish that material.

Young explorerA galaxy has a bright center hidden inside lots of dust. A space telescope saw light from gas flowing away nearby. Scientists used a computer model to work out how the hidden center lights up that gas. They think its light shines more like a narrow flashlight than a lamp lighting every direction. The dusty covering also seems to be spreading outward, so the center may be starting to clear some space around itself. But plenty of dust still hides it.

AGN Archaeology: A Systematic Search for Fading AGN in MaNGA

Quinn O. Casey, Ryan C. Hickox, Jonathan H. Cohn+8 more

AstronomerThe authors develop an empirical model for the fractional AGN contribution to optical spectra using the BPT emission-line diagnostic diagram. Applied to MaNGA IFU data, it selects 34 galaxies with weaker nuclear AGN activity than their extended AGN signatures, interpreted as evidence of fading activity. Most selected systems are edge-on galaxies undergoing minor mergers. A separate, simple disk-galaxy model with ionization cones shows that orientation affects BPT classification in both single-fiber and IFU observations. The mean distance to the extended AGN emission implies a light-travel time of 1.1 × 10^4 years, which the authors use to infer a lower limit on the typical AGN-phase lifetime of t_AGN > 1.3 × 10^5 years. This is consistent with, rather than proof of, SMBH growth through brief accretion bursts. The sample offers an approximately 10^4-year baseline for probing accretion histories and post-AGN evolution.

PublicSupermassive black holes can power bright galactic centers as they feed on surrounding material. Using a new method to estimate how much of a galaxy’s optical spectrum comes from this activity, researchers identified 34 galaxies in the MaNGA survey whose centers show weaker activity than gas farther out. They interpret this contrast as evidence that the central activity has faded, while distant gas still carries signs of its brighter past. Most of these galaxies are seen edge-on and are undergoing minor mergers. A simple model also shows that viewing angle can affect how such galaxies are classified. The average distance to the outer emission corresponds to about 11,000 years of light travel. From this, the authors infer that a typical active phase lasts more than 130,000 years, consistent with black holes growing through brief feeding episodes. These are inferred histories, not direct observations of galaxies changing over thousands of years.

Young explorerA giant black hole can make the middle of a galaxy shine brightly when it eats nearby stuff. Scientists found 34 galaxies where the middle looks less active than the gas farther away. They think the black holes used to be busier and are now slowing down. Light takes time to reach the faraway gas, so that gas can hold clues about what happened long ago. The scientists also made a simple model showing that looking at a galaxy from a different side can change how we judge its activity.

A multi-epoch VLBI study of compact symmetric objects as contaminants in the search for milli-lenses

Diego Álvarez-Ortega, Felix M. Pötzl, Carolina Casadio

• Cosmology and Nongalactic Astrophysics

AstronomerThe SMILE pilot follow-up identifies eight of nine remaining milli-lens candidates as compact symmetric objects (CSOs), including four new classifications; J0923-3435 remains ambiguous. Multi-epoch, multi-frequency VLBI and complementary radio measurements reveal component spectral-index asymmetries and previously undetected connecting emission that rule out lensing for the eight classified sources. For CSOs with known redshifts, inferred equipartition lobe magnetic fields are approximately 20–320 mG and projected separations are approximately 60–240 pc. No measurable expansion is detected, implying kinematic-age lower limits of approximately 50–950 years. Integrated spectra of J0210-2213 and J2347-1856 favor an inhomogeneous external free-free absorber over the tested homogeneous and inhomogeneous synchrotron self-absorption models. The analysis provides a framework for distinguishing CSO contaminants from potential milli-lenses in the full SMILE survey, which aims to probe the abundant low-mass dark matter halos predicted by Lambda Cold Dark Matter.

PublicAstronomers investigated nine radio sources that might show tiny gravitational-lensing effects, in which gravity bends light from a background source. Such lenses could help test the large population of small dark matter halos predicted by the standard cosmological model. Instead, radio observations identify eight candidates as compact symmetric objects: radio sources with paired lobes whose appearance can mimic lensing. Four were classified this way for the first time. Differences in the components’ radio spectra and newly detected emission connecting them rule out lensing for those eight; the ninth, J0923-3435, remains uncertain. For sources with known redshifts, the lobes are separated by roughly 60–240 parsecs in projection. Their expansion was too small to measure, yielding lower limits on their ages rather than exact ages. In two sources, spectral modeling favors absorption by unevenly distributed external ionized gas over the alternative absorption models tested. The same approach is intended to help screen the larger SMILE survey.

Young explorerGravity can bend light and make something far away look like more than one thing. Astronomers checked nine tiny radio pictures that might show this trick. Eight turned out to be a different kind of radio source with two parts, not a gravity-made copy. The clues included different radio signals from the parts and a faint connection between them. The scientists still cannot tell what the ninth one is. Their detective work will help them check more pictures.

DOWSING, Dust Observations With SCUBA-2 In Nearby Galaxies: I. Dust in M81

M. Uzuner, M. W. L. Smith, S. Eales+16 more

AstronomerResolved Herschel PACS/SPIRE and JCMT SCUBA-2 observations of M81 at 70–850 micrometres are analysed with single-temperature modified blackbody (SMBB) fitting and PPMAP temperature-resolved dust mapping. With fixed emissivity index beta = 1.9 and opacity kappa at 350 micrometres = 1.92 cm²/g, the inferred integrated dust masses are (1.77 ± 0.09) × 10^7 solar masses for SMBB and (2.65 ± 0.13) × 10^7 solar masses for PPMAP. The higher PPMAP estimate is interpreted as the expected consequence of accounting for multiple dust temperatures along a line of sight, which single-temperature fits can miss. Both methods recover enhanced dust surface density along the spiral arms and temperatures declining outward from a warm central region. Variable-beta fits show moderate variation in well-constrained pixels, but strong temperature–beta degeneracy motivates the fixed-beta analysis. Combining dust maps with HI data yields an outward gas-to-dust ratio gradient of 0.065 dex/kpc. Comparison with the metallicity gradient implies an outward decline in the dust-to-metals ratio, potentially consistent with more efficient grain growth in the inner disc. The inferred star formation rate is approximately 0.27 solar masses per year and is strongly concentrated along the arms.

PublicInfrared and submillimetre observations map dust across the nearby spiral galaxy M81. Two modelling methods find denser dust along its spiral arms and the warmest dust near its centre, with temperatures falling farther out. The estimated total dust mass depends on how the dust temperatures are modelled: a method assigning one temperature to each image pixel gives about 18 million solar masses, while a method allowing a range of temperatures gives about 27 million. These estimates use the same assumed dust-emission properties; the researchers interpret the larger estimate as reflecting dust that a single-temperature model can underestimate. Combining the dust maps with atomic hydrogen observations indicates that the gas-to-dust ratio increases outward. A comparison with the galaxy’s chemical composition also implies that a smaller share of its metals is locked in dust farther out, possibly because dust grains grow more efficiently in the inner galaxy. That explanation remains an interpretation. M81 forms about 0.27 solar masses of stars per year, mostly along its spiral arms.

Young explorerM81 is a big galaxy with curling arms. Scientists studied light from its dust and made maps. They found more dust along the arms, and the dust is warmest near the middle. They tried two ways to work out how much dust there is. Letting dust have different temperatures gave a bigger answer than treating it as having just one temperature in each little part of the picture. So the answer depends on how they work it out. New stars are forming mostly along the curling arms, too.

The HST-Hyperion Survey: X-ray AGN Enhancement in the Hyperion Proto-supercluster

Ashlen Coburn, Finn Giddings, Derek Sikorski+18 more

AstronomerThe study measures the X-ray-selected AGN fraction in the Hyperion proto-supercluster at z approximately 2.5, its overdense peaks, and its outskirts, relative to a coeval field sample. It combines Chandra COSMOS-Legacy X-ray data with COSMOS2020 photometry and photometric redshifts, ground-based spectroscopy, and HST-grism observations, incorporating redshift information statistically through a Monte Carlo framework. Hyperion has an AGN fraction of 7.4% (+3.2/-1.8 percentage points), compared with 3.2% (+0.6/-0.5) in the field, a difference of approximately 2.3 sigma. The enhancement is concentrated in overdense peaks, with a fraction of 12.3% (+5.5/-3.4): 15.0% (+6.9/-4.4) in the most massive peaks and 6.2% (+11.9/-2.1) in less massive peaks. The outskirts, at 2.1% (+3.6/-1.1), show no evidence of enhancement relative to the field. These observational results suggest, but do not establish, that dense environments may preferentially trigger AGN during early cluster assembly.

PublicDo crowded regions of the early universe encourage activity around supermassive black holes? Researchers investigated Hyperion, a massive developing supercluster at a redshift of about 2.5, using X-ray observations to identify active galactic nuclei and other observations to estimate which galaxies belong to the structure. About 7.4% of Hyperion galaxies hosted X-ray-selected active nuclei, compared with 3.2% in a comparison sample at the same cosmic epoch. The difference is suggestive rather than conclusive, with a statistical significance of about 2.3 sigma. The excess was concentrated in Hyperion's densest regions, where the fraction reached about 12.3%; its less crowded outskirts showed no evidence of an excess. The findings suggest that dense surroundings may help trigger black hole activity while galaxy clusters are assembling, but they do not establish that the environment causes the activity.

Young explorerGalaxies are huge groups of stars, and some have giant black holes with bright, active centers. Scientists looked for X-ray light from these centers in a big gathering of galaxies called Hyperion. They found that galaxies in its most crowded parts more often had active centers than galaxies in a comparison group. The less crowded edges did not show the same extra activity. Being crowded together might help switch on this activity, but the scientists are not sure yet.

The ALPINE-CRISTAL-JWST Survey: The Tully-Fisher Relation at z = 4-6

Diego A. Gómez-Espinoza, Juan Molina, Edo Ibar+27 more

AstronomerJWST/NIRSpec IFU observations of 18 main-sequence star-forming galaxies in ALPINE-CRISTAL-JWST at z=4–6 identify five disk-like systems, giving a survey disk fraction of 0.28±0.11. These disks have stellar masses of 10^9.5–10^10.5 solar masses, intrinsic rotation velocities of 91–127 km/s, and intrinsic velocity dispersions of 66–129 km/s. Both stellar and baryonic Tully-Fisher relations lie below local relations and are likely offset from those at cosmic noon (z≈2.3). With slopes fixed to their z=0 values, stellar-mass zero-point offsets are −0.96±0.18 dex relative to local galaxies and −0.50±0.18 dex relative to cosmic noon; baryonic offsets are −0.57±0.20 and −0.30±0.20 dex, respectively. These measurements, based on five disks and an assumed local slope, are consistent with zero-point evolution driven by evolving dark matter halo properties, modulated by a reduced dark matter contribution to galaxy-scale dynamical mass; they do not uniquely establish that interpretation.

PublicAstronomers used JWST to study how the masses of very distant galaxies relate to their rotation speeds. Of 18 star-forming galaxies at redshifts 4–6, five were classified as disk-like. These five have lower stellar and ordinary-matter masses at a given rotation speed than the relationships measured for nearby galaxies indicate, and they probably also differ from galaxies at a later epoch called cosmic noon. The researchers measured these shifts while assuming that the relationships retain the slopes seen nearby, so the findings depend on that assumption and a small disk sample. The results are consistent with changes over cosmic time in the galaxies’ surrounding dark matter halos, together with dark matter contributing less to the mass governing motions on galaxy scales, but this explanation is not proven.

Young explorerGalaxies are huge groups of stars, and some spin like wheels. Astronomers used the JWST telescope to look at 18 galaxies from long ago. Five looked like spinning disks. Compared with galaxies near us, those five had less star material for how fast they spun. The scientists think changes in invisible matter called dark matter might help explain the difference, but they are not sure.

Feedback-Driven Star Formation and YSO Distribution around H II Regions Sh2-140 and Sh2-145

C Rishi, Neelam Panwar, Ajay Kumar Singh

AstronomerThe study examines BRC 44 and LDN 1204, located between the H II regions Sh2-140 and Sh2-145 in the larger Cepheus OB2 association. Infrared data from Spitzer and WISE reveal a spatial correlation between massive stars and young stellar objects. The authors interpret this as evidence for a possible sequential pattern of star formation and a role for massive-star feedback in shaping the complex’s star-formation history. Their earlier work on BRC 44 suggested radiatively triggered star formation, but the spatial correlation reported here does not by itself establish triggering or a temporal sequence.

PublicAstronomers used infrared observations from the Spitzer and WISE space telescopes to study young stars and clouds in the Cepheus OB2 stellar association. They found that the locations of young stars are spatially related to those of massive stars. This pattern suggests that star formation may have progressed across the region, with massive stars influencing where later stars formed. Earlier work on one cloud, BRC 44, also suggested that radiation helped trigger star formation. These are interpretations of the observed pattern, not proof that massive stars caused new stars to form.

Young explorerAstronomers looked at clouds in space where stars are being born. They found a pattern in where baby stars sit compared with very big stars. They think the big stars may have helped new stars form in different places, one after another. But the pattern alone does not tell them for sure.

Formamide formation on forsterite and Mg(OH)₂·H₂O

Dario Campisi

• Chemical Physics

AstronomerThis quantum-chemical study investigates NH2 addition to H2CO as a route to formamide in two Mg-bearing models relevant to protoplanetary disks: isolated Mg(OH)2·H2O and the bare forsterite (010) surface. DFT calculations indicate that the molecular model facilitates proton transfer in the addition intermediate through an Mg-coordinated O–H group. On forsterite, the calculated addition pathway is barrierless when NH2 is initially physisorbed close to formaldehyde, with subsequent proton transfer yielding formamide. For Mg(OH)2·H2O, the reaction step from the pre-reactive complex is predicted to occur on nanosecond timescales at temperatures approaching 300 K. These are theoretical results for the specified models and configurations, not observational detections; the calculated kinetics provide input for astrochemical models.

PublicComputer calculations suggest a possible way to make formamide, a molecule important as a precursor to amino acids and RNA, on magnesium-containing materials relevant to planet-forming disks. The study modeled reactions between formaldehyde and NH2 using both a small hydrated magnesium-containing molecule and a bare silicate surface representing a dust grain. Both models helped transfer a proton after the reactants joined, leading toward formamide. On the silicate surface, the initial joining step had no calculated energy barrier when NH2 started close to formaldehyde. In the small molecular model, the reaction step from an already assembled pair of reactants was predicted to take nanoseconds near 300 kelvin. These predictions offer data for models of chemistry in space, but do not show that this process has been observed there.

Young explorerScientists used a computer to explore how a molecule called formamide might be made in places where planets grow. They tried two tiny models: a little group of atoms containing magnesium and a rocky surface like a bare dust grain. The calculations suggest these materials can help the ingredients join and move a tiny piece called a proton to make formamide. On the rocky surface, the ingredients needed to start close together for the joining step to have no energy hurdle. This is a computer prediction, not something the scientists watched happen in space.

CosmicGrain: An On-the-fly Dust Physics Module

E. Huscher, K. Finlator

AstronomerCosmicGrain is a publicly available Gadget-4 dust module using explicit, dynamically active dust superparticles with resolved gas-dust drag, radiation pressure, and collisional gas-dust heating and cooling, plus subgrid grain growth and destruction processes. An eleven-rung physics ladder (S0-S10) at 1024^3 resolution isolates process contributions in a Milky Way-mass halo. In these simulations, gas-dust drag dominates ISM dust enrichment, raising dust levels by about a factor of 100, while each other process changes the R200 dust abundance by only 10-30%. Tracking distinct grain histories yields strongly asymmetric silicate-to-carbon destruction by shattering, attributed to silicates' smaller birth sizes. The simulated radial dust-to-gas and dust-to-metal ratios agree reasonably with those of the Milky Way, and carbon dust preferentially enriches the CGM relative to silicates. These findings are simulation results, not new observational measurements.

PublicThe researchers introduce CosmicGrain, freely available software that simulates how cosmic dust moves and changes in a galaxy with a halo similar in mass to the Milky Way's. It follows dust particles as they interact with gas and light, grow, collide, and are destroyed. By comparing eleven versions with different physical processes, the team finds that drag between gas and dust has the largest effect on dust enrichment in the simulated galaxy's interstellar gas, increasing dust levels about a hundredfold. The simulations also suggest that silicate and carbon dust break apart differently because silicate grains start smaller, and that carbon dust more readily enriches the gas surrounding the galaxy. The model reasonably reproduces the Milky Way's radial patterns of dust relative to gas and metals, but its process-by-process findings come from simulations rather than direct observations.

Young explorerScientists made a computer model of dust in a galaxy like our Milky Way. In their model, tiny dust bits move through gas, grow, bump together, and break apart. They tried different versions to see what mattered most. Gas tugging on the dust made the biggest difference to how much dust built up between the stars. Two kinds of dust also behaved differently. Some dust patterns looked reasonably like those in the Milky Way, but this was a computer experiment, not watching real dust move.

GetGaia 2.0: automatic membership and systemic motions of stellar systems with Gaia

Andrés del Pino

• Instrumentation and Methods for Astrophysics

AstronomerGetGaia 2.0 is a public Python package for automated Gaia membership inference and systemic-motion estimation. Its expectation-maximization probabilistic model combines full-covariance astrometry, color-magnitude information, spatial distributions, and available Gaia or external line-of-sight velocities. Field quasars provide estimates of local Gaia reference-frame systematics. Outputs include systemic proper motion and parallax with full covariance, detection significance, contamination estimates, and structural parameters. Synthetic-catalog tests yield 90–100% membership purity; this is a simulation-based validation, not a measured purity for every real system. Applied to Gaia DR3 for known Local Group dwarfs within 850 kpc and 95 Galactic globular clusters, with progressively added literature information, the package measures systemic proper motions for 55 dwarfs and 93 clusters at significance of at least 3σ. Of these, 29 dwarfs and 86 clusters are recovered with position alone as the supplied literature information. Proper motions agree with published values within 0.1 mas/yr for 47 dwarfs and all 93 clusters, with median differences of 0.032 and 0.009 mas/yr, respectively; no discrepancy exceeds 3σ, and uncertainties match those of dedicated studies. Gaia line-of-sight velocities alone yield systemic velocities for 71 clusters within 1 km/s of spectroscopy. The authors describe the package as ready for forthcoming Gaia releases.

PublicGetGaia 2.0 is freely available software that uses Gaia data to identify which stars likely belong to a dwarf galaxy or globular cluster and estimate the system’s overall motion across the sky. It combines information about stars’ positions, motions, colors, and brightnesses, plus velocities toward or away from us when available. In tests using simulated star catalogs, 90–100% of the selected stars were genuine members. Using real Gaia DR3 observations, the software measured motions for 55 dwarf galaxies and 93 globular clusters with statistical significance of at least 3σ. Its measurements were consistent with published studies, with comparable uncertainties. These tests support automated analysis without manually selecting member stars, although membership remains probabilistic and the method is limited to systems Gaia can detect.

Young explorerStars can look close together even when they do not belong together. GetGaia 2.0 is a computer program that uses Gaia’s star information to work out which stars probably belong to the same group and how that group moves across the sky. Scientists tested it with pretend star lists and real observations. It worked well, but it cannot be completely sure about every star.

Dust Survival in Lensed Quiescent Galaxies at z>1 Depends on How They Quench

Sarah Bodansky, Katherine E. Whitaker, Gourav Khullar+18 more

AstronomerALMA Band 6 continuum observations at rest-frame wavelengths above 250 micrometres of eight strongly lensed, spectroscopically selected quiescent galaxies at z approximately 1–2.5, combined with five archival REQUIEM systems, reveal dust-to-stellar-mass ratios spanning more than two orders of magnitude, from below 10^-5 to above 10^-3. Two galaxies have spatially resolved, extended dust emission. Comparisons with dust-destruction tracks suggest that roughly half the sample, preferentially at higher redshift, is consistent with rapid quenching and harsh dust destruction; lower-redshift, more slowly quenched systems are consistent with milder destruction. This may indicate evolution in the dominant quenching mode, rather than establishing it. The two dust-richest systems exceed even the mildest destruction tracks, with J1201-3952 showing the highest dust fraction approximately 1.8 Gyr after quenching. If genuinely quiescent, their inferred dust masses approach maximum stellar yields, pointing to ISM grain regrowth and/or TP-AGB dust production. Single-band measurements leave a systematic uncertainty of ±0.3 dex from unknown dust temperature, and obscured star formation cannot be excluded in these two systems.

PublicGalaxies that have largely stopped forming stars are expected to lose their dust rapidly, within roughly 100 million years, yet some remain surprisingly dusty. Researchers used ALMA observations of eight galaxies magnified by gravitational lensing, together with archival data for five others, to investigate this puzzle. Their estimated dust content relative to stellar mass varies by more than a factor of 100, and two galaxies show extended dust emission. Comparisons with models suggest that galaxies which stopped forming stars rapidly experienced stronger dust destruction, whereas those that shut down more slowly could preserve more dust. The two dustiest galaxies contain more dust than even the gentlest destruction models predict. One has the sample's highest relative dust content about 1.8 billion years after its inferred shutdown. If these two galaxies really have stopped forming stars, dust grains may have grown again between stars or received fresh material from aging stars. However, the observations measure only one wavelength band: unknown dust temperatures make the dust estimates uncertain, and hidden star formation could still be occurring in these two galaxies.

Young explorerSome galaxies have mostly stopped making new stars, but they still have dust floating between their stars. Scientists studied 13 galaxies and found that some have much more dust than others. Their clues suggest that stopping star-making quickly may destroy more dust, while stopping slowly may leave more behind. Two galaxies seem especially dusty. Maybe their dust grew again or old stars made more. But scientists are not sure: the dust's temperature makes it hard to tell how much is there, and those two galaxies might still be making stars hidden by dust.

The 10 Mpc Volume

R. Brent Tully, Gagandeep S. Anand, Helene M. Courtois+7 more

AstronomerHubble Space Telescope stellar observations provide accurate distances for most unobscured galaxies brighter than MB = -13 mag within 10 Mpc, while complementary WISE mid-infrared observations yield global stellar mass estimates. This volume-limited census reveals galaxies organized into groups within filaments, with filament bulk motions attributed to gravitational attractors such as Virgo and repulsors such as the Local Void. Each group is dominated by one galaxy; ten galaxies at distances of 1–9 Mpc contain most of the sample’s stellar mass. A curious deficit occurs in a luminosity interval fainter than these dominant systems. Dominant halo galaxies, including dwarfs in separate halos, tend to retain gas and form stars, whereas secondary halo members are frequently gas depleted and show no evidence of star formation. All but one galaxy in the complete sample have well-formed red giant branches, indicating early-onset star formation.

PublicObservations of bright stars with the Hubble Space Telescope have established accurate distances for most unobscured galaxies above a specified brightness within 10 megaparsecs. Infrared observations from WISE also estimate how much mass these galaxies contain in stars. The resulting nearby census shows galaxies gathered into groups along filaments. The filaments’ collective motions are interpreted as responses to gravitational features such as the Virgo Cluster and the Local Void. Each group is dominated by one galaxy, and just ten galaxies contain most of the sample’s stellar mass. There is also a puzzling shortage of galaxies in a brightness range below the dominant ones. The dominant galaxies usually have gas and continue making stars, even when they are small galaxies in their own surrounding halos. Secondary galaxies sharing a halo are often short of gas and show no signs of making stars. With one exception, the complete sample’s galaxies contain a recognizable population of old red giant stars, indicating that star formation began early.

Young explorerAstronomers used telescopes to study nearby galaxies—huge families of stars. They found that galaxies often live in groups along long strands, and each group has one galaxy that stands out. Just ten galaxies hold most of the mass in stars in the group of galaxies studied. The main galaxies usually have gas to make new stars. Other galaxies living beside them often have little gas and show no signs of making stars. There are also surprisingly few galaxies in one range of brightness. Almost every galaxy in the complete set has old red giant stars, which tell astronomers that it started making stars long ago.

Magnetic contribution to outer-disk rotation in the spiral galaxy NGC 5055

Natalia Woźniak, Joanna Jałocha, Łukasz Bratek+1 more

AstronomerThe study reconstructs the purely toroidal magnetic field required to explain the difference between fitted outer-gas rotation in NGC 5055 and a modelled gravitational reference, assuming circular, axisymmetric midplane motion. Analytic disk decompositions provide consistent rotation–density pairs; the blended reference approximately preserves inner rotation while approaching the measured outer HI+He density profile. It is not an independently measured stellar rotation curve. With hydrogen inertia, no pressure and zero field at the reconstruction’s inner boundary, constant exponential scale heights of 1, 0.25 and 0.2 kpc require peak fields of approximately 5.47, 10.95 and 12.24 microgauss near 34.9 kpc. Extrapolated flaring exponential and Gaussian profiles instead peak at approximately 5.25 and 5.96 microgauss near 33.8 kpc. Prescribing an 8-microgauss inner-boundary field makes the flaring-profile fields decline overall, reaching approximately 5.73 and 6.30 microgauss near 39.7 kpc. These reconstructions depend on the gravitational reference, vertical gas structure and boundary field. Comparison with total radio fields supports the inferred field scale but does not establish a magnetic origin for the rotation excess.

PublicCould magnetic fields help explain the outer gas rotation in the galaxy NGC 5055? The researchers calculated the field needed to account for the difference between fitted gas rotation and a model of rotation under gravity. That gravitational reference is modelled, not an independently measured stellar rotation curve. Assuming a field that circles the galaxy, different choices for the gas layer’s thickness and the field at the calculation’s inner edge give different answers. With a zero inner-edge field, the calculated peaks range from roughly 5 to 12 microgauss. Comparison with radio-based total magnetic fields supports this general field scale, but does not show that magnetism causes the rotation excess. The estimates remain dependent on the model assumptions.

Young explorerGas moves around a galaxy called NGC 5055. Scientists used maths to ask whether a magnetic push or pull could help explain how it moves. Their answers change depending on how they imagine the gas is spread out and where they start the calculation. The magnetic strength looks possible, but they have not shown that magnetism is the reason.

The Milky Way-like radial structure in nearby galaxies

Yuze Zhao, Jianhui Lian, Zheng Zheng+16 more

AstronomerThe study identifies 65 nearby galaxies within 50 Mpc whose surface-brightness profiles show plateaus resembling the Milky Way’s inner feature around one effective radius, rather than a purely exponential disk. Multi-band surface-brightness and color profiles reveal different trends among the 42 galaxies with bar classifications: 25 are barred and 17 are non-barred. Barred systems show radial color variations more consistent with stellar population ageing, whereas non-barred systems align more closely with dust reddening, suggesting an attenuation contribution to their plateaus. The diverse color gradients in barred galaxies are interpreted as evidence for multiple possible pathways, including population variations and dynamical stellar-mass redistribution. Both groups tend to occupy denser environments than a comparison sample without plateaus, suggesting a possible environmental role. The approximately 3.6% occurrence rate may indicate an uncommon evolutionary stage, but does not establish one. The Milky Way may be an intermediate case in which population variations and bar-associated dynamics both contribute, given its strong stellar population dependence and persistent stellar-mass-profile feature.

PublicThe Milky Way’s brightness does not decline smoothly across its disk: an inner region has a distinctive flatter stretch, or plateau. Researchers identified 65 nearby galaxies with similar features and compared how their brightness and color change with distance from their centers. Among galaxies classified by whether they have a central stellar bar, the color patterns suggest different possible explanations. In barred galaxies, changes in the ages of stars may help create the plateau, and bar-driven rearrangement of stars may also matter. In galaxies without bars, dust dimming the starlight may contribute. Galaxies with plateaus also tend to live in more crowded surroundings than a comparison group without them, although this does not establish an environmental cause. These features occur in about 3.6% of galaxies in the study, which may mean they mark an uncommon stage of development. The Milky Way may combine changes in its stellar populations with the effects of its bar; the study does not establish a single explanation.

Young explorerOur galaxy, the Milky Way, has a place where its glow stays more even instead of fading steadily. Scientists found 65 nearby galaxies with a similar patch of glow. They looked at their colors for clues. In some, older stars might help explain it. In others, dust hiding some starlight might help. A bar-shaped group of stars in the middle might also move stars around. The Milky Way may have more than one thing making its special glow, and scientists are still figuring it out.

Is Morphology All You Need? Quantifying Imprints of Past Star Formation in the Present-Day Morphologies of Galaxies

Juan Pablo Alfonzo, Kartheik G. Iyer, Masayuki Akiyama+10 more

AstronomerKatachi-PRIME combines morphological information from gri broadband images with SED-based inference using implicit likelihood inference and learned morphological priors. It estimates stellar mass, specific star formation rate, redshift, age (t50), dust attenuation, and gas-phase metallicity. The authors report tighter constraints than traditional five-band photometry and a population-dependent connection between morphology and inferred star formation history. Stable morphologies in main-sequence and quiescent galaxies carry predictive information about star formation approximately 4–7 Gyr and 3–5 Gyr into the past, respectively. By contrast, starburst and green-valley populations tend to undergo structural disruptions that obscure information about all but recent star formation. The method is presented as a way to extract more physical information from future broadband surveys; its historical estimates are inferences, not direct observations of past activity.

PublicA galaxy’s shape can provide clues that its combined light alone misses. The researchers introduce Katachi-PRIME, a method that combines galaxy images with information about light at different wavelengths to estimate properties such as stellar mass, star formation activity, distance-related redshift, and dust. They report better constraints than a traditional approach using five broad wavelength bands. The usefulness of shape depends on the galaxy: stable shapes help infer star formation roughly 4–7 billion years ago in steadily star-forming galaxies and 3–5 billion years ago in quiet galaxies. Galaxies experiencing bursts or transitioning toward quieter activity tend to have structural disruptions that hide older clues. These are estimates of past activity, not direct views of that past.

Young explorerA galaxy is a huge group of stars. Scientists made a new way to use both its shape and its light to guess what it is like and when it made stars. They report better guesses than using its light alone. Some steady shapes hold clues from long ago, but jumbled shapes can hide the older clues.

First Results from JACKS: A VLA Ammonia View of Gas Heating and Star-forming Cores in the Central Molecular Zone

Xu Zhang, Xing Lu, Elisabeth A. C. Mills+7 more

• Solar and Stellar Astrophysics

AstronomerJACKS is a JVLA C-configuration K-band survey designed to relate the CMZ's warm, turbulent gas and unexpectedly low star-formation rate to compact-gas thermal and kinematic structure. Its 31 mosaic fields follow the ACES footprint, covering metastable NH3 (1,1)–(5,5), five non-metastable NH3 lines, the 22-GHz water maser line, H64α and H66α, and broad continuum windows. Nominal resolutions are approximately 1.5 arcseconds (0.06 pc at the Galactic Centre) and 0.4 km/s for NH3. Preliminary imaging demonstrates water-maser self-calibration, compact and extended continuum emission, filamentary ammonia structure, and complex compact sources with multiple velocity components. Combination tests with SWAG and HOPS recover progressively larger angular scales. These early products demonstrate survey capability; quantitative temperatures, opacities, and core-population measurements await the uniformly reduced data set.

PublicThe Central Molecular Zone near our galaxy's centre contains warm, turbulent gas but forms fewer stars than expected from its supply of dense gas. The JACKS radio survey is designed to investigate how those conditions relate to the temperatures and motions of small gas structures that might form stars. Early images reveal threadlike ammonia-emitting structures, compact sources with several distinct gas velocities, and both compact and spread-out radio emission. Tests combining JACKS with other ammonia surveys recover emission on larger scales, helping connect small structures to their surrounding clouds. These are preliminary demonstrations of what the survey can do, not yet quantitative measurements of gas temperatures or the population of dense cores, nor an explanation for the low star-formation rate.

