Tonight’s sky of new research

De-lensing cosmic birefringence with joint reconstruction

Sebastian Belkner, Julien Carron

AstronomerThe study jointly reconstructs lensing gradient and curl modes and anisotropic cosmic birefringence at the maximum-a-posteriori point, with reconstructed spectra serving as near-optimal statistics. It analytically predicts the joint response and noise, validates these predictions in simulations, and demonstrates unbiased amplitude inference. The approach addresses lensing B-mode sample variance and partial degeneracy with lensing curl. At SPT-3G+ depths, the authors predict fivefold smaller errors than quadratic estimators through removal of lensing B-polarization sample variance, potentially tightening constraints on parity-violating new physics. This is a methodological and simulation-based forecast, not an observational detection.

PublicResearchers have tested a method for looking for direction-dependent rotation of the cosmic microwave background’s polarization, an effect called cosmic birefringence that could help constrain new physics. The method estimates this rotation together with two components of gravitational lensing, which can obscure or partly mimic the signal. Analytical predictions for the method’s response and noise were checked using simulations, which also showed amplitude estimates without systematic bias. For observations reaching SPT-3G+ sensitivity, the authors predict uncertainties five times smaller than those from quadratic estimators, by removing a source of uncertainty from lensing. The abstract reports a forecast, not a detection of cosmic birefringence.

Young explorerScientists want to see whether light left over from the early universe has had its polarization, a bit like an arrow it carries, turned by different amounts in different parts of the sky. Gravity can bend the light and make this hard to figure out. They tested a new way to untangle these effects using computer-made skies. They predict it could make the answer five times less uncertain than an older method when used with observations as sensitive as those planned for SPT-3G+. They have not reported finding the turning in the real sky.

The formation of the first cosmic structures in hybrid Milgromian cosmology

Tomas Ondro, Nikolaos Samaras

AstronomerThe authors compare hydrodynamical simulations of fiducial ΛCDM, a progenitor νHDM cosmology, and an optimized νHDM variant using RAMSES and Phantom of RAMSES. The hybrid models combine MOND dynamics for density perturbations with standard FLRW background expansion and a hypothesized approximately 11 eV/c² sterile neutrino as hot dark matter, allowing initial conditions that fit the third peak of the Planck CMB power spectrum. Their first comparison of the simulated total matter power spectra across redshifts probes differences in the onset and evolution of structure formation. At late times, z ≲ 1, the MOND–sterile-neutrino models exceed ΛCDM matter power on all collapsing scales. Density and velocity fields also show distinct differences between the gravity prescriptions. Comparison with joint estimates from Planck, DES Y1, SDSS, and eBOSS suggests excess power in the hybrid models at the associated resolution scales. The authors acknowledge the model dependence of those observational estimates but interpret the apparent excess as arising from the hybrid cosmologies’ design; these are simulation findings, not a detection of sterile neutrinos.

PublicThis study uses computer simulations to compare the standard cosmological model with two alternatives that combine modified gravity with a hypothetical lightweight particle called a sterile neutrino. The researchers track how matter becomes clumped as the universe evolves. At relatively late cosmic times, both alternative models produce more clumping than the standard model on all scales where matter is collapsing. Their simulated density and motion patterns also differ. Comparisons with combined astronomical data suggest that the alternatives may produce too much clumping at the scales examined. However, the estimates drawn from those data depend on the cosmological model used to interpret them. The study tests the consequences of the proposed models; it does not establish that sterile neutrinos exist.

Young explorerScientists made computer versions of the universe to see how matter gathers into clumps. They tried the usual rules and different rules with a particle that might exist. Later in the computer universes, the different rules made more clumping. That may be too much compared with what astronomers infer from the sky, but the comparison is not certain.

3D dark matter map of the JWST COSMOS-Web field using diffusion-based generative priors

Diana Scognamiglio, Brandon Zhao, Katherine L. Bouman+17 more

• Machine Learning

AstronomerThe authors reconstruct the three-dimensional matter distribution in the 0.54 deg² COSMOS-Web field using deep JWST weak-lensing imaging with an effective source density of 121 galaxies arcmin⁻². A physical lensing forward model combined with a diffusion-based Bayesian generative prior trained on cosmological simulations yields posterior samples across 20 lens planes out to z ≃ 2, doubling the redshift reach of previous HST-based 3D reconstructions. The inferred maps separate structures overlapping in projection and recover non-Gaussian structure over multiple spatial scales, including overdensities associated with independently identified galaxy clusters absent from earlier weak-lensing maps. Posterior sampling represents uncertainty in the inferred matter distribution rather than a unique map. Null and simulation-based tests support a lensing origin for the recovered structures and consistency with the fiducial ΛCDM cosmology; the reconstruction nevertheless incorporates a simulation-trained prior. The work demonstrates a route toward probabilistic mapping of the evolving cosmic web with current wide-field lensing surveys.

PublicResearchers used deep James Webb Space Telescope images to infer a three-dimensional map of matter, including dark matter, in the COSMOS-Web field. They used weak gravitational lensing—the subtle distortion of distant galaxy images by intervening matter—to distinguish structures at different distances that overlap in a flat map. Their method combines a physical model of lensing with a statistical model trained on cosmological simulations. The reconstruction reaches roughly twice as far in redshift as earlier Hubble-based 3D maps, approaching an era of rapid galaxy growth. It identifies concentrations of matter associated with independently known galaxy clusters that earlier lensing maps missed. Rather than offering one certain picture, the method produces a range of possible maps compatible with the observations and its modeling assumptions. Tests support the structures being traced by the lensing signal and show consistency with the study’s assumed standard cosmological model.

Young explorerSome matter in space is invisible, but its gravity can slightly change how faraway galaxies look. Scientists used pictures from the James Webb Space Telescope to help work out where that matter might be. Their map helps tell apart things that look piled on top of each other but are really at different distances. A computer learned patterns from pretend universes to help make the map. The scientists made many possible maps because they cannot know exactly where everything is. Their checks suggest the patterns in the maps come from real clues in the pictures.

Measuring the ultraviolet background at z≃3 from the quasar proximity effect in DESI DR1

Patrick Shaw, Rupert A. C. Croft

AstronomerUsing 6,245 DESI DR1 quasars at 2.75 ≤ z < 3.25, the authors infer the UV-background hydrogen photoionization rate from the line-of-sight Lyα proximity effect. The sample requires M1450 ≤ −25.5 and signal-to-noise ratios ≥ 3 redward of Lyα. They reconstruct continua with principal component analysis trained on Hubble Space Telescope spectra and fit stacked transmission profiles with a halo model incorporating both quasar-induced absorption suppression and enhanced absorption in overdense environments. Independent quasar clustering-bias measurements constrain the environmental contribution. Mock spectra from the Astrid hydrodynamical simulation at z = 3, matched to the sample’s luminosity and noise properties, test recovery of known input rates and calibrate the observational inference. The resulting rate at z ≃ 3 is ΓHI = (1.376 +0.095/−0.076) × 10⁻¹² s⁻¹, with statistical errors from bootstrap resampling of DESI sightlines. The separately estimated systematic uncertainty, +0.837/−0.521 × 10⁻¹² s⁻¹, is substantially larger than the statistical uncertainty.

PublicThe authors use light from 6,245 quasars in DESI’s first data release to estimate how quickly the ultraviolet glow between galaxies ionizes hydrogen at a redshift of about 3. Quasars themselves ionize nearby hydrogen, making that gas absorb less light. The team models this reduced absorption while accounting for the extra absorption caused by denser gas around quasars. They test and calibrate their analysis using simulated spectra before deriving the rate from the real observations. Their inferred rate is 1.376 × 10⁻¹² ionizations per second per neutral hydrogen atom. The statistical uncertainty is +0.095/−0.076 × 10⁻¹² per second, but the estimated systematic uncertainty is much larger: +0.837/−0.521 × 10⁻¹² per second. Thus, the precision suggested by the statistical errors alone does not capture the full uncertainty.

Young explorerSpace has gas and a glow of light we cannot see with our eyes. Scientists studied light from very bright objects called quasars to learn about that glow. Near a quasar, the gas blocks less light because the quasar’s light changes the gas. The scientists used those clues, checked their method with computer-made pretend observations, and estimated how quickly the space glow changes hydrogen gas. Their answer is not exact, and some uncertainties are much bigger than others.

Stress-Testing Small-Scale Cosmological Inference With Empirical Galaxy--Halo Connection Models

Hanyue Wang, Kate Storey-Fisher, Philip Mansfield+4 more

AstronomerThis simulation-based study compares SHAM and HOD models as tools for inferring cosmology from small-scale galaxy clustering. Using the Aemulus-β multi-cosmology simulation suite with substructure merger trees, the authors fit models to a stellar-mass-selected UniverseMachine mock catalog and infer the structure-growth parameter S8 through cosmological evidence modeling. In these tests, SHAM recovers the input S8 without bias at approximately 2–3% precision, regardless of the treatment of numerically disrupted subhalos, despite using relatively small simulation volumes and a limited set of cosmologies. The tested HOD models, including those accounting for assembly bias, give approximately 6–11% precision and implementation-dependent offsets of up to about one standard deviation. SHAM also generally predicts higher-order statistics excluded from the fit more accurately. The authors interpret the HOD performance as suggesting that excessive parametric flexibility and model misspecification can weaken and bias inference. These are mock-catalog results, demonstrating potential rather than establishing performance on observed galaxy samples.

PublicHow galaxies cluster on small scales can reveal how cosmic structure grows, but the answer depends on how researchers connect galaxies to their surrounding dark matter halos. This study tested two common modeling approaches, SHAM and HOD, using a simulated galaxy catalog rather than observations. SHAM recovered the simulation’s input value of a cosmic structure-growth parameter, S8, without bias and with about 2–3% precision. The tested HOD models were less precise, at about 6–11%, and some estimates were shifted by roughly one standard deviation, depending on implementation. SHAM also generally did better at predicting additional clustering statistics that were not used to tune the models. The authors suggest that the flexibility and imperfect assumptions of the tested HOD models may undermine their accuracy. The results point to a promising way to extract cosmological information, but the test does not establish the same accuracy for real galaxy data.

Young explorerScientists made a pretend universe on a computer and tried two ways to describe how its galaxies bunch together. They used each way to work out a number about how clumps in that universe grow. One way, called SHAM, found the number more precisely and without a systematic shift in this test. The other way, called HOD, gave less precise answers and sometimes leaned away from the right number. SHAM also usually did better at describing extra patterns it had not practiced on. This is promising, but doing well in a pretend universe does not yet show how well it will work with real galaxies.

Structural axes of sources in the SUMSS survey and their alignments

D. Blinov, T. Bhattarai, I. Liodakis+2 more

AstronomerThe study tests local alignment of kiloparsec-scale radio structural axes in SUMSS, complementing VLBI searches in the comparatively undersampled far southern sky. A catalog of structural position angles for 4087 sources in 629 mosaics was generated using neural-network estimates, corrected for image-to-sky coordinate distortion, and visually vetted. The search used a coordinate-invariant parallel-transport statistic on HEALPix tessellations, with genetic-algorithm refinement of candidate regions. Significance was calibrated using mock skies that preserve the declination-dependent position-angle distribution and undergo the full search procedure. Although several regions appear strongly aligned locally, none is statistically significant after accounting for the look-elsewhere effect. The candidates are consistent with chance fluctuations; the analysis finds no statistically significant evidence for structural-axis alignment in SUMSS images. The position-angle catalog provides a resource for future morphology and population studies.

PublicDo distant radio sources tend to point in the same direction as their neighbors? This study searched for such patterns in images from the Sydney University Molonglo Sky Survey, covering southern skies that have been comparatively sparsely sampled by another radio-observing technique. The researchers measured the orientations of 4087 sources, using artificial intelligence for initial estimates followed by corrections and visual checks. Several areas initially looked unusually well aligned. But when the team compared the complete search with simulated skies that preserved a known dependence of measured orientations on sky position, none of those patterns remained statistically convincing. Searching many places increases the chance of finding an impressive-looking pattern by accident. The findings are consistent with chance and provide no statistically significant evidence of alignment in these survey images, rather than proving that alignment never occurs.

Young explorerThe researchers looked at radio pictures of faraway things in space to see whether nearby ones seemed to point the same way. A few groups looked as if they matched. But when you look in lots of places, matching groups can turn up just by luck. The team checked this with pretend skies made for comparison. They found no convincing sign that the matching directions were more than chance.

Reconstructing the Large-Scale Velocity Field from DESI DR1 with Bayesian Inference

Raeed Mundow, Adi Nusser

AstronomerThe authors apply linear-theory and Zel'dovich reconstructions to the DESI DR1 Bright Galaxy Survey within a common Bayesian framework, inferring initial density fields with a Gaussian prior and likelihood. Both produce maximum a posteriori (MAP) fields, but only the linear posterior is sampled. The reconstructions recover similar large-scale density structures and coherent peculiar-velocity patterns more than roughly 50 h^-1 Mpc inside the survey boundaries. Cosmicflows-4 group radial velocities, predominantly from the overlapping SDSS Fundamental Plane sample, agree closely with MAP predictions when averaged in bins of predicted velocity, despite substantial object-by-object scatter. Both methods give similar reflex-dipole profiles, measuring mean shell velocities relative to those at randomly sampled centres, out to about 225 h^-1 Mpc. These profiles depend weakly on the prior normalization sigma_8 and fall below the fiducial linear LambdaCDM reference within 50 h^-1 Mpc; sparse sampling limits the largest radii. An exploratory BAO test that shifts galaxies and randoms to a target redshift of z=8 using reconstructed displacements sharpens the acoustic feature for both methods, slightly more for Zel'dovich. Survey geometry and galaxy bias remain the principal limitations.

PublicThe researchers used two mathematical approaches to reconstruct how matter is distributed and how galaxies move beyond the motion caused by cosmic expansion, using the DESI Bright Galaxy Survey. The approaches produce similar large-scale maps well inside the survey's edges. Their predicted motions also agree closely with independent galaxy-group velocity measurements when those measurements are averaged in groups defined by the predictions, although individual measurements scatter substantially. Both approaches give similar patterns of average motion across distance. At smaller distances, these patterns lie below a standard cosmological reference prediction, while sparse data limit the farthest distances. In an exploratory test, computationally shifting galaxy positions and comparison points using the reconstructed motions sharpened the acoustic feature used to study cosmic distances, slightly more with the Zel'dovich approach. This is a reconstruction result, not a direct observation of the full matter and velocity fields. Survey boundaries and how galaxies trace matter remain important limitations.

Young explorerScientists used a galaxy survey to make two kinds of maps showing where matter might be and how galaxies might move. Far from the edges of the survey, the maps looked much alike. Their guesses about motion matched other measurements well when many galaxies were grouped together, but single measurements varied a lot. Moving the map's dots in a computer also made a special pattern clearer. The maps are still imperfect because the survey has edges and galaxies do not show exactly where all the matter is.

Linear perturbation theory and structure formation in a Horndeski theory of gravity without dark matter

Lorenzo Gervani, Antonaldo Diaferio, Francesco Pace

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study investigates large-scale structure formation in a scalar-tensor Horndeski model without dark matter, constrained to recover Refracted Gravity in the weak-field limit. The authors identify the density-dependent gravitational permittivity ε(ρ) with the scalar-field function G₄(φ). For a flat, matter-dominated, homogeneous and isotropic background, the scalar field drives accelerated expansion, and the model can reproduce the observed redshift evolution of the Hubble–Lemaître parameter. However, their linear perturbation analysis predicts that cosmic structure begins forming only at z ≲ 1. Thus, despite its background-expansion capability, the model fails to describe large-scale structure correctly.

PublicThe researchers examine a theory that changes how gravity works rather than including dark matter. They connect it to Refracted Gravity, in which gravity’s strength depends on the density of ordinary matter. In their theoretical model, an additional field can also make the universe’s expansion accelerate, and the predicted expansion history can match observations. But their calculation of how small density differences grow into cosmic structure reveals a major problem: structure starts forming too late, at redshifts of about 1 or less. Matching the expansion history therefore does not make this model a successful account of the universe’s large-scale structure.

Young explorerScientists tried a different rule for gravity to explain the universe without dark matter. In their calculations, this rule could make the universe spread out faster and faster, in a way that can fit what astronomers see. But it had a big problem: it made matter start gathering into huge groups too late. So this gravity idea does not correctly explain how the universe’s big patterns formed.

Cosmological evolution and late-time attractors in axion-monopole interacting dark energy

Emmanuel N. Saridakis

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

AstronomerThis theoretical study analyzes a dark-sector model in which magnetic-monopole dark matter interacts with an ultralight dark-energy axion through Witten-effect, field-dependent dyon masses. An autonomous-system analysis, supported by analytical and numerical evolution, finds that stable de Sitter attractors with finite positive Hubble parameter require a positive cosmological constant and lie at axion-potential minima; extrema at maxima are unstable. Without an explicit cosmological constant, transient axion-driven acceleration remains possible. The coupling also produces matter-era tracking as an attracting slow-drift regime, not an exact critical point. The interaction-effective dark-energy equation of state can cross the phantom divide while the physical equation of state remains non-phantom. Using the full Bogomol'nyi-Prasad-Sommerfield dyon mass preserves the main dynamical features, although field evolution and coupling strength depend on microscopic dyon properties. These are model results, not observational findings.

PublicThe researchers theoretically explore whether an interaction between dark matter and dark energy could sustain the universe’s accelerated expansion. Their model assigns dark matter to magnetic monopoles and part of dark energy to an ultralight axion field. Analytical and numerical calculations find that stable, steady accelerated expansion requires a positive cosmological constant, with the axion settled at a minimum of its potential. Without that constant, axion-driven acceleration can still occur temporarily. The interaction also creates a slowly changing tracking behavior during the matter-dominated era. An effective description of dark energy can cross a boundary called the phantom divide, even though its physical equation of state does not become phantom. A more complete treatment of the interacting particles retains the main behavior but changes details. The study explores a possible model; it does not report observational evidence for these particles or their interaction.

Young explorerThe researchers used math and computers to explore an idea about why the universe might grow faster and faster. In their idea, two hidden ingredients interact. The calculations say one ingredient could make the universe speed up for a while, but a lasting, steady speed-up needs an extra ingredient called a positive cosmological constant. This is an idea they tested with calculations, not something they saw happening in the sky.

Response to "Late Time Dynamical Dark Energy and the CMB-Distance Ladder Tension"

Michael S. Turner, Dragan Huterer

AstronomerThis response addresses statements in Efstathiou (arXiv:2607.29562) that the authors regard as apparently conflicting with Turner & Huterer (arXiv:2606.05358). They reaffirm their earlier result that direct determinations of H0 can be sensitive to the late-time expansion history, while also identifying significant agreement between the two works. The abstract provides no quantitative findings or methodological details with which to assess the disagreement.

PublicThe authors respond to another paper about determining H0, the present-day expansion rate of the universe. They defend their earlier finding that direct estimates of this rate can depend on how the universe expanded during its later history. They also emphasize substantial agreement with the other paper, despite some apparently conflicting statements. The abstract gives no numbers or details about how large this dependence might be.

Young explorerScientists are discussing how to work out how fast the universe is growing now. These authors say the answer can depend on how the universe grew in its later years. Another paper seems to disagree with them on some things, but they say the papers also agree on a lot. This short description does not say how big a difference it makes.

Bright Siren Cosmology Beyond Fisher: DALI Forecasts for Third-Generation Gravitational Wave Observatories

Mayara H. Pacheco, Josiel M. S. de Souza, Odylio D. Aguiar+1 more

• General Relativity and Quantum Cosmology

AstronomerThis forecasting study tests the first non-Gaussian DALI correction, Doublet, against Fisher and non-approximate (“Exact”) likelihoods using simulated bright-siren catalogs for a Cosmic Explorer and triangular Einstein Telescope network. The analysis adopts frequency-domain inspiral waveforms and selection-motivated counterpart-detection priors, propagating distance information into w0waCDM inference. Doublet reduces forecast cosmological uncertainties by approximately a factor of two relative to Fisher, bringing them closer to Exact results. For 300 simulated detections out to z=1, the forecast H0 precision is about 2.7% with Doublet versus 2.5% with Exact. Parameter uncertainties differ from the exact cosmological likelihood by about 10% on average for Doublet, compared with about 195% for Fisher. Importantly, the adopted non-Gaussian gravitational-wave priors systematically displace inferred luminosity distances from their fiducial values, including in Exact reconstruction, and this displacement propagates into cosmological parameters. Doublet reduces computational costs by roughly 55-fold for gravitational-wave analysis and 12-fold for cosmological likelihood evaluation, with an estimated 55-fold reduction overall. These are simulation-based forecasts under the adopted assumptions, not observational constraints.

PublicResearchers used simulated gravitational-wave events with detectable light counterparts to test a faster way of forecasting how precisely future observatories could measure the universe’s expansion. Their method, called Doublet, allows for more complex uncertainty patterns than the conventional Fisher approximation. For simulated observations by a Cosmic Explorer and Einstein Telescope network, Doublet forecast uncertainties about half as large as Fisher’s and closer to those from a more computationally demanding, non-approximate calculation. With 300 simulated detections extending to redshift 1, the forecast precision on today’s expansion rate was about 2.7%, versus 2.5% in the non-approximate analysis. The estimated total computing cost fell roughly 55-fold. A key caveat is that the adopted prior assumptions systematically shifted inferred distances and affected the cosmological parameters, even in the non-approximate calculation. The study demonstrates forecasting potential, not measurements from real detections.

Young explorerScientists made pretend signals from space on a computer to practice learning how fast the universe is growing. They tested a faster shortcut for working out how uncertain their answers would be. It came closer to a slower, more complete calculation than an older shortcut did. But some starting assumptions still nudged the answers away from the pretend universe’s values. These were practice tests, not real discoveries.

Mapping large-scale structure without galaxy formation - combining fast radio bursts with CMB lensing

James M. Sullivan, Kiyoshi Masui, Ryan Raikman+2 more

AstronomerUsing FLAMINGO simulations, the authors find that the free-electron distribution closely traces total matter and estimate electron field-level bias parameters for the first time. With simulation-based calibration of a handful of electron parameters, they treat the electron field as effectively a second realization of the matter distribution on large scales. They forecast cosmological constraints from combining FRB dispersion correlations with CMB weak lensing, assuming localized FRBs with measured redshifts. Under conservative assumptions, the forecast constraints on sigma_8 and Omega_m are comparable to or better than those from FRB dispersion combined with galaxy-shape weak lensing, with no strong dependence on baryonic feedback models or galaxy-formation parameters. These are simulation-based findings and forecasts, not constraints measured from an observed FRB sample.

PublicFast radio bursts can reveal how free electrons are spread through space, offering a way to map the universe’s matter. In simulations, the researchers find that free electrons follow the overall matter distribution very closely. They then forecast how well future burst data could measure cosmological parameters when combined with the gravitational bending of light from the cosmic microwave background. Assuming the bursts can be located and their redshifts measured, this combination could match or outperform a method that pairs burst data with measurements of distorted galaxy shapes. The forecasts focus on large scales and do not depend strongly on uncertain models of how galaxies form and affect surrounding gas. These are predictions of the method’s potential, not measurements of cosmological parameters from existing burst observations.

Young explorerQuick flashes of radio waves from space can help scientists find tiny particles called electrons. In computer-made universes, the scientists found that these electrons spread out almost like all the matter does. They predict that clues from the flashes, together with clues from how gravity bends very old light, could help us learn how much matter the universe has and how clumpy it is. To do this, they would need to know where the flashes come from and measure a clue to how far away they are. They have tested the idea with computers, not yet measured the universe this way.

SBi₃PCF: cosmology with Dark Energy Survey Year 3 cosmic shear

David Gebauer, Anik Halder, Zhengyangguang Gong+1 more

AstronomerThe authors report the first cosmic-shear survey-data analysis of the integrated three-point correlation function (i3PCF) and the first simulation-based inference analysis of a three-point cosmic-shear correlation function on survey data. Using SBi3PCF with the DES Y3 shape catalogue, they detect the i3PCFs ζ± at signal-to-noise 12.8 and jointly fit them with the two-point functions ξ± in wCDM. The CosmoGridV1-based forward model includes the survey mask, shape noise, intrinsic alignment, baryonic feedback, photometric-redshift uncertainty and shear-calibration bias. The analysis remained blinded until coverage, learned-likelihood accuracy and internal-consistency tests passed. Joint constraints are Ωm = 0.272 (+0.038/−0.033), S8 = 0.784 (+0.024/−0.021) and w0 = −1.04 (+0.25/−0.19). Adding ζ± improves the Ωm–S8–w0 figure of merit by a factor of 1.59 relative to ξ± alone, matching earlier simulation predictions. The gain comes from angular scales ≥15 arcminutes and aperture radii ≥50 arcminutes, where baryonic effects are subdominant. Constraints agree with other DES Y3 and independent lensing analyses and differ from Planck 2018 + BAO by at most 2.4σ in this parameter space. The result demonstrates a fully simulation-based analysis of this statistic on survey data, rather than a simulation-only forecast.

PublicResearchers have extracted additional information about the Universe from the tiny distortions that gravity produces in galaxy images in the Dark Energy Survey’s Year 3 catalogue. They combined the usual two-point measure of these distortions with an integrated three-point measure, detecting the latter with a signal-to-noise ratio of 12.8. Their inference method used simulations that account for survey limitations and several sources of uncertainty, and the analysis choices were fixed before the results were revealed. Combining the two measures improved a joint measure of precision for three cosmological parameters by a factor of 1.59, as earlier simulations had predicted. The estimates describe the matter content, the strength of matter clustering and a parameter governing dark energy; the dark-energy estimate, w0 = −1.04 (+0.25/−0.19), is consistent with −1. The extra information came from scales where the effects of ordinary matter on the lensing signal are relatively small, not absent. The findings agree with other lensing analyses and differ from the combined Planck 2018 cosmic-microwave-background and baryon-acoustic-oscillation results by no more than 2.4 standard deviations. This is a demonstration on real survey data of a method intended to help future surveys.

Young explorerGravity can bend light and make faraway galaxies look a little stretched. Scientists studied these tiny stretches using two kinds of pattern: one links pairs, and another links groups of three. Adding the three-part pattern helped them learn more about how matter is spread through space and about dark energy. They used computer-made universes to help understand the real galaxy pictures and checked their method before looking at the answers. The answers still have uncertainty, but they mostly agree with other studies. This gives scientists another useful way to study the Universe.

Gauge-invariant non-universal scalar couplings in teleparallel gravity

Giovanni Otalora, Rudranil Roy

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

AstronomerThis theoretical study constructs a gauge-invariant teleparallel framework allowing a scalar field to couple non-universally to gravity while retaining the gravitational sector of the teleparallel equivalent of General Relativity. A field-dependent gravitational charge controls the scalar-sector tetrad’s coupling to the universal translational gauge potential, with a Stückelberg completion preserving local translational gauge invariance. The authors derive the field equations, antisymmetric constraint, and consistency relations. In homogeneous, isotropic cosmology, the Stückelberg constraint supplies a first integral for the non-universal coupling. Standard stiff-fluid behavior is recovered asymptotically during kination, but potential domination alone does not guarantee accelerated expansion. Compatible expanding solutions dynamically suppress departures from universality, with examples approaching power-law inflation or de Sitter expansion. With a universally coupled perfect fluid and constant scalar potential, a late-time solution contains a subdominant matter-like term in the background Friedmann equation and approaches de Sitter expansion. These are theoretical solutions, not observational findings.

PublicThe researchers develop a mathematical model in which a scalar field can interact with gravity differently from universally coupled matter, while the gravitational part of the theory retains a form equivalent to General Relativity. They explore how this possibility affects a smoothly distributed, uniformly expanding universe. Some theoretical solutions make the difference in gravitational coupling fade as the universe expands, and some approach sustained accelerated expansion. However, having the scalar field’s potential energy dominate is not enough by itself to produce acceleration. In a model that also includes a universally coupled fluid and a constant scalar potential, the equations yield a small contribution that behaves like matter in the expansion equation, followed by an approach to de Sitter expansion. This does not establish an additional population of matter or report an observed effect; it identifies possible cosmic histories within the proposed theory.

Young explorerScientists made a math model to ask what might happen if a special field felt gravity differently from other things. In some of their possible universes, that difference gets smaller as space grows. Some examples also let space grow faster and faster, but only when extra rules are met. These are possibilities worked out with math, not things the scientists have seen happen.

Cosmic-Ray Signals from Dark Matter Annihilation into Scalars with Baryon Number

Mattia Di Mauro, Caleb Gemmell, Dan Hooper+1 more

• High Energy Physics - Phenomenology
• High Energy Astrophysical Phenomena

AstronomerThe authors calculate cosmic-ray antideuteron and antihelium-3 event yields in a proposed dark-matter annihilation scenario with color-singlet scalar mediators carrying baryon and lepton number. Including Galactic propagation and detector sensitivities, they consider parameters compatible with seven-year AMS-02 antiproton data. Broad regions of the dark-matter–mediator mass plane predict observable antideuteron fluxes at AMS-02 and GAPS. Antihelium-3 detection is more challenging, but potentially detectable fluxes occur for light mediators and moderately light dark matter, with fluxes generally enhanced over standard WIMP predictions. Predicted antihelium-to-antideuteron event ratios are of order 0.1, closer to those suggested by reported AMS-02 candidate events than conventional WIMP predictions. These are model predictions, not confirmed detections of dark matter or heavy antinuclei.

PublicCould antimatter particles arriving from space help reveal dark matter? This study calculates signals from a proposed model in which dark matter annihilates into intermediate particles that enhance production of antideuterium and antihelium-3 nuclei relative to antiprotons. The calculations account for travel through the Galaxy and detector sensitivity, while staying compatible with seven years of AMS-02 antiproton measurements. Many combinations of particle masses predict antideuterium signals observable by AMS-02 and GAPS. Antihelium-3 would be harder to detect, though some combinations could produce detectable signals. The predicted balance of the two types of antimatter is closer to that suggested by reported AMS-02 candidate events than conventional WIMP models predict. Those candidate events are not confirmed detections, and the study does not establish that dark matter produced them.

Young explorerScientists wonder whether mysterious dark matter could make tiny bits of antimatter that travel through space. They used a proposed model to work out how many of two kinds might reach special detectors. Their calculations say one kind could be easier to spot than the other. Some possible sightings helped inspire this work, but they are not confirmed. This study does not show that scientists have found dark matter.

Presupernovae Strongly Constrain Electrophilic MeV Bosons

Yu Cheng, Damiano F. G. Fiorillo, Chui-Fan Kong+1 more

• High Energy Physics - Phenomenology
• High Energy Astrophysical Phenomena

AstronomerThe authors derive constraints on hypothetical MeV-mass electrophilic bosons from massive stars in the years before a supernova, using their potential contribution to diffuse Galactic 511-keV emission through decays producing positrons. Although cooler than supernovae, these progenitors remain hot much longer and can emit more particles overall. For dark photons, the lower plasma frequency also reduces the screening that suppresses MeV excitations in supernovae. The analysis finds pre-supernova bounds on dark photon couplings up to two orders of magnitude stronger than supernova bounds for masses of 1–3 MeV, with similar improvements for other electrophilic species, including axion-like particles. These are constraints on hypothetical particles, not detections.

PublicMassive stars in the years before they explode may provide stronger tests of some hypothetical particles than the explosions themselves. The authors find that, although these stars are cooler, they stay hot for much longer and could release more of the particles overall. Their decays could produce positrons that contribute to a diffuse glow from our Galaxy at an energy of 511 keV. For hypothetical particles called dark photons, conditions inside the stars also suppress production less than conditions in supernovae. The analysis places limits on dark photon interaction strengths up to 100 times tighter than supernova limits for masses between 1 and 3 MeV, with similar improvements for some other proposed particles. This does not establish that any of these particles exist.

Young explorerA giant star can stay very hot for years before it explodes. Scientists worked out that this long, hot time could make more of some tiny, never-found particles than the explosion does. If those particles exist, they could help make a glow in our galaxy. By checking how much glow they could make, scientists can put stricter limits on some ideas about these particles. They have not found the particles.

Comment on "Long-range magnetic fields in the ground state of the Standard Model plasma"

Jingwei Wang, Yiming Liu, Ligong Bian

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

AstronomerThis theoretical study revisits the two-loop parity-odd photon polarization calculated by Boyarsky, Ruchayskiy, and Shaposhnikov (2012). The authors identify omitted opposite-fermion-flow partner diagrams in both the tadpole and exchange-bubble topologies. They quantify how restoring the exchange-bubble coefficients affects the static magnetic response, but the abstract gives neither the magnitude nor the direction of that effect.

PublicThe researchers reexamine a theoretical calculation concerning light and magnetic response. They report that an earlier calculation left out partner contributions in two types of mathematical diagrams. They calculate how correcting the coefficients for one of those types affects the response to a static magnetic field. The abstract does not state how large the correction is or whether it increases or decreases the response; this is a calculation, not an observational finding.

Young explorerScientists checked some tricky math about light and magnetism. They found that an older calculation had left out some matching pieces. They worked out how adding some of those pieces changes the answer, but this short description does not tell us how big the change is.

Gravitational-wave lensing beyond the diffraction integral: proper-time methods and the bound lens

Ginevra Braga, Raul Jimenez

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

AstronomerThis theoretical study develops a proper-time worldline formulation of gravitational-wave lensing that avoids imposing the usual one-way, paraxial and thin-lens approximations at the outset. Geometric optics and the diffraction integral emerge through stationarity, the latter for paraxial thin-lens paths. For a point mass, the Duru-Kleinert gauge and Kustaanheimo-Stiefel map yield an exact propagator that recovers the point-lens amplification factor for a distant observer; geometric optics requires both w >> 1 and wy >> 1. The authors attribute this agreement to the Coulomb potential rather than the validity of the standard approximations: the eikonal condition fails near the lens and at large angles, and the one-way step is a non-relativistic limit. For a source orbiting its lens, their exact time-domain treatment includes backscattered echoes, motion during lensing delays, and path-dependent retarded times and Doppler factors, precluding a single amplification factor. In the diffraction regime, the Shapiro phase alone omits other lensing effects; geometric optics misses 46–100% of the lensing near conjunction at w = 0.3. Paraxial geometry fails on the far side, while applying a static amplification factor along the orbit produces errors of approximately (1–2)wM/R near conjunction and of the echo amplitude elsewhere. These are theoretical results, not reported observations.

PublicGravitational waves can behave as waves rather than simple rays when gravity bends them around a lens. This theoretical paper develops a mathematical treatment that does not start with several simplifying assumptions used in standard lensing calculations. For a point-mass lens viewed from far away, it recovers the familiar amplification formula, but the authors caution that this agreement does not make those assumptions generally reliable. They also calculate the signal from a gravitational-wave source orbiting its lens. The source moves while different parts of the signal travel, and some waves scatter back as an echo. Consequently, one fixed amplification formula cannot describe the whole signal. In one wave-dominated case, a ray-based calculation misses 46–100% of the lensing near an orbital alignment. The work identifies theoretical limitations of common calculations; it does not report a detected echo or a new observation.

Young explorerGravitational waves are ripples that gravity can bend. Scientists used math to work out what happens when the thing making the ripples circles the thing bending them. Some ripples can even come back as an echo. Because the source keeps moving, a simple rule for making the signal stronger or weaker does not always work. This is a calculation, not an echo they have heard.

Macrocanonical Generator Networks: Data-Efficient Neural Surrogates for Amortized Physics Simulation

Niall Jeffrey, Benjamin D. Wandelt

• Machine Learning
• Machine Learning

AstronomerThe authors introduce macrocanonical generator networks as fast neural surrogates for stationary physical processes. Rather than optimizing each generated sample to match prescribed multiscale statistics, they train a generator to match those constraints in expectation, retaining physically realistic sample-to-sample fluctuations. They prove that gradient-descent training induces preconditioned gradient-descent dynamics in sample space with symmetry-preservation properties inherited from microcanonical gradient descent. They also show that residual generators initialized near the identity and trained with a small learning rate locally preserve entropy during early optimization and mitigate mode collapse. In experiments with cosmology and fluid simulations—not observational data—the networks generate realistic samples from very small training sets, sometimes a single example. Reported per-sample generation speedups exceed a million-fold relative to the reference simulator and a thousand-fold relative to microcanonical gradient descent; generation requires one forward pass after training. The authors propose reusing trained generators for downstream pretraining, including simulation-based inference, within multi-fidelity workflows.

PublicComputer simulations of physical systems can be expensive to run. This study introduces an AI method that learns to produce new simulated examples quickly by matching statistical patterns across different scales. Instead of forcing every example to have exactly the same statistics, it matches them on average, allowing realistic variation between examples. Tests using cosmology and fluid simulations produced realistic samples from very little training data—in some cases, just one example. Once trained, the method generated each sample more than a million times faster than the reference simulator and more than a thousand times faster than a comparison method that optimizes each sample separately. These are simulation-test results, not observations of the Universe, and the speed comparisons concern sample generation after training. The authors propose using the trained models to support further scientific machine learning.

Young explorerScientists use computers to make pretend versions of how things in nature behave, but making them can take a long time. The researchers taught an AI to make new examples by learning patterns from a few computer-made examples—sometimes just one. In tests about the Universe and flowing liquids, the trained AI made realistic-looking examples much faster. These were computer tests, not discoveries made by looking at the sky.

Universality of Primordial Anisotropies in Gravitational Wave Background

Boyuan Jiang, Ryo Saito, Ying-li Zhang

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

AstronomerThis theoretical study introduces the model-independent Cosmological Form Factor (CFF) framework to describe how long-wavelength perturbations modulate short-scale statistics of the primordial stochastic gravitational-wave background. It addresses why mechanisms with distinct physical origins, including fossil and propagation effects, can produce similar multipole dependences. Within the broad class of mechanisms considered, the authors show that statistical isotropy, locality, and the basic properties of long-wavelength perturbations universally constrain the allowed angular and polarization structures. Amplitudes and frequency dependence, by contrast, retain information about the underlying mechanism. The framework separates universal from model-dependent features and provides a basis for interpreting future observations; it does not report an observational detection.

