Tonight’s sky of new research

Optimal summary statistics to constrain w0waCDM with the DESI BGS

Simon Bouchard

AstronomerThis presentation focuses on simulation-based clustering methods for the magnitude-limited DESI Bright Galaxy Survey at 0.1 < z < 0.4. It targets information omitted by standard two-point analyses and perturbation-theory models restricted to quasi-linear scales: non-Gaussian and non-linear structure in the density field. The abstract reports roughly 40% tighter constraints on some ΛCDM parameters from accessing this information, but does not specify the parameters or whether this gain is demonstrated with observations or simulations. An extension to w0waCDM is underway, aiming to improve sensitivity to evolving dark energy at low redshift; no results for that extension are reported.

PublicDESI measures light from thousands of galaxies at once to help study the Universe and how dark energy may change over time. This work explores methods supported by computer simulations to extract information from galaxy clustering that standard analyses leave unused. Focusing on DESI’s Bright Galaxy Survey, the authors report about a 40% improvement in how tightly some parameters of the standard cosmological model can be constrained. The abstract does not say whether that improvement was demonstrated using real observations or simulated data. The team is also extending the method to study changing dark energy, but does not yet report results from that extension.

Young explorerGalaxies make patterns in space. Scientists are trying a way to read more of those patterns, using computer-made pretend universes to help. They say this can make some answers about the Universe more precise, though this short description does not say whether they tested it on real galaxies or pretend ones. They also want to use the method to learn whether dark energy changes over time, but they do not have that answer here yet.

Gravitational Production of Non-minimally Coupled Vector Dark Matter in Warm Inflation

Phongsakorn Sereewat

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

AstronomerThis theoretical study calculates purely gravitational production of massive vector dark matter with a non-minimal Einstein-tensor coupling, ξ Gμν Xμ Xν, during warm inflation. The background has V = λφ^4 and a dissipation coefficient linear in temperature, is constrained by CMB observations, and spans dissipation ratios from Q0 = 10^-4 to 1. The calculation includes Standard Model bath freeze-in through graviton exchange and cosmological gravitational particle production (CGPP). In freeze-in, the ξ-induced contact interaction enhances light-vector production through the longitudinal mode but suppresses heavy-vector production through destructive interference. For CGPP, a non-small slow-roll parameter during warm inflation enhances light-dark-matter production by up to three orders of magnitude relative to cold inflation. Combining the channels excludes most of the light freeze-in branch within this framework, leaving mX approximately below 2.4 × 10^-5 GeV, a narrow window around 10^10 GeV for strong dissipation, and a heavy branch above approximately 10^14–10^15 GeV. Only the heavy branch remains viable throughout the range where the absolute value of ξ is approximately 1 or less. These are model-dependent theoretical constraints, not dark-matter detections.

PublicThe researchers calculate how gravity could have created a proposed type of dark-matter particle during warm inflation, an early period of cosmic expansion with a hot particle bath. Their model uses a quartic inflation potential, a dissipation coefficient proportional to temperature, and dissipation ratios from 10^-4 to 1; cosmic microwave background observations constrain this background, but do not establish the proposed dark-matter particle. Two production routes are included: collisions of ordinary particles mediated by gravity, and particle creation by the changing cosmic background. An additional coupling to spacetime curvature boosts the collision route for light dark matter but reduces it for heavy dark matter through destructive interference. The changing-background route can produce up to 1,000 times more light dark matter than in cold inflation. Together, the calculations rule out most of the model's light-mass collision-production branch, leaving masses approximately below 2.4 × 10^-5 GeV, a narrow window near 10^10 GeV when dissipation is strong, and masses above roughly 10^14–10^15 GeV. Only the heavy branch stays viable across coupling values whose absolute value is approximately 1 or less. These conclusions apply to the proposed model, not to dark matter in general.

Young explorerScientists used math to ask whether gravity could have made invisible stuff called dark matter when the universe was very young, growing quickly, and hot. They studied two possible ways: tiny bits of ordinary matter bumping together with gravity's help, and the universe changing as it grew. In their model, the second way could make up to 1,000 times more light dark matter than in a colder version of this early growth. Counting both ways leaves only some possible particle masses. The very heavy particles are the only group that still works across the full range of coupling strengths they describe as having an absolute value of about 1 or less. This is a calculation about what might have happened, not a discovery of dark matter.

FAIR Universe Weak Lensing ML Uncertainty Challenge: Dataset and Cosmological Inference Competition

Biwei Dai, Po-Wen Chang, Erwan Allys+37 more

• Artificial Intelligence
• Computer Vision and Pattern Recognition
• Machine Learning
• Data Analysis, Statistics and Probability

AstronomerThis work presents the FAIR Universe Weak Lensing Machine Learning Uncertainty Challenge, a NeurIPS 2025 competition, as a benchmark dataset and evaluation study for cosmological inference under systematic uncertainties. The dataset is designed to reflect realistic weak-lensing observations and includes multiple systematic biases, providing a controlled testbed rather than a new observational cosmological result. The paper summarizes winning approaches using conditional-optimal-transport data augmentation, AI-agent-driven parameter inference, ensemble learning, Vision Transformers, and physics-informed features. Together, the benchmark and solutions provide a community resource for assessing robust inference methods; the abstract reports no quantitative performance gains or cosmological constraints.

PublicWeak gravitational lensing—the subtle bending of light by matter—helps astronomers map matter in the universe and study how cosmic structure forms. Machine learning could extract information that traditional analysis methods miss, but realistic biases and imperfect simulations make reliability a challenge. This paper presents a dataset and evaluation study from the FAIR Universe competition at NeurIPS 2025. The dataset includes several systematic biases to test how well methods handle uncertain conditions. The authors also describe the winning teams’ approaches, including combining models, using AI agents, and incorporating physics-based information. The work offers a shared testing resource, not a new measurement of the universe, and the abstract gives no numerical comparison of the methods’ performance.

Young explorerMatter in space bends light a tiny bit. Scientists can use those bends to learn where matter is. This paper describes a practice challenge for computer helpers that study the bends. The practice data include tricky problems, so scientists can test whether the helpers still give trustworthy answers. The paper also explains ideas used by the winning teams. It is about testing better tools, not announcing a new discovery in space.

Constraining Cosmic Deceleration using the Solar System

Paridhi Jain, Oem Trivedi, Maxim Khlopov+2 more

• Earth and Planetary Astrophysics
• General Relativity and Quantum Cosmology

AstronomerThe study investigates Solar System dynamics as an independent, complementary constraint on the present-day cosmological deceleration parameter q0. Modeling cosmic acceleration as a weak Hooke-type radial perturbation, the authors derive relatively robust planetary perihelion-precession bounds placing the absolute value of q0 at approximately 10^9 or less. Trans-Neptunian objects and Oort cloud dynamics offer potentially tighter, but more model-dependent, constraints approaching 10^5. Monte Carlo uncertainty propagation and sensitivity analyses assess statistical robustness and dependence on orbital measurements. Forecasts suggest that future precision astrometry and outer-planet missions could improve these limits by several orders of magnitude; these improvements are not current observational results.

PublicCould the motions of objects in our Solar System help constrain how the universe's expansion is accelerating? The authors model a very weak additional radial force associated with cosmic acceleration and use orbital behavior to derive limits on the present-day cosmological deceleration parameter, q0. Planetary orbits give relatively robust bounds: the absolute value of q0 is approximately one billion or less. Objects beyond Neptune and in the distant Oort cloud could yield tighter limits approaching 100,000, but those estimates depend more strongly on modeling assumptions. The study tests how measurement uncertainties affect the bounds. It also forecasts that future, more precise position measurements and missions to the outer planets could improve the limits by several orders of magnitude, complementing conventional cosmological methods rather than replacing them.

Young explorerScientists asked whether watching planets and other faraway objects move around the Sun could help us learn about the universe's speeding-up expansion. They worked out how a tiny extra push or pull might change those paths. Planet paths give a fairly dependable limit on a number called q0: its absolute value is about one billion or less. Objects much farther from the Sun might give a tighter limit, near 100,000, but that depends more on the scientists' model. They checked how uncertain measurements affect their answers. Better measurements and future trips by spacecraft to the outer planets might make the limits much tighter, but that has not happened yet.

Is Dark Energy Inhomogeneous?

Oem Trivedi, Abraham Loeb

• General Relativity and Quantum Cosmology

AstronomerMotivated by dark matter deficient galaxies, the authors develop a phenomenological framework to test whether large regions could also be deficient in dark energy, distinguishing such regions from ordinary matter voids through nonlinear expansion, coherent peculiar velocities, and density-momentum correlations. Their calculations indicate that a 10% dark energy deficiency could suppress a representative nonlinear void’s expansion by approximately 2.7%, producing peculiar velocity residuals of order 60–100 km/s over 30–50 Mpc. Deficiencies of order 20% over several hundred megaparsecs could affect the locally inferred Hubble constant and potentially contribute to the H0 tension, but must satisfy stringent isotropy and dynamical consistency constraints. The authors propose tests using DESI, Rubin, peculiar velocity surveys, and void catalogues; the abstract reports no observational detection of dark energy deficiency.

PublicCould some large regions of the Universe contain less dark energy, the component driving cosmic acceleration? This study develops a framework for exploring that possibility, rather than reporting that such regions have been found. Its calculations suggest that a region with 10% less dark energy could expand more slowly and leave distinctive patterns in galaxy motions, helping distinguish it from a region that simply contains less matter. Much larger regions with roughly 20% less dark energy might also affect local estimates of the Universe’s expansion rate, potentially contributing to the disagreement known as the Hubble tension. That explanation remains conditional on strict checks of directional uniformity and consistent motions. The authors propose ways to search for these effects with galaxy surveys and measurements of cosmic motions.

Young explorerThe Universe is getting bigger, and something called dark energy helps it grow faster. Scientists wondered whether some huge patches might have less dark energy than others. Their calculations suggest that those patches could grow more slowly and make galaxies move in special patterns. They have not found such a patch in this study. They suggest watching how galaxies move to see whether the idea is right.

Detecting Baryon Acoustic Oscillations from Galaxy Clusters: Distance Constraints

Xiaoyun Shao, Paula S. Ferreira, Carlos A. P. Bengaly+3 more

AstronomerThe authors measure the BAO feature in 169,679 WH24 galaxy clusters selected from the DESI Legacy Imaging Surveys, described as the largest cluster sample with spectroscopic redshifts to date. Two-point correlation functions yield detections at approximately 4σ or higher in both redshift bins, 0.17≤z<0.35 and 0.35≤z<0.5. At effective redshifts 0.25 and 0.43, the fitted dilation parameters are α=0.97±0.07 and 1.01±0.04, giving D_V/r_d=6.70±0.48 and 11.25±0.47, respectively. Adopting the Planck 2018 sound-horizon calibration and flat ΛCDM gives H_0=66.6±4.9 km s⁻¹ Mpc⁻¹. Combining the cluster BAO measurements with CMB and Pantheon+ Type Ia supernova observations constrains dynamical dark energy in the Chevallier–Polarski–Linder parametrization; ΛCDM remains within the 68% joint credible region in the w_0–w_a plane. The results support clusters as complementary BAO tracers, rather than establishing evolving dark energy.

PublicResearchers used the positions and spectroscopic redshifts of 169,679 galaxy clusters to detect a characteristic pattern in their spacing called baryon acoustic oscillations, or BAO. They detected this pattern at approximately four-sigma significance or higher in each of two redshift ranges and used it to measure cosmic distances. Assuming a flat universe with a cosmological constant and cold dark matter, and using a sound-horizon calibration from Planck 2018, they inferred a present-day expansion rate of 66.6±4.9 kilometres per second per megaparsec. They also combined the cluster measurements with cosmic microwave background and supernova observations to test whether dark energy changes over time. Those constraints remain consistent with a cosmological constant; they do not establish changing dark energy. The study shows that galaxy clusters can complement other tools for measuring cosmic distances and testing cosmological models.

Young explorerGalaxies can gather in big groups called clusters. Scientists studied almost 170,000 clusters and found a special pattern in how far apart they are. They used that pattern like a giant ruler to help measure distances in space. Together with other observations, this helped them test ideas about how the universe grows. Their results still fit the idea that dark energy stays constant, but they do not prove that this idea is the only answer.

Vacuum energy interacting with dark matter and dark radiation: alleviating the H₀-S₈ seesaw

Li-Yang Gao, She-Sheng Xue, Xin Zhang

• General Relativity and Quantum Cosmology

AstronomerThe authors test whether late-time vacuum–dark-matter energy exchange can suppress the S8 increase induced by dark radiation or early dark energy (EDE). The coupling scales as m̄H^α and is negligible before recombination for α ≤ −2; transfer along the geodesic cold-dark-matter four-velocity produces dark matter without density perturbations, suppressing structure growth. Fits to Planck 2018, DESI DR2 BAO and Pantheon+ (CBS) favour vacuum-to-dark-matter transfer at 1.8–2.7σ and lower S8 by 0.02–0.08, but do not raise H0: the dark-radiation exchange model gives H0 = 68.83 ± 0.91 km s⁻¹ Mpc⁻¹, still 3.1σ below SH0ES. Adding the SH0ES calibration (CBSH), the exchange offsets the dark-radiation-induced S8 increase, yielding S8 = 0.800 ± 0.016 at H0 = 71.34 ± 0.70 km s⁻¹ Mpc⁻¹, and offsets about one-third of the EDE-induced increase for α = −2; coupling preferences are only 1.1–2.0σ. Suppression is concentrated at z ≲ 0.3: the lensing amplitude at KiDS-Legacy redshifts falls by only 1–2%, dark-radiation shear χ² changes by less than 3, and EDE's excess shear χ² is reduced but not eliminated. The exchange can partially counter the structure-growth consequences of early-time modifications, but does not ease the Hubble tension and is not required by current data.

PublicSome proposed changes to the early universe raise its inferred expansion rate today, but also predict stronger clustering of matter. This study tests an additional idea: energy could pass from the vacuum into dark matter late in cosmic history, slowing the growth of clustering. Fits to several cosmological datasets show modest preferences for this transfer, not a firm detection. Without the SH0ES calibration of the expansion rate, the exchange reduces the clustering measure S8 but does not raise the expansion rate or resolve its disagreement with SH0ES. When that calibration is included to favour a high expansion rate, the exchange offsets the extra S8 associated with dark radiation and about a third of that associated with the early-dark-energy model in one tested case. However, most of the reduction occurs very recently in cosmic history, so the predicted gravitational-lensing signal at the distances probed by KiDS-Legacy falls by only 1–2%. The proposed exchange can soften part of the clustering problem, but it does not ease the expansion-rate disagreement, and current data do not require it.

Young explorerScientists have ideas about the young universe that could help explain how fast space is growing now. But those ideas also make matter bunch together more. This study tried adding another idea: much later, energy from empty space could turn into dark matter and slow down the bunching. When scientists compared their models with sky data, this helped a little, but it did not fix the disagreement about how fast space is growing. The data do not show that this energy change has to happen.

CMB Bounds on Primordial Black Holes via Radiation Capture: Linear Perturbations

M. Farhang, S. M. S. Movahed

AstronomerThe authors model gravitational capture of primordial photons and ultra-relativistic neutrinos by primordial black holes (PBHs) using a covariant energy-momentum transfer four-vector. They extend a background-only treatment to linear perturbations, modifying both continuity and Euler equations to include energy and momentum exchange. Within this framework, Planck CMB temperature and polarization data constrain the PBH abundance fraction to f_pbh ≲ 0.05–0.002 for masses of 10^15–10^17 solar masses, with strong mass dependence and bounds up to two orders of magnitude tighter than background-only analyses. Separately, forecasts for a cosmic-variance-limited survey reaching ell_max = 7000, assuming a fiducial f_pbh = 0, project bounds of f_pbh ≲ 10^-2–2 × 10^-4 across 10^13–10^17 solar masses. These projected limits are not observational results.

PublicThis study asks how black holes formed in the early Universe might capture surrounding light and fast-moving neutrinos through gravity, changing patterns in the cosmic microwave background, the Universe’s ancient afterglow. The researchers develop a model that includes changes in both energy and momentum, as well as small variations from place to place. Applying it to Planck temperature and polarization measurements gives upper limits on the primordial-black-hole abundance fraction of about 5% to 0.2%, depending strongly on black-hole mass, for masses between 10^15 and 10^17 times the Sun’s mass. These limits can be up to 100 times tighter than those from analyses that treat only the average cosmic background. The study also forecasts stronger limits from an idealized future survey; those are predictions, not measurements. The analysis constrains how abundant these black holes could be within the model rather than reporting their discovery.

Young explorerScientists wondered whether black holes from when the Universe was very young could catch light and tiny, speedy particles with their gravity. They made a mathematical model to see how this might change the patterns in the old light we can still see from that time. Comparing the model with measurements helped them put limits on how many of these black holes there could be. They did not discover the black holes. They also worked out how a future look at the old light might give better limits, but that part has not been measured yet.

Investigating the Viability of Dedicated Microhertz Gravitational Wave Pulsar Timing

C. F. Sheridan, E. F. Keane

• Instrumentation and Methods for Astrophysics

AstronomerThis study forecasts the sensitivity of dedicated, high-cadence pulsar timing arrays to microhertz gravitational waves, rather than reporting a detection. The proposed configurations time a small sample of millisecond pulsars daily for one or two years using 100-m or 500-m class radio telescopes. Sensitivities to power-law signals and individual sources are calculated under an idealised noise model with negligible systematics, yielding optimistic detection thresholds. A 500-m class telescope would likely improve upper limits on individual sources and gravitational-wave backgrounds at 0.1–1 microhertz, whereas a 100-m class telescope would at best match EPTA second-data-release performance in that band. A further proposed configuration using SKA-Mid and DSA to observe 24 pulsars is forecast to perform comparably to the 500-m class option with much less telescope time. These feasibility estimates remain conditional on the optimistic noise assumptions.

PublicThe researchers explore a proposed way to search a poorly studied range of gravitational waves by measuring the timing of signals from rapidly spinning pulsars. Existing pulsar timing campaigns target slower waves; observing selected pulsars every day for one or two years could extend their reach to higher frequencies. The calculations suggest that a 500-m class radio telescope could tighten limits on how strong gravitational waves can be between 0.1 and 1 microhertz, while a 100-m class telescope would at best match existing limits from the EPTA’s second data release. A proposed combination of SKA-Mid and DSA observing 24 pulsars could offer similar sensitivity to the larger telescope while requiring much less observing time. These are forecasts, not new observations or detections, and they assume unusually clean measurements with negligible systematic errors.

Young explorerSome stars send us regular radio pulses, a little like clocks ticking in space. Scientists propose checking a few of these star clocks every day to look for very slow ripples in space called gravitational waves. Their calculations suggest that a very large radio telescope, or a proposed team of telescopes, might help set better limits on how strong those ripples could be. They have not found the ripples this way yet, and their plan assumes the measurements would have very little unwanted noise.

Ultralight scalar field domain walls and Galileo GNSS atomic clocks

Alessandro Di Marco, Feliciana Sapio, Massimo Visco+10 more

AstronomerThe study examines the potential effect of an Earth-sized ultralight scalar-field domain wall on Galileo satellite clocks and the feasibility of detecting a crossing. The authors develop and implement statistical procedures to characterize background noise in a subnetwork of N clocks, estimate false-alarm rates, and analyze detection efficiency. These methods support a coincidence analysis and provide a preliminary framework for controlled searches and for deriving constraints on the associated particle-physics parameters. Conducted in the context of Galileo for Science (G4S_2.0), the work does not report a domain-wall detection or numerical constraints in the abstract.

PublicResearchers investigate whether clocks aboard Europe’s Galileo navigation satellites could detect a hypothetical Earth-sized structure called an ultralight scalar-field domain wall. They develop and implement statistical tools to understand clock noise, estimate how often noise could trigger a false alarm, and assess how efficiently a search could detect a crossing. Looking for coincident signals across several clocks could support a more reliable search. The work provides a preliminary search framework, not a reported discovery, and could help constrain the particle-physics parameters associated with these hypothetical structures.

Young explorerScientists are studying whether clocks on Galileo satellites could help look for a strange, invisible wall about as big as Earth. Nobody reports finding one here. The scientists made number-checking tools to study the clocks’ usual little wiggles and work out how often those wiggles might look like a wall passing by. Checking several clocks together could help them search more carefully.

BAO and Type Ia Supernovae in LTB Cosmology: Constraints on Radial Inhomogeneity and Acoustic-Ruler Evolution

Myrto Magklara, Leandros Perivolaropoulos

AstronomerThe study combines DESI DR2 BAO and DES-Dovekie Type Ia supernovae to constrain compensated underdensity profiles and acoustic-ruler evolution in LTB cosmology with a cosmological constant. The calculation accounts for distances and unequal radial and transverse stretching of an initially common ruler. Transverse BAO plus supernovae isolate relative ruler evolution without absolute calibration; radial BAO provide complementary constraints. With full covariance and identical calibration freedom, the LTB fit improves χ² by 8.523 relative to flat ΛCDM for three additional parameters, mainly through the supernovae. DESI strongly rejects the particular deep profile preferred by supernovae and angular BAO alone. Nevertheless, a narrow nearby depression and a broader, shallower, more distant depression fit almost equally well, differing by Δχ² = 0.647. Thus, the combined data constrain specific geometries but do not uniquely reconstruct the density profile or ruler evolution. The inference depends on supernova selection and on interpreting released BAO summaries using local ruler transport at effective redshifts. Homogeneous simulations show that the improvement does not establish a detection of inhomogeneity. Within the local approximation, common LTB ruler evolution shifts angular BAO and the transverse component of three-dimensional BAO together, so it cannot by itself explain their discrepancy.

PublicThe researchers tested whether a region containing less matter than its surroundings could help explain measurements from Type Ia supernovae and baryon acoustic oscillations, a cosmic measuring pattern. Their models track how this pattern stretches differently along our line of sight and across the sky. A model with an underdense region fits the combined DESI DR2 and DES-Dovekie data better than the standard flat ΛCDM model, but it also has three extra adjustable parameters, and most of the improvement comes from the supernova data. Simulations of a homogeneous universe show that this improvement does not establish that a real underdensity has been detected. DESI strongly rules against one particular deep depression favored by a subset of the data, yet a narrow nearby depression and a broader, shallower one farther away fit almost equally well. The measurements therefore do not identify a unique matter distribution. The conclusions also depend on supernova selection and assumptions used to interpret the BAO measurements. In the approximation studied, stretching the common measuring pattern cannot alone explain a discrepancy between two BAO measurements.

Young explorerScientists used measurements of stars exploding and a pattern in space to ask whether one part of the universe has less matter than the space around it. Some models with a less-full patch matched the measurements better, but that does not prove the patch is really there. Tests with pretend universes showed why scientists must be careful. Two different patch shapes worked almost equally well, while one especially deep patch did not match all the measurements. So the scientists have narrowed down the possibilities, but they do not yet have one clear answer.

Gravitational waves and the exit from de Sitter in Inflation without an Inflaton

Daniele Bertacca, Raul Jimenez, Sabino Matarrese+2 more

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

AstronomerThis theoretical study develops Inflation without an Inflaton, in which second-order de Sitter graviton gradient stress sources primordial curvature. With exact Bunch-Davies evolution, the scalar solution satisfies all four second-order scalar Einstein equations in pure de Sitter. In contrast, oscillatory cancellations prevent tensor enhancement; the calculated one-loop tensor correction is approximately 0.04 times the squared dimensionless tensor amplitude relative to the leading tensor power. The exit prescription introduces a global vacuum-depletion clock that delays local release by N_w e-folds after each scale’s horizon exit, producing equal enhancement across scales. Depleted vacuum energy is transferred to a non-vacuum sector modeled as radiation. Deep in radiation domination, the predicted curvature power is c_w Δ_h^4 exp(N_w)/20, with clock-dependent c_w, n_s−1 = −4ε, and n_T = −2ε. The resulting spectrum is described as adiabatic and Gaussian; super-horizon curvature is conserved to better than 10⁻⁴, and changing the adiabatic exit fluid changes it by less than 0.2%. A direct radiation exit requires approximately 31–50 e-folds of delay, corresponding to 3×10⁻⁶ ≲ r ≲ 0.036. The predicted interferometer-band gravitational-wave background is Ω_GW h² ≈ 2×10⁻²¹–3×10⁻¹⁷, with prospective access by BBO and ultimate DECIGO over specified portions of this range. Above k_end exp(−N_w), scalar power steepens to k⁻¹; for sharp release and N_w ≳ 45, this suppresses μ-distortions. These are model calculations and experimental prospects, not reported detections.

PublicCould the early universe’s rapid expansion produce the seeds of cosmic structure without a separate inflaton field? This paper develops a theoretical model in which quantum gravitational ripples generate those seeds. Its calculations enhance the disturbances associated with curvature, but not the gravitational waves themselves. A crucial ingredient is a proposed timing rule: after each scale passes beyond the horizon, it waits the same number of expansion e-folds before local release as vacuum energy is depleted into a component modeled as radiation. The predicted pattern depends partly on this timing prescription. In the calculation, the resulting curvature disturbances remain nearly unchanged once the universe is radiation dominated. The model also predicts gravitational-wave signals that future experiments could test over parts of its allowed range. The abstract reports theoretical results and detection prospects, not observational confirmation.

Young explorerScientists are exploring an idea about how the very young universe grew so fast. In their math, tiny ripples in space could help make the little uneven patches that later became cosmic structure, without needing a special extra field. The idea needs a special waiting rule for how the universe changes afterward. Future searches for space ripples could help test it, but this paper does not show that it really happened.

Coupled dark energy and apparent phantom crossing: a potential-independent lower bound

Domenico Sapone, Esteban Arratia

• General Relativity and Quantum Cosmology

AstronomerDESI baryon acoustic oscillation measurements combined with CMB and type Ia supernova data prefer an effective dark-energy equation of state below −1 in the past and above −1 today. The authors derive a potential-independent bound for explaining this apparent crossing with a canonical scalar field coupled to dark matter, rather than an actual crossing by the field. The expansion history H(z) fixes a minimum fractional dark-matter mass loss after recombination and limits the field's motion, imposing a minimum constant coupling beta = d ln m/d phi. For field-dependent coupling, the bound applies to its largest magnitude; equality occurs when the field comes to rest within the observed range. For DESI DR2 best-fit histories, this scenario requires about 5–7% mass loss by redshift approximately 0.8 and beta_min = 0.047–0.058. Accounting for data uncertainties, public DESI DR2 chains give 95% lower limits on the absolute value of beta ranging from 0.025 to 0.038. Published coupled-quintessence fits all satisfy the bound, but constant-coupling fits reproduce only a shallow crossing. Within this explanation, the bound implies an extra dark-matter attraction of at least a few tenths of a per cent of gravity and a lensing signal at least a few per cent weaker than dark-matter clustering would suggest; these are theoretical implications, not reported detections.

PublicMeasurements from DESI, combined with the cosmic microwave background and type Ia supernovae, favor—but do not establish—a change in dark energy's behavior across a mathematical dividing line called −1. A simple scalar-field model cannot actually cross that line, but an interaction with dark matter could make it appear to cross. The researchers calculate the minimum interaction strength needed for this explanation, regardless of the field's potential. For the best-fitting DESI DR2 expansion histories, dark-matter particles would need to lose about 5–7% of their mass after recombination and by redshift approximately 0.8, requiring a minimum coupling of 0.047–0.058. Including observational uncertainties gives 95% lower limits on the absolute value of the coupling ranging from 0.025 to 0.038. Previously published models satisfy the bound, although models with an unchanging coupling reproduce only a shallow crossing. If this explanation is correct, it also requires an extra attraction between dark-matter particles at least a few tenths of a per cent as strong as gravity, and bending of light at least a few per cent weaker than dark-matter clustering would suggest. These effects are implications of the model, not detections reported here.

Young explorerSpace is getting bigger, and scientists call the mysterious thing behind its speeding up dark energy. Some measurements hint that dark energy has changed how it behaves, but we are not sure. The scientists studied one possible explanation: dark energy might interact with invisible stuff called dark matter, making dark-matter particles lighter. For the explanation that best matches these measurements, a particle starting with 100 little portions of mass would need to lose about 5 to 7 of them. The scientists worked out how strong the interaction would have to be. If this idea is right, dark-matter particles would also pull on each other a little extra, and light would bend a little less than their clumping would suggest. The study does not show that these things have really happened.

Little Red Dots from Primordial Black Holes: Non-Gaussianity and Accretion Evade μ-Distortion Constraints

Shyam Balaji, Bryce Cyr, Sarah R. Geller+4 more

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

AstronomerJWST observations of Little Red Dots at redshifts roughly 4 and above suggest supermassive black holes with masses roughly one million solar masses or greater, challenging conventional growth from Population III remnants. This study uses Bayesian Markov chain Monte Carlo analyses to explore primordial black hole seeding from lognormal and cut-power-law primordial power spectrum enhancements, varying local non-Gaussianity and accretion histories under the COBE/FIRAS CMB mu-distortion constraint, both with and without a requirement to produce supermassive black hole seeds. Both models can seed the LRD population while satisfying this constraint for an absolute value of f_NL of order 1 and peak amplitude A of order 10^-3, with standard Eddington-limited accretion incorporated. The analyses show preferences for both positive and negative f_NL, but the negative preference depends strongly on accretion history and disappears for duty cycles roughly 0.1 or smaller. These are model-compatibility results, not observational evidence establishing a primordial origin; next-generation CMB spectral distortion missions could test the hypothesis.

PublicRecent JWST observations of distant objects called Little Red Dots suggest that black holes weighing at least roughly a million Suns already existed at redshifts around 4 and higher. Their rapid appearance is difficult to explain through conventional growth from the remnants of the first stars. The researchers tested an alternative: black holes formed from fluctuations in the very early universe that later grew into these giants. Their statistical analyses found that two models of enhanced early fluctuations could provide suitable seeds without violating COBE/FIRAS limits on distortions in the cosmic microwave background, the universe's ancient background light. This works with non-Gaussianity parameter f_NL having an absolute value of order 1, a fluctuation-spectrum peak amplitude of order 10^-3, and standard Eddington-limited growth. The models favor both positive and negative f_NL, but the negative preference disappears if the black holes actively accrete for roughly 10 percent of the time or less. The study shows that primordial seeds remain a possible explanation, not that they have been discovered. Future measurements of background-light distortions could test the idea.

Young explorerA space telescope called JWST has seen tiny-looking red dots far away. They may contain black holes as heavy as a million Suns or more, even when the universe was young. Scientists used math to ask whether black holes born very early could grow into these giants. Two kinds of models could work without breaking a rule set by measurements of the universe's old light. But the answer depends on how often the black holes eat nearby material and grow. This is a possible story, not proof that it happened. Future measurements of that old light could help test it.

Cosmic Corpses: Dead stars as Factories of the most Extreme Objects in the Universe

Ankit C. Khunt, Swagat S. Mishra

• Popular Physics
• General Relativity and Quantum Cosmology

AstronomerThis pedagogical account reviews white dwarfs, neutron stars, and black holes, emphasizing how quantum mechanics, nuclear interactions, and General Relativity govern their formation and properties. It also considers primordial black holes as a possibility arising from rare, large density fluctuations in the early Universe and briefly discusses their potential contribution to dark matter. The abstract presents an explanatory overview rather than new observations or simulation results; primordial black-hole formation and their dark-matter role are not established findings here.

PublicThis educational overview explains how gravity and the properties of matter shape the fates of stars, including white dwarfs, neutron stars, and black holes. It describes how quantum physics, forces within atomic nuclei, and Einstein’s theory of gravity help explain their formation and characteristics. It also introduces the possibility that some black holes formed from unusually dense regions in the early Universe and could make up part of dark matter, without claiming that either possibility has been confirmed.

Young explorerStars do not stay the same forever. This article explains how they can become things called white dwarfs, neutron stars, and black holes, and how gravity and the stuff inside stars help decide what happens. It also talks about an idea: some black holes might have formed when the Universe was very young, rather than from stars. Those black holes might be part of the mysterious stuff called dark matter, but the article does not say this is known for sure.

Collider-observable curvaton

David Cyncynates, Takuya Okawa

• High Energy Physics - Phenomenology

AstronomerThis theoretical study develops a technically natural curvaton model with decay mediated by a superrenormalizable Higgs interaction. Calculated quantum and thermal corrections to the curvaton potential remain controlled throughout its cosmological evolution. At high inflationary scales, dissipation proceeds through off-shell processes in the Standard Model plasma. The authors find broad viable parameter space; the region where the curvaton mass and dimensionful Higgs-portal coupling are closest in scale falls within the projected discovery reach of proposed light Higgs-mixed scalar searches. This is a theoretical viability and search-reach result, not an observational detection.

PublicThe researchers study a theoretical early-universe model involving a field called the curvaton, which decays through an interaction with the Higgs. Their calculations indicate that quantum effects and heat do not destabilize the model during its cosmic evolution. For high inflationary energy scales, the curvaton loses energy through interactions in the hot plasma of Standard Model particles. Many model settings remain viable. Proposed searches for light particles mixed with the Higgs could test the region where two key model scales are most similar, but the study reports no detection.

Young explorerScientists used math to study an idea about the very young universe. Their idea includes something called a curvaton that can give up its energy by interacting with something called the Higgs. They checked whether heat and tiny quantum effects would spoil the idea, and their calculations say it can still work. Some proposed future searches might find signs of certain versions of the idea, but nobody has found a curvaton in this study.

The first-order phase transitions and gravitational waves from an effective theory inspired by four-stack intersecting D6-brane models

Haotian Huangfu, Tianjun Li, Qi Sun+2 more

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

AstronomerThis theoretical study predicts a stochastic gravitational-wave background from the symmetry breaking SU(2)R1 × SU(2)R2 → SU(2)R in a Pati–Salam effective theory inspired by intersecting D6-brane models. The ultraviolet construction fixes the gauge structure and particle multiplicities, but scalar masses and quartic couplings remain renormalized inputs. A one-loop finite-temperature potential with ring resummation tracks a strongly supercooled, few-TeV transition through nucleation, percolation, completion, and reheating. A leading-order friction diagnostic does not support runaway bubble walls; the calculated signal is dominated by sound waves, with subleading turbulence and a peak suppressed by the finite acoustic lifetime. For a fast-wall reference case, the predicted peak is at 0.611 Hz with h²ΩGW = 1.232 × 10⁻¹¹. The authors examine sensitivity to wall speed, renormalization scale, and thermal screening, and make noise-only comparisons with proposed detector configurations, including DECIGO and BBO. These are model predictions, not an observed signal or a demonstrated detection prospect.

PublicThe researchers calculate how a possible change in the early Universe could have produced a background of gravitational waves. In their model, bubbles of a new state form and grow during a strongly supercooled transition. Their calculation favors sound waves as the main source of gravitational waves, rather than bubble walls that keep accelerating, and the sound waves’ limited lifetime weakens the predicted signal. One fast-wall example peaks at 0.611 cycles per second, within the frequency range targeted by the proposed DECIGO and BBO observatories. This is a theoretical prediction, not a detection. Its strength depends on model and calculation choices, and the detector comparisons account only for noise.

Young explorerScientists used math to imagine a big change when the Universe was very young. In their idea, bubbles grew, and sound waves helped make tiny ripples in space. They calculated what those ripples might be like for future machines to look for. They have not found these ripples, and the answer depends on choices in their model.

Probing Exotic Electron-Electron Interactions via Adiabatic Spin Inversion in MRFM

Chunlong Li, Shien Yang, Yiwei Huang+2 more

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

AstronomerThis theoretical proposal uses magnetic resonance force microscopy (MRFM) with oscillating-cantilever-driven adiabatic reversals (OSCAR) of electron spins to search for short-range, spin-dependent electron–electron interactions potentially mediated by light bosons beyond the Standard Model. A ferromagnetic tip supplies both a dense polarized-spin source and the magnetic-field gradient needed for force detection, without magnetic shielding between source and sensor. A linearized treatment of the coupled spin–mechanical dynamics yields resonance-frequency shifts for V2 and V3 and a second-harmonic force signal for the velocity-dependent V8 interaction. Interrupted-OSCAR differential detection and distance-dependent measurements are investigated as ways to distinguish exotic signals from conventional magnetic backgrounds. Sensitivity projections use representative ensemble and single-spin MRFM parameters and depend on specified noise and statistical assumptions. The scheme could complement existing searches and potentially improve V2 constraints over selected submicrometer interaction ranges; no experimental detection is reported.

PublicThe study proposes a way to search for hypothetical forces between electrons that depend on their spin and might be carried by new, lightweight particles. The method would use a tiny vibrating lever and a magnetic tip, with controlled reversals of electron spins turning possible new forces into changes in the lever’s vibration. The authors calculate different expected vibration signatures for three candidate interactions and examine ways to separate them from ordinary magnetic effects. Using representative parameters from existing magnetic resonance force microscopy experiments, they estimate how sensitive the proposed search could be. Under their noise and statistical assumptions, it might strengthen limits on one interaction at selected distances below a micrometer. This is a proposed experiment with calculated sensitivity, not evidence that a new force has been found.

Young explorerElectrons have a property called spin. Scientists wonder whether a tiny, unknown push or pull could depend on that spin. This study suggests looking for it with a very small vibrating lever and a magnetic tip. Carefully flipping the electrons’ spins might make the lever wiggle differently if the new force exists. The scientists worked out what to look for and how to check that ordinary magnetism was not fooling them. They have not found the new force; they are proposing a way to search for it.

Horizon-penetrating rotating black-hole configurations in VCDM

Antonio De Felice

• General Relativity and Quantum Cosmology

AstronomerThis theoretical and numerical study constructs stationary, rotating, possibly charged VCDM configurations on the constant-auxiliary Einstein-Maxwell branch. Regularity of the metric alone does not ensure regularity of VCDM's preferred foliation. The Kerr-Newman and Kerr-Newman-de Sitter geometries admit nonzero constant-mean-curvature foliations crossing the future black-hole horizon and, where present, the future cosmological horizon. A horizon-regular flux formulation distinguishes hyperboloidal and expanding asymptotic ends. Seventeen survey configurations, a fixed-geometry mean-flux scan, and paired flat/de Sitter comparisons down to κM = 0.01 show that flux variations change preferred-foliation shear without changing the background seen by standard test matter. Paired local lapse and shear differences have effective powers near two over the computed range; the lapse comparison requires fixed time normalization. Residuals, geometric reconstructions, and selected grid comparisons test the numerical solutions. An exact bound excludes lapse zeros in the regular stationary exterior block where Δr > 0. The study distinguishes singular finite-proper-distance endpoints from asymptotic trumpet ends and derives conditional bounds on a stationary spacelike inner limit. Cosmological interpretation requires additional matching assumptions; dynamical selection and the rotating interior endpoint remain undetermined.