Young explorerNear the middle of our galaxy, there is warm gas swirling around, but it makes fewer stars than scientists expected. Scientists are using a radio telescope to look closely at little gas clouds that might make stars. Their first pictures show long, thin strands of gas and small places where gas moves in different ways. These early pictures show that the survey is working. Scientists still need to study the data carefully to measure how warm the gas is and learn more about these little clouds.

Constraining the timescale of activity in Mrk 1018

Rebecca McElroy, Scott M. Croom, Thomas Dunn

AstronomerMUSE integral-field observations from the Close AGN Reference Survey reveal an extended emission-line region at a projected distance of 3.77 kpc from the nucleus of the changing-look AGN Mrk 1018. Line ratios indicate AGN ionisation, while the low velocity dispersion of 77 ± 1 km/s rules out an ionised outflow in the authors' analysis. The inferred lower limit on the light-travel time, 12,300 ± 2,300 years, implies nuclear activity lasting at least this long. The authors therefore interpret both observed, several-year changing-look transitions as variations within a much longer active phase.

PublicObservations of the galaxy Mrk 1018 reveal a glowing gas region far from its active centre. The gas's light indicates that it is ionised by the central activity, and its small spread of velocities rules out an outward-flowing stream of ionised gas in the researchers' analysis. From the region's projected distance, they infer that light needed at least about 12,300 years to reach it, with an uncertainty of 2,300 years. This implies that the galaxy's centre has been active for at least that long, even though its two observed changes in appearance each took only several years. Those rapid changes therefore appear to be part of a much longer period of activity.

Young explorerA galaxy called Mrk 1018 has a bright middle that has changed how it looks in just a few years. Astronomers found glowing gas far away that is lit up by that middle. Light takes a very long time to get there, so they worked out that the middle must have been active for at least about 12,000 years. Its quick changes seem to be little changes during a much longer time of being active.

Violent relaxation in hierarchical stellar systems: pathways toward massive black hole formation in the early Universe

Dominik R.G. Schleicher, Francesco Flammini Dotti, Matías Liempi+6 more

AstronomerJWST observations using gravitational lensing have detected massive stellar systems at high redshift. This study considers how such systems could evolve rapidly despite long stellar two-body relaxation times. For systems composed of many gravitationally bound clusters, the authors define an analogous cluster-level relaxation time, implying faster evolution that depends on the number of stars per cluster. They describe early, non-collisional cold collapse as enhancing stellar mass segregation and derive a criterion based on the masses of two components for dynamical decoupling of the massive component. Cluster mergers, including repeated mergers, tend on average to produce larger radii. The authors therefore identify cold collapse of a dense, massive cluster after few or no mergers as the most promising route considered for massive black-hole formation: with enough massive stars, the massive population can decouple centrally and undergo core collapse, leading to a central massive object. This is a proposed evolutionary pathway, not an observational detection of black-hole formation; repeated mergers instead favor massive, more extended stellar systems.

PublicThe James Webb Space Telescope has detected massive groups of stars in the early Universe with help from gravitational lensing. The study explores how these systems might change quickly, even when encounters between individual stars would normally suggest slow evolution. If a system contains many star clusters bound together by gravity, interactions between whole clusters could speed up its evolution. The authors also describe how a young, dense cluster's early collapse can concentrate its heavier stars, and derive a condition under which those stars could become dynamically separate from the rest. They argue that a dense cluster with enough massive stars, after few or no cluster mergers, offers the most promising pathway considered for forming a massive black hole through collapse at its center. This is an explanation of what could happen, not an observation of a black hole forming. Repeated cluster mergers tend instead to make larger, more spread-out star systems.

Young explorerA space telescope called Webb has spotted huge groups of stars in the early Universe. The researchers explored what might happen as groups like these change. They say a tightly packed group could squeeze inward, gathering its heavier stars near the middle. If there are enough heavy stars, that middle group could collapse further and might help make a giant black hole. They have not watched this happen. When star groups join together many times, they tend to make a bigger, more spread-out group instead.

The Pristine survey XXXI. A stream offset from the Stream: very metal-poor stellar debris trailing 100(°) from the LMC-SMC system

Akshara Viswanathan, Kim A. Venn, Julio F. Navarro+23 more

• Solar and Stellar Astrophysics

AstronomerHigh-resolution Gemini/GHOST spectroscopy of 33 candidate red giants yields 12 high-confidence Magellanic stellar Stream members selected by energy and angular momentum: one star at [Fe/H] approximately -1.6, ten very metal-poor stars ([Fe/H] < -2), and one extremely metal-poor star ([Fe/H] < -3). The new VMP stars span more than 100 degrees of the trailing Stream, follow the Clouds' kinematics, and are offset by about 20 degrees from both the HI Stream and previously known, more metal-rich debris, suggesting a metallicity-dependent spatial distribution. Combined with literature members, the additions approximately double the known red giant sample and extend its metallicity range to approximately -0.5 to -4.3. Orbital integrations in a time-dependent Milky Way–LMC potential support a Clouds association; collisionless test particles initialized in a diffuse LMC stellar halo reproduce the broad debris distribution but do not establish a unique origin. Possible sources include the extended stellar halos of the LMC or SMC and disrupted satellites. The observations provide constraints for future interaction simulations.

PublicAstronomers have identified 12 high-confidence red giant members of a stream of stars stripped from the Magellanic Clouds, including 11 stars with very little iron compared with the Sun. They measured the light spectra of 33 candidates using Gemini/GHOST. The newly identified very iron-poor stars stretch across more than 100 degrees of sky and move in line with the Clouds, but lie about 20 degrees away from both the hydrogen gas stream and previously known, more iron-rich stellar debris. This suggests that stars with different chemical compositions occupy different parts of the debris. Together with earlier work, the discoveries roughly double the known red giant sample. Calculated orbits support a connection to the Clouds, and a simplified simulation reproduces the debris' broad spread. The stars' precise origin remains uncertain: they could have come from the Clouds' extended outer stellar populations or from smaller galaxies that were torn apart.

Young explorerTwo galaxies called the Magellanic Clouds have a long trail of stars. Astronomers studied the light from 33 stars and picked out 12 that they are quite sure belong to the trail. Most of those 12 have very little iron. These iron-poor stars spread across a huge part of the sky, away from the trail's gas and stars with more iron. Computer calculations help connect them to the Clouds, but we still do not know exactly where they started. They might have come from the Clouds' outer parts or from smaller galaxies that were pulled apart.

A Large-Sample Study of Interstellar Reddening in Galactic Star Clusters

Ernst Paunzen, Teja Begari

• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerThe authors derive mean colour excesses and associated errors for 5,377 Galactic open clusters spanning Galactocentric distances of 2–20 kpc. Their statistical approach uses the shared formation history and homogeneous metallicity of cluster members, including more massive upper-main-sequence stars, rather than fitting individual stellar spectral energy distributions. They apply classical colour-colour diagrams (the Q-method) using (B-V), (BP-RP), (U-B), (U-BP), (U-RP), and (U-G), with fitting standard lines described as independent of age and metallicity. Comparisons with existing dust and extinction maps show generally good agreement. Within ±1,500 pc of the Sun, they report a very patchy dust-composition structure. The results provide a basis for a future reddening map and for cluster metallicity estimates through isochrone fitting with distances and reddening held fixed; these applications are not presented as completed results.

PublicDust between stars absorbs some of their light and changes their apparent colours, complicating astronomical observations. This study estimates that colour change for 5,377 star clusters in our Galaxy, at distances of 2–20 kiloparsecs from the Galactic centre. Because stars in an open cluster formed together and have similar chemical composition, the researchers can analyse their colours as a group, including some more massive stars. Their estimates include uncertainties and generally agree with existing dust maps. They report a very patchy pattern in the dust composition within about 1,500 parsecs of the Sun. The measurements could support a new map of interstellar dust and future estimates of cluster chemical composition, but the abstract does not report those further products as completed.

Young explorerDust in space can make stars look dimmer and change their colours. The researchers looked at 5,377 groups of stars that were born together. Comparing the stars’ colours helped them work out how much the dust changed the light, though the answers are not exact. Their answers mostly matched earlier dust maps. They also found that dust near our Sun is very patchy. They hope these results will help them make a new dust map.

Multi-layer magnetic structure toward NGC 1333 revealed by a square-degree optical polarimetric survey

G. A. P. Franco, J. M. Girart, F. O. Alves

AstronomerA nearly one-square-degree R-band polarimetric survey of approximately 840 stars toward NGC 1333 combines Gaia DR3 and StarHorse distances with polarization-distance trends and Stokes parameters to separate foreground and cloud contributions. The observations identify a polarized foreground at 160–300 pc and a cloud component beyond 300 pc. Following foreground subtraction in Stokes space, the inferred plane-of-sky field orientation changes smoothly from 126.3° ± 0.8° in the northwest to 162.2° ± 0.6° in the southeast, with both regions remaining well ordered. Angular dispersion function analysis yields turbulent-to-ordered field ratios of 0.054 (+0.025/−0.022) and 0.095 (+0.021/−0.047), corresponding to estimated plane-of-sky strengths of 59 (+44/−23) and 46 (+50/−13) μG, respectively. Residual foreground fluctuations may affect these estimates. CO observations show multiple velocity components with spatially varying contributions. Corrected optical polarization agrees with Planck’s large-scale orientation, whereas near-infrared and JCMT/POL-2 observations show localized deviations in denser structures. The results support a coherent cloud-scale field with a smoothly varying projected orientation and localized departures in dense regions.

PublicAstronomers studied the magnetic field toward the star-forming region NGC 1333 by measuring the polarization—the preferred orientation of light waves—from about 840 stars. Material between Earth and the cloud adds its own polarization signal, complicating the view. Using stellar distances, the team estimated and subtracted that foreground contribution. The corrected observations indicate that the magnetic field projected onto the sky is well organized, with its direction changing smoothly across the cloud. Other observations broadly agree on the large-scale direction but reveal local differences in denser regions. The researchers also estimated the field’s strength, though leftover foreground variations may affect those estimates. The study shows how combining stellar distances with polarization measurements can help separate overlapping structures.

Young explorerA cloud where stars form has an invisible magnetic field. Scientists studied light from many stars to work out which way that field points. Nearby material made the view confusing, so they used the stars’ distances to help untangle it. They found a mostly tidy pattern that turns gently across the cloud, with some differences in denser places. Some nearby material may still make their estimates uncertain.

Octavius: A High-Performance Analysis Toolkit for Galaxy Simulations

Jean-Paul Duminy, Jakub Szpila, Romeel Davé

• Instrumentation and Methods for Astrophysics

AstronomerOctavius is an open-source, hybrid-parallel toolkit for analysing galaxy-formation simulations, rather than observational data. It combines simulation snapshots with halo catalogues, identifies galaxies using a six-dimensional friends-of-friends algorithm, and writes halo, subhalo, and galaxy properties to HDF5 catalogues. Benchmarks against Caesar show order-of-magnitude speed improvements and more than a fivefold reduction in peak memory. The authors report near-linear strong scaling and peak memory that scales linearly with the number of halo-assigned particles; computational load grows superlinearly for larger haloes, and the pipeline is currently I/O-limited. Its extensible Python plugin architecture supports SIMBA, SWIFT-KIARA, SWIFT-EAGLE, SWIFT-COLIBRE, and TNG snapshots, plus AHF, HBT-HERONS, and SUBFIND halo catalogues. Outputs include masses, dust-attenuated galaxy photometry, and kinematic, radial, morphological, and virial quantities, accessible through a user API.

PublicLarge computer simulations of galaxy formation produce so much data that analysing their results is itself a major computing challenge. The authors present Octavius, an open-source tool that identifies galaxies in simulation outputs and compiles their properties, along with those of their surrounding matter structures. In performance tests against the earlier Caesar toolkit, Octavius delivered roughly tenfold speed improvements while using less than one-fifth as much peak memory. It also benefits efficiently from added computing resources, although reading and writing data currently limits the overall pipeline. The software supports several simulation formats and can calculate properties such as mass, motion, shape, and galaxy brightness including the effects of dust. These are capabilities and tests of simulation-analysis software, not new observations of real galaxies.

Young explorerScientists make pretend universes on computers to explore how galaxies form. These pretend universes have so much information that sorting it can take a long time. A new tool called Octavius finds galaxies in that information and makes lists of things like how heavy they are and how they move. In tests, it worked much faster and needed much less computer memory than an older tool. Moving all the information into and out of the computer's working space still slows it down. It studies computer-made galaxies, not pictures of real ones.

G92.4+5.0: A Perseus Arm superbubble associated with the H II region CTB 102

Rebecca A. Booth, Jo-Anne Brown, Tom Landecker+4 more

AstronomerNew and archival radio continuum, rotation-measure, and HI observations, supplemented by H-alpha surveys, trace the Perseus Arm superbubble G92.4+5.0 associated with CTB 102. Its upper region is faint in HI but detected in H-alpha. The measured extent is at least approximately 170 pc across and 420 pc tall, with expansion speeds of approximately 12 km/s in the lower regions and 22.5 km/s in the upper regions. The elongation and faster expansion at greater height are consistent with Kompaneets-model evolution; fitting that model yields an estimated age of 1–6 Myr. This supports, but does not establish, a scenario in which the cluster currently ionizing CTB 102 powers the expansion. Alternatively, an earlier stellar generation may have powered the superbubble, with the present cluster subsequently forming in its walls.

PublicAstronomers used radio and hydrogen-emission observations to map CTB 102, a vast cavity associated with a region of ionized gas in the Milky Way’s Perseus Arm. Superbubbles like this are carved out by winds and explosions from groups of massive stars. The observations show that this one is at least about 170 parsecs wide and 420 parsecs tall, and that its upper regions expand faster than its lower regions. Light from ionized hydrogen helps reveal the upper portion, which is faint in neutral-hydrogen radio emission. Its elongated shape and expansion pattern agree with a model that gives an estimated age of 1–6 million years. The stars now ionizing CTB 102 might also power the bubble’s expansion, but an older generation could instead have created it, with the current stars forming later in its walls.

Young explorerBig stars can blow winds and explode, making huge bubbles in space. Astronomers studied one called CTB 102 using radio signals and light from gas. They found a very tall bubble whose upper parts are spreading faster than its lower parts. Comparing it with a model suggests it is between one and six million years old. The nearby group of stars might be pushing it outward, or older stars might have made the bubble before the stars we see now formed in its walls. The scientists do not yet know which story is right.

Rotational Excitation of HC₅NH⁺ by He: Collision Dynamics and Astrophysical Applications

Ziyu Xiang, Liman Tian, Tong Sun+2 more

AstronomerThis study computes rotational excitation data for HC5NH+–He collisions using a two-dimensional potential energy surface at the CCSD(T)-F12B/cc-pVTZ-F12 level. Quantum close-coupling cross sections are thermally averaged over a Maxwell–Boltzmann distribution to obtain rate coefficients. The calculated data are then used in a non-LTE radiative transfer model of HC5NH+ in TMC-1. A global χ² fit to seven observed lines gives best-fitting n(H2) = 1.63 × 10^5 cm−3 and, as labelled in the abstract, N(H2) = 5.09 × 10^11 cm−2, with reduced χ² = 0.87. The model reproduces the observed line intensities well. The collision rates are theoretical calculations, while the fitted physical parameters are model-dependent inferences from the observed spectra.

PublicResearchers calculated how collisions with helium can change the rotation of the molecular ion HC5NH+, helping them interpret the light it emits in space. They used these theoretical collision rates in a model of the cold interstellar cloud TMC-1, allowing for molecular excitation that is not in local thermal equilibrium. Fitting the model to seven observed spectral lines produced good agreement with their intensities and a best-fitting hydrogen molecule density of about 163,000 per cubic centimetre. That density is inferred through the model, rather than measured directly; the collision rates themselves come from quantum calculations.

Young explorerMolecules in a cold cloud in space send out light as they spin. Scientists used maths to work out how bumps with helium could change one kind of molecule’s spinning. Their model matched seven light signals seen from the cloud, helping them understand what the gas there might be like.

SDSS-V LVM: Spatial Resolution Effects on Diagnostic Diagrams in the Magellanic Clouds

A. Z. Lugo-Aranda, Lesly C. Castañeda, H. J. Ibarra-Medel+22 more

AstronomerUsing SDSS Local Volume Mapper observations and spatially degraded versions of those data, the study tests ISM emission-line diagnostics at 19, 42, and 170 pc in the SMC and 17, 68, and 272 pc in the LMC. One- and two-dimensional Kolmogorov–Smirnov tests show that resolution loss most strongly affects [OIII] λ5007/Hβ, followed by [SII] λλ6717+6731/Hα and [NII] λ6584/Hα. The SMC exhibits significant distribution changes already at 42 pc, whereas the LMC remains relatively stable even at 272 pc; the authors interpret this contrast as greater intrinsic susceptibility to spatial mixing in the SMC. Degrading resolution dilutes extreme values and drives diagnostic distributions toward their mean loci. Diffuse ionized gas is especially sensitive, while Hα-selected ionized regions are more robust. Diagnostics incorporating equivalent widths and kinematics also respond differently by galaxy and resolution. The authors conclude that sub-50 pc resolution is needed to resolve detailed structure in low-metallicity galaxies, emphasizing caution when interpreting coarse-resolution extragalactic diagnostics.

PublicHow much detail a telescope can distinguish can change what astronomers infer about gas in a galaxy. This study used Local Volume Mapper observations of the Small and Large Magellanic Clouds and deliberately blurred the data to test that effect. As spatial detail was lost, unusually high or low emission-line ratios were diluted by surrounding gas, making the measurements look more alike. The Small Magellanic Cloud changed significantly even at an intermediate resolution, while the Large Magellanic Cloud remained comparatively stable at the coarsest resolution tested. The authors interpret this as evidence that mixing together different areas affects the Small Cloud more strongly. Diffuse ionized gas was particularly vulnerable, while regions selected by their Hα emission were more consistent. The authors conclude that resolving detailed structure in low-metallicity galaxies requires resolution finer than 50 parsecs and caution that coarser observations can alter gas diagnostics.

Young explorerScientists looked at glowing gas in two galaxies, then made their pictures blurrier to see what details disappeared. Bright and faint patterns in the gas’s light blended together, so places that had looked different started looking more alike. One galaxy, the Small Magellanic Cloud, changed more than the Large Magellanic Cloud. Spread-out glowing gas was especially easy to mix up. The lesson is that blurry pictures can hide differences, so scientists need to be careful when using them to learn about gas.

Probing Dark Matter-Electron Scattering with the Central Molecular Zone

Thong T.Q. Nguyen, Shyam Balaji, Carlos Blanco+1 more

• High Energy Physics - Phenomenology
• High Energy Astrophysical Phenomena

AstronomerThe study investigates dark matter–electron scattering as a source of H2 ionization in the IRS 13E3 molecular core near the Galactic Center, alongside cosmic-ray ionization. Using an ionization rate inferred from H3+ observations of the central parsecs, the authors derive constraints on heavy and ultralight dark photon mediators, a heavy leptophilic mediator, and electric dipole moment interactions in the strongly interacting regime. This probes interactions for which overburden limits terrestrial searches. The analysis identifies potentially substantial dark matter–induced ionization, not a detection of dark matter, and motivates future observations of dense molecular cores near the Galactic Center.

PublicDense gas near the center of our Galaxy may offer a way to test how dark matter interacts with ordinary matter. The researchers examine whether dark matter could knock electrons out of hydrogen molecules in the IRS 13E3 gas core, adding to the ionization caused by cosmic rays. They use an ionization rate inferred from observations of the molecular ion H3+ in the Galaxy’s central region to limit several possible dark matter interactions. These tests address interactions that are difficult to study with detectors on Earth because material above the detectors interferes with the searches. The work does not establish that dark matter caused the observed ionization; it highlights a promising approach for future observations.

Young explorerNear the middle of our galaxy are thick clouds of gas. Scientists studied whether invisible stuff called dark matter could knock tiny pieces called electrons out of the gas molecules. They used clues from the gas to work out limits on what dark matter might do. They have not shown that dark matter really did this, but looking at these clouds again could help them learn more.

Eddies that ride the flow: a model of turbulence with Richardson dispersion and anomalous dissipation

Raul Jimenez, Svitlana Mayboroda, Camillo de Lellis+2 more

• Fluid Dynamics
• Analysis of PDEs
• Numerical Analysis
• Plasma Physics

AstronomerThis theoretical and numerical study constructs a divergence-free synthetic velocity field on an n-dimensional periodic domain, rather than reporting astronomical observations. Its central device is to transport eddy-generating centres and re-convolve them, preserving the spectral envelope instead of deforming the eddy patterns directly. The field is designed to combine Richardson pair dispersion with a dissipative anomaly; proofs of both properties, and of Yaglom’s relation for an advected scalar, are attributed to companion papers at small Kubo number. Numerical diagnostics give a sweeping deficit of 0.038 ± 0.019, consistent with zero, versus 0.091 ± 0.019 for a frozen-field comparison. For pairs initially coincident but given independent Brownian kicks, median separation scales as particle diffusivity to the power 0.0333 ± 0.0038 over 22 decades, indicating weak—not absent—diffusivity dependence. An advected scalar’s independently measured variance-budget terms balance dissipation to 15% over 1.2 decades. Restoring measured diffusive transfer yields agreement with the inertial–convective prediction S_L = −χr at 0.9995 ± 0.0018. Under an imposed mean gradient, χ still changes by 14% across a factor of 5.8 in diffusivity.

PublicThe authors build an artificial mathematical model of turbulent flow, not a measurement of turbulence in nature. It combines two important behaviours: particles spread apart, and mixing retains a dissipative effect even as microscopic diffusion becomes very small. The key construction moves the centres of swirling patterns while preserving their distribution across spatial scales. Numerical tests find that particles starting together can separate with only a weak dependence on the random kicks they receive. Tests of a substance carried by the flow also approximately balance its mixing budget and closely match a theoretical prediction after diffusion is accounted for. Companion papers supply mathematical proofs under a small-Kubo-number condition; the reported numerical agreement should not be read as proof that every turbulent flow behaves this way.

Young explorerImagine a pretend swirly flow with tiny dots floating in it. The researchers made a mathematical version where dots starting together can drift apart, even when their random nudges are very tiny. They also checked how the flow mixes something it carries. Their calculations support the model, but this was not an experiment watching a real flow.

The Pristine survey XXVIII. Journey to the Galactic outskirts: Mapping the outer halo red giant stars down to the very metal-poor end

Akshara Viswanathan, Amanda Byström, Else Starkenburg+14 more

AstronomerThe authors publish two red giant branch catalogues selected from Pristine DR1 (PDR1) and Pristine-Gaia synthetic (PGS) photometric metallicities, spanning −4.0 < [Fe/H] < +0.1. Selection uses the absence of a well-measured Gaia DR3 parallax within a brightness range where dwarfs generally have useful parallaxes. Distances are estimated through BaSTI-isochrone fitting with photometric metallicities. Typical distance uncertainties are 12%; comparisons with inverted-parallax and Starhorse distances show scatter up to 20% for PDR1 giants and 40% for PGS giants. PDR1 offers a low-to-no-bias view of metallicity versus distance, whereas PGS has a distance–metallicity selection bias but provides all-sky coverage, particularly at very low metallicity. The authors use PDR1 to examine the halo metallicity distribution to approximately 100 kpc through Gaussian mixture modelling and, with spectroscopic radial velocities, map metallicity in integrals-of-motion space. They also tentatively associate 41 PGS stars, extending to 70 kpc, with a very metal-poor stellar counterpart of the Magellanic Stream; this association is not established.

PublicResearchers have released two catalogues of red giant stars to investigate the Milky Way’s relatively unexplored outer halo. They estimate the stars’ distances and iron content from survey data, then use one catalogue to study how stellar composition varies out to about 100 kiloparsecs. The distance estimates have typical uncertainties of 12%, with larger scatter when compared with other distance methods. The catalogues have different strengths: one gives a less biased picture of composition with distance, while the other covers the whole sky but has selection effects linking distance and composition. The team also identifies 41 very iron-poor stars, reaching 70 kiloparsecs away, that might belong to a stellar counterpart of the Magellanic Stream. That possible connection remains tentative.

Young explorerScientists made two big lists of giant stars far out in our galaxy. They used the stars’ light to estimate how far away they are and how much iron they contain. The estimates are not perfect, and each list has strengths and weaknesses. They also found 41 stars that might belong to a long stream of stars, but they are not sure yet.

A slow spin to win: The gradual kinematic evolution across metallicities of the proto-Galaxy to the high-α disc

Akshara Viswanathan, Danny Horta, Adrian M. Price-Whelan+1 more

• Solar and Stellar Astrophysics

AstronomerUsing Gaia DR3 red-giant kinematics and estimates of [α/M] and [M/H], the authors examine azimuthal velocity versus metallicity in carefully separated high- and low-α samples. They model the velocity distribution at a given metallicity with two Gaussian components representing disc-like and halo-like populations, initially fixing their velocity means and dispersions. An extension allows the disc component’s mean velocity and dispersion to vary between spline knots to quantify high-α spin-up. They also compare with metallicity-binned Gaussian mixture fits and explore orbital circularity as an alternative to azimuthal velocity. The inferred metal-poor high-α disc spins up gradually across [M/H] approximately −1.7 to −1.0. The low-α sample instead shows a sharp transition near [M/H] approximately −1.0, attributed to accreted debris dominating its metal-poor end. These observationally based modelling results support a slow, monotonic proto-Galaxy spin-up rather than the rapid event previously inferred near [M/H] approximately −1.0, and emphasize the importance of α-based sample selection.

PublicResearchers used Gaia DR3 observations of red giant stars to investigate how the early Milky Way developed a more orderly, rotating disc. They compared stars’ motion around the Galaxy with their metallicity and separated stars by their relative abundance of alpha elements. A statistical model distinguished disc-like and halo-like motions. In the high-alpha group, the model indicates a gradual increase in rotation across metallicities [M/H] of about −1.7 to −1.0. The low-alpha group shows an abrupt change near −1.0, which the authors attribute to debris from material acquired by the Galaxy dominating the metal-poor part of that sample. The findings therefore favor a gradual buildup of rotation in the early Milky Way, rather than a sudden spin-up near −1.0 as previously inferred. This interpretation depends importantly on how stars are selected by their chemical composition.

Young explorerLong ago, stars in our Milky Way moved in a less tidy way. Scientists used Gaia DR3 observations of big red stars to look for clues about how the galaxy began turning more neatly. They sorted the stars by what they are made of and used a math model to study their movements. One group gives clues that the turning grew little by little. Another group looks as if it changed suddenly, but the scientists say that is because many stars in part of that group came from material the Milky Way gathered from elsewhere. Their study suggests the young Milky Way began turning more smoothly slowly, not all at once.

Resolving the black hole sphere of influence in a hyper-luminous obscured quasar at redshift 4.6

Mai Liao, Roberto J. Assef, Chao-Wei Tsai+17 more

AstronomerThe authors report the first dynamical SMBH mass measurement at z > 2, using high-spatial-resolution observations of [C II] 157.7 μm and CO (12–11) 216.93 μm emission that resolve the sphere of influence in an obscured quasar at z = 4.6. The radial velocity-dispersion profile shows a clear Keplerian rise, requiring an SMBH of approximately 6 × 10^9 solar masses. They propose that obscured quasars permit tracers such as [C II] to survive in their inner regions and may therefore be promising targets for further dynamical SMBH mass measurements in the early Universe.

PublicResearchers report measuring the mass of a supermassive black hole in the early Universe from the motions of gas close to it. Their high-resolution observations of an obscured quasar at redshift 4.6 reveal an inward rise in the spread of gas velocities with the pattern expected from a central black hole's gravity. This indicates a black hole about 6 billion times the Sun's mass. The authors identify this as the first such dynamical mass measurement beyond redshift 2. They suggest that obscured quasars may let detectable gas tracers survive close to their black holes, potentially making these objects useful for more measurements; that explanation remains a proposal.

Young explorerA huge black hole's gravity makes nearby gas move fast. Scientists looked closely at gas around a hidden, bright object in the young Universe. The gas motions told them that a black hole there has about as much mass as 6 billion Suns. They think hidden objects like this might be good places to measure more black holes, but that idea still needs checking.

A two-phase model of galaxy formation: IV. Seeding and growing supermassive black holes in dark matter halos

Yangyao Chen, Houjun Mo, Huiyuan Wang

• Cosmology and Nongalactic Astrophysics
• Solar and Stellar Astrophysics

AstronomerThis theoretical framework follows SMBH–galaxy–halo co-evolution through subhalo merger trees. Pop-III stars seed BHs during the first collapse of pristine gas in mini-halos reaching the H2-cooling threshold, with seeding modulated by UV radiation and dynamical heating until IGM enrichment permits Pop-II formation. The model produces seeds of 10–100,000 solar masses at redshifts approximately 20–30 in halos of 100,000–100 million solar masses. Growth proceeds through episodic super-Eddington accretion during disturbance-induced nuclear bursts, sustained sub-Eddington capture of sub-clouds within self-gravitating gas clouds in rapidly assembling halos, and finally quiescent, merger-dominated growth. Nuclear bursts are key to producing SMBHs in this model. Competing growth channels yield a multi-piece, redshift-dependent BH–stellar mass relation. Predictions are broadly consistent with existing observations and include a BH population reminiscent of JWST little red dots; this resemblance is a model outcome, not confirmation of the proposed evolutionary pathway. The authors also discuss potential future tests.

PublicThe researchers propose a model for how supermassive black holes could form and grow as galaxies and their surrounding dark matter structures develop. In the model, the first stars produce black hole seeds with a wide range of masses. These seeds grow first through intense bursts of gas feeding near galaxy centers, then through steadier feeding from smaller gas clouds, and eventually mainly through mergers. The central bursts are crucial for seeds to become supermassive in this framework. The model also predicts that the relationship between black hole mass and a galaxy’s stellar mass changes over cosmic history. Its predictions broadly agree with existing observations and produce black holes resembling the population of objects called little red dots discovered by JWST. That resemblance is encouraging, but it does not establish that the proposed growth process actually occurred; future tests are discussed.

Young explorerHow did black holes get so big? Scientists made a model—a possible story they can test. In their model, the first stars leave behind small black holes. These grow by swallowing gas, sometimes in big bursts, and later mostly by joining with other black holes. The model makes a group that looks a bit like mysterious little red dots a telescope called JWST has found. That is a useful clue, but it does not prove the story is right.

Possible photometric signatures of nebular-dominated emission in 1.5 < z < 8.5 JADES galaxies

James A. A. Trussler, Alex J. Cameron, Daniel J. Eisenstein+21 more

AstronomerThe authors develop a photometric search for nebular-continuum-dominated galaxies using JADES medium-band imaging to identify Balmer jumps over 1.5 < z < 8.5. Because Balmer jumps are also general recombination signatures of young starbursts, approximately 3 Myr old or younger, selection additionally requires log10(ξion,obs/[Hz erg−1]) > 25.60 and a relatively non-blue UV slope. Candidates constitute approximately 11% of galaxies at z ≈ 6, decreasing to approximately 2% at z ≈ 2; these fractions are not completeness-corrected. They are optically faint, with median Mopt = −17.95, and show extreme emission lines, with median rest-frame equivalent widths of 1567 Å for Hα and 2292 Å for [O III] + Hβ. These candidates are not confirmed cases of top-heavy star formation. The authors emphasize that the hot H II regions, collisionally enhanced two-photon continuum, and strong UV lines expected with top-heavy populations complicate selection: nebular dominance need not produce the largest Balmer jumps, highest observed ionising efficiencies, or reddest UV slopes. Continuum spectroscopy is required to establish a two-photon UV downturn in the candidates.