PublicDifferent processes in the early universe could produce similar patterns of variation across the sky in a background of gravitational waves. This theoretical study introduces a framework called the Cosmological Form Factor to explain those similarities by describing how large-scale disturbances affect smaller-scale gravitational-wave patterns. For the broad group of processes studied, general physical principles determine the possible sky patterns and polarization structures, which describe how the waves are oriented. Other features, such as the strength of the variations and how they change with wave frequency, still carry clues about their origin. The work is intended to help interpret future gravitational-wave observations, rather than report a detected signal.

Young explorerImagine a background of tiny ripples in space left over from the early universe. Different things could have made patterns in those ripples that look alike. Scientists made a mathematical way to explain why some patterns could be shared, while other clues could help tell their causes apart. This is an idea for understanding what we might see in the future, not a report that these patterns have been found.

CMB Spectral Distortions from Resonant Conversions in Atomic Dark Sectors

Duncan K. Adams, Jared Barron, Bryce Cyr+1 more

• High Energy Physics - Phenomenology

AstronomerThis theoretical study computes primordial CMB spectral distortions from resonant conversion between Standard Model photons and photons in an atomic dark sector at 10^3 ≲ z ≲ 10^6. Conversion is enhanced when the photons’ induced thermal masses coincide. The authors solve the early-time Boltzmann equation for the irreducible freeze-in or freeze-out dark-photon abundance, update generic millicharged-sector limits using the ACT DR6 constraint on N_eff, and calculate distortions with the Landau–Zener formalism after modeling both sectors’ thermal masses. For approximately equal dark-electron and dark-proton masses—the positronium limit—existing COBE/FIRAS spectral data exclude previously unconstrained parameter regions within the model. Forecasts for the proposed FOSSIL satellite indicate potential sensitivity to ultra-low dark electric charges that are difficult to probe otherwise; these are prospective constraints, not detections.

PublicThe researchers explore a hypothetical hidden sector containing dark counterparts of electrons, protons, and light. Their calculations ask whether ordinary light and dark light could have converted into one another in the early universe, changing the spectrum of the cosmic microwave background. Using existing measurements from COBE/FIRAS, they find that some versions of this model are ruled out when the dark electron and dark proton have roughly equal masses. They also use ACT DR6 measurements to update limits on dark sectors with tiny electric charges. Predictions for the proposed FOSSIL satellite suggest it could test dark particles with extremely small dark electric charges. The study constrains possible hidden particles; it does not report their discovery.

Young explorerScientists wondered if there might be hidden kinds of particles and light. They used math to ask whether ordinary light could have changed into hidden light when the universe was very young. That could have changed the pattern of the old light we can see today. Comparing their math with measurements showed that some versions of this idea do not fit, especially when two kinds of hidden particles weigh about the same. A proposed space mission might check more versions someday. No hidden particles were discovered.

Cosmology of Inelastic Self-Interacting Dark Matter: Linear Evolution and Observational Constraints

Xin-Chen Duan, Yue-Lin Sming Tsai, Ziwei Wang

• High Energy Physics - Phenomenology

AstronomerThe authors model linear cosmological evolution in a two-component, inelastically self-interacting dark sector with a small mass splitting and thermal initial conditions. They derive coupled background and perturbation equations for power-law and low-velocity-saturating conversion cross sections. Exothermic conversion supplies kinetic energy to the lighter species, producing pressure support, small-scale suppression and dark acoustic oscillations in the predicted matter power spectrum. The cutoff at k > 1 h Mpc^-1 depends on the cross-section normalization and velocity dependence, dark matter mass and mass splitting. Using a modified Boltzmann solver, they recast constraints from Lyman-alpha forest data and high-redshift UV luminosity functions, obtaining non-monotonic but closed exclusion regions as efficient conversion competes with depletion of the heavier species. These are linear-theory predictions and indirect constraints, not a detection of the proposed dark sector.

PublicThis theoretical study asks how dark matter might shape cosmic structure if it consists of two slightly different-mass kinds of particles that can convert into one another. In the model, energy released by conversion gives the lighter particles extra motion. The resulting pressure reduces the growth of small structures and creates a pattern of oscillations in the predicted distribution of matter. The authors calculate these effects and reinterpret existing observations of intergalactic gas absorption and ultraviolet light from early galaxies to constrain the model. The constraints depend on competing effects: stronger conversion releases energy more efficiently but can also quickly use up the heavier particles. The work suggests a way to test otherwise secluded dark matter; it does not establish that these particles exist.

Young explorerDark matter is something scientists study to understand how things gather together in space. Here, scientists tried a math model with two kinds of dark matter, one a little heavier than the other. When the heavier kind changes into the lighter kind, it gives the lighter kind extra motion. In their model, that motion makes it harder for small clumps to grow. They compared their calculations with clues from space to see which versions might work. They have not shown that these two kinds of dark matter are real.

Eigenvalue formulation of Stochastic Inflation and application to large perturbation generating inflationary features

Swagat S. Mishra, Edmund J. Copeland, Anne M. Green

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

AstronomerThis theoretical study develops a self-contained eigenvalue method for determining the probability distribution P(N) of the stochastic number of inflationary e-folds from the adjoint Fokker–Planck equation. For quantum diffusion on a flat potential without classical drift, it recovers the previously derived distribution: an exponential tail and an intermediate P(N) ∝ N^(-3/2) regime between the peak and tail. For constant-drift inflation, the narrow-well limit admits an analytic solution resembling the drift-free case, with a mildly suppressed tail. In the broad-well limit, obtaining the full eigenvalue and eigenfunction spectrum requires a piecewise construction; the resulting distribution has an enhanced peak and a strongly suppressed tail. These are theoretical results relevant to large inflationary perturbations that may collapse into primordial black holes, not observational evidence for their formation.

PublicRandom fluctuations during inflation, an early period of cosmic expansion, can produce large disturbances that might later collapse into primordial black holes. This paper develops a mathematical method to calculate the probabilities of different amounts of expansion in such models. In a simple case with random fluctuations but no systematic drift, the method reproduces an earlier result. Adding a constant drift has different effects in the two model limits studied: a narrow well only slightly reduces the probability of unusually large amounts of expansion, while a broad well strongly reduces it and makes the distribution more sharply peaked. These are theoretical calculations, not observations of primordial black holes.

Young explorerImagine the very young universe growing while getting random little nudges. Scientists made a new math tool to work out how likely different amounts of growing would be. In one simple test, their tool agreed with an older answer. When they added a steady push, very large amounts of growing became a little less likely in one version of the model and much less likely in another. Big disturbances from this early growing might make black holes, but this work does not show that any black holes actually formed.

Memoirs of the curvaton: non-perturbative non-Gaussianity and supermassive primordial black holes

S. Allegrini, A. J. Iovino, G. Perna+1 more

• High Energy Astrophysical Phenomena
• General Relativity and Quantum Cosmology

AstronomerThis theoretical study constructs the local map ζ = F(ζ_G) for curvatons beyond a quadratic potential. Using the abbreviated action to connect frozen and oscillatory evolution, the authors incorporate a field-dependent onset of oscillations and changes to the effective equation of state in the adiabatic regime. They derive mappings for quadratic, monomial, quartic, and cosine potentials, finding that self-interactions can enhance or suppress non-Gaussianity depending on the potential and initial conditions. Their non-perturbative treatment also shows that strong non-Gaussianity can suppress the power spectrum. As an application, they propose a bottom-up scenario in which strongly positive curvaton non-Gaussianity permits primordial supermassive black hole seeds at peak amplitudes A_pk ~ 10^-3 while remaining compatible with COBE/FIRAS μ-distortion bounds. An axion-like curvaton is identified as a particularly natural setting. The proposed connection to JWST's observed Little Red Dots is a possible primordial explanation, not an observationally established origin.

PublicThe researchers explore a theoretical field called the curvaton, which could have shaped unevenness in the early universe after inflation. They calculate how interactions within this field change the pattern of those variations, making departures from a bell-shaped statistical distribution either stronger or weaker depending on the model and starting conditions. Strong departures can also reduce the power of the variations. In one proposed scenario, this behavior could allow primordial seeds of supermassive black holes to form without violating COBE/FIRAS limits on distortions of the cosmic microwave background spectrum. The authors suggest this as a possible origin for the Little Red Dots seen by JWST; the study does not establish that those objects formed this way.

Young explorerScientists used math to explore an idea about how the very young universe became uneven. An imagined field could make some places much more different from others. They suggest this might help make the beginnings of enormous black holes and might explain little red dots seen by a space telescope. It is a possible explanation, not something they have proved happened.

Can cosmic voids ease the Hubble tension? Local expansion in w₀wₐCDM

Tommaso Moretti, Noemi Frusciante, Giovanni Verza

• General Relativity and Quantum Cosmology

AstronomerThe authors model void-induced shifts in low-redshift Hubble-rate inferences in flat w0waCDM using a hydrodynamical treatment of isolated, spherical inverse top-hat underdensities. The calculated effect is dominated by the enclosed density contrast and present-day matter density parameter; dynamical dark energy contributes only subdominant late-time corrections. For a Planck-calibrated ΛCDM background, matching SH0ES requires a present-day enclosed contrast of approximately −0.44, substantially deeper than a KBC-like underdensity. A KBC-like void reduces the discrepancy to about 2σ but does not eliminate it. Allowing dynamical dark energy, including parameter regions motivated by recent DES and DESI analyses, changes this result only at the percent level. A phenomenological reconstruction maps the reported redshift dependence of locally inferred H0 onto an effective enclosed matter profile, but is a consistency test of local-structure effects, not evidence for an evolving background H0. Within the spherical void setup considered, local underdensities affect Hubble-rate inferences but do not resolve the Hubble tension.

PublicCould living in a region with less matter than average help explain why local measurements of cosmic expansion disagree with the value inferred from Planck? The authors investigate this possibility with a model of a spherical, relatively empty region, rather than establishing that such a region surrounds us. In their calculations, a region resembling the proposed KBC local underdensity reduces the SH0ES–Planck disagreement to about two standard deviations, but cannot remove it. Fully matching SH0ES in a Planck-calibrated model would require a substantially deeper shortage of matter. Letting dark energy change over time alters the result only at the percent level. The authors also show how reported differences in locally inferred expansion rates at different redshifts could be represented by a matter-density profile, but caution that this is a consistency check, not an explanation based on a changing background H0. Their conclusion is limited to the spherical void model studied: local structure can influence expansion measurements, but does not settle the disagreement.

Young explorerScientists get different answers when they work out how fast the universe is growing. This team used a model to ask whether living in a big space with less stuff than usual could help explain that. In their model, a less-full space like one suggested near us helps the answers get closer, but does not make them match. They would need a space with much less stuff to make that happen. This does not show that we really live in such a space, and the team’s round-space model does not solve the puzzle.

Gravitational waves from super-Hubble bubbles

Pulkit S. Ghoderao, Arttu Rajantie, Danièle Steer

• High Energy Physics - Theory

AstronomerThe authors investigate a cosmological first-order phase transition in which true-vacuum bubbles nucleate during inflation but collide and percolate only in the radiation-dominated era. If collisions occur soon after inflation ends, the bubbles can be much larger than the Hubble length. In this scenario, the comoving bubble radius sets the peak gravitational-wave frequency, allowing it to lie well below the MHz frequencies typical of bubble collisions at the end of inflation. For collisions beginning at the same time, super-Hubble bubbles also yield a greatly enhanced gravitational-wave amplitude relative to Hubble-sized or smaller bubbles. A simple illustrative model demonstrates that the resulting signals could fall within the frequency and amplitude ranges accessible to LIGO, NANOGrav, LISA, and other future experiments. This is a theoretical possibility, not a reported detection.

PublicThis theoretical study explores bubbles of a new vacuum state forming during inflation, an early period of cosmic expansion, but colliding only afterward, when radiation dominated the Universe. If the collisions happened soon after inflation ended, the bubbles could have been larger than the Hubble length, a scale associated with the Universe’s expansion. Such large bubbles could produce gravitational waves with much lower peak frequencies than usually expected from collisions at the end of inflation. Their waves could also be much stronger than those from smaller bubbles whose collisions began at the same time. Using a simple illustrative model, the authors show that these signals could be within reach of LIGO, NANOGrav, LISA, and other future experiments. They do not report observing such a signal.

Young explorerImagine the very young Universe making enormous bubbles—not soap bubbles, but bubbles where space was in a different state. Scientists explored an idea in which these bubbles formed while the Universe was growing very fast and bumped into each other later. Their simple model suggests that very big bubbles could make stronger, slower wiggles in space than smaller bubbles bumping together at the same time. Some tools that listen for space wiggles might be able to notice them. This is an idea scientists studied, not something they have seen happen.

Sample Variance Cancellation for Future Spectroscopic Surveys

James M. Sullivan, Martin White

AstronomerLyman-alpha radiative transfer can modify the angular dependence of LAE clustering, potentially biasing cosmological constraints on structure growth and redshift-space distortions. Such effects have appeared in simulations, but their amplitude in nature and detailed form remain uncertain. Within a restricted linear, Gaussian model, the authors outline a procedure for hypothetical LAE data containing an unknown radiative-transfer or other unmodeled angular effect. Cross-correlation with a second tracer at the same redshifts that lacks the modified angular dependence, such as Lyman-break galaxies, enables sample-variance cancellation. The proposed workflow detects a nontrivial angular dependence through a conditional field-level realization, recovers its functional form using a derived optimal filter, and estimates its amplitude and uncertainty with an adapted quadratic estimator. The authors argue that a modest-sized high-redshift survey could suffice within this framework; this is a methodological result, not an observational detection or measurement of the effect in nature.

PublicSurveys of distant galaxies can help reveal how cosmic structure grows, but the way Lyman-alpha light travels through matter could distort the apparent clustering pattern and bias cosmological estimates. Simulations have shown this effect, but its strength and exact form in the real universe remain unclear. The authors propose comparing galaxies selected through Lyman-alpha emission with another population at the same cosmic distances whose clustering does not have the same distortion. Under simplified statistical assumptions, this comparison could reveal whether an unexpected directional pattern exists, determine its shape, and estimate its strength and uncertainty. The study presents a method for future data rather than a detection in real observations.

Young explorerScientists study patterns of faraway galaxies to learn how the universe grows. But the way some light travels might make those patterns look different. The researchers suggest comparing two groups of galaxies, one without that same change, to help spot and measure it. Their idea works in a simplified model; they have not measured this change in the real sky.

Dark graviton sensing with magnetically levitated superconductors

Valentina Danieli, Paola C. M. Delgado, Federico R. Urban

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

AstronomerThis theoretical study calculates the response of a magnetically levitated superconductor to a hypothetical spin-2 dark-matter field, the dark graviton, over decihertz-to-kilohertz frequencies, treating matter and electromagnetic couplings separately. The matter coupling generates a strain-like tidal acceleration relative to the rigid apparatus's centre of mass, displacing the superconductor relative to the readout pick-up loop, analogous to a slow, continuous, massive gravitational wave. The electromagnetic coupling induces an effective current and oscillating magnetic field that drives the superconductor's superdiamagnetic response. With significant experimental improvements, the projected matter-coupling sensitivity could surpass existing fifth-force experiments in the audio band. These sensors could also rank among the most sensitive laboratory probes of the electromagnetic coupling, especially at low frequencies, provided technical and readout noise are controlled. These are calculated responses and conditional sensitivity prospects, not a dark-matter detection.

PublicResearchers have calculated how a superconductor held aloft by magnetic forces might detect a hypothetical form of dark matter called the dark graviton. They examined two possible interactions: one with matter that would shift the floating superconductor relative to its detector, and one with electromagnetism that would produce an oscillating magnetic field and make the superconductor respond. The study considers signals from decihertz to kilohertz frequencies. With substantial experimental improvements, this approach could outperform existing searches for an additional force in the audio-frequency range. It could also become one of the most sensitive laboratory tests of dark gravitons interacting with electromagnetism, particularly at low frequencies, but only if unwanted noise is kept under control. The work predicts possible detector responses; it does not report finding dark matter.

Young explorerScientists used calculations to ask whether a special piece of material floating on magnets could help find a hidden kind of matter that might exist. If this hidden matter is real and interacts in the ways they studied, it could make the floating piece move or create a changing magnetic field that the piece responds to. A much-improved experiment might notice these tiny effects, but other little shakes and disturbances would need to be kept very quiet. The scientists have not found the hidden matter.

Particle--antiparticle asymmetry from charge separation at expanding horizons

She-Sheng Xue

• High Energy Physics - Phenomenology

AstronomerThe authors propose a mechanism for the observed matter–antimatter asymmetry in a Friedmann cosmology with a time-varying cosmological term. In their model, massive particle–antiparticle pairs are continuously produced from the spacetime vacuum and separated by horizons. Assuming horizons absorb global charge, separation across the many horizons within today's Hubble volume produces effective volume-wide U(1) violation at a rate Γ_C = κ_C Γ_M. The mechanism is embedded in a cosmic history the authors describe as explaining n_s, A_s, r and the low-multipole power anomaly. An effective Lagrangian combines the U(1)-violating coupling g_c δO_S Φ² with the C- and CP-odd time bias −∂_μ f(R) J^μ. For f(R) = c_a ln(absolute value of R), the particle-production chemical potential is approximately 2c_a Ḣ/H. The asymmetry per pair approaches an attractor during the pair-dominated episode and freezes when the cosmological term is exhausted. Matching the observed asymmetry requires the absolute value of c_a divided by τ_S to be approximately (0.65–1.0) × 10^-4, where T_S = τ_S H/(2π); the model fixes the asymmetry's sign through the arrow of time. Yukawa decays are proposed to transfer a uniform-sign asymmetry to baryons, leptons and dark-matter particles. Currents from charged decay products are predicted to yield a present-day magnetic field of 10^-14–10^-11 G on the coherence length of reheating. These are model mechanisms and predictions, not direct observations of horizon charge separation or the predicted magnetic field.

PublicWhy is there more matter than antimatter? This paper proposes an explanation rather than reporting a direct observation of the process. In its model of an expanding universe, a changing cosmological term continuously creates particle–antiparticle pairs from the spacetime vacuum. Cosmic horizons separate the partners and, the authors assume, absorb their charge. A coupling to the direction of time then favors one member of each pair over the other. The authors place this mechanism within a cosmic history they describe as explaining several properties of primordial fluctuations, including an anomaly on large angular scales. The imbalance settles toward a stable value and stops changing when the cosmological term is exhausted. Reproducing the observed imbalance requires the absolute value of a coupling called c_a divided by a temperature parameter called τ_S to be approximately (0.65–1.0) × 10^-4; the model's vacuum temperature is T_S = τ_S H/(2π), where H is the expansion rate. Decays would pass the same direction of imbalance to baryons, leptons and dark-matter particles. The model also predicts that currents from charged decay products generate a magnetic field that would be 10^-14–10^-11 gauss today, on a length scale associated with reheating. That field is a prediction here, not a reported measurement.

Young explorerOur universe has more matter than antimatter. The scientists suggest a way this might have happened. In their idea, the growing universe keeps making pairs of particles, and space has boundaries that separate the partners. A special rule connected to time moving forward favors one kind over the other. Later, the particles break down and pass the extra amount to other particles, including dark matter. The idea also predicts a very weak magnetic field today. This is a proposed explanation, not something the scientists watched happen.

Opening the Window of Ultra-Light PBHs by Exorcising the Poltergeist

Yann Gouttenoire, Nicholas Leister, Pedro Schwaller

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

AstronomerThis theoretical study revisits reheating through evaporation of primordial black holes lighter than 10^9 g. Monochromatic treatments predict nearly simultaneous evaporation, abrupt reheating, and a large Poltergeist scalar-induced gravitational-wave signal. Including the irreducible collapse mass tail predicted by general relativity, df_PBH/d ln M proportional to M^3.78, instead smooths reheating and suppresses the signal by orders of magnitude. The authors interpret this suppression as reopening the ultra-light PBH window; the scenario is not presented as an observed origin of the hot Big Bang.

PublicTiny black holes formed in the early universe might have evaporated and supplied the heat for the hot Big Bang. Calculations that give all these black holes the same mass predict a sudden burst of heating and a strong signal of gravitational waves—ripples in spacetime. This theoretical study includes a spread of masses predicted by general relativity and finds more gradual heating and a much weaker wave signal. The authors argue that this makes the tiny-black-hole scenario viable again, but it is not evidence that it actually happened.

Young explorerMaybe tiny black holes helped make the early universe hot as they disappeared. If they were all the same size, they would disappear together. This study says a predicted mix of sizes would make the heating gentler and the ripples in space much weaker. It is an idea scientists are studying, not something they have seen happen.

How bursty star formation shapes spectral diversity at high redshifts: breaking degeneracies in early galaxy formation

Viola Gelli, Charlotte A. Mason, Daniel P. Stark+4 more

AstronomerMotivated by JWST observations of abundant z>10 galaxies and diverse spectra, this study models bursty star formation histories as an explanation for the UV luminosity function (UVLF) excess. Within the model, matching the z~6 UVLF and observed recent SFR upturn and downturn fractions requires strong stochasticity, with UV scatter of about 0.9 mag at halo mass 10^10 solar masses, increasing toward lower masses. This prescription also reproduces UVLFs and upturn/downturn fractions over z~6–11. It predicts that recent upturns, defined by SFR3/SFR50>5, increasingly dominate the bright end at higher redshift, accompanied at fixed UV magnitude by higher median emission-line equivalent widths, bluer UV slopes, weaker Balmer breaks, and broader property distributions. Downturn fractions, defined by SFR3/SFR50<0.2, are particularly sensitive to stochasticity. The baseline model underpredicts the z~14 UVLF. Two alternatives can match it: increased burstiness or increased star formation efficiency. From z=10 to 14 at fixed UV magnitude, the former predicts roughly twice the downturn fraction and 1.5 times the weak-Hβ-emitter fraction (EW<50 Å), whereas the latter predicts a constant downturn fraction and a declining weak-emitter fraction. These are model predictions, not established observational trends; spectroscopy spanning a broad UV-magnitude range could distinguish the explanations.

PublicJWST has found unexpectedly many galaxies at redshifts above 10, along with a wide variety of spectra. This study explores whether galaxies forming stars in bursts, rather than steadily, could explain those findings. The researchers’ models need strong bursts, especially in lower-mass dark matter halos, to match observed galaxy brightness counts and indicators of recently rising or falling star formation around redshift 6. The same model also matches these measures across roughly redshifts 6–11, but underpredicts the abundance at redshift 14. The researchers therefore compare two possible fixes: more variable star formation or more efficient star formation. Both can match the brightness counts, but they predict different spectra. Between redshifts 10 and 14, the burstier model predicts more galaxies whose star formation has recently dropped and more with weak Hβ emission; the more efficient model predicts an unchanged share with recent drops and fewer weak emitters. These differences have not been established as observations here. Spectra of galaxies across a broad brightness range could help test which explanation works.

Young explorerJWST has spotted more galaxies in the very early universe than expected. Scientists used computer models to ask whether these galaxies made stars in big bursts, with quieter times in between. That idea matched some observations, but the model still did not make enough of the earliest galaxies. The scientists tried two possibilities: bigger bursts, or turning material into stars more efficiently. Both could explain how many bright galaxies there were, but they predicted different patterns in the galaxies’ light. Looking carefully at that light could help scientists find out which idea fits.

Gaia's dark partners: A new signature of dissipative dark matter

Badal Bhalla, David Dunsky, Akshay Ghalsasi+3 more

• High Energy Physics - Phenomenology

AstronomerThe authors evaluate dynamical exchange of dark compact objects (DCOs) into stellar binaries in dissipative dark matter (DDM) scenarios. A cooling dark matter subcomponent could form a dark disk and DCOs, not necessarily black holes, with low velocity dispersion; slow perturbers make exchange particularly efficient. Across a wide range of model parameters, even conservative assumptions yield exchange rates sufficient to account for Gaia’s candidate star–black hole systems, while some parameter regions predict rates well above observational estimates. This is a proposed formation channel, not a detection of DDM or confirmation of the candidates’ nature. Current and future binary data could potentially provide competitive constraints on DDM parameters and dark-sector cooling.

PublicGaia has found several pairs that appear to contain a star and a black hole. This study explores whether such pairs could arise from a hypothetical kind of dark matter that can cool, forming a disk and compact, invisible objects. These objects need not all be black holes. If one moves slowly past a pair of stars, it can eject one star and take its place. The authors calculate that this process could occur often enough to explain Gaia’s observed candidates across many versions of the model, even with conservative assumptions. Some versions predict more exchanges than observations suggest. The study does not show that this kind of dark matter exists, but suggests that Gaia’s data could help test it.

Young explorerGaia has found some stars that seem to have invisible partners called black holes. Scientists explored an idea: maybe a special kind of dark matter could cool down and make invisible, tightly packed objects. A slow-moving object might push one star out of a pair and become the other star’s new partner. Their calculations say this could happen often enough to explain the pairs Gaia has found, but some versions of the idea predict too many swaps. This does not prove the idea is right. Watching more star pairs could help scientists test it.

Tiny Galaxies, Mighty Nitrogen: Linking Chemical Anomalies to Compact Galaxies at High Redshift using JWST/JADES

Urvi Thakurdesai, Xihan Ji, Yuki Isobe+18 more

AstronomerUsing JWST/NIRSpec spectroscopy, the authors compare stacked rest-frame spectra of morphologically compact and extended galaxies at 4 < z < 7. The compact stack shows nitrogen emission, including NIV] and [NII], alongside carbon and oxygen lines. Detection of [OIII] λ4363 permits a direct electron-temperature determination of oxygen abundance. Inferred log(N/O) and log(C/O) are higher in compact systems than in extended systems by approximately 0.7 and 0.5 dex, respectively. The compact-stack abundance patterns resemble those of previously identified nitrogen-enhanced high-redshift galaxies and second-generation Milky Way globular-cluster stars. These population-level measurements suggest, but do not establish, a connection between compactness and enrichment pathways. Deeper NIRSpec IFU observations are needed to investigate the origin, spatial distribution, and evolutionary significance of the patterns.

PublicThe researchers used JWST spectra to compare compact and more spread-out galaxies in the early Universe. By combining spectra within each group, they found that compact galaxies have higher proportions of nitrogen and carbon relative to oxygen: about 0.7 and 0.5 units higher, respectively, on a base-10 logarithmic scale. The compact galaxies’ chemical patterns resemble those seen in some previously known nitrogen-rich early galaxies and in a population of stars in Milky Way globular clusters. The findings suggest that a galaxy’s compact shape may be connected to how it becomes chemically enriched, but they do not establish the cause or show that every compact galaxy shares this pattern. Deeper JWST observations will be needed to investigate where these elements are distributed and how the patterns arose.

Young explorerScientists used the JWST telescope to study light from galaxies from long ago. They combined the light from galaxies that look tightly packed and compared it with light from galaxies that look more spread out. The tightly packed group showed more nitrogen and carbon compared with oxygen. These are different kinds of ingredients that make up matter. Being tightly packed might be connected to how galaxies get their ingredients, but scientists do not yet know why. They need to look more closely to find out.

Lyα in Compact Broad-Line Emitters, Including Little Red Dots, Is More Closely Linked to the Host Galaxy than to the Broad-Line Nucleus

Yongda Zhu, Zheng Ma, Xiaojing Lin+16 more

• Cosmology and Nongalactic Astrophysics

AstronomerDeep JWST/NIRSpec spectroscopy from DIVER detects Lyα in six of 12 compact broad-line emitters at z=4.2–5.5 in GOODS-N, including little red dots, little blue dots, and other broad-line AGN. Although all sources show a broad-line region, detected Lyα lines have FWHM ≈300–1000 km/s, narrower than broad Hα at 1100–3300 km/s, and strong Hα relative to UV does not consistently accompany strong Lyα. Including upper limits, observed Lyα equivalent widths and luminosities track Lyα production inferred from dust-attenuated, AGN-subtracted host SED models more closely than Hα/UV. This favors a closer association with the host, but does not exclude nuclear emission: every detection exceeds its host-model prediction by a factor of 1.5–18. The detections have a median effective Lyα escape fraction of 0.09, which the authors interpret as suggesting typically modest, widely varying ionizing escape from CBEs, rather than directly measuring it.

PublicResearchers used deep JWST spectra to study 12 compact galaxies with visible active black holes in the early universe. They detected Lyman-alpha light from hydrogen in six. Those lines were narrower than the broad hydrogen-alpha lines associated with gas near the black holes, and their strengths more closely followed estimates for the host galaxies than a measure based on hydrogen-alpha and ultraviolet light. This suggests that the observed Lyman-alpha is more closely linked to the surrounding galaxy than to the active black hole. The origin is not fully settled: all six detections were 1.5–18 times stronger than the host models predicted, leaving room for a contribution from the nucleus. The estimated median effective Lyman-alpha escape fraction among detections was 9%. The authors interpret this as a clue that the escape of ionizing light is generally modest and varies substantially, not as a direct measurement of that escape.

Young explorerScientists used the Webb telescope to look at 12 faraway galaxies with black holes that are feeding on gas. They found a special kind of hydrogen light in six of them. That light seemed more connected to the galaxy around each black hole than to the gas very close to it. But the light was brighter than their galaxy models expected, so some could still come from near the black hole. They have clues about where the light comes from, but not a final answer.

A full chemical network treatment of supermassive black hole seed formation from dark matter annihilation or decay

Han Wu, Sarah Schon, Aaron C. Vincent

• Cosmology and Nongalactic Astrophysics
• High Energy Physics - Phenomenology

AstronomerQuasars discovered at z ~ 6–10.1 motivate alternatives to stellar-remnant seeds, which the authors argue cannot grow sufficiently massive even with efficient super-Eddington accretion. They investigate whether decay or annihilation of dark matter below about 200 eV could supply the UV flux needed for direct collapse of primordial, dust- and metal-free gas at z ~ 20. This radiation would photodissociate molecular hydrogen, suppressing cooling-driven fragmentation and star formation. One-zone thermal simulations using Grackle explore radiation from both the cosmological background and early halos across dark matter lifetimes, annihilation cross sections, and masses. The study identifies model parameter regions permitting direct collapse and corresponding maximum halo-mass requirements; it does not report an observed dark matter radiation signal or a directly observed collapse.

PublicDiscoveries of very massive black holes in the early universe raise the question of how they grew so quickly. This study explores a proposed shortcut: a pristine gas cloud collapsing directly into a black hole seed instead of forming stars first. Ultraviolet light could help by breaking apart hydrogen molecules that otherwise cool the gas and encourage it to fragment. The researchers simulate whether very light dark matter particles, through decay or annihilation, could provide enough of this light. Their simplified gas-cloud calculations identify conditions under which direct collapse could be possible, along with associated limits on halo mass. These are model-based possibilities, not evidence that dark matter actually supplied the light.

Young explorerAstronomers have found huge black holes from when the universe was very young. How did they get so big so fast? Scientists used computer models to explore whether a gas cloud could become a black hole without making stars first. They tested whether light from mysterious dark matter could help. Their models suggest this might work under some conditions, but they have not seen it happen.

Isophotal signatures of the brightest cluster galaxy - intracluster light transition

Giulia Golini, Sarah Brough, Louisa Canepa+2 more

AstronomerSeparating brightest cluster galaxies (BCGs) from intracluster light (ICL) remains definition- and method-dependent. The authors report a common inflection in radial surface-brightness, ellipticity, and position-angle profiles of BCG+ICL systems at 60–85 kpc, identified in Wendelstein Wide Field Imager observations at z < 0.1, deep Hyper Suprime-Cam observations at 0.2 < z < 0.4, and Horizon-AGN and Hydrangea cosmological hydrodynamical simulations. An automated second-derivative method locates the transition without parametric decomposition or arbitrary surface-brightness thresholds. Its persistence across photometric bands, redshift ranges, and simulations supports its robustness. The authors interpret the feature as a characteristic structural transition in the combined light distribution that may reflect hierarchical cluster assembly, rather than establishing an unambiguous BCG–ICL boundary. They propose the framework as a scalable tool for forthcoming LSST and Euclid surveys.

PublicIt is difficult to decide where a galaxy cluster’s brightest galaxy ends and the diffuse light between its galaxies begins, and that choice can strongly affect inferred cluster properties. The researchers found a recurring change in how brightness, apparent shape, and orientation vary with distance from the center, at radii of 60–85 kiloparsecs. The feature appears in telescope observations of clusters across different distance ranges and in computer simulations. Their automated method detects changes in these profiles without imposing a preset brightness cutoff or fitting separate mathematical components. The agreement across observations, light bands, and simulations supports the feature’s reliability, but does not establish a definitive dividing line. The authors suggest it may reflect how clusters assembled and propose using the method in future large surveys.

Young explorerIn a big group of galaxies, the brightest galaxy’s glow blends into faint light spread between the galaxies. That makes it hard to tell where one ends and the other begins. Scientists found a similar change in the glow’s brightness, shape, and direction in telescope pictures and computer-made models. They think this change might be a clue to how the galaxy group grew, but it is not a proven dividing line. Their new way of finding the change could help them study many more galaxy groups.

Galactic-Scale Distribution of 10Be and Its Implications for the Early Solar System 10Be/9Be

Yusuke Fujimoto, Steven J. Desch, Jiro Shimoda+1 more

• Earth and Planetary Astrophysics
• High Energy Astrophysical Phenomena
• Solar and Stellar Astrophysics

AstronomerMeteoritic inclusions indicate substantial short-lived 10Be in the early Solar System, but its origin remains debated. The authors present the first three-dimensional simulations of a Milky Way-like disc jointly following the multiphase interstellar medium, cosmic rays (CRs), and 10Be production and transport. In these models, Galactic CR interactions dominate production; supernova remnants supply at most about 10% of the 10Be inherited by newly formed stars. The 10Be/9Be ratio traces CR energy density and declines smoothly with galactocentric radius. Star-forming gas is roughly fivefold CR-enriched relative to the mean interstellar medium because star formation occurs where supernovae inject CRs, an effect missed by one-zone estimates. Allowing for a possibly higher Galactic star formation rate 4.6 Gyr ago, the models can reproduce the meteoritic ratio through inheritance alone, without local irradiation or late injection. Suppressing GCR-induced production in dense gas tenfold still yields the meteoritic value in the innermost disc, though elsewhere it falls short by a factor of a few. The inferred solar birth radius spans 3–8 kpc depending strongly on CR diffusivity, highlighting uncertainty in low-energy CR transport.

PublicMeteorites preserve evidence that the young Solar System contained a substantial amount of beryllium-10, a radioactive form of beryllium. Scientists debate whether it came from the cloud that formed the Sun or was made or added locally. New three-dimensional simulations of a galaxy like the Milky Way suggest that the Sun could have inherited it from its birth cloud. In the simulations, most beryllium-10 is produced by interactions involving Galactic cosmic rays, while supernova remnants contribute at most about 10% of what newborn stars inherit. Gas forming stars is exposed to roughly five times the average cosmic-ray energy density. If the Galaxy formed stars more rapidly 4.6 billion years ago, as is possible, this enrichment lets the models explain the meteorite evidence without local irradiation or a late addition of material. The result is not a direct measurement of the Sun’s birthplace: uncertain cosmic-ray transport gives inferred birth distances of 3–8 kiloparsecs from the Galactic centre. Reducing production in dense gas tenfold still matches the meteorite value in the innermost disc but leaves other regions a factor of a few short.

Young explorerOld space rocks hold clues that a special kind of material, called beryllium-10, was around when our Sun was a baby. Scientists made a computer model to explore where it came from. In their model, tiny, speedy particles called cosmic rays made most of it, and clouds where stars are born could pass it on to new stars. If our galaxy was making stars faster back then, this could explain what the space rocks tell us without needing to add the material later. But it is still a possible explanation, not proof, and the scientists are not sure exactly where in our galaxy the Sun was born.

The STARfall pathway: forging intermediate-mass black holes through stellar collisions in dense star clusters

Filippo Simonato, Manuel Arca Sedda, Taeho Ryu+15 more

AstronomerThis modeling study investigates repeated stellar collisions as a route to very massive stars and intermediate-mass black hole seeds. The authors develop STARfall, a semi-analytic tool tracking a massive stellar binary through binary-single interactions, mergers, collisions, and stellar evolution while accounting for host-cluster evolution. Their models show that clusters with central densities above 10^6 solar masses per cubic parsec can undergo a collision runaway, termed a starastrophe, within 3 million years. Despite strong stellar winds, the resulting very massive stars can collapse into black holes reaching 10^3–10^4 solar masses. Rapid core collapse and high central density are identified as essential conditions for very massive star assembly. Comparisons with observed systems suggest that compact Cosmic Gems Arc clusters and several Milky Way globular clusters could have hosted this process. Inferred Little Red Dot central densities may also support it, despite longer core-collapse timescales. These are model-based formation scenarios, not observational confirmations of intermediate-mass black holes in these systems.

PublicCould crowded star clusters make medium-sized black holes by repeatedly smashing stars together? This study explores that possibility with a mathematical model called STARfall. In the models, exceptionally dense cluster centers can trigger a rapid chain of stellar collisions within 3 million years. The growing stars can become massive enough to collapse into black holes weighing roughly 1,000–10,000 times as much as the Sun, even while losing material through strong stellar winds. The models require both very crowded centers and a rapid concentration of stars toward the center. Comparisons with observed clusters in the Cosmic Gems Arc and the Milky Way suggest that some could once have supported this process. Little Red Dots may also offer suitable conditions. The study does not confirm that these systems contain such black holes.

Young explorerImagine lots of stars crowded close together. Scientists used a model to explore what could happen if some stars kept bumping into each other and joining together. A star might grow very big, then collapse into a black hole. The model suggests this could happen in some very crowded groups of stars, but it does not prove that those groups really made black holes this way.

Revisiting the Missing Baryon Problem: Baryon Redistribution Across Halo Evolution

Changjo Seo, Seyoung Jeon, Emanuele Contini+8 more

AstronomerUsing the NewCluster simulation, the authors trace halo assembly histories and gas tracer particles to investigate why halo baryon fractions fall below the cosmic mean. They identify three evolutionary phases: early growth through cold accretion in low-mass halos, suppression likely dominated by supernova feedback, and recovery in massive halos through deeper potential wells and hot-mode accretion. In the simulation, suppression emerges after surrounding intergalactic gas becomes persistently hotter than the halo virial temperature, influencing redshift evolution particularly at low halo masses. At fixed halo mass, baryon-fraction scatter also correlates with large-scale environment: baryon-rich halos preferentially lie closer to filaments. These simulation findings support a time-resolved picture involving both feedback and environment; the proposed dominance of supernova feedback in the suppression phase remains an interpretation.