PublicThis mathematical study explores spinning black holes, possibly carrying electric charge, in a gravity theory called VCDM. In this theory, a smooth spacetime geometry is not enough: a preferred way of dividing spacetime into slices must also remain regular. The researchers construct time-independent configurations whose slices pass through future black-hole horizons and, in the de Sitter cases, future cosmological horizons. Their numerical calculations show that changing a quantity called flux can change how these slices are distorted without changing the background experienced by standard test matter. An exact mathematical bound also rules out zeros of the lapse, a quantity describing the spacing of time slices, in the specified regular exterior region. These are theoretical constructions, not observations. The work does not establish which configuration would develop dynamically or determine the endpoint inside a rotating black hole, and a local cosmological interpretation needs further assumptions.

Young explorerThe researchers used math to study spinning black holes. In their theory, they must check both the shape of space and a special way of slicing space and time, like cutting a loaf of bread. Their math makes slices that pass through a black hole's boundary. But this is not a picture of a real black hole, and they still do not know how these patterns would form or how they end deep inside.

Quasinormal Modes of Black holes in the generalized Schwarzschild-de Sitter solution of f(R) gravity

Dhruba Jyoti Gogoi, Himanshu Chaudhary, Tiberiu Harko

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

AstronomerThis theoretical study calculates scalar, vector, and axial tensor quasinormal modes for a static, spherically symmetric Schwarzschild-type solution in modified f(R) gravity. The metric contains a linearly growing term and a logarithmic correction and depends on four integration constants. Using higher-order WKB and an analytical method, the authors find that suitable parameter choices yield QNMs close to Schwarzschild values. Increasing the model parameter A produces nonlinear increases in oscillation frequency and damping rate. The parameter η has similar effects at small A but opposite effects at larger A, with scalar perturbations behaving distinctly from the vector and axial tensor cases. Parameter-space contours support these calculated trends, and time-domain profiles illustrate signal evolution. These are model calculations, not observational detections or evidence favoring this theory over general relativity.

PublicThe researchers calculated how disturbances would oscillate and fade around a black-hole-like solution in a modified theory of gravity. They studied three kinds of disturbances and found that, for some choices of the model’s settings, their characteristic oscillations closely resemble those of a Schwarzschild black hole in general relativity. Increasing one setting, A, makes the predicted oscillations faster and makes them fade more rapidly, with the changes following a nonlinear pattern. Another setting, η, has similar effects when A is small but reverses those effects when A is larger; one kind of disturbance also responds differently from the other two. The team calculated profiles showing how the signal changes over time. These findings describe theoretical behavior, not measured gravitational waves.

Young explorerA disturbed black hole can ring and then grow quiet, a little like a bell. Scientists used math to work out this ringing in a different theory of gravity. With some settings, it rings almost like the black hole in the usual theory. Changing the settings can make the ringing faster or slower and make it fade differently. They calculated what could happen; they did not hear a real black hole doing this.

SuperWIMPs in the Kination Era: Imprints on N(eff) and CMB Spectral Distortions

Geneviève Bélanger, Abhishek Roy

• High Energy Physics - Phenomenology
• High Energy Astrophysical Phenomena

AstronomerThis theoretical study examines correlated cosmological and collider signatures of late, out-of-equilibrium decays producing dark matter and non-thermal neutrinos. In the scotogenic model, the lightest singlet fermion N1 is produced through late decay of the lightest inert doublet scalar via the superWIMP mechanism. An early kination-dominated era changes the expansion rate, allowing parameter regions that are underabundant in standard cosmology to reproduce the observed dark matter relic density. Energy exchange between injected neutrinos and photons can generate CMB spectral mu-distortions, detectable shifts in N_eff, or both. For lightest inert doublet scalar masses of 200–500 GeV, the analysis predicts complementary signatures accessible at the LHC. These are model-based possibilities, not reported detections. The authors argue that the connection extends to other late-decay scenarios and could let future CMB measurements and collider searches jointly constrain dark matter production and the early thermal history.

PublicThe researchers explore a possible way dark matter could have formed: unstable particles decaying into dark matter and neutrinos relatively late in the early Universe. In their model, an early period of expansion dominated by a component called kination makes it possible to produce the observed amount of dark matter in cases where the usual cosmic history would produce too little. The injected neutrinos could exchange energy with photons, leaving small changes in the spectrum of the cosmic microwave background or in the inferred amount of radiation in the Universe. For parent-particle masses of 200–500 GeV, the study also predicts complementary signals that could be searched for at the Large Hadron Collider. No such signals are reported as detected; the work proposes ways future cosmic-background measurements and particle searches could test this dark matter production mechanism.

Young explorerScientists are testing an idea about how invisible stuff called dark matter might have formed. They imagine that, when the Universe was young, some particles broke apart and made dark matter and tiny particles called neutrinos. If the Universe expanded differently for a while, this idea could make the amount of dark matter we see evidence for today. It might also leave tiny clues in the Universe’s oldest light and clues that scientists could look for in a big particle machine. The scientists have worked out what might happen; they have not found those clues yet.

A Self-Interacting Dark-Matter Route to Supermassive Kerr Black Holes via Super-Eddington Bondi Accretion: Mass-Spin Evolution

Chian-Shu Chen, Feng-Li Lin

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

AstronomerMotivated by recent JWST observations, this theoretical study extends critical relativistic Bondi accretion of repulsively self-interacting dark matter from Schwarzschild to Kerr black holes with rotating inflow. In a stationary, equatorial, quasi-spherical framework, smooth critical solutions exist over a finite inflow-angular-momentum range bounded by the Kerr marginally bound capture values. Rotation modifies the sonic structure and accretion efficiency, while critical density cancellation and dark-sector/halo matching retain their Schwarzschild form. The model supports efficient super-Eddington growth until the finite halo supply becomes limiting. Illustrative population evolutions suggest that stellar-mass seeds could grow and spin up together, offering a possible joint mass–spin route to early supermassive Kerr black holes rather than observational confirmation of this mechanism.

PublicRecent JWST observations have motivated explanations for how black holes could grow rapidly in the early Universe. This theoretical study explores one possibility: spinning black holes feeding on dark matter whose particles repel one another. Within the study’s simplified, steady-flow model, this material can support very rapid growth, and its rotation can also make the black hole spin faster. The model allows smooth inflow only over a limited range of the material’s angular momentum, and rapid growth eventually becomes limited by the surrounding dark-matter supply. Illustrative calculations suggest a possible path from black holes with masses comparable to stars to early supermassive, spinning black holes; they do not establish that this process occurred in nature.

Young explorerHow did some black holes get so big so early? Scientists used a math model to explore one idea: a spinning black hole might grow quickly by swallowing a kind of dark matter whose tiny bits push one another away. The swirling food could also make the black hole spin faster. But the fast growing cannot keep going without enough food nearby. This is a possible explanation, not something the scientists have seen happening.

Naturalness in the Past from a Time-Dependent Supersymmetry Scale

Tony Gherghetta, Kunio Kaneta, Wenqi Ke

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

AstronomerThe authors propose that electroweak naturalness may depend on cosmic epoch. In a no-scale supergravity framework, a rolling quintessence modulus controls the supersymmetry-breaking scale, allowing superpartners to have been much lighter in the early universe while remaining heavy today. Correlated visible-sector Kähler modular weights and modulus-dependent superpotential Yukawa couplings can suppress fifth-force and varying-constant effects. However, radiative stability of the quintessence potential requires additional tuning of the field-dependent vacuum energy. The effective theory has implications for early-universe phase transitions, relic abundances, and gravitational waves; the abstract reports a theoretical scenario, not observational evidence.

PublicThis theoretical study explores whether a puzzle about the electroweak scale could depend on the age of the universe. In the proposed model, an evolving field changes the scale of supersymmetry breaking, allowing hypothetical partner particles to have been much lighter in the early universe than they are today. Linked choices in the model can suppress extra forces and changes in physical constants, but keeping the evolving field's potential stable against quantum corrections requires additional careful adjustment. The scenario could affect early cosmic transitions, the amounts of particles left over from the early universe, and gravitational waves. The abstract does not report observations confirming it.

Young explorerImagine that some particles have partners we have not found. Scientists suggest a way those partners could have been much lighter when the universe was young and heavier now. Their idea uses something that slowly changes as the universe grows older. The idea still needs careful adjustments to work, and it has not been shown to be true. It could change what scientists expect from the universe's earliest days, including ripples in space called gravitational waves.

Quality time in extra dimensions: axion quality and radion cosmology

Falguni Biswas, Yeshan Juberi, Ahmed Rakin Kamal

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

AstronomerThis theoretical study examines axion protection against additional symmetry breaking in a five-dimensional circle compactification with a dynamical radius and an axion arising from an Abelian gauge field. Two radion-stabilization mechanisms use Casimir energy from electrically neutral fields, with or without a periodic scalar winding around the circle; both admit Minkowski and de Sitter minima. At the Minkowski minima, radion masses are 100–170 TeV, and electrically charged matter produces a residual strong CP angle of order 10^-17 while negligibly shifting the radius. Magnetic gauging remains compatible when its extra degree of freedom is included in the Casimir spectrum, provided its coupling is sufficiently small. Increasing the radius suppresses charged-matter breaking relative to QCD but enhances the magnetic breaking contribution. The authors also calculate radion decay channels, including the graviphoton. In a possible radion-dominated era without scalar winding or magnetic gauging, a Higgs-curvature coupling ξ=7 gives a visible-sector reheating temperature of about 85 MeV and ΔN_eff≈0.02. Entropy from radion decay can dilute the axion abundance so that f_a=10^14 GeV and an initial misalignment angle ≈0.43 reproduce the observed dark matter abundance, versus ≈0.065 during radiation domination. These are model-dependent theoretical results, not observational detections.

PublicThe researchers explore a theoretical model with an extra spatial dimension curled into a circle. A hypothetical particle called the axion could help explain why the strong nuclear force shows so little violation of a symmetry called CP, but additional effects can undermine that explanation. The study describes two ways that quantum vacuum energy could stabilize the circle’s size. In the model’s flat-spacetime solutions, electrically charged matter causes only a tiny residual CP violation. Another effect, called magnetic gauging, remains compatible only if its coupling is sufficiently small. Making the circle larger reduces one threat to the axion explanation but strengthens the other. The authors also investigate a possible early period when the field controlling the circle’s size dominated the universe. Under specified assumptions, its decay could reheat ordinary matter and dilute axions enough for them to account for all the observed dark matter. This is a theoretical possibility, not evidence that extra dimensions or axion dark matter have been found.

Young explorerScientists used math to imagine a tiny extra direction curled into a circle. They explored ways to keep the circle from changing size and to protect an idea about a particle called an axion. In one possible story about the early universe, changes in the circle could help leave the right amount of axions to explain the invisible matter we call dark matter. But this is a math model, not a discovery of the circle or the particle.

Measuring the Hubble Constant Using Strongly Lensed Gravitational Wave Signals

Shun-Jia Huang, Yi-Ming Hu, Xian Chen+4 more

• General Relativity and Quantum Cosmology

AstronomerThe authors propose constraining H0 with strongly lensed gravitational-wave signals by reparameterizing the waveform to expose its sensitivity to H0. The method could provide meaningful constraints without an identified electromagnetic counterpart to the GW source, provided the lens redshift is known. Fisher-matrix and Markov Chain Monte Carlo assessments forecast a relative H0 uncertainty of approximately 0.3–2% from a single strongly lensed event for the space-based detector TianQin, with precision depending on the available electromagnetic information. These are prospective constraints, not an observational measurement.

PublicThe paper proposes a new way to measure the universe’s expansion rate using gravitational waves whose signals are bent by gravitational lensing. The authors find that the altered signal contains information about the expansion rate. Their method could work even without identifying light from the gravitational-wave source, as long as the redshift of the lens is known. Statistical forecasts for the space-based detector TianQin suggest that one strongly lensed event could yield a relative uncertainty of about 0.3–2%, depending on how much information from light is available. This is a prediction of the method’s potential, not a measurement already made.

Young explorerSpace is stretching, and scientists want to know how fast. This paper suggests studying ripples in space that get bent as they travel past something heavy. The scientists’ calculations suggest that one such signal might help measure how fast space stretches, even if they cannot find light from where the ripples began. They would still need information about the thing bending the ripples. This is an idea they have studied with calculations, not a measurement they have already made.

Model-independent Constraints on Dark Energy Density from CMB-SPA, DESI DR2 BAO, and Updated Type Ia Supernova Compilations

Zhenyuan Wang, Yun Wang

AstronomerThe authors constrain X(z) = ρ_DE(z)/ρ_DE(0) at five redshift knots over 0 < z < 2.33 without adopting a parametric equation of state, combining SPT-3G, Planck 2018, and ACT DR6 CMB data with DESI DR2 BAO and three alternative SN Ia compilations: Pantheon+, Union3.1, and DES-Dovekie. All three combinations favor a see-saw profile: X(z) exceeds unity at low redshift, crosses unity near z ≈ 1, and falls below unity at higher redshift. The preference against a cosmological constant is compilation-dependent and weaker for the five-knot reconstruction, at 2.3–2.8σ, than for the (w0, wa) parameterization, at 3.0–3.2σ. Their probe-pair analysis attributes the profile to BAO–CMB tension in the h r_d–Ω_m plane; SN Ia–CMB Ω_m tension instead produces a small, nearly uniform upward shift. Euclid and Roman BAO measurements at z ≳ 1 are proposed as tests of the BAO–CMB discrepancy's origin. A derived CMB-SPA distance prior (R, ℓ_A, ω_b) retains essentially all X(z) information from the power spectra without lensing reconstruction; adding that reconstruction provides only marginal additional dark-energy information.

PublicIs dark energy constant, or does its density change over cosmic history? This study combines cosmic microwave background measurements, galaxy-distance measurements, and three alternative collections of exploding-star data. Rather than imposing a particular formula for dark energy's evolution, the researchers estimate its density at five redshifts. Each data combination favors a density above today's value at low redshift and below it at higher redshift. However, the evidence for change is not conclusive: its strength depends on the exploding-star dataset and is weaker than when a commonly used formula is assumed. The analysis traces the pattern mainly to a mismatch between the galaxy-distance and microwave-background constraints. Future Euclid and Roman measurements could test the origin of that mismatch; they have not yet resolved it.

Young explorerScientists are checking whether dark energy, which helps the universe expand faster, has always stayed the same. They used clues from space, and their calculations hint that it may have changed. But the clues do not all agree, so they are not sure. Future measurements could help check the hint.

Loss-Cone-Limited Dark Matter Capture by Early Black Hole Seeds

Brian Zhang, Grant J. Mathews

• Astrophysics of Galaxies
• General Relativity and Quantum Cosmology

AstronomerThis theoretical study evaluates collisionless dark-matter capture by early black-hole seeds using Eddington-inverted NFW-like halos, a relativistic direct-capture boundary, and orbit-averaged Fokker–Planck angular-momentum transport. It explicitly tracks loss-cone depletion and refilling. Ordinary stellar relaxation produces negligible dark-matter-driven growth for the fiducial seeds. Primordial black holes, modeled as massive perturbers, can enable order-of-magnitude growth in sufficiently compact halos, with refilling dependent on their abundance and individual mass. Triaxial or chaotic centrophilic orbits are included as a phenomenological upper-envelope supply channel and can support an early capture burst. However, self-consistent evolution generally exhausts the accessible low-angular-momentum reservoir, sharply reducing capture and saturating the black-hole mass. Fixed-background NFW models therefore overestimate sustained growth, particularly in the full-loss-cone limit. A TNG50-calibrated NFW benchmark yields negligible growth even with optimistic refilling. The calculations disfavor this channel as a generic solution to early supermassive-black-hole growth, while allowing radiatively dark growth in rare compact environments with efficient refilling.

PublicHow did supermassive black holes become so large so early? This study calculates whether swallowing dark matter could help, rather than reporting an observed growth event. The model follows both the capture of dark matter and the processes that redirect more of it toward a young black hole. In sufficiently compact dark-matter halos, hypothetical primordial black holes could stir the dark matter enough to allow roughly tenfold growth. Other favorable orbital arrangements could produce a rapid initial burst. But the supply usually runs out: once the black hole consumes the dark matter on accessible capture paths, growth stalls. Models that leave the surrounding reservoir unchanged therefore overestimate lasting growth. One benchmark halo model gives negligible growth even under optimistic assumptions. The authors conclude that this mechanism is unlikely to explain early supermassive black holes in typical NFW-like halos, though rare compact environments could permit growth without emitted light.

Young explorerScientists used a math model to ask whether young black holes could grow by swallowing dark matter. In some special, tightly packed places, their model says they could grow quickly at first. But then they usually run out of dark matter moving along paths they can catch. So this probably cannot explain most early giant black holes, though it might help in rare places.

The galaxy-electron cross-spectrum with ACT, SPT-3G and DESILS LRGs

Selim C. Hotinli

AstronomerThe authors measure the galaxy–electron cross-power spectrum P_ge(k) for DESI Legacy Imaging Surveys photometric luminous red galaxies by cross-correlating a velocity-weighted galaxy momentum template with ACT DR6 and, for the first time, SPT-3G CMB temperatures. A surrogate-field Monte Carlo accounts for the survey mask, lightcone evolution and photometric-redshift weights to establish the absolute normalization in physical units. Detections reach 11.7σ with ACT, 8.4σ with SPT-3G and 12.3σ when combining SPT-3G with the non-overlapping ACT northern cap. Despite independent instrumental systems, and with about two thirds of the SPT-3G galaxies shared between surveys, channel-by-channel amplitudes agree within 0.7σ. All 26 null tests on the adopted night maps are consistent with zero. Converting the signal to a gas fraction requires external host-halo masses, which P_ge does not measure. Using masses inferred from sample number density and a published CMB-lensing calibration of the same galaxies, the authors estimate that gas within the virial radius accounts for 25–33% of the halo’s cosmic baryon budget.

PublicResearchers measured how gas is distributed around a sample of galaxies using its subtle imprint on the cosmic microwave background, the ancient light seen across the sky. They combined galaxy survey information with measurements from ACT and, for the first time for this measurement, SPT-3G. Both telescope surveys detected the signal strongly, their results agreed closely, and 26 checks designed to reveal spurious signals found none. Estimating the amount of gas also requires knowing the masses of the galaxies’ surrounding halos; this measurement alone cannot provide those masses. Using separate mass estimates, the researchers infer that gas inside the halos’ virial boundaries amounts to 25–33% of the ordinary-matter budget expected for those halos.

Young explorerScientists looked for tiny changes in very old light to learn about gas around galaxies. Two telescopes found matching clues, and the scientists checked carefully for mistakes. They used those clues to estimate how much gas is nearby. But the answer also depends on how heavy the galaxies’ big surrounding halos are, so they needed other information to make that estimate.

Impact on time delays due to milli-lensing by subhalos on lensed gravitational waves

Ishan Swamy, Anupreeta More, Ojas Patil

AstronomerThis modeling study investigates time-delay perturbations from dark matter subhalos of 10^6–10^9 solar masses with NFW density profiles in galaxy-scale, quadruply imaged fold and cusp lens configurations. The modeled subhalo populations perturb delays between macro-images by a few hours. If neglected, these anomalies may affect LIGO–Virgo–Kagra searches for strongly lensed gravitational waves. Millisecond-level timing precision achievable with current and future GW detectors motivates this probe of low-mass substructure, compared with the few-hour precision of electromagnetic observations. No additional subhalo-generated milli-images appeared in the 200 realizations analyzed for each configuration. These are modeling results, not observational detections; further statistical studies are needed to establish expected delay perturbations and milli-image detection or non-detection rates.

PublicSmall clumps of dark matter can alter the arrival times of signals bent by a galaxy’s gravity. This study modeled how such clumps, with masses from one million to one billion Suns, affect two arrangements in which a galaxy produces four lensed images of a source. The models shifted the delays between those images by a few hours. Such shifts could complicate searches for gravitationally lensed gravitational waves if they are ignored. Gravitational-wave timing can achieve millisecond precision, offering a way to probe smaller dark matter clumps than electromagnetic timing measurements can. None of the 200 model realizations for each arrangement produced extra images caused by the clumps themselves. These are predictions from modeling, not observed discoveries, and more statistical work is needed to determine how common the effects should be.

Young explorerA galaxy’s gravity can send a signal along different paths, so it reaches us at different times. Scientists used models to see how smaller clumps of invisible dark matter might change those arrival times. In their models, the clumps changed the waiting time by a few hours but made no extra copies of the signal. This could matter when searching for waves in space. Scientists still need more tests to learn how often it happens.

Cosmic topology. Part IId. Eigenmodes and correlation matrices of lens spaces

Mikel Martin Barandiaran, Catherine Petretti, Stefano Anselmi+16 more

AstronomerThis theoretical study computes full harmonic-space CMB covariance matrices for scalar perturbations in positively curved FLRW lens spaces L(p,q), allowing arbitrary lens spaces and observer positions. These generally anisotropic and inhomogeneous topologies produce observer-dependent off-diagonal covariances. Kullback–Leibler divergence relative to a simply connected three-sphere of equal curvature indicates that topological signatures can remain significant in a cosmic-variance-limited regime when the shortest loop through the observer, d_NC, exceeds the last-scattering-surface diameter, d_LSS, by up to 10%. Distinguishability depends mainly on d_NC/d_LSS, incorporating curvature, p, q and observer position. For arbitrarily small positive spatial curvature, lens spaces and observer positions exist with 0.985 d_LSS < d_NC < 1.1 d_LSS: matched circles would be too small for detection to date, while statistical signatures could remain discoverable. This is a theoretical detectability result, not an observational detection of topology.

PublicThe Universe’s overall connected shape remains unknown. Researchers calculated how a family of positively curved universes, called lens spaces, would affect patterns in the cosmic microwave background, the light left over from the early Universe. Their calculations suggest that statistical patterns could reveal this shape even when the shortest route around the Universe through our location is up to 10% longer than the diameter of the surface from which that light reaches us. This possibility assumes measurements limited only by the unavoidable variation in the cosmic signal. The predicted patterns depend on the particular shape, its curvature and where the observer is located. Even with arbitrarily small positive curvature, some models could leave detectable statistical clues without producing matching circles large enough to have been detected so far. The study does not establish that our Universe has such a shape.

Young explorerCould space have a shape that lets a trip all the way around bring you back home? Scientists used math to explore some shapes like that. They calculated how those shapes could change patterns in very old light we see in the sky. Their work suggests that the patterns might give us clues even when another clue, matching circles, would be too small to have been spotted so far. The clues would depend on the shape of space and where we are in it. They have not found that our Universe really has one of these shapes.

Self-Interacting Dark Matter: From Particle Physics Theories to Structure Formation Simulations

Martin Rosenlyst, Vinh Tran, Oliver Zier+7 more

• High Energy Astrophysical Phenomena
• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThis work presents a unified theory-to-simulation framework for self-interacting dark matter (SIDM), linking a broad survey of elementary and composite particle models to explicit inputs for structure-formation simulations. The mapping covers cosmological initial conditions, internal-state masses and populations, reaction networks, velocity- and angle-dependent cross sections, dissipative losses, and decay rates and recoil kinematics. In AREPO-2, the authors implement and validate algorithms for isotropic and anisotropic scattering, multi-state elastic and inelastic reactions, and dissipative processes, together with a dedicated dark-matter decay module. Tests range from beam-lattice deflection, thermalization, and decay to isolated-halo gravothermal core collapse and cosmological box and zoom-in simulations. The implementations recover analytical predictions and published benchmarks and agree across numerical schemes. These are theoretical and numerical validation results, not observational evidence for SIDM.

PublicThe authors build a bridge between theories of self-interacting dark matter—dark matter whose particles can interact with one another—and computer simulations of how cosmic structures form. They explain a broad range of particle models and give recipes for translating their properties into simulation settings, including collisions, energy loss, and particle decay. They also add and test corresponding methods in the simulation code AREPO-2. Tests of particle behavior, dark-matter halos, and simulated cosmic regions reproduce analytical predictions and previously published benchmarks, with agreement between different numerical approaches. The work provides tools for studying these dark-matter possibilities; it does not report observations showing that dark matter actually has these interactions.

Young explorerScientists made computer tools to explore what might happen if dark-matter particles could bump into one another, lose energy, or turn into other particles. They checked the tools with test problems, and the answers matched what the tests expected. These tools can help scientists study how big clumps of dark matter might form and change. They do not show that real dark matter does all these things.

Rapid Graviton Thermalization through a Scalar--Gauss--Bonnet Coupling

Hongguang Zhang, Zhengyang Qiu, Sirui Wang+1 more

• High Energy Physics - Theory

AstronomerThis theoretical study finds rapid graviton thermalization in an effective scalar-mediated model, conditional on the effective theory being valid over the reaction domain. A thermal fermion bath keeps a massive scalar near equilibrium, while scalar decay into graviton pairs and the inverse process drive an initially empty graviton sector toward a Bose–Einstein distribution with zero chemical potential. For a scalar mass of 1 TeV, interaction scale Λ_int = m_φ/0.03, and Yukawa coupling y = 0.03, graviton occupations reach within 0.1% of equilibrium across 0.1 ≤ p/T ≤ 5 after approximately 0.024 initial Hubble times. This range includes the thermal energy-spectrum peak, and the calculation includes expansion and energy transfer from the bath. The scalar stays near equilibrium, its vacuum decay widths remain narrow, and the graviton interaction remains perturbative over the reaction domain. A present-day thermal spectrum is also derived for a specified decoupling and entropy history; no observational detection is reported.

PublicCould gravitons reach thermal equilibrium much faster than the universe expands? This theoretical calculation shows that they can under particular model conditions. A bath of particles keeps a massive intermediary particle near equilibrium; that particle can turn into pairs of gravitons, and the reverse process can also occur. For one chosen set of parameters, the calculated graviton population becomes very close to a thermal distribution in a small fraction of the universe’s initial expansion time. The result depends on the effective model remaining valid for the interactions considered, rather than demonstrating that this happened in the real universe. The authors also calculate a thermal spectrum for today, assuming a specified history of how the gravitons stopped interacting and how cosmic entropy evolved.

Young explorerScientists used math to imagine tiny particles called gravitons sharing energy with other particles in the universe. In their model, the gravitons quickly settled into a balanced pattern, even while the universe grew. This shows what could happen if the model works, not something scientists have seen happen.

Thermal Krylov complexity and entropy of inflationary modes with different comoving-wavenumber dependences

Tao Li, Lei-Hua Liu

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

AstronomerThis theoretical study derives thermal Krylov complexity and entropy for primordial scalar modes in canonical single-field inflation, a non-trivial sound-speed model, and a modified-dispersion model, with differing comoving-wavenumber dependences. Starting from a purified two-mode thermal state, the authors analyze unitary evolution in an ideal closed system. Within the parameter range studied, the sound-speed correction raises the mean values and oscillation amplitudes of both Krylov quantities, while modified dispersion introduces stage-dependent oscillatory structure. An independently introduced effective open-system parametrization yields a normalized Krylov distribution governed by a geometric ratio combining thermal occupation, coherent spreading, and effective attenuation. The authors derive explicit complexity and entropy expressions and their low- and high-temperature limits. The sound-speed correction enhances this ratio in the adopted range; with modified dispersion, coherent spreading and attenuation compete. These are model-based results, not observational findings.

PublicThe researchers use mathematical models to study how quantum disturbances during an early period of cosmic expansion spread through a space of possible quantum descriptions. They compare three inflation models: a standard single-field model, one with altered sound speed, and one with a changed relationship between a disturbance's wavelength and frequency. In an ideal isolated system, the sound-speed change increases the average values and oscillations of two mathematical spreading measures within the settings examined. The changed frequency relationship instead produces oscillations that depend on the stage of evolution. The researchers separately introduce an effective model allowing attenuation and derive formulas describing how thermal occupation, spreading, and attenuation jointly shape the measures, including at low and high temperatures. This is a theoretical comparison, not a report of observed features of the early universe.

Young explorerScientists used math to imagine tiny ripples in the very young universe. They tried three different sets of rules and watched how the ripples' quantum patterns spread in their calculations. With one rule change, two spreading scores became bigger and wobbled more in the cases they tried. Another rule change made the wobbling different at different stages. They also made a separate math model where spreading and fading can compete. These are ideas explored with math, not things they saw happening in the sky.

How much dark matter really matters?

Jenny Wagner

• General Relativity and Quantum Cosmology

AstronomerThis essay examines the model dependence of dark-matter inference from strong gravitational lensing. Standard reconstructions fit predefined mass-density models to lensing observables; the author argues that these models overestimate the dark-matter content of the deflectors. Removing those models from the reconstruction reveals that the observations directly constrain local properties of the deflecting masses. The abstract gives no quantitative estimate of the overestimate or of the dark matter required, framing the issue as a distinction between observational constraints and assumptions imposed by reconstruction models.

PublicStrong gravitational lensing occurs when the mass of a foreground cosmic structure curves spacetime and bends light from a source behind it. Astronomers use this bending to infer the structure's mass and, when dark matter is thought to dominate, learn about that unseen matter. This essay argues that commonly used models can make the inferred amount of dark matter too large. The author says that setting those models aside reveals which local properties of the light-bending mass the observations directly constrain. The abstract does not say how much less dark matter is needed; it questions how much of the inferred amount comes from observations and how much from model choices.

Young explorerHeavy things in space can bend the path of light coming from something behind them. Scientists study that bent light to learn about matter they cannot see, called dark matter. They use models to help work out how much is there. The writer argues that these models can make it seem like there is more dark matter than there really is. The question is how much the light tells us and how much comes from the model. This summary does not give an amount.

Joint probes of dark matter annihilation from neutrino detectors and CMB targets

Ruifeng Leng, Shao-Ping Li

• High Energy Physics - Phenomenology

AstronomerThe authors propose combining neutrino searches with the effective number of neutrino species and CMB spectral distortions to test dark matter annihilation into neutrinos. A simple, model-independent analysis identifies detection windows for these cosmological observables that overlap with the experimental sensitivities of Super-Kamiokande, JUNO, Hyper-Kamiokande, and DUNE for MeV–GeV dark matter with large annihilation into neutrinos. These are prospective joint-probe opportunities, not a detection of dark matter. The small electron-antineutrino excess hinted at by Super-Kamiokande does not uniquely establish an astrophysical or cosmological origin.

PublicIf dark matter particles annihilate into neutrinos, detecting those neutrinos alone would not reveal where they came from. This study proposes also checking two clues from the cosmic microwave background, the ancient light of the universe: the effective number of neutrino species and distortions in that light’s spectrum. A simplified analysis finds circumstances in which these cosmic clues and several neutrino experiments could probe the same dark matter scenarios. This is a proposed combined test, not evidence that dark matter has been found; even the small excess of electron antineutrinos hinted at by Super-Kamiokande has an uncertain origin.

Young explorerScientists wonder if mysterious dark matter can turn into tiny particles called neutrinos. But finding neutrinos would not tell us for sure where they came from. The researchers suggest looking for clues in both neutrinos and very old light from space, like checking two clues to solve a mystery. Their calculations suggest the clues could work together, but they have not shown that dark matter made any neutrinos we have seen.

Background-independent one-loop renormalization of tensor and scalar primordial spectra

Guillermo Ballesteros, Jesús Gambín Egea, Flavio Riccardi

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

AstronomerThe authors present a background-independent framework for renormalizing one-loop primordial spectra, applying it to scalar-induced tensors sourced by a minimally coupled spectator field and to scalar spectra generated by potential self-interactions. Universal WKB behavior of internal modes allows analytic extraction of ultraviolet poles, which are absorbed into local counterterms without specifying the background evolution or the full dynamics of the field in the loop. The result is finite, model-independent expressions suitable for numerical analysis, rather than observational measurements.

PublicThis theoretical work develops a way to remove troublesome infinities from calculations of fluctuations in the early universe. The authors apply it to two cases: tensor fluctuations driven by a spectator field and scalar fluctuations arising from a field’s interactions with itself. Their method handles the short-wavelength contributions without requiring a specific history of the universe’s expansion or a complete description of the interacting field’s behavior. It produces finite mathematical expressions ready for numerical study, not new observations.

Young explorerScientists use math to study tiny ripples in the very young universe. Sometimes that math gives an infinite answer that needs to be handled carefully. These researchers found a way to tidy up those calculations for two kinds of ripples without first choosing every detail of how the universe changed. This is a new math method, not something they saw through a telescope.

ACT-DR6 consistent inflation in generalised entropic cosmology and f(Q) gravity

Shin'ichi Nojiri, Sergei D. Odintsov

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

AstronomerThis theoretical study constructs inflationary scenarios in generalised entropic cosmology and its equivalent f(Q) gravity that are consistent with ACT-DR6 observations combined with Planck and BAO data. A reconstruction scheme is used to obtain explicit f(Q) inflationary histories, while coupling to a scalar field allows compatible inflation across large classes of f(Q) models through the choice of scalar potential. The authors also present FRW equations for a generalised entropy that includes Tsallis, Rényi and Barrow entropies as special cases, and use the entropy–f(Q) correspondence to construct ACT-DR6-consistent entropic inflation. With a scalar field, they demonstrate compatible inflation for any generalised entropy considered in the paper by choosing suitable potentials. These are model constructions compatible with the cited data, not an observational identification of the underlying gravity theory or entropy; the suggested connection to a unifying early-universe entropy remains tentative.

PublicThe researchers build theoretical models of inflation, an early period of rapid cosmic expansion, using modified gravity and a generalised description of entropy. They construct models compatible with observations from the Atacama Cosmology Telescope together with Planck and BAO data. Their framework includes several previously proposed forms of entropy. They also show that adding a scalar field and choosing its potential appropriately can make a broad range of models compatible with the observations. This flexibility does not establish which model describes the universe. The authors suggest that their work may help identify a common description of entropy in the early universe, but that remains an interpretation rather than an observed result.

Young explorerScientists made math stories about how the universe might have grown very quickly when it was very young. They found stories that fit clues from looking at the universe. By changing parts of their math, they could make many different stories fit. That does not mean they know which story really happened. They hope this work will help them understand the young universe better.

Gravitational Waves from Multiple Cosmic Superstrings and the Overshoot Problem

Luca Brunelli, Michele Cicoli, Muhammad Hassan+2 more

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

AstronomerThe authors analyze a post-inflationary dynamical system containing multiple cosmic-superstring species whose tensions depend on a rolling modulus. In this model, gravitational-wave radiation from the early decay of effective strings formed by wrapped NS5- and D3-branes provides friction that prevents the modulus from overshooting its late-time minimum. Fundamental strings persist until the modulus oscillates around the minimum, decaying when they account for about one-third of the total energy density. The predicted gravitational-wave spectrum can retain multiple high-frequency peaks despite dilution during a subsequent epoch of modulus domination. This is a theoretical candidate signature of generic string-theory features, not a reported detection.

PublicThis theoretical study explores an early-universe scenario in which several kinds of cosmic strings decay and release gravitational waves, or ripples in spacetime. The strings’ tensions depend on an evolving field. In the model, waves from the first strings to decay provide a braking effect that keeps this field from passing beyond its eventual resting point. Another kind of string lasts longer and decays when it holds about one-third of the universe’s total energy. The authors predict that the combined waves could have several distinct peaks at high frequencies, even after a later stage of cosmic evolution weakens them. Such a pattern could offer a way to look for features of string theory, but no observation is reported.

Young explorerScientists used math to imagine tiny strings in the very young universe. In their model, some strings disappear early and make ripples in space. Those ripples act like a brake, helping another part of the model slow down instead of going too far. Other strings last longer before making more ripples. The scientists think these ripples might leave a special pattern we could look for, but they have not seen it.

On a cosmological Oppenheimer-Snyder model: matching McVittie and FLRW spacetimes

Brien C. Nolan

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study derives necessary and sufficient conditions for smoothly matching an expanding McVittie spacetime to a spatially flat FLRW spacetime across a hypersurface of arbitrary, potentially changing causal character. Beyond characterizing special cases, it reduces the general matching conditions to three nonlinear first-order ODEs with one initial-value constraint. For a specified McVittie region, the authors prove semi-global existence: solutions and the required FLRW spacetime exist uniquely globally to the future, while the matching hypersurface exists uniquely almost everywhere. Crucially, its embedding conditions necessarily fail at least once, though only at isolated points. To the past, the hypersurface reaches the McVittie past singularity. Generically, the boundary contains both spacelike and timelike portions, preventing the isotropic region from serving globally as an interior for the McVittie exterior. Unlike the everywhere-timelike boundary in the Oppenheimer–Snyder model, this behavior leads the authors to conclude that a globally defined isotropic source for the McVittie spacetime does not exist.

PublicCan a mathematical model of a black hole in an expanding universe be given an interior that is the same in every direction? This theoretical paper investigates that question for the McVittie model by trying to join it smoothly to a spatially flat FLRW model of the universe. The authors derive equations describing the join and prove that their solutions continue uniquely into the future. However, the join itself encounters unavoidable failures at isolated points. More fundamentally, its boundary generally has both timelike and spacelike sections, rather than behaving everywhere like the surface separating an object's interior from its exterior. The authors therefore conclude that this kind of interior cannot provide a globally consistent source for the McVittie model. This is a mathematical limitation of the proposed construction, not an observation of actual black holes.

Young explorerScientists used math to ask whether a black hole in a model of a growing universe could have an inside that looks the same in every direction. They tried to fit the inside and outside together like two puzzle pieces. The math showed that the join cannot work everywhere as the edge of an inside. So this kind of inside does not work for the whole model. They studied a math picture, not a real black hole.

Cosmological Collider Signals From a Triangle Loop

Zhehan Qin, Zhong-Zhi Xianyu

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

AstronomerThis theoretical study derives, for the first time, the leading analytical cosmological collider signals from a massive scalar triangle loop in the inflationary bispectrum and trispectrum. Combining a directional cutting rule with partial Mellin–Barnes representations, the authors obtain local and nonlocal trispectrum signals in a soft limit and the leading squeezed-bispectrum signal. All of these leading signals are reproduced by the corresponding bubble diagram with a single effective pinched coupling. The authors state that the framework can also generate subleading signals and accommodate arbitrary internal masses, spins, and interactions, providing a systematic route to analytical loop signals in general cosmological correlators. These are analytical results, not observational detections.