PublicThe researchers present a way to find galaxies whose light may come mainly from glowing gas rather than directly from stars. Using JADES images taken through medium-width filters, they select galaxies with a characteristic change in brightness called a Balmer jump, together with signs of efficient production of gas-ionising light and ultraviolet colours consistent with little direct starlight. The candidates have very strong emission lines and faint optical light. They account for about 11% of galaxies around redshift 6 and about 2% around redshift 2, although these estimates are not corrected for missed objects. Such galaxies could help investigate whether early star formation favoured massive stars, but the selection does not establish that interpretation. The expected gas physics can also weaken simple selection clues. Spectroscopy of the underlying continuum is needed to confirm the proposed two-photon ultraviolet signature.

Young explorerIn some faraway galaxies, glowing gas might shine brighter than the stars themselves. Scientists used pictures taken through different filters to look for galaxies like these. They found some good possibilities, but they still need to check them. Looking more closely at how the light changes from one colour to another could help show whether unusually many big stars were being born.

Spinning compact object and chaos in galactic centres

Ushasee Paria, Uditi Nag, Yeasin Ali+1 more

• General Relativity and Quantum Cosmology
• Chaotic Dynamics

AstronomerThis modelling study examines particle dynamics near a spinning supermassive black hole embedded in an asymmetric surrounding mass distribution. It combines the Artemova-Björnsson-Novikov pseudo-Newtonian potential, which mimics Kerr-like spin dependence, with an axisymmetric, shell-like halo expanded to dipole order to introduce asymmetry. Fixed-point stability analysis and Newton-Raphson basins of convergence complement earlier chaos diagnostics, probing local stability and revealing sensitivity to initial conditions and fractal basin boundaries. Within this approximate model, black-hole spin substantially reshapes the equilibrium landscape: depending on its magnitude, it can enhance asymmetry-induced chaos or simplify phase space. These are model results, not observational measurements of galactic centres.

PublicA galaxy’s centre contains a supermassive black hole and surrounding stars and gas whose gravity can make nearby motion complicated and chaotic. This study uses a mathematical model to explore how the black hole’s spin interacts with an uneven surrounding distribution of matter. The researchers examine equilibrium points and map which starting guesses lead a numerical method to each equilibrium, finding intricate, fractal boundaries. In their model, changing the black hole’s spin can either strengthen chaotic motion associated with the uneven surroundings or make the possible motions simpler. The findings come from an approximate treatment of gravity, rather than observations of an actual galactic centre.

Young explorerImagine a huge black hole in the middle of a galaxy, with stars and gas around it. Their gravity can make things move in very tangled ways. Scientists made a maths model to see how the black hole’s spinning changes those movements. In their model, different amounts of spin could make the movements more tangled or simpler. This is something they found in their model, not something they watched happen in a real galaxy.

Detection of Gravitational Anomaly at Low Acceleration from a Highest-quality Sample of 36 Wide Binaries with Accurate 3D Velocities

K.-H. Chae, B.-C. Lee, X. Hernandez+4 more

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

AstronomerThe authors combine Gaia DR3 astrometry, new observations, and published data for 36 isolated wide binaries within 150 pc to test gravity at accelerations of 10^-11–10^-9 m s^-2. Radial velocities are relatively well constrained, although Gaia does not provide line-of-sight separations and velocities with precision comparable to its sky-plane measurements. Multiple observational diagnostics are used to control contamination from unresolved companions. Defining Gamma = log10(sqrt(G/G_N)), they infer Gamma = 0.102 (+0.028/-0.021) below 10^-9.1 m s^-2, corresponding to G/G_N = 1.60 (+0.24/-0.14), which they interpret as ruling out Newtonian gravity. Crucially, the anomaly is dominated by two binaries whose measured 3D relative speeds exceed their estimated Newtonian escape speeds. Excluding these systems reduces Gamma to 0.042 (+0.027/-0.024) below 10^-9.1 m s^-2; the remaining sample gives 0.057 (+0.035/-0.031) below 10^-9.5 m s^-2 and 0.085 (+0.059/-0.045) below 10^-10.1 m s^-2. The conclusion is therefore strongly sensitive to those two systems. The authors call for further radial-velocity monitoring and speckle imaging of larger samples to refine the result.

PublicResearchers studied the motions of 36 widely separated pairs of nearby stars to test gravity where its pull is very weak. Combining Gaia measurements with new and published observations, they infer gravity about 1.6 times as strong as Newton's law predicts and interpret this as evidence against that law in this setting. However, most of the discrepancy comes from just two pairs, whose relative speeds exceed the estimated escape speeds under Newtonian gravity. Removing those pairs makes the inferred discrepancy much smaller. The team used several observational checks to limit misleading effects from hidden stellar companions, but measurements along our line of sight remain less precise than those across the sky. Further monitoring and observations of more pairs are needed to refine the finding.

Young explorerScientists watched 36 pairs of stars that are very far apart from each other. They wanted to see whether gravity pulls them the way Newton's rule says it should. The stars' movements hinted at a stronger pull, but most of that hint came from just two pairs. Leaving those two out made the hint much smaller. The scientists want to watch more star pairs and check again.

Implications of a contracted dark matter halo for the Milky Way's inferred virial mass

Diego Dado, Shaun T. Brown, Azadeh Fattahi+2 more

AstronomerUsing ARTEMIS simulations of Milky Way-mass haloes with varying baryon-induced contraction, the authors test how restricted radial coverage and profile choice bias inferred global halo properties. Observational uncertainties are assumed negligible to isolate systematic errors. Fits confined to inner radii, particularly within about 30 kpc, cause NFW models to underestimate virial mass by a factor of about 2 on average, reaching about 4 in some systems, and concentration by about 2. Einasto and generalized-NFW profiles fit locally well but retain similar global biases; a contracted-halo prescription instead recovers unbiased masses with stable extrapolation across the tested radial ranges. Extending tracers beyond roughly 50 kpc largely removes the mean mass bias for all models. All profiles except NFW recover the dark matter density at the Solar radius to within about 5%. The authors interpret these biases as sufficient to reconcile recent low inner-rotation-curve Milky Way mass estimates with the canonical approximately 10^12 solar masses, rather than as a new measurement of the Galaxy's mass. Residual halo-to-halo scatter of at least 0.1 dex, about 25%, suggests a likely precision floor even under idealized conditions.

PublicEstimating the total dark matter surrounding the Milky Way from motions close to its centre may give a misleadingly low answer. In simulations of galaxies with masses similar to the Milky Way, the researchers tested mathematical models using information from only part of each dark matter halo. Even with measurement errors treated as negligible, a commonly used model underestimated the total halo mass by about half on average, and by a factor of about four in some cases. More flexible models could fit the inner region very well while still misjudging the whole halo. A model accounting for the halo's contraction caused by ordinary matter avoided the average mass bias in these tests. Using tracers farther out, beyond roughly 50 kiloparsecs, largely removed the average bias for every model tested. These simulated effects could explain why some recent Milky Way mass estimates are lower than the conventional value of about a trillion Suns; they do not establish a new measured mass. Differences among simulated haloes still left roughly 25% or more scatter, suggesting a limit to how precise such estimates may be.

Young explorerOur galaxy sits inside a huge cloud of dark matter that we cannot see directly. Scientists used computer-made galaxies to ask: can we work out how much is in the whole cloud by looking only near the middle? Some ways of guessing made the cloud seem much lighter than it really was in the computer. A way that allowed ordinary matter to squeeze the cloud did better. Looking farther out helped too. This could help explain why some guesses about our own galaxy seem low, but the computer tests do not tell us its exact weight.

GLIMPSED: Direct evidence for a fast active galactic nucleus-driven outflow from a z=6.64 little red dot host galaxy

Damien Korber, Rui Marques-Chaves, Daniel Schaerer+15 more

AstronomerJWST/NIRSpec medium-grating observations reveal GLIMPSED-329380 at z=6.64 behind Abell S1063, with spatially resolved host and AGN components analysed separately. Broad host [O III] λ5008 and Hα emission traces an extreme ionised outflow with FWHM ≈5350 km/s, a width associated with AGN-dominated systems. The Balmer decrement indicates dusty outflowing gas but no attenuation in the narrow lines. Emission-line diagnostics imply 12+log(O/H) ≈7.96, about 18% solar, and slight nitrogen enrichment, log(N/O) ≈−0.68. Despite its extreme width, the inferred mass-loading factor (>5–10%) and kinetic power (>10^43 erg/s) do not suggest a significant effect on the galaxy unless the outflow is very dusty. The AGN resembles little red dots through its V-shaped spectrum, exponential hydrogen-line profiles, numerous forbidden [Fe II] detections, Balmer break and broad absorption near 4550 Å. The authors interpret this fast-outflow detection as direct evidence of AGN activity in an LRD, noting that such detections are rare in surveys dominated by low-resolution spectra.

PublicAstronomers using the James Webb Space Telescope discovered a distant galaxy, GLIMPSED-329380, whose active central region appears to drive an exceptionally fast stream of electrically charged gas. They separated light from the galaxy and its active nucleus, finding extremely broadened emission lines that trace the outflow. The escaping gas contains dust, whereas the gas producing the narrow emission lines shows no detectable dust dimming. Despite the outflow’s extreme motion, the estimates do not indicate a major effect on the galaxy unless much more dust is present in the outflow. The active nucleus also has several spectral features resembling those of objects called “little red dots.” The authors present the fast outflow as direct evidence of an active galactic nucleus in one of these systems, a signature that lower-resolution surveys rarely reveal.

Young explorerAstronomers used the Webb telescope to study a very faraway galaxy. They found signs that its bright, active center is blowing dusty gas outward very, very fast. But fast gas does not always mean a big change for the galaxy: this wind may not have much effect unless it contains lots of dust. The galaxy’s center also looks like a kind of object astronomers call a “little red dot,” helping them understand what makes these objects shine.

Machine learning technique for morphological classification of galaxies from SDSS. IV. CNN-Assisted Expert Validation of Morphological Catalogues for Merging, Irregular, Edge-on, Barred, Ringed, and Dust-lane Galaxies at 0.003 < z < 0.1

D. V. Dobrycheva, I. B. Vavilova, O. V. Kompaniiets+5 more

AstronomerThe authors visually validated CNN-selected SDSS galaxies at 0.003 < z < 0.1, inspecting all merging, irregular, ringed and dust-lane candidates across their catalogue feature-score ranges, but only the highest-scoring subsets of the larger edge-on and barred catalogues. The verified samples contain 612 merging, 9372 irregular, 16822 edge-on, 811 barred, 2145 ringed and 575 dust-lane galaxies. Comparison with Galaxy Zoo 2 indicates both refined classifications and expanded coverage beyond its selection domain. Principal sources of CNN misclassification include projection effects, foreground stars, faint tidal structures and intrinsically ambiguous morphologies. For the spectroscopic subset, BPT and WHAN diagnostics using MPA-JHU emission-line measurements show that 87.8% of ringed galaxies with LINER-like ratios have H-alpha equivalent widths consistent with ionisation by evolved stars rather than an active nucleus. Five strong new polar-ring candidates are identified, not confirmed. The catalogues offer benchmarks for morphology, secular evolution, nuclear activity and machine learning; their differing inspection selections should be retained when interpreting the samples.

PublicA computer can quickly sort galaxies by appearance, but viewing angle, foreground stars and confusing structures can lead it astray. Researchers checked computer-selected galaxy images by eye and built verified catalogues of merging, irregular, edge-on, barred, ringed and dust-lane galaxies, including objects outside Galaxy Zoo 2's selection range. They checked every candidate in four categories, but only the highest-scoring candidates in the edge-on and barred categories. For galaxies with suitable spectral data, they also examined what might power glowing gas. Among ringed galaxies with a particular emission-line pattern, 87.8% had measurements consistent with older stars, rather than an active galactic nucleus, supplying the energy. They also identified five promising, but unconfirmed, polar-ring galaxy candidates. The catalogues can support studies of galaxy structure and improve future automated classifications.

Young explorerGalaxies can look like rings, have dark stripes, or seem to be bumping into each other. A computer helped find pictures with these shapes, and people checked them carefully. Sometimes the computer was fooled by how a galaxy was tilted or by a star in front of it. The team made checked lists and found five possible galaxies with unusual rings, but those still need confirmation.

Vision-Language Model Ensembles Achieve Human-Expert Accuracy for Galaxy Merger Classification

Marco Chiaberge, Elias Stengel-Eskin, Massimo Stiavelli+1 more

• Instrumentation and Methods for Astrophysics

AstronomerThis proof-of-concept combines 15 vision-language model classifier configurations across four architectures in a Bayesian framework to classify merger morphologies in 41 truth-known VELA+SUNRISE mock galaxy images. For confident classifications (pM >= 0.8 or pM <= 0.2), the ensemble achieves 83.3% accuracy and 58.3% completeness, compared with reported human accuracy and completeness of 85% each. It estimates a population merger fraction of 0.52 +/- 0.09, within 0.66 sigma of the true value of 0.585. Bayesian weighting improves accuracy by 17.1 percentage points and sensitivity by 29.2 percentage points relative to majority voting. The ensemble makes five errors, versus six reported for human classifiers; differences in error profiles and in the fraction of uncertain classifications are not statistically significant in this sample. These mock-image results support potential survey applications, but real observational samples require additional calibration and validation.

PublicResearchers tested whether a group of image-and-language AI models could identify galaxies undergoing mergers. The test used 41 simulated galaxy images with known answers, not real telescope observations. By combining the models using Bayesian statistics, the team achieved 83.3% accuracy for confident classifications, close to the reported human accuracy of 85%. However, the AI's completeness was lower: 58.3%, compared with 85% for humans. The combined models also estimated the overall fraction of merging galaxies consistently with the known simulated fraction. Statistical weighting worked better than simply taking a majority vote. The small test does not establish meaningful differences between human and AI error patterns, and the method still needs calibration and testing on real galaxy images before use in observational surveys.

Young explorerScientists asked a team of computer helpers to look at pretend pictures of galaxies and decide which galaxies were joining together. The scientists already knew the answers, so they could check the helpers' work. When the helpers were sure, they got the answer right about as often as trained people did, but they missed more of the galaxies that were joining. This was only a small practice test. The helpers still need to be checked using real pictures from space.

A Census of the 200 Most Massive Galaxies Spectroscopically Observed with JWST at zspec ∼3-15

Mengyuan Xiao, Pascal A. Oesch, Longji Bing+26 more

AstronomerThis JWST spectroscopic census targets 200 massive galaxies at zspec~3–15 using an evolving stellar-mass threshold motivated by the halo mass function and anchored at log(Mstar)>10 at z~5. The targets represent the most massive 3% of systems in publicly available prism observations, rather than a complete census of early massive galaxies. Physical properties are inferred from joint spectroscopic and photometric SED fitting, with LRDs and broad-line AGN contaminants removed to define a clean sample. Normal star-forming galaxies with Av<1 mag dominate at z≳6; dusty star-forming galaxies with Av>1 mag and quiescent galaxies become more common at lower redshift. Inferred dust attenuation decreases toward higher redshift. The authors identify 29 massive quiescent galaxies, including recently quenched systems whose star formation declined rapidly within the past ~100 Myr. Traditional UVJ and recently proposed (ugi)s selections show substantial inconsistency for these massive z>3 galaxies, motivating a revised, spectroscopically calibrated (ugi)s criterion. Inferred formation histories suggest both a dust-enriched route to quiescence and a more direct route from normal star-forming galaxies, while normal star-forming systems appear to undergo both gradual and rapid assembly. These interpretations suggest that rapid assembly, dust enrichment, and quenching were already important within the first billion years.

PublicUsing JWST spectra and other light measurements, researchers studied 200 galaxies selected to be among the most massive in publicly available observations of the early Universe. This is a selected sample, not a complete inventory. After removing certain contaminants, they found that galaxies forming stars with relatively little dust dominate at earlier times, while dustier star-forming galaxies and galaxies with little ongoing star formation become more common later. They identified 29 massive galaxies with little ongoing star formation, including some whose star production is inferred to have dropped rapidly within the preceding roughly 100 million years. Reconstructed histories suggest that galaxies could stop forming stars by at least two routes: one involving a dusty phase and another more direct route. These are interpretations of their histories, not observations of individual galaxies changing over time. The researchers also propose an updated color-based way to identify quiet galaxies because existing methods disagree substantially with their spectroscopic sample. Overall, the findings suggest that rapid growth, dust buildup, and the shutdown of star formation were already shaping massive galaxies within the Universe’s first billion years.

Young explorerGalaxies are huge groups of stars. Scientists used the JWST telescope to study light from very long ago. They found that big galaxies making stars were usually less dusty at earlier times. Later, dusty galaxies and galaxies making few new stars were more common. The light gives clues that some galaxies stopped making stars quickly. Scientists think there may have been more than one way for this to happen, but they did not watch the changes happen.

XRISM Reveals a Kinematically Coherent Core System of the Nearby Cool-Core Cluster Abell 2199

Kazunori Suda, Kyoko Matsushita, Kosuke Sato+14 more

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena

AstronomerA deep 251 ks XRISM/Resolve observation probes the cool core of Abell 2199. In the integrated central 3′ × 3′ (104 × 104 kpc²) spectrum, the ICM redshift agrees with that of the brightest cluster galaxy within the optical-redshift uncertainty, indicating a kinematically coherent core offset from the mean cluster redshift by approximately 200 km/s. The observed velocity dispersion of approximately 100 km/s corresponds to a three-dimensional Mach number of 0.16 and a non-thermal pressure fraction of 1.4 ± 0.2%. These results place Abell 2199 among the most dynamically quiescent relaxed clusters observed with XRISM, despite radio jets and a plume-like feature possibly associated with sloshing. Order-of-magnitude estimates suggest turbulent dissipation could supply approximately 20% of the radiative cooling losses for large-scale driving such as sloshing, with larger fractions for smaller AGN-feedback scales; this is an estimated heating contribution, not a measured energy balance. A localized enhancement of the Fe XXV Heα y line is detected southeast of the core, spatially coincident with a Chandra surface-brightness discontinuity.

PublicA long X-ray observation with XRISM reveals unusually quiet gas motions in the center of the galaxy cluster Abell 2199. The gas and the cluster’s brightest galaxy have matching line-of-sight motions within the measurement uncertainty, suggesting they move together as a core, about 200 kilometers per second away from the cluster’s average motion. The gas has a measured velocity spread of about 100 kilometers per second, corresponding to only about 1.4% of its total pressure coming from non-thermal motions. The core is therefore remarkably calm despite radio jets and a plume-shaped feature that might reflect gas sloshing. Rough estimates suggest that turbulence driven by large-scale sloshing could replace about one-fifth of the energy the gas loses through radiation, and potentially more if driven on smaller scales by activity around the central galaxy’s black hole. That heating contribution remains an estimate. The researchers also detect a stronger iron emission line in a southeastern patch that overlaps a sharp change in X-ray brightness seen by Chandra.

Young explorerScientists used an X-ray telescope to look at hot gas in the middle of a big group of galaxies called Abell 2199. They found that the gas is moving quite gently, even though jets are there too. The gas and the brightest galaxy seem to be traveling together. The scientists think little swirls in the gas might help keep it warm as it loses heat, but they have only estimated how much help those swirls give. They also found one patch where a special kind of X-ray light from iron is stronger.

Emulating the complex galactic-scale orbital dynamics of LISA massive black hole pairs with normalizing flows

Pedro R. Capelo, Carlos Moreno Martinez, Nodens Koren+6 more

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena

AstronomerThe authors present a conditional-normalizing-flow emulator of galactic-scale massive black hole orbital decay, trained on semi-analytical orbital integrations in multi-component merger remnants with rotating stellar discs and bars. Across a broad range of black hole masses, orbital configurations and bar properties, the emulator reproduces the training simulations’ decay-time distributions at orders-of-magnitude lower computational cost. Applied to galaxy populations from a cosmological simulation, using morphological information about barred and non-barred galaxies, it predicts that stellar bars can alter the distribution of massive black hole binary formation times across cosmic time. These are simulation-based inferences, not observational measurements or estimates of the full time to coalescence. The framework addresses stochastic orbital evolution that can invalidate an inspiral model based on dynamical friction alone, with potential relevance to future gravitational-wave predictions.

PublicWhen galaxies merge, their massive black holes may move toward one another, eventually forming a pair that could merge and release gravitational waves. Predicting how long this takes is difficult: rotating bars of stars can speed up or slow down the formation of a tightly bound black hole pair. The researchers trained an artificial intelligence model on calculated black hole orbits to imitate this early orbital evolution much faster. The model reproduced the calculations’ spread of orbital decay times while reducing computing costs by orders of magnitude. Applying it to galaxies in a cosmological simulation suggested that stellar bars change the distribution of times needed for black hole pairs to form. This is a prediction based on simulations, not a direct observation, and it does not establish how long the black holes take to complete a merger.

Young explorerWhen two galaxies come together, their giant black holes can move closer and become a close pair. A bar-shaped group of stars can help them get closer faster or make them take longer. Scientists taught a computer to copy calculations of how the black holes move, so it could work much faster. In their pretend galaxies inside a computer, the star bars changed how long it took black holes to become close pairs. This does not mean scientists watched real black holes do this, or worked out when they would finally join together.

On an empirical method to build near-equilibrium axisymmetric and triaxial galaxy models

Pierfrancesco Di Cintio, Alessandro Alberto Trani, Valentina Cesare

AstronomerThe authors present a numerical technique for constructing axisymmetric and triaxial N-body realizations of self-gravitating systems from self-consistent spherical models with known phase-space distributions. Building on the adiabatic squeezing technique of Holley-Bockelmann et al. (2001), the method is intended, ideally, to control the effective ellipticities of the particle distribution. The abstract reports preliminary tests and outlines a possible improvement, but gives no quantitative performance results.

PublicThe paper presents a computer-modeling method for turning a spherical system of particles held together by their own gravity into a flattened or elongated one. It starts with a spherical model whose particle positions and motions have a known statistical description, then builds on an existing technique called adiabatic squeezing. The aim is to control the resulting shape. The authors discuss early tests and a possible improvement, but the abstract does not establish how accurately the method controls the shape. This is simulation work, not an observational finding.

Young explorerThe researchers describe a way to reshape a round swarm of tiny dots inside a computer. The dots pull on one another with gravity, and the method aims to make the swarm flatter or longer in a controlled way. They discuss some early tests and an idea that might make the method better. They are working with computer models, not reporting something they saw in the sky.

[CII] as a global cold gas tracer in novel hydrodynamical simulations

Valentina P. Miranda, Patricia B. Tissera, Jorge González-López+1 more

AstronomerThis simulation study investigates which gas phases contribute to [CII] 158 μm emission using four existing p-gadget-3 simulations with krome chemistry and a semi-analytical emission model applied in postprocessing. The configurations comprise an isolated Milky Way-mass-size galaxy and co-rotating, counter-rotating, and perpendicular major mergers of two such galaxies. The models reproduce the [CII] luminosity–star formation rate relation, but mergers exhibit an additional emission component not accounted for by star formation alone; quiescent and starburst stages also show deviations from the relation. On global scales, the authors find [CII] to trace molecular gas and both cold and warm atomic gas. Across the configurations, approximately 50% of the total emission is associated with molecular gas, while 30–40% is associated with atomic and ionised hydrogen. They interpret the results as evidence that evolutionary history strongly influences [CII] emission, with mergers and starbursts enhancing emission through collisions with molecular hydrogen. These are model-based findings intended to inform future observations, not new observational measurements, and the gas-phase origin of [CII] remains unsettled.

PublicA particular kind of infrared light, called [CII] emission, helps astronomers study gas in galaxies, but researchers disagree about exactly which gas it traces. This study models that light in computer simulations of one isolated galaxy and three ways that two galaxies can merge. The models broadly reproduce the link between [CII] brightness and the rate of star formation, but merging galaxies have extra emission that star formation alone does not explain. Quiet periods and bursts of star formation also depart from that link. In these simulations, about half the emission is associated with molecular gas, while 30–40% is associated with atomic and ionised hydrogen. The authors suggest that a galaxy’s history matters: mergers and bursts of star formation may boost this light through collisions involving molecular hydrogen. These predictions come from simulations rather than new telescope observations.

Young explorerGas in galaxies can give off a special kind of light that helps scientists learn about it. The scientists made computer models of a galaxy alone and pairs of galaxies coming together. In the models, galaxies coming together made extra light that new stars alone could not explain. The scientists think bumps between tiny gas particles help make this light. These are clues from computer models, not new pictures of real galaxies.

Diverse Metallicities in Protoclusters at z ∼3.4 detected by Deep Learning

Yoshihiro Takeda, Nobunari Kashikawa, Kei Ito+12 more

AstronomerSubaru/MOIRCS spectroscopy of four PCFNet-selected candidate regions confirms four protoclusters in three regions at z = 3.316, 3.403, 3.408 and 3.425, with galaxy density peaks exceeding five times a uniform distribution. Confirmed-member detection rates agree with PCFNet predictions. SED fitting using up to ten photometric bands places members on the star-formation main sequence. The most massive halo in each protocluster is estimated from its most massive member galaxy to have log(M_halo/M_sun) = 12.4–12.8, consistent with cosmological simulations at these redshifts and with progenitors of typical present-day clusters of roughly 10^14 solar masses. Voronoi Tessellation Monte Carlo analysis incorporating PCFNet membership probabilities indicates star-formation-rate densities significantly above the cosmic value at z ≈ 3.4. Metallicities inferred from [O III]/Hβ are marginally higher than in the field in two protoclusters, at only 1.4–2 sigma; the others are statistically consistent with the field. Competition between enriched-gas recycling and metal-poor inflow is proposed as an environment-dependent interpretation, not established as the cause.

PublicFollow-up observations with Subaru/MOIRCS confirmed four developing galaxy clusters in three of four regions selected by the deep-learning model PCFNet. These distant structures have galaxy density peaks more than five times those expected for a uniform distribution, and the rate of confirmed members agrees with the model’s predictions. Their galaxies form stars at rates typical for galaxies of their stellar mass, but the crowded regions produce substantially more stars per unit volume than the cosmic average at that epoch. Indirect estimates of their largest dark-matter halo masses agree with simulations of possible ancestors of typical present-day galaxy clusters; their future evolution was not observed. Two structures show weak hints of greater chemical enrichment than galaxies outside the protoclusters, while the others show no statistically significant difference. The authors suggest that competing supplies of recycled, enriched gas and incoming, less-enriched gas may help explain this diversity, but the evidence does not establish that explanation.

Young explorerA computer helped astronomers choose places to look for big groups of galaxies that are still growing. Using a telescope, they confirmed four such groups. The galaxies are crowded together, so these places make many more new stars in the same amount of space than the universe does on average. But each galaxy makes stars at a normal pace for its size. Two groups might have a little more of the heavier ingredients made by stars, but the clues are not strong enough to be sure. Astronomers think different kinds of gas coming into the galaxies could help explain the differences.

A strategy for astrometric quasar selection with Gaia DR3 and its application to discover new luminous z>2 quasars

J. Li, J. P. U. Fynbo

AstronomerThe authors develop a purely astrometric quasar-selection recipe using Gaia DR3. Analysis of confirmed quasars and stationary sources finds a Rayleigh-like proper-motion signal-to-noise distribution and demonstrates the importance of accounting for correlations between proper-motion components and nonlinear error propagation. They use the Mahalanobis distance from zero proper motion, fitting Gaia-CRF3 with a scaled chi-squared distribution with k=2 and scale 1.1485. Their approximately two-sigma Gaussian-equivalent cut, D²_M(μ)<7.097, is combined with a parallax condition and ruwe<1.4. They report improved completeness and purity relative to literature strategies, with approximately 95% quasar purity. Recovery is 90.25% for SDSS DR16Q confirmed quasars; the abstract separately reports 95% recovery of known quasars. As a discovery application, they identify 24 very luminous z>2 quasars, including ten new discoveries and seven objects whose previously determined redshifts are corrected. Improved selection for future surveys is a proposed application.

PublicThe study presents a way to select quasars using Gaia DR3 measurements of apparent motion and parallax, rather than relying on their light's other properties. The method carefully accounts for measurement uncertainties and how they are related. The authors report that it selects a cleaner, more complete quasar sample than earlier approaches, with about 95% of selected objects being quasars. It recovers 90.25% of confirmed quasars in one tested catalogue; the abstract also gives a separate 95% recovery figure for known quasars. Applying the method, the team identifies 24 very luminous quasars at redshifts above two, including ten new discoveries, and corrects earlier redshift estimates for seven. They propose using the recipe to improve future surveys.

Young explorerThe researchers made a better way to pick out quasars, very bright things far away in space. They looked for tiny dots that seem almost still, while being careful about mistakes in the measurements. Their search found 24 very bright quasars, including ten new discoveries. They hope this method will help future searches too.

Stellar Bars Reshape the Spatial Distribution of UV-bright Clumps in Nearby Galaxies

Zhimin Zhou, Jianfei Liu

AstronomerArchival HST/WFC3 F275W imaging of 70 barred galaxies and 95 unbarred controls matched in stellar mass, optical color, redshift, and background noise yields 95,486 UV-bright star-forming clumps identified with a uniform dendrogram procedure. Relative to controls, barred galaxies exhibit a clump deficit at intermediate radii broadly corresponding to the bar, a local recovery near the bar ends at R/R_bar ~ 1, and preferential alignment along the bar major axis. These spatial differences are stronger at high galaxy mass. Normalized bar length is more closely associated with radial redistribution and central F275W concentration than bar ellipticity, but its association with azimuthal structure is less uniform. Clump luminosity and size distribution functions remain broadly similar between samples. The findings suggest that bars primarily reorganize the locations of recent star formation rather than substantially changing individual UV clump luminosities or sizes; they do not establish whether bars change the total amount of recent star formation.

PublicResearchers used archival ultraviolet images from the Hubble Space Telescope to compare 70 galaxies with central stellar bars against 95 otherwise similar galaxies without bars. They identified 95,486 bright clumps associated with recent star formation. Barred galaxies had fewer clumps across the region roughly occupied by the bar, a local recovery near its ends, and more clumps aligned along its length. These differences were stronger in more massive galaxies. The bar's relative length was more closely linked to the radial arrangement of clumps and the concentration of central ultraviolet light than its degree of elongation. Yet the clumps in the two groups had broadly similar brightness and size distributions. The observations suggest that bars mainly rearrange where recent star formation occurs, without substantially changing the brightness or sizes of individual ultraviolet clumps. Whether bars change the total amount of recent star formation remains uncertain.

Young explorerSome galaxies have a long bar of stars across their middle. Scientists looked at pictures of galaxies with and without these bars and found bright patches where stars have recently formed. Galaxies with bars had fewer patches in the bar region, with more appearing again near the bar's ends. The patches also tended to line up along the bar. But the patches had roughly similar brightnesses and sizes in both kinds of galaxy. This suggests that a bar mostly changes where new stars appear. It does not tell us for sure whether the galaxy makes more or fewer new stars overall.

General-relativistic neutrino-radiation hydrodynamics of crust ejection in magnetar giant flares

Tetyana Pitik, David Radice, Jacob Fields+1 more

• Nuclear Theory

AstronomerThe radio afterglow of SGR 1806-20’s 2004 giant flare has been interpreted as evidence for ejection of at least roughly 10^-9 solar masses of baryons. This study tests a proposed crust-ejection mechanism using general-relativistic neutrino-radiation hydrodynamics simulations with AthenaK and reaction-network nucleosynthesis calculations. For flare pressures corresponding to magnetic fields of 10^15–10^16.5 G, the models unbind 10^-10–5 × 10^-8 solar masses. The ejecta electron fraction remains within a few hundredths of its crustal value, with weak interactions affecting it mainly in the most energetic flares. Fast, high-entropy expansion leaves mostly alpha particles and free neutrons. Stronger flares produce nuclei reaching the third r-process peak, but nuclei with mass number A ≥ 90 constitute at most about 8 × 10^-4 of the ejecta, or about 3.5 × 10^-11 solar masses per flare; their mass fraction is below 10^-5 for B ≤ 10^15.5 G. Any nova brevis would be powered mainly by free-neutron decay. The models assume spherical symmetry, whole-surface flares, and no magnetic field. Magnetic confinement and localized flares should reduce ejection, so the authors regard the masses as upper limits at a given flare pressure and expect negligible r-process production in realistic flares.