PublicDark matter halos contain less ordinary matter than would be expected from the universe-wide average, a discrepancy called the missing baryon problem. This study uses a computer simulation, rather than new observations, to follow how halos gain and lose their share of ordinary matter. The researchers identify three stages: small halos first grow by taking in cold gas, their supply is then suppressed, probably mainly by energy released by exploding stars, and massive halos later recover ordinary matter through stronger gravity and the intake of hot gas. Suppression appears after nearby gas stays hotter than the halo’s characteristic temperature, especially affecting smaller halos. Among halos of the same mass, those richer in ordinary matter tend to be nearer large cosmic filaments. The results suggest that both the surrounding gas and energy released by stars shape how ordinary matter is distributed over time.

Young explorerScientists used a computer model to watch how big space clumps collect ordinary stuff, like gas. In the model, small clumps first gather cold gas. Later, gathering gets harder, probably mostly because exploding stars push gas around. Bigger clumps can gather more gas again because their gravity is stronger. Nearby gas that stays too hot can also make collecting harder. Clumps near long strands of matter tend to have more ordinary stuff than other clumps of the same weight. These are clues from a computer model about how space clumps change as they grow.

H 0557-385: A Candidate Missing Link Between Radio-Quiet Seyferts and Young Radio Galaxies

J. Chauhan, T. D. Russell, A. Lohfink+9 more

• High Energy Astrophysical Phenomena

AstronomerA 0.076–258.8 GHz spectral analysis of the Seyfert 1 galaxy H 0557-385 (z = 0.034), combining new ATCA observations with archival MWA, ASKAP and ALMA data, challenges its radio-quiet classification based on radio-to-optical flux ratio. The spectrum requires a compact, self-absorbed component with a stratified GPS/HFP shape, turning over at 9.4 (+0.6/−0.5) GHz, plus an extended, optically thin power-law lobe with spectral index −0.78 that dominates below approximately 1.6 GHz. Derived estimates of size (~15 pc), equipartition magnetic field (2.8 mG), synchrotron age (≤1,800 yr), and time-averaged jet power (~5 × 10^41–5 × 10^44 erg s−1) resemble those of young compact steep-spectrum and GPS radio galaxies. The present data cannot distinguish a growing lobe in a genuinely young radio galaxy from relic plasma left by an earlier jet episode. The authors interpret the source as a newly ignited or recently re-triggered radio galaxy within an optical Seyfert, making it a candidate link between radio-quiet AGN and large-scale radio galaxies. High-resolution imaging and multi-epoch monitoring are needed to test the alternatives.

PublicH 0557-385 has long been called a radio-quiet galaxy because its radio emission is weak relative to its optical light. A new analysis spanning a wide range of radio frequencies suggests that this label misses its physical character. The radio spectrum requires two components: a compact region that absorbs some of its own radio emission and a more extended lobe that dominates at lower frequencies. Properties inferred from the analysis resemble those of young radio galaxies powered by jets, rather than typical radio-quiet active galaxies. However, the observations cannot establish whether the extended emission comes from a lobe now growing around a young jet or is material left over from an earlier episode of jet activity. The authors therefore propose that this galaxy could help connect radio-quiet active galaxies with large radio galaxies. Sharper images and repeated observations are needed to distinguish the possibilities.

Young explorerA galaxy called H 0557-385 was thought to be fairly quiet in radio waves, a kind of light our eyes cannot see. Scientists studied its radio waves and found signs of a small radio-making region and a bigger cloud. They think the galaxy may have recently started, or restarted, sending out a jet of material. But they cannot yet tell whether the bigger cloud is growing now or was left behind by an older jet. They need sharper pictures and more looks over time to find out.

X-rays from Low-mass Active Galaxies in the Galaxy And Mass Assembly (GAMA) Survey

Stellan Bechtold, Amy Reines, Richard Plotkin+1 more

AstronomerNew Chandra observations detect X-ray emission in six of seven GAMA-selected broad-line AGNs hosted by galaxies with stellar masses below 5 × 10^9 solar masses. Detected 0.5–8 keV luminosities span log(L/erg s⁻¹) ≈ 40.5–43.8. Luminosities generally above X-ray binary predictions and positions close to optical nuclei favor accreting massive black holes as the dominant emitters. Fits for four sources give photon indices of approximately 1.7–2.2, with little evidence for intrinsic absorption in most cases. Virial masses and hard-X-ray bolometric corrections imply nominal Eddington ratios of approximately 0.004–1.1, but with substantial uncertainties; optical tracers generally imply higher luminosities and Eddington ratios, especially for the X-ray nondetection. X-ray-bright sources broadly follow optical AGN scaling relations involving Hα and [O III], but most fall below the established X-ray–mid-infrared relation, possibly because of host-galaxy contamination. Four sources are consistent with the expected UV-to-X-ray spectral slope relation, while three show evidence of relative X-ray weakness. The sample illustrates diverse accretion-related X-ray properties and the value of multiwavelength diagnostics, including for interpreting high-redshift broad-line AGN candidates.

PublicChandra observations found X-rays in six of seven low-mass galaxies selected for signs of active black holes. The emission is generally brighter than expected from populations of X-ray-emitting binary stars and lies close to the galaxies’ centers, favoring feeding massive black holes as its main source. The galaxies nevertheless show varied X-ray behavior: three have evidence of weaker X-rays relative to ultraviolet light than expected. Estimates of how rapidly the black holes are feeding are substantially uncertain, and estimates based on visible light generally suggest greater power than those based on X-rays. Some infrared comparisons may also be affected by light from the host galaxies. The findings highlight why astronomers need several kinds of light to understand these systems.

Young explorerAstronomers looked at seven galaxies with relatively few stars and found X-rays in six of them. These rays probably come mostly from hot material falling toward big black holes near the galaxies’ middles. The galaxies do not all shine the same way. Looking at different kinds of light helps astronomers learn what is happening, but some answers are still uncertain.

He I λ10830 Resonant Scattering in M17: Toward a Diagnostic of Optical Depth and Gas Kinematics

Hiroaki Sameshima, Daisuke Taniguchi, Noriyuki Matsunaga+2 more

AstronomerMagellan/WINERED spectra at R ≈ 70,000 sample six pointings from CEN 1 across M17’s southwestern bar. He I λ10830 is multi-peaked at every pointing, whereas Paγ, recorded in the same exposures, is single-peaked. Because Paγ does not undergo resonant scattering, this contrast argues against a purely kinematic origin of the He I peaks; the shared exposures exclude an instrumental origin. The authors attribute the splitting to resonant scattering, consistent with Draine’s prediction. Comparisons using systemic-velocity-independent width and asymmetry measures show that, at two pointings far from CEN 1, no static, spherically symmetric model at any optical depth matches both measures: the profiles are more red-weighted than models of comparable width. This behavior cannot arise from uniform motion but is expected for scattering in expanding gas. The authors argue that resolved He I λ10830 profiles could diagnose both kinematics and optical depth in the He+ zone.

PublicObservations at six positions in the star-forming region M17 show several peaks in a helium spectral line but only one peak in a hydrogen line measured in the same exposures. The hydrogen line traces gas motion without the resonant scattering that affects the helium line. This comparison argues against gas motion alone explaining the helium peaks, and the shared exposures rule out an instrumental explanation. The researchers interpret the peaks as evidence that helium-line photons repeatedly scatter through the gas, as previously predicted. At two positions far from the ionizing source CEN 1, static, spherical models cannot reproduce both the width and the imbalance toward the red side of the helium profiles. Scattering in expanding gas is a possible explanation for that mismatch. The authors suggest that these helium profiles could become a way to study both gas motion and how strongly the gas scatters this light.

Young explorerScientists looked at light from a glowing gas cloud called M17. One kind of helium light made several bumps in their measurements, while a kind of hydrogen light made just one. They think the extra bumps happen because the helium light keeps bouncing around in the gas before it gets out. At two places, models of gas sitting still could not explain the shapes of the bumps. Gas spreading outward might explain them better. The scientists hope these light patterns can help them learn how the gas moves and how much it makes light bounce around.

Estimating LuSEE-Night's Sensitivity to Cα Radio Recombination Lines

Fatima Yousuf, Aurelia Gerber, Zack Li+37 more

AstronomerThis modeling study assesses carbon radio recombination lines (CRRLs) from the cold neutral medium as potential foregrounds and diagnostic signals for LuSEE-Night's planned 1–50 MHz lunar-far-side observations. The authors include Doppler, collisional, and radiation broadening, estimate line strengths by fixing either peak or frequency-integrated optical depth, and consider uniform and region-dependent sky prescriptions informed by previous low-frequency observations. Six sky models are propagated through the expected beam and polyphase-filter-bank spectrometer response, including approximately 390 Hz zoomed-mode resolution. Simulated individual-line detections at SNR=5 require integration times ranging from 30 hours in the most optimistic model, with optical depth around 10^-3, to 27.6 years in the most conservative models, with optical depth around 10^-4. Stacking 361 simulated carbon alpha lines between 10 and 50 MHz reduces the corresponding estimates to approximately 11 minutes and 151 hours. These are model-dependent forecasts, not detections; they suggest that a stacked detection could be achievable within a realistic mission lifetime even under the conservative optical-depth assumptions considered.

PublicCold gas between stars can produce faint radio features from carbon that may both complicate LuSEE-Night's observations and reveal the gas's temperature, density, and surrounding radiation. The planned experiment will observe from the Moon's far side. Researchers simulated these features and the instrument's expected response using six models of the sky. Depending on the assumed signal strength, detecting a single feature could require anything from 30 hours to 27.6 years of observing. Combining 361 simulated carbon features between 10 and 50 MHz greatly improves the forecast: the estimated observing time falls to about 11 minutes in the most optimistic case and 151 hours in the most conservative cases. These predictions suggest a combined detection may be practical, but they are not actual observations and depend on the models' assumptions.

Young explorerCold gas between the stars can make tiny radio signals. Scientists used computer models to see whether a future radio listener on the far side of the Moon could hear them. One signal might take a very long time to notice. Combining lots of signals could make them easier to find. The models suggest this could work, but the Moon listener has not heard them yet.

Evidence for strong shocks in the ISM of small radio sources

Valeria Lopez, Mark Lacy

AstronomerThe study compares two radio-loud AGN samples selected by cross-matching VLASS with DESI DR1 at 0.15 < z < 0.5, requiring [OI] 6300 detections above 5 sigma. Projected radio sizes of 10–15 kpc identify jets classified as confined within their hosts, while sizes above 25 kpc identify jets classified as having broken out. Profile fitting, W80 measurements, and [OI]/H-alpha versus [OIII]/H-beta diagnostics show that confined sources have broader [OIII] emission, lie systematically closer to the LINER region, and are less frequently detected in [NeV] 3426. Redshift and dust do not explain the [NeV] detection difference. Broad components are not systematically blueshifted, so the distinction is in line width rather than outflow velocity. The authors interpret these findings as evidence for strong jet-driven shocks in the host interstellar medium; the diagnostics do not constitute a direct measurement of shock velocities.

PublicThis study compares active galaxies whose radio jets are still inside their host galaxies with those whose jets extend beyond them. Using radio and optical survey data, the researchers find that galaxies with confined jets have broader oxygen emission lines, indicating more disturbed gas. Their emission-line patterns also shift toward a region associated with different gas-excitation conditions, and they less often show a neon line that traces intense ultraviolet light from the black hole's accretion disk. The neon difference is not explained by dust or redshift. The broad lines are not consistently shifted toward us, so they indicate greater gas disturbance rather than systematically faster outflows. Together, the findings support the authors' interpretation that confined jets drive strong shocks through their galaxies' gas.

Young explorerSome galaxies have powerful jets coming from their centers. The researchers compared galaxies where the jets are still inside with galaxies where the jets reach outside. Light from the gas shows that gas in galaxies with jets still inside is more stirred up. Other clues in the light also differ. The researchers think the trapped jets are making strong shock waves in the gas. The clues support that idea, but they do not show that the gas is always rushing toward us faster.

Interstellar and intergalactic medium in the ultraviolet band

M. S. Kirsanova, S. A. Balashev, M. V. Barkov+11 more

• Plasma Physics

AstronomerThis overview outlines astrophysical and astrochemical questions concerning the interstellar and intergalactic media that could be addressed by Spektr-UF, a Russian ultraviolet space observatory being prepared for launch. UV absorption and emission lines provide diagnostics of physical conditions, chemical abundances, and processes in these environments. Prospective applications include helium reionization and the Universe’s thermal history, ongoing star formation, galactic chemical evolution at intermediate redshifts, hidden baryons and metals, small-scale interstellar cloud structure, photodissociation regions, and protoplanetary disks. The article also discusses modeling UV emission from nebulae around fast-moving pulsars. Spektr-UF’s anticipated sensitivity and spectral resolution motivate these prospects; the abstract reports an overview of opportunities rather than new observational results.

PublicThe paper explores how ultraviolet light could help scientists study the material between stars and between galaxies. Patterns of light absorbed or emitted by atoms and molecules reveal what this material contains and what conditions are like within it. The Russian space observatory Spektr-UF, currently being prepared for launch, is expected to provide sensitive, detailed ultraviolet observations. These could help trace how the Universe’s temperature and galaxies’ chemical makeup changed, locate matter that is difficult to detect, and map ongoing star formation. Other topics include interstellar clouds, disks where planets can form, and models of glowing material around fast-moving pulsars. These are research prospects, not discoveries already made by Spektr-UF.

Young explorerThere is material in the spaces between stars and galaxies. A kind of light called ultraviolet can give scientists clues about what that material is made of and what it is like. This paper describes how a space telescope called Spektr-UF might help read those clues and study places where stars and planets form. The telescope is still being prepared for launch, so these are things scientists hope to learn, not things it has found yet.

Mass-Metallicity Relation of the Fossil Disk in Six Nearby Galaxies using JWST RGB Stars

Avinash Ck, Divakara Mayya, Alessandro Bressan+4 more

AstronomerThe authors report the first mass–metallicity relation for fossil disk populations, derived from resolved RGB stars in JWST/NIRCam images of six nearby galaxies. They infer masses and metallicities by comparing colors, magnitudes, and stellar number densities near the TRGB in F115W−F200W versus F200W diagrams with 4 and 13 Gyr PARSEC isochrones. The inferred metallicities closely match those reported for galaxies at z>8 and follow a power law with fossil disk mass, with slope γ≈0.26, comparable to typical gas-phase MZR slopes across redshifts. These are stellar-model-based inferences, rather than direct gas-metallicity measurements. The authors present the approach as a new avenue for near-field cosmology, offering previously unavailable precision for fossil disk mass and metallicity estimates.

PublicUsing James Webb Space Telescope images of six nearby galaxies, researchers report the first relationship between the mass of their fossil disk stellar populations and their heavy-element content. They estimated both quantities by comparing the colors, brightnesses, and abundance of red giant stars with stellar models. More massive fossil disk populations tend to have higher heavy-element content, following a pattern similar to relationships measured using gas in galaxies. Their inferred heavy-element levels also closely resemble those reported in very distant galaxies at redshifts above 8; this similarity does not itself establish that the populations share the same history. The work offers a new way to investigate cosmic history through stars in nearby galaxies.

Young explorerScientists used the James Webb Space Telescope to look at red giant stars in six nearby galaxies. They compared the stars with models and found a pattern: the old disk star groups with more mass tended to have more heavy elements. These nearby stars could give scientists a new way to learn about the universe’s past.

An automated photometric pipeline for measuring the corotation radius of spiral galaxies

Kimia Yazdani, Sahel Mesforoush, Wayne B. Hayes

• Computer Vision and Pattern Recognition
• Data Analysis, Statistics and Probability

AstronomerThe authors present an automated photometric pipeline for identifying candidate corotation radii, where the spiral pattern and disk material have matching angular speeds. Using deprojected dual-band images, the method fits periodic models to azimuthal brightness profiles and locates sign reversals in the phase offset between young and old stellar tracers. Candidates receive adaptive uncertainty intervals and goodness-of-fit metrics. Against a reference constructed solely from published measurements and evaluated leave-one-out, the pipeline identifies at least one correct radius in 80.0% of 90 galaxies, recovers 63.6% of known corotation radii, and achieves a recall–purity harmonic mean of 0.58, the highest reported values in the comparison. These scores measure agreement with a literature-derived reference rather than independent ground truth. Unlike the comparison methods, which were applied to smaller curated samples, the pipeline was run on the full reference sample without pre-selection. The authors describe it as survey-scalable, flexible with respect to spiral mode, and able to recover multiple corotation radii in complex systems.

PublicA spiral galaxy’s arm pattern and its disk material need not move around at the same rate. The corotation radius is the distance from the center where their rates match. This study presents an automated way to find candidate matching distances from images in two wavelength bands, tracking how the relative positions of young and old star populations change across the disk. In a test involving 90 galaxies, the method found at least one matching radius in 80.0% of galaxies and recovered 63.6% of the radii in the published reference. It achieved the highest comparison scores, although the reference comes from earlier measurements rather than an independent test of the true radii. The other methods had also been used on smaller, specially selected samples. The authors say the pipeline can handle large surveys and identify more than one corotation radius in galaxies with complicated spiral patterns.

Young explorerA spiral galaxy has a pattern of arms, and its stars move around too. At some distances from the middle, the stars and the arm pattern can go around at the same rate. Scientists made a computer tool that looks at pictures of younger and older stars to find where this might happen. They checked it against earlier measurements in 90 galaxies, and it found at least one matching place in most of them. Those earlier measurements are not a perfect answer key, so the places it finds are still candidates. The scientists say the tool could help them study many more galaxies.

The vertical distribution of molecular gas in the fourth quadrant of the Milky Way

L.-H. Lin, F. Wyrowski, S. Neupane+2 more

• Solar and Stellar Astrophysics

AstronomerAPEX observations probe the poorly studied vertical molecular-gas distribution in two fourth-quadrant arm-tangent regions: Galactic longitudes 329.0 to 327.0 degrees for Norma-Outer and 310.0 to 308.5 degrees for Scutum-Centaurus. The 7-pixel LASMA receiver on the 12 m telescope mapped 12CO 3-2 emission over latitudes extending from -2 to +2 degrees, corresponding to heights of approximately 200 pc in absolute value near the tangent points. The noise is about 0.4 K in main-beam brightness temperature per 0.5 km/s channel. These observations extend beyond the latitude coverage of most recent surveys, which are restricted to absolute Galactic latitudes below 1 degree and/or emphasize the northern Galactic plane; surveys over 20 years ago had coarse beams and non-Nyquist sampling. Two-Gaussian fits near the arm tangencies yield narrow and broad components with FWHM thicknesses of 25 pc and about 100 pc. The authors propose either two thin-disk subcomponents associated with arm and interarm gas, respectively, or thin and thick disks that appear thinner in CO 3-2 than in CO 1-0. The latter interpretation would indicate a steeper interstellar-medium density gradient at greater heights. Compared with clumps at absolute relative heights below 50 pc, those between 50 and 100 pc have lower excitation temperatures and surface densities, with fewer high values in their distributions. A similar mass trend is tentative. The physical identification of the two fitted components remains interpretive, not an established result.

PublicResearchers mapped molecular gas in two regions where our view runs along Milky Way spiral arms, using the APEX telescope. The maps extend from -2 to +2 degrees in Galactic latitude, reaching roughly 200 parsecs from the Galactic plane near these locations. The observed vertical gas distribution can be fitted with two components, with thicknesses of 25 parsecs and about 100 parsecs. What those components represent is uncertain. They might both belong to the thin disk, with the narrower component tracing spiral-arm gas and the broader one tracing gas between arms. Alternatively, they might trace thin and thick disks that appear thinner in the observed CO 3-2 emission than in CO 1-0 emission. That second interpretation would suggest that gas density falls more steeply at greater heights. Gas clumps between 50 and 100 parsecs in absolute relative height have lower excitation temperatures and surface densities than clumps below 50 parsecs, with fewer high values. A similar pattern in clump mass is only tentative.

Young explorerScientists used a telescope to look at gas in two parts of our Milky Way. They found that the gas's spread above and below the galaxy's middle can be described by a narrow layer, 25 parsecs thick, and a wider layer, about 100 parsecs thick. A parsec is a way to measure space distances. They are not sure whether these are different parts of one thin disk or a thin disk and a thicker disk. Gas clumps farther from the middle showed lower temperature measurements and less material per area than nearby clumps. They might also have less mass, but that clue is not yet clear.

Tidal Evolution of Satellite Dwarf Galaxies. I. Tidal Tracks of Stellar Mass and Structure

Feihong He, Fangzhou Jiang

AstronomerUsing 480 controlled N-body simulations of satellites containing dark matter and stars orbiting a Milky-Way-mass host, the authors quantify stellar responses to tidal stripping across a broad range of initial halo and stellar structures. They provide a library of tidal tracks and fitting functions for stellar mass, half-mass radius, mean surface density, and line-of-sight velocity dispersion as functions of the bound dark-matter subhalo mass fraction. In these simulations, stellar compactness controls how long stellar mass remains relatively intact as dark matter is stripped, while the Sérsic index and inner dark-matter density slope govern late-stage stellar mass loss and remnant contraction or expansion. The simulation-based framework is intended for semi-analytical satellite-evolution models; tidal reshaping is presented as a possible contributor to observed dwarf-galaxy structural diversity, not as an established explanation for all of it.

PublicA large galaxy’s gravity can strip material from smaller satellite galaxies and reshape them. This study explores that process with 480 computer simulations of galaxies containing stars and dark matter orbiting a host with the mass of the Milky Way. The simulations track changes in the satellites’ stellar mass, size, average surface density, and the spread of stellar speeds as dark matter is lost. They show that how tightly the stars are packed helps determine how long the satellite retains its stars while losing surrounding dark matter. The initial distribution of stars and the central dark-matter structure also affect later star loss and whether the remaining galaxy shrinks or expands. The authors supply formulas for modelling these changes. This process may explain some of the variety seen among dwarf galaxies, but the study does not establish how much.

Young explorerA big galaxy’s gravity can pull material away from a little galaxy moving around it. Scientists made 480 computer versions of little galaxies to explore what happens. In their computer experiments, little galaxies with tightly packed stars could keep those stars while losing some of the dark matter around them. How the stars and dark matter were arranged also helped decide whether the little galaxy later got smaller or bigger. These are computer results that may help explain why real little galaxies have different shapes and sizes.

Constraining Dust Properties Along the Minor Axis of Andromeda

Sihan Jiao, Linjing Feng, Henrik Beuther+16 more

AstronomerNew IRAM 30m/NIKA2 1.15 mm observations along M31’s minor axis resolve approximately 40 pc at 11 arcsec. Combined with Herschel and JCMT SCUBA-2 maps, pixel-by-pixel single-component modified blackbody fits show that including 850 μm and 1.15 mm measurements reduces the dust temperature–emissivity-index degeneracy. The fits yield an average β ≈ 1.8, systematically below far-infrared-only estimates, and higher β in the 5 kpc ring than in the 10 kpc ring. The authors suggest that elevated inner-region β could reflect dust-composition changes potentially associated with enhanced starlight heating; this is an interpretation, not an established cause. The results emphasize the importance of long-wavelength SED coverage for constraining β, with the inferred values dependent on the adopted single-component fitting model.

PublicResearchers combined new millimeter-wavelength observations of dust in the Andromeda galaxy with existing shorter-wavelength maps. Measuring dust across a broader range of wavelengths helps separate two effects that can otherwise be difficult to distinguish: its temperature and how its emission changes with wavelength. Their model fits give an average emission index of about 1.8, lower than estimates based only on far-infrared data. They also infer a higher index in the ring 5 kiloparsecs from the galaxy’s center than in the ring at 10 kiloparsecs. Changes in dust composition, possibly associated with stronger starlight heating toward the inner region, could explain the difference, but that explanation remains uncertain.

Young explorerScientists looked at dust in a galaxy called Andromeda using kinds of light our eyes cannot see. Adding a new kind of light helped them better tell how warm the dust is and how it shines. Their calculations suggest that dust in an inner ring shines differently from dust in a ring farther out. The dust might be made of different stuff, perhaps connected to stronger heating by stars, but the scientists do not know for sure.

HI Emission Recovery in the Low-Redshift Radio Population: Host-Galaxy and Radio-Luminosity Dependence in FASHI and LoTSS

Soumen Kumar Bera, Taotao Fang, Chuan He+1 more

AstronomerCross-matching FASHI DR1 with the LoTSS DR2 value-added catalog yields 4,392 one-to-one associations. In a 2,912-square-degree comparison region, the authors measure HI recovery for 25,573 low-redshift, spectroscopic, radio-selected sources whose expected HI lines lie within the FASHI band. Radio-loud AGN have a lower unadjusted recovery rate than star-forming sources: 9.27% versus 14.88%, with an odds ratio of 0.585 (0.491–0.697). However, their host populations differ substantially, including a 1.34-dex difference in median specific star formation rate. Within overlapping stellar-mass and star-formation ranges, no statistically significant residual class difference is detected: adjusted odds ratio 1.60 (0.87–2.94). In that overlap, each dex of 144 MHz luminosity is associated with recovery odds higher by a factor of 2.03 (1.54–2.68), after adjustment for measured host properties, redshift, and an approximate sensitivity proxy. This association is carried primarily by star-forming sources, not the radio-AGN subsample. These are empirical relationships with detectable HI emission, not evidence that radio activity changes HI mass; the catalog and recovery measurements characterize which radio sources a blind HI survey samples.

PublicResearchers compared two radio-survey catalogs to find out which radio sources were also detected through emission from neutral hydrogen gas. Among 25,573 eligible sources in their comparison sample, sources classified as radio-loud active galactic nuclei were detected less often than star-forming sources: about 9% versus 15%. But the groups also differed substantially in their host-galaxy properties. When the researchers compared sources with overlapping stellar masses and star-formation rates, the remaining detection-rate difference was not statistically significant. Greater low-frequency radio luminosity was still linked to a higher chance of hydrogen detection after accounting for several measured factors, mainly among star-forming sources. This does not show that radio activity adds or removes hydrogen gas. The study describes which parts of the radio-source population a hydrogen survey detects.

Young explorerScientists compared two radio maps of space to see which galaxies showed a signal from hydrogen gas. Galaxies making new stars were found more often than galaxies with bright radio activity around their centers. But that difference was not clear when they compared galaxies with similar properties. The study does not show that radio activity makes galaxies gain or lose gas.

Probing the Faint Outskirts of Star-Forming Galaxies with 1<z<9 Using Stacked Images

Cheng Jia, Enci Wang, Yangyao Chen+8 more

AstronomerUsing deep JWST/NIRCam imaging from CEERS, JADES, and PRIMER, the study stacks 14,812 face-on star-forming disk galaxies at 1 < z < 9 with log(M*/M_sun) > 8.5 to measure faint outer light profiles. Stacks are binned by stellar mass and redshift, accounting for cosmological surface-brightness dimming, angular-size scaling, and PSF convolution, with residual backgrounds estimated from blank-sky stacks. Colors generally become bluer outward, supporting an inside-out growth interpretation, although galaxies with log(M*/M_sun) < 9.5 at z > 2.5 show a weak reversal in their outermost color gradients. Outer profiles are generally well described by exponential declines. Scale lengths measured beyond 2Re have mass and redshift dependences similar to the conventional mass-size relation, suggesting that outer light is linked to processes governing inner-galaxy growth rather than serving as a direct tracer of ex-situ stars. Little wavelength dependence in the outer scale lengths suggests a limited role for dust attenuation at these radii.

PublicAstronomers combined deep James Webb Space Telescope images of 14,812 disk-shaped, star-forming galaxies to study their very faint outer regions. Grouping galaxies by mass and redshift made this faint light easier to measure. Most groups become bluer toward their edges, a pattern consistent with galaxies growing from the inside outward. Some lower-mass galaxies at higher redshifts show a slight reversal at their farthest edges, suggesting a more complicated mix of stars. The outer light generally fades exponentially, and its extent changes with galaxy mass and redshift in much the same way as conventional galaxy size measurements. The authors interpret this similarity as evidence that the outskirts are connected to the processes growing the inner galaxy, rather than directly revealing stars acquired from other galaxies. Measurements at different wavelengths also suggest that dust has only a limited effect on these outer regions.

Young explorerGalaxies are huge groups of stars, and their edges can be very faint. Astronomers combined telescope pictures of many galaxies to see those edges better. Most looked bluer farther out. That is a clue that these galaxies may grow from the middle outward, but some had a slightly different color pattern at the very edge. The starlight usually faded smoothly away from the middle. The researchers think the edges and the middle may grow in connected ways, though these clues do not tell the whole story.

The TNG50-SKIRT Atlas: Multi-wavelength properties of galaxy discs in the TNG50 simulation

Abdissa Tassama Emana, Maarten Baes, Angelos Nersesian+5 more

AstronomerThis study measures exponential disc scale lengths from one-dimensional surface-brightness profiles of TNG50-SKIRT Atlas synthetic images. The analysis selects nearly face-on, star-forming galaxies with exponential r-band profiles and uses a consistently defined disc region across bands. Most TSA galaxies exhibit exponential discs in realistic mock observations. The simulated sample reproduces the observed scale length–stellar mass and scale length–luminosity relations, but with systematically larger scale lengths at fixed mass or luminosity; morphology dependence is weak. Scale lengths correlate strongly between bands and decrease toward longer wavelengths. Normalisation by the stellar-mass scale length yields an optical-to-near-infrared trend consistent with observations. Comparisons of dust-attenuated images, dust-free images, and intrinsic stellar population maps identify radial stellar-age gradients as the primary driver, with metallicity gradients secondary. Dust enhances the short-wavelength dependence but is not its main origin. Absolute scale-length offsets remain between simulations and observations.

PublicResearchers used synthetic images of simulated galaxies to study how their discs look at different wavelengths of light. They focused on star-forming galaxies viewed nearly face-on whose brightness declines exponentially across the disc. The simulated discs generally have shorter brightness scale lengths at longer wavelengths, meaning their light is more centrally concentrated. This wavelength trend agrees with observations when measured relative to the scale length of the stellar mass distribution, although the simulated discs remain systematically larger than real ones at the same stellar mass or luminosity. Comparisons with and without dust indicate that changes in stellar age across the discs drive most of the wavelength effect. Changes in stellar metal content contribute less, while dust strengthens the effect at short wavelengths.

Young explorerScientists made pretend pictures of galaxies using a computer. In different kinds of light, the same galaxy’s glowing disc can look more spread out or more gathered toward the middle. Their tests suggest that differences in how old the stars are matter most, while dust helps too. The pretend galaxies still do not match real ones perfectly.

GAMA-23 deep field with uGMRT Band-2: source catalogue and source count

Rashmi Sagar, Abhirup Datta, Aishrila Mazumder

AstronomerApproximately five hours of uGMRT Band-2 observations at 120–250 MHz produced a 183 MHz image of the GAMA-23 field covering 5.86 deg², with a 15.4 × 8.2 arcsec restoring beam and off-source RMS noise of 320 μJy beam⁻¹. The resulting catalogue contains 569 sources detected at ≥5σ. Flux densities and positions were cross-checked against existing radio catalogues. Power-law spectral fits give indices of −0.68 (+0.18/−0.23) for the ASKAP EMU comparison and −0.72 (+0.19/−0.24) for the NVSS comparison. Normalised source counts agree with models and previous observations at a nominal catalogue threshold of 1.7 mJy, although sensitivity varies across the image.

PublicResearchers used about five hours of observations with the upgraded Giant Meterwave Radio Telescope to map low-frequency radio emission from a patch of sky in the GAMA survey. The map covers 5.86 square degrees and yields a catalogue of 569 radio sources detected above a five-times-noise threshold. Comparisons with other radio catalogues checked the sources’ brightness measurements and positions, and measurements across frequencies characterised how their radio brightness changes. The source counts agree with models and earlier observations. However, the map is more sensitive in some places than others, so its ability to detect faint sources is not uniform.

Young explorerAstronomers used a special telescope to make a map of radio signals from a patch of sky. They listed 569 things whose signals stood out clearly enough from the background fuzz. They checked their map against other radio maps. The counts fit what earlier studies and models showed, but some parts of the new map can pick up fainter signals than others.

Does Topology-Dependent Chemistry Influence the Interstellar PAH Inventory? Insights from the Absence of Cyanotriphenylenes

Huanyu Ren, Gabi Wenzel, Thomas H. Speak+8 more

AstronomerThe study tests whether thermodynamic stability alone explains the PAH inventory in TMC-1 using triphenylene (C18H12), the smallest fully benzenoid PAH predicted by Clar’s rule. The authors synthesized cyanotriphenylenes and measured their first microwave rotational spectra over 6.5–16 GHz, providing polar tracers of the non-polar parent. An astronomical search using these parameters yielded no detection. This suggests, but does not establish, a relative depletion of triphenylene despite its exceptional stability. A proposed ring-node representation classifies triphenylene as topologically non-compact and reveals tentative clustering of detected and undetected PAHs by topology. The authors interpret this pattern as evidence that stability alone may be insufficient and that formation and destruction kinetics may matter. Proposed explanations are sequential growth decay along bottom-up pathways and rapid consumption of bay-region intermediates by reactive unsaturated small species.

PublicWhy are some ring-shaped carbon molecules found in the cold cloud TMC-1 while others seem to be missing? This study examined triphenylene, an exceptionally stable molecule whose apparent absence challenges the idea that stability alone determines which molecules accumulate. Because triphenylene itself is non-polar, the researchers made related molecules containing a cyano group and measured their characteristic microwave signals in the laboratory. A search for those signals in space found no detection, suggesting—but not proving—that triphenylene is relatively scarce in TMC-1. The team also proposed a way to classify these molecules by how their rings connect. They found a tentative pattern linking this structure to detections and non-detections. Their interpretation is that chemical growth and destruction processes may help determine which molecules survive, rather than stability alone.

Young explorerIn a cold cloud in space, scientists have found some tiny molecules made of connected carbon rings. They looked for clues to another one called triphenylene, whose rings hold together especially well. First, they made related molecules in a laboratory and measured signals that could help them search in space. They did not find those signals in the cloud, but that does not prove triphenylene is not there. The scientists think the way the rings connect may matter: some molecules might be harder to build or might quickly change into other molecules. That idea still needs testing.

A detailed star formation history of the distant Milky Way satellite Canes Venatici I: An old dwarf spheroidal forming most of its stars after reionisation

Pedro Pérez-García, Carme Gallart, Matteo Monelli+6 more

AstronomerArchival HST/ACS imaging yields the deepest colour-magnitude diagram yet for the Milky Way dwarf spheroidal satellite Canes Venatici I, reaching approximately 2 magnitudes below the old main-sequence turn-off. CMD fitting indicates a dominant star-formation episode peaking about 11.8 Gyr ago, well after reionisation, and continuing until approximately 10.4 Gyr ago, with global metallicities spanning [Z/H] = −2.4 to −1.5 dex. Despite its old, metal-poor population, CVnI formed its stars later than comparable Milky Way satellites dominated by a single burst. Tests with synthetic and real populations support the reliability of these inferences. The authors propose that mass accretion kept CVnI above, but near, a theoretical redshift-dependent threshold for sustaining star formation, and that supernova feedback made its halo subcritical near z ≈ 2, permanently quenching star formation. This evolutionary scenario remains an interpretation; early gravitational interactions with the Milky Way cannot be excluded, as suggested by recent orbital calculations.

PublicResearchers used archived Hubble Space Telescope images to reconstruct when stars formed in Canes Venatici I, a small galaxy orbiting the Milky Way. Comparing the stars’ colours and brightnesses with models indicates that most formed during one main period, peaking about 11.8 billion years ago and continuing until about 10.4 billion years ago. Its stars are old and poor in elements heavier than helium, but their main formation period occurred later than in otherwise similar satellite galaxies. Tests using artificial and real star populations supported the reconstruction. The researchers suggest that the galaxy’s history of gaining mass helped it keep forming stars, until the effects of exploding stars pushed it below a theoretical mass threshold needed to continue. That explanation is not established, and an early gravitational encounter with the Milky Way may also have played a role.

Young explorerCanes Venatici I is a little galaxy near our big galaxy, the Milky Way. Scientists studied pictures of its stars to work out when they were born. They think most were made during one very long spell, a very long time ago—but later than in some similar little galaxies. The scientists wonder whether exploding stars helped stop it from making more stars. The Milky Way’s gravity might also have helped. They do not know for sure why it stopped.

Black Hole Mass Estimation of a Background Quasar in the Vicinity of the cD Galaxy Holm 15A

Emmanuel Ríos-López, Omar López-Cruz, Ana Luisa González-Morán+1 more

AstronomerGTC/OSIRIS spectroscopy of the central region of Abell 85 identifies the point-like X-ray source SDSS J004150.75-091824.3, projected 13.74 arcseconds from the cD galaxy Holm 15A, as a background quasar at z = 1.56386 ± 0.00397. This rules out its proposed identification as a rogue black hole gravitationally bound to Holm 15A. Single-epoch spectroscopy yields an estimated quasar black-hole mass of log(M_BH/M_sun) = 8.72 ± 0.26.

PublicA compact X-ray source appears close to the galaxy Holm 15A in the sky, but spectra taken with GTC/OSIRIS show that it is a background quasar rather than a rogue black hole gravitationally bound to that galaxy. The researchers measure its redshift as 1.56386 ± 0.00397 and use a single set of spectral observations to estimate that its central supermassive black hole has about 525 million times the Sun’s mass, with an uncertainty of roughly a factor of 1.8.

Young explorerA bright spot in the sky looks close to a galaxy called Holm 15A. By studying its light, astronomers found that it is really a quasar far behind the galaxy, not a wandering black hole held by that galaxy’s gravity. They also used its light to estimate how heavy the quasar’s huge black hole is, though the estimate is not exact.