PublicTheoretical models of inflation, an early phase of cosmic expansion, can contain subtle mathematical signatures of massive particles. These signatures are often difficult to calculate when the particle interactions form a triangular loop in the calculation. This study derives the leading signatures for a massive scalar particle in specific limits of mathematical quantities describing three-way and four-way correlations. The researchers also show that a simpler loop calculation, with one effective interaction, reproduces those leading signatures. They describe how their framework could handle more complicated cases. The work improves theoretical calculations; it does not report evidence that these signatures have been observed.

Young explorerScientists use math to explore what might have happened when the universe was very young. Some of their calculations have tricky triangle-shaped loops. In this study, they worked out the main patterns made by one kind of loop and showed that a simpler calculation gives the same main patterns. This is a discovery about the math, not something they have spotted in the sky.

MadStree: automated evaluation of tree-level de Sitter correlators

Jiaqi Chen, Yi-Xiao Tao, Xinyi Wang+1 more

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

AstronomerThe authors derive recursive reduction formulae and d log-form differential equations for arbitrary tree-level and loop-integrand cosmological correlators, accounting for the external relations of massless bulk propagators. They describe systematic solution of these equations and implement the method in the Mathematica package MadStree. In their example benchmarks, they evaluate up to one million points per master integral, finding an average computational cost of order microseconds per numerical point per master integral. These are computational results for the tested examples, not observational findings or a universal performance guarantee.

PublicThis work introduces a mathematical method and a Mathematica software package, MadStree, for evaluating calculations of correlations in cosmology. The method reorganizes the calculations and supplies equations that can be solved systematically. In the authors’ examples, they evaluated up to one million numerical points for each basic integral, with an average computing time of roughly microseconds per point per integral. The paper reports a calculation tool and example speed tests, rather than new observations of the universe.

Young explorerSome math problems about the universe are very hard to work out. The researchers made a new recipe and a computer tool to help solve them. In their tests, the computer worked through lots of examples very quickly. This is a new way to do the math, not a new thing they saw in the sky.

Two-peak gravitational wave spectra from supercooled two-field phase transitions

Daniel Araújo, João Gonçalves, Danny Marfatia

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

AstronomerThis theoretical study examines gravitational-wave spectra from supercooled first-order phase transitions in two-field conformal models. Using three representative toy models, the authors derive analytical criteria for two-step transitions and show how two-field dynamics can produce a genuine two-peak gravitational-wave spectrum. They identify parameter regions in which the predicted peaks would be observable with LISA and the Einstein Telescope, and illustrate the analysis with a realistic conformal dark SU(3) model. These are model predictions, not reported gravitational-wave detections.

PublicThe researchers explore whether certain theoretical changes in the state of the early universe could produce gravitational waves with two distinct peaks in their spectrum. They build three simplified models involving two interacting fields, work out conditions for a transition to happen in two steps, and show how the field dynamics can generate the two peaks. For some model settings, they predict that LISA and the Einstein Telescope could observe such signals. They also apply the analysis to a more realistic model of a dark sector. The study predicts possible signals; it does not report a detection.

Young explorerScientists used math to imagine the young universe changing in two steps. In their models, two invisible fields can make ripples in gravity with two special peaks, a little like two notes in a song. They predict that LISA and the Einstein Telescope could spot these ripples if the models have the right settings. They have not found these ripples yet.

First detection of the forbidden rotational spectrum of H₃⁺: JWST/MIRI observations of the shocked gas in HH 168

David A. Neufeld, Joel D. Green, Dan M. Watson+1 more

AstronomerJWST/MIRI observations toward HH 168 in Cepheus A West reveal the first detection, astronomical or laboratory, of the pure rotational spectrum of H3+, whose forbidden transitions are enabled by centrifugal distortion. Twenty-six lines exceed 5 sigma in one or both of two fields; the strongest is (J,K) = (5,0) → (4,3) at 16.325 micrometers. Their velocities and spatial distribution follow hot shocked H2 rather than ionized gas. The rotation diagram gives approximately 730 K, but the populations are nonthermal and are best explained by subthermal excitation in gas hotter than 2000 K. Among models of shocks entering mildly irradiated molecular gas, an H2-constrained dissociative J-type shock predicts H3+ emission within a factor of approximately 1.5 of observations. A nondissociative C-type shock fits H2 better but underpredicts H3+ by a factor of 5–6. Poorly known excitation by energetic collisions limits interpretation. Archival MIRI data also reveal the spectrum in the HH 211 bow shock. These lines offer a new probe of ionization in shocked molecular gas.

PublicAstronomers using JWST have detected a previously unseen set of infrared lines from H3+, a molecular ion central to interstellar chemistry. Other kinds of H3+ transitions were already known, but these rotational transitions had never been observed in space or in a laboratory. In the shocked region HH 168, the team detected 26 lines that follow hot molecular hydrogen rather than ionized gas. Although a simple analysis gives a temperature near 730 kelvin, the pattern of lines is not that of gas in thermal equilibrium; the researchers favor excitation in gas hotter than 2000 kelvin. Shock models give mixed results: one comes close to the H3+ brightness, while another better matches hydrogen but predicts too little H3+ emission. Uncertain collision physics complicates the comparison. The spectrum also appears in archival observations of HH 211. It offers a new way to study ionization in shocked gas.

Young explorerA tiny particle called H3+ helps make new chemicals in space. With the Webb telescope, astronomers found a kind of light from this particle that nobody had seen before. It comes from places where gas is hit by shocks and gets very hot. The scientists compared the light with models, but none explains everything yet. The light gives them a new way to learn about the gas.

First detection of suprathermal CH⁺ rotational emissions from chemical pumping: JWST/MIRI observations of the HH 168 molecular shock

David A. Neufeld, Joel D. Green, Dan M. Watson+1 more

AstronomerJWST/MIRI observations of HH 168 detect CH+ pure rotational emission R(17)–R(31) at 13.7–21.3 microns, sampling upper levels J = 18–32 with energies of 0.57–1.65 eV. Eleven lines exceed 5 sigma in both observed fields and coincide spatially and in radial velocity with hot H2. With collisional excitation negligible, the radiative cascade yields the first measured rotational distribution of ground-state reaction products from C+ + H2 → CH+ + H. Photon intensities decline almost linearly with J, consistent with roughly equal formation rates into levels up to J ≈ 33; producing J = 32 requires more than 2 eV of reactant energy. A Boltzmann distribution with φT ≈ 6200 K fits slightly better, where φ is the fraction of available energy deposited in rotation; this is not a direct gas-temperature measurement. The interpretation implies reactant energies equivalent to several thousand kelvin. Line positions lie up to 150 km/s redward of ExoMol predictions and provide the first measured CH+ rotational intervals above J = 16.

PublicObservations with the James Webb Space Telescope reveal infrared light from rapidly rotating CH+, a positively charged molecule, in HH 168. Its emission follows the location and motion of hot molecular hydrogen. CH+ forms when a carbon ion reacts with a hydrogen molecule, but the reaction needs an extra supply of energy. Because collisions contribute negligibly to exciting the observed rotation, the emitted light records how rotation was distributed among the newly formed molecules. The measurements are consistent with formation at similar rates across many rotational states, although a different, Boltzmann-shaped distribution fits slightly better. Both interpretations point to highly energetic reactants, rather than directly measuring the gas temperature. The observations offer a new way to investigate how energy drives this interstellar chemical reaction and also refine the molecule’s rotational energy spacings.

Young explorerIn a place in space called HH 168, scientists saw tiny molecules giving off invisible light as they slowed their spinning. Making these molecules takes an energetic meeting between other tiny particles. Their light gives scientists clues about how fast they were spinning when they formed. More than one explanation fits the clues, but the light helps scientists learn how molecules are made in space.

A DOLPHOT/Euclid Study of the Resolved, Faint Outer Milky Way Globular Cluster AM-1

Daniel R. Weisz, Alessandro Savino, Andrew E. Dolphin+3 more

• Instrumentation and Methods for Astrophysics

AstronomerEuclid Q1 VIS and NISP imaging resolves stars in the faint outer-halo globular cluster AM-1, at approximately 120 kpc, to about 1 mag below its main-sequence turnoff in all four bands. The authors develop and publicly release a Euclid module for DOLPHOT v2.1, empirical PSFs, and a calibration derived entirely from public Q1 images. Dedicated PSF photometry reaches 5-sigma depths of I_E = 27.1, Y_E = 25.3, J_E = 25.5, and H_E = 25.3, approximately 1–1.5 mag deeper than the public Q1 catalog. Comparisons with archival HST/WFPC2 CMD modeling and 2MASS-anchored VISTA Hemisphere Survey photometry show agreement within approximately 0.02 mag in I_E, J_E, and H_E, but an approximately 0.07 mag offset in Y_E. Inferred properties include an age of approximately 10.6 Gyr, [Fe/H] approximately -1, present-day stellar mass of approximately 20,000 solar masses, and M/L_V approximately 2.2. Its approximately 12–16 pc half-light radius and round, low-concentration profile support earlier descriptions of AM-1 as extended and diffuse; its accreted origin is attributed to previous dynamical work. Spatially varying PSFs are an anticipated refinement for Euclid Data Release 1, not a demonstrated result here.

PublicAstronomers used publicly available Euclid images to study individual stars in AM-1, a faint star cluster far out in the Milky Way’s halo. They developed software and models of how stars appear in the images, allowing them to measure fainter stars than those listed in the existing public catalog. Their analysis estimates that AM-1 is about 10.6 billion years old and contains roughly 20,000 times the Sun’s mass in stars today. Its broad, diffuse shape agrees with earlier studies. Previous work on its motion identifies it as a cluster acquired by the Milky Way. Comparisons with other observations generally support the new brightness measurements, although one of the four observing bands shows a larger discrepancy. The team released its tools publicly and anticipates further improvements with a future Euclid data release.

Young explorerAM-1 is a faraway group of very old stars that belongs to our Milky Way. Scientists made new computer tools to pick out faint stars in pictures from Euclid. The stars helped them work out how old and spread out the group is. They shared their tools so other scientists can study more stars, too.

Classical Cepheids in the 4MOST era I: Methodology for 4MOST variable stars and NLTE abundance gradients in the Milky Way

R. Albarracín, M. Bergemann, N. Storm+9 more

AstronomerThe authors present a Payne neural-network method trained on non-local thermodynamic equilibrium (NLTE) spectra to infer classical Cepheid atmospheric parameters and abundances for 17 elements, treating 15 in NLTE and C and Cr in LTE. Applied to archival Cepheid spectra spanning metallicities of approximately −0.87 to +0.35 dex, the method yields NLTE abundances that are consistent across pulsation phase for stars with multi-epoch observations; LTE estimates show larger dispersions and biases. The derived radial abundance distributions agree well with Galactic chemical-evolution model expectations, confirm gradient flattening beyond a Galactocentric radius of roughly 15 kpc, and include the first reported NLTE gradients for Co, Ni, Y, and Eu. The authors also report robust inference at 4MOST-HR resolving power, preparing for the forthcoming 4MIDABLE-HR sample. Improved constraints on Galactic chemical evolution and Cepheid distance-scale calibration are prospective applications, not demonstrated revisions to H0.

PublicCepheid stars brighten and dim regularly, helping astronomers measure distances and study the Milky Way. Estimates of their chemical makeup can introduce systematic errors into distance measurements. This study uses a neural network trained on model spectra that account for departures from local thermodynamic equilibrium, a simplifying assumption about conditions in stellar atmospheres. When applied to existing Cepheid observations, the method gives more consistent chemical abundances throughout the stars’ pulsation cycles than the simpler treatment. The researchers also find that changes in chemical abundance with distance from the Galaxy’s center become less steep beyond about 15 kiloparsecs, in broad agreement with models of the Milky Way’s chemical history. The method is intended to support future 4MOST surveys and improve the foundations of Cepheid distance measurements; the study does not report a new measurement of the Universe’s expansion rate.

Young explorerSome stars get brighter and dimmer in a regular pattern. Astronomers use them to help work out how far away things are. The researchers used a computer helper to read these stars’ light and work out what they are made of. Their more careful method gave steadier answers as the stars changed. They also found that the mix of ingredients changes more slowly with distance in the outer part of our galaxy. The method could help scientists study many more stars in future.

The impact of MUSE sky subtraction on unresolved stellar population end products: Study cases of NGC 1097 and NGC 1433

Camila de Sá-Freitas, Fuyan Bian, Patrícia Sánchez-Blázquez

AstronomerTwo MUSE/VLT case studies examine how sky-frame selection and sky variability affect inferred stellar populations in extended targets. One tests consecutive observations over two hours at airmasses of 1.25–1.05; the other compares observations of the same target under different sky conditions. For galaxies at 0.0014 < z < 0.0077, the [NI] sky line at wavelength 5200 overlaps the Mgb bandpass, making accurate subtraction particularly important for metallicity measurements. In NGC1097, regions with target-to-sky relative fluxes above 10 yield consistent stellar population properties despite sky-frame variations of up to approximately 18%; the reported brightness thresholds are fluxes above 1500 × 10^-20 erg/s/cm^2 and Johnson-V approximately 19.0. In NGC1433, comparisons across nights show that faint regions are much more sensitive to sky conditions, with inferred metallicities ranging within ±0.2. These measurement differences can affect interpretations of stellar mass assembly and gas origin; they do not establish a merger or an in-situ star-formation episode. The findings identify observational limitations and inform future MUSE sky-subtraction strategies, rather than establishing a universal tolerance for sky variability.

PublicGround-based telescopes record light from Earth's sky as well as from galaxies. Astronomers must subtract that sky light, and this study examines how the choice of sky observations affects results from the MUSE instrument on the VLT. In brighter regions of the galaxy NGC1097, the inferred properties of stars remained consistent even when the sky observations varied by about 18%. Fainter regions of NGC1433 were more vulnerable: observations on different nights produced substantially different estimates of the stars' metal content. The study also identifies a sky-emission line that can interfere with an important metallicity indicator over a particular range of galaxy redshifts. These effects matter because inaccurate metal estimates could lead to misleading accounts of how galaxies formed their stars and acquired gas. The results concern measurement reliability, not actual changes in the galaxies between nights.

Young explorerWhen a telescope looks at a galaxy, it also sees light from the sky around us. Scientists try to take away that extra light to see the galaxy clearly. This study found that bright parts of one galaxy were easier to measure reliably, while faint parts of another were harder. Different sky light could make the stars seem different, even though the study did not show that the stars had changed.

Local Pitch Angles of Galactic Structures in Nearby Galaxies with JWST: I. Spiral Arms and Interarm Substructures in Disk-Dominated Systems

Stella Faria-Costa, Irapuan Rodrigues, Ivânio Puerari

AstronomerThis spatially resolved JWST study measures global and local spiral pitch angles in seven nearby galaxies using four NIRCam and four MIRI filters per galaxy. A two-dimensional Fourier transform identifies the dominant azimuthal mode and corresponding p_max, enabling spiral reconstruction and arm/interarm masks. Circular-window correlations with cosine filters in the (ln R, theta) plane map local pitch angles across multiple scales. NIRCam yields the most robust main-pattern measurements, while MIRI provides higher contrast for dusty interarm feathers at the smallest window size, D_w = 0.25. Main arms typically have absolute pitch angles of about 15–30 degrees; feathers have systematically larger angles, often exceeding 50 degrees. The findings establish scale-dependent pitch angles and distinct angular regimes for different structural components. The authors interpret NIRCam and MIRI as complementary tracers of the large-scale stellar backbone and finer dust structure, and present the method, alongside a companion barred-galaxy study, as a framework for investigating distinct dynamical environments.

PublicResearchers used JWST images of seven nearby galaxies to measure how tightly their spiral arms and smaller, dusty features called feathers wind around them. They combined a method that identifies the overall spiral pattern with measurements in smaller regions. The main arms typically had pitch angles of about 15–30 degrees, while feathers had larger angles, often above 50 degrees, meaning they were less tightly wound. The measured angles depended on the size of the region examined and the structure being traced. JWST’s NIRCam gave the most reliable measurements of the main spiral pattern, while MIRI made dusty features between the arms stand out more clearly at the smallest scale tested. Together, the images provide complementary views of large-scale stellar structure and finer dust patterns.

Young explorerSome galaxies look like giant swirls. Scientists used pictures from the JWST space telescope to study seven nearby galaxies. They measured how tightly the big spiral arms curl and compared them with smaller dusty shapes called feathers. The feathers usually curled less tightly than the big arms. One camera showed the big starry swirls best, while another made the little dusty shapes easier to see. Looking at big and small parts of a galaxy revealed different kinds of curves.

Local Pitch Angles of Galactic Structures in Nearby Galaxies with JWST: II. Dust Lanes and Gas Flows in Bar-Dominated Systems

Stella Faria-Costa, Irapuan Rodrigues, Ivânio Puerari

AstronomerA spatially resolved analysis of six barred spiral galaxies observed by PHANGS–JWST combines a two-dimensional Fourier transform with circular-window correlation to map local pitch angles across wavelengths and spatial scales. In bar-dominated regions, dust lanes have typical absolute pitch angles of approximately 35–70 degrees, substantially larger than spiral-arm values. Several galaxies show systematically smaller angles in inner regions and larger angles farther along the bar, tracing changes in local curvature. Larger analysis windows recover overall lane geometry, while smaller windows reveal irregularities and secondary structures. MIRI generally provides the clearest dust morphology and more precise characterization of local pitch-angle variations; NIRCam complements this with the underlying stellar distribution. These measurements describe the local orientation and curvature of dust lanes associated with bar-driven gas flows, rather than spiral-arm density-wave patterns. Together with the companion disk-galaxy study, the findings support a scale-dependent framework for using local pitch angles as observational diagnostics of distinct dynamical regimes.

PublicResearchers mapped the shapes of dust lanes in the central bar regions of six spiral galaxies using PHANGS–JWST observations. Their measured pitch angles, which describe local orientation and curvature, typically have absolute values of about 35–70 degrees, larger than those measured for spiral arms. In several galaxies, the angles are smaller toward the inside and larger farther along the bar. Examining larger areas reveals the lanes’ overall shapes, while smaller areas expose irregularities and additional structures. MIRI images generally show the dust most clearly, while NIRCam provides a complementary view of the stars. The researchers interpret these dust-lane angles as tracing structures associated with gas flows driven by galactic bars, not the density-wave patterns commonly associated with spiral-arm angles. The findings support using these measurements at different scales to study different kinds of motion within galaxies.

Young explorerScientists looked at six galaxies with long bars across their middles. They studied dark-looking lanes of dust and measured how those lanes bend and point. The angles were usually about 35–70 degrees, counting their size without a plus or minus sign, and were bigger than angles measured for spiral arms. In some galaxies, the angles changed along the bar. Looking at big patches showed the lanes’ main shapes; looking at little patches showed bumps and smaller shapes. These observations help scientists study how gas moves around galactic bars.

Time-Delay Recovery in AGN Reverberation Mapping via Mutual Information

R. A. A. Souza, E. Hatziminaoglou, D. O. Fontinele+3 more

AstronomerThe authors apply time-lagged mutual information (MI), using the Kraskov-Stoegbauer-Grassberger nearest-neighbour estimator with k = 5 and a 150-iteration Random Subset Selection bootstrap, to Swift light curves in eight energy bands for Mrk 509, NGC 5548, NGC 4151, and NGC 4593. MI reproduces UV/optical inter-band disc-reprocessing lags established with the interpolated cross-correlation function, but its performance degrades toward optical bands, where low variability amplitudes yield poorly defined MI peaks. In the X-ray bands, where X-ray/UV coupling is known to be weak, it does not recover consistent lags across the sample except for NGC 4593. Drawing on their previous multifractal analysis, the authors discuss the relationship between MI performance and each band's multifractal spectral width, Δα. They propose Δα as a candidate diagnostic of MI-based reverberation-mapping reliability, rather than establish it as a validated predictor.

PublicResearchers tested a method for measuring delays between brightness changes at different wavelengths in four galaxies with active nuclei, using Swift observations across eight energy bands. Unlike standard cross-correlation methods, mutual information can capture nonlinear relationships between the brightness changes. It recovered previously established delays between ultraviolet and visible-light bands, although the results became less clear toward visible wavelengths, where brightness variations were smaller. It generally did not find consistent X-ray delays, with NGC 4593 the exception; the abstract notes that the physical connection between X-ray and ultraviolet variations is known to be weak. The authors also propose that a measure of the complexity of the variations, called multifractal spectral width, might help identify when the method will work. That diagnostic remains a candidate, not an established result.

Young explorerScientists watched light from the bright centers of four galaxies to see whether changes in one kind of light came before changes in another. They tested a way to spot complicated patterns. It found some delays that scientists already knew about, but it had trouble when the light changed only a little. For X-rays, it found consistent delays in just one of the four galaxies. The scientists also have an idea for checking when their method might work well, but that idea is not proven yet.

HINSPHERES: Spherically Symmetric Radiative Transfer Modeling of HINSA and the Radial HI-to-H₂ Transition in Molecular Clouds

Yuchen Xing, Di Li, Xin Lyu+10 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors present hinspheres, an open-source framework for interpreting HI narrow self-absorption (HINSA) from cold atomic gas mixed with molecular material. Unlike single-Gaussian analyses with uniform spin temperature, it assumes spherically symmetric concentric shells, solves line-of-sight radiative transfer, and jointly fits HI abundance, temperature, and kinematics. Synthetic-data tests across different core ages yield mean relative parameter errors of 4.6–6.8%; a resolution–noise grid gives median recovery errors below 16% for cores within 1 kpc at FAST resolution and noise below 0.2 K. These are simulated performance estimates, not observational error measurements. Applied to L1574 and L1544, the framework infers radial HI abundance profiles spanning about three orders of magnitude, structure missed by the single-Gaussian method. The derived chemical ages are 6.5 million and 8.7 million years, respectively. The results support its use for studying the HI-to-H2 transition, including young cores with non-Gaussian profiles, within the adopted spherical-shell model.

PublicAs diffuse gas develops into dense regions where stars can form, hydrogen changes from individual atoms into molecules. Cold atomic hydrogen mixed into molecular clouds leaves a narrow absorption feature that can help trace this change. The researchers introduce open-source software called hinspheres, which models a cloud core as nested spherical layers rather than treating its absorption as one simple curve. In tests using simulated data, it recovered model parameters with average relative errors of 4.6–6.8%. When applied to observations of the dark cores L1574 and L1544, it inferred that atomic hydrogen abundance varies by roughly a factor of 1,000 across each core—variation missed by the simpler method. The model also estimated chemical ages of 6.5 million and 8.7 million years, respectively. These profiles and ages are model-derived interpretations, and the method assumes spherical layers.

Young explorerIn space, hydrogen atoms can join in pairs as clouds change into places where stars may form. Scientists made a computer tool to study the cold hydrogen still on its own. The tool pictures a cloud’s middle in layers, like an onion. It worked well on pretend clouds made for testing. When scientists used it to study two real clouds, the model suggested that some layers have much more unpaired hydrogen than others. The onion shape is an assumption that helps the tool work, not something the scientists proved the clouds look like.

B-fields In STar-forming Region Observations (BISTRO): Population-Level Universality and Environmental Structuring of 450/850 μm Polarization Signatures

Ray S. Furuya, David Berry, Pierre Bastien+65 more

• Instrumentation and Methods for Astrophysics

AstronomerPOL-2/JCMT observations of 69 molecular cloud regions at 450 and 850 μm, matched to a 12.6-arcsecond beam, show generally lower polarization fractions at 450 μm. The median of 30 measured P450/P850 ratios is 0.69 ± 0.02 (systematic) ± 0.03 (statistical). Among 35 regions with reliable total- and polarized-intensity spectral indices, the source medians are α = 3.33 and γ = 2.85–3.04; the median γ − α is −0.57 to −0.45, with γ < α in 24–27 regions. These ranges reflect extreme placements of 3σ limits for polarized intensity below the noise floor. Regional median position angles agree within 10 degrees in 10 of 13 cases, disfavoring geometric explanations that would rotate the angles. No robust class difference or monotonic low-mass–high-mass–CMZ ordering is established. Class-difference significance depends on excluding the Rosette Molecular Cloud, although the high-mass class consistently has the lowest median. Environment is confounded with physical resolution: the beam spans 0.008–0.51 pc across the sample. Within all seven fields with sufficient column-density range, the 450 μm polarization fraction decreases with Herschel column density. Pooled-pixel coefficients are not a universal pixel-level law because they combine within-cloud trends, between-cloud differences, and OMC 1's influence. The observations benchmark grain-alignment models but establish neither an environmental ordering nor a unique mechanism.

PublicObservations of 69 molecular cloud regions show that the fraction of light that is polarized—preferentially oriented in a particular direction—is usually smaller at 450 micrometers than at 850 micrometers. Across 30 measured ratios, the median shorter-wavelength polarization fraction is about 69% of the longer-wavelength value. The polarization directions generally agree at the two wavelengths, making explanations that would rotate those directions less likely. The researchers did not robustly establish a difference among low-mass, high-mass, and Central Molecular Zone clouds, or a progression through those environments. Comparisons are complicated because the observations cover different physical scales at different distances, and some statistical conclusions depend on whether one cloud is included. In all seven fields with enough variation in column density, the shorter-wavelength polarization fraction falls as column density increases. Combining pixels from different clouds does not yield a single rule for individual pixels. These findings can help test ideas about grain alignment, but they do not identify one unique cause.

Young explorerAstronomers looked at 69 cloudy places in space with a telescope. They compared two kinds of light and found that less of one kind had its wiggles lined up. The wiggles usually pointed nearly the same way in both kinds. The team could not show a clear pattern across different kinds of clouds, and they do not yet know exactly why the light behaves this way.

The hierarchical structure of the Milky Way I. A model-agnostic clustering of 1 billion stars in 5D

William H. Oliver, Tobias Buck

AstronomerThe authors apply AstroLink, a hierarchical density-based clustering algorithm, to a locally magnitude-complete subsample of over one billion Gaia DR3 stars with five-dimensional astrometry. After correcting for selection effects and applying distance contraction and feature scaling, they identify 7,410 statistically significant clusters at S = 3.8σ. Availability-aware metrics and bidirectional best matches link the hierarchy to catalogues of open clusters, globular clusters, dwarf galaxies, and stellar streams. Compact systems are often recovered as reciprocal matches, with many showing internal substructure; extended structures are generally fragmented or only partly recovered. A substantial fraction of detected clusters lack catalogue counterparts, but physical validation is required before treating them as new structures. The analysis demonstrates model-agnostic hierarchical clustering at Gaia DR3 scale while highlighting limitations in recovering extended systems.

PublicResearchers searched data for more than a billion stars from Gaia DR3 for groups nested within larger groups, without assuming a particular model for the Milky Way’s structure. After accounting for selection effects and transforming the data, their AstroLink algorithm identified 7,410 statistically significant groupings. Comparisons with existing catalogues showed that compact systems were often recovered well, sometimes with smaller groups inside them, whereas sprawling structures were usually split up or recovered only in part. Many detected groups had no counterpart in the catalogues used for comparison. These are candidates for previously unrecognized structures, not confirmed discoveries: further physical checks are needed.

Young explorerOur Milky Way has groups of stars, and some groups have smaller groups inside them. Scientists used a computer to look for these patterns in information about more than a billion stars. It found thousands of groups. It often found small, tightly packed groups well, but it sometimes found only pieces of big, spread-out ones. Some groups were not in the lists the scientists checked. They might be new, but the scientists need to check more before they can be sure.

Studying the Fullerene Nest: JWST Observations of the Planetary Nebula Tc 1. II. A Spectroscopic and Spatial Study of C₆₀ and C₇₀ Emission

M. M. Giese, J. Cami, S. Van Schuylenbergh+31 more

AstronomerJWST MIRI/MRS spectroscopy of the planetary nebula Tc 1 resolves neutral C60 and C70 emission in unprecedented detail, separating fullerene bands from atomic lines and improving band profiles and ratios. Combined fullerene emission accounts for approximately 2.6% of the total infrared output, suggesting that about 0.6% of the carbon budget resides in fullerenes. No clear evidence is found for C60+, C70+, or C60−. Individual band profile shapes show no spatial variation across the observed pixels. Resolved ro-vibrational structure appears in the 17.4 and 18.9 μm C60 bands, with similar structure in the 12.5, 14.8, 17.7, and 21.8 μm C70 bands; the authors interpret this as further establishing that all emitting fullerenes are in the gas phase. The C60 7.0/18.9 μm ratio is approximately 1.4–1.9, compared with approximately 1.3 previously reported, although significant C70 contributions to every band except 8.5 μm complicate analysis. Emission is concentrated in a thin, asymmetric shell 5–6 arcseconds from the central star, at the outer edge of the nebular core, which was ejected in a single brief episode at least approximately 4,000 years ago.

PublicObservations with the James Webb Space Telescope reveal detailed infrared signatures of carbon molecules called fullerenes in the planetary nebula Tc 1. The researchers identify neutral C60 and C70, but find no clear evidence for the electrically charged forms they searched for. Fine structure in several emission bands supports their conclusion that the emitting molecules are in gas rather than solid material. Together, the fullerenes produce about 2.6% of the nebula’s infrared output, suggesting they contain roughly 0.6% of its carbon. Their emission is concentrated in a thin, uneven shell around the central star. The improved spectra separate molecular features from atomic emission, although overlap between the two fullerene species still complicates measurements. The shell sits at the edge of a nebular core ejected in one brief event at least about 4,000 years ago.

Young explorerScientists used the Webb telescope to study a cloud around a star. They found light from two kinds of tiny carbon molecules. The light gives clues that these molecules are floating in gas. Most of their glow comes from a thin, uneven shell around the star. Some of their light overlaps, so telling the two kinds apart is tricky.

Impact of the large scale environment on the baryonic scaling relations of disc galaxies: Insights from the GASP survey

C. Bacchini, A. Marasco, B. Vulcani+7 more

AstronomerUsing MUSE/GASP observations of 81 favourably inclined discs at z ≈ 0.05, the authors measure stellar and ionised-gas distributions, kinematics, and specific angular momenta across field, group, and cluster environments and different ram-pressure-stripping stages. Within the scatter, the stellar and baryonic Tully–Fisher and specific angular momentum–mass relations show no significant large-scale environmental dependence. The stellar and baryonic TFR slopes are approximately 3.6 and 3.5, respectively, regardless of kinematic tracer; SAMR slopes of approximately 0.65–0.75 agree with tidal torque theory. The ten S0–S0/a galaxies behave similarly, consistent with, but not establishing, a faded-spiral origin. Only the gas SAMR shows an environmental signature: stripped galaxies lie approximately 0.16 dex below unperturbed systems. The authors attribute this mainly to enhanced star formation and consequently higher gas masses inferred through the Schmidt–Kennicutt law, rather than kinematic disturbances or disc truncation. Within the MUSE coverage of ≲6 disc scale lengths, the results suggest preservation of formation-acquired angular momentum despite environmental processing, mergers, and ejective feedback.

PublicDoes a galaxy’s surroundings change the relationship between its mass and its rotation? The authors studied stars and glowing gas in 81 disc galaxies in isolated settings, groups, and clusters, including galaxies undergoing gas stripping. Within the spread in the measurements, the main relationships involving stellar or total ordinary-matter mass showed no significant dependence on environment. A difference appeared only in the relationship between gas mass and specific angular momentum, a measure of rotational motion per unit mass. The authors interpret this difference mainly as a consequence of stronger star formation raising the indirectly estimated gas masses, rather than disturbed rotation or shortened gas discs. The findings suggest that these galaxies have retained the angular momentum acquired when they formed, but this conclusion applies only to the regions covered by the observations, not necessarily the entire galaxies.

Young explorerGalaxies are huge groups of stars and gas that can spin. The scientists looked at 81 disc-shaped galaxies to see whether living near other galaxies changed how their weight and spinning motion fit together. They found no clear change in most of the patterns they measured. One gas pattern was different, but they think this mostly came from how they estimated the amount of gas. Their observations suggest the galaxies kept their old spinning motion in the parts they could study.

Tidally-induced vertical asymmetries in the LMC bar and disk

Shuyu Wang, Marie Schölch, Mercè Romero-Gómez+2 more

AstronomerUsing seven representative KRATOS N-body simulations of the LMC–SMC–Milky Way system, the authors quantify how SMC pericentric passages affect vertical structure and kinematic asymmetries in an LMC-like bar and disk under different initial conditions. They separate bar and disk particles using persistent homology and characterize vertical asymmetries with Fourier decomposition. All interacting simulations develop strong m=1 vertical asymmetries in both components after pericenter, interpreted as warping; some also show m=2 bar asymmetries indicative of buckling. Gaia DR3 mock catalogs are constructed to investigate whether astrometric uncertainties could produce the observed vertical asymmetries, although the abstract gives no separate outcome of that test. The simulated asymmetries are compatible with those measured in Gaia DR3, supporting tidal encounters as an explanation rather than directly establishing the LMC’s encounter history. Comparison with Gaia DR3 suggests that a higher SMC-to-LMC mass ratio may better reproduce the observed bar tilt and places the most recent SMC pericentric passage at most 210–300 million years ago.

PublicThe Large Magellanic Cloud has a central bar of stars that may be tilted relative to its disk, while its outer disk may be warped. This study tests whether close encounters with the Small Magellanic Cloud could explain those features. In seven computer simulations of the two galaxies and the Milky Way, every interacting model developed a warped bar and disk after the smaller galaxy’s closest approach. Some models also showed signs of the bar buckling. These are simulation findings, and the authors report that the resulting distortions are compatible with measurements from Gaia DR3. The comparison tentatively favors models in which the smaller galaxy has more mass relative to the larger one, and suggests that their latest closest approach occurred no more than roughly 210–300 million years ago.

Young explorerA galaxy called the Large Magellanic Cloud may have a bent disk of stars and a tilted bar of stars in its middle. Scientists used computer models to see what happens when a smaller galaxy passes nearby. In the models, the smaller galaxy’s gravity bent the disk and bar. Some bars also buckled. The models look compatible with what astronomers measure, so a nearby galaxy might help explain the bends.

Season by season causal analysis of the continuum and velocity-resolved Hβ emission of NGC 5548

Ayan Mitra, Vasilios Zarikas

• Instrumentation and Methods for Astrophysics

AstronomerAn adapted Synergistic-Unique-Redundant Decomposition analysis explores possible causal influences in five seasons of NGC 5548 data from 1989–1993. The authors examine 7,200 decompositions of the H-beta blue wing, core and red wing together with either total H-beta or the 5100 Angstrom continuum, varying lag configurations, seasonal flux-state counts and base delays of 1–30 days. In 1989, unique continuum information about the core reaches target-entropy fractions of 0.799 and 0.387 for two and three states, with leakage of 0.047 and 0.276. In 1992, red-wing history provides unique information about the future blue wing across both variable sets and state counts, peaking at 0.106–0.166. For the 1991 core, two-state continuum–blue-wing and continuum–red-wing synergistic components contribute 0.187 and 0.125 at 20 days, with leakage 0.087, despite a vanishing unique continuum term. Core–wing redundancy suggests inputs for simpler predictive models, while late-lag leakage approaching 0.97 in the total-H-beta set motivates additional driver measurements and richer histories. These inferred information relationships complement reverberation mapping and generate causal hypotheses for the evolving broad-line region; they do not establish those hypotheses as physical causes.

PublicResearchers analyzed five years of historical observations of NGC 5548 to look for possible cause-and-effect relationships in its changing light. Their method separates information supplied by one signal alone, information shared by signals, and information available only when signals are considered together. They compared different parts of the H-beta emission line with either the whole line or the nearby continuum light. The patterns differed between years: in 1989, the continuum alone carried information about the line’s central part; in 1992, the history of the red wing helped predict the future blue wing. In one 1991 analysis, combinations of the continuum and a wing carried information about the core even though the continuum’s unique contribution vanished. These are statistical clues, not proof of physical causation. Large information leakage in some analyses points to a need for additional measurements and more complete time histories. The results offer hypotheses about the changing broad-line region that complement existing reverberation-mapping measurements.

Young explorerScientists studied five years of changing light from a place in space called NGC 5548. They looked for clues about whether earlier changes in one part of the light could help them guess later changes in another part. Sometimes one clue helped by itself, and sometimes two clues helped when used together. The patterns were different in different years. These clues give scientists ideas about what might be affecting what, but they do not prove it. More measurements could help them check those ideas.

Studying the Fullerene Nest: JWST Observations of the Planetary Nebula Tc 1. III. Tracing Fullerene-Linked Dust Variation

Simon Van Schuylenbergh, Jan Cami, Els Peeters+27 more

AstronomerJWST MIRI/MRS spatially resolved spectra of the fullerene-rich planetary nebula Tc 1 show that dust and fullerene emission are not co-spatial. The spectra distinguish broad 6–9 μm and 9–13 μm plateaus and a 30 μm feature. The invariant shape of the 6–9 μm plateau across the field indicates emission from stochastically heated material. Spatial spectral variations resolve at least three components within the 9–13 μm plateau, peaking at 9.5, 11 and 12 μm. The authors identify SiC as the likely carrier of at least the 11 μm component, with evidence that SiC grains might also produce the 12 μm component. Spatial changes in relative component strengths hint at dust processing. The 9.5 μm component correlates strongly with the SiC component(s), suggesting a similar emitting material rather than establishing its identity.

PublicInfrared observations with the James Webb Space Telescope reveal that dust and fullerenes glow in different locations within the planetary nebula Tc 1. The researchers distinguish three broad features in the infrared spectrum. One keeps the same shape throughout the observed region, indicating emission from material heated in intermittent bursts. Another contains at least three overlapping components whose relative strengths vary from place to place. Silicon carbide likely accounts for the component at 11 micrometers and might also explain the one at 12 micrometers. A third component, at 9.5 micrometers, closely tracks the likely silicon-carbide emission and may come from similar material. The changing mixture of emission hints that the dust is being altered, but the material identifications and dust-processing interpretation remain uncertain.

Young explorerScientists used the James Webb Space Telescope to study a cloud in space called Tc 1. They found that dust and material called fullerenes shine in different places. They also found several kinds of infrared glow mixed together, with different mixtures in different parts of the cloud. Some of that glow probably comes from a material called silicon carbide. The changing mixture gives scientists a clue that the dust may be changing, but they are not sure yet.