PublicGiant flares from magnetars may blast material off these neutron stars: the radio glow following one flare in 2004 has been interpreted as evidence for such an outflow. This study uses computer simulations to test whether pressure from a flare could drive a shock into the star’s crust, ejecting material that then makes heavy elements. The simulated flares do eject crust, but the escaping material ends up mostly as helium nuclei and free neutrons. Stronger simulated flares make some very heavy nuclei, yet these account for only a tiny fraction of the ejected mass. A proposed brief glow called a nova brevis would therefore be powered mainly by neutron decay. These are model predictions, not observations of newly formed elements. The calculations omit magnetic fields and assume that the flare covers the entire star; the authors expect more realistic conditions to eject less material and produce negligible amounts of heavy elements through the rapid neutron-capture process.

Young explorerA magnetar is a kind of star that can have huge bursts. Scientists used a computer to ask whether a burst could knock bits off its hard outside and make heavy kinds of atoms. In their pretend stars, some bits flew away, but very little became heavy atoms. The model left out things that could hold the bits down, so real bursts may knock off even less.

Is the hard X-ray polarization of Cyg X-1 stable?

Matthew G. Baring, Jacob Casey, Ephraim Gau+22 more

AstronomerHard-state observations of Cyg X-1 during and near XL-Calibur’s July 2024 balloon flight combine approximately 19–64 keV polarimetry with joint NICER, NuSTAR, and Swift-BAT spectroscopy over 1.0–195.0 keV. The previously reported four-day polarization degree was 5.0% (+2.7/−3.0 percentage points), with the polarization angle aligned with the jet. Day-by-day analysis indicates variability: on July 12–13, the polarization degree was 16.8 ± 4.9%, with an angle approximately 25° offset from the jet; the remaining days were consistent with the integrated values. Concurrently, the spectral model’s reflection fraction parameter increased by a factor of two. The authors interpret the resulting constraints on an additional component’s polarization and flux as more readily accommodated by geometric changes in the corona near the black hole than by scattering near the stellar companion; this is a favored interpretation, not a demonstrated origin.

PublicX-ray observations of Cyg X-1 around XL-Calibur’s July 2024 balloon flight suggest that the polarization of its light—the preferred orientation of its light waves—changed over a few days. Earlier results averaged over four observing days showed about 5% polarization aligned with the system’s jet. The new daily analysis finds 16.8 ± 4.9% polarization on July 12–13, oriented about 25° away from the jet; the other days were consistent with the earlier average. At the same time, a parameter describing reflection in the researchers’ X-ray model doubled. The authors argue that changes in the shape or arrangement of the corona near the black hole are more likely to explain these findings than light scattering near the companion star, but the explanation is not established.

Young explorerScientists watched X-ray light from a place called Cyg X-1, where a black hole has a star nearby. They found signs that, for part of their watch, more of the light waves lined up together, and they lined up in a different direction. Their model of light bouncing around also changed. The scientists think the shape of a region close to the black hole may have changed. That seems to fit better than light bouncing near the nearby star, but they are not sure.

The retirement party of GRS 1915+105: the radio fading to quiescence of the archetypal microquasar

S. E. Motta, R. P. Fender, A. Marino+21 more

AstronomerLong-term MeerKAT monitoring and deep July 2026 observations show GRS 1915+105 reaching its lowest recorded radio flux densities after more than 25 years of near-Eddington activity and over six years of Compton-thick obscuration. Following a Jy-level flare in early 2025, the 1.28 GHz flux density declined monotonically to about 0.2–0.4 mJy by March 2026; after May 9 it was no longer formally detected in 10-minute monitoring observations. Deep July observations nevertheless detected about 150 μJy in L band and 90 μJy in S band, corresponding to a 1.28 GHz radio luminosity of approximately 2 × 10^28 erg s^-1. The 1.28–2.62 GHz spectral index is −0.67 ± 0.41, consistent with mixed optically thick and thin emission or an intrinsically steep core-jet spectrum. With the accretion flow obscured in X-rays, the authors interpret the radio decline as the first direct evidence of intrinsic central-engine fading rather than increased obscuration. Whether this ends the outburst that began in 1992 or represents a temporary switch-off remains unresolved. If quiescence is beginning, disc-instability models predict a duration of order 10^4 years.

PublicThe black-hole binary GRS 1915+105 has faded to the weakest radio levels ever recorded from it, potentially signaling the end of an outburst that began in 1992. Thick obscuring material hides its feeding flow from X-ray view, making radio emission the best current way to track its activity. MeerKAT observations followed a steady radio decline after a strong flare in early 2025. Brief observations stopped formally detecting the source after May 9, 2026, but deeper observations in July still found faint radio emission. The researchers interpret this decline as evidence that the central engine is genuinely weakening, not simply becoming more hidden. It is not yet clear whether the system is entering a long quiet period or only switching off temporarily. If a quiet period is beginning, models predict it could last roughly 10,000 years; that is a conditional prediction, not an observed outcome.

Young explorerAstronomers are watching a black hole and its star companion. Radio signals from this pair have become fainter than ever measured before, though careful listening with a telescope still found a tiny signal. The scientists think the activity near the black hole is slowing down, rather than just hiding behind more stuff. They do not yet know whether this is a short break or the start of a very long quiet time.

A Machine Learning Approach to Coupling Photoionization & Multi-Frequency Radiation Hydrodynamics

Sergei Dyda, Randall C. Dannen

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

AstronomerThis computational study couples photoionization microphysics to radiation hydrodynamic simulations of line-driven winds using machine learning. Models trained on XSTAR outputs predict the line-driving force multiplier from gas ionization, optical depth, and the blackbody temperature of the irradiating spectral energy distribution (SED). Implementation in Athena++ enables rapid runtime evaluation of radiative acceleration without directly solving photoionization during hydrodynamic evolution. Among the models tested, random forests achieve the highest accuracy and reproduce force multipliers across the three-dimensional parameter space more accurately, with less training data, than precomputed tables with trilinear interpolation. The authors propose generalizing the framework to more complex radiation fields and arbitrary spectral shapes; these extensions are not reported as demonstrated results.

PublicThe researchers developed a machine-learning shortcut for simulations of gas winds pushed by radiation through interactions with spectral lines. They trained models on calculations from the XSTAR code, then incorporated them into the Athena++ simulation software to estimate radiation's push without repeatedly performing expensive calculations of how radiation ionizes the gas. In their tests, random forest models were the most accurate and needed less training data than a conventional lookup-table approach to reproduce the calculated force multipliers. This is a computational result, not an observation of a wind. The training describes the radiation spectrum using a blackbody temperature; extending the method to more complicated spectra is a proposed next step.

Young explorerLight can push gas and make it blow like a wind. To help computers pretend this is happening, the researchers taught a computer helper using answers from detailed calculations. The helper could quickly estimate how strongly the light pushes, instead of doing the hard calculation again and again. One kind of helper worked best in their tests and copied the calculated answers more closely than looking them up in a table. They hope to teach it about more complicated kinds of light, too.

Systematic Study of Cosmic Rays in Star-Forming and Starburst Galaxies using Fermi-LAT and Multiwavelength Data

Hinako Ochi, Tsunefumi Mizuno, Yasushi Fukazawa+5 more

AstronomerA systematic analysis of seven sources using 15 years of Fermi-LAT data finds declining gamma-ray energy flux below a few hundred MeV in M82 and NGC 253, suggesting substantially less cosmic-ray electron emission than previously inferred. Spectral energy distribution fits incorporating the new GeV measurements and reported radio and TeV results indicate electron-to-proton ratios comparable to the Milky Way’s, but cosmic-ray energy densities 2.5–8 times lower than magnetic-field energy densities, unlike the Milky Way. A two-component decomposition of M31’s gamma-ray emission identifies a soft-spectrum central component smaller than 0.33 degree, interpreted as evidence for a considerable unresolved-source contribution. Revised fluxes place all sampled starbursts at levels comparable to or below the calorimetric limit, with inferred efficiencies of 0.33–1.20; sampled star-forming galaxies instead have efficiencies around 10%. A theoretical interstellar-emission model reproduces these efficiencies and is proposed as a framework for interpretation and prediction.

PublicGamma rays can reveal how high-energy particles called cosmic rays interact with material inside galaxies. Using 15 years of Fermi-LAT observations, researchers studied seven sources. In the starburst galaxies M82 and NGC 253, the measured spectra suggest that cosmic-ray electrons contribute much less gamma-ray emission than previously thought. Combining these observations with earlier radio and higher-energy gamma-ray results, their models indicate electron-to-proton proportions similar to those in our Milky Way, but less energy in cosmic rays than in magnetic fields. In M31, they identified a compact central component whose emission suggests a substantial contribution from sources that cannot be individually distinguished. Revised estimates put the sampled starbursts near or below the expected calorimetric limit, while the other sampled star-forming galaxies are much less efficient gamma-ray producers. A new theoretical model matches the inferred efficiencies, offering a way to interpret and predict such emission.

Young explorerTiny, speedy particles in galaxies can help make a kind of light called gamma rays. Scientists studied this light for 15 years. In two galaxies where many stars are being born, the light suggests that one kind of tiny particle helps less than scientists thought. In another galaxy, some light may come from sources too close together to see separately. The team also made a model that matches how efficiently these galaxies make gamma rays.

Double Neutron Star Mergers and Fast Blue Optical Transients: A Circumbinary Disk Connection

Aldana Grichener, Ruggero Valli, Mathieu Renzo+5 more

• Solar and Stellar Astrophysics

AstronomerThe authors use scale-free hydrodynamical simulation results to construct a framework for post-common-envelope circumbinary disk interactions and implement it in COMPAS. Across a grid of binary-evolution and disk prescriptions, these disks generally drive substantial orbital shrinkage and reduce the predicted double neutron star merger rate by up to 28%, primarily by inducing premature mergers between a neutron star and the giant's stripped core. Such mergers are proposed as luminous fast blue optical transient progenitors, with a fiducial modeled rate of approximately 11 Gpc^-3 yr^-1. The models indicate little contribution from natal kicks to transient offsets and predict associations with young stellar populations, though not necessarily active star-forming regions. Removing progenitors that would otherwise yield short-delay double neutron star mergers further challenges their role in early r-process enrichment. Disk accretion raises the chirp masses of surviving double neutron star mergers, offering a possible explanation for GW190425's mass. These are modeling results and proposed interpretations, not observational confirmation of the disk-driven channels.

PublicWhen a pair of stars sheds a shared outer envelope, some of the gas can remain in a disk around the pair. Using computer simulations to build a model of how this disk affects the stars, the researchers predict that it often draws them closer together. In their models, some neutron stars merge with their companions' exposed cores before a pair of neutron stars can form, reducing the eventual neutron star merger rate by as much as 28%. The authors suggest these earlier collisions could power luminous fast blue optical transients, but this connection is not established. Their models predict that such flashes would occur among young stars, though not necessarily where stars are currently forming. Losing these rapidly merging neutron star pairs would also make it harder for neutron star mergers to explain early enrichment by elements made through rapid neutron capture. For pairs that survive, feeding on disk gas increases a particular combination of their masses measured through gravitational waves, potentially helping explain the mass of GW190425.

Young explorerSometimes two stars throw off a big cloud of gas, but some gas stays in a ring around them. Scientists used computer models to see what that ring might do. In the models, it often pulls the stars closer. Sometimes a tiny, very tightly packed star crashes into the middle of its partner sooner than it otherwise would. The scientists think this could make a bright blue flash, but they have not shown that it really does. Other pairs survive and gain extra material from the ring. These are ideas tested in computers, not things the scientists watched happen.

High precision timing of seven binary millisecond pulsars with the European Pulsar Timing Array

K. Liu, A. Chalumeau, H. Hu+21 more

AstronomerThe authors present phase-coherent timing solutions for seven binary millisecond pulsars monitored by the European Pulsar Timing Array, combining observations from five major European radio telescopes and their coherent combination, LEAP. Bayesian timing and noise analyses yield broadly improved astrometric and orbital parameter precision, including some first measurements. For PSRs J0125-2327, J1741+1351 and J2043+1711, astrometry provides distances and transverse velocities, while Shapiro delays support mass inferences. Analysis of secular orbital-period changes provides kinematic distance estimates for J0125-2327, J1125+7819 and J1741+1351. Annual-orbital parallax signatures are detected for J0125-2327 and J1741+1351, yielding a strongly favored unique ascending-node and inclination solution for the former and a tightly constrained ascending node for the latter. Orbital periods and their derivatives also set upper limits on gravitational-wave strain at sub-nanohertz and microhertz frequencies, rather than establishing detections. The authors suggest that binary orbits could provide stringent microhertz constraints and potentially complement standard pulsar-timing-array analyses.

PublicResearchers precisely tracked the regular radio pulses from seven rapidly spinning stars, each orbiting a companion. Combining European telescope observations improved measurements of their positions and orbits. For three systems, the team determined distances and sideways speeds and inferred masses from delays in the pulses caused by gravity. Subtle timing signatures also helped establish how two systems’ orbits are oriented, with a strongly favored unique orientation for one. The researchers used orbital periods and their changes to set upper limits on gravitational waves in two very low-frequency ranges; this was not a gravitational-wave detection. They suggest that these binary systems could eventually complement existing pulsar-timing searches, especially at microhertz frequencies.

Young explorerSome spinning stars send us radio pulses like very steady ticks, and some have a partner star. Scientists carefully timed the ticks from seven of these pairs to learn more about where they are and how they move. They also used the stars’ orbits to limit how strong certain ripples in space could be. They did not discover those ripples, but this method might help scientists study them in the future.

The Influence of the Inclination of the Accretion Disk in Black Hole X-Ray Binaries on the Energy Spectrum Characteristics

Aijun Dong, Shangyao Jing, Weilong He

AstronomerIn some black hole X-ray binaries, the photon index Γ anticorrelates with the 3–25 keV X-ray Eddington ratio below a transition value and correlates positively above it. Previously identified transition ratios span roughly 0.1%–10% across systems, with the origin of this variation uncertain. Analyzing light curves and energy spectra during the declining phases of 15 outbursts from eight systems, the authors find approximately consistent transition ratios across different outbursts of the same binary. Across different binaries, they report a positive linear correlation between the transition ratio and the cosine of the accretion disk inclination. They interpret this as evidence that viewing geometry significantly influences the observed spectral evolution; the reported correlation does not by itself establish the physical cause.

PublicSome black holes with companion stars undergo X-ray outbursts. As their X-ray brightness changes, the relationship between brightness and the shape of the X-ray spectrum reverses at a particular threshold. That threshold differs between systems. Researchers examined the fading stages of 15 outbursts from eight systems and found that each system’s threshold was approximately repeatable across outbursts. Between systems, the threshold, measured relative to the Eddington luminosity, was higher for disks viewed more face-on. The authors interpret this pattern as evidence that the viewing angle matters for the observed X-ray changes, although the correlation alone does not prove the explanation.

Young explorerGas in a disk around a black hole can shine in X-rays, a kind of light our eyes cannot see. Scientists watched 15 bursts of this light from eight black hole systems as the bursts faded. They found that the way the X-ray light changed switched at about the same brightness level each time for the same system. That level was different for different systems and was linked to the angle from which we see the disk. The scientists think our viewing angle helps explain the difference, but they have not proved that it is the cause.

Discovery of the redback pulsar PSR J2053+6905 and multi-epoch optical observations of the system

A. V. Karpova, J. D. Taylor, A. V. Bobakov+8 more

AstronomerA targeted Green Bank Telescope search discovered the 1.68-ms binary pulsar PSR J2053+6905 in a redback candidate previously identified optically and in X-rays, spatially coincident with gamma-ray source 4FGL J2054.2+6904. Initial timing yields precise Keplerian parameters and a mass function, with potential evidence for scintillation and long radio eclipses. Multi-epoch optical photometry reveals pronounced light-curve asymmetry and substantial long-term variability. Spectroscopy gives a radial-velocity semi-amplitude of 337 ± 4 km/s; combined with the pulsar mass function, this constrains the mass ratio to Mp/Mc = 7.05 ± 0.08. Symmetric direct-heating fits restricted to stable light-curve segments imply approximate masses of 2.1 and 0.3 solar masses for the pulsar and companion, respectively, and constrain Roche-lobe filling and day- and night-side temperatures. These mass estimates depend on the light-curve model. The authors interpret the long-term profile evolution as likely caused by a cold stellar spot dissipating or migrating.

PublicAstronomers discovered PSR J2053+6905, a pulsar that spins once every 1.68 milliseconds and orbits a companion star. They found its radio pulses with the Green Bank Telescope after earlier optical and X-ray observations had flagged the system as a promising candidate. Tracking the pulses and measuring the companion’s motion showed that the pulsar is about seven times as massive as its companion. The companion’s brightness changes unevenly during each orbit, and that pattern also changes over longer periods. By fitting relatively stable portions of these brightness measurements with a model in which the pulsar heats its companion, the team estimated masses of roughly 2.1 times the Sun’s mass for the pulsar and 0.3 times for the companion. Those estimates depend on the model. A cool spot moving or fading on the companion is the authors’ likely explanation for the longer-term changes. The radio data also show possible signs of signal flickering and long eclipses.

Young explorerAstronomers found a tiny star that spins incredibly fast and sends out radio pulses, like a lighthouse. It travels around with another star. That other star gets brighter and dimmer in a changing pattern. The scientists used the pulses and the stars’ motion to learn that the spinning star is about seven times heavier than its partner. They also used a model of how one star warms the other to estimate their weights, so those estimates are not certain. They think a cooler patch moving or fading on the partner star may help explain why its brightness pattern changes.

FALCON (FERMI-ALMA Calibrator ObservatioN): Cross-matching ALMA Calibrators with Fermi-LAT Blazars

Kanako Narita, Yoshiyuki Inoue, Bunyo Hatsukade+1 more

AstronomerThe FALCON catalogue cross-matches the ALMA Calibrator Source Catalogue with 4LAC-DR3 to assemble a millimeter-selected sample of 949 unique gamma-ray-associated sources, approximately 25% of the 4LAC-DR3 blazar population. For sources with measured redshifts, millimeter and gamma-ray luminosities show a strong, statistically significant correlation that persists after controlling for redshift. Fermi-detected blazars have systematically flatter millimeter spectral indices than gamma-ray non-detected ALMA calibrators. The redshift-controlled luminosity correlation weakens progressively from high-synchrotron-peaked BL Lacs toward flat-spectrum radio quasars. These observational findings support an intrinsic millimeter–gamma-ray connection and are consistent with a common jet origin governed by Doppler boosting and time-averaged jet power, rather than establishing that interpretation uniquely.

PublicBlazars are active galactic centers whose fast-moving jets point nearly toward Earth. The researchers combined ALMA and Fermi catalogue data to build FALCON, a sample of 949 sources associated with gamma-ray emission. Among sources with measured redshifts, which allow luminosities to be calculated, those brighter at millimeter wavelengths also tend to be brighter in gamma rays. This strong statistical link remains after accounting for redshift effects, although it is weaker in some blazar classes than others. Gamma-ray-detected blazars also have flatter millimeter spectra than ALMA calibration sources without gamma-ray detections. The findings support a physical connection between the two kinds of emission, consistent with both arising in the jets and being influenced by jet power and the brightening caused by motion toward us; they do not prove that explanation.

Young explorerSome galaxies send out very fast streams of stuff that point almost right at us. Scientists made a list of 949 objects seen in two kinds of light our eyes cannot see. For the ones whose brightness they could work out, objects shining more strongly in one kind usually shone more strongly in the other, too. The match was stronger for some kinds of galaxies than others. This is a clue that both kinds of light may come from the fast streams, but it is not proof.

Multi-epoch monitoring of the faint northern component in 3C 84 during 2016-2021

Kotaro Niinuma, Motoki Kino, Nozomu Kawakatsu+7 more

• Astrophysics of Galaxies

AstronomerMulti-epoch 7 mm VLBI observations from 2016–2021 probe N1, the sub-parsec-scale northern jet component of 3C 84. Its peak position fluctuates by approximately 0.2 mas at a separation of about 2.5 mas from the central radio core C1. A linear fit gives a declination proper motion of 0.054 ± 0.019 mas per year, corresponding to an apparent speed of 0.062 ± 0.021 times the speed of light, but the displacement is comparable to the positional scatter and systematic motion is not statistically supported. By contrast, the peak flux density changes by roughly a factor of two over several months. The authors propose two interpretations: N1 could be the counterpart of the southern hotspot C3, stalled by a compact, dense cloud, with variability caused by changing free-free absorption through the non-uniform cloud; alternatively, N1 could be a heavily absorbed northern jet segment visible through a gap, with variability reflecting intrinsic jet changes and interactions with a non-uniform ambient medium. Neither interpretation is established; the observations constrain N1’s origin and the circumnuclear environment.

PublicRadio observations made between 2016 and 2021 tracked a feature called N1 in the northern jet of 3C 84. Its measured position wandered slightly, but the data do not establish steady motion. Its peak radio brightness, however, changed by about a factor of two over several months. The researchers suggest two possible explanations. N1 might be a jet hotspot stopped by a dense cloud, with changes in how much radio emission the cloud absorbs causing the brightness variations. Alternatively, it might be a section of the northern jet seen through a gap in absorbing material, with its brightness changing because of activity within the jet and interactions with uneven surroundings. These remain possible explanations rather than confirmed accounts of what N1 is.

Young explorerAstronomers watched a bright radio spot called N1 in a stream of material in space. It got brighter and dimmer over a few months, but they could not tell that it was steadily moving. Maybe a thick cloud stopped the spot and hides different amounts of its radio light. Or maybe we see part of the stream through a hole in material in front of it, and the stream itself is changing. The astronomers do not yet know which idea is right.

The complex periodic variability of PKS 0301-243: hints of a supermassive black hole binary candidate

Jintong Wang, Yunguo Jiang, Shifeng Huang

AstronomerOptical monitoring of the blazar PKS 0301-243 identifies a 269-day periodicity, with uncertainties of +13/−14 days, in Zwicky Transient Facility g and r data. Corrected global significances are 2.75σ and 2.18σ, respectively, with seven cycles across approximately 2000 days. Katzman Automatic Imaging Telescope data show a longer 889-day periodicity, with uncertainties of +47/−46 days and corrected global significance of 1.97σ, spanning approximately five cycles over 4500 days. Multiple methods independently identify both periodicities, but their modest significances warrant caution. The authors interpret the shorter period as possibly orbital and the longer period as potentially due to jet precession; neither interpretation confirms a supermassive black hole binary. A binary model incorporating a relativistic jet and circumbinary disc could reproduce the observed light-curve ensemble. Adopting a total mass of 10^8.95 solar masses and mass ratio q = 0.1 yields a milliparsec-scale separation and gravitational-wave-driven coalescence time of 1122 ± 144 years. These model-dependent estimates motivate PKS 0301-243 as a possible nanohertz gravitational-wave source and multimessenger target, not a confirmed detection.

PublicThe blazar PKS 0301-243 shows hints of repeating changes in visible brightness: one roughly every 269 days and another roughly every 889 days. Researchers found these patterns using several analysis methods, but their statistical significance is modest, so they need cautious interpretation. The team suggests that the shorter cycle might reflect two supermassive black holes orbiting each other, while the longer cycle might come from a changing direction of a fast-moving jet. A model containing two black holes, a jet, and a surrounding disc could reproduce the observed brightness patterns, but does not establish that this explanation is correct. With assumed black hole masses, the model predicts a merger in about 1100 years and suggests a possible source of very low-frequency gravitational waves. Neither the black hole pair nor those waves are confirmed here.

Young explorerScientists watched a bright object far away and found hints that its light gets brighter and dimmer in a repeating pattern. Maybe two giant black holes are circling each other, and a jet of material is slowly changing direction. But the clues are not strong enough to be sure. The scientists made a model that could explain the flickering; they have not confirmed the two black holes.

On the Nucleon Effective Mass in Neutron Stars Cooling

Yuuki Sugiyama, Akira Dohi

• High Energy Physics - Theory
• Nuclear Theory

AstronomerThis modeling study examines how effective nucleon masses affect neutron-star cooling, which depends strongly on the equation of state through interior neutrino emission. The authors use Walecka models to treat Dirac and Landau masses within a unified framework, calculate emissivities including the direct Urca process, and evaluate cooling curves. Their calculations show that both mass definitions affect the cooling of massive neutron stars, although most previous cooling simulations do not distinguish them. Uncertainties involve the attractive scalar-meson interaction and the distinction between Dirac and Landau masses. Cooling simulations using two realistic relativistic mean-field equations of state, differing only in effective-mass properties among their characteristic parameters, give broadly consistent results. The findings suggest that effective-mass treatment may be an important modeling uncertainty; they are simulation results rather than observational measurements.

PublicNeutron stars contain extremely dense matter and cool largely by releasing particles called neutrinos from their interiors. This study uses computer models to explore how that cooling depends on the effective masses of neutrons and protons, quantities that describe their behavior within dense matter. The calculations find that distinguishing two definitions of effective mass changes the predicted cooling of massive neutron stars. Tests with two more realistic descriptions of dense matter broadly support the simpler models. These are theoretical results, not measurements of stars, and suggest that how effective masses are treated may be an important source of uncertainty in cooling predictions.

Young explorerA neutron star is a star made of very tightly packed matter. It cools by sending out tiny particles. Scientists used computer models to see how the way its building blocks behave could change how fast it cools. Their models suggest this matters, but they did not measure real stars cooling in this study.

Constraining tau-sterile neutrino mixing with high-energy astrophysical neutrinos

Mauricio Bustamante, Qinrui Liu

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

AstronomerWhether a sterile neutrino mixes with the three active flavors remains unresolved, and its mixing with tau neutrinos is the least constrained. The study shows that TeV–PeV astrophysical neutrinos offer a complementary probe: sources produce almost no tau neutrinos, but cosmological-baseline oscillations yield a tau fraction of about one third at Earth. Sterile–tau mixing would suppress this fraction irrespective of sterile-neutrino mass, whereas sterile mixing with electron or muon neutrinos would be nearly undetectable by this approach. Fitting IceCube's measured flavor composition while leaving the source composition free gives an upper limit on the squared absolute value of U_tau4 of 0.88 at 90% confidence level, not a detection of sterile mixing. Forecasts combining IceCube with present and planned telescopes, including IceCube-Gen2 and HUNT, suggest limits of 0.24–0.29 by 2040 and 0.12–0.14 by 2050. The projected 2050 limits would match some current terrestrial limits, but not the strongest.

PublicScientists do not yet know whether a hypothetical sterile neutrino mixes with the three known neutrino types. This study examines a way to test its mixing with tau neutrinos, which is especially difficult to constrain in Earth-based experiments. Astrophysical sources produce almost no tau neutrinos, but changes between neutrino types during their long journeys make roughly one third tau neutrinos by the time they reach Earth. Mixing with a sterile neutrino would reduce that share, regardless of the sterile neutrino's mass. The method is nearly insensitive to sterile mixing with electron or muon neutrinos. Using IceCube's measured mix of neutrino types, and allowing the source mix to vary freely, the researchers place a 90% confidence upper limit of 0.88 on the tau–sterile mixing parameter, the squared absolute value of U_tau4. This is a constraint, not evidence that sterile neutrinos exist. Combining present and planned telescopes, including IceCube-Gen2 and HUNT, could improve the limit to 0.24–0.29 by 2040 and 0.12–0.14 by 2050. Those forecasts would match some of today's Earth-based limits, but not the strongest.

Young explorerNeutrinos are tiny particles that can change from one kind into another as they travel. Faraway sources make almost none of the kind called tau, but about one in three should be tau when they reach Earth. Scientists wonder whether another kind, called a sterile neutrino, could make fewer tau neutrinos arrive. They used measurements from a detector called IceCube to put a limit on how much this mixing could happen; they did not discover the mystery kind. Their limit is 0.88 at a confidence level of 90%. They predict that using more detectors, including planned ones called IceCube-Gen2 and HUNT, could bring the limit down to 0.24–0.29 by 2040 and 0.12–0.14 by 2050. Those are hopes based on forecasts, not measurements already made. Even the 2050 limits would not beat the strongest limits from experiments on Earth today.

The Goldilocks Prior: Physically Consistent Inference of Neutron Star Properties from Gravitational Wave Observations

Sanika Khadkikar, B.S. Sathyaprakash

• General Relativity and Quantum Cosmology

AstronomerThe authors introduce the Goldilocks Prior for binary neutron star gravitational-wave inference, motivated by biases from priors that neglect parameter correlations or handle tidal degrees of freedom inconsistently. Constructed from a broad, semi-parametric ensemble of equations of state and tailored to detector sensitivity, it captures joint correlations among chirp mass, mass ratio, and both tidal deformabilities. In mock merger simulations covering equal and unequal masses, spinning and non-spinning systems, and a range of signal-to-noise ratios, it consistently reduces biases in tidal posteriors relative to uniform and previously proposed equation-of-state-informed priors. These results demonstrate performance on simulated signals, not observational validation; the framework is intended to improve inference for current and future observations.

PublicGravitational waves from merging neutron stars can reveal how extremely dense matter behaves inside them. But the starting assumptions used to interpret those signals can skew the answers if they ignore connections between the stars' masses and how easily the stars deform under gravity. The authors propose a new set of starting assumptions, called the Goldilocks Prior, built from a broad collection of models of neutron-star matter and adjusted for detector sensitivity. In simulated merger signals with different masses, spins, and signal strengths, this approach consistently reduced bias in estimates of tidal deformation compared with the alternatives tested. The findings support its potential to improve future analyses, but the abstract reports tests on simulated signals rather than real observations.

Young explorerWhen two neutron stars come together, they make ripples in space. Scientists use those ripples to learn what the stars are like inside, but the guesses they start with can pull their answers off track. The researchers made a new way to choose starting guesses that keeps connected clues together. They tried it on pretend star crashes made in simulations, and it gave less skewed answers about how the stars stretch than the other ways they tested. It may help with real ripples too, but these tests used pretend ones.

Reanalysis of GW170817 and GW190425 under the Goldilocks Prior

Sanika Khadkikar, B. S. Sathyaprakash

• General Relativity and Quantum Cosmology

AstronomerThis analysis applies the Goldilocks Prior, which incorporates correlations from candidate equations of state and broadens them according to expected detector sensitivity, to GW170817 and GW190425. Relative to standard analyses, the inferred component tidal deformabilities change substantially: for GW170817, both stars are inferred to be more deformable, with the lighter star’s most probable Λ2 increasing from approximately 215 to 443 compared with a uniform prior. For GW190425, the allowed deformability range narrows considerably. Propagating event likelihoods through spectral and Gaussian-process hierarchical EoS models yields consistent GW170817 EoS constraints across the source-prior treatments despite the altered component inferences. For GW190425, EoS constraints differ beyond numerical scatter even after source-prior removal, indicating that prior choice affects likelihood recovery at low signal-to-noise ratio. Joint EoS constraints remain largely unchanged because GW170817 dominates.

PublicHow researchers analyze gravitational-wave signals can affect what they infer about neutron stars. This study reanalyzes two mergers using the Goldilocks Prior, a method that incorporates relationships predicted by many candidate descriptions of dense matter. For GW170817, it favors stars that deform more under their companion’s gravity than standard analyses suggested; the favored deformability of the lighter star nearly doubles. For GW190425, it narrows the range of allowed deformabilities. These are changes in the inferred properties, not changes in the stars themselves. The combined constraints on how dense matter behaves remain largely unchanged because GW170817 provides the dominant information. However, the weaker GW190425 signal shows that analysis assumptions can affect the recovered constraints even after researchers try to remove those assumptions’ direct influence.