UV spectra of little red dots: Broad-line N/C, gas recycling and black hole masses

Albert Sneppen, Darach Watson, Lucy R. Ivey+8 more

AstronomerSirocco radiative-transfer models of supermassive black holes accreting within dense gas cocoons reproduce LRD X-ray-to-near-infrared spectral energy distributions and predict weak broad UV emission and metal absorption features now detected in several LRDs by JWST SPURS spectroscopy. In the simulations, equal-charge nitrogen and carbon ions are largely co-spatial, allowing the broad N IV]/C IV and N III]/C III] ratios jointly to constrain electron density and N/C abundance. Applied to SPURS-GN-2 at z = 7.19, this interpretation requires N/C = 12 (+3, −2) times solar and log10[n_e/(cm^-3)] = 9.7 (+0.3, −0.5). The inferred enrichment implies that around half the broad-line CNO nuclei have undergone hydrogen burning; replacement of the ionised gas on a century timescale favours recycling to sustain it. In two of four LRDs, observed absorption-line blueshift velocities clearly increase with the absorber's required ionisation energy. The models interpret this through spatially stratified absorption in gas launched near escape speed and subsequently decelerated by gravity. For GN-2, the inferred deceleration requires radiation pressure close to the Eddington limit for a black hole of 10^6–10^7 solar masses. Typically strong absorption-line saturation makes direct abundance-ratio estimates misleading.

PublicDeep JWST spectra have detected faint ultraviolet emission lines and metal absorption lines in several compact sources called “little red dots.” Models involving black holes feeding inside dense gas cocoons predicted these features, and the researchers use those models to interpret the observations. For one source, SPURS-GN-2, the nitrogen and carbon emission indicates a nitrogen-to-carbon ratio about 12 times the Sun's, with an uncertainty of −2 to +3 times solar. The inferred enrichment suggests that roughly half the carbon, nitrogen and oxygen nuclei in the broad-line gas have experienced hydrogen burning. Because this gas is replaced on a roughly century-long timescale, the authors favour recycling of enriched gas. In two of four sources, absorption-line velocities show a pattern that the models explain as outward-moving gas slowing under gravity. The interpretation for GN-2 also requires radiation pressure near the black hole's Eddington limit. Strong saturation of the absorption lines complicates direct chemical measurements.

Young explorerScientists studied light from faraway things called “little red dots.” They compared it with computer models of black holes wrapped in thick gas. The models help explain the light and suggest that one dot has much more nitrogen compared with carbon than the Sun does. Some clues also fit gas moving outward and slowing down. Scientists think the gas may be reused, but that is an explanation they are testing.

Beyond just a torus? Re-contextualising the AGN type paradigm using data-driven host galaxy quenching histories

Sahyadri D. Krishna, Vivienne Wild, Paul C. Hewett+3 more

AstronomerThe orientation-based AGN unified model accounts for the visibility of broad emission lines but not differences in host-galaxy properties. Using mean-field independent component analysis (MFICA) spectral decomposition, the authors extract stellar populations for approximately 3,000 optically selected Type-1 and Type-2 AGN hosts from SDSS DR7, matched in redshift (0.16–0.4) and [OIII] luminosity (6.5 < log10[L[OIII]/L_sun] < 9.5). They infer that only about 10% recently underwent rapid post-starburst quenching, within roughly 1 Gyr; Type-2 hosts in this subset quenched at most 100 Myr more recently than Type-1 hosts. Among the approximately 90% with normal recent star-formation histories, Type-2 hosts have slightly younger stellar populations. Possible explanations include a connection between torus covering factor and stellar populations, host-galaxy obscuration, or AGN-type evolution without major starbursts or rapid quenching; the findings do not establish which explanation applies.

PublicActive galactic nuclei are bright galaxy centers whose spectra can show or lack broad emission lines. A dusty structure viewed from different directions can explain this distinction, called Type-1 versus Type-2, but does not explain all differences between their host galaxies. Researchers separated the light of stars from the bright nuclei in about 3,000 galaxies to reconstruct their star-formation histories. They infer that only about 10% experienced a burst of star formation followed by a rapid shutdown within roughly the past billion years. In that group, the shutdown in Type-2 hosts occurred at most 100 million years more recently than in Type-1 hosts. Most hosts instead have normal recent star-formation histories, with slightly younger stars in Type-2 hosts. The authors suggest several possible explanations involving dust or changes in nucleus type, but the study does not determine which is responsible.

Young explorerSome galaxies have centers so bright that it is hard to see their stars. Scientists separated the starlight from the bright-center light in about 3,000 galaxies. They found that only about one in ten had made lots of stars and then quickly stopped in the recent part of the galaxy’s long life. Most had not done that. Galaxies in one group had slightly younger stars than galaxies in the other group. Dust hiding the centers, or changes in the centers over time, might help explain the difference, but the scientists do not yet know which explanation is right.

Effects of Resolution and Local Stability on Galactic Disks: I. Multiple Spiral Mode Formation via Swing Amplification

SungWon Kwak, Ivan Minchev, Christoph Pfrommer+2 more

AstronomerSimulations of Milky Way-like disk–halo systems without imposed exciting perturbations examine how numerical resolution, local disk stability, and halo responsiveness affect spiral modes m=1–6. In marginally unstable, lower-resolution disks, numerical noise seeds faint features within 0.5 Gyr; higher resolution delays spiral and bar formation, especially in more stable disks. All sufficiently resolved live-halo models with dark-matter-to-stellar particle mass ratio ≤10 show a cascade: higher-m modes form and decay before lower-m modes emerge, while the center of activity shifts inward. The authors interpret initial short-wavelength growth through local swing amplification and recurrent rapid amplitude modulation through interference among coherent components with different pattern speeds. Fixed-potential or coarsely resolved halos produce strong early spirals but no coherent cascade. The m=3 mode marks the onset of inner-disk angular-momentum transport preceding bar formation, a process absent in fixed-potential models. These simulations indicate that a responsive, adequately resolved halo sustains and regenerates multi-mode spirals despite small total angular-momentum exchange.

PublicComputer simulations explore how spiral patterns can develop in galaxies like the Milky Way without an imposed disturbance. When the simulations represent a responsive dark-matter halo in sufficient detail, patterns with more spiral arms appear and fade first, followed by patterns with fewer arms, while the main activity moves inward. Increasing numerical detail delays the appearance of spirals and a central bar, particularly in more stable disks, showing that artificial numerical noise can affect their timing. The researchers interpret the changing patterns as a combination of local gravitational amplification and interference between spirals rotating at different rates. Simulations with an unresponsive halo or too little halo detail do not reproduce the same orderly sequence. The results suggest that the halo’s gravitational response helps renew spiral structure even when its overall exchange of angular momentum with the disk is small; these are simulation findings, not direct observations of galaxies.

Young explorerScientists made computer versions of galaxies to see how their spiral shapes grow. In some models, shapes with more spiral arms appeared and faded before shapes with fewer arms, and the action moved toward the middle. A surrounding cloud of invisible matter helped the spirals keep forming when it could respond to the galaxy’s gravity. The computer needed enough detail to show this pattern clearly. These are clues from computer galaxies, not pictures of real ones changing.

An Enhanced Isothermal Jeans Approach to Constraining Dark Matter Self-Interactions from Galactic Kinematics

Zixiang Jia, Fangzhou Jiang, Shubo Li+3 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe authors extend the isothermal Jeans semi-analytical model for self-interacting dark matter (SIDM) halos to include velocity-dependent scattering, an empirical core-collapse treatment, and more robust solution identification. Fits to SPARC rotation curves include galaxies with baryon-dominated centers. Roughly one-sixth of the galaxies admit both core-growth and core-collapse solutions; the remainder favor a unique evolutionary state within the model. Joint constraints exhibit an L-shaped degeneracy: nearly constant, low cross sections (σ₀ ≈ 2 cm²/g, ω ≳ 500 km/s) and strongly velocity-dependent models (σ₀ ≈ 100 cm²/g, ω ≈ 60 km/s) remain viable. Thus, although the authors report evidence for velocity dependence, nearly constant scattering is not excluded. Assuming core growth gives best-fit parameters σ₀ ≈ 5 cm²/g and ω ≈ 250 km/s. The constraints agree with previous independent probes. SIDM fits outperform simple adiabatic-contraction CDM profiles and rival empirical feedback-based CDM profiles; the authors also report no correlation with stellar-to-halo mass ratio, a feedback-strength proxy. Within this modeling, SIDM changes galaxy–halo scaling relations little but yields systematically lower concentrations. Future low-mass kinematic data are needed to break the scattering-parameter degeneracies.

PublicThe researchers used measured galaxy rotation curves to test a model in which dark matter particles can scatter off one another. Their improved calculation allows scattering to depend on particle speed and includes both expanding and collapsing central dark matter cores. These are model interpretations, not direct observations of dark matter collisions. About one in six galaxies can be explained by either core state, so the rotation measurements do not always distinguish them. The analysis also leaves two broad possibilities open: relatively weak scattering that changes little with speed, or stronger scattering that depends strongly on speed. The model fits the data better than one simple cold dark matter prescription and about as well as another that accounts empirically for feedback from ordinary matter. The results support self-interacting dark matter as a promising explanation for differences among dwarf galaxies, but do not uniquely establish it. More measurements of motions in low-mass galaxies could help distinguish the remaining possibilities.

Young explorerScientists watched how galaxies turn and tested an idea about dark matter, the invisible stuff around them. What if tiny bits of dark matter could bump into each other? Their new calculations can explain the turning patterns, but sometimes more than one answer works. They have not seen these bumps happen. More galaxy measurements could help them work out which answer fits best.

Origins of Extreme Emission-Line Ratios in z > 3 Galaxies: Insights from the Lumen Model

Lucie Scharré, Michaela Hirschmann, Adèle Plat+11 more

AstronomerObserved optical emission-line ratios in star-forming galaxies at z ≈ 3–8 differ strongly from those at z ≈ 0–2. The authors develop Lumen to model nebular emission from spatially distributed HII regions in cosmological simulations, apply it to IllustrisTNG50, validate its low-redshift predictions, and test proposed explanations using N2-BPT, S2-VO87, and O32-R23 diagnostics. In these models, α-enhancement alone cannot explain most observations; combining it with a higher IMF upper-mass cutoff and AGN contributions produces moderate offsets. The most extreme [OIII]/Hβ and [OIII]/[OII] ratios require elevated ionization parameters powered by massive star clusters of ≳10^5–10^6 solar masses, consistent with recent JWST observations. The highest [NII]/Hα ratios additionally require nitrogen enhancement. Gas densities near 10^4 cm⁻³ boost several ratios but suppress [SII]/Hα, creating tension with current observations. Models combining harder ionizing spectra, elevated ionization parameters from massive clusters, and enhanced nitrogen reproduce the observed population across all three diagrams and motivate new star-forming demarcation lines.

PublicStar-forming galaxies in the early universe show different patterns of light from glowing gas than galaxies at later times. To investigate why, the researchers developed a gas-emission modeling framework called Lumen and applied it to a cosmological simulation, checking its predictions against nearby-universe observations. Their models suggest that no single simple change explains the observed patterns. The most extreme oxygen-line ratios call for strong ionization driven by massive star clusters, while the strongest nitrogen-line ratios also need extra nitrogen. Increasing gas density helps explain some features but weakens a sulfur signal in a way that conflicts with current observations. A combination of more energetic ionizing light, strong ionization from massive clusters, and increased nitrogen matches the observations across three diagnostic comparisons. This is a model-based explanation, rather than a direct measurement of all these conditions, and it motivates new boundaries for classifying star-forming galaxies by their emitted light.

Young explorerGas around young stars glows, and its light gives clues about what is happening in a galaxy. Astronomers see different light patterns in galaxies from long ago. The researchers made computer models to try to explain them. Their best-matching models use big groups of stars that shine very energetic light, plus extra nitrogen in the gas. Just packing the gas more tightly does not match all the clues. The models help explain what astronomers see, but they do not prove that every faraway galaxy works exactly this way.

SDSS-V LVM: Revealing the Physical and Chemical Structure of the Helix Nebula

R. Orozco-Duarte, J. E. Méndez-Delgado, J. A. Toalá+27 more

AstronomerThe first spatially contiguous integral-field spectroscopic study of the Helix Nebula, using SDSS-V Local Volume Mapper observations, provides nearly complete coverage and maps physical conditions, ionisation structure, and abundances from 41 optical emission lines. The maps show strong ionisation stratification: He II traces highly ionised gas toward the central cavity, low-ionisation material dominates the bright shell, and neutral or transition-zone gas is enhanced farther out. Typical electron densities are approximately 100 cm^-3, with temperatures differing by several thousand kelvin between ionisation zones. The derived oxygen abundance is near solar, 12 + log(O/H) ≈ 8.7. The central abundance pattern suggests a significant contribution from unobserved O3+, favouring ionisation effects rather than genuine chemical inhomogeneity as the main explanation for apparent abundance variations. Evidence for a roughly 1 dex sulfur deficit is consistent with the planetary-nebula sulfur anomaly. Helium and nitrogen abundances place the Helix near the classical Type I boundary, suggesting moderate enrichment by its progenitor.

PublicAstronomers used the SDSS-V Local Volume Mapper to map light from nearly the entire Helix Nebula, revealing how its gas conditions and chemical composition vary across the cloud. The observations show a layered structure: highly ionised gas lies toward the central cavity, less ionised gas dominates the bright shell, and neutral or partly ionised gas is more prominent outside. The gas is sparse, with typically about 100 electrons per cubic centimetre, and temperatures vary by several thousand degrees between regions. The estimated oxygen abundance is close to the Sun's. Apparent differences in oxygen abundance probably reflect oxygen in different electrical charge states, including a state not directly observed, rather than real differences in composition. The researchers also find evidence of a sulfur deficit of about a factor of ten. Helium and nitrogen levels suggest that the star that produced the nebula moderately enriched its gas.

Young explorerAstronomers studied the light from almost all of a big space cloud called the Helix Nebula. They found that its gas is arranged in layers, and some parts are hotter than others. The gas also changes in how many tiny particles its atoms have lost. That may make some places look as though they have different amounts of oxygen, even if they do not really. The cloud seems to have about as much oxygen, compared with hydrogen, as the Sun does, but the researchers found signs of less sulfur than expected. They also think the star that made the cloud added some elements to its gas.

Infrared spectroscopy of gas-phase hydrogenated and methylated pyrenes: from laboratory spectra to the simulated 3.4 μm emission band

Karine Demyk, Christine Joblin, Louan de Bentzmann+2 more

AstronomerThe study tests aliphatic-containing pyrene derivatives as contributors to the satellite emission accompanying the aromatic 3.3 μm band. Gas-phase infrared spectra spanning 1.4–25 μm were recorded at species-dependent temperatures of 373–673 K, and multicomponent fits yielded empirical temperature dependences for band positions and widths. These laboratory constraints were combined with a Monte Carlo model to simulate emission following UV-photon absorption below the dissociation limit (<6 eV), then compared with JWST PDRs4All observations of the Orion Bar. The simulated spectrum of 1,2,3,6,7,8-hexahydropyrene satisfies the constraints for fitting the red component of the 3.4 μm band at 3.403 μm, supporting it as a candidate contributor rather than establishing a definitive molecular identification. 1-methylpyrene may contribute to the underlying emission plateau, but its lack of a strong infrared band complicates detection. Experimental spectra and temperature-dependent analyses are available in cosmicPAH-IRDB.

PublicResearchers investigated which molecules might produce part of an infrared glow observed in space. They measured laboratory spectra of pyrene and related molecules at different temperatures, then used computer simulations to predict how these molecules would emit infrared light after absorbing ultraviolet light. Comparing the predictions with James Webb Space Telescope observations of the Orion Bar, they found that a hydrogen-enriched molecule called hexahydropyrene could explain a component of the glow at 3.403 micrometers. This is a promising match, not a confirmed identification. Another molecule, 1-methylpyrene, might contribute to a broader background glow but is harder to recognize because it lacks a strong infrared feature.

Young explorerMolecules can glow with light our eyes cannot see. Scientists studied some molecules in a laboratory and used a computer to work out how they might glow in space. One molecule’s predicted glow matched a small part of the light a telescope saw in a place called the Orion Bar. That makes it a good clue, but the scientists cannot yet say for sure that this molecule made that light.

Revealing a multi-zone circumnuclear dust response in UGC 11487 through phase-resolved WISE W1--W2 diagnostics

I.O. Izviekova, O.V. Kompaniiets, I.B. Vavilova+1 more

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena
• Instrumentation and Methods for Astrophysics

AstronomerA phase-resolved WISE/NEOWISE analysis of the MIR-selected TDE candidate UGC 11487/WTP14adeqka over 2014–2024 finds a delayed, broader W2 response, colour hysteresis, and cooling from approximately 900 K to 500–600 K. Positive-fluence centroids give a preferred delay of 224 ± 45 days, corresponding to a characteristic response scale of 0.188 ± 0.038 pc. The effective infrared luminosity peaks near 3 × 10^43 erg s^-1, with integrated infrared energy of (2.9–3.8) × 10^51 erg. A single self-similar MIR response is strongly disfavoured (ΔBIC = 281.7); a two-component phenomenological model is the preferred compact description. Representative hydrodynamically motivated clumpy dust-echo calculations reproduce the empirical diagnostics, supporting, but not uniquely establishing, a structured, multi-zone dust response. The aperture-matched ultraviolet-to-radio host SED indicates a moderately star-forming, isolated barred disc without a dominant persistent AGN component. The findings support an obscured TDE-like accretion transient reprocessed by circumnuclear dust, rather than establishing a confirmed TDE.

PublicA decade of infrared observations tracked a long-lasting flare in the galaxy UGC 11487. Its longer-wavelength infrared glow arrived later and lasted longer, while the emitting dust cooled from about 900 K to 500–600 K. The measured delay corresponds to a characteristic scale of about 0.19 parsecs around the galaxy’s centre. A simple model with one repeating response shape fits poorly; a two-component model works better. Calculations involving clumpy dust in multiple zones also reproduce the observed behaviour, though they do not prove that exact arrangement. The evidence supports a hidden, tidal-disruption-like outburst whose energy was absorbed and re-emitted by surrounding dust. The event remains a candidate, not a confirmed tidal disruption.

Young explorerAstronomers watched dust in a galaxy glow after a hidden bright outburst. One kind of infrared glow came later and lasted longer, and the dust cooled down. Their models suggest that several dusty areas helped make the glow. They have clues about what caused the outburst, but they are not sure yet.

Unsupervised selection and characterisation of little red dots in JWST surveys with manifold learning

Michele Ginolfi, Filippo Mannucci, Alessandro Marconi+9 more

• Instrumentation and Methods for Astrophysics

AstronomerThe study tests unsupervised selection of little red dot (LRD)-like sources without predefined colour cuts, using UMAP to map approximately 242,000 isolated, well-measured ASTRODEEP-JWST sources into two dimensions. Proximity reflects similarities in broadband colours, morphology and photometric redshift. Spectroscopically confirmed LRDs anchor the identification of candidate regions, with validation against archival DJA NIRSpec spectra. Confirmed LRDs concentrate in two regions differing mainly in redshift, whose effects are reflected in their colours. On the spectroscopically classified subset, the main region achieves approximately 0.78 purity at 0.82 completeness, competitive with or cleaner than published colour cuts; the selection yields approximately 100 additional candidates, not confirmed LRDs. The map also recovers brown-dwarf and broad-line AGN populations and isolates rare pathological outliers. These findings support spectroscopically anchored unsupervised mapping as a population-selection tool, but the quoted performance is subset-specific and does not resolve the debated physical nature of LRDs.

PublicLittle red dots are compact, reddish sources discovered in the distant universe by JWST, and astronomers still debate what they are. Researchers used machine learning to arrange about 242,000 sources on a map according to similarities in their colours, shapes and estimated distances. They then used little red dots already identified through spectra to locate promising parts of the map, rather than imposing preset colour rules. The known dots clustered in two regions, differing mainly in redshift. In the main region, tests on sources with spectral classifications found that about 78% of selected objects were little red dots, while the selection recovered about 82% of the known dots in that test subset. The method also produced about 100 additional candidates that remain unconfirmed. It offers a useful way to find candidates, not an answer to what these mysterious sources are.

Young explorerAstronomers have found tiny red-looking spots far away in space, but they are not sure what they are. A computer helped sort pictures of space into a map, putting similar things together. The red spots scientists already knew about gathered in two places. That helped them find more possible red spots, but those still need checking.

How to raise a supermassive black hole: interpreting early JWST AGN with the AESOPICA simulations

Sophie Koudmani, Jan Scholtz, Anthony J. Taylor+11 more

• High Energy Astrophysical Phenomena

AstronomerJWST has uncovered abundant early-Universe AGN with apparently overmassive black holes relative to local scaling relations, but growth histories, selection effects, and mass-estimation systematics remain possible explanations. AESOPICA explores these issues with twelve FABLE-based cosmological simulations in 60 cMpc boxes, varying seed masses from 100 to 100,000 solar masses, accretion efficiency including super-Eddington bursts, and supernova feedback. A mock JWST broad-line survey pipeline, BALMERSOPICA, models detectability for specified gratings and exposure times. In the simulations, any explored seed mass can reproduce the bulk of the JWST AGN population if accretion is efficient, although light seeds require the most favourable conditions tested. Broad-line selection preferentially recovers apparently overmassive systems, with the largest offsets from the intrinsic black hole–stellar mass relation in inefficient-accretion models. Selected simulated AGN follow the local, weakly evolving black hole mass–stellar velocity dispersion relation, supporting—but not proving—assembly of black holes before their stellar components are fully established. Because efficient accretion rapidly erases seed-mass signatures, the authors identify the low-mass black hole mass function and host gas-phase metallicities as promising discriminants between seeding channels.

PublicJWST has found many actively growing black holes in the early Universe that appear unusually massive compared with the stars in their galaxies. It is not yet clear whether this reflects rapid growth, which objects are easiest to detect, or uncertainties in measuring their masses. The researchers tested possible explanations using twelve computer simulations and a simulated JWST survey. Their models can build most of the observed population from either small or large starting black holes if growth is efficient, though the smallest starting points need the most favourable conditions tested. The mock survey also preferentially detects black holes that look unusually massive for their galaxies. Another relationship in the selected models—between black hole mass and the motions of a galaxy’s stars—supports the interpretation that black holes can assemble before the stellar component is fully established. These are simulation findings, not a determination of how the observed black holes actually formed. The authors suggest that the abundance of low-mass black holes and the chemical composition of gas in their galaxies could help distinguish their origins.

Young explorerJWST has spotted many growing black holes from when the Universe was young. They look surprisingly big compared with the stars in their galaxies. Scientists made pretend universes on computers to explore why. In those models, black holes could start small or large and still become big if they grew fast enough, but the smallest ones needed the best growing conditions. The pretend telescope was also more likely to spot black holes that looked extra big for their galaxies. This does not tell us for sure how the real black holes began. The scientists think looking for smaller black holes and studying what their galaxies’ gas is made of could give us more clues.

A Novel Approach to 3D Dust Mapping of the Central Molecular Zone

Arianna Vasini, Mattia C. Sormani, Jason L. Sanders+12 more

AstronomerThe authors develop a non-parametric method to infer the three-dimensional dust distribution in the Milky Way’s Central Molecular Zone from stellar proper motions and extinctions, using extinction as a proxy for dust column density. A model of the positions and velocities of stars in the co-spatial nuclear stellar disc supplies probabilistic distance information. Although the method assumes no functional form for the dust distribution, it does rely on this stellar model. Tests on analytically generated mock dust distributions and structures drawn from hydrodynamical simulations show robust, effective reconstruction of the mock CMZ structure. The approach is fundamentally distinct and largely independent of existing methods, whose near/far cloud placements still conflict. Application to real data is discussed as a prospect; the abstract does not report an observed three-dimensional CMZ map.

PublicResearchers have developed a new way to work out where dust lies in three dimensions near the centre of the Milky Way. It combines stars’ motions across the sky with how much their light is dimmed by dust. A model of the stars’ locations and motions helps estimate their uncertain distances, allowing the method to infer where the dust is. It does not require the dust to follow a predetermined shape, but it does depend on the stellar model. Tests using artificial dust arrangements, including ones taken from computer simulations, successfully recovered their three-dimensional structure. The study discusses future use on real observations rather than presenting a new observed map. Such a map could help researchers understand gas flows, star formation and the travel of energetic particles near the Galactic Centre.

Young explorerDust near the middle of our galaxy is hard to place: we cannot easily tell which bits are closer and which are farther away. Scientists made a new way to use how stars move across the sky and how much dust dims their light to help find the dust. They also need a model of where the stars are and how they move. Their method worked well on pretend dust clouds made for tests, including clouds from computer simulations. They have not yet shown it making a map from real star measurements in this study.

The origin and distribution of diffuse HI in the close interacting MHONGOOSE galaxy systems

D. Kleiner, W. J. G. de Blok, J. Healy+6 more

AstronomerDeep MeerKAT HI observations of two close systems in MHONGOOSE reach a 3σ column-density sensitivity of 10^17.9 cm^-2 over 16 km/s at 4 kpc scales. HI is detected in seven galaxies: NGC 3511/3513, the NGC 4781–NGC 4790–UGCA 308 triplet, and two newly identified dwarf satellites, 2MASX J1255 and MKT 25413. Six lie on the star-forming main sequence with typical HI fractions. MKT 25413 instead has log(MHI/Msun) = 5.7, reported as the lowest detected galactic HI mass outside the Milky Way satellite population, and unusually weak star formation and a low HI fraction for its stellar mass. Diffuse HI surrounds the galaxies. Stellar, Hα and H2 kinematics from VLT/MUSE and ALMA show ordered rotation, while atomic-to-molecular gas ratios resemble those of star-forming field galaxies. Except for UGCA 308, the interacting galaxies show no major stellar morphological disruption; no stellar counterparts to the intragroup HI tails, bridges or clouds are detected down to μg = 29 mag arcsec^-2. The authors interpret the diffuse HI as material redistributed by mild tidal fly-bys within the past few hundred megayears, and infer that it remains bound but out of equilibrium and is falling back toward the discs.

PublicVery sensitive radio observations detected neutral hydrogen gas in seven galaxies belonging to two close groups, including two newly identified dwarf companions. Six galaxies have the usual gas supplies and star-formation activity for their type. The exception, the faint dwarf MKT 25413, has unusually little neutral hydrogen and weak star formation for its stellar mass. The researchers report that its detected neutral-hydrogen mass is the lowest yet measured in a galaxy that is not a Milky Way satellite. Faint hydrogen also surrounds the galaxies in tails, bridges and clouds, with no accompanying stars detected to the study’s imaging limit. Despite these gas structures, the interacting galaxies retain orderly rotation, and most show no major disturbance in their stars. The authors suggest that gentle encounters over the past few hundred million years pulled loosely distributed gas out of the galaxies without severely disturbing their stellar structures. They interpret this gas as still gravitationally bound and falling back toward the galaxies, rather than permanently escaping.

Young explorerScientists looked at seven galaxies, huge groups of stars, and found faint gas around them. Most were making stars as expected, but one small galaxy had unusually little gas and was making very few stars. The galaxies were still spinning neatly, and most of their stars did not look badly disturbed. The scientists think the galaxies passed near their neighbors and gently tugged some gas out into tails and bridges. They think that gas is still held by the galaxies’ gravity and is falling back in.

Inferring the Total Mass of Galaxy Halos Using Photometry

Chris Brook, Arianna di Cintio, Claudio Dalla Vecchia+2 more

AstronomerThe authors present the first observational test of the simulation-predicted relation between R1, the radius where stellar surface density reaches 1 solar mass per square parsec, and dark matter halo mass M200. Using SPARC galaxies, they measure R1 from photometrically derived stellar surface density profiles and infer halo masses from rotation curves. The observed relation agrees well with cosmological simulations and has low intrinsic scatter across the explored mass range. The results support R1 as a physically motivated halo-mass estimator obtainable from imaging alone, with the observational validation limited to the sample and mass range studied.

PublicA galaxy’s size may help reveal the mass of its surrounding dark matter halo. Here, size means the distance from the galaxy’s center where the density of stars drops to a specified low level. Researchers measured this size from images of galaxies in the SPARC database and compared it with halo masses inferred from how the galaxies rotate. They found a tight relationship that agrees with earlier computer simulations, providing its first observational validation. Within the range studied, the findings support using galaxy images alone to estimate halo masses, although the relationship has some scatter rather than giving an exact mass for every galaxy.

Young explorerA galaxy is a huge group of stars, surrounded by invisible stuff called dark matter. Computer models suggested that a galaxy’s size could help us guess how much dark matter surrounds it. Scientists checked this by looking at galaxy pictures and how the galaxies spin. For the galaxies they studied, the sizes matched the dark matter amounts much as the models expected. That means pictures could help scientists make good guesses about dark matter, though the guesses would not be perfect.

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

Kyu-Hyun Chae, Hyoseok Park, Youngsub Yoon

• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerThe authors test a Bayesian MCMC orbit-reconstruction algorithm in which the semi-major axis is explicitly free, with or without a prior, addressing a claim that this treatment substantially changes inference of the gravitational parameter G from 36 wide binaries in the Chae et al. sample. For that sample and the Alpha Centauri AB–Proxima system, they report that the explicit-a algorithm with an observational constraint is fully equivalent to an implicit-a algorithm using an internal consistency relation involving projected separation. They also present modeled orbits for Alpha Centauri AB–Proxima under Newtonian and Milgromian (MOND) gravity. The authors attribute a recent claim of Newtonian gravity from the 36-binary sample to either a fatal coding error or arbitrarily enlarged uncertainties; this is their methodological critique, not an independent observational finding summarized here. They emphasize system-specific parameter inference, follow-up of anomalous systems, and Bayesian MCMC methods for low-acceleration gravity tests.

PublicWidely separated pairs of stars can help test gravity because their relative positions and motions constrain their orbits. This paper examines whether two ways of fitting those orbits give different answers about gravity. Using a sample of 36 stellar pairs and the Alpha Centauri AB–Proxima system, the authors report that the methods are equivalent when the stated observational constraint is included. They also calculate possible Alpha Centauri AB–Proxima orbits under Newtonian gravity and an alternative called MOND. The authors dispute another study’s claim that the 36 pairs support Newtonian gravity, attributing it to a coding error or unjustifiably enlarged uncertainties. They stress careful modeling of each system and further observations of unusual cases; the abstract does not establish which gravity model is correct.

Young explorerStars that are far apart can still pull on each other. Scientists can study how they move to learn about gravity. This team tried two ways of working out their paths and says they agree when the star measurements are included properly. The team also thinks another study made mistakes. This paper does not settle which idea about gravity is right.

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

Amir H. Khoram, Sirio Belli, Trevor Mendel+16 more

AstronomerThis observational study examines environmental dependence in the formation and quenching histories of massive galaxies at 1.7 < z < 3.5. It combines 139 Blue Jay JWST/NIRSpec galaxies and 57 DAWN archive prism spectra, using joint spectro-photometric Prospector fits and two environmental tracers: COSMOS-Web galaxy number density and LATIS Lyα tomography of intergalactic neutral hydrogen. Among massive quiescent galaxies, the inferred formation-to-quenching interval increases with density. Detected AGN and Na D outflows are confined to galaxy overdensity δ# < 0.5 and elevated Lyα absorption, δHI > 1, mostly occurring together in massive quiescent galaxies. About 65% of the sample follows a correlation between the environmental tracers. Two outlier regions contrast sharply: a galaxy-rich, neutral-gas-poor Hyperion protocluster core contains earlier-forming quiescent galaxies without significant AGN activity or outflows, whereas a galaxy-poor, neutral-gas-rich region within 60 comoving Mpc of the densest cores hosts rapidly quenched galaxies with frequent AGN and outflows. Full ionization of the core gas and ongoing massive-halo assembly in the latter region are interpretations, not established findings. The results emphasize that galaxy counts alone miss important environmental distinctions at cosmic noon.

PublicThe surroundings of a galaxy may help shape when it forms stars and when that activity stops, but counting nearby galaxies does not tell the whole story. Researchers studied massive galaxies in the early Universe using spectra alongside maps of galaxies and cool, neutral hydrogen gas. In massive galaxies that had stopped forming stars, the inferred time between formation and shutdown was longer in denser environments. Two unusual regions stood out. A crowded core of the Hyperion protocluster had little traced neutral gas and contained galaxies that formed earlier, without significant activity in their centers or detected outflows. Another region had fewer galaxies but abundant neutral gas, and hosted rapidly shut-down galaxies with frequent active centers and outflows. The researchers suggest that gas in the crowded core may be fully ionized, while the second region may still be assembling. These interpretations remain uncertain, and the observations do not establish what caused star formation to stop.

Young explorerGalaxies are huge groups of stars. Scientists looked at faraway galaxies and the gas around them to learn why some stopped making stars. One crowded place had little of the kind of gas they could trace. Another had fewer galaxies but lots of that gas, and some galaxies there had stopped making stars quickly. Counting galaxies was not enough: looking at the gas helped too. Scientists still do not know exactly what made the galaxies stop.

Jets and winds from the most powerful compact object in NGC 5408

Roberto Soria, Manfred W. Pakull, Christian Motch+2 more

• Astrophysics of Galaxies

AstronomerA multiband imaging and spectroscopic study identifies NGC 5408 X-2 as a candidate super-critical accretor despite its apparent X-ray faintness. Observations show variable radio emission with a 5-GHz luminosity of a few × 10^35 erg/s, a red optical continuum, exceptionally broad low-ionization lines with FWHM ≈1700 km/s and P-Cygni profiles, narrow photoionized lines including strong He II 4686, point-like hard X-rays, and marginally resolved soft X-rays. The optical continuum faded by 2 mag between 2010 and 2024, accompanied by declining broad- and narrow-line intensities. A nearby ≈20-pc He++ nebula is associated with candidate Wolf-Rayet stars. The authors interpret X-2 as a stellar-mass black hole with super-Eddington accretion power ≳10^40 erg/s, and propose a Compton-thick ULX viewed at high inclination, with a flaring jet and X-rays emerging through a polar funnel. They attribute the optical continuum and broad lines to an optically thick outflow, potentially from the disk or an LBV-like donor, or more speculatively from common-envelope ejection. A short-lived hyper-Eddington phase is suggested rather than established.

PublicA source called X-2 in the galaxy NGC 5408 may hide a powerful feeding black hole despite looking faint in X-rays. Observations at radio, optical, and X-ray wavelengths reveal changing radio emission, unusually broad emission lines that indicate fast-moving material, and a red optical source that faded by two magnitudes between 2010 and 2024. Its broad and narrow emission lines also weakened. The researchers interpret these clues as evidence for a stellar-mass black hole taking in matter at an exceptionally high rate. They propose that thick surrounding material blocks much of our direct X-ray view, while some X-rays escape through a polar opening, and that the system has a flaring jet. The optical light may come from a dense outflow, but whether that material comes from the feeding disk, a companion star, or a more speculative episode of a shared stellar envelope being expelled remains uncertain. The proposed brief, extreme feeding phase is not yet established.

Young explorerAstronomers watched a spot in another galaxy using different kinds of light. Its radio light changed, and its visible light grew dimmer over the years. They think a small black hole might be gobbling up matter very fast there, even though it looks faint in X-rays. Thick material may hide much of the X-ray light, and gas may be blowing away from the system. The astronomers have clues, but they are not yet sure exactly what is happening or where the blowing gas comes from.

XMM-Newton and NuSTAR quasi-simultaneous follow-up of the very high energy flare of PKS 1725+123 in August 2025

L. Marcotulli, A. Gokus, L. Heckmann+12 more

AstronomerQuasi-simultaneous XMM-Newton (50 ks) and NuSTAR (180 ks) observations tracked PKS 1725+123 (z=0.586) for almost five days, beginning about three days after the announcement of its August 2025 very-high-energy flare. XMM-Newton resolved soft (photon index >2) and hard (photon index <2) power-law components, dominating below and above 2 keV, respectively. The authors interpret this crossover as likely tracing the synchrotron–high-energy transition in the SED valley. During the roughly 14-hour XMM-Newton pointing, the synchrotron component shifted out of the X-ray band; over the following roughly four days, NuSTAR measured a factor-of-1.5 brightening of the hard component, associated with the high-energy SED component shifting into the band. The inferred evolution within an observer-frame week of the flare was from a temporary intermediate-synchrotron-peaked state back toward the source's normal low-synchrotron-peaked state. The authors report this as the first continuous X-ray tracking of a blazar VHE flare's evolution over such an extended interval, emphasizing the value of long-term, quasi-simultaneous follow-up.

PublicXMM-Newton and NuSTAR followed the blazar PKS 1725+123 in X-rays after a very-high-energy flare announced in August 2025. Monitoring began about three days after the announcement and lasted almost five days. The observations revealed two overlapping X-ray components: one dominated at lower energies and the other at higher energies. The researchers interpret their overlap as likely marking a transition between two parts of the source's overall emission spectrum. During about 14 hours, the component identified as synchrotron emission shifted out of the X-ray range. Over the next roughly four days, the higher-energy component brightened by a factor of 1.5 as that part of the spectrum shifted into the X-ray range. The authors conclude that the blazar was moving from a temporary state back toward its usual spectral state within a week of the flare. They describe this as the first continuous X-ray coverage of a blazar flare's evolution over such a long interval.

Young explorerAfter a very bright burst from a space object called a blazar, scientists watched it with two X-ray telescopes for almost five days. They saw two kinds of X-ray light mixed together. One kind moved out of the X-ray range they were watching, while the other grew brighter. The scientists think the blazar was changing back toward its usual pattern of light after the burst. Watching for several days helped them follow that change.

SS 433 Eastern Jet Turbulence Revealed by Spatially-Resolved IXPE Data Analysis

Ningyue Fan, Jack T. Dinsmore, Roger W. Romani

AstronomerA reanalysis of the 2023 IXPE observation of the eastern extended X-ray jet in SS 433/W50 with LeakageLib improves polarization constraints relative to standard PCUBE and spectropolarimetric analyses and enables spatially resolved measurements. A model assigning independent polarization properties to the head, spine, and sheath improves the fit over a single-zone model at >3 sigma significance. The sheath has lower polarization than the head and spine, while electric vector position angles are consistent across the regions, indicating magnetic fields aligned with the jet axis. The authors interpret the measurements as evidence for enhanced magnetic turbulence at the jet boundary; Kelvin-Helmholtz instabilities are a possible driver, not an established cause.

PublicResearchers reanalyzed an X-ray observation of the eastern part of the extended jet in SS 433/W50 to study its magnetic field. Their analysis measures polarization, a preferred orientation of the light, separately in the jet's head, central spine, and outer sheath. Allowing these regions to have different polarization properties fits the data significantly better than treating the jet as one uniform region. The outer sheath is less polarized, but the polarization directions are consistent throughout, indicating magnetic fields aligned along the jet. The researchers interpret the weaker polarization at the boundary as a sign of greater magnetic turbulence. An instability called Kelvin-Helmholtz could drive that turbulence, but the analysis does not establish its cause.