Probing faint radio activity from cores to filaments in two z=2.24 protoclusters with uGMRT

Yuheng Zhang, Xianzhong Zheng, Fangxia An+4 more

AstronomerDeep 1.26 GHz uGMRT observations of the z=2.24 protoclusters BOSS1244 and BOSS1542 identify 10 and 2 robust radio counterparts among 187 and 105 Hα-emitting members, respectively, plus five potential counterparts from forced photometry. Two Hα emitters and the massive quiescent galaxy QG1 in BOSS1244 exhibit strong radio excesses relative to Hα-based star formation rates, making them strong radio-excess AGN candidates. Median stacks of 173 and 102 remaining radio-undetected Hα emitters yield positive signals at 2.8σ and 3.2σ; their luminosities are consistent with expectations from the median Hα-based star formation rates. After excluding robust counterparts, stacks are brightest nearer QG1 in BOSS1244 and the filament spine in BOSS1542, but the environmental differences are not statistically significant, and stellar mass has no significant dependence on environmental distance. The environmental ordering remains tentative; deeper, multifrequency, higher-resolution radio observations are needed to distinguish weak AGN activity from variations in star-formation-related radio emission.

PublicAstronomers used the upgraded Giant Metrewave Radio Telescope to study radio emission from galaxies in two developing galaxy clusters, BOSS1244 and BOSS1542. They found 10 secure radio matches in the first system and two in the second, along with five possible matches. Three galaxies in BOSS1244 emit much more radio radiation than expected from their estimated rates of star formation, making them candidates for hosting active galactic nuclei. Combining the signals of many galaxies too faint to detect individually revealed average radio emission consistent with star formation. The combined radio signals were brightest in denser regions of both systems, but the differences were not statistically significant. More sensitive observations at several radio frequencies and with finer detail are needed to establish whether this apparent environmental pattern is real and, if so, what causes it.

Young explorerScientists listened for radio signals from galaxies in two big groups that are still forming. A few galaxies were bright enough to hear on their own. Three had more radio sound than scientists expected from making new stars, so something else might be helping. By putting lots of very faint signals together, the scientists found that making stars could explain the average signal. Galaxies in more crowded places seemed a little louder together, but the scientists are not sure that difference is real. They need better observations to find out.

MeerKAT reveals an ultra-steep spectrum radio halo in Abell 370

Graham Lawrie, Roger Deane

AstronomerDeep MeerKAT observations at 580–1015 MHz robustly map the diffuse radio halo in the massive, dynamically non-relaxed cluster Abell 370 (z=0.375), improving on earlier low-significance, low-fidelity detections. The emission extends approximately 1.1 Mpc, substantially farther than previously reported, and has an integrated in-band spectral index of α = −1.54 ± 0.05, consistent with an ultra-steep spectrum. Radio and X-ray surface brightness show a strong, sub-linear correlation with slope k = 0.60 ± 0.08. The halo is underluminous relative to the P1.4 GHz–M500 scaling relation, consistent with the known ultra-steep-spectrum radio-halo population. Together, these findings strongly support its classification as an ultra-steep-spectrum radio halo and provide further support, rather than proof, for turbulent re-acceleration.

PublicNew MeerKAT radio observations give a clearer picture of a vast region of faint radio emission in the galaxy cluster Abell 370. Earlier observations left its nature uncertain. The newly mapped emission spans about 1.1 million parsecs, substantially larger than previously reported, and becomes much weaker toward higher radio frequencies. Its radio brightness is strongly linked to its X-ray brightness, although the two do not increase in direct proportion. The halo is also relatively faint in radio waves for the cluster’s mass. Together, these findings strongly support classifying it as an ultra-steep-spectrum radio halo. They also support a model in which turbulence re-energizes particles, but do not prove that explanation.

Young explorerAstronomers used a radio telescope to look at a huge group of galaxies. They found that a faint glow of radio light stretches much farther than earlier pictures showed. The glow is much weaker at higher radio frequencies. These clues help scientists work out what kind of glow it is. They also support an idea that swirling motions give tiny particles more energy, but that idea is not proven.

Could globular clusters in the vicinity of the galactic centre have contributed stars to the nuclear star cluster in the past?

Kalambay M., Kuvatova D., Ishchenko M.+3 more

AstronomerDirect N-body simulations follow Terzan 2, Terzan 4, and Terzan 5 for 8 Gyr in a time-varying Galactic potential derived from IllustrisTNG-100, including stellar evolution and compact-remnant formation. A velocity reduction factor, Vred = 1.00–0.10, parametrizes dynamical friction in the central environment. All three clusters supply stars to the Galactic nuclear star cluster (NSC) during close pericentre passages even without velocity reduction: the combined bound count and accreted mass increase from 730 stars and 278 solar masses at Vred = 1.00 to 5,420 stars and 1,175 solar masses at Vred = 0.10. Terzan 4 dominates throughout because of its more frequent, closer pericentre passages. The simulated accreted population is bimodal, with a component below one solar mass whose capture is independent of Vred and a neutron-star and black-hole tail extending to 20 solar masses that grows as Vred decreases. Only Terzan 4 supplies white dwarfs at every tested Vred. These model-dependent results suggest a greater compact-remnant contribution from these Terzan clusters than from previously studied clusters, but tidal stripping of surviving globular clusters alone remains insufficient to explain the total NSC mass.

PublicComputer simulations explored whether three dense star clusters—Terzan 2, Terzan 4, and Terzan 5—could supply stars and stellar remnants to the nuclear star cluster at the Milky Way’s centre. The models followed 8 billion years of evolution and tested different amounts of slowing to represent dynamical friction near the Galactic centre. All three clusters contributed material even without this imposed slowing; stronger slowing increased the total captured mass. Terzan 4 contributed the most because it passed closer to the centre more often. The captured population included low-mass stars, neutron stars, and black holes, with more compact remnants captured as the imposed slowing increased. These are simulation results, not observed transfers. They suggest these clusters could be an important source of stellar remnants, but stripping stars from surviving clusters cannot by itself explain the central cluster’s total mass.

Young explorerScientists used computers to model three big groups of stars moving around our galaxy. In the models, some stars and leftover pieces of stars joined a crowded star group in the middle. One group, called Terzan 4, gave the most. But stars taken from groups like these are not enough to explain all the mass in the middle.

Dust in cold and warm dark matter in a suite of zoom-in simulations of Milky Way analogues

Adam Ussing, Robert Mostoghiu Paun, Darren Croton+3 more

AstronomerUsing 24 hydrodynamical zoom-in comparison simulations of Milky Way analogues, the authors investigate whether galaxy dust properties can distinguish CDM from a 3.5 keV WDM particle model. Dust is assigned in post-processing primarily through a dust-to-metals ratio, with alternative prescriptions also explored. The CDM sample favors higher dust masses, with a median excess of 6.6% at z=0 and a peak median difference of 25% at z≈0.25. Approximately 90% of the dust lies in the inner halo region in both samples, with a slightly higher fraction in CDM. Contrary to previous work, the Gini coefficient does not consistently distinguish the models; its differences are driven primarily by sensitivity to individual halo structure. At z=0, neither the dust-to-stellar mass nor dust-to-SFR functions differ significantly between samples under any tested dust production prescription. At redshifts with the largest dust-mass differences, alternative prescriptions yield larger separations in total dust mass and scaling relations. These simulation findings suggest possible diagnostic differences, but do not establish an observational distinction between dark matter models.

PublicCould dust in galaxies help reveal what dark matter is like? This study explores that possibility using 24 comparison simulations of galaxies similar to the Milky Way, contrasting cold dark matter with a warm dark matter model whose particle mass is 3.5 keV. The simulated cold-dark-matter galaxies tend to contain more dust: the median excess is 6.6% at the present-day epoch and reaches 25% at an earlier epoch. In both models, about 90% of the dust is concentrated in the inner part of the surrounding dark matter halo. But the differences are not a clear-cut test. A measure of how unevenly dust is distributed does not reliably separate the models, because it is strongly affected by each halo’s individual structure. At the present-day epoch, the models also show no statistically significant differences in how dust relates to stellar mass or star-formation rate. Different ways of assigning dust to the simulations produce larger model separations at some earlier epochs. These are simulation results, not observed evidence favoring either kind of dark matter.

Young explorerScientists made computer versions of galaxies like our Milky Way. They tried two ideas about dark matter, the invisible stuff whose gravity helps shape galaxies, and worked out how much dust the pretend galaxies would have. The galaxies made with one idea usually had a little more dust than those made with the other. In both groups, most of the dust stayed near the middle. But the galaxies were different from one another, and some dust clues could not clearly tell the two ideas apart. This was a computer experiment, not a discovery of which kind of dark matter is really out there.

Intermediate-redshift ultra-luminous infrared galaxies as transitioning objects between main sequence and starburst galaxies

J.-H. Kim, D. Rigopoulou, M. Pereira-Santaella+4 more

AstronomerNew ALMA observations target a representative sample of 22 ULIRGs at 0.46 < z < 0.81, spanning dust temperatures of 25–50 K and infrared luminosities of 10^12.0–10^12.7 solar luminosities. CO(2–1) is detected in 14 sources (64%); these detections have similar star formation efficiencies, corresponding to gas depletion timescales of hundreds of Myr. Using both an sSFR-based main-sequence relation and a relation based on CO and infrared luminosities, the authors statistically place the sample between main-sequence and starburst galaxies. Star formation efficiency strongly indicates position relative to these branches. Morphologies and star-forming properties suggest that minor mergers could temporarily enhance SFR and efficiency, but this interpretation does not exclude other evolutionary phases or pathways.

PublicObservations with the Atacama Large Millimetre Array examined 22 galaxies that shine intensely in infrared light. Carbon monoxide emission was detected in 14, allowing the researchers to assess how efficiently those galaxies form stars from their gas. Their efficiencies are similar, with estimated gas-use timescales of hundreds of millions of years. Two ways of comparing galaxies statistically place this sample between ordinary star-forming galaxies and more intense starbursts. That supports their proposed role as probes of an intermediate regime, but does not establish a single evolutionary path. The galaxies’ shapes and star-forming properties suggest that mergers with smaller galaxies could temporarily boost star formation and its efficiency; other explanations remain possible.

Young explorerScientists looked at 22 galaxies that glow very brightly in a kind of light our eyes cannot see. In 14, they found a signal from gas and used it to work out how quickly the galaxies turn their gas into stars. The group fits between galaxies that make stars at an ordinary pace and galaxies having a big burst of star-making. The scientists think joining with a smaller galaxy might give star-making a temporary boost, but they have not shown that this is the only way it happens.

A Comprehensive Analysis of the Hα Luminosity Functions at z∼1.3 and z∼2.0 in the CANUCS Lensing Fields with JWST NIRISS

Qianqiao Zhou, Yuxuan Pang, Xin Wang+12 more

AstronomerUsing CANUCS JWST grism observations of five lensing-cluster fields and their parallel fields, the authors measure Hα luminosity functions from 762 spectroscopically identified emitters: 433 at 1.1 < z < 1.5 and 329 at 1.8 < z < 2.2. Source-specific effective-volume and completeness analyses yield luminosity functions reaching intrinsic Hα luminosities of about 10^40.6 and 10^41 erg s^-1 at z ≈ 1.3 and 2.0, respectively, with completeness above 80%. Multiple independent sightlines help mitigate, rather than eliminate, cosmic variance. Including cosmic variance, the inferred faint-end slopes are −1.51 (+0.06/−0.04) and −1.42 (+0.09/−0.06), interpreted as mild evolution between the bins. Bright AGN contribute negligibly to this sample. Estimated integrated cosmic star formation rate densities are 0.103 (+0.008/−0.007) and 0.149 (+0.016/−0.013) solar masses per year per cubic megaparsec, respectively. Metallicity studies and applications to other slitless surveys are prospective uses, not results reported here.

PublicAstronomers used JWST observations to measure how common galaxies are at different brightnesses in Hα, a light-emission line used to estimate star formation. Their sample contains 762 galaxies in two redshift ranges centered near 1.3 and 2.0. Gravitational magnification by foreground galaxy clusters helped reveal faint emitters, while observations along several separate directions reduced the impact of variations from one cosmic region to another. After accounting for these variations and for missed sources, the team found a modest change in the relative abundance of faint emitters between the two ranges. They estimate a higher total star formation rate per unit cosmic volume at redshift 2.0 than at 1.3, with uncertainties in both estimates. Bright active galactic nuclei make a negligible contribution to this sample. The authors also propose using these galaxy samples to study chemical composition and applying their methods to future surveys.

Young explorerAstronomers used the James Webb Space Telescope to study a special kind of light from 762 faraway galaxies. Big groups of galaxies in front helped magnify some of that light, making faint galaxies easier to see. The team counted galaxies with different brightnesses in two groups whose light comes from different times in the universe. Their counts suggest a small change in how common the faint galaxies were. They also estimated that the earlier group was making more stars in the same amount of space, though the estimates are not exact.

Revisiting the Einstein Cross with X-shooter spectra: New estimates of accretion disk parameters and broad emission line profiles from microlensing

R. Jerez-Nicurcar, A. Esteban-Gutiérrez, V. Motta+1 more

AstronomerX-shooter spectroscopy of the lensed quasar Q2237+0305 (the Einstein Cross) spans 3000–20000 Å, providing the broadest spectroscopic wavelength coverage reported for this system. Using characteristic emission lines as references, the authors estimate differential chromatic microlensing and extinction between macro-images, finding no significant extinction-induced spectral differences between images C and A. They combine new and literature estimates into three chromatic microlensing measurements to constrain an accretion-disk model with r_s ∝ λ^p. Bayesian comparison of multi-epoch observations with mock microlensing magnification maps yields r_s = 4.9 (+2.3/−2.6) sqrt(M/0.3 M_sun) light-days and p = 0.77 (+0.47/−0.28). The inferred wavelength dependence favors a departure from the canonical thin-disk value p = 4/3, although the parameter uncertainties remain substantial.

PublicResearchers studied the Einstein Cross, a quasar seen as multiple images through a foreground galaxy acting as a gravitational lens. Their observations cover the widest wavelength range yet reported for this system. They found no significant spectral difference between images C and A attributable to extinction by material in the lensing galaxy. They also used wavelength-dependent microlensing—the uneven magnification of the quasar’s light—to investigate its accretion disk. Combining observations from several times with earlier measurements, they compared the data with simulated magnification maps. Their inferred disk size and its variation with wavelength favor a temperature pattern different from the standard thin-disk prediction, but the estimates have substantial uncertainties.

Young explorerA faraway bright object called a quasar looks like several pictures because a galaxy in front acts like a magnifying glass. Scientists studied the colors in those pictures to learn about the quasar’s hot disk. They compared the light with computer-made models. Their best guess suggests the disk’s temperature changes differently from what a usual model predicts, but they are not sure yet.

The Connection between Halo Assembly History and the Stellar Distribution II: A Radially Stratified Fossil Record of Past Halo Mass

Shuo Xu, Song Huang, Conghao Zhou+2 more

• Cosmology and Nongalactic Astrophysics

AstronomerUsing a halo-mass-complete sample at z=0.4 from the IllustrisTNG-300 hydrodynamical simulation, the authors quantify how central-galaxy stellar structure records halo assembly. Their fossil correlation measures the association between a galaxy property at the sample epoch and progenitor halo mass, while rank retention measures whether halos selected by that property belonged to the most massive population at earlier epochs. Stellar-mass fossil correlations peak non-monotonically at intermediate redshifts, shifting from z≈1 in inner regions to z≈0.7 in outer stellar halos, with peak epochs robust across group-to-cluster scales. Partial correlations with halo accretion rate indicate that these peaks mark the end of each component’s accretion-sensitive buildup. Annular stellar masses beyond 10 kpc are less biased tracers of the most massive intermediate-redshift halos than richness, and the outer stellar halo better traces the satellite population at those epochs. The simulated radial fossil record arises mainly from ex-situ assembly; these are simulation findings, not observational measurements.

PublicA computer simulation suggests that different layers of stars in massive central galaxies preserve clues to different stages of their surrounding dark-matter halos’ growth. Studying simulated galaxies at redshift 0.4, the researchers found that inner stellar regions were most strongly linked to halo mass around redshift 1, while outer regions were most strongly linked to a somewhat later time, around redshift 0.7. Their analysis connects these times to when each stellar region stopped building up in a way sensitive to halo growth. The pattern comes mainly from stars formed elsewhere and later incorporated into the central galaxy. In the simulation, stellar mass in outer rings also identifies the most massive halos at intermediate times with less bias than richness, a galaxy-count measure, and better traces their satellite populations. These results suggest a way to study halo history, but the reported findings come from a simulation rather than observations.

Young explorerScientists used a computer to make pretend galaxies and watch them grow. They found that stars near a big galaxy’s middle and stars farther out kept clues about different times in its past. Many of those clues came from stars that first formed in other galaxies. It is like finding different pages of a history book in different parts of a galaxy, but this finding is from the computer model.

The Cool Circumgalactic Echo of the Stellar-to-Halo Mass Relatio

Zeyu Chen, Enci Wang, Huiyuan Wang+10 more

AstronomerUsing stacked Mg II λλ2796, 2803 absorption in DESI galaxy–quasar pairs, the study maps the cool CGM across nearly three decades in stellar mass. The radial equivalent-width profile, W_MgII ∝ D^k, becomes shallower with increasing stellar mass, with k = 0.70 log(M*/M☉) − 9.12. Mg II equivalent width closely tracks the stellar-to-halo mass relation, peaking at the same characteristic stellar mass, approximately 3 × 10^10 M☉. This peak coincides with a transition from super-virial to sub-virial cool-gas kinematics. The authors interpret excess non-gravitational motions in low-mass halos as consistent with recycled accretion and feedback-driven circulation, and infer halo-centric heating in massive halos that may help maintain quenching. The observations link peak star formation efficiency to the strongest cool-CGM absorption, interpreted as the most abundant cool-gas reservoirs, but do not establish a causal role for feedback in setting the SHMR peak.

PublicResearchers used the absorption of background quasar light to study cool gas surrounding galaxies of different stellar masses. They found that the gas absorbs most strongly around galaxies containing roughly 30 billion solar masses in stars—the same scale at which the stellar-to-halo mass relation peaks, indicating the greatest star formation efficiency. The absorption also declines less steeply with distance around more massive galaxies. At the shared peak, the surrounding gas changes from moving faster to moving slower than the halo’s gravitational benchmark. The authors suggest that gas recycling and circulation driven by feedback help explain the motions around lower-mass galaxies, while heating in massive halos may help keep star formation shut down. These observations connect surrounding cool gas with how efficiently galaxies form stars, without proving what causes the connection.

Young explorerGalaxies have cool gas around them. Scientists studied light shining through that gas and found its strongest signs around galaxies that are best at turning their share of material into stars. The gas also moves differently around smaller and bigger galaxies. This is a clue that the gas and star-making are connected, but it does not yet tell us exactly why.

Forward modeling linear variable filter data: High resolution PAH and Paschen-α maps from SPHEREx

Andrew K. Saydjari, Connor Hainje, Benjamin Dodge+3 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors present a scalable forward-modeling method for SPHEREx emission-line mapping that avoids visible striping associated with spatially variable wavelength sampling in conventional band-averaged products. They organize the data into a pixel-level database, mask stellar contamination, and infill missing pixels using a conditional, data-driven, anisotropic Gaussian process. Applied to fields including the Rosette nebula, Corona Australis, M33, and M31, the method produces 3.3 and 3.4 μm PAH and Paschen-α maps at 8.5 arcsec FWHM on 6.4 arcsec pixels. SPHEREx provides spectral resolution R ∼ 35, compared with WISE at R ∼ 2. Comparisons with other gas and dust tracers demonstrate the maps’ quality and complementary utility, with reported 3.3 μm sensitivities reaching σ(I₃.₃) = 2.7 × 10⁻⁸ erg s⁻¹ cm⁻² sr⁻¹. The method is designed to scale to all-sky mapping; the demonstrated maps cover selected fields. The authors estimate, rather than demonstrate, that a two-year survey extension with modest scanning changes would match or exceed WISE PAH sensitivity across the sky.

PublicResearchers used NASA’s SPHEREx to make detailed infrared maps of emission from polycyclic aromatic hydrocarbons, or PAHs, which help reveal conditions in gas and dust between stars. Their new processing method avoids visible stripes that can appear when SPHEREx measurements are combined in more conventional ways. It masks contamination from stars and statistically fills missing pixels, so some map values are inferred rather than directly measured. The team produced maps of PAH emission and a hydrogen emission line in selected regions of our galaxy and in the galaxies M33 and M31, then compared the PAH maps with other gas and dust maps. The method can be scaled to the whole sky, but the demonstrated maps cover selected regions. The authors also estimate that extending the survey by two years and slightly changing its scanning pattern could bring whole-sky PAH sensitivity to at least the level achieved by WISE; that is a forecast, not an achieved result.

Young explorerScientists used a space telescope called SPHEREx to make maps of light from tiny molecules in space. These maps help them study the gas and dust between stars. They found a way to make maps without visible stripe marks. Where pieces were missing, a computer used the other information to make careful guesses. They made maps of several places, not the whole sky. They think two more years of looking, with a small change in how the telescope scans, could help them make sensitive maps of the whole sky, but that has not happened yet.

Search for a Dispersion Measure Excess Toward Nearby Galaxy Halos Using Fast Radio Bursts from the Second CHIME/FRB Baseband Catalog

Affan Khadir, Ayush Pandhi, Jason Hessels+23 more

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena

AstronomerA statistical stacking analysis of dispersion measures (DMs) from 1,748 sub-arcminute-localized sources in the Second CHIME/FRB Baseband Catalog probes foreground galaxy circumgalactic media (CGM). For halos within 50 Mpc, the mean DM excess inside one virial radius is 119 ± 44 pc cm⁻³ (p = 0.0053; approximately 2.6σ). The sample extending to 150 Mpc contains 628 sightline–halo intersections and shows a tentative decline in mean DM with impact parameter (p = 0.0046; approximately 2.6σ), predominantly driven by galaxies with 10 ≤ log(M*/M☉) ≤ 11. Modeling the profile as n_e(r) ∝ r⁻³β yields β = 0.68 with uncertainties of +0.15 and −0.16 and an extrapolated central electron density of (1.7–21.1) × 10⁻³ cm⁻³, consistent with X-ray stacking constraints for Milky Way-like galaxies. A significant DM deficit at very small impact parameters is interpreted as likely arising from FRBs hosted by galaxies in the sample. Its cross-correlation signature matches theoretical predictions if 20 FRBs originate within 150 Mpc, suggesting a larger nearby FRB fraction than previously thought rather than establishing individual host associations. The authors forecast a 5σ CGM detection with 10,000 similarly localized FRBs and identify source redshifts of approximately 0.4–0.75 as ideal for intervening-CGM studies.

PublicFast radio bursts can reveal ionized gas around galaxies through their dispersion measures, which trace electrons along the bursts’ paths. Researchers combined measurements from 1,748 precisely located bursts to look for gas surrounding nearby foreground galaxies. For galaxies within 50 megaparsecs, they measured an average excess dispersion measure inside the galaxies’ virial radius, with evidence at about 2.6 sigma. A larger sample showed tentative evidence that the signal decreases farther from galaxy centers, mainly around galaxies similar in stellar mass to the Milky Way. A model fitted to that pattern gives a gas-density profile consistent with earlier X-ray studies. An unexpected deficit near galaxy centers may occur because some bursts come from the sampled galaxies themselves; a theoretical comparison supports this interpretation but does not confirm individual hosts. The researchers predict that 10,000 similarly localized bursts could provide a much stronger detection of the surrounding gas.

Young explorerGalaxies have gas around them that is hard to see. Scientists used quick flashes of radio waves from space to look for that gas. By studying many flashes together, they found clues that the gas is there and may get thinner farther from a galaxy’s middle. The clues are not yet strong enough to be very sure. Some flashes might also come from the nearby galaxies themselves. The scientists think many more flashes could make the gas much easier to find.

A Poisson-bracket operator for Hamiltonian separability: intrinsic geometry and exact defects

Vladimir Martinusi

• Dynamical Systems
• Mathematical Physics
• Chaotic Dynamics
• Exactly Solvable and Integrable Systems

AstronomerThis mathematical study introduces a five-input Poisson-bracket operator that reproduces the Levi-Civita conditions for additive Hamilton–Jacobi separation on canonical pairs. On a symplectic product structure, its off-diagonal values have an intrinsic geometric interpretation, and their vanishing gives a local separation theorem. Its cubic dependence on the Hamiltonian yields an exact perturbation expansion, a linearised separability operator, and a defect functional. For Hamiltonians with a cyclic angle, a relation to the Melnikov integrand lets the homoclinic-orbit integral of the defect determine first-order separatrix splitting. The paper obtains closed-form defects for satellite-theory polar-nodal normal forms and Kerr geodesics. For coordinate selection, the defect identifies the Euler two-centre problem’s separating focal distance as its unique nondegenerate minimum and relates the Sanders and Vasiliev prescriptions to different weightings of one Stäckel residual. In tests using a flattened logarithmic potential, the residual selector and Binney’s shell-orbit fit improve both actions over the median prescription for 48 and 50 of 50 orbits, respectively. In a Miyamoto–Nagai potential, the operator selector reduces the 90th-percentile action spread across 50 orbits from 2.90% to 0.91%. These are mathematical results and model-orbit tests, not observational findings.

PublicSome equations describing motion become easier to solve when written in coordinates that let them split into separate parts. This paper develops a mathematical tool for testing when that separation is possible and for measuring a failure to separate. The authors connect the tool to geometry and, under specified conditions, to a first-order calculation of how a boundary between types of motion splits under a perturbation. They derive formulas for satellite-motion models and Kerr geodesics, and use the tool to help choose coordinates for orbit calculations. Tests in two model gravitational potentials show improvements in calculated orbital quantities compared with particular existing methods. In one 50-orbit test, a measure of variation fell from 2.90% to 0.91%. These results concern mathematical analysis and model tests, not observations, and do not establish that the method is best for every orbit or gravitational model.

Young explorerA motion puzzle can be easier if you find a way to split it into smaller puzzles. The researchers made a math tool to check when that works and help choose a useful way to describe an orbit. They tried it on model orbits, and some calculations improved. They did not make new observations of things in space.

Numerical-Relativity Particle-in-Cell Simulations: Self-Gravitating Collisionless Matter in Dynamical Spacetimes

Jiaxi Wu, Elias R. Most

• General Relativity and Quantum Cosmology
• High Energy Astrophysical Phenomena
• Plasma Physics

AstronomerThe authors present a three-dimensional numerical-relativity particle-in-cell framework for the Einstein–Vlasov system, describing collisionless relativistic matter coupled to dynamical spacetime. Implemented in AthenaK, it combines Z4c evolution in moving puncture gauge with conservative stress-energy deposition on adaptively refined meshes. A Boris-type particle pusher exploits a Lorentz-force-like formulation of geodesic motion. The coupled scheme is validated against spherical dust collapse, then used to follow prolate collapse through collisionless caustics into black-hole formation and to investigate relativistic-cluster stability and nonlinear migration. A further simulation follows two overdensities within a common collisionless envelope through black-hole formation, binary inspiral, merger, and accretion onto the remnant. These are computational demonstrations of the framework, not astronomical observations or a demonstrated resolution of questions about extremal black-hole formation.

PublicThe researchers introduce a computer method for studying how matter moving without collisions interacts with gravity, including when gravity becomes strong enough for black holes to form. The method tracks particles while also calculating how spacetime changes. They check it against a spherical-collapse test and use it to study elongated collapsing matter and the behavior of dense clusters. In another simulation, two concentrations of matter inside a shared surrounding envelope form black holes, spiral together, merge, and continue gathering matter. These are simulated events, not observed ones. The work provides a tool for investigating difficult gravitational problems rather than settling all the questions that motivated it.

Young explorerScientists made a new computer tool to follow tiny bits of matter that move without bumping into each other. It helps them study how gravity pulls matter together. In one computer experiment, two bunches of matter became black holes, circled each other, and joined together. This happened in a simulation, not in a picture of the sky.

EGS-z11-R0: a red, dust-rich galaxy at Cosmic Dawn

Giulia Rodighiero, Andrea Ferrara, Michele Catone+23 more

AstronomerJWST/NIRSpec spectroscopy confirms EGS-z11-R0 at zspec = 11.452 ± 0.021 through significant C IV and C III] detections, making it the most distant spectroscopically confirmed red galaxy reported in this study. Its UV slope, betaUV ≈ −1.0, is unusually red relative to the canonical MUV–betaUV relation at z ≈ 10–12. Emission-line diagnostics indicate a hard ionizing spectrum consistent with extreme star formation; a composite stellar-plus-AGN contribution is also compatible with the data, but is not established. CIGALE modeling of spectroscopy and multiwavelength photometry favors log(M*/Msun) ≈ 9.2–9.6, a star formation rate of 10–40 Msun per year, and AV ≈ 1.2 mag. These model-dependent estimates support the presence of a chemically evolved, dust-enriched galaxy at z ≈ 11.5.

PublicResearchers used JWST spectra to confirm that EGS-z11-R0 is an exceptionally distant galaxy, measuring its redshift as 11.452 ± 0.021 from carbon emission lines. Unlike the predominantly blue galaxies found at similarly early epochs, it has an unusually red ultraviolet spectrum. Modeling its spectrum and images favors substantial dust obscuration and a star formation rate of 10–40 times the Sun’s mass per year. The emission lines are consistent with intense star formation, although an active galactic nucleus could also contribute; that possibility is not confirmed. The findings support the presence of a dust-enriched, chemically evolved galaxy very early in cosmic history.

Young explorerAstronomers used the JWST telescope to study a galaxy very, very far away. Its light shows us what it looked like long ago. Most galaxies found from that early time look very blue, but this one looks much redder. The scientists’ best model suggests that dust helps make it look red and that it is making lots of stars. An extra-bright center might help light it up too, but they are not sure.

Magnetic properties of the Abell 3391-3395 system revealed using wide-field MeerKAT polarimetry

V. Gustafsson, M. Brüggen, C. Tasse+1 more

• Cosmology and Nongalactic Astrophysics

AstronomerMeerKAT full-polarization observations of the interacting Abell 3391-3395 system, using a three-pointing mosaic, yielded an RM grid of 434 polarized background sources with a field-averaged density of 73 sources per square degree. On- and off-target regions were defined from wavelet-filtered eROSITA X-ray contours. The clusters exhibit a statistically significant enhancement in RM scatter relative to the off-target region. The X-ray bridge has comparatively low RM scatter, although a structure-function comparison at matched angular scales tentatively indicates larger RM differences in the bridge than off-target. Together with low per-source depolarization, these findings suggest, rather than establish, a bridge magnetic field relatively ordered on approximately 10 kpc scales but less ordered on larger scales. Diffuse bridge synchrotron emission was not detected, providing improved upper limits on its emissivity.

PublicAstronomers used the MeerKAT radio telescope to investigate magnetic fields around the interacting galaxy clusters Abell 3391 and Abell 3395 and the bridge between them, already known from X-ray observations. They measured how foreground material rotates the polarization of radio waves from 434 background sources. These rotations vary significantly more across the clusters than in a comparison region. The bridge shows relatively little overall scatter, but a separate comparison of differences between sightlines gives tentative evidence for more variation than outside the system. Combined with the small loss of polarization in individual sources, the results suggest that the bridge's magnetic field is relatively orderly over about 10 kiloparsecs, but less orderly over larger distances. This interpretation remains uncertain. No diffuse radio glow was detected in the bridge, allowing tighter limits on how strongly it emits.

Young explorerTwo huge groups of galaxies have a bridge between them that shows up in X-ray pictures. Scientists used a radio telescope to study signals coming from far behind the groups. Magnetic fields along the way can twist those signals. The scientists found clearer changes around the galaxy groups. In the bridge, the clues suggest that the magnetic field may be lined up more neatly in smaller patches and less neatly across bigger areas, but they are not sure yet. They also looked for a faint radio glow from the bridge and did not find it.

The Hunt for Red Dual AGNs I: Spatially-Resolved Mid-IR Dual AGNs in the DESI Legacy Imaging Surveys

Ryan W. Pfeifle, Kimberly A. Weaver, Barry Rothberg+13 more

AstronomerThe study reports 155 spatially resolved mid-infrared dual-AGN candidates selected using WISE W1-W2 colors in systems classified as merger candidates from DESI Legacy Imaging Surveys images. Spectroscopic follow-up confirms 78 candidates as galaxy mergers: 13 contain bona fide mid-IR dual AGNs, while 65 remain strong dual-AGN candidates requiring further examination. Another 48 candidates are rejected as non-merger contaminants, and 29 await spectroscopic coverage. The confirmed and high-confidence dual-AGN candidates span separations of 14.5-129 kpc, with more than half above 50 kpc. Their nuclear optical BPT classifications are diverse, with Seyfert-Seyfert and Seyfert-HII pairings dominant. Among confirmed mid-IR dual AGNs, 31% occur in mergers involving at least three galaxies. Whereas conventional searches typically emphasize optical selection and separations of 10 kpc or less, simulations predict early obscuration and a substantial dual-AGN population beyond 10 kpc. These preliminary findings underscore the value of multiwavelength selection, but most merger-confirmed systems still lack definitive dual-AGN confirmation.

PublicResearchers searched for merging galaxies in which both galaxies have active central supermassive black holes. Using infrared colors and optical images, they selected 155 possible systems. Follow-up spectroscopy has confirmed 78 as galaxy mergers, but only 13 have so far been confirmed to contain two active galactic nuclei; the other 65 need further examination. Another 48 candidates were rejected as non-merger contaminants, and 29 still await spectroscopy. The confirmed and strong candidates have galaxy-center separations of 14.5-129 kiloparsecs, with more than half above 50 kiloparsecs—well beyond the separations usually targeted in such searches. Simulations had predicted that pairs could occur at these wider separations and could be obscured early in a merger. The findings highlight why combining infrared and optical observations matters, although many of the proposed pairs remain unconfirmed. Of the confirmed pairs, 31% belong to mergers involving three or more galaxies.

Young explorerSome galaxies are coming together, and each can have a giant black hole in its middle. When the black holes are active, their neighborhoods shine brightly. Scientists looked for pairs of these bright galaxy centers using infrared light and pictures of galaxies. They found 13 pairs they could confirm, plus many more that still need checking. Many of the confirmed and possible pairs are much farther apart than scientists usually look. Looking with different kinds of light helps scientists find pairs they might otherwise miss.

Too shy to spin? Cosmic wallflowers as proto-globular clusters

Floor van Donkelaar, Lucio Mayer, Pedro R. Capelo

• High Energy Astrophysical Phenomena

AstronomerUsing the high-resolution MassiveBlackPS simulation at z ~ 7.6, this study compares stellar rotation in star-forming clusters produced by gravitational instability in galactic discs and isolated circumgalactic systems born from cosmic filaments, termed cosmic wallflowers. The simulated disc clusters are strongly rotation-dominated and reach higher rotational velocities, while wallflowers rotate more slowly and span a broad range of v/σ. In rotational velocity and stellar surface density, a lower-density, weakly rotating subset of wallflowers lies close to the observed Milky Way globular cluster population; disc clusters remain offset. Denser, more rotationally supported wallflowers may follow another evolutionary pathway, possibly connected to massive black hole seed formation. Gas-rich wallflowers preferentially occupy the low-rotation regime. These simulation findings suggest that formation environment and baryonic content shape initial cluster dynamics. Weakly rotating, gas-rich wallflowers are proposed as proto-globular cluster candidates, but their evolution into present-day systems through angular momentum loss and dynamical heating remains a possibility rather than a demonstrated outcome.

PublicA computer simulation of the early universe suggests that where a star cluster forms can influence how it spins. The study compares clusters born inside galaxy discs with isolated clusters formed from cosmic filaments outside those discs, nicknamed cosmic wallflowers. In the simulation, disc clusters are strongly supported by rotation, while wallflowers spin more slowly and show a wider balance between ordered rotation and random stellar motions. Some lower-density, slowly rotating wallflowers resemble observed globular clusters in the Milky Way in both rotation speed and the amount of stellar mass packed into a given area. Wallflowers rich in gas tend to fall in the slow-rotation group. The researchers propose that these could be young precursors of globular clusters, if their motions change over time. Denser, more rotation-supported wallflowers might instead have a different future, possibly connected to the formation of massive black hole seeds. These are simulated patterns and proposed evolutionary links, not observations of clusters becoming globular clusters or black holes.

Young explorerScientists used a computer to imagine how groups of stars formed when the universe was very young. Some groups were born inside galaxies, and others formed outside them along long strands of material. In the computer, the groups inside galaxy discs spun strongly. The outside groups, nicknamed cosmic wallflowers, spun more slowly. Some slow-spinning wallflowers were a bit like old groups of stars we see in our own galaxy. The scientists think these wallflowers might grow into groups like those, but the computer study has not shown that they really will.

Constraining Baryonic Feedback at z∼1 with the Hα Luminosity Function

Ivan Rapoport, Vincent Desjacques, Ehud Behar+1 more

AstronomerThis simulation study tests how baryonic feedback affects the Hα luminosity function in Illustris and IllustrisTNG. The emission models include star-forming H II regions, collisional excitation and recombination in diffuse gas, and AGN-driven photo-excitation, with direction- and metallicity-dependent dust attenuation, thermal sputtering, and Lyman-series photon propagation. A single parameter connecting star formation rate to H II-region Hα luminosity is calibrated against observed luminosity functions at z ≈ 1–1.5. For simulated galaxies with Hα luminosities ≥10^41 erg s⁻¹, diffuse gas supplies approximately 5–15% of the total Hα emission in both simulation sets. AGN photo-excitation modestly enhances the bright end overall, despite dominating the Hα emission of the most luminous Illustris galaxies. The lower-feedback IllustrisTNG models fit the observed luminosity function across all emission prescriptions considered, whereas the higher-feedback Illustris predictions struggle at both ends. The authors highlight tension with stacked kSZ measurements and argue that combining these probes can constrain feedback, gas properties, and emission-line physics.

PublicHow strongly processes within galaxies affect their gas and star formation remains uncertain. This study explores that uncertainty using two sets of galaxy simulations and models of Hα, a particular kind of light emitted by hydrogen. The researchers adjusted one model parameter to match observed counts of galaxies at different Hα brightnesses. In the simulations, spread-out gas contributes about 5–15% of the total Hα light for galaxies above the study’s stated brightness threshold. Excitation by active galactic nuclei changes the predicted abundance of very bright galaxies only modestly overall, although it supplies most of the Hα light in the brightest Illustris galaxies. The lower-feedback IllustrisTNG models reproduce the observed brightness distribution better than the higher-feedback Illustris models. These are model-dependent findings, not direct measurements of the different light sources. The authors emphasize that tension with a separate set of measurements, called stacked kSZ measurements, makes combining the two tests valuable.