Young explorerScientists studied ripples in space from two pairs of stars crashing together. They used a different way to work out how easily the stars could be stretched. The new answers changed, but the stars did not! Their combined picture of the stuff inside the stars stayed mostly the same, because one crash gave stronger clues.

DIS-secting the universe with high-energy neutrinos

Rhorry Gauld, Lorenzo Guerra, Ulrich Haisch+1 more

• High Energy Physics - Phenomenology

AstronomerThis computational study revisits electroweak radiative corrections to charged-lepton kinematics in neutrino charged-current deep inelastic scattering, particularly observables sensitive to collinear photon emission. A flexible Monte Carlo framework implements full next-to-leading-order electroweak corrections, supplemented by higher-order logarithmically enhanced final-state QED radiation and coherent scattering contributions. Comparisons with exclusive NLO QCD plus parton-shower predictions from POWHEG-BOX, using different shower models and settings, inform recommendations for experimental analyses. The calculations assess changes to the observed-muon-energy versus incoming-neutrino-energy correlation and to mean inelasticity averaged over a realistic neutrino flux. Radiative corrections can exceed 10%; above approximately 10^4 GeV, photon-initiated and coherent W-boson production make sizeable contributions that are absent from the compared event generator. These are theoretical predictions, not reported observational measurements.

PublicWhen a high-energy neutrino interacts with matter, it can produce a muon whose energy helps researchers estimate the neutrino’s energy. This study uses computer calculations to examine how radiation and additional particle-production processes alter that connection and the average fraction of neutrino energy transferred away from the outgoing charged lepton. The calculated corrections can exceed 10%. Above about 10,000 GeV, processes involving incoming photons and coherent production of W bosons contribute substantially, but are missing from the simulation program used for comparison. The authors compare simulation approaches and offer recommendations for experimental analyses; they do not report a new measurement.

Young explorerScientists sometimes learn about a tiny particle called a neutrino by studying a muon it makes when it bumps into matter. But the muon can give away some energy as light, making the neutrino’s energy harder to work out. The scientists used computer calculations to study this and other effects. They found that the predicted changes can be important, and that one simulation program leaves out some processes that matter at very high energies. This study is about calculations, not a new sighting of particles.

Eccentricity distribution of extreme mass ratio inspirals

Davide Mancieri, Luca Broggi, Morgan Vinciguerra+2 more

• Astrophysics of Galaxies
• General Relativity and Quantum Cosmology

AstronomerThe study models eccentricity distributions for extreme mass ratio inspirals (EMRIs) produced by two-body relaxation in nuclear star clusters, following evolution to plunge into a Schwarzschild massive black hole (MBH). The modeled plunge distribution peaks near eccentricity 0.2; for MBH masses of 10^5–10^6 solar masses, up to 20% of forming EMRIs have plunge eccentricities above 0.5. The high-eccentricity population arises partly from EMRIs forming at large semi-major axes and usually neglected “cliffhanger EMRIs.” These are modeling results, not observational detections, and emphasize the need to retain eccentricity in waveform models and detection strategies for LISA. The authors also identify potentially inadequate coverage of the relevant energy- and angular-momentum-flux parameter space in FastEMRIWaveforms for MBHs below 10^6 solar masses. At 10^5 solar masses, about 75% of modeled EMRIs two years before plunge, and 50% six months before plunge, lie outside the available flux parameter space. They advocate extended flux grids and improved interpolation to broaden accurate modeling.

PublicA modeling study suggests that a small object spiraling into a much more massive, non-spinning black hole can keep a noticeably stretched orbit right up to its final plunge. The study follows systems formed through gravitational encounters in dense star clusters around galactic centers. For central black holes weighing 100,000 to one million Suns, the models predict that up to 20% of these systems reach the plunge with orbital eccentricity above 0.5, rather than becoming nearly circular. These are theoretical findings, not observed events. Such stretched orbits matter for predicting the gravitational-wave signals that the future LISA observatory will seek. The study also finds that a waveform software package, FastEMRIWaveforms, does not currently cover much of the modeled population around the lower-mass black holes considered. The authors call for broader numerical coverage and better interpolation methods to improve signal modeling.

Young explorerImagine a little object going around a giant black hole, getting closer until it falls in. Scientists used a model to work out what its path might look like. They found that some paths could stay stretched out, like ovals, instead of becoming round like circles. They have not watched these falls happen. Knowing the possible shapes could help scientists look for tiny ripples in space with a future detector called LISA. They also found that their computer tools need to cover more possible paths.

JWST's Dusty Blue BOAT -- GRB 221009A

Nguyen M. Khang, Gavin P. Lamb, Helena-M.S. Grabham+6 more

AstronomerA re-analysis of GRB 221009A afterglow spectra uses VLT X-Shooter observations at 0.5, 4, and 10.5 days and JWST NIRSpec/MIRI observations at 13.3 days. The authors identify a strong degeneracy between line-of-sight extinction and intrinsic spectral index, especially in the optical, explaining conflicting earlier estimates. A joint double smoothly broken power-law fit across all epochs yields total extinction A_V = 4.40 ± 0.01 and a blue intrinsic continuum with β = 0.447 ± 0.001; these values are conditional on the adopted fit. Although the spectra marginally favor a wind environment, the authors reject it using the light-curve evolution. Consistency between the fitted spectrum and temporal decline in a uniform-density medium requires an early jet break at approximately 0.5–1.0 days. The inferred electron distribution index, p = 1.89 < 2, challenges standard particle-acceleration models. The results suggest, rather than directly establish, that a narrow, energetic jet core dominates the early optical-to-X-ray emission.

PublicDust along our line of sight makes the fading light from the exceptionally bright gamma-ray burst GRB 221009A difficult to interpret. Researchers re-analyzed spectra from the VLT and JWST and found that estimates of dust dimming and the afterglow’s original color are strongly intertwined, helping explain earlier disagreements. Their combined model favors substantial dust dimming and an intrinsically blue afterglow. Although the spectra alone slightly favor a wind-shaped environment, the way the afterglow fades argues against that interpretation. A uniform-density environment works only if an early change in fading is attributed to the jet’s geometry. The inferred energies of accelerated electrons challenge standard models, and the authors suggest that a narrow, powerful jet core supplied most of the early optical-to-X-ray light.

Young explorerScientists studied the fading glow after a very bright burst in space. Dust hides some of its light, making its true color hard to work out. Their best-fitting model says the glow was blue before the dust dimmed it. They think a narrow, powerful stream of material may explain the early light, but that is an explanation, not something they directly saw.

Structural quasi-universality in highly magnetized differentially rotating neutron stars

Pratul Manna, Surajit Kalita

• Solar and Stellar Astrophysics
• General Relativity and Quantum Cosmology

AstronomerUsing the XNS numerical code, the authors investigate neutron-star equilibrium configurations across a range of equations of state, rotation profiles, and magnetic field strengths. For fixed-angular-momentum sequences, they find a generalized quasi-universal relation between normalized moment of inertia and compactness spanning uniform rotation, differential rotation, and strongly magnetized toroidal configurations. The relation is largely insensitive to the equation of state, with deviations driven primarily by magnetic field strength and differential rotation. Analytic expressions describe these dependencies within a unified phenomenological model. Applications quantify systematic biases in magnetar luminosity estimates and assess the rotational kinetic energy of the post-merger remnant of GW170817; the abstract gives no numerical estimates. These are numerical-model findings and applications, rather than direct observational confirmation of the relation.

PublicNeutron stars contain matter whose behavior is uncertain, making their properties difficult to infer. Using computer models, the researchers find an approximate link between how compact a neutron star is and how strongly it resists changes in its spin. This link changes little when different descriptions of the star’s internal matter are used, even for models with uneven rotation or strong magnetic fields. Magnetic strength and uneven rotation nevertheless cause departures from the shared pattern, which the researchers describe with mathematical formulas. They apply the model to estimates of magnetar brightness and the energy stored in the rotation of the remnant associated with GW170817. The findings come from numerical models, not direct measurements establishing the link.

Young explorerScientists made computer models of tiny, very heavy stars that spin and have strong magnets. They found an almost-shared rule connecting how tightly packed a star is with how hard it is to change its spin. Strong magnets and parts spinning at different speeds can change the rule a little. It could help scientists understand real stars, but it was found in computer models.

X-ray Reflection as Diagnostic of Supermassive Black Hole Binary Properties

Julie Malewicz, Tamara Bogdanović, David R. Ballantyne+2 more

AstronomerUsing 24,570 computed X-ray reflection spectra, this study explores diagnostics of supermassive black hole binaries from two mini-disks on circular orbits at a fixed separation of 100 GM/c^2. The models vary mass ratio, spins, inclination, orbital phase, and total accretion rate, examining the relativistic Fe Kα line near 6.4 keV and Compton hump near 20–30 keV. Within this model set, the Fe Kα blue-peak energy is a relatively robust inclination diagnostic potentially accessible from a single-epoch spectrum. Tracking the line centroid over a few epochs may constrain orbital phase and mass ratio. Spin signatures are subtler and subject to measurement degeneracies, although increased radiative efficiency may produce markers of high spin in the composite spectrum. These are model-based prospects, not reported measurements of a binary. The approach offers preliminary parameter constraints ahead of full parametrized spectral fitting and could complement PTA and LISA gravitational-wave measurements, particularly for inclination and for spin, which is inaccessible to PTAs.

PublicCalculated X-ray spectra suggest a way to learn about pairs of supermassive black holes from the radiation reflected by the small disks feeding them. The researchers computed 24,570 spectra for pairs moving in circular orbits at one fixed separation, while changing properties such as viewing angle, relative masses, and spins. In these models, the energy of a peak in an iron emission line is a relatively reliable clue to the viewing angle and might be useful with just one observation. Changes in the line’s central energy across several observations might reveal the pair’s orbital phase and help constrain its relative masses. Spin is harder to infer because different properties can produce similar spectral effects, though rapid spin may leave some clues. The study proposes a way to make preliminary estimates, rather than reporting measurements of an actual pair, and could provide information complementary to gravitational-wave observations.

Young explorerImagine two enormous black holes circling each other, each with a little disk of material around it. Scientists used a computer to work out what their reflected X-ray light might look like. In their models, a bump in that light could help show which way we are looking at the pair. Watching the bump change might also give clues about where the black holes are in their circle and how their masses compare. Telling how fast they spin would be much trickier. These are clues from computer models, not things the scientists have measured from a real pair in this study.

A Brief Review on the Statistical Properties of Fast Radio Bursts

Yu Sang, Hai-Nan Lin

AstronomerThis review synthesizes statistical properties from current fast radio burst catalogs, covering dispersion measure, redshift, energy and luminosity functions, repetition rates, and host-galaxy demographics. For repeaters, it examines energy, fluence, flux, and waiting-time statistics, alongside time-series analyses reported to reveal memory effects and chaotic dynamics. It distinguishes observations of periodic activity from their theoretical interpretation and surveys polarization as a probe of source magneto-ionic environments. Observational biases and selection effects are emphasized throughout; FRB progenitors and emission mechanisms remain unresolved.

PublicFast radio bursts are flashes of radio waves from beyond our galaxy that last only milliseconds. This review brings together statistical studies of burst catalogs, examining their energies, distances, repetition patterns, and the galaxies where they occur. For repeating sources, it discusses patterns in burst strength and timing, including analyses that indicate memory effects and chaotic behavior. It also reviews observed periodic activity, proposed explanations for it, and how radio-wave polarization can probe the sources’ magnetic and ionized surroundings. The review stresses that detection biases affect these patterns, and that what produces the bursts remains unknown.

Young explorerFar beyond our galaxy, there are tiny, quick flashes of radio waves. Some happen again and again. Scientists have gathered what studies say about how strong the flashes are, when they happen, and what kinds of galaxies they come from. Some sources have been seen becoming active on a repeating schedule, but scientists are still trying to explain why. They must also remember that some flashes are easier to spot than others. We still do not know what makes these flashes.

Modeling Multi-band Active Galactic Nuclei Lightcurves Using a Self-supervised Attentive Neural Process Network

Tzuken Shen, Chengcheng Xin, Joshua Fagin+3 more

• Astrophysics of Galaxies

AstronomerThe authors present an attentive neural process for joint probabilistic reconstruction of six-band LSST quasar light curves and inference of black hole mass, Eddington ratio, and intrinsic variability timescale, with full-covariance parameter posteriors. A shared masked attention mechanism combines information across bands while accommodating irregular, asynchronous sampling and heteroscedastic noise. Training and evaluation use simulated ten-year light curves from a relativistic accretion-disk reprocessing model, sampled with the fielded Rubin baseline cadence and per-visit photometric noise. Light-curve training is self-supervised, using only sparse noisy observations rather than the underlying noiseless curves. On held-out simulations, the model performs comparably to a near-optimal Gaussian-process baseline overall and better in power-spectrum reconstruction and damped-random-walk timescale estimation. The latent representation offers potential downstream uses, and the observation-driven objective enables future fine-tuning on real LSST data; real-data performance is not demonstrated here.

PublicLSST is expected to observe tens of millions of quasars. This study develops a machine-learning method to reconstruct their changing brightness in six color bands and estimate properties including black hole mass and the characteristic timescale of brightness changes, while reporting uncertainties. The method combines measurements across bands and can handle uneven observing schedules and varying measurement noise. In tests using simulated ten-year observations, it performed about as well overall as a strong statistical comparison method and better at recovering some aspects of variability. These results come from simulations, not real LSST observations. The method is designed to allow later fine-tuning on real data.

Young explorerQuasars are bright things in space whose light changes. Scientists taught a computer to fill in gaps in pretend observations and estimate properties of their black holes. It worked about as well as another method, and better at some tasks. They still need to try it on real LSST observations.

Magnetically supramassive and hypermassive compact stars

Koji Uryu, Shijun Yoshida, Eric Gourgoulhon+6 more

• General Relativity and Quantum Cosmology

AstronomerUsing COCAL, the authors numerically construct relativistic compact-star equilibria with mixed poloidal and toroidal magnetic fields. They find magnetically supramassive solutions exceeding the maximum mass of static, spherically symmetric solutions by more than 10%. For some extremely strong-field configurations, they also obtain magnetically hypermassive solutions exceeding the maximum mass of uniformly rotating models at the Kepler mass-shedding limit. The abstract notes that sizable magnetic mass enhancements require fields of roughly 10^17–10^18 G. These are computed equilibrium solutions, not observed stars; their dynamical stability is not established in the abstract.

PublicNumerical calculations suggest that extremely strong magnetic fields can allow compact stars to have more mass than otherwise possible. Using a code called COCAL, the researchers calculated balanced star models with two combined magnetic-field patterns. Some models exceed the maximum mass of static, spherical stars by more than 10%. A few with especially extreme fields even exceed the maximum mass of models rotating uniformly at the limit where they would begin shedding matter. Substantial mass increases require fields of roughly 10^17–10^18 gauss. These findings concern theoretical equilibrium models, not observed stars, and the abstract does not establish whether the configurations remain stable over time.

Young explorerScientists used a computer to work out what some very squeezed stars could be like. Their calculations suggest that a super-strong magnetic field could help a star hold more stuff than it could without that field. Some of their pretend computer stars could even hold more than stars spinning as fast as they can without losing stuff. These are computer models, not stars the scientists spotted in space, and we do not yet know from this work whether they could stay that way.

Ultra-High-Energy Tau Neutrinos as Probes of Lorentz Invariance

Vedran Brdar, Samiur R. Mir

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

AstronomerThis study forecasts GRAND and POEMMA sensitivity to Lorentz invariance violation (LIV) through ultra-high-energy tau-neutrino detection. The authors generate cosmogenic neutrino fluxes with SimProp and combine them with flavor-transition probabilities incorporating LIV, translating altered flavor transitions into expected tau-neutrino event rates. For individual nonzero LIV operators of various dimensions, projected sensitivities surpass existing lower-energy limits by orders of magnitude. Allowing multiple nonzero LIV parameters can substantially modify those sensitivities through their interplay. These are forecasts rather than observational constraints or evidence for LIV; the authors predict that future ultra-high-energy tau-neutrino observations could provide exceptionally stringent tests.

PublicNeutrino telescopes have detected cosmic neutrinos with energies reaching roughly 100 PeV. This study asks whether future experiments, GRAND and POEMMA, could use still-higher-energy neutrinos to test Lorentz invariance, a fundamental symmetry of physics. The researchers model cosmogenic neutrinos and calculate how possible violations of that symmetry would change the expected number detected as tau neutrinos. When only one violation parameter is allowed at a time, the projected tests are orders of magnitude more sensitive than existing lower-energy limits. Allowing several parameters to act together can substantially change that sensitivity. The work predicts the experiments’ potential; it does not report a detection of symmetry violation.

Young explorerTiny particles called neutrinos travel through space. Scientists want to use future experiments called GRAND and POEMMA to check whether very energetic neutrinos follow an important rule of physics. They used computer calculations to see how breaking that rule might change how many neutrinos of one kind the experiments would detect. Their calculations suggest the experiments could check the rule much more closely than earlier tests, but the answer changes when several possible changes to the rule act together. They have not found that the rule is broken.

Phase Offsets Between the Minimum Light and Radial Velocity in Long Secondary Period Stars

D. M. Skowron, I. Soszyński, P. Iwanek+1 more

AstronomerUsing ASAS-SN photometry and Gaia radial-velocity (RV) curves for 983 long-secondary-period (LSP) red giants, the authors confirm a relatively narrow distribution of offsets between minimum RV and minimum light, with mean Δφ = −0.15 ± 0.10 cycles (−0.96 ± 0.64 rad). Miras show a similar offset, so this diagnostic alone cannot distinguish LSPs from pulsational variability. In contrast, LSP stars depart from the period–RV-amplitude relation of pulsating red giants: their RV amplitudes remain only a few km/s despite their long periods. Stacked light and RV curves are notably homogeneous and retain a coherent phase relation. Under the binary interpretation, the measured offset requires obscuring material to be displaced in orbital phase from the companion, consistent with—but not proof of—a low-mass companion generating a dusty wake in the giant’s wind.

PublicMany luminous red giant stars have mysterious long cycles of brightness change, called long secondary periods. Researchers compared brightness measurements from ASAS-SN with Gaia measurements of motion toward and away from us for 983 such stars. They found a consistent timing offset between the stars’ faintest point and their minimum radial velocity. But Mira stars, which pulsate, show a similar offset, so that timing alone does not reveal the cause. A clearer difference is that the long-secondary-period stars have velocity changes of only a few kilometres per second despite their long cycles, unlike the general trend in pulsating red giants. If an orbiting companion causes these cycles, the timing implies that the material blocking the giant’s light is offset from the companion along the orbit. This fits models of a small companion creating a dusty wake in the giant’s wind, but does not establish that explanation.

Young explorerSome big red stars grow brighter and dimmer in a slow, puzzling pattern. Scientists studied 983 of them and found that their dimming and their movement toward and away from us follow a similar timing pattern. Other stars that swell and shrink can have similar timing, so that clue alone does not solve the puzzle. One possible explanation is a small star companion making a dusty trail that blocks some light. The results fit that idea, but scientists have not shown that it is the answer.

The Composition of M-dwarf Exoplanet Hosts: Atmospheric Parameters and O, Mg, Si, and Fe Abundances from IR Spectroscopy

Zachary G Maas, Natalie R. Hinkel, Gregory N. Mace+5 more

• Earth and Planetary Astrophysics

AstronomerThe authors derive chemical abundances from high-resolution H-band spectra of 40 planet-hosting M dwarfs and two M dwarfs in wide binaries with FGK primaries, obtained with IGRINS and NIRSPEC. Observed spectra are compared with synthetic grids generated using MOOG and MARCS atmospheres. OH and H2O features constrain effective temperatures, Fe I and FeH constrain [Fe/H], and atomic features yield Mg and Si abundances. The resulting abundances are broadly consistent with previous M-dwarf measurements. Combining chemistry with UVW velocities and population-membership probabilities identifies GJ 1252 and the previously recognized L181-1 as potential thick-disk stars. Kepler 42 is also likely a thick-disk member based on its kinematics and low [Fe/H], although uncertain Mg and Si abundances complicate classification. The host-star Si/Mg and Fe/Mg molar-ratio distributions imply exoplanet core-mass fractions of 20–40%; these are composition-based inferences rather than direct measurements of planetary interiors.

PublicSmall, faint stars called M dwarfs commonly host small planets, but their chemical makeup is difficult to measure because molecules crowd their visible-light spectra. This study instead uses high-resolution infrared spectra of 40 planet-hosting M dwarfs and two additional M dwarfs with stellar companions. By comparing the observations with model spectra, the researchers estimate temperatures and iron, magnesium, and silicon abundances, finding broad agreement with earlier studies. Chemistry and stellar motions suggest that GJ 1252 and L181-1 may belong to the Milky Way’s thick disk, with L181-1 already known as a member. Kepler 42 is another likely member, though uncertain magnesium and silicon measurements complicate its classification. The planet-hosting stars’ element ratios also imply planetary cores containing 20–40% of a planet’s mass. This is an inference from stellar chemistry, not a direct measurement of the planets’ insides.

Young explorerA star’s light can give clues about what it is made of. Scientists studied light from small stars, including 40 with planets, and compared it with computer models to estimate how much iron, magnesium, and silicon the stars contain. Those clues suggest that the planets’ central cores could make up about one-fifth to two-fifths of their weight, but the scientists did not look inside the planets.

MP-DualNet: A Dual-Branch Deep Learning Approach for Magnetopause Boundary Detection Using Simulated SXI Images

Cheng Zhong, Zhongwei Yang, Tianran Sun+5 more

• Instrumentation and Methods for Astrophysics

AstronomerMP-DualNet is an end-to-end, dual-branch deep learning framework for magnetopause detection in simulated observations from SMILE’s Soft X-ray Imager (SXI). It combines coarse classification of magnetopause visibility and relative position within the field of view with pixel-level boundary segmentation, addressing limited coverage and variable viewing geometry. Training and evaluation use line-of-sight magnetopause envelope maps derived from global hybrid simulations spanning different solar wind and interplanetary magnetic field conditions. Reported classification accuracy exceeds 0.94, segmentation intersection-over-union exceeds 0.97, and the test-set mean absolute angular displacement from the reference boundary is 0.488 degrees. Tests show robustness across noise levels and generalization to an independent storm event. These simulation-based results support potential use with future SXI soft X-ray observations of solar wind charge exchange emission; operational performance on mission observations and future 3D reconstruction are not demonstrated here.

PublicResearchers developed an artificial intelligence method to locate Earth’s magnetopause, the boundary central to interactions between the solar wind and Earth’s magnetic environment. The future SMILE mission will image this region in soft X-rays, but its camera’s limited view and changing viewing angles can make the boundary difficult to identify. The method first checks whether and where the boundary appears, then traces it in detail. In tests using simulated observations, it achieved over 94% classification accuracy and an average angular difference of 0.488 degrees from the reference boundary. It also performed consistently across different noise levels and in a separate storm-event test. These are results from simulations, not actual SMILE observations. They suggest the method could help future studies of the boundary’s three-dimensional shape and space weather.

Young explorerEarth has a magnetic region with an edge that scientists want to find in space pictures. They taught a computer to check whether the edge is in a picture and then trace it. The computer did well on practice pictures made with simulations, even when the pictures were noisy. Scientists hope it will help with pictures from a future space mission called SMILE, but these tests were not done with real pictures from that mission.

Systematic Search for Cataclysmic Variables in Radio Surveys: First Radio Detection of IX Velorum

Suhasini S. Rao, Gregory R. Sivakoff, Craig O. Heinke+3 more

• High Energy Astrophysical Phenomena

AstronomerA systematic search of VLASS, RACS, VAST, and EMU at 0.7–4 GHz detected six cataclysmic variables (CVs) in at least one epoch, with specific luminosities of 10^16.5–10^17.5 erg/s/Hz, consistent with previously radio-detected CVs. The verified optical catalog contains 2225 CV candidates, including 1374 Gaia-matched sources within the radio-survey footprints. Five detections were previously known; IX Vel, the closest nova-like CV, was detected in radio for the first time, showing quasi-persistent low-level emission during a 10-hour EMU observation at 943.5 MHz. Stacking nondetection images yielded individual upper limits for 423 CVs in VAST. Survey-wide stacks of Gaia-matched CVs showed no statistically significant population emission. An EMU stack comprising 14 epochs of five CVs within 100 pc constrained their median persistent specific luminosity to <3 × 10^14 erg/s/Hz.

PublicAstronomers searched four large radio surveys for objects called cataclysmic variables and detected radio emission from six of them. Five were already known radio sources, but IX Vel was detected in radio for the first time. It showed faint, nearly persistent emission during a 10-hour observation. Most observations produced no detections, so the team combined images to search for signals too faint to see individually. These combined images did not reveal a statistically significant signal from the broader population. Combining observations of five nearby objects also set an upper limit on their median steady radio output. These limits constrain how bright undetected emission could be; they do not establish that the objects emit no radio waves.

Young explorerAstronomers looked for radio waves from space objects called cataclysmic variables. They found signals from six, including one called IX Vel that had never been heard this way before. Its faint signal stayed around for much of a ten-hour look. Most of the objects were too quiet to detect. The astronomers put many pictures together to look for fainter signals, but still did not find a clear signal from the group. That does not mean there are no radio waves—some could be too faint to find.

Thorium and Europium production in the early Galaxy: Implications for nucleocosmochronology

L. Magrini, R. E. Giribaldi, M. Palla+17 more

• Cosmology and Nongalactic Astrophysics

AstronomerThis study tests log(Th/Eu) as a nucleocosmochronometer using new Th and Eu abundances for eight TITANS reference stars observed with UVES at the VLT, combined with homogeneous literature samples. At low metallicity, the observed ratios show no significant metallicity dependence once stars with anomalous actinide abundances are excluded, supporting broadly uniform early Galactic Th and Eu co-production rather than establishing an exactly constant initial ratio. Ages inferred using a theoretical initial r-process production ratio are consistent with an old, metal-poor halo population, but individual uncertainties remain substantial. Higher spectral resolution is needed to improve Th measurements, and combining coeval stars could yield statistical gains. Future high-resolution multi-object spectroscopy of homogeneous coeval samples, especially globular clusters, is proposed as a route to stronger constraints on early Milky Way formation and the age of the Universe.

PublicThe relative amounts of thorium and europium in ancient stars offer a way to estimate their ages. Researchers measured these elements in eight reference stars and combined the results with earlier measurements. Among stars with little metal content, they found no significant change in the thorium-to-europium ratio with metal content after excluding stars with unusual abundances of actinide elements. This supports the idea that thorium and europium were generally made together in similar proportions in the early Milky Way. Using a theoretical starting ratio, the researchers obtained ages consistent with an old population in the Galaxy’s halo, although the uncertainty for each star remains large. Sharper spectra and measurements of groups of stars born at the same time could improve this method. Future observations, particularly of globular clusters, could help constrain when the Milky Way formed and the age of the Universe; those improvements are prospects, not results of this study.

Young explorerScientists want to find out how old some very old stars are. They measured two kinds of material in eight stars and compared their results with earlier measurements. Leaving out stars with unusual mixtures, they found a pattern that supports using these materials like a clock. But they must assume how much of each material the stars started with, so the clock is not very exact yet. Their answers fit the idea that these stars are very old. Better measurements and studying stars born together could help make the clock more useful.

Cepheid Metallicity in the Leavitt Law (C-MetaLL) survey: X First spectroscopic characterization of Galactic Type II Cepheids and calibration of the Period-Wesenheit-Metallicity relations

T. Sicignano, M. Romaniello, A. Bhardwaj+13 more

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies

AstronomerThis study examines composition effects on Type II Cepheid distance relations using a homogeneous spectroscopic sample. Of 80 Galactic T2Cs observed with UVES at the ESO Very Large Telescope, 74 yielded stellar parameters and iron and oxygen abundances from a self-consistent equivalent-width analysis, nearly doubling the available spectroscopic metallicity sample. The abundances were used to test theoretical instability-strip predictions and, combined with Gaia parallaxes, to derive Period–Wesenheit–metallicity relations. Their metallicity coefficients range from approximately −0.02 to +0.17 mag dex⁻¹ and are statistically consistent with zero in every relation, in agreement with theoretical predictions. Distances estimated for 22 Galactic globular clusters hosting T2Cs agree within uncertainties with independent literature estimates. The results support a minor metallicity dependence and the reliability of T2Cs as Population II distance indicators, rather than establishing an exactly zero effect or providing a new Hubble-constant measurement.

PublicType II Cepheids are stars that repeatedly brighten and fade. The link between their pulsation periods and luminosities lets astronomers use them to measure distances, offering an independent route toward measuring how fast the universe expands. This study tested whether differences in chemical composition could bias those distances. Researchers observed 80 such stars in our Galaxy and measured iron and oxygen abundances for 74. Combining the abundance measurements with Gaia parallaxes, they found that the effect of metal content on the distance relations was small and statistically compatible with no effect. They also estimated distances to 22 globular star clusters, finding agreement within uncertainties with independent estimates. These findings support the stars’ usefulness as distance markers, although they do not prove that chemical composition has no influence.

Young explorerSome stars get brighter and dimmer over and over. Astronomers can use how quickly they do this to help work out how far away they are. The researchers checked whether differences in what these stars are made of could change the answer. They found that those differences seem to matter only a little, if at all, though they cannot be sure the effect is exactly zero. Their distances to 22 groups of stars also matched other estimates within the room for error. That helps show these blinking stars can be useful distance guides.

Survey of Surveys Data Release 3. Homogenised stellar parameters across nine spectroscopic surveys

A. Avdeeva, E. Pancino, A. Turchi+12 more

• Astrophysics of Galaxies

AstronomerThis work homogenises effective temperature, surface gravity, and metallicity estimates across major Milky Way spectroscopic surveys. Machine-learning regressions model survey-to-reference corrections and their uncertainties, using an internal scale built from APOGEE, GALAH, and LAMOST LRS, extending it to six additional surveys, and anchoring it to PASTEL measurements. Independent overlap tests show improved consistency: calibrating GALAH and LAMOST LRS temperatures independently onto the APOGEE scale reduces their median offset from 44.5 K to 6.2 K. The catalogue contains about 10.13 million stars, with 6.10 million in the recommended high-quality subset and 3.69 million in the metallicity-optimised subset. Against Gaia benchmark stars, the high-quality subset has median residuals of 30 K in effective temperature, 0.03 dex in log g, and −0.02 dex in [Fe/H]. The metallicity-optimised subset has median [Fe/H] residuals of 0.003 dex against benchmark stars, 0.05 dex for globular clusters, and −0.02 dex for open clusters. These are sample-level median residuals, not individual-star uncertainty estimates. An example application confirms metal-poor stars with thin-disc-like orbits, including stars with [Fe/H] < −2; this orbital description does not itself establish thin-disc membership.

PublicDifferent surveys can assign somewhat different temperatures, surface gravities, and metal contents to the same stars because their instruments and analysis methods differ. The researchers used machine learning to bring measurements from several Milky Way surveys onto a shared scale, anchored to high-quality reference measurements. Tests on stars observed by multiple surveys show better agreement: one comparison reduced the typical temperature offset from 44.5 to 6.2 kelvin. The resulting catalogue includes about 10.13 million stars, with a recommended high-quality selection of 6.10 million. Checks against reference stars and star clusters assess its consistency, although the reported median differences do not describe the uncertainty of every individual star. As a demonstration, the researchers confirm stars with very low metal content moving on orbits like those of the Galaxy’s thin disc, showing how the catalogue can help investigate unusual stellar populations.

Young explorerDifferent teams looked at the same stars but sometimes got slightly different answers about how hot they are and what they are made of. The researchers helped those answers match better and made a list of about ten million stars. They checked their work using trusted star measurements. The list also helps them study unusual stars that have very little metal but travel on paths like stars in our Galaxy’s thin disc.