Young explorerScientists looked again at special light from a space jet to learn about its invisible magnetic field. The light has a clearer favorite direction in the jet's middle and head than at its edges. This suggests that the magnetic field mostly points along the jet but is more jumbled near the edges. The scientists have an idea about what might make the edges jumbled, but they do not know for sure.

Quasi-normal Modes and Instabilities of Rotating Relativistic Stars

Yong Gao, Masaru Shibata

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

AstronomerThis theoretical and numerical study derives the coupled fluid–spacetime eigenvalue equations from the second-order action in full general relativity and computes quasi-normal modes of rapidly rotating stars with outgoing-wave boundary conditions. For MIT-bag strange-star models, the spectra realize Chandrasekhar’s instability picture, distinguishing Chandrasekhar–Friedman–Schutz and Jacobi-like neutral conditions and the transition to dynamical bar-mode growth. For neutron-star models, the authors determine f-, r-, and other inertial-mode spectra and radiative damping or growth times; f–inertial-mode interactions show avoided crossings and exchanges of damping or growth rates. Quasiradial collapse thresholds from static stability analysis are independently checked by following the fundamental F-mode frequency to zero. For uniform rotation, the authors find that dynamical instability begins at a higher central density than secular instability. The implementation can also resolve highly damped w-modes. These are calculated properties of stellar models, not observational measurements.

PublicThe researchers used Einstein’s theory of gravity to calculate how rapidly spinning compact stars vibrate and when those vibrations fade or grow unstable. Their calculations treat the star’s material and the surrounding spacetime together. In models of hypothetical strange stars, they identify distinct instability boundaries and the transition to a growing, bar-shaped distortion. In neutron-star models, different kinds of vibration interact, exchanging how quickly they fade or grow. The team also checks the predicted onset of collapse in two independent ways. For stars rotating uniformly, their models place the onset of rapid, dynamical instability at a higher central density than the onset of slower, secular instability. These are theoretical and numerical findings, not observations of actual stars.

Young explorerA spinning star can wobble, a little like a spinning top. The scientists used math and computer calculations to work out how very tightly packed stars might wobble. In their star models, some wobbles fade away and others grow bigger. Different wobbles can also affect each other. They used two different checks to find when a model star would start to collapse. They did not watch real stars do these things; they calculated what their models would do.

Photon arrival time lags in 3D radiative transfer with SKIRT

Yuto Mochizuki, Bert Vander Meulen, Masahiro Tsujimoto+4 more

• Instrumentation and Methods for Astrophysics

AstronomerThis computational study adds photon arrival-time lags to the SKIRT Monte Carlo radiative-transfer code, enabling joint spectral and timing modelling of reprocessed emission in three dimensions. The implementation tracks photon path lengths and converts them into delays relative to direct emission. Tests with simple geometries reproduce expected lag distributions and energy dependence for free-electron scattering and photoelectric absorption followed by fluorescence. In a realistic AGN model, the simulations yield distinct lag components from inner and outer structures and energy-dependent delays associated with the Fe Kα fluorescence line. Cross-correlation functions between the line and broad bands recover the peak lag and its finite width, attributed to extended geometry and intrinsic variability. These are simulation results, not observational detections. The framework is intended to support joint interpretation of X-ray spectroscopy and timing, including data from XRISM and NewAthena, with reverberation mapping among the anticipated applications.

PublicX-rays that interact with cold matter around compact objects can reach us later than X-rays that travel directly toward us. Their energies and delays offer clues to the surrounding material’s shape and physical conditions. The researchers upgraded the SKIRT computer simulation to calculate these delays by tracking how far photons travel. Tests reproduced the expected behaviour in simple arrangements. In a model of an active galactic nucleus, material in inner and outer structures produced separate delay components, including delays linked to iron fluorescence. The analysis also recovered the strongest delay and the spread of delays caused by the model’s extended structures and changing emission. These findings come from simulations rather than observations of a particular galaxy. The new capability is intended to help researchers interpret X-ray measurements that combine energy and timing information.

Young explorerImagine a flash of light taking two paths: one goes straight to you, while the other meets some material and takes longer to arrive. Scientists made a computer model that keeps track of these late arrivals for a kind of light called X-rays. They tested it with simple shapes and then with a model of the bright center of a galaxy. In that model, material in different places made the light arrive after different waits. This was a computer experiment, not a new sighting in the sky. The scientists hope it will help them work out how material is arranged around objects in space.

Fermi-LAT Detection of Extended GeV Emission toward the Middle-aged Supernova Remnant G156.2+05.7

Wei-Liang Xu, Qing-Wen Tang, Long Li

AstronomerAn analysis of 17 years of Fermi-LAT data toward the middle-aged SNR G156.2+05.7 detects extended gamma-ray emission, described by a 2D Gaussian with R68 approximately 0.84 degrees. The Gaussian is preferred over a foreground CO template but is statistically indistinguishable from a uniform disc under the AIC. A log-parabola is preferred over a power law at approximately 3.4 sigma, providing evidence for spectral curvature. SED modelling incorporating radio and CO observations and published X-ray constraints supports, under the adopted assumptions, a joint leptonic–hadronic interpretation. The LAT spectrum favours a hadronic contribution over a purely leptonic interpretation, but a proton-dominated alternative remains competitive, leaving the GeV partition model-dependent. In the joint model, electrons produce the radio synchrotron emission and part of the gamma-ray emission, while steep-spectrum protons supply the remaining gamma rays. At the adopted reference distance of 2.7 kpc, the fitted electron cutoff of approximately 1.2 TeV is compatible with thermal-dominated X-rays; the proton cutoff is fixed by assumption at 1 TeV, not measured. Enhanced northeast and southwest emission may reflect an asymmetric or clumpy environment. Alignment with optical H-alpha filaments is suggested but unestablished. No significant long-term flux variability is found.

PublicSeventeen years of Fermi-LAT observations reveal a spread-out source of gamma rays toward the supernova remnant G156.2+05.7. The measurements also show evidence that its energy spectrum curves rather than following a simple power law. Comparing the gamma rays with radio observations and existing X-ray constraints, the researchers find that a model involving both electrons and protons can explain the data. The gamma-ray spectrum favours some contribution from protons over an explanation involving electrons alone. However, a mainly proton-based model also remains competitive, so the relative contributions are uncertain. The northeast and southwest portions are brighter in gamma rays, possibly because the surrounding material is uneven or clumpy. A suggested connection to optical filaments has not been established. No significant long-term change in brightness was detected.

Young explorerScientists studied very energetic light coming from the direction of the leftovers of an exploded star. The light spreads across a patch of sky, with two parts looking brighter. Tiny particles called electrons and protons might help make this light, but scientists are still working out how much each kind makes. They did not find a clear change in its brightness over many years.

Extreme Multiwavelength Variability in the Recurrent Intermediate-type Changing-look Seyfert Galaxy SDSS J234728.73+242745.7

Jiahua Wu, Liming Dou, Yanli Ai+14 more

• Astrophysics of Galaxies

AstronomerJ234728.73+242745.7 is identified as a recurrent intermediate-type changing-look Seyfert galaxy. Nearly three decades of optical spectroscopy show Type 1.0 to 1.5 to 1.2 transitions, disappearance and reappearance of broad He II 4686, and a broad-line Balmer decrement changing from 4.5 to 7.2 to 2.4. The host-corrected g-band high-to-low flux ratio is 5.4 ± 0.4, versus 2.7 ± 0.8 in Swift/XRT observations across the transition. Correcting for inferred low-state continuum reddening of A_V = 0.66 ± 0.23 mag brings optical/UV ratios close to the X-ray ratio, but this correction is model-dependent; intrinsically weaker X-ray variability could also contribute. X-ray spectra provide no compelling evidence for intrinsic gas absorption or its variability, with an intrinsic column upper limit of about 5 × 10^20 cm^-2. Conversely, EP/WXT monitoring in the recent high state shows order-of-magnitude X-ray fluctuations on monthly-to-sub-year timescales, exceeding contemporaneous optical variations. ASKAP radio measurements remain near 2 mJy since mid-2020. The combined evidence favors intrinsic accretion-state changes as the primary driver, without excluding secondary variable obscuration. A loop-like MIR color–magnitude track is interpreted as the delayed response of an extended torus.

PublicAstronomers report that the active galaxy J234728.73+242745.7 repeatedly changes its spectral appearance as its center brightens and fades. Optical observations spanning nearly 30 years show broad helium emission disappearing and returning, alongside changes in hydrogen emission. Monitoring also finds coordinated changes from X-rays to mid-infrared light, while the measured radio emission remains steady. Across one changing-look transition, visible light varied more strongly than X-rays; changing dust extinction could help explain this difference, but that explanation depends on the model used. During a recent bright state, X-rays instead fluctuated much more strongly than visible light. The authors favor changes in the material feeding the central black hole as the main cause, with changing obscuration possibly contributing. They interpret a looping pattern in infrared color and brightness as a delayed response from surrounding dust, rather than a directly established mechanism.

Young explorerThe bright middle of a galaxy has been getting brighter and dimmer, and some signs in its light have disappeared and come back. Scientists think the biggest reason is a change in how material feeds the black hole in the middle. Dust might hide some light too, but they are not sure how much. The dust around the center may also take time to respond when the light changes.

How Fast do Black Holes Spin?

Chen Yuan, Vitor Cardoso

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

AstronomerThe authors use 500 high-resolution BHAC general relativistic magnetohydrodynamic simulations to study accretion-driven spin evolution of Kerr black holes with initial spin parameters χ = 0–0.99. Starting from a Fishbone–Moncrief torus, they vary magnetic-loop structure, torus position, magnetic-field strength, and radial loop modulation. Horizon mass and angular-momentum fluxes yield time-averaged spin evolution rates in the quasi-stationary phase. The inferred equilibrium spin ranges from χ_eq ≈ 0.88 in the fiducial model to ≈ 0.98 in a weak-flux model. The trends are consistent with stronger net horizon-threading magnetic flux enhancing jet torques and lowering equilibrium spin. Applied to Sgr A*, even an optimistic rapid-evolution estimate exceeds 10^13 years, pointing to the importance of earlier growth or mergers. These simulation-dependent results offer a framework for interpreting reported high spins in X-ray binaries and active galactic nuclei and assessing near-horizon high-energy processes requiring near-extremal spin; they are not new observational spin measurements.

PublicHow fast a black hole spins may depend on the magnetic fields carried by the gas falling into it. In 500 computer simulations, researchers varied the gas disk and its magnetic fields and calculated how the black hole's spin would change. The simulations gave balance points, where the spin stops increasing or decreasing on average, ranging from about 0.88 to 0.98 on the study's spin scale. The trends support an explanation in which stronger magnetic flux through the black hole's boundary increases the braking effect of jets, while weaker flux allows faster equilibrium rotation. Applying the calculations to Sgr A*, the researchers estimate that even rapid spin evolution under the modeled conditions would take more than 10 trillion years, pointing instead to earlier growth or mergers as important to its spin history. The findings may help explain previously reported fast-spinning black holes, but they come from simulations, not new observations.

Young explorerA black hole can spin while gas falls into it. Scientists made 500 computer pretend-worlds to see how that spin might change. In their models, magnetic fields could help jets act like brakes: stronger magnetic effects tended to mean a slower final spin, while weaker ones allowed a faster spin. For one black hole called Sgr A*, their calculations suggest that changing its spin this way would take a very, very long time. What happened to it long ago may matter more. These are clues from computer models, not something the scientists watched happen.

Multimuon Events from Cosmic Rays with the ALICE Detector

Mario Sitta, ALICE Collaboration

• High Energy Physics - Experiment

AstronomerALICE collected cosmic-ray data during 2015–2018, totaling 62.5 days of real observation time. The analysis selects events with more than four detected muons, studying the muon multiplicity distribution for 4 < N_mu < 50 and measuring the event rate for N_mu > 100, where large statistical fluctuations limit the data. Comparisons use air-shower Monte Carlo simulations with QGSJET-II-04, EPOS-LHC, and SIBYLL 2.3d, assuming pure-proton and pure-iron primary compositions as light and heavy extremes. Although the models struggle to describe precisely the energy-dependent proton and iron trends, only QGSJET-II-04 reasonably reproduces both observables when a heavy composition is assumed across the studied energy range. This is a model-dependent comparison, not a direct determination of the primary composition.

PublicThe ALICE experiment at CERN recorded particles arriving from cosmic-ray showers during 62.5 days of observation spread across 2015–2018. Researchers examined events containing more than four detected muons, a type of particle produced in these atmospheric showers. They compared the observed numbers of muons and the rate of events with over 100 muons against three computer models, testing incoming cosmic rays made entirely of protons or entirely of iron nuclei as contrasting possibilities. Only the model called QGSJET-II-04 reasonably matched both measurements when a heavy cosmic-ray composition was assumed. That agreement does not prove the cosmic rays were all iron: the models have difficulty capturing how the proton and iron predictions vary with energy, and the highest-muon events have large statistical fluctuations.

Young explorerParticles from space can make showers of tiny particles when they hit the air. Scientists used a detector called ALICE to count some of the shower particles, called muons, that arrived together. They compared their counts with three computer models. One model came fairly close to the counts when it imagined heavy particles starting the showers. But the models were not perfect, and the biggest groups were hard to measure reliably, so this does not tell us for sure what the space particles were.

Quark deconfinement as a natural trigger of Type-I critical collapse: black holes from neutron stars deemed stable

Hrishikesh Borthakur, Ritam Mallick

AstronomerSpherically symmetric general-relativistic simulations find that a first-order hadron–quark phase transition can drive radially stable neutron stars to black-hole collapse even when a stable hybrid configuration exists at the same baryon mass. The dynamical threshold is 0.12 solar masses lower in baryon mass than the static threshold, allowing black holes lighter than the heaviest stable star. The threshold exhibits Type-I critical behavior: near it, evolution lingers around an unstable hybrid star of equal baryon mass, with the dwell time governed by that configuration’s unstable mode. The effect persists for finite conversion rates, but over a narrower window. These are simulation results under spherical symmetry, not reported observations.

PublicComputer simulations show a possible way for a neutron star to collapse into a black hole when its matter changes from hadrons to quark matter. Surprisingly, collapse can occur even when a stable star containing both kinds of matter could exist with the same amount of baryonic matter. The simulated collapse threshold is lower than the threshold inferred from static stellar models, meaning black holes could be lighter than the heaviest stable star. Near the dividing line between outcomes, the simulated star temporarily lingers in an unstable mixed-matter state. The effect remains possible when conversion takes a finite time, though under a narrower range of conditions. The calculations assume spherical symmetry; the abstract reports no observational detection.

Young explorerScientists used a computer to study a very tightly packed star. In their model, changing the stuff inside the star could make it collapse into a black hole—even when a stable star with the same amount of matter was possible. Just before collapse, some model stars lingered in a shaky state. The scientists saw this happen in their computer model, not in a real star in the sky.

Extended 2.25/8.60 GHz Observations of the Magnetar Swift J1818.0-1607

Zhi-Peng Huang, Zhen Yan, Zhi-Qiang Shen+11 more

AstronomerSimultaneous 2.25/8.60 GHz monitoring of Swift J1818.0−1607 with the Shanghai Tian Ma Radio Telescope over MJD 58936–59427 reveals substantial temporal and frequency-dependent evolution of its average radio pulse profiles, attributed to relative changes in leading, central, and trailing components. The mean spin-frequency derivative is −1.65(4) × 10^-11 s^-2; its magnitude initially increases and subsequently decreases. Flux density likewise rises and then declines, with sporadic variability and broadly consistent changes between bands at most epochs. The two-point spectral index evolves from approximately −1.8 shortly after the outburst to near zero around MJD 59030–59050, then repeatedly decreases and increases; 41 of 54 later-campaign measurements have α > −1. Three mode-changing classes primarily affect the central component, the central and trailing components, or the leading and central components, respectively. Each class includes events with corresponding component responses in the other band, but response strength and direction depend on the event. Central-component Type I variations are generally stronger at 8.60 GHz.

PublicRadio observations of the magnetar Swift J1818.0−1607 show that both its rotation and its radio pulses changed during the monitoring period. It generally rotated more slowly over time, with the slowing first becoming stronger and then weaker. Its radio brightness initially rose and later declined, with additional irregular fluctuations. Observations at two radio frequencies usually showed broadly similar brightness changes, although the balance between the frequencies varied repeatedly. The pulse shape also evolved as its front, middle, and rear parts changed in relative strength. Researchers identified three kinds of switching behavior involving different combinations of these parts. Each kind included events with a related response at the other frequency, but those responses were not always equally strong or in the same direction. Changes centered on the middle part were generally more pronounced at the higher frequency.

Young explorerAstronomers watched a space object called a magnetar as it spun and sent out radio pulses. It usually spun more slowly as time went on. Its radio signal grew brighter at first and then dimmer, with extra ups and downs along the way. The pulses changed shape too: their front, middle, and back parts did not always stay equally strong. The team listened at two radio frequencies. Changes often showed up in both, but they did not always match exactly.

On Photon Propagation in Strong Magnetic Fields: Time Delays from Pulsars

A. W. Romero Jorge, A. Pérez Martínez, E. Rodríguez Querts+1 more

• High Energy Physics - Phenomenology

AstronomerThis theoretical study derives polarization-dependent photon dispersion relations and phase velocities in strong magnetic fields using one-loop QED at finite temperature and density. It treats propagation parallel and perpendicular to the field in both the magnetized QED vacuum and an electron–positron medium with nonzero chemical potential. The authors estimate neutron-star photon delays using a simplified magnetosphere with toroidal field geometry and a radially varying chemical potential in the degenerate limit, and compare their predictions with observational timing constraints. Strong-field QED and plasma corrections are discussed as possible sources of measurable departures from the light cone, with potential timing and polarimetric signatures for magnetars. Crucially, the delays are phase-velocity-based, indicative order-of-magnitude predictions, not reported detections.

PublicThe researchers calculate how very strong magnetic fields could change the way light travels, depending on its polarization and whether it moves along or across the field. Their theory considers both empty space affected by quantum physics and a medium containing electrons and positrons. Using a simplified model of the magnetic surroundings of a neutron star, they estimate possible light-travel delays and compare them with limits from timing observations. Such effects could potentially leave clues in observations of magnetars, but the study does not report a detection. The delay estimates are rough predictions based on the speed of the light wave's phase, rather than an established measurement of a signal's travel time.

Young explorerLight travels in waves. The scientists used math to ask how a very strong magnet near a star might change those waves as they move. They used a simple model to guess how much delay there might be. Their guesses are only rough, and they have not shown that telescopes have seen this happen.

Radiative relativistic reconnection powering the hard-state emission of X-ray binaries: synchrotron-driven pair loading, MeV tail, and seed photons

Valeriia Rohoza, Maria Petropoulou, Hayk Hakobyan+2 more

AstronomerThe study investigates whether relativistic magnetic reconnection can supply both the Comptonization seed photons and the MeV tail of hard-state black hole X-ray binaries. In 3D particle-in-cell simulations of pair plasma, particles cool through inverse Compton scattering below the synchrotron self-absorption threshold and synchrotron emission above it. Approximately 40% of incoming magnetic power becomes inverse Compton radiation, while at least roughly 10–20% becomes synchrotron radiation. Particles escaping magnetic flux ropes accelerate rapidly and emit synchrotron photons reaching tens of MeV. Analytical estimates and radiative calculations for Cygnus X-1 indicate that photon-photon pair production attenuates this emission above about 1 MeV, leaving an escaping tail consistent with observations and extending to at least about 10 MeV. Most absorbed power feeds secondary pairs, whose Thomson optical depth can reach order unity; their synchrotron emission peaks near 0.1 keV and could provide the seed photons. These simulation and modeling results support, rather than establish, a reconnection-based synchrotron self-Compton explanation of hard-state emission.

PublicThe origin of some radiation from black hole X-ray binaries remains uncertain: what supplies the low-energy light that gets boosted into X-rays, and what produces the higher-energy gamma-ray tail? Researchers explored a possible shared explanation using three-dimensional plasma simulations and radiation calculations for Cygnus X-1. In their model, rearranging magnetic fields accelerate particles, which emit energetic light. Some of that light interacts with other photons to create new particle pairs. The pairs then emit lower-energy light that could supply the starting photons for X-ray production. The gamma rays that escape form a high-energy tail consistent with observations. This is a simulation-supported explanation, not a direct observation of the proposed process.

Young explorerNear a black hole, particles can give light a big energy boost. But where does the starting light come from? Scientists used a computer model to test an idea: changing magnetic fields speed up particles, which make light. Some light makes new particles, and those particles make more starting light. The model also makes very energetic light like astronomers see, but it does not prove this is what really happens.

Electromagnetic signatures of gradual magnetic dissipation in jets from supermassive black holes

Stavros Dimitrakoudis, Maria Petropoulou, Stamatios I. Stathopoulos+1 more

AstronomerThis numerical study extends LeHaMoC from a spherical emitting region to an extended, segmented blazar jet with gradual magnetic-reconnection-driven energy dissipation. Radiative exchange between segments is iterated to steady state, including relativistic effects associated with their relative motion. Compared with simply summing the emission escaping from independent segments in the optically thin regime, the coupled calculation enhances the inverse-Compton spectral contribution by a factor of three. Nevertheless, inverse-Compton emission remains far less luminous than synchrotron emission, even with external radiation fields. The authors conclude that gradual magnetic dissipation produces nearly universal, synchrotron-dominated spectra within this modeling scenario; these are computational findings, not observational measurements. The framework can be adapted to other jet-dissipation scenarios.

PublicBlazars have fast, narrow jets of plasma aimed nearly toward us. This study develops a computer model of how such a jet shines when energy stored in its magnetic field is released gradually over a wide range of distances from its central supermassive black hole. Unlike a calculation that simply adds up separate sections, the model allows light from different sections to interact with particles elsewhere in the jet. In the calculations, this increases the contribution from light boosted by collisions with energetic particles by a factor of three. Even so, that contribution remains much weaker than the light emitted by charged particles moving in magnetic fields, including when light from outside the jet is added. The results suggest that the modeled gradual energy-release process produces broadly similar spectra dominated by this magnetic-field-related emission. This is a modeling result rather than a new observation.

Young explorerSome giant black holes have long, fast streams of tiny particles shooting away from them. Scientists made a computer model to explore how one of these streams makes light. They let light from one part of the stream reach other parts, instead of treating each part as separate. In their model, this made one kind of light stronger, but another kind, made as particles move in magnetic fields, was still much brighter. This is what their computer model showed, not something they measured in the sky.

SN 2019qem: decades of extreme mass loss before the explosion of a luminous, long-lived Type IIn supernova

Joysankar Majumdar, Mariusz Gromadzki, Takashi J. Moriya+43 more

• Solar and Stellar Astrophysics

AstronomerSN 2019qem is a luminous, long-lived Type IIn supernova studied with host-subtracted optical and mid-infrared photometry and 26 optical spectra spanning −22 to +699 d. It rose in approximately 30 d to M_I = −20.5 mag and a bolometric luminosity of 7.0 × 10^43 erg s⁻¹, radiating 6.9 × 10^50 erg in the optical within 575 d. Early flash emission and unresolved narrow Balmer lines reveal dense, slow circumstellar material (CSM). Electron scattering shapes the Hα wings from +78 to +445 d; the persistent 400–700 km s⁻¹ blueshift favors an optically thick, asymmetric interaction region over newly formed dust. Thin-shell CSM-interaction fits, with shock velocity constrained by Hα widths, favor approximately 7 solar masses of ejecta encountering approximately 9 solar masses expelled roughly two years before explosion, followed by a wind corresponding to approximately 0.6 solar masses per year for an assumed wind speed of 100 km s⁻¹. The preferred model sweeps up approximately 32 solar masses by +544 d. A mid-infrared excess brightening for two years while the optical fades is interpreted as dust heated by continuing interaction. The low-mass, star-forming host has sub-solar metallicity at the explosion site. The inferred mass-loss history is consistent with luminous-blue-variable-like eruptions; taken at face value, the model-dependent mass budget implies an initial progenitor mass of at least approximately 40 solar masses.

PublicObservations of the bright, long-lasting supernova SN 2019qem suggest that its star shed enormous amounts of gas before exploding. Its light peaked after about 30 days, and its spectra reveal dense, slowly moving gas around the explosion. The researchers modeled the light as powered by the exploding star’s debris colliding with that surrounding material. Their preferred model suggests that the star expelled about nine times the Sun’s mass roughly two years before the explosion, with substantial mass loss also occurring during its final decades. These amounts and dates are inferred from modeling, not directly measured. A persistent shift in a hydrogen emission line is interpreted as evidence for an opaque, uneven collision region rather than newly formed dust. Meanwhile, infrared emission brightened for two years as visible light faded, tracing dust heated by the continuing collisions. The inferred outbursts resemble those associated with luminous blue variable stars, but this does not establish the star’s identity. If the inferred mass budget is correct, the star began life with at least about 40 times the Sun’s mass.

Young explorerA big star exploded, and astronomers watched it shine for a long time. Its light showed that there was lots of gas around it. They think the exploding star’s pieces crashed into gas the star had thrown out before, helping keep it bright. A computer model suggests the star tossed out a huge amount of gas about two years before it exploded, but that is an estimate, not something they watched happen. Dust warmed by the crashes also glowed with light our eyes cannot see.

Noisy pipelines II: Non-parametric Noise Inference for LISA

Charlie Hoy, Joseph Bayley, Ollie Burke+1 more

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

AstronomerThe authors present an initial non-parametric approach to LISA instrumental-noise inference that requires no prior knowledge of the observatory. Correlations complicate noise modelling because the covariance cannot be assumed diagonal across frequencies or data streams. Fitting the full noise covariance matrix with splines and inverse Lorentzians, the model estimates power and cross spectral densities from seven days of simulated noise-only data. Whitening with the median model estimate yields data consistent with the expected unit normal distribution. This is a simulation-based demonstration, not a test on observed LISA data or data containing gravitational-wave signals. Integration into a global fit and combination with modelled approaches to constrain the frequency dependence of unknown noise artifacts are envisioned applications, not demonstrated results.

PublicLISA is expected to detect gravitational waves from sources including pairs of massive black holes, but understanding its instrumental noise will be essential to interpreting those signals correctly. The authors introduce a flexible method that estimates noise without requiring prior knowledge of the observatory, including how noise is correlated within and between its data streams. In a test using seven days of simulated data containing only noise, the method estimated the noise patterns and transformed the data to match the expected standard bell-shaped distribution. This is an initial demonstration, not a test on real LISA observations or on data containing gravitational-wave signals. The authors suggest the method could eventually help analyse signals and noise together and investigate unexpected noise features.

Young explorerLISA is a planned way to listen for tiny ripples in space, but its own equipment will make noise too. Scientists tried a new way to work out what that noise looks like. They tested it on seven days of pretend data with only noise, and it made the noise behave as expected. They have not yet shown here that it works when the space ripples are mixed in. They hope it can help them understand future data.

Binary black hole mergers in massive Einstein-scalar-Gauss-Bonnet gravity

Harry L. H. Shum, Llibert Aresté Saló, Miguel Bezares+1 more

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

AstronomerThe authors study fully nonlinear binary black hole merger simulations in massive Einstein-scalar-Gauss-Bonnet gravity with a linear Gauss-Bonnet coupling. Without a well-developed EsGB initial-data solver, they find that the conventional massless-scalar workaround produces confined junk radiation that contaminates late-time dynamics in the massive theory. They propose modifying the early-time equations of motion to suppress this artifact and enable study of the scalar-field dynamics through merger. A preliminary analysis of scalar and tensor ringdown finds that the quadrupole scalar mode is initially dominated by a spin-2 contamination frequency, while its late-time morphology is governed primarily by the scalar mass frequency. These are simulation findings, not observational detections.

PublicComputer simulations explore how two black holes merge in an alternative theory of gravity that includes an additional field with mass. The researchers find that a commonly used way of setting up the simulations leaves unwanted artificial radiation trapped nearby, affecting the later evolution. They propose temporarily modifying the simulation equations at the beginning to reduce this problem. Their preliminary analysis of the ringing after merger finds a changing pattern in one component of the extra field: an early rhythm associated with gravitational waves gives way to behavior governed mainly by a frequency associated with the field's mass. The study concerns a theoretical model, not observations of a real merger.

Young explorerScientists used computers to imagine two black holes joining together under a different set of gravity rules. Their model includes an extra field that can wiggle. They found that the way they started the computer experiment made unwanted wiggles stick around, so they suggested changing the starting steps to calm them down. Their first look at the wiggles after the black holes join shows that one pattern changes over time: first it follows one rhythm, then mostly another linked to the extra field's mass. This happened in a computer model, not in a real black hole event they watched.

Axion Electrodynamics in Presence of a Stellar Non-homogeneous Background Magnetic Field

Bernard Teles de Menezes

• High Energy Physics - Phenomenology

AstronomerThis theoretical study reassesses axion electrodynamics in spatially nonuniform background magnetic fields. It generalizes Primakoff mixing between axion-like particles (ALPs) and photons to these backgrounds and calculates ALP production in a thermal magnetized plasma. Adopting Eddington’s standard solar model as the phenomenological setting, the authors use helioseismological and neutrino measurements to impose new bounds on the theory’s parameter space. The abstract gives neither numerical bounds nor a report of ALP detection.

PublicThe researchers calculate how hypothetical axion-like particles could mix with light in magnetic fields whose strength or direction varies from place to place. They also calculate how these particles could be produced in hot, magnetized plasma. Using Eddington’s model of the Sun, they draw on measurements of solar vibrations and neutrinos to place new limits on the theory’s possible parameters. These are theoretical calculations constrained by observations, not a detection of the particles; the abstract does not state the numerical limits.

Young explorerScientists used math to study tiny particles that might exist. They worked out how these particles could change into light and back in a magnetic field that is different in different places, and how hot material could make them. Using a model of the Sun and measurements of its shaking and tiny particles called neutrinos, they narrowed down which ideas could fit. They did not report finding the new particles.

Multimessenger astrophysics drives the case for an Australian Gravitational-Wave observatory

Fiona H. Panther, Paul D. Lasky, Nikhil Sarin

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

AstronomerThis study assesses the prospective multimessenger contribution of an Australian gravitational-wave observatory to second- and third-generation networks. It projects that including an Australian detector could enable up to eight joint gravitational-wave and kilonova detections annually, with sky-localization uncertainties better than 1–10 square degrees. The study also finds that an Australian observatory operating at second-generation sensitivity could substantially benefit multimessenger science within a global next-generation network. These are prospective capabilities, not reported event detections. The authors emphasize that this science case forms only part of the broader assessment needed for an Australian observatory.

PublicAn Australian gravitational-wave observatory could help a worldwide network pinpoint cosmic events and connect their gravitational-wave signals with light from kilonovas. The study estimates that networks including an Australian observatory could detect up to eight such paired events each year, locating them within sky regions smaller than 1–10 square degrees. Even an Australian detector with second-generation sensitivity could offer important benefits alongside next-generation observatories elsewhere. These are estimates of what a future observatory could enable, not detections already made, and the authors note that the overall case for building one requires broader consideration.

Young explorerScientists are studying whether a new listening station in Australia could help find faraway space events. It would listen for tiny ripples in space and help telescopes know where to look for light from the same event. The study says it could help, but this is a plan for the future, not something the new station has already done.

Late-time echoes from planar wave-packet scattering by an ultracompact star

Shanshan Deng, Jian-hua He

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

AstronomerTime-domain multipole mode-sum simulations follow an incident plane scalar wave scattering from an ultracompact, horizonless, constant-density star and compare its response with that of a Schwarzschild black hole. The early response closely resembles black-hole ringdown, arising from scattering near the exterior unstable photon sphere. Late-time echoes result from trapping near the interior stable light ring and leakage through the exterior potential barrier. Although individual multipoles produce regular echoes, coherent superposition creates interference and irregular profiles, while preserving temporal organization with alternating peak separations. A proof-of-concept signal-to-noise analysis suggests resolvability by third-generation gravitational-wave detectors under an assumed strain normalization; this is a conditional sensitivity estimate based on scalar-wave simulations, not an observational detection.

PublicComputer simulations explore how a wave scatters from an idealized, extremely compact star without a black hole’s event horizon. At first, the simulated signal closely resembles a black hole’s fading ringing because waves scatter in the surrounding region. Later, waves temporarily trapped deeper inside the star leak out as delayed echoes. Combining different wave components makes these echoes look irregular, although alternating gaps between peaks preserve an underlying timing pattern. The study models scalar waves rather than directly simulating gravitational waves. A separate proof-of-concept calculation suggests that third-generation gravitational-wave detectors could resolve the weak late signals at an assumed signal strength; no actual detection is reported.

Young explorerScientists used a computer to send pretend waves toward a very tightly packed star. At first, the waves acted much like waves near a black hole. Later, some waves that had been caught inside escaped as echoes. The echoes mixed together and looked messy, but still had a timing pattern. The scientists also explored whether future detectors could notice such faint signals, assuming how strong they would be. They did not hear real echoes.

The Late-time Afterglow of GW170817 and Implications for Jet Dynamics

Aman Katira, Kunal P. Mooley, Kenta Hotokezaka

AstronomerGW170817’s afterglow remains detectable seven years after the binary neutron star merger. A reanalysis of the X-ray data identifies potential sources of discrepancies among groups’ reduction techniques. Analysis of updated panchromatic data finds no significant evidence for a new afterglow component, including one associated with the kilonova ejecta, and implies that the jet remains mildly relativistic. The light curve declines significantly more slowly than standard synchrotron jet models with sideways spreading predict. The authors interpret this as indicating either late-time energy injection or velocity-dependent microphysical parameters and discuss the implications for jet dynamics.

PublicSeven years after the neutron star collision GW170817, its fading afterglow is still detectable. Researchers reexamined the X-ray observations and identified possible reasons why different teams’ processing methods produced discrepant results. Combining updated observations across wavelengths, they found no significant evidence for a new source of afterglow emission, contrary to some earlier claims. Their analysis indicates that the jet of material from the collision is still moving at mildly relativistic speeds. The glow is fading more slowly than standard models of a sideways-expanding jet predict, which could mean that extra energy is arriving late or that the physical processes producing the light change with the material’s speed.

Young explorerTwo neutron stars crashed together, and we can still see their fading glow seven years later. Scientists checked the light again and found no clear sign of a new part of the glow. They think a stream of material from the crash is still moving very fast. The glow is fading more slowly than their usual models say it should. Maybe it is getting extra energy, or maybe the way the moving material makes light is changing.

Second-scale periodicity in FRB 20201124A: coincident with critical RM evolution epochs and its possible implications

Wen-Long Zhang, Chen-Ran Hu, Chen Du+13 more

AstronomerThe two epochs with reported ~1.7 s periodicity in FRB 20201124A, MJD 59310 and 59347, coincide with transitions between quasi-steady and strongly varying Faraday rotation measure predicted by a magnetar/Be-star binary model. Refitting the secular RM evolution within that framework gives an estimated chance-coincidence probability of ~2.5%. A coherent joint search of bursts from both epochs, assuming linear spin-period evolution, yields P0 = 1.70603 s and Pdot = 6.1 × 10^-10 s/s at the reference epoch, with ~3.9σ Gaussian significance, consistent with the earlier measurement. The authors propose that these epochs mark magnetar passages through the companion's decretion disk. Captured material might suppress low-latitude emission so that polar-cap emission dominates, or accretion might increase magnetic obliquity and strengthen periodic modulation. These are proposed mechanisms, not established results; the timing coincidence suggests a connection between burst activity and environmental dynamics within the binary interpretation.

PublicA repeating source of fast radio bursts, FRB 20201124A, has shown a roughly 1.7-second rhythm on two observing dates. The researchers find that those dates coincide with transitions in how material around the source rotates the radio waves' polarization, as predicted by a model involving a highly magnetic neutron star called a magnetar and a Be-star companion. Within that model, they estimate a roughly 2.5% probability of the coincidence occurring by chance. A combined analysis of bursts from both dates also supports the previously reported rhythm, with a statistical significance of about 3.9 sigma, assuming the period changes linearly over time. The authors suggest that the magnetar was passing through a disk of material around its companion. Material captured from the disk could make emission near the magnetar's magnetic poles more prominent or more strongly modulated, revealing its rotation. This explanation remains a proposal rather than a confirmed picture of the source.

Young explorerAstronomers studied a place in space that sends out quick flashes of radio waves. On two days, the flashes seemed to follow a beat about every 1.7 seconds. Those days also matched changes in how nearby material affected the waves. The scientists think a tiny, very magnetic star might be moving through a disk of material around another star. That material might help us notice the spinning star's beat. Their checks support the beat, but they have not proved that this story explains it.

Radiation Magnetohydrodynamic Simulation of sub-Eddington Circumbinary Disk in a 10:1 Massive Black Hole Binary

Vishal Tiwari, Chi-Ho Chan, Tamara Bogdanović+2 more

AstronomerA global 3D radiation magnetohydrodynamic simulation models a circumbinary disk around a massive black hole binary with total mass 2 × 10^7 solar masses, mass ratio 0.1, and separation 100 GMtot/c². Relative to an otherwise identical locally isothermal MHD simulation, including radiation produces a thinner, denser, more filamentary disk with a less eccentric inner edge. The RMHD disk accretes at approximately 0.23 of the Eddington accretion rate and produces thermal emission peaking in the near-UV/optical, with luminosity approximately 1% of the Eddington luminosity. Compared with an equal-mass binary of the same total mass, the unequal-mass system's modeled circumbinary thermal emission is several orders of magnitude brighter and much more variable at far-UV/soft X-ray frequencies. Its dominant light-curve period is two binary orbits, versus 2.5–5 orbits for the equal-mass case. These simulation results highlight radiation's influence on disk structure and emission, with potential implications for electromagnetic counterpart searches associated with LISA gravitational-wave precursors and heavier binaries targeted by pulsar timing arrays; they are not observational detections.