Young explorerScientists made computer galaxies to learn how changes to their gas affect a special light from hydrogen. They compared their pretend galaxies with real galaxy observations. The models with gentler effects on the gas matched the observed pattern of brightness better. Spread-out gas made a small part of the light, too. But another kind of measurement raises questions, so scientists still have more to figure out.

Diffuse Galactic Backgrounds with SPHEREx: A Pilot Study of Background Modeling and Its Impact on Extinction

Wanggi Lim, Jae Hwan Kang, Keunho J. Kim+1 more

AstronomerThis observational pilot study uses SPHEREx spectra to model diffuse Galactic background emission, a major systematic uncertainty in infrared extinction studies. Large Median Filter maps span 0.75–5 micrometers, but the extinction analysis is restricted to the cleaner subset at wavelengths of at least 3 micrometers. In this Galactic-plane field, comparison with an earlier masked-median model yields a median channel-by-channel background difference of about 6%. The maximum absolute change in normalized optical depth is approximately 7.4 near 3.205 micrometers. These field-specific results underscore the importance of wavelength-dependent background modeling and demonstrate a practical framework for controlling background systematics and improving constraints on dust opacity and extinction.

PublicResearchers used SPHEREx observations of one trial region in the Milky Way’s plane to study diffuse infrared light that complicates measurements of how dust blocks light. They made background maps from 0.75 to 5 micrometers using a method called a Large Median Filter, but analyzed dust extinction only at the cleaner wavelengths of 3 micrometers and longer. Compared with an earlier background model, the median difference across wavelength channels was about 6%. The largest absolute change in normalized optical depth, a measure used in the extinction analysis, was about 7.4 near 3.205 micrometers. This pilot result shows why the background must be modeled separately at different wavelengths; it does not establish that the same differences occur throughout the Galaxy.

Young explorerScientists want to learn how space dust blocks light, but a glow behind the dust makes that tricky. They used SPHEREx to study one small test patch of our galaxy. They mapped infrared light from 0.75 to 5 micrometers, but used only the cleaner part, at 3 micrometers and longer, to study the dust. Two ways of estimating the glow differed by about 6% in the middle of their comparisons. A dust-blocking calculation called normalized optical depth changed by as much as about 7.4 near 3.205 micrometers. That does not mean the dust changed: it shows why estimating the glow carefully matters. Other patches might give different results.

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

J. Li, J. P. U. Fynbo

AstronomerThe authors develop and test a purely astrometric quasar-selection recipe using Gaia DR3. For confirmed quasars and stationary sources, proper-motion signal-to-noise follows a Rayleigh-like distribution; correlations between the two proper-motion components and nonlinear error propagation are important. They use the Mahalanobis distance from zero proper motion, fitting Gaia-CRF3 with a scaled chi-squared distribution having k=2 and scale s=1.1485. Their approximately 2-sigma Gaussian-equivalent cut is D²_M(μ)<7.097, combined with a parallax condition and ruwe<1.4. The selection recovers 90.25% of SDSS DR16Q confirmed quasars and reportedly achieves approximately 95% quasar purity, improving completeness and purity relative to literature strategies. The abstract separately states 95% recovery of known quasars without explaining its relationship to the SDSS recovery figure. An application identifies 24 very luminous z>2 quasars, including ten new discoveries and seven with corrected redshifts. Improved selection for future surveys is a proposed use, not a demonstrated survey outcome.

PublicThe researchers tested a way to find quasars using Gaia DR3 measurements of apparent motion and parallax, rather than selecting them by their light properties. Their method checks whether an object's measured motion is consistent with zero while accounting carefully for linked measurement errors, and also applies parallax and data-quality cuts. It recovered 90.25% of confirmed quasars in one comparison catalogue and achieved a reported purity of about 95%—meaning roughly 95 out of 100 selected objects were quasars. The abstract also quotes 95% recovery of known quasars, without explaining how that figure relates to the first test. Applying the method, the team identified 24 very luminous quasars at redshifts above 2, including ten new discoveries, and corrected earlier redshift estimates for seven others. The authors suggest that the method could improve future quasar surveys.

Young explorerQuasars are very bright things far away in space. The researchers tested a way to find them by looking for things that seem to stay still in Gaia's sky measurements. Because measurements can be a little wrong, they carefully checked those errors too. Their method found most of the quasars in a group already known to scientists, but it was not perfect. They also identified 24 very bright, faraway quasars. Ten were new discoveries, and they corrected earlier clues about how far away seven others were. They hope this method will help people find more quasars.

Beyond the Disc--Spheroid Dichotomy at 0.6 < z < 8.0: Evidence for a Morphological Indeterminacy Regime from JWST

Igor Kolesnikov, Reinaldo Ramos de Carvalho, Jeong Hwan Lee+3 more

AstronomerThe study compares morphological classifications over 0.6 < z < 8.0 using JWST observations of 15,567 galaxies and 6,099 synthetic galaxies from IllustrisTNG. Its unsupervised-supervised hybrid approach uses the non-parametric MEGG system, combining the second moment of the light distribution, entropy, Gini, and Gradient Pattern Analysis without relying on visual labels or prescribed light profiles. Parametric and non-parametric classifications broadly agree at z < 2.5 but diverge systematically at higher redshift. The authors call this the Morphological Indeterminacy Regime (MIR), where classical disc and spheroidal categories do not uniquely describe the population; the mixed-interpretation fraction rises with redshift, reaching approximately 0.55 at z > 2.5. Cross-domain and projection-invariance tests support classification stability across data sets and viewing angles. At 2.5 < z < 8.0, MIR galaxies have median log(M★/M☉) ≈ 9.7, intermediate between discs at approximately 9.5 and spheroids at approximately 10.1; irregulars have mass distributions similar to MIR galaxies. The interpretation that MIR systems are dynamically young galaxies not yet settled into the classical Hubble sequence is an inference from these findings, rather than a direct dynamical measurement.

PublicGalaxy shapes can offer clues to how galaxies assembled, but familiar shape labels become less clear in the early Universe. This study compares classification methods using JWST observations of 15,567 galaxies alongside 6,099 simulated galaxies. A machine-learning approach measures patterns in galaxy light without depending on visual labels or assuming a particular light profile. The methods broadly agree below a redshift of 2.5, but systematically disagree at higher redshifts, corresponding to earlier cosmic times. The authors call this a Morphological Indeterminacy Regime: the same galaxy can receive different interpretations rather than a unique disc or spheroid label. The share of such mixed-interpretation galaxies increases with redshift, reaching about 55% above redshift 2.5. Tests suggest the classifications are stable across data sets and viewing angles. These galaxies tend to have stellar masses between those of lower-mass discs and higher-mass spheroids, with mass distributions resembling those of irregular galaxies. The authors interpret the pattern as evidence for young, still-assembling systems that have not yet settled into familiar galaxy shapes; that explanation is not a direct measurement of their internal motions.

Young explorerGalaxies are huge groups of stars, and their shapes can help us learn how they grew. Scientists studied telescope pictures and computer-made galaxies. For galaxies seen much earlier in the Universe, different ways of sorting shapes often gave different answers. About half of the galaxies in that earlier group had these mixed answers. Tests suggested this was not simply because the galaxies were viewed from different directions. The scientists think many of these galaxies may still have been growing and settling into shape, but that is their explanation, not something they watched happen.

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

Yufan Zhou, Tianchi Zhang, Shihong Liao+3 more

• Cosmology and Nongalactic Astrophysics

AstronomerThis study compares idealized N-body simulations of the Milky Way–M31 system under pure Newtonian, ΛCDM, and w₀wₐCDM scenarios, varying galaxy masses and proper motions within current observational constraints. Hubble expansion has negligible effects at low M31 tangential velocities, particularly for systems merging within a Hubble time. Above 66.5 km/s, ΛCDM runs show noticeable merger delays relative to Newtonian runs and can change the simulated system’s eventual fate, although the isolated-pair idealization and assumed expansion history break down in this regime. Delays are smaller in w₀wₐCDM runs, and including M33 and the Large Magellanic Cloud reduces merger-time differences. These are simulation-dependent findings, not a determination of the Milky Way–M31 outcome; the actual influence of expansion remains contingent on more precise masses and proper motions.

PublicCould the universe’s expansion affect whether and when the Milky Way and Andromeda merge? Researchers tested this with simplified computer simulations using different galaxy masses, motions, and descriptions of cosmic expansion. When Andromeda’s sideways motion is low, expansion makes little difference. At higher sideways speeds, above 66.5 kilometers per second, some expanding-universe simulations delay the merger or even change the system’s eventual outcome. However, the simplifying assumptions become unreliable in those cases, so this is not a firm prediction for our galaxy. Adding the galaxies M33 and the Large Magellanic Cloud reduces the differences in merger timing. More precise measurements of the galaxies’ masses and motions are needed to establish how much expansion actually matters.

Young explorerOur galaxy, the Milky Way, and another galaxy called Andromeda might someday join together. Scientists used computer models to ask whether the universe getting bigger could change that. In their models, it barely mattered when Andromeda moved slowly sideways. When it moved faster sideways, the growing universe could make the galaxies take longer to meet, or change whether they joined at all. But those models leave things out and become less reliable in those cases. Scientists still need to learn more about how heavy the galaxies are and how they move before they can say what will really happen.

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

Fabio Pacucci, Raffaella Schneider, Harley Katz+88 more

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena

AstronomerThis white paper advocates a coordinated JWST Multi-Cycle Treasury program to constrain early black hole seeding, growth, and co-evolution with host galaxies, and to clarify the nature of broad-line emitters and Little Red Dots (LRDs). JWST has revealed abundant faint active galactic nuclei and compact high-redshift LRDs, but the interpretation of LRDs as accreting massive black holes remains debated. High inferred black hole number densities and apparent excesses of black hole mass relative to stellar mass in some systems challenge simple seeding and growth scenarios, while current samples cannot disentangle seed signatures from subsequent growth. The proposed program would combine grating spectroscopy, deep MIRI imaging, and repeated observations for variability analysis, using uniformly selected samples extending to low black hole and host-galaxy masses. Self-consistent black hole mass functions, Eddington-ratio distributions, and host properties could provide stronger complementary constraints; these are proposed capabilities, not results of a completed program.

PublicJWST has found many faint active galactic nuclei, where black holes are feeding on surrounding material, along with compact objects in the early universe called Little Red Dots. Their nature is still debated: feeding massive black holes are one leading explanation for the dots. The inferred abundance of early black holes, and signs that some are unusually massive compared with their galaxies’ stars, challenge simple ideas about how black holes began and grew. Existing observations cannot reliably separate their beginnings from their later growth. This white paper proposes a coordinated JWST observing program spanning multiple observing cycles, combining detailed spectra, deep infrared images, and repeat visits to track changes in brightness. By studying consistently selected samples that include lower-mass black holes and galaxies, the program could better test black hole origins, growth, and connections to galaxy evolution. It is a proposal for stronger tests, not a report that these mysteries have been solved.

Young explorerJWST has spotted lots of faint, bright centers of galaxies and tiny red-looking objects very far away. Some of those little red dots might get their light from matter falling toward big black holes, but scientists are not sure. They also do not yet know how the first big black holes started or grew. This paper suggests a plan: use JWST to look carefully at the same patches of sky again and again, and study their light in different ways. That could help scientists learn what the red dots are and how black holes and galaxies grow together. The plan has not answered those questions yet.

Effect of ultralight dark matter on compact binary mergers

Kabir Chakravarti, Soham Acharya, Sumanta Chakraborty+1 more

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

AstronomerThe study models how an ultralight dark matter (ULDM) environment could affect compact-binary merger rate densities. A baseline astrophysical model covering eccentric and quasi-circular binaries is extended to include ULDM accretion and dynamical friction. The modeled merger population indicates that nonzero ambient ULDM densities can potentially change merger statistics relative to the baseline. Comparison with GWTC-3 gives the best agreement for an ambient density of approximately 10^6 GeV/cm^3 and eccentricity approximately 0.5. These are model-comparison findings, not a detection of ULDM; the authors identify potential observational signatures and possible constraints on dark matter's existence and density distribution in galaxies.

PublicCould dark matter around pairs of compact objects change how often they merge? The researchers explored this with a model that includes a proposed ultralight form of dark matter. In the model, matter falling onto the objects and drag from their surroundings affect their orbits and can change the merger statistics. Comparing the predictions with gravitational-wave events in the GWTC-3 catalogue, the researchers found the closest agreement for particular choices of dark matter density and orbital shape. This does not establish that ultralight dark matter is present, but suggests that merger statistics could help test the idea and constrain how dark matter is distributed in galaxies.

Young explorerTwo objects in space can circle each other and then join together, making ripples in space. Scientists made a model to ask whether a kind of invisible matter might change how often this happens. Some choices in their model fit the ripple records better than others. That is a clue they can study, not proof that this invisible matter is there.

Probing circumstellar interaction with spectroscopy of ZTF hydrogen-rich superluminous supernovae

Yang Hu, Ragnhild Lunnan, Priscila J. Pessi+30 more

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerThe study analyses 304 optical spectra of 106 ZTF hydrogen-rich superluminous supernovae and models Hα profiles with Monte Carlo electron-scattering calculations. Narrow Balmer emission supports SLSN-IIn classifications for 105 objects, including six with additional Ia-CSM-like characteristics and three with possible flash-ionisation features; one broad-Balmer-only object is classified as SLSN-II. Post-peak Balmer profiles span approximately symmetric exponential shapes through asymmetric profiles with blue excesses or shoulders. Blue-excess objects favour higher fitted photon-emitting shell velocities and tend to be fainter than objects with persistently symmetric profiles. SLSNe-IIn overlap lower-luminosity SNe IIn in Hα pseudo-equivalent width and FWHM, while their pseudo-equivalent-width evolution is more diverse than in the broad-lined SLSN-II comparison sample. The median Balmer decrement rises from 2.85 before +100 days to 4.40 afterwards and remains below that of the Ia-CSM comparison sample. No Balmer-line morphology unique to SLSNe-IIn is identified in the available lower-luminosity comparison, although some show prolonged high-ionisation emission. The authors interpret the results as supporting interaction with dense circumstellar material produced by enhanced pre-explosion mass loss, and suggest a possible hidden Ia-CSM population among luminous hydrogen-rich interacting supernovae.

PublicResearchers examined 304 spectra—measurements that separate light by wavelength—from 106 exceptionally bright, hydrogen-rich stellar explosions observed by the Zwicky Transient Facility. All but one showed narrow hydrogen emission lines consistent with the explosion interacting with dense surrounding material. After peak brightness, the hydrogen-line shapes varied: some stayed nearly symmetric, while others showed extra emission on their blue side. The latter tended to be fainter, and computer modelling favoured faster-moving light-emitting shells for them. However, the available comparison revealed no hydrogen-line shape exclusive to these superluminous events rather than less luminous interacting supernovae. The results support, but do not directly establish, a picture in which enhanced mass loss before the explosion creates the dense surrounding material. The authors also suggest that some luminous interacting explosions may belong to a hidden Ia-CSM population.

Young explorerScientists studied the light from 106 very bright exploding stars. In almost all of them, the light had clues that the explosion was hitting thick gas around the star. The clues did not all look the same, and some looked like clues from less bright explosions. Scientists think the stars may have shed lots of gas before exploding.

Current Closure and Gamma-Ray Signatures of Spark-Gap and Current-Sheet Activities in Radiative Black Hole Magnetospheres

Koki Kin, Shota Kisaka, Kenji Toma+2 more

AstronomerAxisymmetric general relativistic particle-in-cell simulations investigate black hole magnetospheric currents, variability, and radiation, including inverse-Compton (IC) scattering and two-photon pair production, with and without synchrotron-curvature (SC) radiation reaction. From an initially vertical magnetic field, a polar spark gap and variable equatorial current sheet develop and jointly sustain the global poloidal current. For the explored parameters, SC cooling induces spark-gap oscillations, while the current sheet is less sensitive to cooling. Time-dependent electric fields in the return-current layer trigger magnetic-field rearrangement followed by reconnection. No significant cross-correlation is found between the two regions' variability, suggesting, rather than establishing, dynamical independence. Post-processing ray tracing finds that high-energy particles dominate the bolometric luminosity, with SC and IC emission reaching up to 1% and 0.1% of the Blandford–Znajek luminosity, respectively. The IC-to-SC luminosity ratio is higher at lower viewing angles, attributed to stronger particle-momentum anisotropy near the pole from efficient field-aligned acceleration. Together with energetic estimates, these simulation results suggest that both regions could contribute to high-energy emission in active galactic nuclei, with spark-gap photons reaching sub-TeV energies.

PublicComputer simulations explore how electric currents and radiation develop around a black hole. Two regions emerge: a polar zone where particles are accelerated and a changing sheet of electric current near the equator. Both help maintain the larger current system. For the conditions tested, including energy loss through synchrotron-curvature radiation makes the polar zone oscillate, while the equatorial sheet changes less in response to cooling. The researchers find no significant correlation between the regions' variations, suggesting they may behave independently. Calculations of the escaping radiation show that the highest-energy particles supply most of the emitted power, and that the balance between two radiation processes depends on viewing direction. These are simulation findings, not observations of a real black hole. They suggest that both regions could help produce high-energy light in active galactic nuclei, with the polar region potentially producing photons at sub-TeV energies.

Young explorerScientists used a computer to imagine what happens around a black hole. Their model made two places where tiny particles can help make very energetic light: one near the top and one around the middle. When the particles lost energy by making one kind of light, the top region began to pulse. The two places did not clearly change together. This is a computer result, not something scientists watched happen around a real black hole.

Faint Thermonuclear Transients from the Double Detonations of Common White Dwarfs

Samuel J. Boos, Lars Bildsten

• Solar and Stellar Astrophysics

AstronomerMultidimensional simulations explore double detonations of low-mass carbon–oxygen white dwarf cores with very thin helium shells, extending a channel whose higher-mass models can reproduce normal Type Ia supernova observables. The low-mass models undergo incomplete core burning and produce low radioactive yields. Although the ejecta are formally unbound in isolation, some could remain bound to a nearby companion. Off-center core ignition and incomplete detonation propagation produce a strongly asymmetric nickel-56 distribution, yielding viewing-angle-dependent spectra and light curves; peak bolometric luminosity varies by nearly 2 magnitudes across viewing directions for a single explosion. The synthetic observables fall within the range of faint Type Iax supernovae, and the 0.50-solar-mass models agree well with the photometry of SNe 2008ha and 2024vjm. These comparisons support a possible explanation for faint Iax events, rather than establishing their progenitors.

PublicComputer simulations investigate explosions of low-mass white dwarfs, in which a blast in a thin helium shell triggers another blast in the carbon–oxygen core. Unlike more massive models associated with normal Type Ia supernovae, these simulated stars burn incompletely and make relatively little radioactive material. That material is distributed unevenly, so the same explosion could look very different from different directions, with peak brightness differing by nearly two magnitudes. Some expelled material might also remain gravitationally bound to a nearby companion star. The predicted light and spectra resemble faint Type Iax supernovae; models with half the Sun’s mass match the measured brightness histories of two examples, 2008ha and 2024vjm. This is a promising model comparison, not proof that those observed explosions happened this way.

Young explorerScientists used computers to explore how a small, very dense star might explode. In their models, a blast in the star’s outer layer starts another blast inside, but it does not burn all the way through. The explosion leaves the stuff that helps it shine in an uneven pattern, so it could look brighter from one side than another. Some of the pretend explosions shine much like two faint star explosions people have seen. That is a clue, but it does not prove the real stars exploded this way.

Polarization Signatures of Magnetic Reconnection Bubbles near Black Holes

Yu-Xiang Huang, En-Wei Liang

• General Relativity and Quantum Cosmology

AstronomerMotivated by polarization variability observed across EHT epochs, this study develops time-dependent general relativistic polarized ray tracing with a phenomenological transient magnetic bubble representing localized reconnection. The bubble weakens and reorganizes the ordered field, induces a conservative local kinematic response, and relaxes with finite magnetic memory, while the spacetime, emission prescription, and polarization transport remain fixed. In the modeled cases, azimuthal perturbations favor outward electric-vector position-angle (EVPA) shifts, radial perturbations favor inward shifts, and vertical perturbations mainly suppress polarized intensity; the perturbations also yield distinct polarized morphologies and Stokes Q–U trajectories. In illustrative M87*-like cases, the phase of the β₂ polarization coefficient traces the contribution of local reconfiguration to the ring’s global EVPA twist. These model results suggest diagnostic signatures for future EHT polarimetry, rather than establishing reconnection as the cause of the observed variability.

PublicThe Event Horizon Telescope has observed changes in polarization—the orientation of light’s vibrations—near a black hole. To explore a possible explanation, researchers modeled a temporary magnetic disturbance representing reconnection, a rearrangement of magnetic fields. Their calculations suggest that disturbances affecting different field directions could produce different changes in polarization: some shift its orientation, while others mainly dim the polarized light. Illustrative models resembling M87* also connect a local disturbance to changes in the polarization pattern around the bright ring. The work offers a way to interpret future observations, but it does not show that reconnection caused the changes already observed.

Young explorerLight near a black hole can wiggle in different directions, and telescopes have seen that pattern change. Scientists made a computer model to ask whether a small change in the magnetic field could help explain it. In their model, different magnetic changes made the light’s wiggle pattern turn in different ways or made the specially lined-up light dimmer. This gives scientists clues to look for, but it does not prove what made the real light change.

SMMAN studies of AGN variability. II. Radio and optical quasi-periodic oscillations and changing variability states in the relativistic jet of the blazar PKS 0754+100

Ashutosh Tripathi, Xin Wang, Xi Yan+2 more

AstronomerSMMAN observations of the BL Lac object PKS 0754+100 reveal approximately 280-day radio quasi-periodic oscillations (QPOs) at 4.8 and 23.6 GHz, with possible counterparts in 15 GHz VLBI observations. The onset of a radio variability-amplitude transition, clearest at 15 and 23.6 GHz, coincides with a likely approximately 1.4-day optical QPO detected by TESS. The transition also occurs near the disappearance of a secondary VLBI knot during the lower-variability state and follows an X-ray flare by 100 days. After the transition to higher variability, the 15 and 23.6 GHz light curves show indications of approximately 400-day QPOs. The authors report this as the first apparent shift of a radio QPO toward a lower oscillation frequency in a BL Lac, occurring near the appearance of a much shorter-period optical QPO. The temporal associations suggest, but do not establish, related mechanisms. A proposed interpretation invokes an internal helical jet structure, with an instability or kink developing through magnetic reconnection and propagating outward.

PublicAstronomers detected roughly repeating changes in radio brightness from PKS 0754+100, a type of object called a BL Lac. The pattern repeated about every 280 days in two radio bands and may also appear in a third. When the radio brightness began changing more strongly, satellite observations detected a likely visible-light rhythm of about 1.4 days. Around this transition, a secondary feature disappeared from detailed radio images; an X-ray flare had occurred 100 days earlier. Later radio observations hint at a slower rhythm of about 400 days. The researchers describe this as the first apparent shift toward a slower radio rhythm in a BL Lac. These patterns are not exact clockwork, and the timing does not prove a shared cause. One possible explanation is a disturbance moving outward through a twisted jet, developing as magnetic fields reconnect.

Young explorerAstronomers watched a faraway object whose radio brightness seemed to change in a repeating pattern, about every 280 days. Later, there were hints that the pattern slowed to about 400 days. Near that change, its visible light also seemed to have a much quicker pattern. These rhythms were not as steady as a clock. The scientists think a moving bend in the object's jet might help explain them, but they do not know for sure.

Self-bound quantum dark fermion stars: saturation, a coupling-capped maximum mass, and tidal signatures of a vector dark sector

Ilidio Lopes

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

AstronomerThis theoretical study finds that dark fermions coupled to both scalar and vector mediators can exhibit nuclear-like saturation: an energy-per-particle minimum at finite density produces cold, self-bound matter and general-relativistic stellar solutions with sharp surfaces. The maximum stellar mass is set by the Lagrangian rather than Chandrasekhar scaling and increases eightfold across the saturation window, which closes at a critical vector coupling. For a 1 GeV fermion and the fiducial saturation density, the resulting ceiling across the coupling family is 3.9 solar masses, not a universal bound for all model choices. Metastable couplings yield disconnected stable branches of dilute, gravitationally bound stars and dense, self-bound stars. Quantum-pressure corrections occupy a surface layer a few Compton wavelengths thick, govern the smallest nuggets, and change stellar masses by less than one part in 10^21. A fiducial 1.4-solar-mass model has radius 13.3 km, compactness 0.155, and tidal deformability 1.6 × 10^3, almost an order of magnitude above the measured neutron-star value cited in the abstract. The author argues that, for specified particle mass and couplings, one well-measured inspiral could distinguish these theoretical stars from neutron stars and scalar-only models; nonzero deformability at maximum mass could distinguish them from black holes in principle. No detection of these dark stars is reported.

PublicThe paper calculates how hypothetical dark matter particles could form compact stars if they interact through two kinds of mediating fields. In the model, the matter settles at a preferred density and holds itself together, producing stars with sharp surfaces. The interactions also limit how massive these stars can become: for a chosen particle mass and reference density, the ceiling across a family of interaction strengths is 3.9 times the Sun's mass. Some interaction choices allow two separate stable families, one diffuse and held together by gravity, the other dense and self-bound. A sample star with 1.4 times the Sun's mass is predicted to have a radius of 13.3 kilometres and to deform under tidal forces much more than the measured neutron-star value used for comparison. The author proposes that a sufficiently precise measurement of an inspiralling pair could distinguish these stars from neutron stars for specified model parameters, and in principle their tidal response could also distinguish them from black holes. These are theoretical predictions, not observations of dark stars.

Young explorerCould invisible dark matter make its own stars? A scientist's calculations say it might, if its tiny pieces interact in a certain way. The imagined stars would hold themselves together and have clear edges. There would also be a limit to how big they could grow. Watching how one stretches while circling a companion might help tell it apart from other stars. These stars have not been found in this study; they are a prediction.

Probing the origin of the LHAASO Peanut with a hidden central accelerator

Agnibha De Sarkar

AstronomerLHAASO detected a highly asymmetric, giant Peanut-shaped structure in ultra-high-energy gamma rays at Galactic latitude b ≈ −17.5°. The study tests a hidden central accelerator within a projected anisotropic particle halo. Its baseline model accounts for the diffuse strip and central excess; enhancing the far excess requires a phenomenological local magnetic-field reorientation toward the line of sight and particle-conserving redistribution of downstream electrons into a prescribed emitting column. Exploring source ages, magnetic-field strengths, and parallel diffusion coefficients, with radiative cooling included in viewing-geometry estimates, shows that relatively rapid parallel transport enhances the far component while retaining a dominant diffuse strip. Representative configurations are compatible with the observed spectral energy distribution, but the modeled far component remains weaker than the central component above 100 TeV, even when their fluxes are comparable at 25–100 TeV. The hidden-accelerator interpretation is plausible, not established, and reproducing the compact components’ relative brightness remains difficult within this phenomenological framework.

PublicLHAASO has detected a large, uneven, peanut-shaped glow in extremely energetic gamma rays. Researchers tested whether an unseen central source accelerating particles could explain it, with particles spreading more readily in some directions than others. Their model accounts for an extended strip of emission and a central bright region. To strengthen a more distant bright region, they introduced a prescribed change in magnetic-field direction and redistributed electrons into a narrow emitting region. Some model configurations are compatible with the observed energy spectrum, but the distant region remains too weak relative to the center at the highest energies considered. An unseen central accelerator is therefore a plausible explanation, not a confirmed discovery.

Young explorerScientists saw a huge, lopsided peanut shape glowing in a kind of light our eyes cannot see. They tested whether a hidden particle launcher in the middle could make it. Their model explains some of the glow, but has trouble making a farther bright spot bright enough compared with the middle. The hidden launcher is still an idea, not something they have found.

Stochastic Acceleration Downstream of Astrophysical Shocks

Antonio Capanema, Pasquale Blasi

• High Energy Physics - Phenomenology
• Plasma Physics

AstronomerThis theoretical study numerically couples the downstream particle transport and turbulent power-spectrum evolution at supernova-remnant shocks, including nonlinear wave damping by resonantly interacting particles. It compares turbulence generated solely upstream and advected through the shock with cases that include additional downstream turbulence. In the calculations, waves self-generated upstream through the Bell instability do not significantly modify the downstream particle spectrum; turbulent cascading in wavenumber space rapidly drains their energy and further limits stochastic acceleration. Additional downstream turbulence, however, can produce meaningful second-order Fermi acceleration and reshape the particle spectrum, potentially altering gamma-ray emission from downstream proton-proton scattering. Although slower than diffusive shock acceleration, stochastic acceleration may matter over the longer times particles are expected to remain downstream, with possible consequences for multimessenger spectra. These are model results and predicted implications, not reported observations.

PublicThe study models how energetic particles and turbulent waves evolve behind the shock waves of supernova remnants. Its numerical calculations compare waves carried in from ahead of the shock with cases where more turbulence is supplied behind it. Waves generated ahead of the shock by the mechanism studied do little to change the particles’ energy distribution, and the transfer of turbulent energy toward smaller scales further weakens their ability to accelerate particles. If extra turbulence is supplied behind the shock, however, repeated random interactions with waves can meaningfully change particle energies. The authors suggest this could alter the gamma rays produced when energetic protons collide with other protons. This extra acceleration is slower than acceleration at the shock itself, but particles may spend much longer behind the shock. The conclusions come from calculations rather than observations.

Young explorerAfter a star explodes, a strong shock wave can speed up tiny particles. Scientists used computer calculations to ask whether swirling waves behind the shock could give those particles more little pushes. In their model, waves brought through from in front of the shock did not help much. But if extra waves were added behind it, they could change how much energy the particles had. That might change the very energetic light the particles help make. This is what the calculations suggest, not something the scientists report seeing.

The Fate of Collisional Neutrino Flavor Conversion: Fixed Points, Period Doubling, and Chaos

Jiabao Liu, Lucas Johns, Hiroki Nagakura

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

AstronomerThis theoretical study constructs homogeneous collective-precession states with stationary flavor populations in two-flavor quantum kinetics with collisional relaxation, addressing the uncertain outcome of collisional flavor instability (CFI). The method accommodates arbitrary energy spectra and energy-dependent collision rates. Numerical examples show persistent oscillations and a period-doubling route to chaos; even in these regimes, the stationary solutions estimate time-averaged flavor populations to within 10% in the reported tests. These fixed points offer physically motivated input for incorporating CFI into astrophysical simulations. Implications for neutrino heating and ejecta nucleosynthesis in core-collapse supernovae and neutron star mergers remain to be established in those settings.

PublicNeutrinos influence how exploding stars and merging neutron stars evolve and make elements, but how these particles change between types in such dense environments remains poorly understood. The researchers developed a mathematical method to estimate the average proportions of two neutrino types while accounting for collisions. Their numerical tests showed both lasting oscillations and increasingly complex behavior leading to chaos. Even then, the method estimated the average proportions to within 10% in those tests. This is a theoretical and numerical result, not an astronomical observation. It could help future simulations assess how neutrino type changes affect heating and element production.

Young explorerWhen stars explode or two neutron stars crash together, tiny particles called neutrinos can change from one kind to another. Scientists made a math model to help work out how much of each of two kinds there might be on average. In their computer tests, the amounts kept changing, sometimes in very complicated ways, but the model still gave close estimates of the averages. They hope this will help them model these space events and how they make new elements. They have not yet shown that it works inside a real explosion or star crash.

Unveiling a Concentration of Hard X-Ray Point Sources in the Nuclear Stellar Disk with XMM-Newton

Shifra Mandel, Kaya Mori, Gabriele Ponti+10 more

• Astrophysics of Galaxies

AstronomerUsing XMM-Newton Galactic Plane Heritage Survey data covering the central 20° × 2° of the Milky Way, the authors identify for the first time a concentration of extremely hard X-ray sources at absolute Galactic longitude below 1.3° and absolute Galactic latitude below 0.3°, overlapping the nuclear stellar disk. They determine that the hardness is intrinsic rather than caused by high line-of-sight column density. Unlike the softer sources, this population does not trace the stellar mass distribution, indicating an overabundance relative to the underlying stars. Comparisons of observed hardness distributions with simulated spectra for several source types suggest that a significant subset of the Galactic Center X-ray population may be intermediate polars containing massive white dwarfs. Formation through dynamical processes remains a possible interpretation, not an established result.

PublicAn XMM-Newton survey of the central 20° × 2° of the Milky Way has revealed a previously unidentified concentration of sources emitting unusually high-energy, or hard, X-rays. These sources lie within 1.3° of zero Galactic longitude and 0.3° of zero Galactic latitude, in a region overlapping the nuclear stellar disk. The researchers find that the hard emission is a property of the sources themselves, rather than an effect of intervening material. Unlike softer X-ray sources, their distribution does not follow the distribution of stellar mass, indicating more sources than that stellar population would suggest. By comparing observations with simulated spectra, the team suggests that a significant subset of the Galactic Center's X-ray sources may be systems called intermediate polars containing massive white dwarfs. The idea that dynamical interactions helped form them remains uncertain.

Young explorerAstronomers used XMM-Newton to study a patch of our galaxy's middle measuring 20 degrees by 2 degrees. They found a new crowd of objects giving off especially energetic X-rays. The crowd is close to the middle: less than 1.3 degrees away in Galactic longitude and less than 0.3 degrees away in Galactic latitude. The scientists found that the X-rays are energetic because of the objects themselves, not because of material in the way. The crowd also does not follow where the mass in stars is spread out. The team made computer models of different kinds of objects to compare with what they saw. Those comparisons suggest that many of the X-ray objects near the galaxy's middle might be systems containing heavy white dwarfs, a kind of star remnant. Encounters between objects might have helped make these systems, but the scientists have not shown that for sure.

The shape and velocity of black hole coronas

Henric Krawczynski, Kun Hu, Sohee Chun

• General Relativity and Quantum Cosmology

AstronomerCygnus X-1 shows approximately 4% X-ray polarization aligned with its radio jet, commonly interpreted as Comptonization of lower-frequency seed photons in a laterally extended corona whose outflow enhances the polarization. The authors calculate the outflow velocities required in velocity-stratified cylindrical corona models as a function of stationary-frame aspect ratio h=H/(2R). Models with h≤0.8 and top-of-corona velocities β=0.5–0.9 reproduce both the observed photon index Γ=1.6 and the polarization; no suitable solutions are found at larger h within the models considered. The authors favor compact coronae near the black hole on energetic and reprocessing grounds, rather than reporting a direct measurement of the corona's absolute size.

PublicX-rays from the black hole binary Cygnus X-1 have a measured polarization of about 4%, aligned with its radio jet. A common explanation is that lower-energy light gains energy by scattering through a hot plasma region called a corona, with fast outward motion strengthening the polarization. The authors model cylindrical coronas to ask how tall they can be relative to their width. Their models match both the observed X-ray spectrum and polarization when the height is no more than 0.8 times the diameter and plasma at the top moves at 50–90% of light's speed. They find no matching solutions for taller proportions in the models studied. They argue that a compact corona close to the black hole is preferred because it could draw energy more efficiently and be less exposed to its own light after that light is reprocessed by surrounding dense material; this is not a direct size measurement.

Young explorerLight from near a black hole called Cygnus X-1 has a small but clear preference for wiggling in one direction, lined up with a jet. Scientists tried calculations of a hot cloud that could make the light look this way. A cloud that is wider than it is tall, with stuff rushing out very fast at the top, could fit what they see. Taller-shaped clouds did not work in the models they tried. They think a small cloud close to the black hole makes sense, but they have not measured exactly how big it is.

Measurement of the Neutrino Spectrum along the Galactic Plane with IceCube

IceCube Collaboration, R. Abbasi, M. Ackermann+97 more

• Astrophysics of Galaxies

AstronomerUsing 10 years of IceCube neutrino-induced particle-shower data, the authors report the first measurement of high-energy neutrino-flux variation along the Galactic plane, fitting flux normalization and spectral index independently of model expectations in multiple regions. At a neutrino energy of 5 TeV, the flux per solid angle in the inner region, absolute value of Galactic longitude less than 30 degrees and absolute value of Galactic latitude less than 8 degrees, is approximately five times that in the outer region, absolute value of longitude greater than 60 degrees and absolute value of latitude less than 8 degrees. The inner and outer spectral indices are respectively 2.76 with uncertainties of +0.18 and -0.15, and 3.13 with uncertainties of +0.57 and -0.37. For the shared emission region with Galactic longitude between 15 and 125 degrees, the neutrino measurements and LHAASO TeV gamma-ray measurements are compatible within uncertainties, assuming hadronic gamma-ray production.

PublicTen years of IceCube data have provided the first measurement of how the high-energy neutrino signal varies along the plane of the Milky Way. The researchers fitted both the signal strength and how it changes with energy without imposing model expectations. At 5 TeV, the neutrino flux per equal area of sky is approximately five times higher in the inner region than in the outer region. The inner region has an absolute value of Galactic longitude below 30 degrees; the outer region has an absolute value above 60 degrees. Both have an absolute value of Galactic latitude below 8 degrees. The fitted spectral indices, which describe the energy dependence, are 2.76 with uncertainties of +0.18 and -0.15 for the inner region and 3.13 with uncertainties of +0.57 and -0.37 for the outer region. In a shared region spanning Galactic longitudes from 15 to 125 degrees, the neutrino measurements agree within uncertainties with LHAASO measurements of TeV gamma rays, provided those gamma rays are produced through processes involving hadrons.

Young explorerScientists used 10 years of IceCube observations to study tiny particles called neutrinos coming from the flat part of our galaxy. For the first time, they measured how the high-energy neutrino signal changes along that part of the sky. At an energy called 5 TeV, the signal from an equal-sized patch of sky was about five times stronger in the inner region than in the outer region. They also measured how the signal changes with energy, but those measurements have some uncertainty. In one shared part of the sky, they compared the neutrinos with very energetic light measured by LHAASO. The measurements could fit together, allowing for uncertainty, if the light was made through processes involving particles called hadrons.

Depth of Maximum of EAS and Mean Mass Composition of Primary CRs from the Spatial and Temporal Distribution of Cherenkov Light According to TAIGA-HiSCORE Data

M. Yu. Ternovoy, V. V. Prosin, E. A. Osipova+73 more

AstronomerThe study presents the energy dependence of the extensive-air-shower maximum depth, X_max, reconstructed from TAIGA-HiSCORE observations during 2021–2025. Reconstruction uses simulation-derived relations linking X_max to the steepness of the Cherenkov-light lateral distribution (P-method) and to the pulse full width at half maximum (tau-method). The reconstructed depths are converted into mean logarithmic primary mass, ⟨ln A⟩, to characterize cosmic-ray composition, and compared with measurements from Tunka-133, the Pierre Auger Observatory, LHAASO, TALE, and other experiments. The abstract gives no numerical results, composition trend, uncertainties, or assessment of agreement between experiments.