Mass loss in AF supergiants: At the verge of the Eddington limit and still with weak line-driven winds

Jiri Krticka, Jiri Kubat

• High Energy Astrophysical Phenomena

AstronomerGlobal atmosphere models of A- and F-type supergiants contain super-Eddington photospheric layers and associated density inversions, consistent with previous studies. Model tests identify hydrogen ionization as the cause. Radial perturbation analysis reveals no instability, whereas the authors find that optically thick super-Eddington layers are susceptible to nonradial instabilities. Their global wind code, using a comoving-frame radiative force, predicts mass-loss rates substantially below observational estimates despite the density inversions. Predictions approach those estimates only for the most luminous stars, near the electron-scattering Eddington limit. Clumping could account for part of the discrepancy. The predicted low mass-loss rates suggest that magnetic fields may strongly influence these winds, offering a possible explanation for observed spectral variability.

PublicComputer models of A- and F-type supergiant stars suggest that hydrogen ionization creates atmospheric layers where the outward force of radiation exceeds gravity. In these models, density increases outward in some regions. Tests found no instability from purely inward-and-outward disturbances, but disturbances that also vary across the star can destabilize these layers when they are opaque. The researchers also predict how much material the stars lose through winds. Their predictions are much lower than estimates from observations, except for the most luminous stars, where radiation pushing on free electrons nearly balances gravity. Uneven clumping of wind material could explain part of this disagreement by affecting observational estimates. The predicted weak mass loss also suggests that magnetic fields could strongly shape the winds, possibly explaining observed changes in the stars' spectra.

Young explorerScientists used computer models to study some giant stars and the gas blowing away from them. In the models, starlight pushes harder than gravity in some layers. Those layers can become unsteady when disturbed in ways that are not just straight in and out. The models predict that most of these stars blow away much less gas than people estimate from watching them. Gas gathered into clumps might explain some of the difference. The scientists also think magnetic fields might guide the gas and help explain changes people see in the stars' light, but that idea is not yet a sure answer.

Photometric eclipse-center variations over the long cycles of Magellanic double-periodic variables

Ronald Mennickent

AstronomerThis study tests whether photometric eclipse centers in Magellanic double-periodic variables depend on their longer cycle, whose origin remains uncertain. OGLE photometry of 109 eclipsing-DPV candidates was analyzed using local-minimum profile fits (Q) and fixed-template shifts (T). Among 49 curated systems with sufficient timing data, 27 show at least one Q or T modulation under the adopted procedure. Selection sometimes depends on fitting choices, but ten retain a selected Q curve across all tested local functions and windows; three have both estimators selected in both eclipses. These detections do not establish changes in conjunction times. Local color interpolation finds 14 of 16 systems measured in both eclipses redder at the deeper, phase-0 eclipse. A separate numerical experiment with one synthetic semidetached DPV produces large photometric timing shifts and quadrature-brightness changes despite fixed conjunctions. However, large tilted-disk cases fail to reproduce the selected observed crossing phases. The observed incidence applies to the evaluable, curated sample, not necessarily all DPVs. Circumstellar brightness changes can generate apparent timing shifts, but this experiment neither fits an observed system nor establishes disk tilt as their cause; genuine conjunction-time changes remain possible.

PublicDouble-periodic variables are interacting pairs of stars whose brightness varies both as they orbit and over a longer cycle of uncertain origin. Using OGLE observations, the researcher looked for changes in when their eclipses appear to reach their centers during that longer cycle. Of 49 carefully selected systems with enough timing data, 27 showed such variations by at least one of two measurement methods, although some detections depended on how the eclipses were fitted. This fraction should not be assumed to apply to all double-periodic variables. In a separate computer experiment, changing the brightness of a disk around a star shifted the apparent eclipse centers even though the stars still lined up at fixed times. That shows how brightness changes could mimic timing changes, not that they explain the observed systems: the single simulated system did not fit a real example, and its strongly tilted disks did not reproduce a particular observed timing pattern. Actual changes in when the stars line up remain possible. The study also found that 14 of 16 systems with color measurements in both eclipses were redder during the deeper eclipse.

Young explorerSome pairs of stars go around each other and take turns blocking each other's light. In many of the pairs studied closely, the darkest part of the dip in light seemed to come earlier or later during a slow brightness cycle. But that does not prove the stars changed when they lined up. In a computer-made example, changing the light from a disk around a star made the dip seem to move even though the stars lined up on schedule. The example shows one way this could happen, but it does not prove what happened in the real star pairs. Their line-up times might really change, too.

Source Imaging of the Multiple Type-II Solar Radio Bursts and their Multiple CME-Shock Signatures in the Corona

V. Vasanth

AstronomerThe study examines multiple metric type-II radio bursts on 1 October 2011, using LEARMONTH spectra spanning 180–25 MHz together with radio and EUV imaging and STEREO/LASCO observations of two CMEs from adjacent active regions. The first type-II burst began during the impulsive phase of the first flare, while the second began near the peak of the third flare and had a larger frequency drift rate. AIA 211 observations show shock-like EUV structures near 09:06 UT and 09:55 UT, coincident with the respective radio bursts and supporting their identification as shocks. Radio sources lie near the nose-front of the first structure and along the flank of the second. The authors interpret these observations as supporting the possibility that shocks from two CMEs generated the multiple type-II bursts. Strong projection and scattering effects complicate the second event; corrections use a spherical cone model and three-dimensional Monte Carlo ray tracing for fundamental-frequency emission in a turbulent solar environment.

PublicObservations of the Sun on 1 October 2011 linked two type-II radio bursts with two eruptions of solar material from neighboring active regions. Ultraviolet images showed wave-like structures at about the same times as the bursts, supporting the presence of shock waves. The first burst's radio sources appeared near the front of its associated wave, while the second burst's sources appeared along the side of its wave. The researchers suggest that shocks driven by the two eruptions could explain the multiple radio bursts. The second event was especially difficult to reconstruct because viewing geometry and radio-wave scattering distorted its apparent appearance, so the team applied model-based corrections.

Young explorerThe Sun had two big eruptions, and scientists saw radio signals and moving waves at about the same times. One radio signal came from near the front of a wave, and another came from its side. The scientists think the two eruptions may have made shock waves that caused the signals. The second event was tricky to see clearly, so they used computer models to help work out what happened.

The slower rotation of planet-hosting stars revisited

Avraham Binnenfeld, Amitay Sussholz, Simchon Faigler+1 more

• Earth and Planetary Astrophysics

AstronomerThis observational reanalysis revisits the reported association between planet hosting and slower stellar rotation using a similar Kepler rotation-period sample, updated Gaia DR3-based stellar parameters, and an updated exoplanet catalogue. After minimal cuts in evolutionary state, metallicity, and distance, the authors model rotation period as a function of effective temperature alone and compare observed-to-temperature-expected period ratios. For periods shorter than 20 days, the median ratio is approximately 15% larger for planet hosts than for stars without detected planets (KS p = 2.4 × 10^-4). The TESS All-Sky Rotation Survey shows a similar trend, but its strongly structured period distribution prevents a robust host–non-host comparison. The updated Kepler result reinforces the previously reported association, but does not establish causation.

PublicAn updated analysis finds that stars with detected planets tend to rotate more slowly than stars without detected planets, after accounting for stellar temperature. Using Kepler rotation measurements and updated star and planet catalogues, the researchers compared each star’s rotation period with the period expected for its temperature. Among stars with rotation periods shorter than 20 days, the median of this ratio was about 15% higher for planet hosts. A separate TESS survey showed a similar tendency, but the pattern of rotation periods in that survey prevented a reliable comparison. The findings strengthen evidence for a connection between stellar rotation and planets, without showing that planets cause slower rotation. Stars without detected planets are not necessarily planet-free.

Young explorerStars spin, and some have planets going around them. Scientists looked again at measurements and found that stars with known planets tended to spin more slowly than stars where no planets had been found, when comparing with what was expected for each star’s temperature. Another set of measurements gave a similar hint, but was too tricky to compare reliably. This does not tell us why the stars spin differently, and some stars may have planets we have not found yet.

The cold substellar frontier in JWST Extragalactic surveys: a robust parallax measurement yields the most distant known ultra-cold Y dwarf

Feng-Yuan Frey Liu, Derek J. McLeod, Xueqing Chen+12 more

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies

AstronomerMulti-epoch JWST/NIRCam imaging over approximately two years yields the first robust parallax for a brown dwarf discovered in a JWST extragalactic deep field. For the extremely cold Y dwarf JADES-GS-BD-5, the authors measure a total proper motion of 49.8 ± 0.3 mas/yr and a parallax of 15.7 (+1.4/−1.3) mas, giving a geometric distance of 64 (+6/−5) pc, roughly three times that of the previously most distant Y dwarfs with measured parallaxes. Its inferred tangential velocity of 15.0 (+1.4/−1.3) km/s is consistent with thin-disk membership. The authors find no evidence for binary acceleration, significant photometric variability, or a plausible host. Its J-band morphology, faint luminosity, and near-infrared profile support an adopted classification later than Y1, consistent with the colour-based proxy cY1.5. The parallax anchors a bolometric luminosity of log(Lbol/Lsun) = −7.08 ± 0.09. Evolutionary models place it in the planetary-mass regime; this is a model-based inference rather than a direct mass measurement. Atmospheric models do not reproduce its spectral energy distribution in detail, suggesting an important role for disequilibrium chemistry and vertical mixing. Additional proper motions are reported for eight of the other nine known JADES Y-dwarf candidates.

PublicAstronomers used roughly two years of James Webb Space Telescope images to measure the distance to JADES-GS-BD-5, an exceptionally cold brown dwarf found in a survey aimed at distant galaxies. Its apparent shift as the observer's viewpoint changes places it 64 parsecs away, with an uncertainty of about 5–6 parsecs—roughly three times farther than the previous most distant Y-type brown dwarfs with distances measured this way. Its motion is consistent with belonging to the Milky Way's thin disk. The team found no evidence of significant brightness changes, acceleration caused by a binary companion, or a plausible host. The distance measurement establishes how faint the object truly is, supporting its identification as one of the coldest brown dwarfs known. Models of how such objects evolve suggest a mass in the planetary range, but the mass was not measured directly. Existing atmosphere models cannot fully explain its light, pointing to the possible importance of chemical imbalances and mixing between atmospheric layers. The object offers a valuable reference for studying atmospheres like those of cold giant planets.

Young explorerAstronomers watched a very cold, faint object called a brown dwarf with the James Webb Space Telescope. By seeing how its position seemed to shift over about two years, they worked out how far away it is. Knowing its distance helped them find out how dim it really is. It is one of the coldest brown dwarfs found so far. Computer models suggest it could have a mass like a planet's, but the team has not measured its mass directly. The models also cannot quite explain all its light, so it may help scientists learn more about very cold atmospheres.

Stars Within Stars: The Interplay Between Main-Sequence Stars and Dark Matter

Boris Betancourt Kamenetskaia, Chris Kouvaris

• High Energy Physics - Phenomenology

AstronomerThis theoretical study models low-mass baryonic stars embedded in hypothetical, self-gravitating asymmetric-dark-matter structures as two gravitating fluids. Such dark structures require sufficient effective pressure to resist gravity; the dark component is assumed to be non-luminous and coupled to baryons only gravitationally. Using a realistic baryonic equation of state, opacity tables, and proton-proton-chain energy generation, the models yield higher baryonic temperatures and luminosities at fixed baryonic mass because of the additional gravitational potential. They allow hydrogen-burning configurations below the standard minimum mass of approximately 0.085 solar masses and can shorten estimated main-sequence lifetimes from hundreds of billions of years to cosmologically relevant timescales. The study also predicts a surface-photon gravitational redshift set by the global dark matter distribution, so extended dark structures could leave signatures even when their outer regions barely affect the intrinsic baryonic structure. These are model predictions and potential observational probes, not detections.

PublicCould an ordinary star behave differently inside a much larger, invisible structure made of dark matter? This theoretical study explores that possibility, assuming dark matter can support itself against gravity and interacts with the ordinary star only through gravity. The calculations indicate that the extra gravity would make a star of a given ordinary-matter mass hotter and brighter. It could also let stars sustain hydrogen burning below the usual minimum of about 0.085 times the Sun's mass. Their greater brightness could substantially shorten their estimated hydrogen-burning lifetimes. The study further predicts that light escaping the star would be shifted toward redder wavelengths by the gravity of the surrounding dark matter, including distant regions that barely change the star itself. Such a shift might help reveal these hidden structures, but the study does not report an observation of one.

Young explorerImagine a little star inside a big, invisible ball of dark matter. Scientists used calculations to ask what might happen if such a ball could exist. Its extra gravity could make the little star hotter and brighter, help an even smaller star shine by burning hydrogen, and make the star use up its fuel sooner. The invisible ball's gravity could also make the light leaving the star look redder. That might give scientists a clue that the ball is there, but they have not found one in this study.

Convection in the interior of Cepheid variable stars

Maxime Stuck, Jane Pratt

• Fluid Dynamics

AstronomerThe abstract identifies this paper as associated with a poster that won a 2025 American Physical Society Division of Fluid Dynamics Gallery of Fluid Motion Award. It notes that the original poster is available online, but provides no scientific methods, observations, simulations, or conclusions to assess.

PublicThis paper is linked to an award-winning poster from the American Physical Society’s 2025 Gallery of Fluid Motion. The abstract points readers to the original poster online but does not explain the research or report any findings.

Young explorerThis paper goes with a poster that won a prize. The note says the poster is online, but it does not tell us what the scientists studied or learned.

The dielectric tensor for a fully anisotropic regularized Kappa plasma

Rudi Gaelzer, Horst Fichtner, Dustin Lee Schröder+2 more

• Plasma Physics

AstronomerSolar-wind and planetary-magnetosphere observations show quasi-stationary nonthermal particle populations with power-law high-energy tails. Motivated by limitations of the standard Kappa velocity distribution, this theoretical work employs a generalized regularized Kappa distribution, the bi-regularized Kappa with drift distribution (bRKd). It allows anisotropy in both thermal-speed and regularization parameters, together with drift parallel to the magnetic field. Regularization introduces a Gaussian-like cutoff at very high energies while retaining a Lorentzian profile at intermediate energies. The authors derive, for the first time, susceptibility-tensor components for a suprathermal species or population described by bRKd, valid for arbitrary wave propagation angle, frequency range, and polarization. They also define and analyze new special functions extending earlier expressions restricted to parallel propagation. These are analytical developments, not new observational measurements.

PublicThe electrically charged gas in the solar wind and around planets often contains more high-energy particles than a gas in thermal equilibrium would. This paper develops mathematical tools for describing how waves behave in such a gas. The model allows particle motions to differ by direction and includes an overall drift along the magnetic field. It also softens the model's extreme high-energy tail with a cutoff, addressing limitations of a commonly used description. The authors derive the quantities needed to describe the gas's response to waves traveling at any angle, across frequency ranges and polarizations. This is a theoretical advance rather than a report of new observations.

Young explorerSpace has tiny charged particles, and some move much faster than others. Scientists made new math to describe how waves move through these particles, even when they move differently in different directions. They worked this out on paper; they did not report watching new waves in space.

A Quantitative Method to Investigate the Spectral Class Time Evolution of Novae

Maria Kopsacheili, Martin Guerrero, Diego Alejandro Vasquez Torres

• High Energy Astrophysical Phenomena

AstronomerUsing ARAS spectroscopy of 26 novae, the authors investigate the apparent tension between progenitor-dependent spectral classes and a recently suggested early He/N–Fe II–late He/N sequence. They introduce κ, the Fe II λ5169 flux divided by the mean flux of five He and N emission lines; κ > 1 denotes Fe II dominance and κ < 1 He/N dominance. They find this diagnostic reliably traces spectral evolution while reducing biases from incomplete coverage. A significant fraction of the sample undergoes at least one transition, and κ closely tracks the optical light curves, repeatedly crossing unity in novae with brightness jitters. These observations demonstrate non-monotonic spectral evolution rather than a universal one-way sequence. The authors link phase durations to progenitor-dependent light-curve shapes and timescales, particularly their dependence on white dwarf mass, explaining how early, sparse spectroscopy can bias classification.

PublicNovae are classified by whether iron or helium and nitrogen dominate their spectra—the patterns of light they emit. But a nova can change categories over time. Studying spectra of 26 novae, the researchers developed a numerical measure that compares the strength of one iron emission line with five helium and nitrogen lines. A significant fraction of the novae switched between the two categories at least once. In novae whose brightness fluctuated, the dominant spectral features switched back and forth, showing that the changes do not always follow a simple sequence. The authors connect the time spent in each category to brightness patterns that depend on the properties of the original system, especially the white dwarf’s mass. Classifying a nova from only a few early spectra can therefore give a biased picture.

Young explorerScientists can sort novae by the patterns in their light. They looked at 26 novae and found that many changed from one kind of pattern to another. Some with wobbly brightness changed back and forth, instead of changing just one way. So looking only a few times near the start can give a misleading picture—like guessing a whole story after seeing just its first few pages.

PROSWIN: Probabilistic Solar Wind Speed Forecasting Using Deep Distributional Regression From Solar Images

Daniel Collin, Yuri Shprits, Luca Chiarabini+3 more

• Machine Learning
• Data Analysis, Statistics and Probability
• Space Physics

AstronomerPROSWIN is a probabilistic machine-learning model that forecasts hourly solar wind speed at Earth four days ahead, combining solar images and magnetograms through a deep neural network coupled to distributional regression. Evaluated on 14 years of data, it yields well-calibrated uncertainties, with less than 1% average deviation, and continuous ranked probability scores of 41.0 km/s for the full timeline and 45.3 km/s for high-speed stream peaks. The authors introduce a model-selection prediction score that rewards both timeline and peak accuracy; PROSWIN achieves 42.3 km/s on this metric. They find that the 171 Å channel usefully complements the commonly used 193 Å and 211 Å channels. Among the selected literature models compared, PROSWIN alone performs accurately on both timeline and peak values without trading one against the other. These evaluation results support probabilistic forecasting, rather than establishing superiority over every solar wind model.

PublicFast streams of solar wind can damage technological infrastructure, so forecasts need to describe not just the expected speed but also how uncertain that prediction is. The researchers present PROSWIN, a machine-learning system that uses images and magnetic-field maps of the Sun to predict hourly solar wind speeds at Earth four days ahead. In an evaluation using 14 years of data, its predicted uncertainties closely matched the errors found in testing. The team also developed a way to select models that rewards accuracy both across time and at the peaks of fast streams, which ordinary error measures can undervalue. Compared with selected models from earlier studies, PROSWIN was the only one reported to be accurate in both respects. The results support forecasts that give a range of possibilities rather than a single speed; they do not mean that every forecast will be correct.

Young explorerThe Sun sends a wind through space. When it blows very fast, it can hurt some of our technology. Scientists made a computer helper that looks at pictures and magnetic maps of the Sun to guess how fast that wind will reach Earth four days later. Instead of giving just one guess, it gives several possibilities and says how sure it is. When scientists tested it using 14 years of information, it did well at guessing both the changing wind and its fastest bursts. It can still make mistakes.

Axial-Dipole and Equatorial-Dipole Coronal Holes: Congruent Magnetic Geometry, Divergent Evolution

Olga A. Panasenco, Yi-Ming Wang, Samuel T. Badman+2 more

AstronomerThe study compares equatorial-dipole coronal holes (EDCHs), associated with the magnetic poles of a strong equatorial dipole, with axial-dipole coronal holes (ADCHs) at solar minimum. Not all low-latitude holes are EDCHs: quadrupole and higher-order components dominated in August 2024. Parker Solar Probe observed deeply sub-Alfvénic fast wind from an EDCH at 9.9 solar radii, traveling at only 60% of an asymptotic speed equal to that of polar wind, which is thought to accelerate faster. Potential-field models using synthetic and observed fields test whether magnetic structure explains this apparent difference. Pure axial and equatorial dipoles are geometrically congruent, so differences must involve their orientation relative to differential rotation or surrounding multipoles. ADCHs are stationary and sustained by converging meridional flow, whereas EDCHs depend on an equatorial dipole built by active-region emergence and removed by flux transport. Across 18-day sequences, the axial dipole at minimum varies by 1%, compared with equatorial-dipole variations of 21% at maximum and 8% in the declining phase. Most EDCH open flux expands less than ADCH flux, and EDCH boundaries are dominated by pseudostreamers with non-monotonic expansion. Magnetic geometry alone does not predict slower EDCH-wind acceleration. If the acceleration difference is real, the authors interpret it as pointing to extended heating by Alfvén-wave turbulence, which these models cannot capture.

PublicAs the Sun’s polar magnetic fields reverse, coronal holes associated with a strong equatorial magnetic dipole can appear at low latitudes. These are not the same as every low-latitude coronal hole, because more complex magnetic patterns can dominate. Parker Solar Probe measured fast solar wind from one such equatorial-dipole hole at 9.9 solar radii from the Sun’s center. There, the wind was moving at only 60% of its eventual speed, even though that eventual speed matched polar wind, which is thought to speed up more quickly. The researchers used magnetic-field models to ask whether the shapes of the coronal structures explain this apparent difference. They found that equatorial-dipole holes are more changeable than polar ones, but their magnetic geometry alone does not predict slower acceleration. If the wind really does accelerate differently, the authors suggest that prolonged heating by magnetic-wave turbulence could be responsible. Their models cannot represent that heating, so this remains an interpretation rather than a demonstrated explanation.

Young explorerThe Sun sends out a wind, and its magnetism helps shape where that wind comes from. A spacecraft found wind from a region near the Sun’s middle that still had a lot of speeding up to do. Scientists used computer models to compare magnetic shapes there with shapes near the Sun’s poles. The shapes alone did not explain why the wind might speed up more slowly. Extra heating from magnetic waves might help explain it, but the scientists have not shown that this is the answer.

Gaia in Technicolor. I. A Simple Variability-Encoded Color-Magnitude Diagram

Brad N. Barlow, Bennett C. Kirby

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

AstronomerUsing near-simultaneous, three-band, multi-epoch photometry released for approximately 11.7 million Gaia DR3 sources, the authors construct a variability-encoded color-magnitude diagram (VECMD). Each source is represented by a line segment approximating its trajectory in absolute magnitude and color, rather than by its time-averaged position. The epoch-based construction requires neither a period nor phase-folding. Examining the underlying trajectories, they find looped, Lissajous-like paths for radial-mode pulsators that can encode radius–temperature phase lags, with the Hertzsprung bump visible in some Cepheid loops. Variable binaries show tight color-correlated lines and/or hooked paths, while accreting and dust-obscured systems show long, high-amplitude tracks aligned with outburst or reddening vectors. Different VECMD regions are dominated by different trajectory morphologies. The authors propose these period-independent signatures for machine-learning classification, with future work planned on the larger epoch-photometry sample expected from Gaia DR4; that classification effort is not presented as a completed result. They also introduce the free IVECMD app for finding, classifying, and analyzing variable stars.

PublicA standard star chart of brightness versus color gives each star one dot, hiding how it changes over time. Using repeated measurements in three color bands released for about 11.7 million sources in Gaia DR3, the researchers built a version that replaces each dot with a short line summarizing those changes. The detailed paths reveal different patterns: pulsating stars can make loops, variable binary systems can make straight or hooked tracks, and systems affected by accretion or obscuring dust can trace long paths. Some Cepheid loops even reveal a feature known as the Hertzsprung bump. These patterns can be studied without first determining how long a star takes to repeat its variations. The authors suggest that the paths could help machine-learning systems classify variable stars, but plan to pursue that work with the larger data sample expected from Gaia DR4. They also present a free app, IVECMD, for exploring and analyzing these stars.

Young explorerImagine a picture that sorts stars by their color and how bright they are. Usually, each star gets just one dot. But some stars change! The researchers used repeated Gaia measurements to give stars little lines showing how their color and brightness change together. Looking more closely, they found that some stars draw loops, while others draw hooks or long trails. These shapes give clues about what the stars are doing. The researchers hope to teach computers to use the shapes to sort stars in future work. They also made a free app for exploring them.

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems IX: A Multi-Wavelength Framework for Source Characterization in JWST Coronagraphic Imaging of the HIP 65426 System

Evelyn L. Bruinsma, Aarynn L. Carter, Sasha Hinkley+28 more

AstronomerA reanalysis of JWST coronagraphic imaging of HIP 65426 using updated JWST and spaceKLIP pipelines yields filter-dependent changes in the astrometry and photometry of HIP 65426 b relative to Carter et al. (2023). Differences reach 2.2σ in separation, 1.5σ in position angle, and 3.7σ in flux. The planet’s spectral energy distribution remains consistent with a young giant planet, best fit by cloudy-atmosphere models with an estimated effective temperature of approximately 1436 K. NIRCam and MIRI imaging identifies 21 additional candidate companion sources; 13 are attributed to astrophysical sources, comprising eight background stars, four galaxies, one source of unknown nature, and no planets. Previously undetected point sources provide an initial astrometric epoch. A galaxy that appears point-like in MIRI but extended in NIRCam illustrates a potential contamination problem for single-epoch, blind companion searches with MIRI.

PublicResearchers reprocessed James Webb Space Telescope images of the HIP 65426 system to update measurements of its known giant planet and look for additional companions. Updates to the data-processing software significantly changed the measured brightness and position in some observing bands, especially the brightness. The planet’s light still best matches models of a young giant planet with a cloudy atmosphere and an estimated effective temperature of about 1436 K; these atmospheric properties are model-based interpretations. The team also identified 21 possible companion sources. Of these, 13 were attributed to astronomical objects: eight background stars, four galaxies, and one object of unknown nature, with none classified as a planet. One galaxy looked like a point of light in MIRI images but appeared extended in NIRCam images, showing how a single observation with MIRI could make a galaxy look like a possible companion.

Young explorerScientists looked again at space-telescope pictures of a star and its known big planet. Better computer tools changed how bright the planet looked and exactly where it appeared in the pictures. Comparing its light with models suggests the planet is hot and cloudy. The scientists also checked other spots of light that might have been nearby worlds. They identified some as faraway stars and galaxies, but did not identify any new planets. One galaxy looked like a tiny dot in one camera and spread out in another, showing why a dot of light is not always a planet.

An analytical framework for atmospheric tides on rocky planets. II. Semidiurnal thermotidal torque

Pierre Auclair-Desrotour, Jacques Laskar, Mohammad Farhat+1 more

• Geophysics

AstronomerThis theoretical study applies an analytical atmospheric-tide framework to isentropic and isothermal atmospheres, examining how thermotidal torque depends on forcing frequency and system parameters. Comparisons with earlier general circulation model (GCM) simulations show good agreement for paleo-Earth and present-day Earth, including a torque peak near synchronous rotation and amplification at Lamb-wave resonance. Introducing a lag between insolation and tidal heating reproduces the GCM spectra’s stronger braking than accelerating torque near resonance. The agreement suggests that substantially delayed, indirect thermal forcing dominates the benchmark simulations, unlike the direct sunlight absorption that dominates present-day Earth’s semidiurnal atmospheric tides. These are analytical and simulation-based findings, not observational confirmation of a particular Precambrian length-of-day history.

PublicHeating an atmosphere can produce tides that alter a rocky planet’s spin, with consequences for its climate. The researchers developed mathematical descriptions of this effect for two idealized types of atmosphere and compared them with earlier computer simulations of ancient and modern Earth. Their calculations reproduce key simulation features, including a stronger response when atmospheric waves resonate. Allowing atmospheric heating to lag behind sunlight also reproduces the simulations’ stronger slowing than speeding of rotation near resonance. This suggests delayed, indirect heating drives those simulations, unlike the direct sunlight absorption that dominates the corresponding twice-daily tides on Earth today. The study does not establish how long ancient Earth’s days actually were.

Young explorerSunshine warms a planet’s air and can make waves that help speed up or slow down its spinning. Scientists used math and compared it with computer-made Earths. Their math matched important patterns, especially when the air warmed after a delay. This helps explain the computer models, but it does not tell us exactly how long a day was on Earth long ago.

Coordinated Space and Ground Monitoring of Accretion Bursts in a Protoplanetary Disk: MIRI and iSHELL observe the long-term modulation of gas within a small inner disk cavity

Jacob Hyden, Andrea Banzatti, Benjamin M. Tofflemire+14 more

AstronomerDQ Tau is an eccentric T Tauri binary with accretion bursts tied to its approximately 16-day orbit. A 40-day, seven-instrument campaign includes nine JWST-MIRI and nine IRTF-iSHELL epochs spanning three successive bursts, with accretion luminosity increases of roughly 9–80 times. CO and H2O line broadening provides estimates of Keplerian emitting radii and their variability. Unlike H I emission and the 5-micron continuum, all hot molecular tracers show declining line luminosities and widths over approximately 30–35 days rather than responding to each burst. These trends are consistent with an emitting region cooling, losing mass, and shifting to larger radii within the approximately 0.2–0.4 au binary-perturbed inner cavity. The authors interpret disk dynamics as more influential than accretion-driven chemical changes, supporting model expectations of chemical relaxation times much longer than the bursts, well beyond 10 days. The variability is consistent with gas accumulating near the disk edge and modulating burst peaks and cavity gas density every approximately 4–5 orbits, but the origin of that modulation remains unclear.

PublicDQ Tau is a pair of young stars whose feeding bursts follow an approximately 16-day orbit. Researchers monitored it for 40 days, covering three successive bursts. Although the light produced by accretion rose sharply, emission from hot molecular gas did not brighten with each burst as some other signals did. Instead, the molecular emission faded and its spectral lines narrowed over about 30–35 days. The team interprets these changes as signs that the emitting gas was becoming cooler and less massive, with emission coming from farther out in the disk’s inner cavity. The findings suggest that gas motion shapes the molecular spectrum more strongly than chemical changes caused by the bursts, consistent with models in which the chemistry takes much longer to adjust. Gas piling up near the disk’s inner edge could explain variations in burst strength over about four to five orbits, but this explanation is not established and the cause of that longer pattern remains unclear.

Young explorerTwo young stars called DQ Tau travel around each other and have bursts of feeding on nearby gas. Scientists watched them through three bursts. Some kinds of light grew brighter during the bursts, but light from hot gas molecules slowly grew dimmer instead. The clues suggest that the glowing gas was getting cooler and that its glow was coming from farther away from the stars. The scientists think moving gas matters more here than changes in what the gas is made of. Gas might also pile up before feeding the stars, making some bursts stronger, but they do not yet know why that would happen.

Using Structure Functions to Characterize Protoplanetary Disk Velocity Residuals

Richard Teague, Sean M. Andrews, Jaehan Bae+4 more

AstronomerHigh-resolution disk observations commonly reveal non-Keplerian motions, but their often-disordered appearance complicates attribution to instabilities or planet–disk interactions. The authors propose a second-order structure-function framework combining structural heuristics, parametric fits, de-noising, and a matched null model. Tests with morphological models recover correlation lengths, radial scaling where genuinely present, and anisotropy. Applied to one numerical simulation each of gravitational, magneto-rotational, and vertical-shear instability, the framework detects structure at high significance, and its heuristics distinguish all three pairs. Gravitational and vertical-shear instability remain the hardest pair to distinguish after observational degradation; these tests do not establish general discrimination across all realizations. In real 12CO observations of TW Hya, the analysis reveals azimuthally elongated velocity structure that persists after removal of the large-scale m=1 component, without identifying a unique physical cause. The study also examines inclination effects and limitations of Gaussian descriptions for coherent features such as spiral arms. The methodology is implemented in eddy.