PublicResearchers used a three-dimensional computer simulation to study a disk of gas surrounding two massive black holes, one ten times as massive as the other. Including radiation made the simulated disk thinner, denser, more threadlike, and less elongated along its inner edge than in a comparison model. The modeled disk shines most strongly in near-ultraviolet and visible light. At far-ultraviolet and soft X-ray frequencies, it is much brighter and more variable than the disk modeled around two equally massive black holes with the same combined mass. Its strongest repeating brightness pattern lasts two binary orbits, compared with 2.5–5 orbits in the equal-mass case. These are simulation findings, not observations of a real system. They may help guide searches for light associated with massive black hole binaries studied through gravitational waves.

Young explorerScientists made a computer model of two black holes circling each other inside a ring of gas. One black hole was ten times as massive as the other. When the model included light and its effects, the gas ring became thinner and more stringy. The model also showed a repeating pattern of brightening and dimming that took about two trips of the black holes around each other. This happened in a computer, not in a real pair that scientists watched. It may help them work out what to look for in the sky.

Neutrino transport and flavor instabilities in a post-merger disk

Erick Urquilla, Swapnil Shankar, Debraj Kundu+6 more

• High Energy Physics - Phenomenology

AstronomerUsing the six-dimensional phase-space particle-in-cell transport code EMU, the authors investigate fast and collisional neutrino flavor instabilities in a GW170817-like post-merger accretion disk. In the modeled radiation field, the differing angular distributions of electron neutrinos and antineutrinos produce electron-lepton-number crossings. Both instabilities occur, with collisional instabilities developing more slowly. Local quantum-kinetic simulations in centimeter-wide periodic domains show that each instability, studied separately, increases heavy-lepton neutrino fluxes. Collisional instability also breaks the initial heavy-flavor symmetry, raising the mean heavy-flavor antineutrino energy above the corresponding neutrino energy. Global simulations attenuate the Hamiltonian by factors of 10^-12 to 10^-5. Although unstable flavor waves are resolved, attenuation slows instability growth enough that neutrinos advect out before saturation. Evolution in these runs is instead governed by effective in-medium mixing angles and mass splittings arising from the combined vacuum, matter, and neutrino-neutrino potentials. These are simulation findings, not observations, and highlight the resolution and scaling needed to capture growth, saturation, and advection together.

PublicNeutrinos can change between different types, or flavors, and these changes may affect what happens after neutron stars merge. This study simulates the disk left by a merger resembling GW170817; it does not report new observations. The modeled neutrino field supports both fast and slower, collision-related instabilities. In small simulated regions, each instability increases the flow of heavy-flavor neutrinos. The collision-related instability also makes heavy-flavor antineutrinos more energetic on average than their neutrino counterparts. However, the whole-disk simulations weaken the equations governing flavor evolution, slowing the instabilities so much that neutrinos leave before the changes fully develop. The work therefore identifies requirements for future simulations rather than establishing the fully developed effects across the disk.

Young explorerWhen two neutron stars crash together, tiny particles called neutrinos can change from one kind into another. Scientists used computer models to study these changes in the disk left behind. In tiny pretend patches, the changes grew. But in the model of the whole disk, the scientists weakened part of the calculation, making the changes too slow to finish before the particles left. They need better simulations to learn what happens next.

Eccentricity as a Magnifying Glass: Precision Population Inference Enabled by Eccentric Neutron Star-Black Hole Mergers

Alberto Salvarese, Hsin-Yu Chen, Aaron Zimmerman+1 more

AstronomerThis study explores how eccentricity-enhanced parameter estimation could improve inference of neutron star–black hole (NSBH) formation channels. Isolated binary evolution is generally favored theoretically and tends to produce nearly circular orbits, whereas recent analyses indicating measurable eccentricity in GW200105 suggest that other channels may contribute. The authors forecast that tighter effective-spin measurements would allow confident identification of negative χ_eff, yielding one clearly spin-orbit-misaligned event per approximately 2.5 eccentric NSBH detections during LIGO-Virgo-KAGRA O5, assuming an isotropic spin-orientation population. Improved neutron-star mass measurements could reveal structure in the mass distribution and tighten constraints on its lower and upper bounds; recovery of a metallicity-dependent black-hole mass distribution also improves. The authors further project that a proposed population eccentricity distribution for dynamical formation channels could be tested by the end of O5. These are prospective population-inference capabilities, not established formation-channel identifications.

PublicHow do pairs containing a neutron star and a black hole form? The usual theoretical picture has the two stars evolve together, tending to leave a nearly circular orbit. Recent analyses of the gravitational-wave event GW200105 instead indicate an elongated orbit, suggesting that other formation routes may also matter. This study explores how such elongated orbits could help gravitational-wave observatories measure the objects’ masses and spins more precisely. The authors predict better chances of identifying spins misaligned with the orbital motion, sharper constraints on neutron-star mass ranges, and improved recovery of how black-hole masses depend on chemical composition. They also predict that a proposed pattern of orbital shapes associated with formation through gravitational encounters could be tested by the end of the observatories’ fifth observing run. These are forecasts of what future detections could reveal, not proof of a particular formation route.

Young explorerA neutron star and a black hole can circle each other like partners in a dance. Scientists want to know how they became partners. One signal suggests a pair followed a stretched-out path instead of a nearly round one. This study says stretched-out paths could help scientists learn more about the partners and test ideas about how they met. Those ideas still need testing.

Reconnection-driven Plasma Loading for Prompt Emission in Tidal Disruption Event Jets

Rin Oikawa, Yuri Sato

AstronomerOnly a small fraction of identified tidal disruption events launch relativistic jets, which are thought to be magnetically dominated outflows powered by the Blandford–Znajek mechanism. The origin of the plasma responsible for their observed prompt emission remains unresolved. This work proposes plasma injection through magnetic reconnection near the black hole during super-Eddington accretion. In the proposed scenario, accumulated magnetic flux produces an equatorial current sheet, where reconnection generates high-energy gamma rays. The authors show that photon–photon interactions can supply enough particles to account for the prompt emission while allowing the jet to remain magnetically dominated out to the emission region. They also find that magnetic dissipation can reproduce the observed prompt-emission properties within this scenario. Predicted MeV and GeV gamma-ray flares offer a test with future gamma-ray observatories; the abstract does not report their detection.

PublicWhen a star passes too close to a black hole, the black hole’s tidal forces can tear it apart. A small fraction of these events produce jets moving close to the speed of light, but the source of the particles needed to explain the jets’ early light remains uncertain. The authors propose that magnetic fields near the black hole rearrange and release energy, producing high-energy gamma rays whose collisions create particles to feed the jet. Their calculations indicate that this process could provide enough particles while leaving magnetic energy dominant in the jet, and that releasing magnetic energy could explain the observed early emission. This is a proposed explanation, not a confirmed mechanism. It predicts gamma-ray flares that future observatories could look for.

Young explorerA black hole can pull so hard on a nearby star that it tears the star apart. Sometimes, a fast stream of tiny particles shoots out from near the black hole. Scientists are not sure where all those particles come from. This study suggests that magnetic fields near the black hole release energy as very powerful light, and that bits of this light collide to make particles for the stream. The idea could explain the light we see from these streams, but it is not yet confirmed. Future telescopes could look for special flashes to help test it.

Multipolar neutrino radiation in binary neutron star mergers: Angular structure, rotational variability, and implications for electron fraction

Kutay Arınç Çokluk, Albino Perego, Federico Maria Guercilena+1 more

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

AstronomerFully general-relativistic simulations with energy-integrated M1 neutrino transport characterize the angular and temporal structure of binary neutron star merger neutrino emission across a representative range of equations of state, total masses, and mass ratios. The main analysis covers only remnants that avoid black-hole collapse during the simulated intervals. Spherical-harmonic decomposition of the energy flux outside the remnant shows that, after the initial transient, emission approaches an axisymmetric, quadrupole-dominated configuration: polar enhancement and equatorial suppression attributed to torus shadowing. The dipole remains subdominant, with no sustained one-sided emission. Anisotropy increases with mass asymmetry and softer equations of state. Coherent azimuthal modulations associated with an m=1 mode overlay this mean geometry. Comparison of the associated half frequency, f_dom/2 ≈ 0.6–0.7 kHz, with local rotation rates suggests, but does not establish, a dynamical connection to remnant structure. The radiation geometry also produces latitude-dependent equilibrium electron fractions; polar material approaches its neutrino-equilibrium target, while equatorial material remains more neutron rich and below equilibrium. These are simulation findings, not observational detections.

PublicComputer simulations explore how neutrino emission varies around the object left after two neutron stars merge. The main analysis considers remnants that do not become black holes during the simulated period. After an initial unsettled phase, the emission becomes roughly symmetric around an axis, stronger toward the poles and weaker around the equator, where the surrounding torus casts a neutrino shadow. There is no lasting dominance of one side over the other. Unequal stellar masses and softer descriptions of dense matter produce greater directional differences. The simulations also show repeating variations that may be linked to the remnant’s rotation, although that connection is uncertain. The radiation affects matter differently by latitude: polar matter approaches neutrino equilibrium, while equatorial matter stays more neutron rich and below equilibrium.

Young explorerScientists used computers to imagine two neutron stars joining together. In the models they studied, the leftover object did not turn into a black hole while they watched. Tiny particles called neutrinos streamed out more strongly from the top and bottom than around the middle. The streams also wiggled in a repeating way. These are computer results, not something seen in the sky.

Relativistic hydrodynamics of a charged fluid from Myers-Pospelov Lorentz-Violating Electrodynamics

Matheus Duarte, Vitor de Souza

AstronomerThis theoretical study derives relativistic charged-fluid hydrodynamics from Lorentz-violating Myers–Pospelov electrodynamics. The authors use the covariant Wigner formalism to obtain semiclassical spectral constraints and a distribution function, then apply Noether’s theorem to construct the energy-momentum tensor, particle current, and conservation laws. For a purely timelike Lorentz-violating background, corrections can be absorbed into effective thermodynamic quantities while retaining isotropic fluid equations. Spacelike backgrounds instead produce explicit preferred-direction contributions, including anisotropic forces and torques, that cannot be absorbed into standard hydrodynamic variables. These are consequences of the assumed theory, not observational evidence for Lorentz violation. The framework is a starting point for developing Lorentz-violating relativistic magnetohydrodynamics, rather than a completed theory of that kind.

PublicThe researchers mathematically explore how an electrically charged fluid would behave if the underlying laws included Lorentz violation, a hypothetical departure from the usual symmetry of relativity. They derive fluid equations from modified equations for particles and electromagnetism. When the assumed modification is purely time-directed, its effects can be incorporated into revised thermodynamic quantities without making the fluid equations favor a spatial direction. When it selects a direction in space, the equations contain direction-dependent forces and twisting effects that cannot be hidden in the usual fluid quantities. This is a theoretical result, not a detection of such effects. It provides groundwork for a future theory that also treats the fluid’s interaction with magnetic fields.

Young explorerImagine a flowing liquid made of tiny bits that carry electric charge. The scientists used math to ask what would happen if nature had a special rule that could pick a favorite direction. In their model, a favorite direction in space adds pushes and twists linked to that direction. A different version of the rule changes the math without picking a favorite direction in space. They did not see a real liquid doing this; they worked out what their imagined rules would mean.

Multiwavelength Classification of Chandra Sources in Omega Centauri

Steven Chen, Oleg Kargaltsev, Jeremy Hare+4 more

• Astrophysics of Galaxies

AstronomerThis study cross-matches more than 200 Chandra X-ray sources in NGC 5139 with multiwavelength catalogs from HST, JWST, and MeerKAT. It applies the MUWCLASS machine-learning classification pipeline to a crowded stellar environment for the first time and introduces a globular-cluster-specific training dataset assembled from previously classified sources in 25 Galactic globular clusters. To address classification challenges caused by crowding, the authors compare MUWCLASS with traditional methods. They confirm previously suggested counterpart associations and identify new confident and candidate associations. Implications for cluster dynamical evolution and binary formation and destruction are discussed in the context of models; the abstract does not report specific source classifications or establish a particular evolutionary scenario.

PublicResearchers studied more than 200 X-ray sources in the densely packed star cluster NGC 5139, matching Chandra detections with catalogs from HST, JWST, and MeerKAT. They used a machine-learning tool to help classify the sources, introducing a training set based on previously classified sources in 25 globular clusters. Because crowded stars make identification difficult, they also compared the tool's results with traditional methods. The study confirms some previously suggested matches between X-ray sources and objects seen in other observations, and finds new matches, some considered confident and others still tentative. The authors discuss what these classifications could mean for models of how clusters change and how pairs of stars form or break apart, without establishing a specific explanation in the abstract.

Young explorerScientists looked at more than 200 places giving off X-rays in a tightly packed group of stars. They compared pictures and lists from different telescopes to help work out which objects were making the X-rays. A computer helper looked for patterns, and the scientists compared its answers with other ways of checking. They confirmed some matches people had suggested before and found new ones, but some are still uncertain. They also discussed how these clues might help explain how the star group changes and how pairs of stars get together or split apart.

2:1 Harmonics in the Radio Light Curves of Supermassive Black Hole Binary Candidates

A. C. S. Readhead, M. F. Aller, R. D. Blandford+16 more

AstronomerThe authors report evidence for 2:1 harmonic periodicities in the OVRO and UMRAO monitoring data for the supermassive black hole binary candidates PKS J0805-0111 and PKS 2131-021, following a previous detection in J1309+1154. If confirmed, these findings would suggest a physical origin favoring 2:1 commensurabilities in strongly periodic blazar light curves. Differences among the three sources may reflect differences in their central engines, but this remains an interpretation. Correlated random variability, observed periods longer than two years, and periodicities that can disappear for long intervals complicate verification. The authors argue that detailed light-curve dissection and harmonic coherence may help establish genuine periodicity and identify binary candidates. They discuss four explanatory models and how future detections—or a lack of detections—of shorter-period candidates could distinguish them, while presenting arguments both for and against the periodicities being real.

PublicRadio monitoring has revealed possible repeating brightness patterns in two blazars suspected of containing pairs of supermassive black holes. In each, the reported patterns have a 2:1 relationship: one repeats twice as often as the other. A similar pattern was previously detected in a third candidate. These findings are not yet confirmed, and they do not establish that the objects contain black hole pairs. Random brightness changes can complicate the evidence, and the apparent cycles, all longer than two years so far, can disappear for long stretches. The researchers discuss four possible explanations and suggest that future searches for shorter cycles could help distinguish them.

Young explorerScientists watched the brightness of faraway objects and found hints of a repeating pattern: one beat may happen twice for every other beat. They wonder whether pairs of huge black holes could be involved, but they do not know yet. The objects also brighten and dim in messy ways, and the beats can seem to stop for a long time. More watching could help show whether the patterns are real.

Bayesian Inference of the Landau Parameter G'₀ from Joint Gamow-Teller Measurements

Zidu Lin, Gianluca Colò, A. W. Steiner+1 more

• Nuclear Theory

AstronomerThe authors infer the leading-order spin-isospin Landau–Migdal parameter G0' using Bayesian analysis within a self-consistent standard Skyrme random-phase approximation model, jointly constrained by experimental Gamow–Teller resonance measurements in lead-208, tin-132, and zirconium-90. At nuclear saturation density, they obtain G0' = 0.48 ± 0.034. This model-dependent inference is close to predictions from a few existing Skyrme models incorporating spin-isospin observables, but below traditional values extracted from pion-exchange models. The authors investigate the roles of the nucleon effective mass and the density dependence of G0' in this discrepancy. The parameter is relevant to nuclear beta and double-beta decay, neutrino absorption in core-collapse supernovae and binary neutron-star mergers, and the critical density for pion condensation in neutron stars; these astrophysical consequences are not directly measured here. The inferred density dependence may guide future energy density functionals for dense matter.

PublicHow protons and neutrons interact affects both atomic nuclei and matter in exploding stars and neutron-star mergers. This study estimates G0', a parameter describing how that interaction depends on particle spin and on whether the particles are protons or neutrons. The researchers combined laboratory measurements of resonances in three nuclei with a nuclear model and Bayesian statistical analysis. At nuclear saturation density, they inferred G0' = 0.48 ± 0.034. The estimate agrees closely with some existing models but is lower than values obtained using pion-exchange models. It depends on the modeling framework rather than being a direct measurement of matter inside stars. The results may help improve models of dense nuclear matter and its interactions with neutrinos.

Young explorerProtons and neutrons are tiny pieces inside atoms. Scientists used measurements of how these pieces move together, plus a computer model, to estimate one rule for how they interact. Their answer was close to some earlier models but different from others. It might help scientists understand matter inside very dense stars, but they did not measure that star matter directly.

Parity-dependent wave absorption and optical characteristics of a cored magnetic black hole

Mohsen Fathi, Faizuddin Ahmed

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study calculates light propagation and coupled gravitational–electromagnetic scattering around black holes supported by a nonlinear magnetic field. A single field action determines the geometry, mass–charge relation, and wave potentials. Across eight solutions of that action, two critical light impact parameters differ by 3.6–7.2%. Absorption is parity dependent: for ℓ=2, the gap between the larger absorption eigenvalues reaches about 9.0 percentage points. A broader frequency scan finds a stronger effect in the second eigenchannel, with the absorption traces differing by up to 24.3 percentage points. Each trace equals twice the absorption of an equal incoherent mixture of incoming gravitational and electromagnetic fields. A controlled wave-operator test identifies an important role for the nonlinear electromagnetic factor κ in the parity gap. Four ℓ=3 cases and charge-matched Reissner–Nordström controls are also examined. These are calculated, complementary optical and wave properties of the same magnetic source, not observational measurements.

PublicThe researchers mathematically studied a black hole supported by a magnetic field whose behavior is nonlinear. Their model uses the same description of that field to determine both the black hole’s geometry and how light and interacting gravitational and electromagnetic waves behave nearby. In eight calculated solutions, two characteristic scales for light passing the black hole differ by 3.6–7.2%. The calculated absorption of waves also depends on their symmetry pattern, with the strength of that difference varying between wave channels and frequencies. A controlled mathematical test indicates that the field’s nonlinear behavior plays an important role in this absorption difference. The work offers two complementary ways to describe the same modeled magnetic source; it does not report observations of an actual black hole.

Young explorerScientists used math to study a black hole with a magnetic field. They calculated how light travels nearby and how the black hole swallows waves. In their model, waves with different patterns can be swallowed by different amounts. These are answers from math, not something they watched happen in space.

Are neutrinos Majorana? Fixed-target and high-energy astrophysical searches decide

Gabriela Barenboim, Mauricio Bustamante, Qinrui Liu

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

AstronomerThis revised paper withdraws its original proposed signature for distinguishing Dirac from Majorana neutrinos. The original proposal invoked a heavy neutral lepton (HNL) producing a high-energy change in active-neutrino flavor mixing only for Majorana neutrinos, as a complement to neutrinoless double beta decay searches and their electron-channel blind spots. It identified the upcoming SHiP beam-dump experiment as a prospective setting for discovering GeV-scale HNLs and measuring their mixing. The revision explicitly states that the proposed Majorana signature does not exist; this is not an observational result. The analysis has been superseded by Barenboim:2026udr, and the original version remains available as v1.

PublicNeutrinos have a fundamental property that physicists have not yet settled: whether they are Dirac or Majorana particles. This paper originally proposed a new way to distinguish the two, using a hypothetical heavy neutral lepton and changes in how neutrino types mix. The idea was intended to complement existing searches, which have blind spots, and discussed the upcoming SHiP experiment as a possible testing ground. Crucially, the revised paper says the proposed telltale signal does not exist. It therefore does not establish a new test or resolve the question, and its analysis has been replaced by another work.

Young explorerScientists are trying to learn what kind of tiny particles neutrinos are. This paper first suggested a new clue they could look for in an experiment. But the updated paper says that clue would not actually be there, so the idea does not work as proposed. It does not tell us which kind neutrinos are.

Hybrid stars with hyperons: structure based on QCD sum rule coupling constants

F. Moradi Jangal, H. R. Moshfegh, K. Azizi

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

AstronomerThis theoretical study models hybrid stars containing hadrons, leptons, and quarks in a relativistic mean-field framework. QCD sum-rule coupling constants are used to calculate bulk nuclear-matter properties and nucleon and hyperon single-particle potentials, constraining the hadronic sector. Beta-equilibrated equations of state combine a sigma-omega-rho hadronic model with either the MIT bag or Nambu-Jona-Lasinio quark model, treating the hadron-quark transition with both Gibbs and Maxwell constructions. The resulting calculations predict mass-radius relations, particle fractions and radial distributions, the tidal Love number K2, and dimensionless tidal deformability Lambda. The abstract reports no numerical predictions or demonstrated agreement with observations; it presents these outputs as relevant for comparison with current multimessenger data.

PublicThe researchers calculate how hypothetical hybrid stars—stars containing ordinary nuclear particles as well as quarks—might behave. They use several theoretical descriptions of matter and two ways of treating the transition from nuclear matter to quark matter. From these models, they predict relationships between stellar mass and radius, how different particles are distributed inside a star, and how strongly a star would deform under tidal forces. These are theoretical predictions intended for comparison with astronomical observations, not evidence that hybrid stars have been detected. The abstract gives no numerical results or conclusions about which model best matches observations.

Young explorerScientists used math to imagine stars with unusual matter inside. They tried different recipes for what the stars could be made of and how that matter could change deep inside. Their calculations predict how heavy and wide the stars might be, what might be inside them, and how easily gravity from something nearby could stretch them. These are ideas to check against what astronomers see, not proof that such stars have been found.

Landau-Zener formula and resonant axion conversion in neutron star magnetospheres

Matti Heikinheimo, Topi Sirkiä, Kimmo Tuominen

• High Energy Physics - Phenomenology

AstronomerThis theoretical and numerical study tests the Landau-Zener approximation for resonant axion-photon conversion in neutron star magnetospheres. The authors find that it often fails for conversion into millimeter-to-optical photons because the characteristic resonance width exceeds the size of the conversion region. Comparing these scales provides a simple validity criterion, which they verify numerically. Outside its validity regime, the Landau-Zener conversion probability can differ significantly from the numerical result. The authors consequently revise axion constraints from neutron star optical-band polarization searches; the abstract does not specify the direction or magnitude of those revisions.

PublicThe researchers examine a calculation used to predict how hypothetical particles called axions could turn into light near neutron stars. Their theoretical analysis finds that the calculation often breaks down for light ranging from millimeter wavelengths to visible light: the region needed for the assumed conversion process is wider than the available conversion region. They develop a simple check for when the calculation is valid and confirm it with numerical calculations. When the check fails, the predicted conversion probability can be substantially inaccurate. They use these findings to revise limits on axions inferred from searches using the polarization of neutron-star light, without reporting an axion detection.

Young explorerScientists are studying whether tiny particles called axions, which have not been found, could turn into light near a neutron star. They found that a math shortcut used to work out the chance of this happening often does not fit: it needs more room than the place where the change can happen. They made a check for when the shortcut works and tested it with computer calculations. This helped them update what searches of neutron-star light can tell us about axions. It does not mean they found any axions.

Odd-parity ringdown gravitational waves of a spherically symmetric black hole with perfect fluid accretion

Rikuto Ohashi, Yasutaka Koga, Hiroyuki Nakano+2 more

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

AstronomerThis theoretical study computes the odd-parity ringdown waveform in the time domain for a Schwarzschild black hole undergoing dilute, steady, spherically symmetric perfect-fluid accretion, to first order in the accretion rate. Odd-parity matter perturbations decouple from metric perturbations, leaving a purely tensorial wave mode on the dynamical background. Within this approximation, the ratio of the imaginary to real frequency components cancels both the secular variation due to black-hole growth and the redshift factor; its departure from the Schwarzschild value therefore isolates the environmental contribution. The frequency’s time dependence supplies a second observable tied to the accretion rate. The authors argue that measuring these quantities across multiple modes could constrain the environment, but report no observational measurement.

PublicA black hole’s ringdown—the gravitational waves it emits as it settles—can probe gravity, but surrounding matter may alter the signal. This theoretical study calculates how the ringdown changes when a nonrotating black hole slowly gains matter from a thinly distributed fluid flowing steadily and symmetrically inward. In this simplified model, keeping only first-order effects of accretion, a ratio comparing the signal’s damping with its oscillation frequency removes changes caused by the black hole’s growth and by redshift, isolating the influence of its surroundings. How the frequency changes over time provides another quantity linked to the rate of matter falling in. The authors suggest that measuring both quantities in several ringing modes could help constrain the surroundings; this is a proposed use of the calculations, not an observed result.

Young explorerA black hole can send out ripples that fade away, a little like a bell’s ringing. The researchers used math to imagine a black hole slowly swallowing matter that flows in evenly from every side. In their simple model, one way of comparing how the ripples wiggle and fade could reveal clues about the matter nearby. Changes in the wiggles could also give clues about how fast the black hole is eating. They hope future measurements could use these clues; they have not measured them here.

Medium effects on neutron star modified and direct Urca cooling rates

B. X. Zhou, Jin-Biao Wei, Z. H. Li+2 more

• Nuclear Theory

AstronomerThe study examines how in-medium modifications of elementary cooling processes affect observable properties of isolated neutron stars, infers mass distributions compatible with the cooling analysis, and compares them with theoretical models. The authors conclude that current cooling data require direct Urca (DU) cooling, moderated by proton superfluidity, in most neutron stars, with the DU onset threshold below canonical masses. Under that condition, medium modifications to modified Urca rates are practically insignificant, whereas neutron-neutron bremsstrahlung plays a dominant role. These are conclusions of the cooling analysis rather than direct observations of the interior processes.

PublicThe researchers study how conditions inside isolated neutron stars change the processes that cool them. They also infer which distributions of stellar masses fit the cooling data and compare them with theoretical models. Their analysis indicates that most neutron stars need a rapid cooling process called direct Urca, tempered by protons being in a superfluid state. This process would need to switch on at masses below those usually considered typical. In that picture, changes to a related process called modified Urca matter little, while cooling associated with interactions between neutrons plays a dominant role. These conclusions are inferred from cooling data, not directly observed inside the stars.

Young explorerNeutron stars cool down, and scientists want to understand how. The researchers compared ideas about what happens inside these stars with clues about their cooling. They think most need a fast way to cool, held back by a special state of the protons inside them. In this picture, interactions between neutrons are also very important for cooling. Scientists worked this out from the cooling clues; they did not watch these things happen inside a star.

Surface Nitrogen enrichment from the LMC to the Early Universe: the roles of rotation, overshooting and mass loss

Gautham N. Sabhahit, Jorick. S Vink

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerStrong nitrogen features observed by JWST in high-redshift galaxies such as GN-z11 motivate very massive stars as potential early nitrogen sources, although surface enrichment depends on poorly constrained mixing, rotation, and mass loss. MESA evolutionary models at 40, 100, and 200 solar masses isolate the effects of convective overshooting and rotation. In these models, very massive stars develop nitrogen-enriched surfaces across a broad metallicity range: at low metallicity, weak winds shut off the overshooting enrichment channel, but rotation of about 90 km/s still produces enrichment; at higher metallicity, stronger winds expose core material largely independently of the adopted mixing. Overshooting produces an abrupt enrichment jump only after winds expose nitrogen-rich layers left by the receding core, whereas rotation transports nitrogen outward continuously, producing a gradual rise. A synthetic LMC population spanning 20–300 solar masses, with modest overshooting and modest rotation drawn from the observed velocity distribution, reproduces the observed nitrogen-enriched fraction without the large core-boundary mixing efficiencies required by non-rotating models. These are model-based findings, not a demonstration that very massive stars explain the nitrogen seen in distant galaxies.

PublicJWST has observed strong signs of nitrogen in distant galaxies, raising the question of how the early Universe made it so efficiently. This study uses computer models to explore very massive stars as possible sources. The models show two ways nitrogen made inside a star can reach its surface: rotation gradually mixes it outward, while stellar winds can strip away outer layers and abruptly expose nitrogen-rich material. Where stars have fewer elements heavier than helium, the winds are weaker, but even modest rotation can still enrich the surfaces of very massive stars. Where those elements are more abundant, stronger winds do most of the work. A simulated population for the Large Magellanic Cloud also matches the observed fraction of nitrogen-enriched stars using modest rotation and mixing. The findings support very massive stars as promising nitrogen sources, but do not establish that they caused the nitrogen signatures in the distant galaxies.

Young explorerA telescope has found signs of something called nitrogen in very faraway galaxies. Scientists used computer models to see how giant stars might bring nitrogen from deep inside to their surfaces. In the models, spinning slowly stirs it outward, or winds blow away the outside layers and uncover it. A pretend group of stars also matched how often astronomers find nitrogen-rich stars in one nearby galaxy. These are clues, but we do not yet know if giant stars explain the nitrogen in those faraway galaxies.

Towards Self-consistent Modeling of Quasi-Stars and their NLTE Spectra: Implications for Little Red Dots

Jake B. Hassan, Rosalba Perna, Mitchell C. Begelman+4 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe study tests whether quasi-stars—massive envelopes surrounding rapidly accreting black-hole seeds—could explain some JWST Little Red Dots (LRDs). It couples stellar evolution calculations to TLUSTY non-local thermodynamic equilibrium (NLTE) spectral synthesis for primordial hydrogen-helium atmospheres. Replacing polytropic assumptions with a mixing-length envelope treatment, with saturated convection and radiative energy setting the inner-boundary luminosity, removes earlier models’ black-hole mass limits and permits evolution to black-hole-to-total mass ratios approaching unity. The modeled spectra show cool photospheres, prominent Balmer breaks, and Balmer and Paschen absorption. NLTE increases Balmer absorption depths by approximately 35–55% relative to LTE, while changing the continuum only slightly. Comparisons with observed LRD spectral energy distributions show broad continuum agreement, but the models fail to reproduce commonly observed strong emission lines. Conditional on the quasi-star interpretation, individual-object comparisons suggest masses of approximately 10^5–10^7 solar masses. The framework supports further tests of the proposed connection rather than establishing that LRDs are quasi-stars.

PublicCould some of the Little Red Dots discovered by JWST be massive gas envelopes surrounding rapidly growing black holes? This study explores that possibility with computer models linking the evolution of these proposed objects, called quasi-stars, to the light they would produce. The models predict cool outer surfaces and distinctive absorption features. A more detailed treatment of the atmospheres makes some absorption features substantially stronger but changes the overall light distribution only slightly. The predicted light broadly resembles the observed Little Red Dots, but there is an important mismatch: the models do not reproduce the strong emission lines commonly seen in them. If the quasi-star interpretation is correct, comparisons suggest masses of roughly 100,000 to 10 million Suns. The study offers a way to test the idea, not confirmation that these objects are quasi-stars.

Young explorerScientists wonder if some tiny red dots seen by a space telescope could be huge balls of gas wrapped around growing black holes. They used computers to work out what light these gas balls might make. Some parts look like the light from the real dots, but other important parts do not match. So the idea is still being tested.

Shadowing the Sun I: Testing Synthetic Granulation Spectra with NEID Solar Eclipse Observations

Elizabeth Gonzalez, Michael L. Palumbo III, Suvrath Mahadevan+17 more

AstronomerUsing NEID solar-feed observations of the October 2023 solar eclipse, the authors compare RVs from 22 spectral lines with synthetic granulation-driven spectra from GRASS-E, a geometry-modified version of GRASS. The eclipse Rossiter-McLaughlin signal spans approximately 1.4 km s−1 peak to trough. For Fe I 5434 angstrom, GRASS-E leaves an RMS residual of 13.47 m s−1, whereas a model with an optimized convective-blueshift polynomial achieves 2.90 m s−1. This improvement suggests, rather than establishes, that sparse center-to-limb observations currently limit GRASS-E. Combining spectral lines yields a weighted RMS of 5.2 m s−1, approximately 0.37% of the RM signal, an accuracy the authors describe as beyond current exoplanet transit observations. The study demonstrates recovery of line-specific center-to-limb convective-blueshift variation from solar eclipses; it does not demonstrate detection of an Earth-mass planet or suppression of granulation to the 0.1–1 m s−1 level relevant to quiet-star RV searches.

PublicShifting patterns on a star’s surface can change its spectrum in ways that obscure the tiny motion caused by an Earth-mass planet. The researchers used observations of the October 2023 solar eclipse to test how well models reproduce these changes across the Sun’s face. They compared measurements from 22 spectral lines with simulated spectra. For one iron line, a model with an optimized description of convection-related wavelength shifts matched the observations substantially better than the granulation simulation. The authors suggest that the simulation is limited by sparse observations spanning the Sun’s center to its edge. Combining several lines gave a mismatch of about 0.37% of the eclipse’s large velocity signal. The result shows that solar eclipses can reveal how convection-related shifts vary across the Sun, but it is not a detection of an Earth-like planet.

Young explorerThe Sun’s surface is always changing, and that can make it hard to spot the tiny wobble a planet gives a star. The scientists watched sunlight during an eclipse, when the Moon covered part of the Sun. They compared what they saw with computer-made sunlight. One model matched much better after they adjusted how it described changes from the Sun’s middle to its edge. This helps scientists learn about the Sun’s moving surface. They did not find a planet in this study.

Protostellar evolution of intermediate-mass stars: implications for the survival of fossil magnetic fields

Luis Villarroel Casanova, Dominik R.G. Schleicher, Daniele Galli+1 more

AstronomerMotivated by observed strong fields in radiative stars, especially Ap/Bp stars, this study uses 1D MESA pre-main-sequence models to investigate when initially convective, intermediate-mass protostars become predominantly radiative and how this might favor fossil-field survival. The modeled transition occurs at approximately 1.3–2.8 solar masses for 1-solar-mass initial seeds, reaching about 4 solar masses for other initial masses at high accretion rates. Average accretion rate and metallicity dominate over accretion-history details, with lower metallicity moving the transition to lower mass. At Z ≥ 0.01 and accretion rates above 4 × 10^-6 solar masses per year, models retain convective envelopes through the end of accretion, potentially dissipating accreted magnetic flux. The results offer a conditional explanation for preferential fossil-field survival in intermediate-mass stars, requiring radiative structure to persist after accretion. An increased incidence of strongly magnetized radiative stars below Z = 0.01 is a prediction, not an observational finding.

PublicSome stars have strong magnetic fields that may be remnants of their early lives. This study uses computer models, rather than new observations, to explore when growing young stars change from interiors dominated by churning gas to interiors dominated by radiation carrying energy. That change may help old magnetic fields survive. In models starting at one solar mass, the transition happens at roughly 1.3–2.8 times the Sun’s mass; some other starting masses and rapid growth rates push it to about four solar masses. The average rate of growth and the abundance of elements heavier than helium matter more than the detailed pattern of growth. Fewer heavy elements lead to a transition at lower mass. Some models keep churning outer layers until growth ends, which could dissipate magnetic fields brought in with incoming material. The findings could help explain why surviving early magnetic fields favor intermediate-mass stars, but only if their radiation-dominated interiors persist after growth stops. The authors also predict that strongly magnetic, radiation-dominated stars should be more common where heavy elements are less abundant.

Young explorerSome stars have strong magnetism that might be left over from when they were babies. Scientists made pretend growing stars in a computer to study what happens inside them. At first, gas churns around inside. Later, energy can travel mostly as light instead, and that change might help the star keep its magnetism. In the computer models, when this happens depends on how fast the star grows and what it is made of. The idea could explain why some stars keep their old magnetism, but only if their insides stay changed after they finish growing. The scientists also predict that stars made with fewer heavy ingredients will more often have strong magnetism; this study has not shown that prediction to be true in real stars.

A Wolf-Rayet nebula in its disruption phase: high-resolution radio observations of PCG 11

C.S. Buemi, P. Leto, F. Cavallaro+12 more

AstronomerHigh-resolution MeerKAT imaging at 2.6 and 3.1 GHz and ATCA imaging at 5.5 and 9.0 GHz resolve the Wolf-Rayet nebula PCG 11 into rim condensations, low-brightness gaps, and finger-like protrusions, tracing its fragmentation in ionized gas. The radio morphology indicates a hollow, equatorially enhanced structure viewed close to its symmetry axis. The authors quantify the fragmentation scale and relate it to the nebular geometry. An unresolved source coincident with WR 75ab has a rising radio spectrum consistent with thermal stellar-wind emission. The nebula processes only a small fraction of the stellar ionizing radiation, indicating substantial photon leakage. The authors interpret PCG 11 as a poorly observed transitional stage in which a coherent instability pattern has fragmented the swept-up shell into a porous structure that remains dynamically coupled to the stellar wind.

PublicRadio images reveal that PCG 11, a nebula shaped by a Wolf-Rayet star’s powerful wind, has a hollow structure with more material around its middle, seen nearly along its symmetry axis. Its scalloped rim breaks into clumps, faint gaps, and finger-like extensions. The nebula absorbs only a small share of the star’s ionizing radiation, indicating that much of this radiation escapes. A compact radio source at the position of WR 75ab also has a spectrum consistent with emission from the star’s hot wind. The researchers interpret the nebula as a rarely observed transitional stage: its swept-up shell is breaking apart and becoming porous, but remains dynamically linked to the stellar wind.

Young explorerA big star blows a very strong wind into gas around it. Scientists used radio telescopes to look at a cloud called PCG 11 and found a hollow shape with a lumpy edge, gaps, and little fingers of gas. Much of the star’s light that can change the gas appears to escape instead of being caught by the cloud. The scientists think the cloud’s shell is breaking into pieces while the star’s wind still helps move it.

Carbon-Reaction Constraints on Stellar Evolution: White-Dwarf Heating, Carbon-Burning Products, and Black-Hole Masses

Akram Mukhamedzhanov

• Nuclear Theory

AstronomerThis modeling study examines how carbon-fusion and carbon alpha-capture rates affect stellar heating, composition, and black-hole mass limits. MESA calculations using published Bayesian carbon-fusion rates shift the balance between nuclear heating and combined neutrino and surface-photon losses in an accreting carbon–oxygen white dwarf to slightly higher masses, central temperatures, and central densities. At an accretion rate of 10^-7 solar masses per year, the Bayesian-median calculation has a central temperature 2.57% higher and density 18.9% higher than the CF88 calculation at this balance point. In a separate initially 20-solar-mass, Z=0.0142 model, changing both the fusion rate to the Bayesian median and the proton-to-alpha branching ratio to that of Yang et al. increases the neon-20 mass at central carbon depletion by 10.8% and decreases sodium-23 by 28.7%, relative to CF88 with MESA’s standard branching. For carbon alpha capture, applying S_tot(300 keV)=118±17 keV b to published Z=10^-5 models yields, by linear interpolation, a maximum black-hole mass below the pair-instability gap of approximately 61.5–77.4 solar masses, conditional on those models’ assumptions. New Z=0.00142 MESA calculations yield smaller bound pre-collapse masses, but differences in stellar assumptions preclude attributing the difference between the curves to metallicity alone. These are calculation-based findings, not direct stellar measurements.