PublicThe researchers used observations recorded by TAIGA-HiSCORE from 2021 to 2025 to study where showers of particles produced by incoming cosmic rays reach their maximum development in the atmosphere, and how that depth depends on the incoming particle’s energy. They inferred the depth from the spatial pattern and pulse duration of Cherenkov light, using relationships established in simulations. They then translated those depths into an estimate of the cosmic rays’ average logarithmic mass and compared their results with other experiments. The abstract does not say whether the inferred composition becomes heavier or lighter with energy, or how closely the experiments agree.

Young explorerWhen a particle from space hits the air, it can make a shower of more particles and a flash of light. Scientists watched that light with a detector called TAIGA-HiSCORE. They used computer simulations to help work out where each shower grew biggest and to estimate how heavy the space particles were. They compared their answers with other experiments, but this short summary does not tell us what kinds of particles they found.

Long before plunge: Uncovering intermediate-mass black holes through their inspiralling compact object companions with LISA

Jean Maurice Meus, Christian Chapman-Bird, Alberto Vecchio

• Astrophysics of Galaxies
• General Relativity and Quantum Cosmology

AstronomerThis study forecasts LISA's sensitivity to low-mass compact objects inspiralling into intermediate-mass black holes of roughly 100–100,000 solar masses, considering equatorial orbits with generic eccentricity and mass ratios of about 10^-5–10^-2. The predicted detection reach extends to redshift approximately 5 for 10,000-solar-mass primaries and 0.1 for 1,000-solar-mass primaries. Eccentricity weakly affects the maximum detection distance but strongly affects which portion of the inspiral is detectable. Sensitivity time-volume depends strongly on component masses, spanning approximately 1–1,000 Gpc³ yr for 100,000-solar-mass primaries, 0.01–1,000 Gpc³ yr for 10,000-solar-mass primaries, and 0.0001–1 Gpc³ yr for 1,000-solar-mass primaries. Sources that do not plunge during the year-long mission contribute tens of percent to the overwhelming majority of the sensitivity time-volume. For white-dwarf companions that could be disrupted before plunge, the predicted reach matches or often exceeds that of electromagnetic surveys. The forecast of a handful to roughly 1,000 intermediate-mass black-hole identifications remains uncertain because merger rates are poorly known; these are prospective capabilities, not reported detections.

PublicThe planned Laser Interferometer Space Antenna, LISA, could help find elusive black holes with masses between roughly 100 and 100,000 Suns by detecting gravitational waves from smaller compact objects spiralling around them. This study estimates what LISA could detect rather than reporting new discoveries. Its reach depends strongly on the objects' masses, while the shape of their orbit mainly changes which part of the inward spiral LISA can observe. Many potential detections would come from systems still spiralling inward when the year-long mission ends, rather than systems reaching their final plunge during the mission. If the smaller object is a white dwarf, it might be torn apart before plunging, and LISA could detect such systems across distances comparable to or greater than those accessible to electromagnetic surveys. The authors estimate that LISA could identify anywhere from a handful to about 1,000 intermediate-mass black holes, but the prediction is uncertain because the frequency of these mergers is poorly known.

Young explorerSome black holes are bigger than small ones but much smaller than the biggest ones, and they are hard to find. Scientists worked out how a future space detector called LISA might find them by noticing tiny ripples in space as a smaller object circles closer and closer. LISA might spot many of these pairs before the smaller object falls in. This study has not found them yet: it says LISA could find a few or perhaps about a thousand, but scientists do not yet know how common these pairs are.

Binary pulsar studies with multi-wavelength sky surveys. II. Companion star follow ups

R. P. Mignani, C. Pallanca, V. Testa+1 more

• Solar and Stellar Astrophysics

AstronomerThis work uses additional survey photometry to update the spectral energy distributions of known stellar companions to nine field binary pulsars and searches multi-epoch catalogue photometry for flux modulation at the binary orbital period. The preceding study searched 11 optical, infrared, and ultraviolet survey catalogues for companions to 144 field binary pulsars selected from the ATNF catalogue. For nine systems with previously identified companions, it obtained new photometric constraints, including possible first ultraviolet or mid-infrared detections for some companions. The present abstract does not report a detection of orbital modulation or quantitative SED results.

PublicThe researchers study stars that orbit pulsars, using their light to help understand how the two stars evolve and affect each other. An earlier search through 11 sky-survey catalogues examined 144 pulsar systems outside globular clusters and added brightness measurements for nine already-known companion stars. Some measurements may be the first detections of these companions in ultraviolet or mid-infrared light. This paper uses the added measurements to update how each companion’s brightness varies with wavelength and checks observations from different times for brightness changes that repeat with the orbit. The abstract does not say whether such repeating changes were found.

Young explorerSome pulsars have another star going around with them. Scientists collected more measurements of light from nine of these star partners. A few might have been spotted in kinds of light our eyes cannot see for the first time. Now the scientists use those measurements to learn more about the stars’ light and look for brightness changes that repeat each trip around. They do not say here whether they found those repeating changes.

A Many-Shapes framework for Galactic Cosmic Rays

Paolo Lipari

AstronomerMeasurements of cosmic-ray proton and helium spectra span more than six orders of magnitude in energy, from a few GeV to approximately 10 PeV, and reveal departures from simple power laws. The proton-to-helium ratio decreases with rigidity below roughly 10^5 GV and increases above it. Existing interpretations invoke a few components from distinct accelerator classes with characteristic source spectra, often supplemented by recently active local sources. The authors discuss an alternative in which sources within a single class can produce a broad range of spectral shapes, whose average yields a power-law total source spectrum. In this framework, statistical fluctuations can generate observable spectral features, and proton and helium spectral slopes can differ even under rigidity-dependent acceleration. This is a proposed interpretation, not an observational demonstration of source-to-source spectral diversity.

PublicSpace-based and ground-based measurements show that the energies of cosmic-ray protons and helium nuclei follow more complicated patterns than a simple power law. Their relative abundance also changes direction: the proton-to-helium ratio falls and then rises as a quantity called rigidity increases. Some researchers explain these patterns by combining particles from a few distinct types of cosmic accelerators, often including one or more nearby sources that were recently active. This paper discusses another possibility: even sources of the same type may produce very different energy distributions. Averaging their contributions could yield an overall power law, while statistical fluctuations could create features in it. The proposed picture could also allow protons and helium to have different spectral slopes despite acceleration governed by rigidity; the abstract does not establish that this is the explanation nature uses.

Young explorerTiny particles called protons and helium nuclei zip through space. Scientists measured them and found that their energies make a pattern with bends, rather than one simple smooth pattern. This paper suggests that places making these particles might each make a different mix of energies, even if those places are the same kind. Adding all their mixes together could make a mostly simple pattern with some bends caused by chance. That is an idea for explaining the measurements, not something scientists have proved.

The Edge of the Warm Corona in Active Galactic Nuclei

Parikshit Partha Biswas, Agata Różańska, Debora Lančová+4 more

• Astrophysics of Galaxies

AstronomerThis study models a warm, dissipative corona above an accretion disk as an explanation for the observed soft X-ray excess in AGN. Ray-traced spectra computed with photoionization and Comptonization include both emitted and reflected components. In the model, the excess strength depends on the corona’s outer radius. The radial transition to a disk atmosphere is governed by line cooling: outward, Compton cooling gives way to line cooling, with a sharp vertical temperature drop at a narrow ionization front where Fe XXV–Fe XXVI recombine to Fe XVII. The transition occurs at an internal-heating value of approximately 1.6 × 10^-23 erg cm^3 s^-1, independent of Eddington ratio in the calculations. At fixed metal abundance, higher accretion rates produce a larger soft-X-ray-emitting area, consistent with recent changing-look AGN findings. The modeled warm-corona emission is otherwise featureless, with the iron K-alpha line arising only from reflection. Lower accretion rates yield a stronger, more gravitationally distorted line because of the corona’s size. Increasing iron abundance moves the ionization front closer to the black hole and strengthens the locally emitted iron line complex. These are model results rather than direct measurements of coronal structure.

PublicActive galactic nuclei show more soft X-rays than expected, and this study explores whether a warm layer above the disk feeding a black hole can explain that excess. The researchers calculate radiation emitted by this layer and reflected radiation. In their model, the excess depends on how far the warm layer extends. Farther from the black hole, cooling through atomic emission becomes more important, producing a sharp temperature drop associated with a change in iron’s ionization state. At a fixed metal abundance, faster feeding produces a larger X-ray-emitting region, consistent with recent findings in changing-look active galaxies. The model also predicts that slower feeding produces a stronger iron reflection line with greater gravitational distortion. More iron shifts the warm layer’s boundary inward and strengthens local iron emission. These calculations offer an explanation for observations, not direct proof of the proposed warm layer.

Young explorerSome galaxies have a black hole with a disk of material around it. They shine with extra X-ray light. Scientists used a computer model to ask whether a warm layer over the disk could make that extra light. In the model, the warm layer spreads farther when material feeds the black hole faster. Iron helps the layer cool and helps set its edge. This is an idea tested with calculations, not a picture of the layer itself.

GRB 241030A: A fallback-accreting magnetar description of the early X-ray emission

Nissim Fraija, Simone Dichiara, Antonio Galván

AstronomerGRB 241030A at z=1.411 shows bright, variable early X-ray emission. The authors model a possible underlying magnetar contribution to the unabsorbed 0.3–10 keV XRT flux over 80–430 s, evolving the spin under fallback-disk and electromagnetic torques. A descriptive realization gives P0≈4.25 ms, B≈3.04×10^15 G and source-frame fallback time ≈143 s, with exploratory temporal-block uncertainty ranges; its effective efficiency reaches the geometry-dependent ceiling of 81.2. In this realization, light-cylinder entry near observer time 255 s initiates negative propeller torque and steepens the decline. The modeled smooth component declines throughout, so additional variable emission contributes to the observed maximum near 180 s. A correlated-residual Bayesian analysis allows a fainter component and broader histories, yielding median P0=16.8 ms with a central 68% interval of 2.76–286 ms. However, posterior predictive checks typically underpredict both the observed flux level and variability. Fallback-modified magnetar activity is therefore a possible descriptive scenario, not an established component or a source of robust initial-spin and disk-interaction constraints. Lense–Thirring precession and other mechanisms are discussed as possible variability origins.

PublicThe early X-ray light from gamma-ray burst GRB 241030A was bright and highly variable. The researchers explored whether part of that light could come from a magnetar—a strongly magnetized, spinning star—whose rotation is affected by surrounding material falling back toward it. One model produces a steadily fading contribution, with an interaction change that makes it fade faster; extra variable emission is needed to help explain the observed brightness maximum. But a statistical analysis allows a much wider range of possible spin histories and generally predicts less light and less variability than observed. The magnetar explanation remains possible, rather than confirmed, and the study cannot reliably determine the star’s initial spin or its interaction with the surrounding material. Other possible causes of the flickering, including a precession effect, are also discussed.

Young explorerScientists saw X-ray light from a space burst brighten and fade unevenly. They tried a model in which a spinning star with a very strong magnet helps make the light, while nearby falling material changes how it spins. The model could explain some fading light, but it does not explain all the brightness and flickering well. So the scientists do not yet know whether this kind of star made that part of the light.

NS 1987A: A Potential Probe of Crustal Superfluidity with Future X-ray Observations

Akira Dohi, Keita Izumi, Asuka Ito+4 more

AstronomerIndirect observations suggest that the compact object in SN 1987A is likely the youngest identified neutron star, NS 1987A. This study uses cooling models to assess how a future thermal X-ray detection could constrain its interior, adopting a generic observatory with Lynx-like sensitivity as a benchmark. For the assumed sensitivity and observing window, the models predict detectability at an age of about 60 years, roughly 2047, unless rapid neutrino cooling such as direct Urca operates. If inner-crust neutron superfluidity is weak, the interior would likely still be non-isothermal at detection, potentially making the emission a probe of inner-crust properties. This is a conditional forecast, not a reported detection; realizing the diagnostic depends on both effective area and angular resolution sufficient to limit contamination from the surrounding remnant.

PublicIndirect evidence suggests that the remains of supernova SN 1987A contain what is likely the youngest neutron star identified so far. Researchers modeled its cooling to explore what a future detection of X-rays from its heat could reveal about its interior. With the assumed sensitivity of a future X-ray telescope, the models suggest it could be detectable around 2047, unless it loses heat rapidly through neutrinos. If neutrons in its inner crust form only a weak superfluid, different parts of the interior may still have different temperatures then, potentially allowing the X-rays to reveal properties of that crust. No such detection is reported here. Success would require both enough light-collecting power and sharp enough images to separate the star's emission from the surrounding supernova remains.

Young explorerClues suggest that a tiny, very dense star may be hiding in the leftovers of an exploded star called SN 1987A. Scientists used models to ask whether a future telescope could see X-rays from its heat. Their models say it might be possible around 2047, unless the star cools too quickly. If parts inside it are still at different temperatures, those X-rays might help scientists learn about its inner crust. This is a prediction, not something they have seen yet, and the telescope would need to separate the little star's light from the glowing leftovers around it.

AGN Feedback Turbulence in Cool-core Clusters: Evidence from XRISM

Congyao Zhang, Eugene Churazov, Irina Zhuravleva+6 more

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies

AstronomerA reanalysis of XRISM observations of A1795 and A2029 tests whether the double-cascade picture suggested for Perseus—AGN feedback and mergers driving turbulence over distinct radial ranges and spatial scales—extends to other cool-core clusters. In A1795, AGN feedback dominates the core velocity dispersion and may supply turbulent heating comparable to radiative cooling. In A2029, merger-driven motions dominate, and only an upper limit is obtained on the AGN feedback contribution. Tailored simulations indicate that an off-axis minor merger approximately 1.6 Gyr ago displaced A2029’s central low-entropy gas, potentially suppressing AGN activity; its return could facilitate renewed feedback. The authors propose an evolutionary interpretation in which merger-driven motions initially dominate and core feedback-driven turbulence re-emerges as clusters relax. The prevalence of double-cascade behavior remains unclear, and separating the drivers requires spatially resolved gas kinematics and detailed modeling.

PublicXRISM X-ray observations reveal different sources of gas motion in two galaxy clusters. In A1795, energy released by the active center of a galaxy dominates the spread of gas velocities in the cluster’s core. The resulting turbulence may provide enough heat to roughly balance the gas’s loss of energy through radiation. In A2029, motions caused by a merger dominate instead, and the researchers could place only an upper limit on the active galaxy’s contribution. Computer simulations suggest that a smaller cluster passed off-center through A2029 about 1.6 billion years ago, displacing central gas and possibly reducing the galaxy’s activity. That gas is now returning and could help the activity restart. The researchers propose that these clusters may illustrate different stages of a cycle: mergers first dominate gas motions, then activity in the central galaxy becomes important again as the cluster settles. This is an interpretation, not an established sequence, and how common this pattern is remains uncertain.

Young explorerHuge groups of galaxies have gas moving around inside them. Scientists used X-ray observations to study two of these groups. In one, an active galaxy in the middle is stirring the gas most strongly near the center. In the other, a crash between galaxy groups is doing most of the stirring. A computer model suggests that the crash pushed some central gas away, and the returning gas might help the middle galaxy become active again. Scientists think the stirring may change as a group settles down after a crash, but they do not yet know how often this happens.

Magnetohydrodynamic spectra and line invariants in the presence of axions

P.M. Akhmetiev, M.S. Dvornikov, A.Yu. Smirnov

• Plasma Physics
• Solar and Stellar Astrophysics
• High Energy Physics - Phenomenology

AstronomerThis theoretical study examines a new form of the magnetic mean-field equations that includes interactions with axions. It finds that asymptotic ergodic invariants of magnetic field lines play a central role in magnetic-field evolution and determine the type of magnetohydrodynamic spectrum of the solutions. The abstract reports a mathematical result, not an observational detection.

PublicThe researchers study mathematical equations describing how magnetic fields evolve when interactions with axions are included. Their analysis finds that quantities characterizing the long-term statistical behavior of magnetic field lines are key to how the fields change and what kinds of patterns the equations allow. This is a theoretical finding, not an observed axion effect.

Young explorerScientists used math to explore how magnetic fields could change if they interact with something called axions. In their math, some features of the magnetic field lines help decide how the field changes. They studied equations rather than watching this happen in nature.

Scalable early warning for binary neutron-star mergers in third-generation gravitational-wave detectors

Martin Gerini, Rodrigo Tenorio, Davide Gerosa

• General Relativity and Quantum Cosmology

AstronomerThe authors propose a low-latency binary neutron-star search combining short-time Fourier transforms with convolutional neural networks for third-generation gravitational-wave observatories. The network learns nonlinear time-frequency morphology to approximate the optimal Bayesian detection statistic, implicitly marginalizing over extrinsic parameters and effectively reducing the search to chirp mass. In a large-scale simulated-signal injection campaign, they compare it with GPU-optimized matched filtering for the Einstein Telescope ETΔ and ET2L configurations, using signals lasting approximately 25 minutes from 5 Hz to 6 hours from 2 Hz. In these tests, the network achieves comparable detection sensitivity while reducing computational costs by more than four orders of magnitude, with processing times falling from minutes to milliseconds. These simulation results suggest a route to rapid early-warning alerts for multi-messenger astronomy; they are not a demonstration on observed mergers.

PublicFuture gravitational-wave observatories are expected to track pairs of neutron stars for hours before they merge, but searching these long signals quickly is computationally demanding. The authors propose a neural network that recognizes the signals' changing patterns in time and frequency. In tests using simulated signals for two proposed Einstein Telescope configurations, it detected signals with sensitivity comparable to a GPU-optimized version of a standard search method, while cutting computational costs by more than a factor of 10,000 and processing times from minutes to milliseconds. The simulations covered signals lasting roughly 25 minutes to 6 hours. The approach could help deliver early alerts so astronomers can prepare to observe a merger in other ways, but that capability has not been demonstrated with real merger observations here.

Young explorerWhen two neutron stars move together before crashing, they make tiny ripples in space. Future detectors should be able to follow those ripples for hours. The researchers taught a computer to spot their patterns and tested it with pretend signals, not real star crashes. In those tests, it spotted signals about as well as another method but did the work much faster. It might one day help warn astronomers before the stars crash, so they can get ready to look.

Relativistic Simulations of Self-Gravitating Radiation Fluids

Bing-Jyun Tsao, Pablo Laguna, Octavio Guerrero

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

AstronomerThe authors present a numerical approach to pure radiation fluids in general relativistic hydrodynamics, treating radiation as a self-gravitating perfect fluid with zero rest mass. They modify Whisky within the Einstein Toolkit, updating source terms, primitive-variable recovery, and Riemann solvers, and validate the modifications with standard shock tube tests. Simulation results include radiation accretion onto a single black hole and a photon-star solution in unstable hydrostatic equilibrium that can collapse or disperse under perturbations. These are numerical results, not astronomical observations.

PublicThe researchers have adapted a computer simulation code to study how radiation behaves under strong gravity, including the gravity of the radiation itself. Their method treats radiation as a flowing fluid with no rest mass. After checking the changes against standard tests involving shock waves, they simulate radiation falling into a black hole. They also model a radiation-supported configuration called a photon star: its balance is unstable, and disturbances can make it collapse or spread out. The study describes computer models rather than observations of real objects.

Young explorerScientists made a computer model to explore how light moves when gravity is very strong. They treated the light like a flowing liquid that also makes its own gravity. In their computer experiments, light fell into a black hole. They also modeled a ball of light called a photon star. Its balance was shaky: a disturbance could make it fall inward or spread out. These were computer experiments, not things they saw in the sky.

Black-hole ringdown at an exceptional point

Kyriakos Destounis

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

AstronomerThe authors compute the amplitude of a linear-in-time contribution to the damped ringdown response at an exceptional point, where photon-sphere and near-horizon modes coalesce. The calculation uses constrained Einstein-Maxwell data for a rotating, charged black hole in de Sitter space. With seven competing modes held fixed, the late-time curvature error is 0.00383% for the mode pair, compared with 0.01401% for a refitted exponential. Tuning the initial disturbance suppresses the linear term without changing the geometry. The calculation thus shows that near mode coalescence, the initial disturbance alone can shift the frequency inferred from a short ringdown fit; this is not a claim that the black hole's intrinsic mode frequencies change.

PublicA disturbed black hole can ring with oscillations that gradually fade. In a mathematical calculation for a rotating, electrically charged black hole in de Sitter space, the researchers examine a special point where two types of oscillation merge. Their combined response can include an extra contribution proportional to time, and accounting for the pair gives a smaller late-time error than fitting a single fading oscillation. The researchers also suppress that extra contribution by changing only the initial disturbance, not the black hole's geometry. This means that near the merging point, fitting a short stretch of the ringing can give different frequency estimates depending on how the disturbance began. These are computational findings, not observations of a black hole.

Young explorerA black hole can ring a little like a bell, with a wiggle that slowly fades. Scientists used math to study a special case where two kinds of wiggle join together. They found that changing how the wiggle starts can change what its speed seems to be when they check only a short bit of it, even though the black hole's shape stays the same.

Pushing the accuracy of the quasi-circular baseline for the SEOBNR family of models

Cheng Foo, Alessandra Buonanno, Héctor Estellés+1 more

• General Relativity and Quantum Cosmology

AstronomerSEOBNRv5iHM updates the quasi-circular, aligned-spin effective-one-body inspiral-merger-ringdown model SEOBNRv5HM, including higher-order modes. It replaces non-quasi-circular corrections with a phenomenological intermediate region, allowing independent ringdown attachment times for each mode, including at its amplitude peak. Calibration and validation use 591 numerical-relativity waveforms from the third Simulating eXtreme Spacetimes catalog, rather than observed signals. For the (2,2) mode, the median maximum unfaithfulness over total masses of 10–300 solar masses is 4.25 × 10^-5, 4.5 times lower than SEOBNRv5HM and 3–8 times lower than other semi-analytical models; 84% of cases fall below 10^-4. At masses of at least 150 solar masses, the median is 9.7 × 10^-6, comparable to NRHybSur3dq8. For polarization comparisons at inclination π/3 with modes through ell = 5, the median maximum unfaithfulness is 4.2 × 10^-4, improving on SEOBNRv5HM by a factor of 2.6 and IMRPhenomTHM by 1.9. These simulation-based improvements apply to the aligned-spin, quasi-circular baseline; greater accuracy and reduced waveform systematics in future precessing and eccentric SEOBNR models are anticipated benefits, not demonstrated results here.

PublicResearchers have improved a mathematical model of the gravitational waves produced as two black holes spiral together, merge, and settle down. The new model, SEOBNRv5iHM, describes nearly circular orbits with black-hole spins aligned with the orbital motion. It changes how the final stages of the signal are joined together, allowing different components of the waves to enter the final settling phase at different times. Tested against 591 detailed numerical simulations, it generally agrees more closely with those simulations than its predecessor and other models used for comparison. For the dominant wave component, one summary measure of disagreement was 4.5 times smaller than for its predecessor across the tested mass range of 10–300 Suns. These are comparisons with simulations, not findings from new gravitational-wave observations. The authors expect the improved model to support more accurate future models that also describe wobbling spins and noncircular orbits, but those extensions are not demonstrated here.

Young explorerWhen two black holes circle each other and join together, they make ripples in space. Scientists use computer models to work out what those ripples should look like. This team improved how a model connects the last part of the circling to the new black hole settling down. They checked it against 591 detailed computer simulations, and it usually matched them better than the older model. This test was done with computers, not with newly observed ripples from space. The team hopes the improvement will also help future models of more complicated black-hole dances.

Reabsorbed Urca neutrinos suppress bulk-viscous damping of neutron star merger oscillations

Prashant Thakur, Yeunhwan Lim

• Nuclear Theory
• General Relativity and Quantum Cosmology

AstronomerThe calculations predict that reabsorption of Urca neutrinos suppresses bulk-viscous damping of neutron-star merger oscillations. Below the direct-Urca threshold, capture neutrinos have mean energies of 19–46 MeV and absorption lengths of metres. An energy-resolved kinetic treatment yields a damping time of 2.7 s for a 1-kHz, 10-km oscillation at nuclear density and a temperature of 4 MeV, compared with 19 ms when neutrinos escape freely. The suppression persists across the sampled states, three equations of state, and rate variations, with nearly frozen composition. The absorption is included in full-kinematics rates but absent from elastic opacity tables; these are theoretical findings, not reported observations.

PublicCalculations suggest that oscillations in merging neutron stars may fade more slowly through one particular damping process than estimates assuming freely escaping neutrinos predict. In the conditions studied, neutrinos produced by particle reactions are absorbed within metres rather than escaping. For one example, accounting for this absorption changes the predicted damping time from 19 milliseconds to 2.7 seconds. The effect persists across the tested descriptions of neutron-star matter and reaction-rate variations, but the abstract does not report an observational measurement.

Young explorerWhen two neutron stars join together, they can wobble. Scientists used calculations to study how tiny particles called neutrinos affect those wobbles. If the star catches the particles instead of letting them escape, one way of calming the wobbles works more slowly. This is a prediction from calculations, not something the scientists report seeing.

Eccentric Stellar-mass Binary Black Holes: Population, Detectability, and Waveform Analysis in the LISA and LIGO Era

Zeyuan Xuan, Smadar Naoz, Kyle Kremer+3 more

• General Relativity and Quantum Cosmology

AstronomerThis study presents a simulated catalog of dynamically formed, stellar-mass binary black holes, combining Galactic-field flybys, eccentric Kozai-Lidov evolution in the Galactic nucleus, and globular-cluster N-body interactions. The model predicts a wide, highly eccentric Milky Way population: approximately 25, 9, 3, 1, and fewer than 1 sources above SNR thresholds of 1, 3, 8, 20, and 50 for a four-year LISA mission, rising to approximately 36, 13, 5, 2, and 1 for ten years. A cosmological extension yields a merger rate of about 9 Gpc^-3 yr^-1 and approximately 150 extragalactic mHz binaries above SNR 1, but only about 1 above SNR 8; these are model predictions, not observed detections. Different dynamical channels produce distinct predicted eccentricity distributions in the LVK band. The analysis also finds that individual harmonics of eccentric Galactic binaries can be detected independently and may masquerade as circular binaries with systematically biased chirp masses, complicating the LISA global fit. Post-Newtonian waveforms are reported to converge reliably in the mHz band for eccentric binaries with masses below roughly 1,000 solar masses. The simulated catalog and LISA Eccentricity Astrophysics Package (LEAP) are publicly available.

PublicComputer simulations suggest that pairs of stellar-mass black holes on strongly elongated orbits could be useful targets for the future space-based gravitational-wave observatory LISA. The study models pairs shaped by encounters in the Milky Way’s field, its central region, and dense star clusters. For a four-year LISA mission, it predicts about 25 Milky Way sources above a low signal-to-noise threshold of 1, but only about 3 above the higher threshold of 8; a ten-year mission raises those estimates to about 36 and 5. Extending the model beyond our galaxy predicts about 150 sources above the low threshold, dropping to about 1 at the higher threshold because their signals are weak. These are forecasts, not discoveries. The simulations also suggest that different formation environments could leave different orbital signatures in the frequency range measured by LVK. A further challenge is that separate tones from one elongated-orbit system may resemble signals from circular-orbit systems, potentially leading to biased mass estimates. The researchers have made their simulated catalog and analysis software publicly available.

Young explorerTwo black holes can travel around each other in a stretched-out loop instead of a circle. As they move, they make tiny ripples in space. Scientists used computers to imagine black-hole pairs made through encounters with other objects and work out which ripples a future space detector called LISA might hear. Their model says there could be a few pairs in our galaxy with stronger signals, and more with very faint signals. They have not found these pairs in this study. One pair can also make several tones, which might trick scientists into thinking they are hearing different pairs.

Neutron Star Mass-Radius Constraints for EXO 0748-676 from 2008-2025 Quiescent X-ray Spectra

Mingyang Wang, Guobao Zhang, Ang Li

• Solar and Stellar Astrophysics
• Nuclear Theory

AstronomerA joint analysis of 20 quiescent X-ray observations of EXO 0748−676 from 2008–2025, comprising 14 Chandra and 6 XMM-Newton exposures, constrains the neutron star’s mass and radius across two quiescent episodes separated by the 2024–2025 outburst. Hydrogen-atmosphere fits to the 0.5–10 keV spectra, with hydrogen column density, mass, and radius tied across observations, yield M = 1.77 (+0.17/−0.22) solar masses and R = 12.62 (+0.56/−0.74) km at a fixed distance of 7.1 kpc; uncertainties are 1σ credible intervals. Compared with independent fits to the two epochs, the combined analysis significantly suppresses the low-mass posterior tail. Allowing for a distance of 7.1 ± 1.2 kpc broadens the conservative constraints to approximately 1.41–2.11 solar masses and 10.15–15.13 km, favoring relatively stiff dense-matter equations of state. The thermal evolution also shows evidence for renewed crust cooling after the latest outburst, enabling comparison of relaxation following two distinct accretion episodes.

PublicResearchers used 20 X-ray observations taken between 2008 and 2025 to estimate the mass and size of the neutron star in the binary system EXO 0748−676. The observations cover two quiet periods separated by an outburst in 2024–2025. By fitting a model of a hydrogen atmosphere and assuming a distance of 7.1 kiloparsecs, they estimate a mass of about 1.77 times the Sun’s and a radius of about 12.62 kilometers. These are model-based estimates, and uncertainty in the distance widens the possible values considerably: approximately 1.41–2.11 solar masses and 10.15–15.13 kilometers in radius. The results favor descriptions of dense matter that resist compression relatively strongly, rather than establishing one definitive description. The changing X-ray emission also provides evidence that the star’s crust began cooling again after the recent outburst.

Young explorerScientists studied X-ray light from a tiny, very heavy star called a neutron star. They used a model to work out how heavy and how big it might be. Their best estimate makes it heavier than our Sun but only about 25 kilometers across. They are not sure of the exact size or weight, partly because they are not sure exactly how far away it is. They also found clues that its outer crust was cooling again after a burst of activity.

The kinetic-energy bottleneck in Fast Radio Burst models

Paz Beniamini, Pawan Kumar

AstronomerThis theoretical analysis derives model-independent constraints on FRB scenarios that convert central-engine energy into particle kinetic energy and then coherent GHz radiation. Inner-magnetospheric models violate brightness-temperature and kinetic-luminosity limits unless particles are continuously re-accelerated in situ; magnetar-strength fields can supply the required parallel electric field out to roughly 10^10 cm. Monster shocks provide continuous acceleration, but a single-pass kinetic-energy interpretation requires extreme particle densities and predicts emission well above GHz frequencies. Even conservative wave conversion is constrained by charge availability, limiting magnetospheric GHz production to roughly 10^10 cm for fiducial parameters. Light-cylinder forced reconnection supplies continuous acceleration but typically converts at most about 10^-6 of the injected energy into radio emission. External-shock masers satisfy the brightness-temperature and kinetic-luminosity constraints, but the analysis finds their upstream winds inevitably optically thick to induced Compton scattering, independently of the principal model parameters. Proposed escape through emission above the maser peak or upstream magnetization of at least about 30 entails very low efficiency; the former also conflicts with narrow FRB spectra. The authors favor near-surface magnetospheric models with continuous acceleration, conditional on radiation escaping the magnetosphere.

PublicFast radio bursts are modeled as energy releases that first accelerate particles and then produce radio waves. This study tests that picture using theoretical limits, rather than reporting new observations. It finds that models producing radio waves close to a magnetar need to keep accelerating particles as they radiate. Some alternatives face severe difficulties: reconnection near the light cylinder typically turns only a tiny fraction of the supplied energy into radio emission, while radio waves from external shocks face strong scattering in the surrounding wind. Proposed ways around that scattering would make radio production very inefficient, and one also conflicts with the narrow range of frequencies seen in FRB spectra. The authors judge models operating near the magnetar’s surface with continuous particle acceleration the most promising, but only if the radio waves can escape its magnetic surroundings.

Young explorerScientists are trying to explain powerful flashes of radio waves from space. They used calculations to check different ideas. Their favorite idea in this study makes the flashes near a star with a very strong magnetic field, where tiny particles keep getting pushed. But there is still a big question: can the radio waves get out? The calculations do not prove this idea is right.

Neutron stars with an agnostic Dark sector: Core and Halo configurations from a two-fluid approach

Asit karan, Tuhin Malik, Asim Kumar Saha+2 more

• High Energy Physics - Phenomenology

AstronomerThis theoretical analysis constructs dark-matter-admixed neutron stars in a two-fluid framework with agnostic hadronic and fermionic dark-matter equations of state. Hadronic matter is anchored by low-density chiral effective field theory and high-density perturbative QCD, while a speed-of-sound parametrization allows thermodynamically consistent intermediate- and high-density behavior without favoring soft or stiff dark-matter equations of state. The models show that dark matter need not compactify a star: light particles produce extended halos and increase tidal deformability, whereas heavy particles produce compact cores and decrease it. The dominant observational constraint accordingly shifts from gravitational-wave tidal deformability for light, halo-dominated models to NICER mass-radius data for heavy, core-dominated models. Within this framework, current data at 1σ constrain the light-dark-matter fraction to f_DM ≲ 0.11. Similar-mass neutron stars with markedly different tidal deformabilities are proposed as a possible dark-matter signature, not reported as a detection.

PublicThe researchers modeled neutron stars containing both ordinary matter and dark matter, allowing a broad range of possible behavior for matter at extreme densities within a fermionic dark-matter framework. Their calculations suggest that dark matter does not always make a star more compact. Light dark-matter particles can form an extended halo that makes the star more easily distorted by a companion’s gravity, while heavier particles can form a compact core that makes it less easily distorted. Gravitational-wave measurements provide the strongest limits for the light-particle models, while NICER measurements of stellar masses and radii matter most for the heavy-particle models. Using current data, the study places an upper limit of about 11% on the dark-matter fraction for light dark matter at the stated 1σ level, within these modeling assumptions. Stars with similar masses but very different responses to tidal forces could be a clue to dark matter, but this study does not report finding such a signature.

Young explorerThe scientists used math to imagine neutron stars with some dark matter mixed in. In their models, light dark-matter particles can make a big cloud around a star, making it easier for another star’s gravity to stretch it. Heavier particles can gather in a small center and make it harder to stretch. Measurements help limit how much dark matter these imagined stars could hold. Two stars that weigh about the same but stretch very differently might be a clue, but the scientists have not shown that dark matter is really inside them.

Evidence for the Moon and Sun shadows with cosmic rays at an average energy of 7×10¹⁷eV

Pierre Auger Collaboration, A. Abdul Halim, P. Abreu+97 more

AstronomerPierre Auger Observatory data provide the first evidence for Moon and Sun shadows in cosmic-ray arrival directions above about 10^16 eV, with an average energy of 7 × 10^17 eV. More than 10.6 million events from three detector arrays yield a combined shadow significance of approximately 3σ, rather than a high-significance detection of each shadow separately. The observed deficits relative to an isotropic flux confirm the Surface Detector’s pointing accuracy using celestial bodies. Combining the Moon and Sun shadows gives an inferred overall angular resolution of 0.59 degrees, with uncertainties of +0.15 and −0.11 degrees.

PublicThe Pierre Auger Observatory has found evidence that fewer extremely energetic cosmic-ray particles arrive from the directions of the Moon and Sun, creating particle “shadows.” Such shadows had been observed at lower energies, but this study reports the first evidence above about 10^16 electronvolts. Using more than 10.6 million particle events, the researchers find a combined statistical significance of about three sigma—evidence, but not an overwhelming detection. These shadows confirm that the observatory reconstructs arrival directions accurately and indicate an angular resolution of roughly 0.6 degrees.

Young explorerTiny particles from space come toward Earth. Scientists looked for places where fewer particles seemed to come from, in the directions of the Moon and Sun—like shadows made of missing particles instead of missing light. They found clues to both shadows among very energetic particles. The clues are not strong enough to be completely sure, but they help show that the detector points the right way.

The Galactic Neutrino Sky: Predictions from Gamma-ray Source Populations

Leo Seen, Ke Fang

AstronomerHigh-energy neutrino emission from the Galactic plane has been detected at 5.7σ significance, with a prominent inner-Galaxy excess. The authors construct ReGal-γ from GeV–PeV γ-ray catalogs by selecting candidate hadronic emitters, yielding a resolved-source template that predicts a stronger inner-Galaxy concentration than diffuse-emission models. Combined with diffuse cosmic-ray emission and unresolved γ-ray source models, it reproduces IceCube’s reported spectral energy distribution and Galactic longitude count profile without additional renormalization. An independent template built from different catalogs supports robustness against source-modeling uncertainties. This offers an explanation for the excess, rather than establishing individual sources as neutrino emitters. Future energy-dependent longitude and latitude measurements could better constrain the models and source distribution.

PublicHigh-energy neutrinos have been detected coming from the plane of our Galaxy, with an especially strong excess toward its inner regions. This study offers a possible explanation: the distribution of sources within the Galaxy. The researchers used catalogs of gamma-ray sources to map objects that might also emit neutrinos. Their model predicts a stronger concentration toward the inner Galaxy than models of diffuse emission do. When combined with models for diffuse emission and gamma-ray sources not individually resolved, it matches both the energy spectrum and the pattern along the Galactic plane reported by IceCube, without extra adjustments to the models’ overall emission levels. A second source map supports the explanation, but the study does not establish which objects emit neutrinos. More detailed measurements could help distinguish the possibilities.

Young explorerScientists have spotted tiny particles called neutrinos coming from our galaxy, with extra ones arriving from the direction of its middle. They made a map using places that shine in gamma rays, a kind of light we cannot see with our eyes. Those places might make neutrinos too. When the scientists added their map to other models, the result matched the neutrino pattern already seen. That is a possible explanation, not proof of where each neutrino came from. More observations could help solve the puzzle.

A Radiation-Hydrodynamic Light Curve Grid and Interpolation Framework for Stripped-Envelope Supernovae

Qiliang Fang, Takashi J. Moriya

AstronomerThe authors present 7,560 radiation-hydrodynamic light-curve simulations of stripped-envelope supernovae from exploding helium-star progenitors, spanning ejecta masses representative of typical events and broad ranges of explosion energy, radioactive nickel mass, and mixing. They develop an interpolation-based framework for inferring parameters from observations. In tests treating the simulated light curves as mock observations, the widely used Arnett model reproduces the overall light-curve morphology, but its inferred ejecta masses show no significant correlation with the input masses. It also introduces a spurious correlation between inferred explosion energy and nickel mass, which are independent in the grid. These simulation-based tests show that a good light-curve fit need not imply reliable physical parameters and underscore the importance of radiation-hydrodynamic modeling for SESN interpretation and population studies.