PublicGas in planet-forming disks often moves differently from what simple orbital motion would predict, but noisy, disordered patterns make the cause difficult to identify. This study proposes a statistical method for finding the size and preferred direction of patterns in those motions. Tests on simplified models and one computer simulation each of three kinds of instability show that the method can recover structure and distinguish the simulated cases. Two of the cases become especially difficult to tell apart when made more like observations. Applied to observations of the disk around TW Hya, the method finds motion patterns stretched around the disk, even after a large-scale pattern is removed. That finding does not establish what causes the motions. Viewing angle and coherent features such as spiral arms also complicate the analysis.

Young explorerPlanets are born in disks of gas, where the gas does not always move in neat circles. Scientists made a new way to look for patterns hidden in messy measurements. They tested it on computer-made disks, then tried it on a real disk around a star called TW Hya. They found patterns in how the gas moves, stretched around the disk. They still have not shown what makes those patterns.

No Significant Rotation of the Spiral Structure in the IM Lup Protoplanetary Disk

Yuto Hiraide, Mastaka Aizawa, Munetake Momose

• Solar and Stellar Astrophysics

AstronomerA visibility-based continuum reanalysis of multi-epoch ALMA data revises the geometry of IM Lup’s dusty disk by a few degrees relative to earlier assumptions. The inferred geometries agree across epochs and with recent gas-based estimates, yielding weaker residuals and more physically plausible radial spiral phase profiles. The remeasured m=2 pattern speeds are consistent with zero rotation within uncertainties, unlike the previously reported local Keplerian-like motion that supported a gravitational-instability origin. The authors attribute that earlier motion to a geometry mismatch affecting the Band 6 (2017, 2019) and Band 7 (2024) spiral phases differently. They also tentatively identify a larger-scale one-armed spiral-like feature beyond the known two-armed spiral; an embedded planet or late-stage infall are possible interpretations, not established causes. High-resolution Band 6 observations over a longer baseline are needed to constrain the pattern speed more accurately.

PublicA new analysis revisits whether the spiral pattern in the dusty disk around the star IM Lup is turning. Earlier ALMA observations had been interpreted as showing motion consistent with material orbiting locally in the disk, supporting the idea that the disk’s own gravity produces the spirals. By revising the disk’s inferred orientation by a few degrees, the researchers obtain a better-fitting description of the observations and find no statistically clear rotation of the spiral pattern. This does not prove that the pattern is stationary. They conclude that the earlier apparent motion can be explained by the assumed disk geometry. They also report a tentative, more extended one-armed spiral-like feature, which might reflect disturbances from an embedded planet or material falling onto the disk, but neither explanation is established. Sharper observations separated by more time are needed.

Young explorerAround a star called IM Lup is a dusty disk with a pattern like two curling arms. Scientists once thought they could see the pattern turning. Now they have checked how the disk is tilted and found that the pictures do not clearly show the pattern turning. That does not mean it is definitely standing still; they need more pictures taken farther apart in time. They also spotted what might be another, bigger curling arm, but they are not sure it is really there or what could have made it.

Prospects for detecting hot-Jupiter tidal decay through transit timing with the mission Earth 2.0

Wenqin Wang, Yue Wang, Di-Chang Chen+3 more

• Instrumentation and Methods for Astrophysics

AstronomerThe study forecasts Earth 2.0 (ET)'s ability to measure tidal orbital decay in Kepler hot Jupiters through long-term transit timing. Four years of simulated ET light curves, generated using expected photometric precision and cadence, are analyzed jointly with archival Kepler and TESS observations, yielding an approximately 24-year baseline spanning 2009–2033. The analysis predicts a factor-of-7.2 improvement in orbital-decay measurement precision. Assuming the stellar tidal quality factor inferred from previous observations, ET is expected to detect decay in three additional systems. These are simulation-based forecasts, not new detections; WASP-12b remains the only hot Jupiter with conclusive observational evidence for orbital decay according to the abstract. Such detections would improve constraints on stellar tidal dissipation and hot-Jupiter tidal evolution.

PublicHot Jupiters are giant planets that orbit close to their stars. Tidal interactions can make their orbits shrink, but the abstract reports that only WASP-12b has conclusive evidence of this happening. Researchers tested how well the Earth 2.0 mission could find more examples by combining four years of simulated future observations with existing Kepler and TESS data. The resulting observing timeline would span about 24 years, allowing small changes in the timing of planets crossing their stars to accumulate. The study predicts that Earth 2.0 could improve the precision of orbital-shrinkage measurements by a factor of 7.2. It could detect shrinking orbits in three additional systems if the stars' tidal behavior matches the assumed value inferred from earlier observations. These are predictions, not discoveries, and would help explain how stars and close-orbiting planets exchange tidal energy.

Young explorerSome giant planets go around their stars very close by. A star and planet can tug on each other in a way that slowly makes the planet's path smaller. So far, scientists have clear evidence of this for just one such planet. They used pretend observations from a future space mission called Earth 2.0, together with real older observations, to test how well they could spot more shrinking paths. Their test suggests the mission might find three more, if the stars act the way the scientists assumed. Those planets have not yet been shown to have shrinking paths.

Results from a Stellar Occultation by (623) Chimaera

Phillip Oakey, Keya Garg, Andrey Moore+25 more

AstronomerThe October 21, 2025 stellar occultation by (623) Chimaera yielded useful data from 16 of 18 telescopes deployed across the United States, with approximately 4.4 km cross-track spacing. The multi-chord sky-plane profile is well described by an elongated ellipse with semi-axes a = 26.2 ± 0.8 km and b = 16.0 ± 1.0 km. Ellipse and limb fits give projected areas of 1316 and 1312 km², respectively; these describe the projected silhouette rather than the full three-dimensional shape. Seven months of contemporaneous Gaia G-band photometry imply a geometric albedo p_G = 0.059 ± 0.005, while comparison with archival occultations and direct observations gives p_G = 0.051 ± 0.004 and p_V = 0.051 ± 0.004. Comparisons with occultation projections show that inversion-based 3-D models accurately predict Chimaera’s orientation at the observed occultation epochs. Chimaera, the largest member of its asteroid family, is scheduled for a spacecraft flyby in the 2030s.

PublicAstronomers measured asteroid Chimaera’s silhouette as it passed in front of a star on October 21, 2025. Sixteen telescopes across the United States recorded useful data, together tracing an elongated, oval-like outline. The fitted oval has a long radius of 26.2 ± 0.8 kilometres and a short radius of 16.0 ± 1.0 kilometres; it measures the asteroid’s outline from our viewing direction, not its complete shape. Brightness observations combined with the size measurements indicate a dark surface, with estimated geometric albedos of roughly 5–6%, depending on the data and wavelength band used. The researchers also found that existing three-dimensional models could accurately predict the asteroid’s orientation during the observed star crossings. These measurements characterize an asteroid due to receive a spacecraft flyby in the 2030s.

Young explorerAn asteroid called Chimaera moved in front of a faraway star and briefly hid it. Sixteen telescopes got useful pictures of the star’s light disappearing and coming back. Together, their measurements showed that the asteroid’s outline looked like a stretched-out circle from where we were watching. The scientists also worked out that its surface is dark. Computer models correctly showed which way the asteroid was turned during the star crossings. A spacecraft is planned to fly past Chimaera in the 2030s.

Evolution of Dust In Protoplanetary Disks With Magnetized Winds

Olcay Goksu, Ralph Pudritz, Timmy Delage

AstronomerMotivated by evidence for weak turbulence in protoplanetary disks, this study uses a parametric hybrid evolution model incorporating turbulent accretion, wind-driven accretion, and wind-driven mass loss. A parameter study finds that wind-dominated disks favor dust growth and concentration relative to turbulence-dominated disks, but streaming-instability conditions occur only within the inner few au and under extreme assumptions: turbulence strength α_turb = 10⁻⁵, accretion dominated by magnetized winds, and wind mass loss comparable to the accretion rate. These are model results, not observational detections of planetesimal formation. Within the parametric framework considered, wind-driven evolution alone does not generate suitable streaming-instability conditions farther out, motivating more physically complete models capable of producing spontaneous, long-lived dust traps.

PublicCan winds help the dust around young stars gather into the building blocks of planets? The researchers explored this question with a simplified model of a disk evolving through turbulence, magnetized winds, and gas loss. Their calculations suggest that wind-dominated disks help dust grow and concentrate more than turbulence-dominated disks do. Even so, conditions suitable for a dust-and-gas clumping process called the streaming instability appeared only close to the star, within a few Earth–Sun distances, and only with extremely weak turbulence, winds driving most of the inward flow, and winds removing gas at a comparable rate. The study does not show planet building happening in an observed disk. Instead, it suggests that the modeled wind-driven evolution alone is insufficient farther out, and motivates more complete models that could develop lasting dust traps.

Young explorerYoung stars can have disks of gas and dust around them. Scientists used a model to ask whether winds could help the dust gather into little pieces that might help make planets. In their model, winds helped dust grow and bunch up more than strong stirring did. But the dust was ready for one possible planet-building process only near the star, with very little stirring and especially strong effects from the winds. The model did not make the right conditions farther away. The scientists want to explore more complete models where dust might get caught and stay together.

BeAR: The Bern Atmospheric Retrieval code - A GPU-accelerated framework for low-resolution, high-resolution, and joint retrievals of exoplanet atmospheres

Esther Wang, Daniel Kitzmann, H. Jens Hoeijmakers+2 more

• Instrumentation and Methods for Astrophysics

AstronomerBeAR, the successor to Helios-r, introduces a GPU-based high-resolution cross-correlation retrieval framework for emission and transmission spectra. Joint retrievals sum high- and low-resolution log-likelihoods evaluated using the same model atmosphere. The implementation supports analytic or sampled line-depth scaling, per-pixel likelihoods, fast filtering, and filtering-adapted model re-injection. Separate retrievals of Gemini South/IGRINS and JWST/NIRSpec dayside spectra of WASP-77Ab reproduce published abundances, C/O ratios, and metallicities within 1.5 sigma, recover the preference for 13CO, and reproduce thermal structure and line contrast within 1 sigma. The joint retrieval supports sub-solar metallicity and near-solar C/O. A forward model takes about 1 ms on an NVIDIA GH200; a 17-parameter IGRINS retrieval takes 27–42 minutes on one RTX 5080 or about 14 minutes on eight RTX 4090 GPUs. Crucially, injection–recovery tests indicate that the posterior uncertainties on abundance ratios are underestimated by about a factor of two.

PublicBeAR is a new version of software that infers planetary atmospheres from their spectra. It combines finely detailed spectra with lower-resolution data using one shared atmospheric model, with calculations accelerated by graphics processors. Applied separately to Gemini South and James Webb Space Telescope observations of the hot giant planet WASP-77Ab, it broadly reproduces earlier estimates of atmospheric composition and temperature structure. Combining the observations supports an atmosphere with a lower proportion of heavy elements than the Sun and a carbon-to-oxygen ratio close to the Sun’s. However, tests that insert and recover model signals reveal an important limitation: the software’s reported uncertainties for abundance ratios are about half as large as they should be.

Young explorerScientists made a fast computer tool to look for clues about a very hot giant planet’s air in its light. Using two sets of observations together, the tool suggests the air has fewer heavy ingredients than the Sun, but a similar balance of carbon and oxygen. Tests with added pretend signals showed that the tool acts too sure about some ingredient comparisons, so scientists need to allow more room for mistakes.

FastChem 4: New chemical elements and improved convergence behaviour

Daniel Kitzmann, Joachim W. Stock, A. Beate C. Patzer

• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerFastChem 4 updates the open-source chemical-equilibrium code for modelling planetary, brown-dwarf, cool-star, and protoplanetary-disk environments. A multidimensional Newton method mitigates slow gas-phase convergence at strongly non-solar abundances, while logarithmic element-density equations remove the need for quad precision and enable low-temperature calculations on platforms supporting double precision. Adaptive Levenberg-Marquardt regularisation, a perturbed-Hessian fallback, and a combined gas-condensate Newton solver improve condensate-solver performance and stability. The expanded thermochemical database includes 800 gas-phase molecules and ions and 511 condensates across 44 elements. Calculated pressure-temperature grids reproduce the classical solar-composition condensation sequence and show marked changes for carbon-rich compositions with C/O = 2. The calculations also find condensed silicon monoxide stable over a limited pressure-temperature range, which the authors describe as consistent with recent JWST brown-dwarf observations; this is a modelling result, not a new observational detection. FastChem 4 is released under GPLv3 with a pre-compiled Python package.

PublicResearchers have released FastChem 4, an updated program that calculates which gases and condensed materials can exist in chemical equilibrium under different conditions. Such calculations help scientists interpret the light from planets, brown dwarfs, cool stars, and planet-forming disks. The update improves calculation speed and stability, particularly for mixtures whose elemental proportions differ strongly from the Sun’s, and expands the chemical database. Tests across a broad range of temperatures and pressures recover the expected condensation sequence for a Sun-like mixture and show substantial changes for a carbon-rich mixture. The calculations also indicate that condensed silicon monoxide can be stable within a limited range of conditions. The authors say this agrees with recent JWST observations of brown dwarfs, but the calculation itself is not a new detection.

Young explorerScientists made a better computer program to work out what different mixtures of chemicals might become in very hot or cold places in space. It helps them understand what they see when they study light from those places. The program works faster and more reliably than before. Its calculations show that changing the ingredients can change which materials form. They also suggest that a material called silicon monoxide can stay in a form that is not gas under some conditions. That is a computer calculation, not a new thing the scientists saw through a telescope.

Using High-Resolution Spectroscopy to Study the Composition, Temperature, and Dynamics of Exoplanet Atmospheres

Mu'allim Yakubu

• Instrumentation and Methods for Astrophysics

AstronomerThis review synthesises fifteen years of observational and methodological progress in high-resolution spectroscopy of exoplanet atmospheres, typically at resolving powers R ≥ 25,000. Resolved molecular rotational-vibrational lines and the large orbital Doppler shifts of close-in planets help separate planetary spectra from relatively stationary terrestrial and stellar contamination. Starting with CO in transmission through HD 209458b’s atmosphere, the technique has identified more than a dozen chemical species across transiting, non-transiting and directly imaged planets. It also constrains abundances and vertical temperature structure through pressure-dependent line depths, and probes atmospheric dynamics through Doppler shifts and asymmetries in planetary cross-correlation functions. The review covers current facilities and the anticipated contributions of ANDES, METIS and HARMONI on the Extremely Large Telescope; it is a synthesis rather than a report of a new detection.

PublicThis review explains how finely detailed spectra reveal the atmospheres of planets around other stars. Different chemicals leave distinctive patterns in light, and the orbital motion of close-in planets shifts those patterns, helping astronomers distinguish them from signals produced by Earth’s atmosphere and the host star. Over fifteen years, this approach has identified more than a dozen chemical species in a range of exoplanets. The spectra also provide clues to chemical amounts, how temperature changes with atmospheric depth, and how atmospheric gas moves. The article reviews established observations and methods, while discussing how current and forthcoming instruments can extend these studies; it does not announce a new discovery.

Young explorerLight can carry tiny patterns that help us learn what is in the air around faraway planets. As a planet moves around its star, its patterns shift, helping astronomers pick them out from other light. Scientists have already found many kinds of chemicals this way. The patterns also give clues about how hot the air is and how it moves. This article tells the story of that work and describes tools that scientists use now and tools still to come.

Magnesium silicate condensation in sub-Neptune envelopes: the fundamental link between chemistry, structure, and observables

William Misener, Peter Gao, Nicole L. Wallack+2 more

AstronomerThe authors introduce Rocky Raccoon, a coupled chemical-equilibrium and atmospheric-structure model for sub-Neptune envelopes containing Mg, Si, O, C, and H species. It computes self-consistent chemical and thermal profiles and, according to the abstract, treats multi-species condensation for the first time. The model predicts that basal magma composition controls magnesium-silicate condensation sequences above a magma ocean, producing two upper-atmosphere endmembers. Oxygen-rich melts yield oxygen-bearing volatiles, sub-solar C/O, and higher mean molecular weight atmospheres with μ approximately 4 amu; oxygen-poor melts yield methane- and silane-dominated atmospheres with super-solar C/O and lower mean molecular weights. The transition is abrupt and depends on melt oxygen abundance and Mg/Si ratio. Different condensation sequences also generate molecular-weight gradients that inhibit deep convection over different regions, changing thermal profiles. These are model findings, not reported atmospheric observations; uncertainties in condensation sequences require further experiments and simulations.

PublicA new computer model explores how a sub-Neptune’s hydrogen-rich atmosphere interacts with its rocky, molten interior. It links atmospheric chemistry and temperature rather than calculating them separately. The model predicts that the molten rock’s composition determines the order in which magnesium silicates condense, steering the upper atmosphere toward two different chemical mixtures. Oxygen-rich molten rock produces an atmosphere rich in oxygen-containing gases, with heavier molecules on average. Oxygen-poor molten rock instead produces an atmosphere dominated by methane and silane, with lighter molecules on average. The switch between these mixtures can be abrupt. The model also predicts changes in how heat moves through the deep atmosphere. These predictions remain sensitive to uncertain condensation chemistry, which needs further experiments and simulations.

Young explorerScientists made a computer model of planets with thick gas blankets above melted rock. In the model, changing the melted rock changes which gases fill the blanket and how heat moves through it. These are computer predictions, not things scientists have seen happen on those planets. More tests are needed.

OGLE-2013-BLG-1125/MOA-2013-BLG-584: Discovery of a gas giant orbiting an M dwarf

E. Bachelet, M. Hundertmark, V. Bozza+2 more

AstronomerThe authors report a Saturn-mass planet in the microlensing event OGLE-2013-BLG-1125/MOA-2013-BLG-584. Modeling OGLE and MOA photometry together with LCO, μFUN, and Mindstep follow-up data, and incorporating additional constraints from Keck II observations obtained in 2018, they infer a planet mass of 105 ± 13 Earth masses and a host mass of 0.139 ± 0.011 solar masses, at a distance of 1.00 ± 0.08 kpc. The system adds to the small sample of giant planets around low-mass stars and provides constraints on planet formation theories.

PublicAstronomers report finding a planet about as massive as Saturn orbiting a low-mass star. They identified the system through gravitational microlensing, in which gravity magnifies the light of a more distant star. By modeling the changing brightness and using additional Keck II telescope observations, they estimate that the planet has 105 ± 13 times Earth's mass, its host star has 0.139 ± 0.011 times the Sun's mass, and the system lies 1.00 ± 0.08 kiloparsecs from Earth. This discovery adds to the small number of known giant planets around low-mass stars, helping constrain ideas about how planets form.

Young explorerAstronomers found a big planet going around a star much smaller than our Sun. The planet is about as heavy as Saturn. They found it by studying how the system's gravity made light from a star behind it look brighter. Their measurements help them work out how heavy the planet and its star are. Finding planets like this gives scientists clues about how planets are made.

Unveiling the Origins of Local Group Galaxies with ELT-SHARP: An Overview of Science Cases

Hai-Feng Wang, Guan-Yu Wang, Peng Yang+8 more

• Astrophysics of Galaxies

AstronomerThis science-case proposal outlines how SHARP, a multi-mode near-infrared spectrograph for Extremely Large Telescopes and future space facilities, could probe disk assembly, dynamical heating, and galactoseismology using resolved stellar populations. Its stated capabilities include single-exposure coverage of 0.95–2.45 micrometers, adaptive-optics-assisted NEXUS multi-object spectroscopy over 1.2 × 1.2 arcminutes at resolving powers up to approximately 17,000, and VESPER multi-IFU spectroscopy for sub-arcsecond kinematic and stellar-population mapping in crowded regions. Combined with complementary surveys, the proposed observations would map six-dimensional phase-space structure and investigate bars, spiral arms, warps, flares, and satellite interactions in the Milky Way and nearby galaxies. The intended constraints concern disk evolution, merger history, and dark matter substructure, potentially testing ΛCDM where small-scale tensions may persist. The abstract presents proposed investigations and instrument capabilities, not new observational results or demonstrated discrepancies with ΛCDM.

PublicThe authors propose using an infrared spectrograph called SHARP to study how the Milky Way and nearby galaxies formed and changed. Infrared observations would help reach stars hidden by dust, while detailed spectroscopy would reveal stellar motions and chemical properties, including in crowded regions. Combining these observations with other surveys could help researchers investigate galactic bars, spiral arms, bent and thickened disks, and the effects of encounters with smaller galaxies. The work could also test predictions about dark matter and the standard model of cosmic structure, which works well on large scales but may face difficulties on smaller ones. These are proposed studies, not reported discoveries.

Young explorerGalaxies are huge groups of stars. Scientists want to use a tool called SHARP to study starlight, including light from stars that dust makes hard to see. They hope to learn how stars move and how galaxies grow and change when other galaxies come close. This is a plan for learning new things, not a report of things they have already found.

SHARP(ening the) view of unresolved globular clusters in ultra diffuse galaxies

Marco Mirabile, Michele Cantiello, Benedetta Di Francesco+7 more

• Astrophysics of Galaxies

AstronomerThis study presents the projected scientific potential of NEXUS@SHARP, a near-infrared multi-slit spectrograph proposed for the upcoming Extremely Large Telescope, rather than new observations of ultra-diffuse galaxies. Globular clusters offer tracers of UDG halos, but current spectroscopy limits characterization beyond the local neighborhood. The authors argue that NEXUS’s combination of high spatial resolution and efficient multiplexing could characterize UDG globular-cluster populations across diverse environments out to 60–70 Mpc with a few hours of ELT time. The anticipated radial-velocity and stellar-population measurements would support dynamical mass estimates and tests of competing formation scenarios, addressing uncertainties about UDG dark matter content and formation within ΛCDM.

PublicUltra-diffuse galaxies are faint systems whose dark matter content and origins challenge current galaxy-formation models. Clusters of stars called globular clusters can help researchers probe these galaxies, but today’s instruments struggle to study enough of them at greater distances. This paper describes the potential of NEXUS@SHARP, a proposed instrument for the upcoming Extremely Large Telescope. The authors project that it could study globular-cluster populations in these galaxies out to 60–70 megaparsecs with a few hours of telescope time. Measurements of the clusters’ motions and stars could help estimate galaxy masses and test explanations for their formation. These are anticipated capabilities, not reported observations.

Young explorerSome galaxies are very faint, and scientists want to know how much matter they hold and how they formed. Groups of stars inside them can give clues. Scientists describe a new tool they hope to put on a huge telescope to study those stars. The paper explains what the tool could do, not what it has already seen.

Why a Multi-Cycle Treasury Program is Essential to Maximize JWST's Scientific Contributions to Galaxy Formation

Genesis Community, Alice Shapley, Steven L. Finkelstein+97 more

• Astrophysics of Galaxies

AstronomerThis is a community survey proposal and advocacy statement, not a report of new observations or simulations. The Genesis Initiative coordinates extragalactic white papers responding to STScI's Multi-Cycle Treasury concept call. The authors argue that, despite unexpected early-universe discoveries during JWST's first five years, key mission goals remain unmet and a quantitative understanding of early galaxy formation requires uniform, statistically controlled legacy datasets beyond the current heterogeneous program portfolio. Citing Hubble's large surveys as a precedent, they advocate community-led JWST surveys of approximately 1,000–2,000 hours with uniform, well-characterized selection functions, which they argue cannot be accommodated within single-cycle programs. They urge STScI to open a Multi-Cycle Treasury channel while JWST's instruments remain at peak performance, with anticipated benefits for coordination with ALMA, Euclid, Roman, Rubin, and future facilities.

PublicThe Genesis Initiative is a community effort advocating large, coordinated observing programs with the James Webb Space Telescope. The authors say Webb's first five years have produced unexpected discoveries about the early universe, but important questions about the first stars and galaxies and their later evolution remain unanswered. They argue that the existing mix of smaller projects cannot provide the consistent, carefully selected galaxy samples needed to answer those questions. Drawing on the lasting value of Hubble's large surveys, they propose Webb surveys lasting roughly 1,000–2,000 observing hours and spanning multiple observing cycles. This is a recommendation for future observations, not a new discovery. The authors urge STScI to create a route for such programs while Webb's instruments are performing at their best and to strengthen connections with other observatories.

Young explorerThe Webb space telescope has found surprising things about galaxies long ago, but scientists still have lots of questions. A group of scientists wants Webb to spend a long time looking at galaxies in a carefully planned way, so the pictures and information are easier to compare. They hope this will help explain how the first galaxies grew into the kinds we see today. This is their plan for what to do next, not something they have already finished.

On the importance of medium-resolution continuum spectroscopy for JWST's extragalactic legacy

Adam C. Carnall, Ho-Hin Leung, Struan D. Stevenson+81 more

• Astrophysics of Galaxies

AstronomerThe authors advocate an extremely deep, medium-resolution JWST NIRSpec MSA survey of a large, representative galaxy sample at z > 1.5, prioritizing high-SNR continuum spectroscopy rather than emission-line detection alone. They argue that most archival NIRSpec observations are too shallow for this purpose and that no planned future instrumentation offers comparable capabilities. They present an empirically derived relation linking rest-optical continuum SNR, apparent magnitude, and exposure time, which they find to be independent of redshift and hence grating choice. Using this relation, they outline—not report results from—a 1000-hour survey targeting continuum SNR = 20 per pixel. The proposed data would constrain stellar ages, metallicities and kinematics, as well as neutral-gas properties and flows, informing studies of quenching, dynamical masses, merger histories, early star formation, reionization, and Little Red Dots. Sky subtraction is identified as critical to achieving the required continuum SNR.

PublicThis paper proposes a major investment of James Webb Space Telescope time to study the faint, broad background of light in distant galaxies’ spectra, rather than just their brighter emission lines. The authors argue that most existing NIRSpec observations are too shallow for this work and that no planned future instrument could replace Webb’s capabilities. Such deeper observations could help researchers estimate the ages, chemical makeup, and motions of stars, investigate gas moving into and out of galaxies, and understand why galaxies stop forming stars. To support planning, the team presents a relationship derived from data that connects the strength of the continuum signal relative to noise with galaxy brightness and observing time; they find this relationship does not depend on redshift. They use it to outline a 1000-hour survey, not to report a completed one. They also emphasize that carefully subtracting light from the sky is essential.

Young explorerThe authors want the Webb space telescope to spend a long time looking at many faraway galaxies. Instead of looking only at the brightest bits of their light, they want to see the much fainter light in between. That could help us learn how old their stars are and how stars and gas move around. They used existing measurements to help work out how long Webb would need to look, and they suggest a plan lasting 1000 hours. This is a plan, not a finished survey. They also say that light from the sky must be carefully removed from the measurements so the faint galaxy light is easier to see.

Detection of Differential Chromatic Refraction with LSST Camera data

Matthew J. Temple, Phoebe N. Lister

• Astrophysics of Galaxies

AstronomerUsing LSST camera commissioning observations released in Data Preview 2, the authors detect differential chromatic refraction (DCR) in galaxies and quasars in the COSMOS field. The atmosphere refracts blue light toward the zenith more strongly than red light, making airmass-dependent astrometric shifts sensitive to the wavelength distribution within a photometric passband. The authors show how this information can complement LSST’s six-band colours to help break degeneracies in extragalactic sample selection and photometric-redshift estimation. LSST’s planned repeated observations across a range of airmasses offer opportunities to exploit DCR; the authors caution against removing scientifically useful DCR information from future releases.

PublicEarth’s atmosphere bends blue light more than red light, so a distant object’s apparent position can shift slightly depending on its light’s colour mix and how much atmosphere the light passes through. Researchers detected this effect in galaxies and quasars using early LSST camera data from a sky region called COSMOS. They show how these shifts can add information beyond LSST’s six colour bands, helping distinguish objects with similar measured colours and estimate their redshifts. With LSST planned to observe each southern-sky location several hundred times through different amounts of atmosphere, the authors argue that future data releases should preserve this useful information.

Young explorerThe air around Earth bends blue light a little more than red light. This can make faraway things in space look as if they move a tiny bit when we look through more or less air. Scientists found this effect in early pictures from the LSST camera. They show how those tiny shifts could give extra clues about faraway galaxies and how far away they are. They want to keep those clues in future pictures, rather than erase them.

MapHub: Daily Relevance Heatmaps of New arXiv Preprints for a Research Community

Kaili Cao, Camille Avestruz, Feige Wang

• Digital Libraries
• Information Retrieval

AstronomerMapHub uses a large language model to assess daily arXiv submissions against participant-specific research portfolios, publishing relevance scores from 0 to 100 in a community heatmap. In the authors’ blind ratings, the highest-scoring 10% of papers contained about 70% of the raters’ own top 5%, pooled across raters, compared with about one-third for a text-matching baseline. For each participant, about 6% of a day’s astro-ph papers score at least 30, and roughly one paper every three days scores at least 60. These relevance results come from the authors’ ratings, not an independent community-wide evaluation. MapHub runs on a standard Claude subscription and is designed for use beyond astronomy.

PublicMapHub is an AI-based guide to new research papers. It compares each day’s arXiv submissions with profiles of researchers’ interests, then displays personalized relevance scores in a color-coded chart. In a blind test using the authors’ own judgments, its highest-ranked tenth of papers included about 70% of their pooled top favorites, versus about a third for a text-matching method. This measures agreement with those raters’ interests, not whether the papers are scientifically correct. The system runs on a standard Claude subscription and is intended to work across research fields.

Young explorerMapHub is a computer helper that looks at new science papers and suggests which ones each scientist might like to read. It shows its guesses with colors. When its makers tested it, its top choices included many of their favorite papers.

Preliminary Goniopolarimetric Simulations for Space Weather Radio (SWARA) Polarimeter

Poorva Singh, Mugundhan V., Anshu Kumari

AstronomerThis study explores goniopolarimetry, which uses electromagnetic-wave polarization to estimate direction of arrival, for the proposed Space Weather Radio (SWARA) Polarimeter, intended to support early warnings of space weather or solar events. Preliminary simulations examine a tri-monopole antenna across its field of view at varying signal-to-noise ratios. Simulated angular localization errors are used to assess the algorithm's sensitivity to galactic background noise; the abstract reports no quantitative performance results or observational validation. Planned work will optimize the monopoles' effective lengths for sensitivity, localization accuracy, and receiver impedance matching, then assess plasma effects through electromagnetic and plasma simulations.

PublicResearchers are exploring a way for a proposed instrument called the Space Weather Radio (SWARA) Polarimeter to determine where radio waves come from by using their polarization. The eventual aim is to help provide early warnings of space weather or solar events. So far, the team has run preliminary computer simulations of a three-element antenna, examining how its ability to locate signals changes with viewing direction and signal strength relative to noise, including noise from our galaxy. The abstract does not give numerical results or demonstrate an early-warning capability. Next, the researchers plan to refine the antenna elements and receiver matching, then simulate how surrounding plasma affects performance.

Young explorerScientists want to build a tool that could help warn us about events on the Sun and weather in space. It would use radio waves to work out which direction a signal comes from. So far, they have tried a three-part antenna in computer simulations, not shown that a real tool can give warnings. They explored how extra radio noise could make it harder to find a signal's direction. Next, they plan to improve the antenna design and use more computer tests to see how the charged particles around it might affect it.

GALI Localization of Off-Grid GRB Directions: A Comparison of Rectangular and Triangular Calibration Meshes

Julia Saleh-Natur, Ehud Behar, Omer Reich+6 more

AstronomerGALI localizes GRBs using count-rate modulations produced by internal shadowing in a three-dimensional scintillator array. An icosphere-based triangular calibration mesh samples the hemisphere more isotropically and improves interpolation relative to the previous rectangular mesh. Full-scale laboratory measurements give mean angular separations between inferred and true source directions of 0.86° ± 0.14° for the triangular mesh versus 1.19° ± 0.28° for the rectangular mesh. Monte Carlo simulations of 50,000 randomly distributed GRBs, each with 1000 detected counts under realistic low-Earth-orbit background conditions, yield 1.91° ± 1.20° and 2.73° ± 2.18°, respectively. The better laboratory performance is attributed partly to approximately 3–4 times more detected counts. Additional simulations indicate sensitivity from 10 keV to about 1 MeV and a peak effective area of about 130 cm² near 100–150 keV. Simulated degree-scale localization with a compact 1U implementation supports the concept's potential for CubeSat GRB and multi-messenger follow-up missions, rather than establishing in-orbit performance.