PublicComputer models suggest that uncertainties in how carbon nuclei react can change when stars heat up, which elements they produce, and the masses of black holes they may leave behind. Using a published statistical estimate of the carbon-fusion rate, the researchers find that an accreting white dwarf reaches the point where nuclear heating balances energy losses at slightly greater mass and at higher central temperature and density than in a standard calculation. A separate massive-star model, with changes to both the reaction rate and its reaction pathways, leaves more neon-20 and less sodium-23 after central carbon burning. Applying a constraint on the reaction between carbon and helium to published models gives an estimated maximum black-hole mass of about 61.5–77.4 times the Sun’s mass below the pair-instability mass gap. That estimate depends on the models’ assumptions. New calculations leave less mass bound to the star before collapse, but the differing assumptions mean this difference cannot be explained by metal content alone.

Young explorerInside stars, tiny bits of matter can join together, making heat and new ingredients. Scientists used computers to see what happens when they change how quickly some of those bits join. In their pretend stars, this changed when heating balanced cooling and how much of some ingredients remained. It also changed estimates of how heavy a black hole left by a star could be. These are computer-model answers, not things the scientists watched happen in real stars, and the answers depend on the rules used in the models.

Up in smoke: carbon-destruction in the terrestrial planet-forming region of a young Class I disk

F.J. Ballieux, M.K. McClure, E.A. Bergin+4 more

• Earth and Planetary Astrophysics

AstronomerAn analysis of carbon species in the JWST spectrum of the Class I protostar HOPS-68, using local thermal equilibrium slab models, detects warm (~400 K) HCN and C2H2 attributed to the base of a disk wind and colder (~40 K) C4H2, CH3, and CS attributed to the outer disk or outflow cavity wall. The spectrum also contains 13CCH2, CH4, and C6H2; ALMA observations show C2H tracing the outflow cavity walls. The authors propose that thermal destruction of refractory carbon grains in the inner disk releases carbon-bearing species, with a disk wind transporting carbon carried by HCN and C2H2 outward. UV-driven gas-phase reactions involving C2H could then produce the observed aliphatic chains. This interpretation suggests that Warm Carbon Chain Chemistry may trace outflows rather than infall. The proposed processing could contribute to Earth's carbon depletion and to aliphatic organics in meteorites and asteroids, but these connections are not established by the detections.

PublicEarth's surface and deep interior contain much less carbon relative to the Sun, and heating carbon-rich dust around young stars is one possible explanation. Studying the young star HOPS-68, researchers detected several carbon-containing molecules with JWST. Their models place some in warm gas near the base of a wind from the surrounding disk, and others in much colder regions farther out. ALMA observations also reveal a carbon-containing molecule along the walls of a cavity made by an outflow. The team proposes that heat releases carbon from dust near the star and that the disk wind carries it outward, where ultraviolet light could help build carbon-chain molecules. If correct, this would mean that chemistry often associated with gas falling inward may instead mark gas flowing outward. The process might help explain both Earth's carbon shortage and carbon-chain compounds in meteorites and asteroids, but those links remain tentative.

Young explorerAround a very young star called HOPS-68, scientists found tiny bits of gas that contain carbon. Some are warm and some are much colder. They think heat near the star might free carbon from dust, and a wind might carry it farther away. There, light from the star could help the carbon make little chains. This is an idea they are studying, not something they know for sure. It might help explain why Earth has so little carbon compared with the Sun.

A Detailed Polarimetric Imaging Study of Type II Solar Radio Burst with the MWA: Detection of Linear Polarization

Puja Majee, Devojyoti Kansabanik, Divya Oberoi

AstronomerThe authors present full-Stokes imaging of a metric type II solar radio burst observed with the Murchison Widefield Array at 78–133 MHz. They report the first detection of linear polarization in a metric type II burst, reaching approximately 12% and varying significantly with frequency and time. Unlike spatially integrated dynamic spectra, imaging can reveal spatial polarization structure that might otherwise be obscured or subject to cancellation. The authors interpret the burst’s spectro-temporal, spatial, and morphological properties as establishing linear polarization as a diagnostic of large-scale coronal and interplanetary magnetic structure. The detection challenges conventional predictions of negligible linear polarization from coherent plasma emission.

PublicShock waves traveling through the Sun’s outer atmosphere and interplanetary space produce radio signals called type II bursts. Using the Murchison Widefield Array, researchers made images that track the polarization—the orientation of the radio waves—of one such burst. They report the first detection of linear polarization in this kind of burst at metric radio wavelengths, reaching about 12% and changing substantially with frequency and time. Earlier approaches that combined emission across the source could hide differences in polarization. The authors interpret the new imaging results as a way to probe large-scale magnetic fields around the Sun and in interplanetary space. The finding challenges expectations that this emission should have almost no linear polarization.

Young explorerA shock wave near the Sun can make radio waves. Scientists made special pictures of one radio burst and found that some of its waves lined up in a way they had not seen before in this kind of burst. How much they lined up changed over time and between different radio frequencies. Scientists think this pattern can help them learn about magnetic fields around the Sun and farther out in space.

MAGIC's interferometric diameters of θ Ophiuchi and β CMa and comparison with asteroseismic modelling

K. Abe, J. Abhir, A. Abhishek+97 more

AstronomerThe authors measure angular diameters of the β Cephei stars θ Oph and β CMa with the MAGIC Stellar Intensity Interferometer and combine them with Gaia and Hipparcos parallaxes to test asteroseismic predictions. The seismic models fit observed pulsation modes through Levenberg–Marquardt local minimisation of stellar evolution parameters. θ Oph's angular-diameter measurements are compatible with its seismic model. For β CMa, the radius inferred using the Hipparcos parallax differs from the seismic prediction at 2.5σ. This tension mirrors an existing disagreement between independent spectroscopic surface-gravity determinations; percent-level stellar-model systematics are insufficient to explain it. The authors interpret a biased Hipparcos parallax as the most likely explanation, rather than an established cause. Interferometric statistical uncertainties are currently comparable to parallax systematic uncertainties. The addition of CTAO-North LST-1 in early 2024 is expected, but not yet demonstrated here, to reduce angular-diameter uncertainties by an order of magnitude, strengthening tests of stellar evolution models and parallaxes.

PublicMassive β Cephei stars pulse on timescales of a few hours, and these vibrations help astronomers study their interiors. The researchers measured the apparent sizes of two such stars, θ Oph and β CMa, using the MAGIC Stellar Intensity Interferometer, then compared the measurements and distance information with models fitted to the stars' vibrations. θ Oph agrees with its model. For β CMa, however, the physical size calculated using the Hipparcos distance measurement disagrees with the model at a significance of 2.5σ. The discrepancy echoes conflicting estimates of the star's surface gravity. The authors find that small systematic errors in the stellar models cannot account for it and consider a bias in the Hipparcos distance measurement the most likely explanation, though this is not proven. Adding another telescope to the setup in early 2024 is expected to make the apparent-size measurements about ten times more precise; that improvement is a prediction, not a result reported here.

Young explorerSome big stars gently swell and shrink, and those movements give scientists clues about what is inside. Scientists measured how big two stars look in the sky and checked their ideas about the stars' insides. One star matched their calculations. The other did not quite match when they used one measurement of how far away it is. They think that distance measurement may be a little off, but they are not sure. Another telescope has joined the team of telescopes, and they expect it to help them measure the stars' sizes much more carefully.

Solar extreme-ultraviolet waves and other associated solar activities

Apoorv Dashora, Ramesh Chandra, Pooja Devi

AstronomerThis observational statistical study examines EUV waves and associated eruptive phenomena during December 2019–December 2025 in Solar Cycle 25, using SDO/AIA EUV data and SOHO/LASCO coronagraph data. Among the observed EUV waves, 12.3% were associated with Moreton waves, 95% with CMEs, 92.7% with solar flares, 44.3% with metric type II radio bursts, and 11.8% with solar energetic particle events. Associated flares span B to X classes. Most Moreton waves were associated with large- or medium-class flares, with only a small fraction linked to C-class flares. These associations do not by themselves establish causation; the suggested contribution to space-weather understanding and forecasting remains prospective.

PublicResearchers studied large, tsunami-like disturbances on the Sun, called extreme ultraviolet waves, using observations from two solar spacecraft during December 2019–December 2025. They found that 95% of the observed waves were linked to coronal mass ejections—eruptions of solar material—and 92.7% were linked to solar flares, ranging from weak to very powerful. Smaller fractions were associated with Moreton waves (12.3%), a particular kind of radio burst (44.3%), or energetic particle events (11.8%). These links show which events occur together, not proof that one causes another. The findings could help researchers understand space weather and potentially improve forecasting, but the study does not demonstrate a forecasting improvement.

Young explorerThe Sun can have huge waves that spread out like ripples. Scientists looked at pictures of the Sun and found that these waves often happened along with big bursts of material and bright flashes called flares. Some flashes were weak and some were very strong. Seeing things happen together does not tell us for sure that one made the other happen. Scientists hope these clues may help them better understand the Sun’s storms and someday predict them.

Eigenfrequency sensitivity in nonadiabatic stellar pulsations

Jan Zalewski

AstronomerThis theoretical study derives an adjoint formulation for eigenfrequency sensitivity in linear nonadiabatic stellar pulsations, retaining the frequency dependence of boundary conditions. Local kernels and cumulative integrals quantify excitation-rate and oscillation-frequency responses to prescribed scalings of the pulsation matrix and its acoustic, thermal, and coupling blocks. Applications to selected radial modes of post-AGB envelope models show distinct spatial and subsystem sensitivities. In the cool model, the ordinary mode is weakly sensitive near both boundaries under slow-branch outer boundary conditions, while the strange mode is strongly sensitive in the outer layers. Selected modes in the hotter model also have appreciable outer-layer sensitivity. Block contributions can reinforce or cancel one another. These are model-based sensitivity results, not observational findings.

PublicThe researchers developed a mathematical method to identify which parts of a stellar model most affect how quickly its pulsations repeat and whether those pulsations grow or fade. They applied it to selected pulsations in models of the outer regions of stars in the post-AGB stage. Different pulsations responded differently: in the cooler model, one type was only weakly affected near the boundaries under the boundary conditions used, while another was particularly sensitive to the outer layers. Some pulsations in the hotter model were also sensitive there. Contributions from different parts of the equations sometimes offset each other. The findings concern theoretical models, not measurements of actual stars.

Young explorerStars can wiggle. The scientists made a math tool to study wiggles in computer models of stars. They asked which parts of a model matter most when they change the math a little. Some wiggles were especially sensitive to the outside layers, but not all wiggles behaved the same way. This was a study of models, not a report of watching real stars.

The Galah survey and symbiotic stars. II. Discovery, validation, and intensive follow-up of 44 new systems accreting at the lowest detectable levels

U. Munari, P. Valisa, N. Masetti+22 more

AstronomerThe authors report 44 newly validated low-accretion symbiotic stars with accretion luminosities at or below 3 solar luminosities, selected from non-pulsating M giants with Halpha excess in Galah. Follow-up during 2021–2025 included high-resolution spectroscopy over 544 nights, flickering searches sensitive to 1 millimagnitude, and Swift UV/X-ray observations. M-giant radial velocities yielded reliable spectroscopic orbits for 22 systems and preliminary orbits for eight more, supported by binary-induced ASAS-SN photometric modulation. Measured accretion levels varied by factors of up to 20, highlighting the importance of sensitive, long-term monitoring. Swift X-ray data exclude neutron-star companions in all targets, consistent with, but not independently establishing, white-dwarf companions. Together with 33 discoveries from Paper I, the 77 systems outnumber the previously known accreting-only Galactic symbiotics and represent more than 10 percent of all known Galactic symbiotic stars. The authors argue that symbiotics likely spend most of their lifetimes in faint, low-accretion states; characterizing these systems therefore informs population estimates and assessments of their possible contributions to Type Ia supernova progenitors and UV excess in elliptical galaxies.

PublicAstronomers report discovering and confirming 44 symbiotic star systems in which a companion draws material from a red giant at very faint, detectable levels. They combined years of observations, including detailed spectra, searches for rapid brightness changes, and ultraviolet and X-ray measurements. They obtained reliable orbits for 22 systems and preliminary orbits for another eight. The measured rate of energy release from incoming material changed by as much as a factor of 20, showing why these faint systems need repeated, sensitive observations. The X-ray data rule out neutron-star companions; white dwarfs are consistent with the findings. Including an earlier study, the team has identified 77 new systems, more than 10 percent of all known symbiotic stars in our Galaxy. The authors suggest these stars probably spend most of their lives in faint states. Finding them could improve estimates of their total numbers and help assess their possible links to certain supernovae and ultraviolet light in elliptical galaxies, rather than proving those links.

Young explorerAstronomers found 44 pairs of stars where one star takes gas from a big red star. The light made by that gas is faint, so the astronomers watched carefully for years. In some pairs, that light changed a lot. They could work out good paths around each other for 22 pairs, but some other paths are still uncertain. Finding these quiet star pairs helps astronomers learn how many might be hiding in our galaxy.

Metamorphic novae. I. Gaia22alz -- Violent relaxation starting from static evolution

Mariko Kato, Izumi Hachisu

• Astrophysics of Galaxies

AstronomerGaia22alz (nova Vel 2022) exhibits light-curve and spectral evolution resembling the slow novae HR Del, V723 Cas, and V5558 Sgr, including multiple large-amplitude peaks (ΔV ≈ 2 mag) around M_V ≈ −5.5 before a decline resembling normal classical novae. The authors model its slow rise and early spectral evolution using metamorphic nova theory: an initially hydrostatic, non-mass-losing envelope transitions through a violent-relaxation, multiple-peak phase into an optically thick wind. They report that the rising-phase model consistently explains these observations. Gaia22alz’s close-binary nature is consistent with their proposed trigger—companion motion within the nova envelope—but does not by itself establish that mechanism. Their results do not support the alternative explanation that X-ray/UV-flash irradiation causes the slow optical rise.

PublicGaia22alz is a nova whose brightness rose slowly and showed repeated large peaks before fading much like other classical novae. Its changing light and spectrum resemble those of three other slow novae. The authors present a model in which the nova’s outer layers first expand without losing material, then undergo an unsettled transition before developing a dense outward flow. They report that this model explains the slow rise and early changes in the spectrum. A nearby companion star could trigger the transition by moving through the expanded material; the binary system is consistent with this idea, rather than proof of it. The results do not support a competing explanation involving illumination by an X-ray and ultraviolet flash.

Young explorerA nova called Gaia22alz slowly grew brighter, had several big brightness peaks, and then faded. Scientists made a model to explain this: its outer gas first spreads out, then changes into gas flowing away. A nearby partner star might help cause that change, but that is not proven. The model fits the early changes in its light and does not support another idea involving a flash of invisible light.

Direct evidence of non-ideal MHD in the solar wind and switchbacks

Forrest Mozer, Oleksiy Agapitov, Kyung-Eun Choi+1 more

AstronomerThe paper reports Parker Solar Probe FIELDS measurements of parallel and perpendicular electric fields in the plasma rest frame during orbit 10, at heliocentric distances below 40 solar radii. Fields are observed at 0.01–0.1 Hz and across a broader frequency range. Calibration errors affect the inferred parallel-field amplitude but do not eliminate its presence. The perpendicular rest-frame field is more vulnerable to errors because its calculation involves subtracting two large terms; the authors present evidence that large errors do not dominate at least much of the time. They interpret the low-frequency fields as evidence that the solar wind and its switchbacks occupy a non-ideal MHD environment, arguing that standard ideal-MHD descriptions, including ideal Alfvén, slow, and fast waves, cannot adequately describe the turbulent dynamics. Applicability to other astrophysical plasmas is suggested, not established.

PublicResearchers used Parker Solar Probe to measure electric fields as they would appear to an observer moving with the solar wind. During the spacecraft’s tenth orbit, closer than 40 solar radii from the Sun, they detected low-frequency electric fields both along and across the magnetic field. Measurement uncertainties change the strength inferred for the along-field signal but do not erase it. The across-field measurement is more sensitive to errors, although the authors present evidence that these errors are not dominant much of the time. They conclude that the solar wind and its switchbacks cannot be adequately described by the standard idealized model of a magnetized fluid and its waves. Similar limitations might affect models of other space plasmas, but this study does not establish that.

Young explorerA spacecraft near the Sun measured electric fields in the solar wind. The researchers say these clues show that a simple set of rules used to describe the wind and its waves is not enough. Some measurements are harder to check than others, so the team looked carefully at possible mistakes. They think other places in space might need better rules too, but that is not yet shown.

Small-Scale Dynamo for Full Spectrum of Hydrodynamic Turbulence in Kazantsev Model

Leonid Kitchatinov

• Fluid Dynamics

AstronomerThe authors propose a method for computing Kazantsev small-scale dynamo coefficients that includes both the inertial and viscous-dissipation ranges of hydromagnetic turbulence. Numerical solutions span magnetic and hydrodynamic Reynolds numbers, Rm and Re, from 10^2 to 10^8. The dynamo threshold initially increases with Re, then saturates at Rm_c ≈ 300 for Re ≥ 10^5. For Pm = Rm/Re much less than one, the magnetic-field growth rate is small and depends logarithmically on Rm; the magnetic-energy spectrum peaks near the Ohmic-dissipation scale, which decreases as Pm increases until reaching the viscous-dissipation scale. Growth accelerates sharply as Pm approaches one, continues increasing above one, and eventually saturates somewhat below the inverse lifetime of the shortest-lived eddies. These are numerical model results, not observations; an explanation is also proposed.

PublicThis theoretical study examines how turbulent motion can amplify magnetic fields on small scales. The authors propose a way to include both larger turbulent motions and the smaller motions affected by viscosity in a mathematical model, then solve it numerically. In the model, the conditions needed for magnetic growth become more demanding as turbulence increases, but eventually level off at a magnetic Reynolds number of about 300. When the ratio of magnetic to hydrodynamic Reynolds numbers is very small, magnetic growth is slow. As that ratio approaches one, growth speeds up sharply, while the scale containing the most magnetic energy shrinks until it reaches the scale where viscosity dissipates turbulent motion. Growth continues to increase above a ratio of one, but eventually levels off. These findings come from numerical calculations rather than observations.

Young explorerCan swirling motions help a magnetic field grow stronger? The researchers made a new math recipe and tested it on a computer. In their model, the magnetic field grows slowly in some conditions and much faster in others, but the growth eventually stops getting faster. They also found that the size of the patterns holding the most magnetic energy can get smaller, but only up to a limit in the model. This is a computer-model result, not something they watched happen in space.

A living catalog of stream interaction regions in the Parker Solar Probe era

R. C. Allen, G. C. Ho, L. K. Jian+15 more

• Space Physics

AstronomerThe authors present a living catalog of stream interaction regions (SIRs) and corotating interaction regions (CIRs) observed by Parker Solar Probe, with corresponding observations from STEREO-A and from ACE and Wind at 1 au. The initial catalog covers PSP orbits one through five. The paper describes event-identification methods, catalog construction, and access to the evolving resource. Its intended use is to support case studies exploiting spacecraft orbital configurations and future statistical investigations of the properties and radial evolution of SIRs and CIRs; the abstract does not report new quantitative findings on that evolution.

PublicResearchers have created an updateable catalog of large-scale structures in the Sun’s outward-flowing material, called stream interaction regions and corotating interaction regions. The initial catalog lists observations from Parker Solar Probe’s first five orbits and links them with corresponding observations from other spacecraft, including ACE and Wind at roughly Earth’s distance from the Sun. The paper explains how events were identified and how to access the catalog. This resource is designed to help scientists study how these structures change with distance from the Sun, rather than presenting a new measured pattern of change.

Young explorerThe Sun sends material out into space, and it can form big moving patterns. Scientists made a list of patterns seen by Parker Solar Probe on its first five trips around the Sun, with matching observations from other spacecraft. They can keep adding to the list. It will help them study how the patterns change as they travel away from the Sun, but this paper does not yet give that answer.

Delayed maximum energy solar energetic particle events: Statistical analysis from Solar Orbiter

R. C. Allen, G. C. Ho, G. M. Mason+9 more

• Space Physics

AstronomerSolar energetic particle events usually exhibit earlier onset at higher energies, but delayed maximum energy (DME) events show apparent delays above a critical energy while retaining typical velocity dispersion at lower energies. This study examines Solar Orbiter DME occurrence and characteristics relative to magnetic footpoints and associated flare locations. DME events preferentially occur when the observer’s footpoints lie westward of the flare. Estimated release locations suggest that a CME-driven shock continues injecting increasingly energetic particles into the connected flux tube as it expands into the inner heliosphere. The authors interpret this as evidence that DME behavior may arise from inner-heliospheric rather than coronal effects, consistent with earlier observations and interpretations of westward-connected events; the inferred release history is not a direct measurement.

PublicHigher-energy particles from solar eruptions usually arrive before lower-energy particles. In some events, however, particles above a certain energy appear to arrive late. Studying these events with Solar Orbiter, researchers found that they occur more often when the spacecraft’s magnetic connection to the Sun is rooted west of the associated solar flare. Estimates of where the particles were released suggest that a shock driven by an expanding solar eruption keeps feeding increasingly energetic particles into the magnetic pathway leading to the spacecraft. This could explain the delays through processes farther from the Sun, rather than in its outer atmosphere, but that explanation remains an interpretation.

Young explorerWhen the Sun has an eruption, it sends out tiny particles. Usually, the faster ones get to a spacecraft first, but sometimes the fastest ones seem late. Scientists found a clue in where the spacecraft’s magnetic path meets the Sun. They think the eruption may keep sending out faster particles as it moves farther away, but they are not sure yet.

The Hot Neptune Initiative (HONEI): IV. TOI-4129 b, an Adolescent Neptune in the Ridge

Sureena Lakhanpal, Shreyas Vissapragada, Luca Naponiello+36 more

AstronomerRadial velocities from HARPS-N and transit photometry from TESS and four ground-based telescopes confirm TOI-4129 b, a low-density planet at the inner edge of the Neptune ridge, the excess of intermediate-size planets with 3–6-day periods. The planet has a radius of 5.7 ± 0.2 Earth radii, a mass of 26 ± 6 Earth masses, and a density of 0.8 ± 0.2 g/cm³, and orbits a K dwarf every 3.27 days. A photometric stellar rotation period of 12.7 days implies a gyrochronal age of 1.20 Gyr, with uncertainties of +0.16 and −0.30 Gyr. Its Transmission Spectroscopy Metric of 112 ± 30 makes it a promising target for atmospheric observations with JWST and Ariel; future constraints on the three-dimensional stellar obliquity are also considered feasible. These prospective observations could test high-eccentricity migration as an explanation for the Neptune ridge, whose origin remains uncertain; the present findings do not establish that migration history.

PublicAstronomers have confirmed TOI-4129 b, a low-density planet about 5.7 times Earth's radius and 26 times its mass. It circles a K dwarf star every 3.27 days, placing it near the inner edge of the Neptune ridge—a puzzling concentration of intermediate-size planets with orbits lasting three to six days. The star's measured rotation suggests the system is about 1.2 billion years old, though this age estimate is uncertain. The planet is a promising candidate for future atmospheric studies with JWST and Ariel, and researchers could also constrain how the star's spin is tilted relative to the planet's orbit. Such observations may help test whether planets in the ridge reached their close-in orbits by migrating along initially very elongated paths. That explanation has not yet been established.

Young explorerAstronomers found a big planet called TOI-4129 b that goes around its star in just over three days. It is much bigger than Earth but not very dense. It sits in a place where lots of medium-size planets bunch together, and scientists do not know why. One idea is that these planets once traveled on very stretched-out paths before moving close to their stars. Scientists hope to study this planet's air and how its orbit lines up with its star's spin to help test that idea. They do not know yet if that is how this planet got there.

Measuring the gas mass of the protoplanetary disk around HD 179218 with CO isotopologues

Nina Weichmann, Ke Zhang, Leon Trapman+1 more

• Instrumentation and Methods for Astrophysics

AstronomerALMA and NOEMA observations of six CO isotopologue transitions in HD 179218 provide a test of CO-based disk mass estimates without the freeze-out affecting colder disks. DALI thermochemical modeling yields a characteristic gas radius of approximately 90 au and a gas mass of approximately 8 × 10^-3 solar masses; spectral energy distribution fitting gives a dust mass of approximately 3 × 10^-5 solar masses. The resulting gas-to-dust ratio is approximately 270 for the fiducial dust opacity with a maximum grain size of 1 mm, above the canonical interstellar value of approximately 100. The best-fitting model keeps CO gaseous throughout the disk, supporting the interpretation that this elevated ratio is not a CO-depletion artifact. Together with the compact millimeter dust distribution, it is consistent with substantial inward dust drift. The authors also infer a gas cavity inside 50 au enclosing the compact millimeter dust disk, an arrangement inverse to a typical transition disk, and attribute it to photoevaporative clearing after inward pebble drift. That evolutionary sequence is an interpretation rather than a directly observed history.

PublicThe planet-forming disk around the luminous star HD 179218 offers an unusually clear way to estimate how much gas a disk contains. Astronomers often use carbon monoxide as a gas tracer, but in colder disks it can freeze onto grains and undergo chemical changes, complicating those estimates. Here, observations from ALMA and NOEMA were fitted with a model in which carbon monoxide stays gaseous throughout the disk. The inferred gas-to-dust mass ratio is about 270, compared with a commonly used interstellar value of about 100, although the estimate depends on assumed dust properties. The millimeter-sized dust is more compact than the gas, consistent with dust drifting inward. The study also finds an inner gas cavity surrounding the compact dust disk. The authors suggest that starlight-driven gas removal cleared this region after the pebbles moved inward; the observations do not directly establish that sequence.

Young explorerA young star has a disk of gas and dust around it. Scientists used telescope observations and a computer model to estimate how much gas and dust it holds. Their model says a gas called carbon monoxide stays warm enough not to freeze, making it easier to use as a clue to how much gas is there. They estimate that the disk has much more gas than dust. The dust sits closer to the star, and the inner region has a gap in the gas. The scientists think dust pebbles may have moved inward before the star’s light helped clear away some gas, but they did not watch that happen.

Precision Requirements for Robust Small Planet Classification

Cayman T. Unterborn, Stephen R. Kane

• Instrumentation and Methods for Astrophysics

AstronomerThe authors analytically propagate mass and radius uncertainties through the Nominally Rocky Planet Zone (NRPZ), which compares bulk densities with a volatile-free rocky range calibrated from stellar abundance distributions. Their sample comprises 37 candidate rocky exoplanets with radii below 2 Earth radii and host-star visual magnitudes below 11. They find that 12 already have measurements precise enough for confident classification as Mini-Neptunes or Super-Mercuries. The remaining planets require approximately a 60% reduction in combined mass and radius uncertainties for reliable classification. Estimated requirements span 1–1,000 new observations and are likely lower limits. The authors argue that such campaigns may be impractical for many targets and that mass-radius models alone are unlikely to classify planets reliably except at outlier densities. They recommend staged follow-up: improved mass and radius measurements to identify and prioritize ambiguous systems, followed, where feasible, by JWST or future atmospheric observations to test whether selected planets retain substantial atmospheres.

PublicHow well can a planet’s mass and size reveal what it is made of? This study examines measurement uncertainties for 37 planets smaller than twice Earth’s radius. The researchers compare their densities with the range expected for rocky planets without volatile material. They find that 12 already have measurements precise enough to classify them confidently as volatile-rich Mini-Neptunes or iron-enriched Super-Mercuries. For the others, the combined uncertainty in mass and size would need to shrink by about 60%. The estimated effort ranges from 1 to 1,000 additional observations, probably a lower limit. The authors argue that this may be impractical for many planets and that mass and size alone may reliably distinguish only planets with unusually high or low densities. They propose improving those measurements first, then, where possible, using JWST or future facilities to check whether selected planets have substantial atmospheres.

Young explorerScientists want to know whether faraway planets are mostly rock, have lots of iron, or have lots of other material. They studied how sure we can be from measurements of how heavy and how big 37 planets are. For 12, the measurements are good enough to put them into an iron-rich or Mini-Neptune group. For the others, the measurements need to be much more exact, and getting them could take lots of work. The scientists suggest measuring more carefully first, then using special telescopes, when possible, to look for thick blankets of gas around some planets. That is a plan, not something this study has already done.

Fitting Resonant Exoplanets Orbits. I. Properties and Applications of Fixed-Point Orbits

Chris W. Ormel, Tian Yi, Shuo Huang

• Instrumentation and Methods for Astrophysics

AstronomerThe authors develop an orbital-fitting method restricted to stable fixed-point orbits (fPOs): coplanar, exactly periodic configurations associated with resonant dynamics. This reduces the free parameters and enforces stability during fitting rather than testing it afterward. They show that dissipative evolution drives resonant systems toward fPO states, motivating the restriction for systems that have avoided large-scale dynamical rearrangements since formation. Using chi-squared minimization, they fit astrometry for PDS 70 and HR 8799 and radial velocities for GJ 876. The HR 8799 fit independently recovers a previously reported resonant solution. PDS 70 solutions divide into two groups; those with planet c more massive than planet b better align with previous measurements. For GJ 876, the fPO fit performs comparably to previous unconstrained fitting, strengthening, but not proving, the case for deep resonance. The method's applicability depends on its restrictive dynamical assumptions.

PublicPlanets whose orbital rhythms are linked by resonance may retain clues to how their systems formed, but checking whether observations support such arrangements can be difficult. This study introduces a fitting method that considers only stable, flat configurations whose collective orbital motion repeats exactly. That restriction simplifies the fit and guarantees stability within the model, rather than checking stability afterward. The authors show that evolution involving energy loss drives resonant systems toward these configurations, motivating their use for systems that have not undergone major orbital rearrangements. Applied to observations, the method recovers an earlier resonant solution for HR 8799. For PDS 70, it finds two groups of solutions, with those making the outer planet c heavier than planet b agreeing better with earlier measurements. For GJ 876, it fits about as well as earlier, less restricted methods, adding support to the interpretation that its planets are deeply in resonance. These fits do not establish that every system follows the assumed arrangement.

Young explorerSome planets go around their star in a shared rhythm, like dancers keeping time together. Scientists made a new way to match planet observations using only flat, repeating dances that stay steady. It is meant for planets whose dances have not been greatly changed since they formed. For HR 8799, it found a dance scientists had found before. For PDS 70, it found two kinds of answers; the kind where the outer planet is heavier fits earlier measurements better. For GJ 876, it worked about as well as an older method, giving scientists another clue that the planets share a strong rhythm. These are possible dances that fit the clues, not proof of exactly how every planet moves.

The Survival Paradox of Close-In Planets Orbiting Red Clump Giants

Wen-Xu Lin, Sheng-Bang Qian, Qi-Bin Sun+9 more

• Solar and Stellar Astrophysics

AstronomerAsteroseismology confirms that the hosts of 24 Boo b, HD 12648 b, and TYC 4282-605-1 b are core-helium-burning red-clump giants that have passed through RGB expansion and subsequent contraction. All three planets currently orbit inside their hosts’ inferred maximum RGB radii, in conflict with tidal-engulfment models predicting engulfment within about 1 au for Sun-like progenitors. At 0.183 au and a 30-day period, 24 Boo b is reported as the closest known planet around a red-clump giant. With only one such planet previously identified, these systems suggest an emerging class rather than an isolated anomaly. The authors interpret the discrepancy as evidence for missing physics in stellar–planetary coevolution; the abstract does not establish a survival mechanism.

PublicAstronomers report three planets whose stars are confirmed, through stellar vibrations, to be red-clump giants: stars that have already swollen dramatically and then shrunk as they began burning helium in their cores. The planets now orbit closer to their stars than the stars’ estimated largest sizes during that earlier expansion. Current models predict that such planets should have been swallowed. One, 24 Boo b, completes an orbit in 30 days and is reported as the closest known planet around a red-clump giant. These three systems suggest that the previously rare puzzle is not a one-off. The researchers interpret them as a sign that current theories are missing something, but they have not established how the planets survived.

Young explorerStars can puff up very big and later shrink again. Scientists found that three stars with nearby planets have already done this. The planets are now so close that scientists’ models say the stars should have swallowed them when they were bigger. But the planets are there! That suggests the models are missing something. The scientists do not yet know how the planets escaped.

Outer pressure bumps beyond the dust disc: Missing Outer Rings in the exoALMA Sample: Physical Mechanisms Suppressing Dust Ring Formation Despite Strong Pressure Bumps

Lilian Luo, Paola Pinilla, Jochen Stadler

AstronomerFor nine exoALMA discs with candidate pressure bumps beyond their observed millimetre continuum extent, the authors reconstruct gas surface density profiles from midplane pressure gradients inferred from ALMA Band 7 12CO and 13CO observations. DustPy models explore turbulence parameters α = 10^-4 and 10^-3 and fragmentation velocities of 1 and 10 m/s; RADMC-3D calculations predict the resulting continuum emission. Across this parameter space, efficient outer dust trapping predominantly produces prominent rings predicted to be detectable in Band 7, in tension with the observations. The 13CO-based reconstructions almost universally predict detectable outer rings, while the 12CO-based models show more variation. Of two tested suppression mechanisms, enhanced outer-disc turbulence most effectively weakens the predicted emission, but its effectiveness depends on the system and the location of the turbulence transition. Delayed bump formation generally fails to prevent rapid outer dust accumulation. These are model predictions rather than detections of outer dust rings.

PublicCould dust be hiding beyond the visible edges of planet-forming discs? The exoALMA survey identified possible gas-pressure bumps in these outer regions, where dust might collect. For nine discs, researchers used gas observations to build computer models of dust evolution and predict its emission. Most models produced bright outer dust rings that ALMA should detect, creating a mismatch with the observations. Models based on two different forms of carbon monoxide differed in how consistently they predicted these rings. Stronger turbulent motion in the outer disc reduced the predicted ring emission most effectively, although the effect depended on the disc and where that stronger turbulence began. Making the pressure bump form later generally did not stop dust from gathering rapidly. The study tests possible explanations for the missing rings; it does not report finding them.

Young explorerYoung stars have big discs of gas and dust around them. Scientists found signs of gas bumps beyond where they see the dust. In computer models, these bumps usually gathered dust into rings bright enough to see—but the observations did not show those rings. Extra swirling in the models helped make the rings fainter, though it did not work equally well for every disc.

Disruption limits around triaxial bodies and implications for ring-bearing minor bodies

Gustavo Madeira, T.F.L.L. Pinheiro

AstronomerThis theoretical study computes equilibrium figures and disruption limits for inviscid fluid satellites orbiting triaxial primaries, representing the gravity field with J2 and C22. Oblateness and equatorial asymmetry move the disruption limit outward from the classical Roche limit; C22 dominates at sufficiently high values, requiring highly oblate primaries. Outside double-synchronous configurations, orientation dependence produces a radial disruption region rather than a single boundary. Increasing orbital inclination moves the limit inward, substantially only at high inclinations. An empirical expression obtained through symbolic regression is applied to ring-bearing minor bodies. The correction is most relevant for Haumea and Chariklo, but the rings of Chiron and Quaoar remain outside the modeled disruption region for realistic particle densities. The authors interpret this as evidence against a strict ring–satellite boundary based on disruption alone, emphasizing collisional evolution, particle properties, and resonant confinement by non-axisymmetric gravity as additional factors in ring longevity.

PublicThe Roche limit is often treated as a dividing line: closer to a body, gravity can tear a fluid moon apart, while farther away, moons can survive. But the classical calculation assumes a spherical central body, unlike many small bodies with rings. This study calculates how flattened, uneven shapes change that limit. In the model, these shapes push the disruption boundary outward, while the body's orientation can turn a single boundary into a range of distances. The correction matters most for Haumea and Chariklo. For realistic ring-particle densities, however, the rings of Chiron and Quaoar still lie beyond the calculated disruption region. The authors conclude that this boundary alone cannot explain where rings persist: collisions, particle properties, and gravitational effects that confine rings also matter.

Young explorerSome small worlds have rings around them. Scientists used math to ask where a world's gravity could pull apart a little moon made of flowing material. They found that a squashed or uneven world can pull it apart farther away than a round world could. But their calculations still leave some rings beyond that zone. So this gravity rule alone does not explain why rings stay rings instead of becoming moons; how the pieces bump together and how gravity keeps them in place matter too.

The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) XII. Constraints on large bodies embedded in discs

M. R. Jankovic, A. V. Krivov, T. D. Pearce+17 more

AstronomerARKS provides millimetre-wavelength constraints on 24 debris discs. For 11 discs with well-constrained vertical thicknesses, the authors use semi-analytic collisional and gravitational-scattering models, accounting for velocity-dependent collisional damping, to estimate the sizes and masses of cascade-feeding planetesimals and, separately, hypothetical stirrers. The inferred cascade-feeding bodies are smaller than 20 km, with total planetesimal masses below 200 Earth masses. Minimum disc masses inferred from millimetre and infrared observations agree well. If gravitational stirring produces the measured thicknesses, the inferred stirrers are larger than the cascade-feeding planetesimals but need not dominate the disc mass. Steady-state collisional models can explain the observed dust masses with reasonable disc masses, and embedded large bodies could explain the measured scale-heights. These are model-based explanations, not detections of the large bodies; more advanced models are needed for the observed non-Gaussian vertical profiles and scale-height dependence on particle size and stellocentric distance.

PublicThe ARKS survey studied 24 dusty discs around stars using ALMA. For 11 discs whose vertical thicknesses were well measured, researchers used models to estimate the unseen bodies whose collisions supply the observed dust. The models suggest these dust-supplying bodies are smaller than 20 kilometres, with a combined mass below 200 Earth masses in each disc. Separate calculations explored whether larger bodies within the discs could gravitationally stir material enough to explain their thicknesses. Such bodies could do so without necessarily holding most of a disc’s mass, but the study does not establish that this is what causes the thickness. The observed dust amounts can be explained by ongoing collisions with reasonable amounts of material. More advanced models are still needed to explain the detailed vertical shapes of the discs and how their thickness varies with particle size and distance from the star.