PublicResearchers created 7,560 computer simulations of how stripped-envelope supernovae brighten and fade, varying the amount of material thrown out, explosion energy, radioactive nickel, and mixing. They also developed a way to use this simulation library to estimate the properties of observed explosions. To test a widely used simpler model, called the Arnett model, they gave it simulated brightness curves rather than real observations. Although it reproduced the curves’ overall shapes, its estimates of the expelled mass did not track the true simulation inputs. It also suggested a relationship between explosion energy and nickel amount that was absent from the simulation grid. The tests warn that matching a supernova’s changing brightness can still yield misleading estimates of its physical properties.

Young explorerScientists made 7,560 pretend exploding stars on computers and watched how their light changed. Then they asked a simpler math tool to work out what went into those pretend explosions. The tool could copy the shape of the changing light, but its guesses about how much star material flew out did not reliably match what the scientists had put in. It also seemed to link two ingredients that were not linked in the pretend stars. So a tool can make a picture that looks right and still get important things wrong.

The low luminosity end of Galactic HMXBs with eROSITA: Establishing a luminosity floor for accreting BeXRBs

Aafia Zainab, Philipp Thalhammer, Nicolas Zalot+18 more

• Astrophysics of Galaxies

AstronomerThe first four SRG/eROSITA surveys extend the luminosity distribution of previously known Galactic high-mass X-ray binaries (HMXBs) down to 10^32 erg/s. The analysis demonstrates substantial scatter from intrinsic variability and distinct luminosity distributions for supergiant and Be X-ray binaries, with reanalysed RXTE/ASM and MAXI data providing comparisons. eROSITA enables systematic study of BeXRBs below the usual monitoring thresholds outside outburst. More than 80% of BeXRBs are detected at luminosities at least ten times those expected for the most X-ray-luminous Be stars. The authors interpret this as evidence that accretion outside outburst is likely the norm, rather than establishing stable accretion individually for every source; previous pointed observations found signatures of stable low-luminosity accretion in only a fraction of the sample. Cold-disk accretion and the propeller mechanism are discussed as context. A small subset of apparently isolated Be stars reaches luminosities comparable to the faintest BeXRBs, suggesting, but not confirming, compact companions.

PublicUsing the first four eROSITA sky surveys, researchers examined previously known high-mass X-ray binary systems in the Milky Way at fainter X-ray levels than earlier wide-area surveys could reach. These systems can vary greatly in brightness, and those containing supergiant stars and those containing Be stars occupy different parts of the brightness distribution. The observations also probe Be-star binaries between their bright outbursts, when other monitoring surveys often miss them. More than 80% of the Be-star binaries were detected at least ten times brighter in X-rays than expected even for the most X-ray-bright Be stars alone. The researchers interpret this as evidence that matter probably continues falling onto their compact companions between outbursts, although the observations do not establish steady feeding in every system. A few apparently solitary Be stars were also unusually X-ray bright, hinting that they may have unseen compact companions.

Young explorerSome stars have a small, very dense partner that can glow in X-rays when it gets material from the star. Researchers used a space telescope to look at known star pairs, including ones too faint for earlier sky surveys to see. Many were still glowing between their big bright flashes. The scientists think this means their little partners usually keep getting material even during quiet times, but they are not sure this happens in every pair. A few stars that seem to be alone also glowed brightly. They might have hidden partners, but that is not yet known.

Density-induced dark-baryon conversion in Δ-admixed hypernuclear neutron stars

Niyar Prabhat Kalita, Vivek Baruah Thapa, Bhanu Prakash Pant+2 more

• High Energy Physics - Phenomenology
• Nuclear Theory

AstronomerThis theoretical study models density-induced neutron conversion into a neutral dark baryon χ in cold, charge-neutral, β-equilibrated neutron-star matter containing hyperons and the full Δ(1232) quartet. The hadronic sector uses the density-dependent covariant density-functional parametrization DDME2; χ abundances follow self-consistently from chemical equilibrium and baryon-number conservation rather than an imposed dark-matter fraction. Within this model, hyperons and Δ resonances shift the neutron chemical potential, delay χ onset, and reduce its abundance relative to nucleonic matter, modifying the equation of state, composition, sound speed, and adiabatic index. For χ masses of 1250, 1300, and 1400 MeV, the complete N+Y+Δ+χ configurations reach maximum masses of 1.806, 1.899, and 2.024 solar masses, respectively; the massive-pulsar constraint therefore disfavors the lighter benchmarks. At 1400 MeV, χ is confined to the inner core of the most massive modeled stars, while canonical configurations remain essentially unaffected. The included scalar Higgs portal has negligible mean-field effects for the adopted couplings, so the predicted stellar changes primarily reflect conversion-driven compositional rearrangement, not Higgs-mediated interactions.

PublicCould the extreme density inside a neutron star turn some neutrons into hypothetical dark particles? This theoretical study explores that possibility while also accounting for hyperons and Δ resonances, other particles that may occur in dense matter. Rather than choosing a fixed amount of dark matter, the researchers calculate how much would form as the particle mixture reaches equilibrium. In their model, the additional ordinary-matter particles delay dark-particle formation and reduce its abundance. The three tested dark-particle masses produce maximum stellar masses of about 1.81, 1.90, and 2.02 times the Sun’s mass; comparison with the massive-pulsar constraint disfavors the two lighter dark-particle choices. For the heaviest choice, the dark particles appear only in the inner cores of the most massive modeled stars, leaving typical configurations essentially unchanged. A possible interaction through the Higgs field contributes negligibly at the strengths assumed here. These are model predictions, not evidence that neutron stars actually contain dark baryons.

Young explorerA neutron star is a very crowded star. Scientists used a model to ask whether squeezing its tiny pieces together could turn some into a new, invisible kind of particle. In their model, other kinds of particles made that change start later and happen less. One choice for the invisible particle let the model make heavier stars than the other choices. For that choice, the invisible particles stayed deep inside only the heaviest stars. This is an idea scientists tested with calculations, not something they have seen inside a real star.

Particle acceleration in Alfvénic turbulence with a strong guide field

Daniel Humphrey, Stanislav Boldyrev, Vadim Roytershteyn

• Astrophysics of Galaxies

AstronomerA numerical and phenomenological study proposes charge-starved current sheets as the sites of particle acceleration in magnetically dominated Alfvénic turbulence with a strong mean field, where conventional mirror and curvature acceleration become inefficient. These sheets correspond to current velocities approaching the speed of light. The study finds approximately log-normal distributions of electric currents, plasma density, charge fluctuations, and accelerated-particle energies. The authors interpret the non-thermal particle distributions as arising from acceleration in these sheets rather than conventional Fermi-type acceleration by turbulent eddies; this is a proposed mechanism based on modeling, not an observational detection.

PublicHow do particles gain energy in turbulent matter dominated by magnetic fields? Using numerical modeling and theoretical reasoning, the authors propose that the acceleration happens in thin regions carrying electric current, where too few charged particles are available to carry the required current and current velocities approach the speed of light. Their study finds that currents, density, charge fluctuations, and particle energies follow approximately log-normal statistical patterns. They argue that these regions could explain unusual particle-energy distributions when a strong background magnetic field makes familiar acceleration mechanisms inefficient, rather than particles gaining energy from swirling turbulent motions. This explanation is based on modeling, not direct observations.

Young explorerTiny particles can gain energy in a place with strong, messy magnetic fields. Scientists used computer models and ideas to suggest that this happens in thin layers where too few particles must carry a very fast electric current. They think these layers, rather than the swirling motions around them, may give the particles their extra energy. This is an idea from their study, not something they watched happen in space.

Transient discs around isolated accreting neutron stars

Marina D. Afonina, Anton V. Biryukov, Sergei B. Popov+1 more

AstronomerThis population-synthesis study models isolated neutron stars in the Milky Way accreting turbulent interstellar gas, tracking whether its angular momentum permits disc formation. Discs typically require spatial velocities ≲40 km s⁻¹, and weaker magnetic fields favour them by reducing the magnetospheric volume. Even with exponential field decay on a characteristic timescale of about 1.5 Gyr, several realistic propeller spin-down prescriptions yield only a small disc-bearing fraction of accretors, as low as about 0.02%. Nevertheless, disc accretors are relatively numerous among the brightest model sources, with estimated counts potentially reaching a few hundred at X-ray fluxes ≳10⁻¹⁴ erg s⁻¹ cm⁻². These are model estimates, not reported detections. The authors speculate that electron cyclotron maser emission could make such objects appear as long-period radio transients and predict spectra and conditions for quenching that emission.

PublicComputer models explore whether aging neutron stars traveling alone through the Milky Way can gather surrounding gas into discs. Turbulence can give the gas enough swirling motion to form a disc, especially around slowly moving stars with weaker magnetic fields. In the models, only a small fraction of gas-accreting neutron stars develop discs—as few as about 0.02% under some assumptions. Yet these disc-bearing stars are relatively numerous among the brightest predicted sources, and the study estimates that a few hundred could reach the stated X-ray brightness threshold. These are predictions, not discoveries. The authors also suggest that the stars might produce radio signals recurring at long intervals through a process called electron cyclotron maser emission, but this connection remains speculative.

Young explorerA neutron star is a very small, dense leftover from a star. Scientists used a computer to imagine how some of these stars might collect gas while moving through space. If a star moves slowly enough, the gas might swirl around it like a little disc. The computer models say this happens to only a few of the stars that collect gas, but some could be bright in X-rays. The scientists also wonder whether these stars could send out radio signals with long waits between them. They have not shown that this really happens.

Resolving the Galactic Center Region's Gamma-Ray Emission and Searching for its Neutrino Counterpart with HAWC and IceCube

R. Alfaro, M. Araya, J. Arteaga-Velázquez+97 more

AstronomerUsing approximately 2,860 days of HAWC data with improved machine-learning gamma/hadron separation, the authors present the first spatially resolved model of the Galactic Center at the highest gamma-ray energies, separating point source HAWC J1745-2857 from Galactic diffuse emission not significant in earlier HAWC analyses. After accounting for the diffuse component, the point-source spectrum extends beyond 100 TeV without evidence of a cutoff, supporting a PeVatron interpretation that is not an artifact of unresolved diffuse emission. Assuming a hadronic origin, the authors derive a neutrino template and search 12 years of IceCube muon-track data, finding no significant excess. Their first neutrino-flux upper limit for this HAWC-derived multi-component spatial model is approximately 12 times the nominal hadronic prediction. The limit does not yet test the optically thin hadronic scenario, but establishes the sensitivity needed for future neutrino tests.

PublicThe center of our Galaxy may accelerate cosmic rays to exceptionally high energies. Using about 2,860 days of HAWC observations, researchers separated its very-high-energy gamma-ray glow into a point source and a more spread-out component. Even after accounting for the spread-out glow, the point source emits gamma rays above 100 TeV, with no evidence that its spectrum cuts off. This supports the interpretation that the Galactic Center is a powerful cosmic-ray accelerator, rather than that interpretation being caused by blended emission. If the gamma rays come from interactions involving cosmic-ray protons or other atomic nuclei, neutrinos should also be produced. A search of 12 years of IceCube data found no significant neutrino excess. The resulting upper limit is about 12 times the predicted neutrino signal, so it does not yet test the version of this explanation in which gamma rays escape without substantial absorption.

Young explorerScientists looked at very energetic light from the middle of our galaxy. They could tell apart one tiny-looking bright spot and a glow spread around it. The bright spot still makes very energetic light after they separate out the glow. That is a clue that something there may give tiny particles enormous boosts. One possible way to make this light would also make tiny particles called neutrinos. Scientists looked for those too, but did not find a clear extra signal. Their search is not sensitive enough yet to check that explanation.

Luminosity Signatures of Dark Sector Particles from Black Hole Evaporation in Neutron Stars

Ioannis Dalianis, Anastasios Irakleous

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

AstronomerThis theoretical study examines an indirect Hawking-radiation signature from microscopic black holes that may form through dark-matter accumulation and collapse inside neutron stars. Unlike efficiently absorbed Standard Model evaporation products, sufficiently weakly interacting, long-lived mediators could escape and decay into high-energy neutrinos, photons, or charged particles. The authors calculate joint energy–angular distributions including mediator propagation, energy-dependent decay, and relativistic decay kinematics, illustrating the mechanism with gravitationally coupled scalars, ALPs, dark photons, and heavy neutral leptons. For relativistic mediators, the normalized, energy-integrated angular profile is approximately independent of black-hole temperature: boost-enhanced propagation and relativistic beaming compensate, leaving the characteristic extent governed mainly by cτ_S/D, the mediator lifetime multiplied by the speed of light and divided by source distance. These angular profiles can closely resemble those from monochromatic mediator production in dark-matter annihilation, but energy spectra and energy-resolved angular distributions remain distinct. The predicted signals may be inaccessible to current observatories; they are proposed targets for future high-energy neutrino and gamma-ray searches, not reported detections.

PublicTiny black holes might form inside neutron stars if dark matter collects and collapses there. This theoretical study explores a possible way to detect their Hawking radiation indirectly. Most ordinary particles emitted by such a black hole would be absorbed inside the star, but certain long-lived particles that interact very weakly could escape and later decay into high-energy particles. The researchers calculate how those secondary particles would be spread across the sky and across energies. For mediators moving close to light speed, the overall angular pattern depends mainly on their lifetime and the source’s distance, rather than the black hole’s temperature. A similar pattern could arise from dark-matter annihilation, but energy information could help distinguish the mechanisms. No detection is reported, and the predicted signals may require future neutrino and gamma-ray observatories.

Young explorerScientists are exploring whether a tiny black hole could hide inside a neutron star. Most particles it sends out would get stuck, but some special particles might escape and then turn into other particles we could look for. The scientists worked out what patterns those particles might make. They have not seen this happen, and today’s tools might not be able to spot it.

IC 1297: The Most Distant Known X-ray Planetary Nebula and One of the Most Luminous

H. Yuan, Q. A. Parker, M. A. Guerrero

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerThe first targeted Einstein Probe observations of a planetary nebula detect central-region X-ray emission in IC 1297 with the Follow-up X-ray Telescope (FXT). Spectral fitting gives kT = 0.086 (+0.054/−0.058) keV, approximately 1 million K, and an absorption-corrected 0.3–2.0 keV luminosity of 2.8 × 10^32 erg s−1. These properties support a shocked-wind hot-bubble interpretation; there is no evidence for X-ray emission from the Wolf-Rayet central star itself. At the adopted distance of approximately 3.8 kpc, IC 1297 is the most distant X-ray-emitting PN known and among the most luminous. A compilation of all 41 known Galactic X-ray-emitting PNe shows a distance–luminosity correlation attributed to selection bias toward luminous sources at large distances. It also shows a luminosity separation between hot bubbles with H-rich and [WR]-type central stars, with the latter reaching luminosities up to an order of magnitude higher; the ten most luminous objects host [WR]/PG 1159 stars. The observations demonstrate FXT's capability to detect and characterize faint, extended soft X-ray sources in distant PNe.

PublicAstronomers used the Einstein Probe's Follow-up X-ray Telescope to detect X-rays from the central region of the planetary nebula IC 1297. The measured spectrum indicates gas at roughly a million degrees, consistent with a hot bubble formed by shocked stellar winds. There is no evidence that the nebula's Wolf-Rayet central star itself emits X-rays. Based on an adopted distance of about 3.8 kiloparsecs, IC 1297 is the most distant known X-ray-emitting planetary nebula and one of the most luminous in X-rays. The team also gathered X-ray properties for all 41 known examples in our Galaxy. More distant detections tend to be more luminous, which the authors attribute to the difficulty of detecting faint sources far away. Hot bubbles around [WR]-type central stars reach X-ray luminosities up to ten times higher than those around hydrogen-rich central stars, and the ten most X-ray-luminous nebulae all contain [WR]/PG 1159 central stars.

Young explorerScientists pointed an X-ray telescope at a cloud of gas around a star called IC 1297. They found X-rays coming from the cloud's middle. The light suggests there is a bubble of gas about a million degrees hot, likely heated when winds from the star crash into gas. They found no sign that the star itself was making X-rays. If their estimate of its distance is right, this is the farthest cloud of this kind ever seen shining in X-rays. They also compared 41 such clouds in our galaxy. Faraway ones tend to look very powerful because the faint ones are harder to find.

Testing influence of tides on gravitational wave emission with SPH code PHANTOM

Marat Sh. Potashov, Sergei I. Blinnikov, Aleksandra V. Mishakina

• General Relativity and Quantum Cosmology

AstronomerThe authors demonstrate a numerical method for estimating tidal contributions to binary neutron star gravitational-wave waveforms using the Newtonian SPH code PHANTOM. For a 1.5 + 1.5 solar-mass binary, comparison with waveforms calibrated against full numerical GR simulations indicates that the tidal contribution can be reliably extracted with about 10^4 SPH particles, provided differences in neutron star compactness between Newtonian gravity and GR are accounted for. Beyond roughly 80 km separation, the relative tidal contribution falls below SPH numerical noise, although point-source waveforms are sufficient for detection at those separations. Hydrostatic/hydrodynamic relaxation of the initial models is essential; without it, numerical noise obscures the entire GW signal.

PublicThis simulation study tests a way to estimate how tidal stretching of two neutron stars affects the gravitational waves they produce. Using the Newtonian simulation code PHANTOM, the authors model two stars, each with 1.5 times the Sun's mass. Comparison with waveforms calibrated using full general-relativity simulations suggests that about 10,000 simulation particles can reliably capture the tidal contribution, but differences in how compact the stars are under the two gravity models must be accounted for. When the stars are more than roughly 80 kilometres apart, the tidal effect is too small to distinguish from numerical noise in this method; the authors say waveforms treating the stars as point-like sources are sufficient for detection at those distances. The starting models must also be allowed to settle into balance, or numerical noise hides the entire simulated gravitational-wave signal.

Young explorerTwo very dense stars can pull and stretch each other as they move together, changing the ripples they make in space. Scientists used a computer model to work out that change and checked it against models based on a more complete description of gravity. Their simpler model could find the stretching effect, but only if they accounted for how tightly packed the stars were and let the pretend stars settle before starting. When the stars were farther apart, the stretching effect was too tiny for this method to pick out from computer noise.

Collisionless relaxation as the origin of the anisotropic, non-thermal, and multi-temperature momentum distributions observed in space plasmas

Torsten Enßlin, Christoph Pfrommer

• Plasma Physics

AstronomerThe authors use Liouville’s theorem to argue that anisotropic compression or expansion, followed by relaxation of the induced anisotropic stress, prevents an initially thermal-equilibrium plasma from returning to thermal equilibrium without particle collisions. The resulting non-equilibrium state must retain anisotropic or non-thermal particle distributions, different electron and ion temperatures, or some combination. This is a theoretical argument, consistent with observed solar-wind distributions rather than a new measurement. Because most astrophysical plasmas are effectively collisionless and undergo substantial anisotropic compression or expansion, the authors expect such departures from equilibrium to be ubiquitous.

PublicParticles in space plasmas, such as the solar wind, are often observed to move differently in different directions, depart from a thermal distribution, or have different temperatures for electrons and ions. The authors offer a theoretical explanation: when plasma is squeezed or stretched unequally in different directions, they argue that it cannot fully return to thermal equilibrium without collisions between particles, even after the resulting directional stress relaxes. Since most astrophysical plasmas have very few collisions and undergo this kind of squeezing or stretching, the authors expect these departures from equilibrium to be widespread. That expectation agrees with solar-wind measurements, but is not itself a new observational result.

Young explorerSpace has tiny particles that often zip around without bumping into one another. Scientists argue that if a cloud of these particles is squeezed or stretched more one way than another, it cannot settle back into its usual heat balance unless particles bump together. They may keep moving differently in different directions, or different kinds of particles may stay at different temperatures. Scientists think this should happen in many places in space, and measurements of the wind from the Sun fit that idea.

Energy Extraction via Magnetic Reconnection from a Rotating Dyonic Black Hole in N = 2, U(1)² Gauged Supergravity

Raid M Suleiman, Shanshan Rodriguez, Dominic O. Chang+1 more

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

AstronomerThis theoretical study analyzes Comisso–Asenjo energy extraction by magnetic reconnection around a rotating dyonic black hole in four-dimensional N=2, U(1)^2 gauged supergravity. In the ZAMO frame, the authors derive the asymptotic hydrodynamic energy per unit enthalpy of reconnection outflows and map conditions allowing a negative-energy branch at infinity. Varying spin, electric and magnetic charges, the NUT parameter, and gauge coupling, they find that stronger coupling or charges approaching extremality raise the cutoff magnetization and reduce the extraction-active region within the ergoregion. Unlike Kerr, spin dependence through the normalization factor Xi and quartic horizon function makes AdS/NUT geometric effects dominate the usual frame-dragging enhancement. Calculated power and efficiency are non-monotonic in spin, peaking around a~0.8. High efficiency does not require near-extremal rotation when gauge coupling is small and charge Q is moderate, but it does require extreme magnetization and nearly radial outflows, restricting active reconnection to a thin shell just outside the horizon. These are model calculations, not observational findings.

PublicCould rearranging magnetic fields draw energy from a spinning black hole? This theoretical study explores that possibility for a black-hole model carrying both electric and magnetic charge in a particular gravity theory. The calculations identify conditions under which one reconnection outflow has negative energy as defined relative to a distant observer, allowing energy extraction. Stronger gauge coupling or charges closer to their limiting values make extraction harder: they increase the required magnetization and shrink the region where it can occur. Faster rotation is not always better; calculated power and efficiency peak at an intermediate spin. Efficient extraction requires extreme magnetization and outflows directed almost radially, limiting the process to a thin layer just outside the horizon. The study does not report observations of this process.

Young explorerScientists used math to ask whether changing magnetic fields could take some spinning energy from a special kind of black hole. In their model, spinning faster did not always help: a middle amount of spin worked best. The process also needed very strong magnetism and could work only in a thin layer just outside the black hole’s edge. This is a math prediction, not something they watched happen in space.

Search for active-sterile neutrino transitions using Pierre Auger Observatory data

Pierre Auger Collaboration, A. Abdul Halim, P. Abreu+97 more

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

AstronomerThe study estimates Pierre Auger Observatory sensitivity to magnetic-moment-induced transitions between active and heavy sterile neutrinos through a dipole portal. These hypothetical interactions can enhance neutrino–nucleon cross sections above a sterile-mass-dependent threshold. The estimated responses of down-going and Earth-skimming detection channels differ, offering a way to distinguish increased neutrino flux from an enhanced interaction cross section. Using the non-observation of ultrahigh-energy neutrino candidates, the authors derive flux-dependent, flavor-independent 90% confidence-level limits on the transition magnetic moment for sterile-neutrino masses of 1–100 TeV. Under the assumed flux scenarios, these limits extend existing bounds into previously unexplored parameter space; they do not constitute a detection of new physics.

PublicCould ultrahigh-energy neutrinos interact more strongly than expected because they can change into hypothetical heavy sterile neutrinos? This study estimates how such a process would affect neutrino detections at the Pierre Auger Observatory. Neutrinos arriving from above and those skimming through Earth would respond differently, potentially helping distinguish stronger interactions from a larger number of incoming neutrinos. Using the absence of observed neutrino candidates, the researchers place limits on the proposed interaction. These limits explore previously untested possibilities, but depend on assumptions about the incoming neutrino flux and are not evidence that sterile neutrinos exist.

Young explorerScientists wondered whether tiny particles called neutrinos might change into a heavier kind of particle that has not been discovered. They worked out how this could change what a big detector sees. Because the search found no neutrino candidates, they could limit how strong this change might be. The answer depends on how many neutrinos they think were coming. They did not discover the heavier particles.

A panchromatic photometric and spectroscopic modeling of SN1987A from 200 to 800d

Luc Dessart

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerRadiative-transfer models aimed at SN1987A span initial masses of 11–21 solar masses at one-third solar metallicity, with fixed ejecta kinetic energy of 1.2 × 10^51 erg and approximately 0.08 solar masses of nickel-56. In this grid, metallicity has relatively little influence at late times. The [OI] flux at 1–2 years varies non-monotonically with initial mass: increasing oxygen abundance initially strengthens it, but higher ejecta density suppresses it above roughly 17–19 solar masses. Assuming CO supplies 90% of C/O-shell cooling reduces [OI] flux by 10–20%. Most of the optical spectrum matches SN1987A across the mass grid, leaving [OI] as the only optical discriminator. The 13-solar-mass model best matches the UV-to-IR data, although strong CO and SiO cooling could permit a higher initial mass. Explaining the excess optical fading after 500 days requires growing dust below about 2,000 km/s in the models. Assuming 0.1-micrometre silicate grains gives inferred dust masses rising from 10^-4 solar masses at 600 days to a few 10^-3 solar masses at 700–800 days. The authors also identify hot-background-star contamination throughout the 200–800-day International Ultraviolet Explorer spectra, attributing the relative UV brightening after 500 days to that contamination.

PublicThe light from an exploded star can reveal its chemical makeup, but turning that light into an estimate of the star’s original mass is not straightforward. Researchers compared models with observations of supernova SN1987A. An oxygen emission feature was the only useful mass discriminator in the models’ optical spectra, yet it did not simply grow stronger with stellar mass: denser debris in the higher-mass models weakened it. A star initially weighing 13 times the Sun gave the best overall match, although stronger cooling by carbon monoxide and silicon monoxide could allow a higher mass. The models also required increasing amounts of dust to explain why the visible light faded faster after about 500 days than radioactive decay alone predicted. Those dust estimates depend on the assumed grain properties. Separately, the researchers found that a hot background star contaminated the ultraviolet observations, explaining an apparent late ultraviolet brightening and warning of similar confusion in studies of other fading supernovae.

Young explorerAfter a star explodes, its glowing leftovers can give clues about what the star was like. Scientists made computer models to compare with one real explosion. One model fit best, but molecules that help the gas cool could change the answer. They also needed growing amounts of dust in their models to explain the fading light. And they found that a hot star in the background was adding extra light to some observations.

Evidence for Ambipolar Diffusion from Ion-Neutral Velocity Drift in HH 212

J. A. López-Vázquez, Chin-Fei Lee, Carlos Tapia+4 more

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies

AstronomerALMA Band 7 observations resolve C17O (3–2) hyperfine emission and H13CO+ (4–3) emission in the Class 0 system HH 212 at approximately 44 au. Radiative-transfer modeling interpreted within non-ideal MHD yields an envelope mass of about 0.12 solar masses and an infall rate of 4.4–5.7 × 10^-6 solar masses per year, consistent with previous estimates. The models infer a systematic radial drift of 0.1–0.3 km/s between the neutral and ionized tracers; the spectral resolution is 0.105 km/s. An inferred ambipolar-diffusion fraction of roughly 0.1–1 and an ion–H2 Hall parameter much greater than unity support partial ion–neutral decoupling, with non-ideal effects becoming more important inward. Estimated rotational-to-gravitational energy ratios decline outward from about 50% at R_cen to 25% at 2R_cen and 4% at 1100 au. For an assumed B0 = 1 mG, magnetic-to-gravitational energy ratios instead rise from about 0.4% to 2.6% and 20% at those radii. Radial-force-balance predictions agree with the modeled drift within approximately 300–400 au but underpredict it farther out. The findings are consistent with, rather than definitive proof of, ambipolar diffusion allowing neutrals to fall inward faster than ions.

PublicObservations with ALMA examined gas around the very young star system HH 212, distinguishing emission from electrically neutral molecules and charged molecules. Models of these observations suggest that the two groups fall inward at slightly different speeds, with neutral gas moving faster. This is consistent with ambipolar diffusion: neutral and charged gas partly slipping past one another rather than moving together. The inferred speed difference is 0.1–0.3 kilometers per second, on the scale of the observations’ velocity resolution at its lower end. The analysis suggests that this separation becomes more important closer to the center. A calculation based on balancing radial forces matches the modeled difference within about 300–400 astronomical units of the center but predicts smaller differences farther out. The results therefore support this explanation without establishing it conclusively.

Young explorerAround a very young star system, gas is falling inward. Scientists used a telescope and models to study two kinds of tiny gas particles: ones with an electric charge and ones without. Their models suggest the uncharged particles may fall faster, slipping past the charged ones. This could explain what they found, but they are not sure yet.

Stellar Disruption and Black Hole Retention in Massive Collisions: The Role of Thermonuclear Feedback

Hongxuan Jiang, Douglas N. C. Lin

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerHydrodynamic simulations of head-on black hole–star collisions, now including gas-coupled CNO burning, show that nuclear reactions can prevent formation of a surviving black hole star. The models cover stellar masses of 100 and 500 solar masses, black-hole-to-star mass ratios q = 0.1 and 0.2, and solar, metal-deficient, and helium-rich compositions. In every model, drag dissipation alone is insufficient to disrupt the star, given the additional gas binding supplied by the captured black hole. Compression near the black hole heats gas above roughly 200 million K, triggering beta-limited hot-CNO burning. Within about one dynamical time after central settling, nuclear energy release becomes a significant fraction of the stellar binding energy; reaching that binding energy leads to loss of most of the stellar mass, whereas below this threshold the release rate declines. At q = 0.2, the solar-composition merger disrupts the star, but a metal-poor counterpart survives despite nearly equal binding energy and total nuclear yield. At q = 0.1, both compositions survive as black hole stars with nuclear luminosities of at least about 10^44 erg/s, far from thermal equilibrium. Weakly bound very massive and helium-rich stars are most easily disrupted. These are simulation outcomes, not observational detections.

PublicA black hole that crashes into a massive star can become trapped and sink to its center. Earlier simulations without nuclear reactions suggested that some stars could survive this encounter. These new simulations include nuclear burning and find that survival is not guaranteed. Gas squeezed around the captured black hole heats to more than roughly 200 million degrees, driving nuclear reactions that can release enough energy to throw off most of the star. The outcome depends on the star’s composition and the black hole’s mass relative to the star. In one comparison, a black hole one-fifth of the star’s mass destroys a star with Sun-like composition, while a similar star with fewer heavy elements survives. With black holes one-tenth of the stellar mass, both types survive, but their intense nuclear burning leaves them far from thermal balance. Very massive and helium-rich stars are easiest to disrupt in these simulations. The study models possible encounters rather than reporting an observed event.

Young explorerScientists used computer simulations to see what might happen if a black hole crashed into a big star. The black hole can sink to the middle and squeeze the star’s gas until it gets very hot. Nuclear reactions can then release enough energy to blow away most of the star. In some simulations, the star survives with the black hole inside. What happens depends on how big the black hole is and what the star is made of.

Radial Velocity Confirmation of Two Binary Systems Detected with the Pulsation Timing Method

Tomomi Otani, A. S. Baran, Kaydence Boyle+1 more

AstronomerFollow-up radial-velocity measurements from Gemini-North and the Nordic Optical Telescopes confirm TIC 202354658 and TIC 69298924 as subdwarf B binaries with white dwarf companions. Both systems were originally identified through pulsation timing and Fourier modulation in TESS ultra-short-cadence photometry. The RV orbital solutions agree with the pulsation-timing predictions and improve the precision of the orbital information. TIC 202354658 has a measured eccentricity of e = 0.313 ± 0.013, relatively large and uncommon for a short-period sdB binary.

PublicAstronomers have confirmed that two hot stars, TIC 202354658 and TIC 69298924, each have a white dwarf companion. The systems were first identified by analyzing changes in their repeating brightness variations in TESS observations. Follow-up telescope spectra measured the stars’ motion toward and away from us, confirming the earlier orbital predictions and providing more precise information about their orbits. TIC 202354658 has a notably noncircular orbit, with an eccentricity of 0.313 ± 0.013—uncommon for a short-period binary containing this type of hot star.

Young explorerAstronomers checked two stars and found that each has a small star called a white dwarf as a partner. Earlier clues came from the stars’ changing light. This time, the astronomers studied how the stars move, and the new clues matched the old ones. One pair follows a more stretched-out path than is usual for pairs like it that go around each other quickly.

The Role of Small-Scale Flux Emergence in Pre-eruptive Magnetic Destabilization

Satoshi Inoue, Huu Minh Triet Nguyen

AstronomerHigh-resolution observations have reported small-scale flux emergence shortly before solar flares, but its role in eruptions remains uncertain. This study tests its influence using three-dimensional MHD simulations of a bipolar active region, initialized with a potential field extrapolated from a sunspot pair and driven by sustained rotation to build shear along the polarity inversion line. Emerging flux with polarity opposite to the main sunspot and approximately 0.6%–3.0% of the total flux is introduced at the bipole center. Compared with simulations without this emergence, the early pre-existing field shows no significant differences, but the current sheet in the sheared field collapses faster and the reconnection-driven eruption begins earlier. The simulations suggest that small-scale emergence accelerates destabilization through enhanced current-sheet thinning and reconnection. They also identify the involvement of highly twisted field lines before eruption as crucial to the onset time; these are simulation findings rather than an observational demonstration of the mechanism.

PublicSmall patches of magnetic field have been observed appearing on the Sun shortly before solar flares, but scientists do not yet know what role they play. This study used three-dimensional computer simulations to test their effect in a magnetic region built around a pair of sunspots. Rotating motions increased the shear in the magnetic field, and the researchers added a small patch of opposite-polarity magnetic flux, representing about 0.6%–3.0% of the total. The added flux made little difference to the existing field early on, but later caused a thin layer carrying electric current to collapse faster. Magnetic reconnection—the rearrangement of magnetic field connections—then triggered an eruption earlier than in simulations without the added flux. The results suggest that small magnetic additions can hasten an eruption in this setup, not that observations have established this explanation. Highly twisted magnetic field lines also played a crucial role in setting the simulated eruption time.

Young explorerScientists have seen little new patches of magnetism on the Sun before some flares, but they do not know exactly what those patches do. They made a computer model of the Sun’s magnetic fields and added a little patch pointing the opposite way. At first, not much changed. Later, the magnetic fields changed their connections sooner, and an eruption started earlier than in the model without the patch. Very twisty magnetic fields also helped decide when it started. This is a clue from a computer model, not proof that the real Sun always works this way.

Solar cycle variations of meridional flow and differential rotation in a non-kinematic dynamo model

Bidya Binay Karak, Mark Miesch

• Plasma Physics

AstronomerThe authors develop a non-kinematic flux transport dynamo model with prescribed large-scale differential rotation and meridional flow, solving only for fluctuating flows and thermodynamics. This avoids requiring the Λ effect or other turbulent-transport parameterisations to generate the large-scale flows. Although constructed in 3D, the model currently operates in axisymmetric mode because its Babcock–Leighton poloidal-field source is assumed axisymmetric. It reproduces cycle-dependent variations in meridional flow and differential rotation, including torsional oscillations in some agreement with observations. The simulations also exhibit some solar-cycle variability without imposed stochastic fluctuations. These results offer a methodology for non-kinematic 3D solar dynamo modelling, rather than a demonstration of fully non-axisymmetric operation.

PublicResearchers have developed a computer model of the processes that generate the Sun’s changing magnetic field. They specify the Sun’s large-scale flows and calculate variations in those flows and in thermal conditions, rather than calculating how the large-scale flows arise. The model produces changes in circulation and rotation over the solar cycle, with the rotation changes showing some agreement with observations. Its simulated cycles also vary somewhat even without added random fluctuations. Although designed for three dimensions, the model currently assumes symmetry around the Sun’s rotation axis because of how one magnetic-field source is represented.

Young explorerThe Sun has a magnetic field that changes in a repeating cycle. Scientists made a computer model to explore how this happens. They tell the model how the Sun’s big flows move, and it works out smaller changes. Some changes it makes are a bit like ones seen on the real Sun. Its cycles are not all exactly alike, even without adding random changes. The model is built to work in three dimensions, but for now it treats every side around the Sun’s spinning axis as the same.

Evolving stellar wind environment around M dwarfs and its influence on magnetic star-planet interactions

Szymon Petyniak, Stefano Bellotti, Aline Vidotto+4 more

• Earth and Planetary Astrophysics

AstronomerThe study uses 18 magnetic-field maps of six M dwarfs, spanning 0.1–0.6 solar masses and rotation periods of 2.7–175.6 days, as inputs to 3D magnetohydrodynamic wind simulations. The simulations yield mass-loss rates of 1.0 × 10^-14–2.3 × 10^-13 solar masses per year and angular momentum-loss rates of 4.6 × 10^27–4.9 × 10^31 erg. For individual stars, the Alfvén radius, mass-loss rate, and angular momentum-loss rate vary over time by factors of up to 1.5, 3.8, and 7.4, respectively. The modeled results follow the observational relation between mass-loss rate and X-ray flux. Wind variability at planetary orbits is examined for DS Leo, YZ Cet, and GJ 1151. The simulations indicate that the changing Alfvén surfaces around DS Leo and YZ Cet cause their planets to move into and out of the sub-Alfvénic regime, changing the character and potential detectability of star–planet interactions. These are modeled wind properties and interaction implications, not direct detections of those interactions or demonstrated effects on habitability.

PublicM dwarfs are the Galaxy’s most common stars, and their changing magnetic fields may alter the stellar winds experienced by nearby planets. Researchers used 18 magnetic-field maps of six M dwarfs to run three-dimensional computer simulations of those winds. For individual stars, the modeled rate of material lost through the wind changed by as much as a factor of 3.8, while the rate of angular momentum loss changed by as much as a factor of 7.4. The models also suggest that planets around DS Leo and YZ Cet cross a shifting boundary between different wind-interaction conditions. This could change how the planets interact with their stars and whether signs of those interactions can be detected repeatedly. The work provides a basis for future studies of planetary habitability; it does not establish whether these planets are habitable.

Young explorerStars can blow winds into space. Scientists used maps of six stars’ magnetism to make computer models of their winds. In the models, the winds changed as the magnetism changed. Planets going around two of the stars moved between places where they could interact with their stars in different ways. That might make clues about those interactions easier or harder to spot. The models do not tell us whether anything could live on those planets.

A Census of Novae in the Small Magellanic Cloud, 1897-2026

Allen W. Shafter

• Astrophysics of Galaxies

AstronomerThis census reviews 26 optical transients reported as novae or nova-like eruptions in the Small Magellanic Cloud, from HV 849 in 1897 through October 2026. Twenty-three are classified as probable classical novae. MAXI J0158−744 and CXOU J005245.0−722844 are very fast, super-Eddington eruptions interpreted as novae on white dwarfs with Be-star companions. SMCN 2002-10a is another possible Be+WD event, but that identification rests only on its quiescent counterpart. Four additional Be+WD candidates detected only in X-rays are briefly discussed.