PublicQuickly finding where a gamma-ray burst came from helps other observatories follow it up. GALI estimates a source's direction from the pattern of signals created as parts of its detector array block radiation from reaching other parts. Researchers improved its calibration by replacing a rectangular grid of reference directions with a more evenly spread triangular grid. In laboratory tests, the average difference between the estimated and actual directions fell from 1.19° to 0.86°. Computer simulations of bursts under realistic orbital background conditions also favored the triangular grid, with average differences of 1.91° rather than 2.73°. The laboratory tests collected roughly three to four times as many signals, partly explaining their better accuracy. Simulations also suggest that a compact version could locate bursts to roughly a degree, pointing to possible use on small satellites; this is not yet a demonstration in orbit.

Young explorerGALI is a detector that could help scientists figure out where a flash of gamma rays came from in space. It uses a pattern of shadows inside it to work out which way to look. Scientists tried a new guide made of triangles instead of rectangles. Tests in the lab showed that the triangle guide helped it point closer to the right place. Computer tests showed improvement too, and suggested a tiny version might work on a small satellite. They have not shown that it works in space yet.

Design and Commissioning of the BURSTT-256 Main Antenna Array for the Fast Radio Burst Survey in the Local Universe

Shih-Hao Wang, Kai-Yang Lin, Chao-Te Li+36 more

AstronomerThis work reports the design, deployment, and commissioning of the BURSTT-256 main array in Taiwan, a pathfinder for wide-field surveys of nearby fast radio bursts (FRBs). Its 256 commercial log-periodic dipole antennas operate at 400–800 MHz, with a real-time factorized beamforming backend currently producing 256 beams over approximately 3200 square degrees. Observations of bright celestial calibrators have calibrated the on-sky performance, sensitivity, and beamforming fidelity; the initial array has a system equivalent flux density of approximately 11 kJy. Custom antennas and optimization are expected to reduce this to approximately 4 kJy in late 2026, rather than representing an achieved sensitivity. Smaller outrigger stations on baselines of order 100–1000 km are intended to enable sub-arcsecond FRB localization through very-long-baseline interferometry. Future expansion to at least 2048 elements would operate at 300–700 MHz over approximately 6000 square degrees. The paper establishes instrumental capabilities and a framework for FRB discovery and localization; it does not report FRB detections or demonstrated sub-arcsecond FRB positions. Identifying counterparts and constraining FRB origins remain scientific goals.

PublicA radio telescope array in Taiwan is being developed to find fast radio bursts, brief flashes of radio waves from space, and pinpoint where they come from. This paper describes the construction and testing of its first 256-antenna main array. It currently forms 256 observing beams covering about 3200 square degrees of sky, and observations of bright celestial radio sources have been used to check its performance. Smaller, distant antenna stations are intended to work with the main array to locate bursts very precisely. Improved antenna sensitivity is expected after optimization in late 2026, while a larger future array is planned to watch an even wider area. These are anticipated improvements, not results already achieved. The paper does not report finding or precisely locating any fast radio bursts. The longer-term aim is to help researchers find related signals and understand what causes the bursts.

Young explorerScientists in Taiwan have built a group of 256 antennas to listen for very short radio flashes from space. They tested how well it listens using bright radio sources in the sky. They want antennas far apart to work together to tell exactly where a flash came from. They also hope to make the telescope better and bigger. This report is about building and testing it, not about finding a new flash. One day, it may help scientists learn what makes these mysterious flashes.

Inertial sub-range detection and characterization for ground-layer turbulence at new extremely large telescope sites in Chile

Marco Sepúlveda, Darío G. Pérez

• Atmospheric and Oceanic Physics
• Data Analysis, Statistics and Probability

AstronomerUsing high-frequency sonic anemometer measurements from GMT and TMT site-testing campaigns in Chile, the authors apply detrended fluctuation analysis (DFA) to identify the atmospheric boundary layer’s inertial subrange and assess statistical isotropy, comparing it with the Fourier-based ARIIS algorithm. Simultaneous isotropy and Kolmogorov k^-5/3 scaling across all measured fields occur in fewer than 7% of observations. Under stable stratification, temperature systematically decouples from velocity and exhibits nighttime Bolgiano–Obukhov k^-7/5 scaling, interpreted as active rather than passive scalar behavior. DFA-detected transitions correlate with characteristic turbulence scales, providing model-free inertial-subrange boundaries. K41-based structure-function estimates of C_n^2 differ significantly from flux-based parameterizations under stable conditions; this comparison does not establish which estimate is correct. The findings motivate stratification-aware optical turbulence characterization for extremely large telescope facilities.

PublicMeasurements at the GMT and TMT telescope sites in Chile show that near-ground atmospheric turbulence often fails to follow a standard model used to characterize turbulence for astronomy. The model’s strict requirements were met in fewer than 7% of observations. In stable nighttime conditions, temperature fluctuations followed a different pattern from air motion, suggesting that temperature actively influences the turbulence rather than simply being carried along by it. The researchers used a method for analyzing fluctuations to identify transitions between turbulence regimes. They also found that two approaches to estimating optical turbulence disagreed substantially under stable conditions, without establishing which was correct. They argue that methods accounting for atmospheric stability are needed.

Young explorerScientists measured moving air and changing temperatures at two places chosen for big telescopes. The air usually did not follow the simple pattern scientists often use to describe it. On calm, stable nights, temperature changes behaved differently from the moving air. The scientists think telescope teams need ways to describe the air that take these differences into account.

The infrared unmodulated pyramid wavefront sensor: simulations, lab and on sky

Muskan Shinde, Nicolas Blind, Isaac Dinis+13 more

AstronomerThis study evaluates a three-sided, unmodulated infrared pyramid wavefront sensor for extreme adaptive optics using end-to-end simulations, laboratory tests, and PAPYRUS observations at OHP. Infrared operation extends the sensor’s linear range, allowing modulation to be removed; the three-sided geometry avoids the classical four-sided pyramid’s roof defect. Simulations reached Strehl ratios of approximately 60% at 1400 nm for seeing up to 4 arcseconds, with improved linearity, reduced optical-gain variations, and less modal cross-talk. Laboratory tests supported the simulations and confirmed pyramid quality. On sky, stable closed-loop operation was achieved over three nights. The infrared sensor running at 1000 Hz, compared with a visible modulated sensor at 500 Hz, delivered approximately 1.63 times the Strehl ratio, 1.26 times the encircled energy, and a factor of 2.03 reduction in residual wavefront error. It tolerated tip-tilt offsets up to 3 lambda/D at 1400 nm. The comparison includes a loop-speed difference: removing modulation enabled faster operation, which contributed to the observed improvement. Similar dimensionless turbulence strengths at OHP and typical VLT conditions support relevance to VLT/RISTRETTO, but performance there remains prospective.

PublicPhotographing Earth-like planets around other stars requires suppressing bright starlight and correcting atmospheric blur. Researchers tested an infrared sensor that measures the distortions needed for those corrections without the extra motion, called modulation, used by a visible-light comparison sensor. Simulations suggested reliable performance, and laboratory tests supported them. During three nights of telescope observations, the infrared system maintained stable correction. Running at 1000 updates per second versus 500 for the visible system, it produced a more concentrated image and reduced the remaining wavefront error by about a factor of two. The faster correction contributed to the improvement, so this was not a comparison at equal operating speeds. The results make the design promising for future planet-imaging systems; they do not demonstrate an image of an Earth-like planet.

Young explorerAir above a telescope can make a star look blurry. Scientists tested a special helper that uses infrared light to tell the telescope how to fix the blur. It worked steadily on three nights and, while working faster, made sharper pictures than the helper they compared it with. It might help telescopes look for faint planets someday, but this test did not take a picture of an Earth-like planet.

Mitigating scanning-induced systematics in Hipparcos and implications for Gaia astrometry

Avraham Binnenfeld, Sahar Shahaf, Richard I. Anderson+2 more

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies

AstronomerOne-dimensional scanning couples astrometric measurements to observation time and scan geometry, potentially introducing spurious periodicities. The authors present a non-parametric extension of the phase-distance correlation (PDC) periodogram that quantifies and reduces scan-angle dependence during period searches. In Hipparcos data, the scan-angle-controlled statistic strongly suppresses recurrent periodicities associated with characteristic scanning-law timescales. In Gaia DR4 prerelease epoch astrometry, it suppresses a recurrent approximately 54-day feature across multiple sources while retaining detectability of independently known orbital signals. The method offers a diagnostic and mitigation of scan-geometry effects, rather than a guarantee that every remaining period is astrophysical. It is relevant to anticipated large-scale companion searches using public Gaia DR4 epoch astrometry; no new companion discoveries are reported in the abstract.

PublicThe way a space telescope scans the sky can create repeating patterns in its measurements that complicate searches for real orbital motion. The researchers developed a statistical method to identify and reduce patterns linked to scanning direction. Tests with Hipparcos observations strongly reduced recurring patterns associated with the satellite’s scanning schedule. In prerelease Gaia DR4 position measurements, the method also reduced a roughly 54-day pattern seen in several sources, while signals from independently known orbits remained detectable. This could help future searches for companions, from exoplanets to dormant black holes, using public Gaia DR4 measurements. These tests do not report new companions or establish that every surviving pattern is real.

Young explorerA space telescope looks at the sky again and again. The way it turns to look can make a star seem to repeat a little wiggle. Scientists made a new way to check for wiggles caused by the telescope’s looking pattern. When they tried it on telescope measurements, those patterns became weaker, but wiggles from already-known orbits could still be found. This may help people look for hidden companions to stars, but it does not mean they have found new ones yet.

Polarization cross-talk from non-stationary sources of image jitter

R. Casini, A. G. de Wijn

• Solar and Stellar Astrophysics

AstronomerThe authors extend a formalism for estimating seeing-induced polarization cross-talk to non-stationary, generally non-isotropic image jitter. They show that the extended formalism approaches the previous formulation in the stationary limit and compare their predictions for non-stationary processes. The demonstration starts with a power-spectral density derived from a circulant autocorrelation function, representing stationary random processes periodic over the time-series length, then introduces off-diagonal spectral features at different frequencies. These constructed examples test the modeling framework rather than report observational measurements.

PublicAtmospheric disturbances can make astronomical images wobble, mixing signals in measurements of light’s polarization. This study extends a mathematical method for estimating that mixing to cases where the wobble’s statistical behavior changes over time and can differ by direction. The extended method approaches the earlier method when the wobble’s statistics remain steady. The authors compare the methods using deliberately constructed examples of changing wobble, rather than new observations.

Young explorerAir can make a picture of the sky wiggle, which can mix up special clues carried by light. The researchers made a math tool for figuring out that mix-up even when the wiggles change over time or differ by direction. They tested it with made-up wiggle patterns, not new pictures of the sky.

Tensor Networks for Block Adaptive Thermal Radiation Transport

Alex A. Gorodetsky, Patrick D. Mullen, Aditya S. Deshpande+4 more

AstronomerThis computational-methods paper combines block-adaptive mesh refinement (AMR) with block-local tensor-train representations of photon specific intensity for thermal radiation transport. Localizing the tensor decomposition confines rank growth from spatially localized, nonseparable structure rather than allowing it to affect the entire domain. The framework includes conservative ghost-cell transfer, coarse-fine flux correction, and refinement criteria that balance spatial discretization and tensor-rounding errors. Numerical experiments resolve localized features while maintaining low-rank structure across much of the domain, with compression factors exceeding approximately 1,000. These are numerical demonstrations, not observational results; the framework provides a foundation for tensor-network transport on the multiscale meshes used in radiation hydrodynamics simulations.

PublicCalculating how thermal radiation travels is demanding because a computer must track light across positions, directions, and frequencies. The authors introduce a method that combines a finer computational grid where detail matters with a compact mathematical representation of the radiation within each grid block. Keeping these representations local helps prevent a complicated feature in one region from making the whole calculation harder to compress. In numerical tests, the method resolved localized features while keeping much of the domain compactly represented, achieving compression factors greater than about 1,000. The work develops a tool for radiation simulations rather than reporting observations of space; how well it compresses depends on the structure of the calculated radiation field.

Young explorerWorking out how heat travels as light can give a computer lots to keep track of. The researchers made a method that divides a pretend space into boxes, adds smaller boxes where more detail is needed, and packs the light information in each box neatly. A tricky part in one box does not have to make every other box tricky too. In computer tests, the method kept small details while packing much of the information into less space. These were computer tests, not pictures or measurements of real stars.

Analytic Marginalization Over Calibration Uncertainties in Gravitational Wave Inference and Application to Black Hole Ringdown

David Dzingeleski, Aaron Zimmerman

• General Relativity and Quantum Cosmology

AstronomerThe authors extend frequency-domain calibration marginalization to the time domain using basis splines, allowing analytic marginalization, and apply it to ringdown analyses of GW250114 and GW250207, the two highest-signal-to-noise events detected so far. For GW250114, strong evidence for two ringdown modes persists after accounting for the small calibration uncertainty. For GW250207, uncertain LIGO-Hanford calibration makes marginalization necessary for a coherent two-detector analysis. Including calibration effects brings the ringdown remnant-mass and spin inferences into agreement with full-signal inferences. Despite this event's high signal-to-noise ratio, no evidence for a second ringdown mode is found, leaving deviations from relativity during ringdown poorly constrained.

PublicGravitational-wave detectors have small uncertainties in how their measurements are calibrated, which can affect the properties inferred from a signal. The researchers developed a mathematical method to account for these uncertainties when studying black hole ringdown, the fading vibrations following a merger. In GW250114, strong evidence for two distinct vibration patterns remains after calibration uncertainty is included. In GW250207, accounting for uncertain calibration at the LIGO-Hanford detector is necessary to analyze both LIGO detectors consistently. With this correction, estimates of the final black hole's mass and spin from its ringdown agree with estimates from the full signal. However, the analysis finds no evidence for a second vibration pattern in GW250207, despite its strong signal, so it cannot tightly limit possible departures from relativity during ringdown.

Young explorerAfter black holes join together, the new black hole can wobble and settle down, a little like a bell after it is struck. Scientists study these wobbles, but their measuring tools are not perfectly certain. They made a new way to allow for that uncertainty. For one signal, called GW250114, they still found strong clues for two kinds of wobble. For another, called GW250207, allowing for the tool's uncertainty made estimates of the black hole's size in mass and how fast it spins match estimates from the whole signal. They did not find clues for a second kind of wobble in that signal, so it could not give a very strict check of Einstein's rules.

Quantum Noise Engineering in Advanced LIGO

Begüm Kabagöz

• Quantum Physics

AstronomerThis review describes quantum noise in Advanced LIGO using complex optical fields and quadratures. Vacuum fluctuations entering the interferometer readout port contribute phase-like measurement imprecision and amplitude-like radiation-pressure back-action. It follows squeezed vacuum from generation through the filter cavity and interferometer to readout, explaining how frequency-independent and frequency-dependent squeezing shape quantum noise and how optical-quadrature correlations translate into correlations between imprecision and back-action. Rather than reporting a new measurement, the review presents LIGO as both a gravitational-wave observatory and a kilometre-scale platform for quantum measurement science.

PublicAdvanced LIGO detects gravitational waves with such sensitivity that quantum fluctuations in light affect its measurements. This review explains two effects: fluctuations that make the measurement less precise, and fluctuations that cause light to exert a varying push on the detector’s mirrors. It traces how specially prepared light, called squeezed vacuum, travels through the instrument and helps control this quantum noise. The article is an explanation of these principles, not a report of a new detection, and highlights LIGO’s role in studying quantum measurement as well as observing gravitational waves.

Young explorerLIGO is a giant machine that uses light to look for tiny ripples in space. Even when scientists are very careful, tiny quantum wiggles can make its measurements fuzzy or change how the light pushes its mirrors. This article explains how scientists prepare the light in a special way to help control those wiggles. It explains how the machine works, rather than announcing a new discovery.

A Theory of Partial Truth for Scientific Statements

Gustavo E. Romero

• History and Philosophy of Physics

AstronomerThis paper develops a restricted formal framework for assessing partial factual adequacy in scientific representations, rather than classifying them simply as true or false. Quantitative claims receive valuations based on normalized discrepancies between asserted and empirically supported values; admissible finite conjunctions are evaluated over distinct elementary claims using arithmetic or relevance-weighted means. These valuations preserve accurate components and are independent of grouping when component counts or total weights are retained. Zero-relevance additions do not change the contextual valuation, although positive-relevance components can compensate for one another. Worked examples explore admissibility, granularity, measurement indeterminacy, and sensitivity to discrepancy scales and weights; an astrophysical application connects the framework to published observations. The target is adequacy to facts under fixed content and valuation criteria, but evidence-based estimates remain fallible. The framework supports conditional comparisons of selected testable consequences, not a calculus for arbitrary formulas or a unique choice of scales and weights, and distinguishes adequacy from confidence, empirical coverage, and convergence toward complete truth.

PublicA scientific description can get some things right and others wrong. This paper develops a limited mathematical framework for assessing that mixture instead of assigning a single true-or-false label. It compares numerical claims with values supported by evidence, then averages the assessments of distinct claims, optionally giving more relevant claims greater weight. Correct parts still contribute, but stronger agreement in one relevant part can offset weaker agreement in another. Worked examples examine how measurement uncertainty, the way claims are divided, and the choice of scales and weights affect comparisons. An astronomy application links the framework to published observations; the abstract does not report a new astronomical finding. The assessments remain fallible and conditional on the choices made. They address selected testable claims, not every possible statement, and do not measure confidence, how much evidence a theory covers, or progress toward a complete truth.

Young explorerA science explanation can have some parts right and some parts wrong. This paper describes a way to give its testable parts scores and put those scores together, sometimes letting more important parts count more. It uses examples, including one connected to things astronomers have observed. But the scores can still be mistaken, and changing how the scoring works can change the comparison. It is a tool for comparing some parts of explanations, not a way to know the whole truth.

First broadband search for fixed-polarization dark photon dark matter with GigaBREAD

Jialin Yu, Stefan Knirck, Gabe Hoshino+4 more

• High Energy Physics - Experiment
• High Energy Physics - Phenomenology
• Instrumentation and Detectors

AstronomerThe authors report the first search for fixed-polarization dark photon dark matter at masses of 44–52 μeV, corresponding to 10.7–12.5 GHz, by reanalyzing GigaBREAD data. This room-temperature broadband dish experiment uses a cylindrical metallic emission surface to convert dark photons into ordinary photons and focus them onto a radio-frequency receiver. Unlike earlier analyses assuming random polarization, the polarization-matched likelihood accounts for the time-dependent projection of a fixed polarization onto the detector axis as Earth rotates. Such approximately fixed polarization may arise from a misalignment-like production mechanism. No evidence for a signal is found. Upper limits on kinetic mixing reach χ ∼ 10⁻¹², about 20% better than a naive rescaling of the previous GigaBREAD limit under the fixed-polarization assumption.

PublicResearchers reexamined data from GigaBREAD to look for hypothetical dark matter particles called dark photons whose polarization stays approximately fixed in space. If dark photons have this property, Earth's rotation would change the detector's response over time. GigaBREAD searches for ordinary light that dark photons could produce at a metal surface, focusing it onto a radio receiver. The new analysis searched a mass range of 44–52 microelectronvolts and found no evidence of a signal. It placed upper limits on how strongly dark photons mix with ordinary photons, at about 10⁻¹². These limits are about 20% stronger than a simple adjustment of the experiment's previous limits for fixed polarization; they are not a detection of dark matter.

Young explorerScientists looked again at measurements from a machine that listens for tiny light signals that a possible kind of invisible matter might make. They checked what might happen if this matter kept pointing the same way while Earth turned. They did not find a signal. Their search helps narrow down how strongly this possible matter could connect with light, but it does not show that the matter is there.

Triaxial μ-PIC for resolving Multi-Hit Ambiguity

A. Takada, M. Abe, Y. Yoshida+6 more

• Instrumentation and Detectors
• High Energy Physics - Experiment
• Nuclear Experiment

AstronomerThe authors designed a triaxial micro pixel chamber (μ-PIC) using Garfield++ simulations and fabricated it with through-glass-via technology. A third readout axis addresses the multi-hit ambiguity of conventional orthogonal-strip μ-PICs when reconstructing winding tracks or operating at high rates. The fabricated detector achieved a gas gain of 1.1 × 10^4 and 22% FWHM energy resolution at 5.9 keV. For two clusters separated by more than 3 mm, the false-hit probability was below 0.78% at 95% confidence, consistent with the simulations. Individual avalanche signals were collected by three independent strip electrodes, with a nearly constant anode:U-cathode:V-cathode charge ratio of 3:2:1. An alternative operating mode achieved a gain of 3.2 × 10^4 without increasing the discharge risk.

PublicResearchers built and tested a gas-based particle detector designed to reduce confusion when several signals occur together. Conventional versions read signals along two perpendicular directions, which can leave uncertainty about where the signals originated. The team used computer simulations to design a version with a third readout direction, then manufactured and tested it. For two signal clusters more than 3 millimetres apart, the probability of a false hit was below 0.78% at a 95% confidence level, agreeing with the simulations. The detector also amplified signals by a factor of 11,000 and achieved an energy resolution of 22% at the tested energy of 5.9 kiloelectronvolts. A different operating mode increased the amplification to 32,000 without increasing the risk of an electrical discharge.

Young explorerScientists made a detector that uses gas to help spot tiny particles. The old design could get mixed up when several signals appeared together. The new one reads signals in three directions instead of two, like using an extra clue to find where something happened. Computer tests helped the scientists plan it, and then they built and tested a real one. It rarely made a false mark in a test with two groups of signals that were far enough apart. They also found a way to make its signals stronger without making electrical sparks more likely.

Fast far-sidelobe modeling for centimeter to sub-millimeter astrophysical observations

Oliver Jeong, Jacques Delabrouille, Michel Piat

AstronomerThe authors present a diffraction-based beam-modeling method intended to reduce the computational cost of predicting far-sidelobe response for centimeter-to-submillimeter telescopes, where instrumental control is important for faint signals such as CMB B modes. Applied to BICEP3, the model shows good qualitative agreement with in situ beam measurements; the abstract does not establish quantitative accuracy. The simulated beam is then used to calculate sidelobe temperature pickup for a scan near the slopes of Cerro Toco in the Atacama Desert, rather than reporting a measured pickup. The framework is presented primarily as a predictive tool for optimizing baffling and scan strategies during conceptual instrument design.

PublicTelescopes seeking faint signals, such as particular polarization patterns in the cosmic microwave background, must control unwanted signals entering from directions far from where they are pointed. The researchers developed a diffraction-based way to model this response more quickly and cheaply than existing electromagnetic calculations. Their model of the BICEP3 telescope agreed qualitatively with measurements made at the instrument, though the abstract does not report a numerical accuracy. They then used the model to predict unwanted temperature signals during a scan near the slopes of Cerro Toco in Chile’s Atacama Desert. The main proposed use is to help designers choose shielding and observing paths before an instrument is built.

Young explorerA telescope can pick up things from the sides, not just from where it is looking. That makes very faint things in space harder to study. The researchers made a faster computer model to work out what might sneak in from the sides. For a telescope called BICEP3, the model looked broadly like real checks of the telescope. They also used it to predict what the telescope might pick up while looking near mountain slopes. The model could help people plan shields and choose where to point future telescopes.

High-frequency water megamasers as precision probes of black holes, galaxies and cosmology: A case for a next-generation sub-mm/mm interferometer

Ingyin Zaw, C.M. Violette Impellizzeri, Dominic W. Pesce+8 more

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies

AstronomerThis paper makes the case for ALMA2040, a proposed next-generation sub-mm/mm interferometer, rather than reporting new maser measurements. Existing 22 GHz VLBI disk-maser observations provide geometric distances, constraints on H0, black hole masses, and sub-parsec disk geometry. ALMA observations of higher-frequency water maser transitions probe physical conditions and disk regions inaccessible at 22 GHz, with higher spatial resolution and less free-free absorption, but detections remain limited to a few bright extragalactic sources in nearby galaxies. The authors argue that tenfold better line sensitivity and baselines three times longer than ALMA's would enable population-level studies and black hole masses and geometric distances from sub-mm masers alone. They further project that incorporation into a VLBI array would resolve maser disks beyond 160 Mpc, extend maser-based mass measurements into the largely untested intermediate-mass black hole regime, probe disk magnetic-field structure through polarization, and test systematics in H0 measurements. These capabilities are forecasts for the proposed facility, not demonstrated results.

PublicWater molecules in disks around active galactic nuclei can produce intense microwave emission called masers. Astronomers already use 22 GHz masers to measure black hole masses and galaxy distances, helping constrain how fast the universe expands. ALMA can detect water masers at higher frequencies that reveal different conditions and regions within these disks, but current detections are limited to a few bright examples in nearby galaxies. This paper proposes ALMA2040, an interferometer with ten times ALMA's sensitivity to spectral lines and three times its antenna separations. The authors argue that these improvements could turn a handful of detections into studies of a broader population and provide independent black hole masses and distances. Combined with a very long baseline telescope array, the proposed facility is projected to distinguish disk structure beyond 160 megaparsecs, study black holes in the largely untested intermediate-mass range, investigate disk magnetic fields, and check for systematic errors in measurements of cosmic expansion. These are proposed capabilities, not new observational findings.

Young explorerWater near some black holes makes very bright signals that telescopes can see. Scientists already use some of these signals to help work out how heavy black holes are and how far away galaxies are. This paper describes an idea for a better telescope called ALMA2040. The scientists think it could find many more water signals and show more details around black holes. Working with other telescopes, it might also help them study magnetic fields and check how fast the universe is growing. These are things they hope the telescope could do, not things it has done yet.

Robust statistical significance for Gravitational Wave inference

Alexandre Sébastien Göttel

• General Relativity and Quantum Cosmology

AstronomerThis study applies evidence networks, amortized neural estimators of Bayes factors, to gravitational-wave model comparison and population inference. Their low-cost estimates enable empirical Bayes-factor distributions under different signal assumptions, allowing calibration of observed model preference against its frequency under a null hypothesis. In a simulated-Gaussian-noise search for orbital precession, the method gives results compatible with current stochastic-sampling approaches. In a simplified population example, it recovers injected isotropic-spin population fractions without discernible bias for up to 10^4 events, addressing the accumulation of stochastic-sampling errors in population analyses. These are simulation-based demonstrations, not claims of precession detection in observed signals. Because the method requires no explicit likelihood evaluations, the authors identify a route toward likelihood-free analyses without Gaussian, stationary noise assumptions; that broader capability is a proposed extension rather than a demonstrated result here.

PublicResearchers tested a neural-network method for comparing explanations of gravitational-wave signals. A comparison score called a Bayes factor measures which explanation the data favor, but does not by itself say how often an equally strong preference would occur if the proposed feature were absent. The method makes repeated comparisons affordable enough to estimate that frequency. In tests with simulated Gaussian noise, a search for orbital precession agreed with established, more computationally costly methods. A separate simplified test recovered the input proportion of a population with randomly oriented spins without detectable bias, for groups of up to 10,000 events. These are simulated tests, not new astronomical detections. The approach could eventually support analyses with more general noise, but that extension has not been demonstrated here.

Young explorerScientists taught a computer to compare two explanations for gravitational-wave signals. They tested it with made-up signals and noise, not a new discovery in the sky. It agreed with another method and did well in a simple test with many signals. It can help scientists check how often noise might make one explanation look convincing.

von Neumann Stability Analysis of Braginskii MHD: Thermal Conduction, Viscosity, Magnetic Diffusion, and Thermoelectric Effects; and an Implementation in Athena++

Alexandra F. Albery, Julian M. Pittard

AstronomerAthena-Aniso is a fork of the finite-volume MHD code Athena++ that implements fully anisotropic thermal conduction, including the Righi–Leduc effect; all five Braginskii viscosity tensors; the Hall effect; and Peltier, Seebeck, Nernst, and Ettingshausen thermoelectric effects. Transport contributions can be weighted by ionisation fraction, with isotropic diffusion for the neutral component, and isotropic bulk viscosity is added. The Biermann battery is not implemented. Dissipative terms support super-time-stepping, while non-dissipative terms are combined with the ideal-MHD flux. The authors derive and implement a CFL condition using von Neumann analysis, finding stability with first-order time integration for dissipative terms and third-order integration for non-dissipative terms. New signal speeds for a modified HLLE solver suppress remaining grid-scale nonlinear instabilities in the non-dissipative terms. The Nernst/Ettingshausen system is found to be ill-posed unless both perpendicular thermal conduction and perpendicular magnetic diffusion stabilise it; a well-posedness criterion is derived. Each implemented effect is numerically tested against derived analytical solutions. These are numerical-method developments and tests, not astronomical observations.

PublicThe authors present Athena-Aniso, an extension of software used to simulate gas and magnetic fields in astrophysics. It adds ways for heat, momentum, and electrical effects to behave differently in different directions, along with several interactions between heat and electricity. It can also account for gas that is only partly ionised. The paper develops rules for choosing stable simulation time steps and modifies the numerical solver to suppress instabilities at the scale of the computational grid. An important limitation is that the coupled Nernst and Ettingshausen effects require both heat conduction and magnetic diffusion perpendicular to the magnetic field to make the equations well-posed. The authors derive a criterion for this and test each implemented effect against mathematical solutions. The work concerns simulation methods, not new observations of space, and it does not include the Biermann battery effect.

Young explorerThe researchers made a new version of a computer program for pretending how gas and magnetic fields move in space. It lets heat and other things in the gas move differently in different directions. They checked the program’s calculations against answers worked out with maths. They also found that some parts need special care so the pretend gas does not develop unwanted wiggles or give unreliable answers. This is a tool for computer experiments, not a new discovery seen through a telescope.

Towards LLM-Powered Automation of a Dark Matter Constraint Repository

Lanqing Yuan, Karthik Ramanathan

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

AstronomerThe authors present an LLM system to help maintain dark matter constraint repositories by monitoring arXiv, extracting limit curves from figures, converting them into repository code, and opening pull requests for human review. They evaluate a tool-using agent that interprets physical conventions and checks its output against a fixed multi-channel pipeline on a 329-paper benchmark, using an upstream-curated repository as the reference. Success requires more than 90% overlap in mass ranges and at least 90% of compared values agreeing within a factor of two. For Fable 5, the agent succeeds on 52.6% of eligible curve comparisons, versus 20.9% for the pipeline. These are extraction-performance results, not new dark matter constraints. The deployed pipeline has submitted limit proposals, but none have merged; governance of AI-generated scientific data remains unresolved.

PublicCollections of published dark matter limits help researchers track results, but widely used collections depend on volunteers. Updating them is difficult because limits often appear only as plots rather than downloadable numerical data. The authors developed an AI system to find papers, read their curves, and propose updates for people to review. In a test involving 329 papers, an AI agent that could use tools and check its work performed better than a fixed processing pipeline: 52.6% versus 20.9% of eligible curve comparisons passed the authors’ test. Passing required close agreement in the covered mass range and agreement within a factor of two for most compared values, so it did not mean exact copying. The deployed pipeline has proposed updates, but none have been accepted into the repository. How to govern AI-generated scientific data remains unresolved.

Young explorerScientists keep collections of charts about dark matter, and volunteers work to keep them up to date. The researchers made a computer helper that tries to copy chart information from new science papers and asks people to check it. In their test, a helper that could use tools and check its work did better than one that followed fixed steps, but it still made mistakes. The helper using fixed steps has suggested updates to the collection, but none have been accepted yet. People still need to work out how to handle science information made by AI.