Young explorerAstronomers studied dusty rings around stars. They used measurements of how thick some rings are, plus maths models, to work out what might be happening inside. Their models suggest that space rocks crashing together could keep making the dust we see. Bigger objects might also tug on the rocks and make the rings thicker. The astronomers have not shown that these bigger objects are really doing this, and they need better models to explain all the shapes they see.

Signature of exocomet transits observed with Ariel

Nóra Takács, Gyula M. Szabó, Andreas Papageorgiou+5 more

• Instrumentation and Methods for Astrophysics

AstronomerThis modelling study assesses Ariel’s potential to detect and characterise exocomet transits through wavelength-dependent photometry; it does not report observed detections. Radiative-transfer models span three dust morphologies, three grain-size distributions and four homogeneous compositions in synthetic bands covering Ariel’s wavelength range. Modelled events typically last 1–2 days with amplitudes of a few millimagnitudes. Colours relative to VISPhot and their wavelength-dependent slopes diagnose dust properties more effectively than transit morphology alone, separating carbonaceous dust and graphite from olivine and pyroxene across the morphologies and grain sizes tested, but not clearly distinguishing compositions within each group. Detectability estimates using the β Pictoris spectral energy distribution and ArielRad simulations indicate that broad-band integration improves signal-to-noise sufficiently for millimagnitude-level detection with short integrations on sufficiently bright targets. Simultaneous optical-to-infrared coverage could therefore constrain broad dust classes, subject to the modelling assumptions. The study also discusses coordinated observations with long-baseline photometric missions.

PublicCould Ariel identify the kinds of dust carried by comets around other stars? This study explores that possibility with computer models, rather than reporting actual detections. The simulated comet passages typically last one to two days and cause very small changes in a star’s apparent brightness. How those changes vary with wavelength provides more information about the dust than the shape of the brightness change alone. In the models tested, this separates carbonaceous dust and graphite from olivine and pyroxene, though it does not clearly distinguish the two materials within either pair. Simulations using the light spectrum of β Pictoris suggest that combining light over broad wavelength bands could let Ariel detect these small signals with short exposures for sufficiently bright stars. The results suggest a way to identify broad dust categories, but depend on the modelling assumptions and are not yet an observational demonstration.

Young explorerA comet near another star can carry dust that changes a little of the starlight we see when it passes in front. Scientists used computer models to ask whether a space telescope called Ariel could spot those tiny changes. In their pretend comet crossings, looking at different colours of light helped sort the dust into two big groups, but could not clearly tell every kind apart. Their tests suggest Ariel might do this for bright enough stars. These are computer predictions, not comets Ariel has already seen.

Naturalization of Vinti's intermediary orbit---or how to get rid of small divisors in Brouwer's satellite solution

Martin Lara

• Dynamical Systems

AstronomerThe work constructs a first-order analytical satellite perturbation solution by naturalizing Vinti’s dynamical system in Deprit’s sense. The solution avoids critical divisors, extending the applicability of classical perturbation methods to the close vicinity of the critical inclination. The procedure also suggests how Brouwer’s classical solution might be reformulated without small divisors; that reformulation is not presented as an established result. The new solution contains terms that may grow without bound, but the abstract reports no adverse effects over intervals in which such a solution may be practically useful. This is an analytical development, not an observational finding.

PublicThe study develops a mathematical method for calculating satellite motion near a particular orbital tilt where traditional formulas encounter difficulties involving division by very small quantities. The new method avoids those troublesome divisions and offers clues for improving another classical calculation method. It is not guaranteed to remain well behaved indefinitely: some terms can grow without limit, although the abstract says their harmful effects do not appear over the time spans for which this type of calculation may be useful. The work concerns mathematical calculations rather than observations.

Young explorerScientists made a new math recipe for working out how a satellite moves. It helps near a certain tilt where older recipes have trouble. Some parts of the recipe could grow too big if used for too long, but the study says they do not cause trouble during the times when the recipe may be useful.

Fractional Orbital Bombardment Systems

David Wright, Steve Fetter

• Physics and Society

AstronomerThis analysis evaluates Fractional Orbital Bombardment Systems (FOBS), which would deliver nuclear warheads through partial Earth orbits, and argues that they offer no game-changing technological or operational advance. The authors assess possible defense evasion and short-warning attacks rather than report an observed attack or demonstrated capability. FOBS could underfly current exoatmospheric defenses, but the required payload reduction may make this unattractive if other countermeasures are considered effective. Very short warning depends on successfully disguising an attack as a satellite launch. The authors warn that fears of a decapitating strike could compress crisis decision-making and destabilize relations. They propose US measures to prevent very-short-warning attacks from succeeding and thereby strengthen deterrence.

PublicThe paper examines a proposed way to deliver nuclear weapons by sending them partway around Earth in orbit. The authors argue that it would not fundamentally transform military capabilities. It could pass below current defenses designed to intercept weapons outside the atmosphere, but carrying a smaller payload may outweigh that advantage if other ways of evading defenses work. An attack might leave very little warning if it were successfully mistaken for a satellite launch. The authors warn that fear of such a surprise attack could push countries toward rushed decisions during a crisis. They argue that the United States could take protective steps to make these attacks unsuccessful and discourage their use.

Young explorerThe writers studied an idea for sending nuclear weapons partway around Earth before they come down. They think it would not be a huge new advantage. If a launch looked like it was carrying a satellite, people might have very little warning of an attack. The writers worry that this fear could make countries rush important choices. They say protective steps could help discourage such attacks.

Shallow lunar fractures dominate the long-lasting seismic coda

Lei Zhang, Qian Huang, Minghao Huang+2 more

• Geophysics

AstronomerApollo seismic records exhibit long-lasting, spindle-shaped codas that previous continuous-medium crustal models failed to reproduce well, even with unrealistically strong velocity contrasts. The authors propose randomly distributed vacuum fractures as insulating boundaries, producing persistent reverberation through total reflection. Simulations with a limited number of simplified fractures in a homogeneous matrix reproduce typical observed waveform characteristics, with envelope correlations above 0.9, reported as substantially higher than in previous studies. The simulations suggest, rather than establish observationally, that fractures in the uppermost approximately 1 km may dominate lunar seismic scattering. The authors present the model as a means to investigate shallow lunar fractures and suppress coda to detect phases reflected from the deep interior.

PublicSeismic recordings from the Moon contain unusually long, gradually swelling and fading trails of shaking. Earlier models attributed these trails to strong differences in how fast waves travel through the lunar crust, but did not match the recordings well. The researchers propose a different explanation: empty cracks repeatedly reflect seismic waves, keeping them reverberating. Computer simulations using even a small number of simplified cracks closely reproduce typical features of Apollo recordings. The simulations suggest that cracks within roughly the top kilometre of crust could cause most of this scattering; this is not a direct measurement of those cracks. The authors say the model offers a way to study shallow fractures and reduce the lingering signal so that reflections from deeper inside the Moon can be detected.

Young explorerWhen the Moon shakes, the shaking can linger for a long time. Scientists think empty cracks might make the shaking bounce around, a little like echoes. They tried this idea in a computer, and it made patterns much like the ones recorded on the Moon. That is a clue that cracks near the surface could be important, but it does not prove the idea is right. The scientists hope it can help them learn about the cracks and pick out signals from deeper inside the Moon.

Calibration of CNEOS Fireball Velocities and the Robustness of Nominally Hyperbolic Events

Volkan Duran, Abraham Loeb

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

AstronomerThe authors calibrate NASA/JPL CNEOS fireball kinematics against 19 independent reference trajectories, with optical, satellite, radar, and infrasound catalogues serving as source-specific controls. In nine modern high-quality comparisons, CNEOS-minus-reference speed residuals have a mean of -1.00 km/s and a standard deviation of 0.86 km/s; variance decomposition attributes 0.77 km/s to the CNEOS component. Radiant residuals show a 0.74-degree per-axis core and one 16.3-degree outlier, leaving the extreme error tail poorly constrained. Seven of 354 complete CNEOS states are nominally hyperbolic without correction. An imposed +0.9935 km/s atmospheric-stage shift adds five threshold crossings, but these are sensitivity cases, not established detections. Polar-IM, dated 2026 April 1, is the strongest post-2018 CNEOS anomaly, yet independent GLM-LI stereo solutions of 57.3 ± 2.0 and 56.7 ± 3.0 km/s lie close to their direction-specific parabolic thresholds. CNEOS can prioritize candidates, but secure interstellar classification requires an independent three-dimensional trajectory with quantified uncertainty for the same event.

PublicA catalogue of bright fireballs can help flag objects that might have arrived from beyond the Solar System, but its speed and direction estimates need careful checking. The researchers compared 19 CNEOS events with independently measured paths. Among nine modern, high-quality comparisons, CNEOS speeds averaged 1.00 km/s lower than the reference speeds. Most direction differences were small, but one large discrepancy shows that rare errors remain poorly understood. Seven of 354 complete catalogue entries nominally indicate hyperbolic paths, making them possible interstellar candidates rather than confirmed visitors. A test that increased the reported speeds added five more candidates, but this was only a sensitivity check. The strongest post-2018 catalogue anomaly, Polar-IM, has independent speed estimates close to the boundary relevant to an interstellar classification. The authors conclude that confirmation needs a separate measurement of the same object's three-dimensional path, including its uncertainties.

Young explorerWhen a space rock rushes into our air, it can make a bright fireball. Scientists checked a list of these fireballs against other measurements and found that the listed speeds and directions are not always quite right. Some rocks on the list might have come from beyond our Solar System, but the list alone cannot prove that. Even one especially interesting fireball still needs careful checking. To be sure, scientists need another measurement of the same rock's path and speed, with a good idea of how much that measurement could be off.

Origin of homochirality in peptides: The first milestone at the origin of life

Søren Toxvaerd

• Populations and Evolution

AstronomerThis article proposes an ordered sequence of milestones in abiogenesis, drawing on published observations and a literature synthesis rather than reporting a demonstrated origin-of-life pathway. It cites studies reporting that peptides in organisms become unstable over long times, losing their homochiral secondary conformations and containing D-amino acids. The authors argue that homochiral peptides emerged first in aqueous environments with high amino-acid concentrations and lower water activity than cellular cytosol. They place the establishment of metabolism and genetics in such peptide-containing environments within Earth's crust approximately 4 billion years ago, followed by dividing cells in hot springs at the crust–Hadean Ocean interface. They also attribute organismal mortality to long-term peptide aging in cytosol; this is an interpretation advanced by the article, not an established causal result demonstrated in the abstract.

PublicThe article proposes a sequence for how life began. It draws on reports that peptides, molecules built from amino acids, can lose their uniform molecular handedness and structure over time in living organisms. The authors suggest that early peptides with consistent handedness arose in concentrated amino-acid solutions where water was less available than inside today's cells. They propose that metabolism and genetics developed in Earth's crust about 4 billion years ago, with dividing cells appearing later in hot springs where the crust met the early ocean. These are proposed historical steps, not directly observed events. The article also argues that peptide aging causes organisms to die, but the abstract does not establish that causal claim.

Young explorerHow did life get started? The authors suggest that tiny building blocks first joined into chains with matching shapes. Later came ways to use energy and pass along instructions, and then cells that could split into new cells in hot springs. This is a proposed story about life's beginning, not something the authors watched happen.

GPUPhot: Kernel-Based Algorithms for Point-Source Detection and Photometry with a Spatially Variable PSF

M. R. Alarcon, S. Lemes-Perera, M. Serra-Ricart+1 more

AstronomerGPUPhot reformulates point-source detection and photometry as fixed-kernel convolutions and element-wise operations on full-frame maps, allowing the entire reduction to run natively on a GPU rather than through iterative per-source fitting. A spatially variable PSF is represented by fixed, flux-conserving principal-component eigenmodes with position-dependent coefficients, decomposing the spatially varying matched filter exactly into a few convolutions while preserving its maximum-likelihood foundation. The authors report sub-pixel astrometric accuracy and few-millimagnitude photometric precision for bright sources, including in fields with strong background gradients and markedly inhomogeneous PSFs. In production at Teide Observatory, the pipeline has processed 3.7 million images totaling 1.2 PB since 2023, with effective end-to-end processing times below 15 seconds per 150-megapixel image, from raw-frame ingestion to an astrometrically and photometrically calibrated source catalog. The openly developed package is released with the paper; the authors also describe its component algorithms as applicable beyond photometry.

PublicA new software package, GPUPhot, measures the positions and brightnesses of point-like objects in astronomical images using a graphics processing unit, or GPU. Instead of repeatedly fitting each object separately, it performs calculations across whole images in a form suited to parallel processing. It also accounts for changes across an image in how point sources appear. The authors report accurate positions and brightness measurements for bright sources even when the background and source shapes vary strongly across the image. Already operating at Teide Observatory, the software has processed 3.7 million images since 2023, totaling 1.2 petabytes of data. It takes less than 15 seconds per 150-megapixel image to go from a raw image to a catalog with calibrated positions and brightnesses. The software is being released publicly with the paper.

Young explorerAstronomers take so many pictures of the sky that their computers can struggle to keep up. A program called GPUPhot uses a special computer chip to work on a whole picture at once, instead of checking each tiny light separately again and again. It figures out where bright dots are and how bright they look, even when different parts of the picture look blurry in different ways. The team says it can measure bright dots very precisely. It is already helping telescopes at Teide Observatory and has worked on millions of pictures. The team is sharing the program so others can use it too.

Latin hypercube sampling to reduce the variance in Monte Carlo integration: a practical guide and an application to gravitational-wave astronomy

Matteo Boschini, Davide Gerosa

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena
• General Relativity and Quantum Cosmology

AstronomerThis practical introduction examines Latin hypercube sampling (LHS) and orthogonal-array LHS (OA-LHS) for reducing numerical variance in Monte Carlo likelihood calculations. Asymptotically, LHS removes variance contributions from individual coordinates, while strength-2 OA-LHS also removes pairwise-interaction contributions; suitable integrands can therefore show orders-of-magnitude improvements over ordinary Monte Carlo. In a computational case study of the selection function used in hierarchical gravitational-wave population inference, however, approximately one million injections yield only a marginal variance reduction with low statistical significance. Constructing the sampling designs costs negligibly little compared with evaluating the injections, so the authors suggest considering them even where gains may be small.

PublicCalculations used to infer the properties of gravitational-wave populations rely on random sampling, which introduces numerical noise. This paper explains two ways to spread samples more evenly across the possibilities being tested. For suitable mathematical problems, these methods can greatly reduce that noise. But in the authors’ gravitational-wave test, using about a million simulated injections, the improvement was only slight and the statistical evidence for it was weak. Because arranging the samples adds very little computing cost compared with evaluating them, the authors suggest the methods may still be worth considering.

Young explorerImagine trying to learn about a big picture by checking tiny spots. This paper explains ways to spread the spots out more evenly instead of picking them all at random. That can sometimes make a computer’s answer much steadier. The researchers tried this in a computer test used to study groups of sources that make ripples in space. After about a million pretend signals, the answer was only a little steadier, and they were not very sure the change was real. Spreading out the spots took very little extra work, so it might still be worth trying.

COSMIO: A Benchmark for Cross-Survey Modality Imputation

Dichang Zhang, Yixuan Shao, Jiaqi Deng+8 more

• Computer Vision and Pattern Recognition

AstronomerThe authors formalize cross-survey modality imputation: inferring an object's appearance in an unobserved survey from its observations in other surveys. They introduce COSMIO, a benchmark of aligned, simulated LSST, Euclid, and Roman observations generated by forward-rendering shared astrophysical scenes with survey-specific instrument characteristics. Tests across survey combinations and missing-data patterns show that methods developed for existing imputation settings transfer poorly to this setting. The authors highlight rare-event imputation as a challenge, particularly early in new surveys, and evaluate zero-shot imputation of galaxy-galaxy strong lenses. On their constructed lens evaluation set, performance deteriorates under rare-event distribution shift, with degradation also affecting downstream lens detection. These findings concern benchmark evaluations, not demonstrated reconstruction of missing real-survey observations.

PublicDifferent sky surveys see objects differently, and many objects are not observed by every survey. This study asks whether machine learning can use one survey's view to estimate another's. The researchers created COSMIO, a test collection of simulated views for LSST, Euclid, and Roman that accounts for their different instruments. Existing methods adapted poorly to this task. Tests involving strong gravitational lenses, where a foreground galaxy bends light from a background galaxy, exposed a particular difficulty with rare examples: poorer estimated images also hurt subsequent lens detection. The results come from constructed evaluation data, rather than a demonstration on missing observations from real surveys.

Young explorerDifferent sky cameras can see the same galaxy in different ways. Scientists made pretend sky pictures to test whether computers could guess a missing camera view. The computers struggled, especially with rare pictures where one galaxy bends another galaxy's light. Those guesses also made the rare pictures harder for a computer to find.

Photometric calibration of the 4m ILMT data

Bhavya Ailawadhi, Talat Akhunov, Monalisa Dubey+10 more

AstronomerThe authors present a photometric calibration approach for point-source observations acquired in Time Delayed Integration mode with the 4-meter International Liquid Mirror Telescope, which surveys the zenith in SDSS g', r', and i'. Using ZTF reference sources cross-matched with Pan-STARRS1, they derive photometric zero-points along the ILMT scan. The procedure is reported to enable consistent, high-precision supernova and quasar light curves for variability and structure-function studies, with reverberation mapping identified as a future application. The abstract gives no numerical calibration precision or results from these scientific applications.

PublicThe International Liquid Mirror Telescope watches the sky directly overhead to search for changing sources and faint objects. This work presents a way to calibrate its brightness measurements by comparing reference sources from ZTF with the Pan-STARRS1 catalog and setting brightness reference levels along each telescope scan. The authors report that this method enables consistent, precise records of how supernovae and quasars brighten and fade. These records are intended for studies of brightness changes, with further applications planned for the future; the abstract does not state how precise the calibration is numerically.

Young explorerA telescope watches the sky above it. To tell whether something in space really gets brighter or dimmer, scientists need to check that the telescope measures brightness consistently. The scientists describe a way to do this using other sky measurements as a guide. They say it helps them make reliable brightness records for exploding stars and bright objects called quasars.

Efficient Identification and Analysis of Space debris Trails in Time-Domain Astronomy

Sarvesh Kumar Yadav, Bhavya Ailawadhi, Talat Akhunov+10 more

AstronomerThe paper presents an automated, unsupervised, end-to-end pipeline for detecting and characterizing satellite and space-debris streaks. Its multi-stage geometric architecture segments raw images and measures streak morphology. Tests in real-world survey environments demonstrate streak-profile recovery, with a reported operational detection limit requiring both integrated SNR ≥ 86 and lengths ≥ 98 arcseconds. The framework is intended to support monitoring of resident space objects and Space Situational Awareness; the abstract does not establish real-time processing performance.

PublicResearchers have developed an automated method to find and describe the trails that satellites and space junk leave in survey images. Tests using real-world surveys showed that it could recover trails meeting reported brightness and apparent-length limits. The method is intended to help monitor objects in orbit, where increasing debris threatens space assets. The abstract identifies real-time monitoring as a goal but does not report processing speeds.

Young explorerSatellites and bits of space junk can make lines in pictures of space. Researchers made a computer tool to find and describe those lines automatically. In tests, it found lines that were bright enough and long enough. The tool could help people keep track of things going around Earth.

Limits to research in astrophysics

F Cantalloube, C No{û}s

AstronomerThis conference proceeding discusses limits on astrophysical research, juxtaposing fundamental physical constraints with finite material resources, including energy, fresh water, and rare-earth elements. The authors frame rapid research growth and increasingly ambitious large-scale projects as part of an extractive model, and call for collective reflection on constraints encountered in daily work. Their stated goal is more sustainable and effective research that protects researchers’ well-being at every career stage. The abstract presents a discussion and an appeal for reflection, not new measurements, simulations, or a quantified assessment of resource limits.

PublicStudying the universe requires resources on Earth, including energy, fresh water, and rare-earth elements, whose availability and extraction are limited. This conference paper asks how those limits, alongside pressures in everyday research, should shape astronomy as projects become larger and more ambitious. The authors argue for collective reflection on how to make research more sustainable and effective while protecting the well-being of people at all career stages. The abstract does not report new experimental findings or test a specific solution.

Young explorerLearning about space takes energy, water, and special materials from Earth, and we cannot get endless amounts of them. The writers ask scientists to think together about how to study space without using too much or making the people doing the work feel unwell. This paper talks about what needs care; it does not say the writers have already found or tested an answer.

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

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

PublicThis work introduces Athena-Aniso, an expanded version of a computer program for simulating astrophysical gas and magnetic fields. It adds ways for heat and momentum to spread differently in different directions, along with several effects linking heat, electricity and magnetism. It can also account for gas that is only partly ionised. The authors derive rules for choosing simulation time steps and modify the numerical solver to suppress certain artificial instabilities. An important limitation is that two coupled effects, called Nernst and Ettingshausen, require both heat and magnetic diffusion perpendicular to the magnetic field for the equations to be well-posed. The team tests each added effect against mathematical solutions. The paper reports simulation tools and numerical tests, rather than observations of space.

Young explorerScientists have added new rules to a computer program that models gas and magnetic fields in space. The rules let heat spread more easily in some directions than others. They checked the new rules using maths problems with known answers. They also found that some rules need other smoothing effects to work properly together. This is a tool for making pretend space experiments on a computer, not a new discovery seen in the sky.

First application of the optimised next neighbour cleaning to data from imaging atmospheric Cherenkov telescopes

Maria Kherlakian, Gernot Maier

AstronomerThe authors implement optimised next neighbour (ONN) image cleaning in the VERITAS reconstruction pipeline. Cleaning contours use a cluster’s minimum total integrated charge and maximum within-cluster pulse-arrival-time difference to suppress night-sky and electronic noise while retaining Cherenkov-light pixels. Relative to double-pass cleaning, they report effective-area increases of up to approximately 25-fold at 60–90 GeV and energy-threshold reductions of up to approximately 22%. Tests on Crab Nebula data yield up to approximately 82 times as many reconstructed excess events below 1 TeV. The abstract also reports a differential-sensitivity improvement of up to approximately eightfold near 20 GeV. With BDT-based gamma/hadron separation cuts, ONN improves detection significance for a 20-hour Crab Nebula dataset and increases excess event rates by approximately 16%. These maxima describe different performance measures and energy selections, not a uniform improvement across the full energy range. The authors identify transient sources and sources with soft spectra as especially promising applications.

PublicVERITAS cameras record faint Cherenkov light alongside unwanted signals from the night sky and electronics. This study implements a method called optimised next neighbour, which decides which groups of camera pixels to keep using both their combined signal strength and how closely their pulses arrive in time. Compared with the existing cleaning method, the authors report better performance at low energies and an energy threshold reduced by up to about 22%. Tests using Crab Nebula observations recovered more events above the background. With an additional method for separating gamma-ray events from other particle events, the excess event rate rose by about 16%, and detection significance improved in a 20-hour dataset. Some reported gains are much larger, but apply to particular energy ranges and performance measures rather than to all observations. The authors suggest the technique is especially useful for sources that change briefly or emit predominantly lower-energy gamma rays.

Young explorerThese telescope cameras catch faint flashes, but they also pick up unwanted specks. Scientists tried a better way to keep groups of specks that flash together and remove distracting ones. In tests using the Crab Nebula, it helped them recover more useful signals. They think it could be especially helpful for studying some brief or lower-energy signals from space.

A semi-autonomous multi-agent pipeline for high-energy astrophysics research with enforced provenance and verifiable self-extension

Fang Zhou

• High Energy Astrophysical Phenomena

AstronomerThe authors present auto_research, a semi-autonomous multi-agent pipeline that retrieves and analyses raw HEASARC data and writes its own analysis tools. Tool admission involves automatic checks, including repeated runs and scans for phrases associated with invented values, followed by cross-provider model code review; a human decides promotion to the trusted branch. Reported numbers must be traceable to recorded tool outputs, the request, or a specified location in a cited paper. Tests expose substantial limitations: 47 of 65 planted defects pass the automatic checks, and one also passes code review, while review rejects 40 of 69 correct changes. In an IXPE benchmark on Cyg X-1, all 14 quantities compared with published results agree within 3 sigma, although the recovered polarization degrees are lower than published values. With weaker models in the main roles, 12 quantities are recovered and two are reported as unmeasured. Additional applications include polarization stability across six observations, polarization versus hardness across 29 observations, and a search for a lag between Stokes q and u; the abstract gives no outcomes for these analyses.

PublicThis study tests an AI-assisted system that retrieves astronomical data, builds analysis software, and writes reports. Its safeguards check new software and require reported numbers to have identifiable sources; a person decides whether software enters the trusted collection. These checks are imperfect: automatic tests let 47 of 65 deliberately introduced defects through. An additional AI review lets only one of those defects through, but also rejects 40 of 69 correct changes. Using IXPE X-ray observations of Cyg X-1, the system obtains 14 compared quantities consistent with published results within the stated statistical tolerance, although its polarization estimates are lower. Less capable AI models recover 12 quantities and label two as unmeasured. The authors also apply the system to other polarization questions, but the abstract does not report what those searches found.

Young explorerScientists made a team of computer helpers to study information from space. The helpers must show where their numbers came from, and their new programs get checked. The checks catch many mistakes, but miss some and sometimes reject good work. In one test, the helpers got answers close to earlier scientists’ answers, though some were lower. People still decide which programs to trust.

CCAT: Prime-Cam Control System and Related Software

Alicia Middleton, James Burgoyne, Victoria Butler+11 more

AstronomerThis instrumentation paper describes development and laboratory testing of the Prime-Cam Control System (PCS), rather than astronomical observations. Prime-Cam is being developed for FYST, under construction at 5600 m on Cerro Chajnantor, and can accommodate up to seven KID-based modules, including 280–850 GHz broadband modules and imaging spectrometers for line-intensity mapping. PCS adapts the Observatory Control System framework developed for Simons Observatory to Prime-Cam and CCAT requirements. Individual hardware devices are managed by long-running software agents, typically deployed in Docker containers, with control through command-line clients, Nextline, or PCS-web. External open-source tools support remote operations, data management, and logging. Laboratory testing is underway in preparation for planned deployment in 2026; the abstract does not report on-telescope performance.

PublicEngineers are developing software to operate Prime-Cam, an instrument planned for the Fred Young Submillimeter Telescope, which is being built high on Cerro Chajnantor. Because observations will typically be operated remotely, the software needs to coordinate many hardware devices and make them straightforward to control from a distance. The team is adapting an existing observatory software framework, using separate background programs to manage individual devices and interfaces that let operators send commands. Other open-source tools help with remote access, data management, and logging. The system is being tested in the laboratory ahead of planned deployment in 2026, not yet reporting results from telescope observations.

Young explorerPeople are building a special camera for a telescope on a high mountain. They are also making computer programs so people can control the camera from far away. Different little programs look after different pieces of its equipment. The team is testing the programs in a lab and getting them ready to use with the telescope in 2026.

Direct Analysis in Real Time Mass Spectrometry (DART-MS) Study of Amino Acids in the Vacuum Stable Liquids EMI-BF₄, EMI-Acetate, DEMA-OTf, DEMA-MsO, and Glycerol

Zach Ulibarri, Samantha E. Adamski, Amy E. Hofmann+1 more

• Applied Physics

AstronomerA DART-MS screening study tested five amino acids at mole fractions of approximately 5×10^-4 to 10^-3 in five vacuum-stable solvents relevant to spacecraft organic analysis. In the four ionic liquids—EMI-BF4, EMI-acetate, DEMA-MsO, and DEMA-OTf—solvent cations dominated the spectra. No amino acids were detected in these liquids except weak histidine in EMI-BF4 at 350 °C, with a median normalized peak intensity of 5%. The protic DEMA liquids did not improve detection. Glycerol enabled detection of histidine, glycine, arginine, and lysine, with histidine frequently producing a dominant line; aspartic acid was undetected in every solvent. The authors identify glycerol as the most promising solvent tested for this application, with an optimal DART helium temperature of 350–400 °C. These screening results do not establish spacecraft performance. A secondary investigation found no clear evidence of water uptake or aqueous alteration in the ionic liquids, relevant to their use in electric propulsion.

PublicMany methods for detecting organic chemicals on spacecraft need liquid solvents, but keeping liquids in the vacuum of space can be difficult and costly. Researchers tested whether a rapid chemical-analysis method could detect five amino acids mixed into five vacuum-stable liquids. Glycerol gave the best results: four amino acids were detected, whereas the other liquids mostly produced signals from the solvents themselves. One of those liquids also yielded a weak signal from histidine. Aspartic acid was not detected in any liquid. The authors identify glycerol as the most promising option among those tested, using a helium temperature of 350–400 °C in the analysis instrument. This was a screening study, not a demonstration of organic detection on a space mission. The researchers also found no clear evidence that the other tested liquids had taken up water or been altered by it.

Young explorerScientists want to help spacecraft look for special chemicals called amino acids. They mixed five kinds of amino acids into different liquids and used a machine to look for them. A liquid called glycerol helped the machine spot four kinds. The other liquids mostly hid the amino acids behind their own signals. One kind could not be spotted in any liquid. Glycerol looks promising in these tests, but that does not yet show how well it would work on a space trip.

Spin Spherical Fourier Neural Operators: Efficient Equivariant Learning for Vector and Spin Fields on the Sphere

Kevin Mulder, Matthew A. Price, Eirini Leftaki+1 more

• Computer Vision and Pattern Recognition
• Machine Learning

AstronomerThis work extends spherical Fourier neural operators to fields of arbitrary spin, relevant to quantities such as CMB polarisation and weak-lensing shear. The construction uses exactly rotationally equivariant lifted spherical convolutions, with spin fields lifted to Mackey functions on the rotation group. Computation proceeds through harmonic representations and sampling theorems on the sphere and rotation group. The resulting spin SFNO layers are empirically equivariant to machine precision. The authors report state-of-the-art performance on existing benchmarks and introduce new benchmarks where spin-aware models outperform scalar counterparts. These are computational method and benchmark results, not observational findings.

PublicSome quantities mapped across a sphere, including the polarisation of the cosmic microwave background and distortions caused by weak gravitational lensing, change their mathematical description when the local reference frame turns. The authors develop a neural-network method that explicitly handles this behaviour and is designed to respond consistently to rotations. Their computational tests find that this rotational consistency holds to machine precision. They also report leading performance on existing benchmark tasks and better performance than scalar models on new benchmarks. The study presents a computing method and test results, rather than new astronomical observations.

Young explorerImagine drawing little arrows all over a ball. If you turn the ball, a computer should still understand how the arrows fit together. The researchers made a new kind of computer model to handle patterns like these. In their tests, it handled turns correctly to the tiny limits of computer arithmetic and did better than comparison models on some test tasks. This was a test of a computer method, not a new discovery in the sky.

Feature-Based and Deep Learning Methods for Astronomical Light Curve Classification

V. Baymakanov, Kh. Khamitov, A. Raimova+7 more

• Machine Learning

AstronomerThis study benchmarks feature-based machine learning against end-to-end deep learning for variable-star classification using the ZTF StarEmbed dataset, comprising about 40,000 objects in seven imbalanced classes. Models using physically motivated features consistently outperform deep networks trained on raw light curves. The authors identify limited labeled data as a contributor to the gap, with multivariate, irregularly sampled, and morphologically diverse light curves presenting additional challenges. The tested deep models fail to generalize with the available training-set size; this does not establish a general limitation of deep learning. Larger labeled datasets and self-supervised pretraining on large unlabeled surveys are proposed for further investigation, not demonstrated remedies. The comparison provides a quantitative baseline for future work.

PublicThe researchers compared two ways of teaching computers to classify stars whose brightness changes. Using about 40,000 objects from the Zwicky Transient Facility StarEmbed dataset, they found that models given selected, physically meaningful descriptions of the brightness changes consistently performed better than deep-learning models given the brightness records directly. Limited labeled training data contributed to the difference, while irregular observation times and varied brightness patterns added challenges. These results concern the models and dataset tested, rather than showing that deep learning cannot work for this task. The authors suggest investigating larger labeled datasets and training methods that first learn from unlabeled observations, but do not show that these approaches solve the problem.

Young explorerSome stars change how bright they look. Scientists tested two ways to teach computers to sort those stars into groups. One kind of computer learner got helpful clues about the brightness changes. Another tried to learn straight from the brightness records. In this test, the learners with helpful clues did better. The other learners had trouble using what they learned on stars outside their lessons. They had a limited set of labeled examples, and the brightness records were tricky. The scientists want to explore whether more examples and different ways of learning could help.

A Unified AI Framework for Rapid and Accurate Waveform Generation of Compact Binary Coalescences

Mengfei Sun, Jin Li, Yuanhong Zhong+4 more

• General Relativity and Quantum Cosmology

AstronomerThe authors develop a unified compact-binary waveform generator combining physical modeling and deep learning through an analytic residual spectral representation, shared learning, and binary-specific decoders. It covers binary black holes, binary neutron stars, and neutron star–black hole systems. Generated waveforms retain the effects included in their respective reference models, such as precession, higher-order modes, matter effects, and binary-neutron-star postmerger radiation. Across waveforms spanning hundreds to thousands of cycles, reported mean mismatches with reference waveforms range from 5.89 × 10^-4 to 5.34 × 10^-2. Batch generation reaches a maximum speedup of about 1800 relative to reference waveform generation; this is not a uniform speedup or accuracy guarantee. The work addresses the waveform-generation demands expected from future third-generation detectors, rather than reporting new gravitational-wave observations.

PublicFuture gravitational-wave detectors are expected to record many long signals from merging pairs of black holes and neutron stars. To help researchers study those signals, the authors developed one system that combines physics models with deep learning to generate predicted wave shapes for all three types of pairing. The predictions include the physical effects represented in the models used as references, rather than independently establishing those effects in observations. Tests found varying levels of agreement with the reference waveforms, and generating waveforms in batches was up to about 1800 times faster. That maximum speed gain does not mean every waveform is generated that much faster or with the same accuracy.

Young explorerWhen two black holes or neutron stars come together, they make ripples in space. Scientists made a computer tool that uses physics and learns from examples to draw what those ripples should look like. It can draw ripples for different kinds of pairs. In tests, it could make groups of drawings much faster than the tools it was compared with, but the drawings did not always match equally well. This work makes predictions to help study signals; it does not report finding new ripples in space.

Geometrical and Optical Design of the GUEST Laser-Ranged Test Masses for the Detection of Gravitational Waves in the μHz range

Dario Vetrano, Giada Bargiacchi, Nicolò Burzillà+5 more

• Cosmology and Nongalactic Astrophysics

AstronomerGUEST aims to detect gravitational waves in the largely unexplored microhertz band through high-precision orbital tracking. This study proposes an optical architecture combining 1-inch and 2-inch corner-cube retroreflectors to accommodate low-velocity, long-range tracking near apogee and high-velocity, short-range tracking near perigee. The spherical layout is designed for an isotropic, homogeneous optical response and efficient packing. Optical cross-section is evaluated with a custom reduced-order model of individual retroreflectors under varying illumination, calibrated by reconstructing the optical response of LARES-2. The model assesses each reflector type's contribution along the GUEST orbit, while sensitivity analyses examine reflector proportions, laser wavelength, spacecraft diameter, dihedral angle offsets, and mechanical configurations. The abstract reports design and modeling work, not a gravitational-wave detection, and provides no quantitative performance results.

PublicThe proposed GUEST mission would search for gravitational waves in a largely unexplored frequency range by tracking a spacecraft's orbit extremely precisely. Its elongated orbit creates two different tracking challenges: the spacecraft is slower when farther away and faster when closer. Researchers propose covering its spherical surface with two sizes of reflectors that send laser light back toward its source. The arrangement is intended to give a uniform response from different directions while using the available surface efficiently. They evaluated the design with a simplified optical model calibrated by reproducing the response of the LARES-2 satellite, and explored how design choices affect it. This is a proposed design assessed through modeling, not a report of detected gravitational waves; the abstract gives no numerical performance results.

Young explorerScientists want to look for tiny ripples in space by watching very carefully how a spacecraft moves. They propose putting two sizes of special mirrors on a round spacecraft to send laser light back. The spacecraft would move slowly when far away and quickly when close, so the mirrors need to work in both situations. The team used a model to study how the mirrors might work together. They have not reported finding any ripples with this design.

An efficient finite element formulation for Newtonian noise analysis

Pieter Reumers, Xhorxha Kuci, Stijn François+1 more

• Applied Physics
• Computational Physics

AstronomerThe authors present a finite-element formulation for seismic Newtonian noise, relevant to the Einstein Telescope’s design sensitivity extending down to 3 Hz. Using Gaussian quadrature, it computes total, bulk, and surface contributions from a seismic wave field on a mesh, with coupling matrices determined solely by geometry and material properties. Linear and quadratic tetrahedral and brick elements are supported. Numerical verification shows excellent agreement with analytical solutions for plane P- and S-waves in a homogeneous elastic full space containing a spherical mirror cavity, under the long-wavelength assumption that permits neglecting cavity scattering. Good agreement is also reported for a test mass above a homogeneous elastic halfspace carrying a Rayleigh wave. These are idealized verification cases, not observational results or demonstrations in heterogeneous media. Implemented in the ANNA toolbox for MATLAB, with GNU Octave compatibility and a Python version available, the framework is proposed as a physically consistent, computationally efficient approach to gravitational-seismic coupling in heterogeneous media.

PublicVibrations from natural sources and human activity change the density of the ground. Those changes alter its gravitational pull and can move the mirrors of a gravitational-wave detector, producing interference called Newtonian noise. This matters for the planned underground Einstein Telescope, designed to detect gravitational waves at frequencies as low as 3 Hz. The researchers developed a computer method that divides the ground into small elements and calculates how seismic waves gravitationally affect a mirror. In simplified test settings, its calculations closely matched analytical solutions. These checks are not measurements at the observatory, and one test assumes wavelengths large enough that scattering by the mirror’s cavity can be ignored. The authors propose the method as an efficient way to calculate these effects in ground with varying properties.

Young explorerWhen the ground shakes, its tiny changes in gravity can tug on a special telescope’s mirrors. That can get in the way of what the telescope wants to detect. Scientists made a computer tool to work out these tugs. It matched known answers in simple pretend settings. They propose using it to calculate the tugs in more complicated ground, too.