PublicThe study compiles 26 temporary optical brightenings reported as possible nova eruptions in the Small Magellanic Cloud between 1897 and October 2026. Of these, 23 are probably classical novae. Two unusually fast and luminous eruptions have been interpreted as novae involving white dwarfs with companions of a type called Be stars, but this explanation is not presented as certain. A third possible pairing is suggested only by the star system seen when it was quiet. The study also briefly discusses four additional candidate pairings detected only in X-rays.

Young explorerAstronomers made a list of 26 times that things in a nearby galaxy suddenly looked brighter. They think 23 were probably star eruptions called novae. Two flashes were very quick and very bright, and scientists think each may have come from a white dwarf star with a partner star. Another might be like them, but the clue comes only from how it looked when it was quiet. They also mention four more possible star pairs seen only in X-rays, not ordinary light.

The Dusty Circumstellar Structure of the Yellow Hypergiant IRC +10420: Constraints from the SED and Near-Infrared Imaging Polarimetry

Kyung-Won Suh

AstronomerRADMC-3D polarized radiative-transfer modeling of the post-red supergiant IRC +10420, assuming a pole-on view, fits the 0.4 μm–1.3 mm SED within 0.07 dex and reproduces K′ total- and polarized-intensity profiles. The adopted geometry combines a flared inner disk, an extended ring and a thin large-grain mid-plane disk within a spherical envelope with density proportional to r^-2.3. The model polarization peaks at 15% at 1.7 arcsec, compared with 14% observed. The authors attribute the polarized-intensity plateau to the ring’s rising surface density and the decline beyond 2 arcsec to 0.5 μm grains at its outer edge; grains at least 0.7 μm in size are excluded in this modeling context. The large-grain disk suggests, rather than establishes, mid-plane settling. Stellar temperatures of 7000–8500 K fit equally well. The inferred dust mass is 0.074 solar masses, mostly equatorial; the envelope implies a mass-loss rate of approximately 10^-5–10^-4 (ψ/100) solar masses per year. Of approximately 6.9 magnitudes of visual extinction, 5 are interstellar. Modeled poleward redirection of starlight makes the pole-on SED overestimate luminosity by a factor of approximately 1.5, yielding approximately 330,000 solar luminosities at the Gaia distance. Subtracting a scaled stellar point-spread function removes most nebular light within approximately 1 arcsec.

PublicIRC +10420 is a massive star evolving toward higher temperatures after its red-supergiant phase. Researchers modeled how surrounding dust absorbs and scatters its light, comparing their calculations with observations across many wavelengths and with images measuring light’s polarization. Assuming we look along the system’s pole, a model containing disks and a ring inside a spherical dust envelope closely matches the observations. This is a model-based interpretation, not a direct picture of every dust structure, and several stellar temperatures fit equally well. The calculations suggest that equatorial dust redirects light toward us, making the star appear about 1.5 times more luminous than it really is. Correcting for this gives an estimated luminosity about 330,000 times the Sun’s.

Young explorerA huge star has dust around it. Scientists made a computer model to see how that dust could change the light we see. A model with dusty disks and a ring matched the observations well, but it may not tell the whole story. The dust may send extra light our way, making the star look brighter than it really is.

Enhanced Mid-Photospheric Heating Around a Solar Pore

Ana Belén Griñón-Marín, Adur Pastor Yabar, Jaime de la Cruz Rodríguez+32 more

AstronomerSpatially coupled NLTE spectropolarimetric inversions of Sunrise iii/SCIP observations reconstruct the thermal, magnetic, and velocity stratification of a solar pore from the photosphere to the chromosphere over approximately two hours. The inferred photosphere contains a cool umbra with strong, predominantly vertical fields. Most photospheric flows are subsonic, but localized boundary downflows reach transonic or potentially supersonic speeds near log τ500 = 0. The pore’s thermal contrast with its surroundings decreases substantially at greater heights. Localized mid-photospheric temperature enhancements form a patchy ring in the Ca II 8542 Å wings, without a clear continuum counterpart; inferred excesses reach approximately 300 K and thermal-energy densities up to 170 J m−3. These regions coincide with enhanced transverse fields and the expanding magnetic canopy. The structure appears in all three rasters, but the cadence cannot distinguish persistent patches from repeated formation. The inferred topology supports an association with canopy processes, without uniquely identifying the heating mechanism.

PublicResearchers used observations from the SCIP instrument aboard Sunrise iii to reconstruct temperature, magnetic fields, and flows at different heights in and around a solar pore. Over roughly two hours, they found a cool central region with strong, mostly vertical magnetic fields. Most flows in the lower atmosphere were slower than sound, although small areas near the pore’s edge showed downward flows near, or possibly above, the local sound speed. Higher up, the temperature difference between the pore and its surroundings became much smaller. The reconstruction also revealed patches about 300 K warmer than their surroundings, arranged in a broken ring and associated with magnetic fields spreading outward above the pore. This pattern appeared in all three scans, but the observations cannot show whether the same patches lasted or new ones kept forming. The magnetic arrangement suggests a connection to the heating, but its cause remains uncertain.

Young explorerScientists looked at a small, cool patch on the Sun and used its light to work out what was happening at different heights. They found strong magnetic fields and little warmer patches making a broken ring around it. The magnetic fields spread outward near these warm patches, so they might be connected to the warming, but scientists do not yet know how. They saw the ring in three scans, but cannot tell whether the same warm patches stayed there or new ones appeared.

An assessment of the Weak Field Approximation

D. Arroyo Caballero, J. C. del Toro Iniesta, D. Orozco Suárez+1 more

AstronomerThis study tests the Weak Field Approximation (WFA) using analytically derived Generalized Response Functions and synthetic Stokes profiles computed with SIR and DeSIRe, rather than new solar observations. Across photospheric and chromospheric lines, the inferred field depends on atmospheric structure, field inclination, and wavelength selection. For photospheric lines, departures from the actual field strength grow well before saturation as the linear relationships between Stokes V, Q, U and intensity-profile derivatives break down. Transverse-field estimates are especially sensitive to wavelength selection, with line wings yielding more reliable estimates. Chromospheric line cores and wings sample different atmospheric layers; their wings can reliably constrain photospheric fields in the cases studied. The results indicate a narrower validity range than commonly assumed and support the WFA’s original perturbative formulation.

PublicAstronomers often estimate the Sun’s magnetic field from the polarization of its light using a simplified method called the Weak Field Approximation. This study tested that method with computer-generated light signals, not new observations. The tests show that its accuracy depends on the Sun’s atmospheric structure, the magnetic field’s strength and direction, and which wavelengths are used. Errors can grow before the method reaches its expected saturation limit. Estimates of the field perpendicular to our line of sight are particularly sensitive to wavelength choice. The outer parts of spectral lines can give more reliable estimates, and the wings of lines associated with the upper solar atmosphere can reveal magnetic fields lower down. The findings suggest the method needs more cautious application.

Young explorerScientists use the Sun’s light to work out what its invisible magnetic fields are like. They tested a shortcut for doing this using pretend sunlight made by computers. The shortcut did not always give the right answer. Which parts of the light they used mattered, so scientists need to choose carefully.

Zeeman-Doppler imaging of early-type stars. Testing Stokes parameter inversions with theoretical magnetohydrodynamic models

O. Kochukhov, A. Al Kanale, J. Braithwaite

AstronomerThis study tests modern Zeeman-Doppler imaging (ZDI) against synthetic spectropolarimetry generated from three-dimensional MHD simulations of early-type stellar fossil fields, rather than against observations of real stars. Within these tests, full-Stokes IQUV inversions recover field components and strength to better than 10% accuracy; IV-only inversions degrade to 15–20% for the most complex geometries. Field-inclination errors are within 10 degrees, rising to 15–20 degrees in those complex cases. Full-Stokes inversions recover poloidal and toroidal energy fractions within a few percentage points. LSD-profile inversions perform comparably to, and sometimes better than, individual Fe II-line inversions. A current-free poloidal constraint satisfied by the input field helps only where unconstrained IV inversions perform poorly. Magnetic–abundance cross-talk is weak, with average spurious abundance inhomogeneities at or below 0.1 dex. The results support reliable recovery of smaller-scale, non-dipolar structure for the tested simulated fields, especially with full-Stokes data.

PublicAstronomers use Zeeman-Doppler imaging to map stellar magnetic fields from changes in the spectrum and polarization of starlight. This study checked the method using artificial observations made from three-dimensional simulations of magnetic fields in early-type stars, so the researchers could compare each reconstructed map with the known input. With all four Stokes measurements, which describe light intensity and polarization, the method recovered magnetic-field strengths and components with errors below 10%. Using only intensity and circular polarization gave errors of 15–20% for the most complex fields. The tests also recovered smaller magnetic features beyond a simple dipole, and using combined signals from many spectral lines worked about as well as, or sometimes better than, using individual lines. These simulation-based results support the method’s reliability, especially when fuller polarization information is available; they are not a direct validation against known magnetic maps of real stars.

Young explorerScientists want to draw maps of the invisible magnetic fields on stars. To check their map-making tool, they made pretend stars and pretend starlight in a computer. Then they asked the tool to draw the magnetic maps and compared them with the answers they already knew. The tool did well, even with some small, tricky shapes. It worked best when it had more kinds of information about the light. These were computer tests, not checks on real stars.

Parker Solar Probe Flies Through the Sun's Magnetic Poles Near 10 Solar Radii

Yeimy J. Rivera, Adam J. Finley, Samuel T. Badman+18 more

• Space Physics

AstronomerParker Solar Probe measurements from two close approaches in mid-2025 indicate that the large-scale coronal magnetic field near solar maximum resembled a simple tilted dipole. Parker sampled the full range of magnetic latitudes, including both magnetic poles below the Alfvén surface. Concurrent in situ measurements farther out reveal solar wind in both magnetic hemispheres with asymptotic speeds near 800 km s-1. The dipolar organization coexists with non-dipolar source-region structure that deforms the fast streams: the positive dipole axis aligns with a coronal hole, the negative axis centers over a pseudostreamer, and significant mass-flux enhancements occur at magnetic separatrices. The authors attribute the contrast with Ulysses's disordered solar-maximum latitude scan to that scan's long collection timescale. These observations suggest that the corona can retain nearly solar-minimum-like order even at solar maximum, while rapid sampling close to the Sun reveals source-region imprints in the wind.

PublicEven when the Sun is at the peak of its magnetic activity, its outer atmosphere can have a surprisingly simple large-scale magnetic pattern. Data from two close passes by Parker Solar Probe in mid-2025 showed a pattern resembling a tilted magnet with two poles. The spacecraft sampled both magnetic polar regions close to the Sun, while measurements farther away found solar wind in both magnetic hemispheres reaching speeds near 800 kilometers per second. Smaller magnetic structures still distorted the fast wind streams, and more material flowed along boundaries separating magnetic regions. The authors suggest that an earlier, more disordered view from Ulysses at solar maximum reflected the much longer time needed to collect its measurements. The findings suggest that the Sun's outer atmosphere can remain nearly as orderly at peak activity as during its quiet phase, without being simple everywhere.

Young explorerThe Sun has an invisible magnetic field and sends out a wind of tiny particles. When the Sun is very busy, that field might look messy. But on two close visits, a spacecraft called Parker found a big pattern like a tilted magnet with two poles. Smaller magnetic patterns still bent the fast wind and made more particles flow in some places. These visits suggest that even a busy Sun can have a tidy big pattern hiding among the smaller, messy parts.

Investigating the timescales traced by dynamical ages in young stellar systems

Isabella Armstrong, Alison Sills, Claude Cournoyer-Cloutier

• Astrophysics of Galaxies

AstronomerThis simulation-based study tests five dynamical age methods to distinguish stellar formation timescales from cluster assembly timescales. The methods track either cluster size evolution or individual stellar trajectories. In the simulation, size-based methods cannot accurately recover ages for bound clusters and instead best trace the onset of expansion; individual-star traceback methods are applicable to both bound and unbound systems. The oldest stellar traceback ages provide an upper limit on stellar ages, while median traceback ages best approximate isochronal ages. The authors suggest that the median traceback time of stars moving away from a cluster is the most reliable proxy for isochronal age and could be applied to any expanding system. These conclusions come from a star formation simulation, not an observational validation with Gaia.

PublicStars can form before they gather into a cluster, so the age of the stars and the time taken to assemble the cluster need not be the same. Researchers tested five ways of estimating these times from stellar motions in a star formation simulation. Methods that follow the cluster’s changing size worked best for identifying when expansion began, but could not accurately determine ages for clusters held together by gravity. Following individual stars backward along their paths could be used for both gravitationally bound and unbound groups. The study suggests that the middle value of the backward-traced times for stars moving away from a cluster is the most reliable match to ages estimated from stellar evolution. This is a simulation-based finding, rather than a demonstrated result from observations.

Young explorerStars can be born first and gather into a group later, so those two things have different clocks. Scientists used a computer-made group of stars to test five ways to read those clocks. Watching how big the group gets was best for telling when it started spreading out. Following the stars’ paths backward gave other clues. The scientists think the middle time from stars moving away may be the best clue to how old the stars are. They tested this idea in a computer simulation, not with a real group of stars.

Three-dimensional radiative transfer modeling of the scattering polarization in the solar Hα line

Jaume Jaume Bestard, Jiri Stepan, Javier Trujillo Bueno

AstronomerThe study computes Hα intensity and linear polarization in a 3D magnetohydrodynamic solar-atmosphere model with nonequilibrium hydrogen ionization. PORTA solves multilevel, full 3D non-LTE polarized radiative transfer including atomic polarization, Hanle depolarization, horizontal transfer, and macroscopic velocities. Synthetic Stokes profiles degraded to ZIMPOL resolution reproduce the observed center-to-limb trend with comparable polarization amplitudes. The synthetic profiles exhibit substantial spatial variability and diverse line-core asymmetries arising from horizontal inhomogeneities and dynamics. Classifying modeled Q/I profiles by asymmetry reveals a statistical association with magnetic-field strength in the Hα formation region: multi-peaked profiles favor stronger fields, while asymmetric single-peaked profiles favor weaker fields with smaller vertical strength variations. This association is consistent with Hanle depolarization, but the profiles also depend on velocity gradients and 3D radiative transfer, underscoring the need for 3D modeling rather than a unique magnetic interpretation of profile shape.

PublicResearchers used a three-dimensional computer model to study how hydrogen’s Hα light can reveal conditions in the Sun’s chromosphere. They calculated both its brightness and its linear polarization, which describes a preferred orientation of the light’s oscillations. After adjusting the simulated signals to match the resolution of ZIMPOL observations, the model followed the observed polarization trend from the center of the Sun’s disk toward its edge, with comparable signal sizes. Within the simulation, polarization profiles with several peaks tended to occur in stronger magnetic fields, while uneven single-peaked profiles favored weaker fields whose strength changed less with height. These are statistical links in the model, not a direct measurement of the Sun’s magnetic fields. Gas motions and three-dimensional atmospheric structure also shape the signals, so interpreting them requires accounting for more than magnetism alone.

Young explorerScientists made a computer model of part of the Sun’s atmosphere to study a special kind of light from hydrogen. The model’s light behaved somewhat like light seen from the real Sun. In the model, light patterns with several bumps tended to go with stronger magnetic fields, while some uneven patterns with one bump tended to go with weaker fields. But moving gas and a patchy atmosphere changed the patterns too. The light may help scientists learn about the Sun’s magnetism, but they must untangle all these clues carefully.

Effect of Turbulence and Inhomogeneities on the Propagation of Kinetic Scale Waves

Trevor A. Bowen

• Space Physics
• Plasma Physics

AstronomerThe study applies moving-medium ray equations to Parker Solar Probe observations of solar-wind ion cyclotron waves (ICWs), constraining gradients in the dispersion relation and comparing them with a Parker spiral model. Empirically constrained gradients, which include turbulent motions, substantially enhance WKB propagation effects. Nevertheless, typical refraction rates remain significantly slower than the expected quasilinear evolution of the observed wave populations. This comparison suggests that local kinetic physics dominates over nonlinear expansion effects, with turbulent gradients insufficient to substantially modify an individual ion-scale ICW during its lifetime. Incorporating kinetic effects of expansion is proposed as a way to improve understanding of ICW generation, absorption, and their role in solar-wind heating.

PublicResearchers used Parker Solar Probe observations and equations describing wave travel to investigate how turbulence affects ion cyclotron waves in the solar wind. Their analysis indicates that turbulence strengthens the effects of spatial variations on the waves’ propagation. Even so, the estimated rate at which those variations redirect the waves is much slower than the expected changes caused by local interactions between particles and waves. This suggests that local particle physics matters more for an individual wave’s evolution, and that turbulent variations do not substantially change it during its lifetime. The authors propose including additional particle-level effects of the wind’s expansion to better understand how these waves form, are absorbed, and contribute to heating.

Young explorerThe Sun sends a stream of tiny particles into space, and waves can travel through it. Scientists used measurements from Parker Solar Probe and math to study how bumps in that stream affect the waves. Their work suggests that the bumps change how the waves travel, but not enough to change one wave very much before it fades away. What happens between the waves and nearby particles seems to matter more.

SWXAI: A Unified Multimodal Explainability Library for Space Weather Forecasting and Heliophysics

Benedict Antonio Mervyn, Anli Ji, Manolis K. Georgoulis+1 more

• Machine Learning
• Space Physics

AstronomerThe authors present SWXAI, an open-source library that unifies explainable-AI workflows for image, time-series, and tabular models used in space weather forecasting and heliophysics. Its common, extensible interface provides validation, adaptation, and persistent explanation objects, alongside domain-specific examples, reproducible notebooks, tests, and documentation. The goal is to reduce fragmented, modality-specific engineering and support reusable, comparable explanations across heterogeneous machine-learning pipelines. A benchmark against direct backend implementations reports substantially less user-written code to generate explanations, with no practical runtime cost. The abstract does not report improved forecast accuracy or establish that the explanations identify physical causes.

PublicMachine-learning systems used to study the Sun and forecast space weather handle many kinds of information, but the tools for inspecting their outputs are often difficult to combine and reuse. The authors introduce SWXAI, a free, open-source library that brings explanation tools for images, time series, and tables into a common framework. It includes examples and documentation to help researchers inspect model outputs and switch models or explanation methods. In a software benchmark, SWXAI substantially reduced the amount of code users needed to write without a practical slowdown. This is a result about making explanation workflows easier to build, not evidence that space weather forecasts became more accurate.

Young explorerScientists use computers to look for patterns in pictures and other information about the Sun. It can be hard to check how those computers give their answers. The researchers made a shared toolbox called SWXAI to help scientists look for clues about those answers. In a test, scientists needed to write much less computer code, and the toolbox did not noticeably slow the work down. That does not mean the computers got better at predicting what the Sun will do.

Relative Entropy Methods for Rotating Stars in the Compressible Euler-Riesz Equations

Gui-Qiang G. Chen, Difan Yuan

• Analysis of PDEs
• Mathematical Physics
• Pattern Formation and Solitons

AstronomerThis mathematical study establishes finite-time relative entropy estimates for axisymmetric, finite-energy entropy solutions of the three-dimensional attractive compressible Euler–Riesz equations near a prescribed compactly supported rotating equilibrium. The solutions must share the equilibrium’s total mass and satisfy a prescribed angular momentum relation. For general pressure laws, compatibility with this constraint and a nonnegative rotational remainder cancel the centrifugal terms. Axisymmetry removes the azimuthal component of the perturbed Riesz-potential gradient, allowing density-weighted potential estimates and the modulated kinetic energy to close the relative entropy inequality. With an additional higher-integrability assumption on density, the analysis extends to the Chandrasekhar pressure law and provides a corresponding stability estimate for rotating white dwarf models. These are conditional mathematical estimates, not observational findings or an unrestricted claim of long-term stability.

PublicThe authors prove mathematical bounds on how a model of a rotating star can depart from a steady configuration over a finite period. Their analysis applies to disturbances that remain symmetric around the rotation axis, preserve the star model’s total mass, and obey a specified angular momentum condition. These restrictions let the researchers control the interacting effects of rotation, fluid motion, and attraction in the equations. With an extra mathematical assumption about density, the bounds also apply to models of rotating white dwarfs. The work concerns equations rather than observations, and it does not establish that every disturbed rotating star remains stable indefinitely.

Young explorerImagine a spinning star that gets a little nudge. The researchers used math to put limits on how much a pretend star in their equations could change for a certain amount of time. Their rules work only for special nudges that stay the same all the way around the star’s spinning axis and follow other conditions. With one extra rule about how tightly matter is packed, the math also works for a kind of star called a white dwarf. They did not watch real stars do this, and they did not show that the stars stay steady forever.

Global MHD simulations of the solar convective zone using a volleyball mesh decomposition. I. Pilot

Andrius Popovas, Åke Nordlund, Mikolaj Szydlarski+1 more

• Computational Physics

AstronomerThis methods and proof-of-concept study addresses bottlenecks in connecting solar convection-zone and dynamo simulations to the surface. Using the task-based DISPATCH framework, the authors introduce a singularity-free “volleyball” mesh of Cartesian patches tessellated on a sphere and an entropy-based HLLS approximate Riemann solver for magnetohydrodynamics. Pilot global simulations span 0.655–0.998 solar radii and begin with a 0.1-gauss ambient magnetic field. In these runs, the mesh shows neither unwanted artefacts nor noise build-up, while convection develops complex turbulent structures. Small-scale dynamo action twists the initial field and locally amplifies its magnitude by more than two orders of magnitude during the initial runtime. These are simulation findings from a pilot setup, not solar observations or a demonstration that the interior–surface modelling disconnect has been fully resolved.

PublicModelling the Sun’s interior and its surface together is difficult because they involve very different sizes, timescales and physical conditions. This study tests new computer methods intended to help bridge that divide. The researchers arrange small box-shaped simulation regions around a sphere in a pattern they call a “volleyball” mesh, then simulate moving, magnetized gas across a region extending from inside the Sun to near its surface. In the pilot simulations, the mesh produces no unwanted numerical patterns or build-up of noise, and the gas develops complicated, turbulent motions. Those motions twist an initially weak magnetic field and make it locally more than 100 times stronger during the initial run. This is a promising test of a modelling approach, rather than an observation of the Sun or a complete solution to linking its interior and surface.

Young explorerScientists want to understand how the Sun’s inside connects to its outside. They tested a new computer model made of little boxes arranged around a ball, a bit like a volleyball. In their pretend Sun, hot gas swirled around and twisted a weak magnetic field, making it much stronger in some places. The new arrangement worked without creating unwanted computer patterns in these first tests. This is an early step toward a better model, not something they watched happen on the real Sun.

Star Planet Interactions

Arghyadeep Paul, Kristina Kislyakova, Manuel Güdel+13 more

• Earth and Planetary Astrophysics

AstronomerThis review synthesises theoretical and observational understanding of radiative, tidal, magnetic, and particle-driven star–planet interactions, using the Solar System as a reference. Far- and extreme-ultraviolet and X-ray irradiation drive atmospheric heating, photochemistry, ionisation, and escape, while winds and magnetic interactions can either protect atmospheres or accelerate their loss. Tides redistribute energy and angular momentum, producing internal heating, migration, and orbital circularisation. Magnetic reconnection and current systems offer additional energy-transfer pathways, with potential effects including enhanced escape, ionospheric and interior heating, radio emission, and enhanced stellar activity. These magnetic effects are presented as possibilities, not newly established detections. The review emphasises coupled evolution and the dependence of long-term outcomes on stellar evolution, planetary properties, atmospheric structure, and magnetic field strength, with implications for future studies of evolution and habitability.

PublicA planet’s environment depends not only on its star’s light, but also on stellar winds, gravity-driven tides, and magnetic connections. This review brings together existing theory and observations to explain how these processes work together; it does not report a new experiment or discovery. High-energy starlight can heat and change an atmosphere and drive gas away. Winds and magnetic interactions can help protect an atmosphere or increase its loss, while tides can heat a planet’s interior and change its orbit. Magnetic connections may also produce radio signals or increased activity on the star. The long-term outcome depends on how the star evolves and on the planet’s atmosphere, magnetic field, and other properties. Understanding these connections can guide future studies of planetary evolution and habitability.

Young explorerA star does more than shine on its planets. Its light can warm their blankets of air and help some air drift away. Stars and planets also tug on each other, which can warm a planet inside and change its path. Their magnetic fields can help keep air safe or help it escape. This article gathers what scientists have learned and what their ideas suggest about these effects. Not every planet changes in the same way.

On Bimodality in the Eccentricity Distribution of Galactic Double Neutron Stars

Aldana Grichener, Paul Disberg, Ryosuke Hirai+1 more

• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena

AstronomerThe observed Galactic double neutron star (DNS) sample contains relatively few systems at intermediate orbital eccentricities, but does not yet provide statistically significant evidence for bimodality. The authors propose that a non-monotonic progenitor-mass–neutron-star-mass relation could generate such a deficit if the second-born neutron star receives a sufficiently small natal kick. Their COMPAS population-synthesis model produces a broadly similar deficit and reproduces the observed orbital period–eccentricity distribution relatively well. Most measured second-born neutron star masses also lie within the model’s predicted ranges at the corresponding eccentricities, offering a complementary diagnostic less sensitive to uncertainties in preceding binary evolution. The model predicts that eccentricity bimodality will become clearer as the Galactic DNS sample grows; this remains a prediction rather than an established population property.

PublicAmong the pairs of neutron stars observed in our Galaxy, relatively few have orbits with a middle-range degree of elongation. The sample is still too small to establish that these systems truly divide into two groups by orbit shape. The researchers propose an explanation involving how a star’s starting mass determines the neutron star mass it leaves behind, provided the second neutron star receives only a small kick at birth. In their proposed relationship, a heavier starting star does not always leave a heavier neutron star. Computer simulations using this idea produce an orbit pattern broadly like the observed one, and most measured masses of second-born neutron stars fit the model’s expected ranges for their orbit shapes. The researchers predict that the two-group pattern will become clearer as more pairs are found.

Young explorerSome neutron stars travel around each other in pairs. Astronomers have found a few pairs whose paths are very stretched out and others whose paths are rounder, but fewer in between. They have not found enough pairs to know whether this pattern is real. The researchers tried a computer model with an idea about how heavy these stars are when they form and how gently the second star gets nudged at birth. The model made a pattern like the one astronomers see. The researchers think finding more pairs will make the pattern clearer, but that still needs to be checked.

Energy Partitioning at the Termination Shock

Judit Szente, Bart van der Holst, Gabor Toth+1 more

AstronomerA global 3D MHD simulation of the outer heliosphere uses a new prescription for partitioning non-adiabatic termination-shock heating among cold solar-wind protons, electrons, and pickup ions, while conserving total ion energy. Earlier prescriptions overestimated the proton temperature jump measured by Voyager 2. In the revised simulations, allocating up to 8.5% of the non-adiabatic heating to thermal solar-wind protons reproduces the observed jump conditions along the Voyager 2 trajectory; the required fraction depends on thermal-proton and pickup-ion number densities. The work provides a framework for incorporating shock-energy partitioning from kinetic simulations into global MHD models, rather than establishing a unique physical heating mechanism.

PublicResearchers improved a three-dimensional computer model of the Sun’s outer surroundings by changing how heating at the termination shock is shared among different particle populations. Earlier simulations made the solar-wind protons’ temperature rise too much compared with Voyager 2 measurements. The revised model reproduces the observed changes along the spacecraft’s path when up to 8.5% of the modeled extra shock heating goes to those protons. That fraction depends on the relative numbers of thermal protons and pickup ions. This is a better match between a simulation and spacecraft observations, not a direct measurement of how the heating is divided.

Young explorerVoyager 2 measured how much some tiny particles warmed up far from the Sun. An older computer model made them too hot. Scientists changed how the model shares heat among different kinds of particles, and it matched Voyager’s measurements better. That helps them study what might happen there, but it does not prove exactly how nature shares the heat.

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

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

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies

AstronomerHigh-resolution VLT/CRIRES+ spectroscopy of selected dark features discovered in JWST/NIRCam F115W images of the inner Orion Nebula confirms that their darkness reflects reduced He I 1.083 μm triplet flux, with a fairly uniform reduction across the line. A simple radiative-transfer model explains the features as absorption of emission from the nebula’s dense, bright ionised layer by intermediate-density helium lying in front of that layer. Possible absorbing structures include clumps, globules, and winds from objects such as proplyds; these are proposed settings for the model, not individually established identifications.

PublicPreviously unknown dark features in JWST images of the inner Orion Nebula prompted astronomers to investigate what makes them dark. Follow-up observations with the VLT confirm that selected features have less light from a particular helium signal, at a wavelength of 1.083 micrometres, with a fairly even reduction across that signal. A simple model explains this as helium gas in front of the nebula’s bright, dense layer absorbing light from behind it. The absorbing gas could be in clumps, globules, or winds from objects such as proplyds, but the abstract does not establish which structures account for each feature.

Young explorerAstronomers found dark patches in pictures of a big cloud in space called the Orion Nebula. They checked some patches and found that less of one kind of helium light reaches us there. Their simple model suggests that helium gas in front catches some light coming from a bright layer behind it, making a dark patch. They do not yet say exactly what holds the gas in each patch.

The Optics of Shadow Bands

Branko Sretenović

• Popular Physics
• Optics

AstronomerThe article develops a proposed explanation for eclipse shadow bands, transient light and dark patterns reported just before and after totality whose physical origin remains unresolved. The analysis combines solar-limb geometry with a wave-based formulation, treating the Sun’s extended structure as a celestial analogue of Young’s double-slit experiment that produces interference fringes on the ground. It yields quantitative predictions for fringe width and spacing and examines other band properties. The abstract does not report observational tests of these predictions.

PublicRippling bands of light and dark sometimes appear on the ground just before and after a total solar eclipse. Their cause remains unresolved. This article proposes that the Sun’s shape and extent allow sunlight to produce an interference pattern, analogous to the bright and dark stripes in a double-slit experiment. The model predicts the widths and spacing of the bands, but the abstract does not report observations testing whether those predictions match real shadow bands.

Young explorerAround a total solar eclipse, wiggly bright and dark stripes can sometimes appear on the ground. Scientists are not sure why. This article suggests that sunlight waves overlap to make the stripes. It predicts how wide and far apart they should be, but does not say whether real stripes match.

Convection in the interior of Cepheid variable stars

Maxime Stuck, Jane Pratt

• Fluid Dynamics

AstronomerThe abstract identifies the paper as associated with a poster that won a 2025 American Physical Society Division of Fluid Dynamics Gallery of Fluid Motion Award and directs readers to the original poster online. It provides no scientific methods, observations, simulations, or conclusions, so no research findings can be assessed from this abstract.

PublicThis paper is linked to an award-winning poster presented at the 2025 Gallery of Fluid Motion, an American Physical Society event. The abstract points readers to the poster online but does not explain the research or report any scientific results.

Young explorerThis paper is linked to a science poster that won a prize. The note says the poster is online, but it does not tell us what the scientists did or learned.

The deuterium-rich atmosphere of a mature super-Jupiter

Jerry W. Xuan, Yayaati Chachan, Jean-Baptiste Ruffio+23 more

• Solar and Stellar Astrophysics

AstronomerJWST observations detect deuterated methane at 48σ in the mature giant exoplanet ε Ind Ab, yielding D/H = (4.4 ± 0.7) × 10^-5. This is similar to Uranus and Neptune and about twice the values for Jupiter, Saturn, and the protosolar nebula. C, O, N, and S are uniformly enriched at a level similar to Jupiter’s. The authors infer that the planet must have accreted solids with D/H ≳ 1%, at least 30 times that of typical Solar System comets. Comparable ratios in the interstellar comet 3I/ATLAS and organic molecules in star-forming regions support their interpretation that these solids were pristine material formed in a very cold environment.

PublicUsing the James Webb Space Telescope, researchers detected methane containing deuterium, a heavy form of hydrogen, in the mature giant planet ε Ind Ab. They measured about 4.4 deuterium atoms per 100,000 hydrogen atoms, with an uncertainty of 0.7 per 100,000. That ratio resembles those of Uranus and Neptune and is about twice those of Jupiter and Saturn. The planet’s carbon, oxygen, nitrogen, and sulfur are also enriched to a level similar to Jupiter’s. From these measurements, the researchers infer that the planet gathered solid material with a deuterium-to-hydrogen ratio of at least about 1%—at least 30 times that of typical Solar System comets. They interpret this as evidence that the solids formed in a very cold environment and retained their original chemical signature.

Young explorerScientists used the James Webb Space Telescope to study a giant planet called ε Ind Ab. They found a gas containing a special, heavier kind of hydrogen. The planet has about twice as much of this heavy hydrogen compared with ordinary hydrogen as Jupiter does. The scientists think this means the planet grew by gathering pieces of material that formed somewhere very cold.

Thermally unfavorable conditions of volatile existence in near-Earth asteroid 1998 KY₂₆, the Hayabusa extended mission's target

Korbin Hansen, Masatoshi Hirabayashi

Astronomer1998 KY26, the target of the Hayabusa2# extended mission, has been proposed as a volatile-bearing dark comet because its anomalous out-of-plane nongravitational acceleration might arise from outgassing, although its possible taxonomic affiliation suggests a largely anhydrous composition. This thermophysical study models whether volatiles could be retained. Across 13 thermal characterizations varying equivalent diameter, thermal conductivity, Bond albedo, specific heat capacity, and spin-pole orientation, modeled orbit-averaged temperatures throughout the surface and interior significantly exceed volatile sublimation temperatures in vacuum. The modeled water outgassing rate would be too high to sustain buried ice. These results challenge the retention of buried water ice under the modeled conditions; they are not a direct detection of outgassing or a determination of the acceleration's cause.

PublicThe near-Earth asteroid 1998 KY26 is a target of the extended Hayabusa2# mission. An unusual acceleration has prompted the suggestion that escaping gas, possibly from water, could be pushing it, but the asteroid may instead belong to a largely water-free class. Researchers modeled temperatures across its surface and interior using 13 sets of assumptions about its size, thermal properties, reflectivity, and spin direction. In every case, temperatures averaged over its orbit were well above those at which frozen volatile substances turn into gas in a vacuum. The models indicate that buried water ice would release gas too quickly to be maintained. This challenges the buried-ice explanation, but does not directly establish what the asteroid contains or what causes its unusual acceleration.

Young explorerA space rock called 1998 KY26 moves in a way that made scientists wonder whether gas escaping from it could be giving it a little push. They used a computer to work out how warm the rock might be, trying 13 different sets of assumptions. The model suggests that even ice hidden inside would turn into gas too quickly to stay there. That makes hidden ice harder to explain, but it does not prove what is inside the rock or what is pushing it.

From Exo-Earth Detection to Atmospheric Characterization: Enabling Phase-Dependent Molecular Detection SNR in EXOSIMS

Searra Foote, Tyler D. Robinson, Rhonda Morgan+3 more

• Instrumentation and Methods for Astrophysics

AstronomerThis simulation study adds phase-dependent atmospheric O2 and H2O detectability to EXOSIMS yield modeling for the planned Habitable Worlds Observatory. The authors use rfast spectral retrievals to estimate molecular-detection SNR requirements versus planetary phase and incorporate them into characterization integration-time calculations. Although required SNR decreases toward crescent phases, simulated molecular detections concentrate at intermediate phase angles, reflecting competition between molecular information content and direct-imaging observability. Compared with fixed characterization thresholds of SNR = 5 for H2O and 8.5 for O2, this treatment increases mean simulated molecular detection yields by 76.8 percent and 29.7 percent, respectively. These are modeling results, not observed atmospheric detections or evidence of life; extension to additional biosignatures is left to future work.

PublicResearchers have improved a simulation used to plan NASA’s upcoming Habitable Worlds Observatory, which aims to search for Earth-like planets around Sun-like stars and study their atmospheres for possible signs of life. The new model accounts for how a planet’s phase—the illuminated portion seen by the telescope—changes the signal quality needed to detect oxygen and water vapor. In the simulations, crescent phases require lower signal-to-noise ratios for identifying these molecules, but most successful detections occur at intermediate phases because molecular information and the ability to observe the planet must both be considered. Compared with fixed signal-quality requirements, the revised model produces average simulated detection yields that are 76.8 percent higher for water vapor and 29.7 percent higher for oxygen. This is an improvement in mission-planning simulations, not a report of newly detected planets, molecules, or life.

Young explorerScientists are planning a space telescope to look for worlds like Earth. They made a computer model to help work out how to look for oxygen and water in those worlds’ air. A planet can look more like a crescent or more like a full circle, and that changes how easy the search is. In their computer tests, the best chances usually came between those shapes. The new model predicted more successful searches than the older rules did. These were pretend searches in a computer, not discoveries of real worlds or living things.

Ejecta fate and deposition in the Didymos-Dimorphos system after the DART impact

Kosuke Kurosawa, Satoshi Takada

AstronomerDART struck Dimorphos in 2022 at 6.1449 km s^{-1}; observations revealed changes in both its orbit around Didymos and the binary system's heliocentric orbit. This study presents an analytical ejecta model based on Maxwell's Z model, relating ejection velocity, angle, and mass to estimate the momentum enhancement factor beta for Dimorphos and the binary system. The model reproduces the observed beta when 0.3–1% of the impact kinetic energy becomes ejecta kinetic energy and the effective target strength is below 100 Pa. It estimates escaping mass at 0.3–3.0% of Dimorphos's mass and globally averaged and minimum deposited ejecta thicknesses of 2.0 m and 0.5 m. These estimates imply whole-surface resurfacing, with boulders larger than 1 m only partially buried. A predicted momentum partition parameter kappa_p as low as 0.6 suggests possible upward revisions to Dimorphos's mass and bulk density. These are model-dependent predictions intended to constrain interpretation of Hera's forthcoming observations, with arrival scheduled for late 2026.

PublicNASA's DART spacecraft hit Dimorphos, the smaller member of a two-asteroid system, in 2022. Observations showed changes in the small asteroid's orbit around Didymos and in the pair's orbit around the Sun. This study uses a mathematical model to predict how material thrown out by the collision moved and added to the impact's push. The model matches the observed momentum enhancement if 0.3–1% of the collision energy went into moving this material and the target's effective strength was below 100 pascals. It estimates that material equal to 0.3–3.0% of Dimorphos's mass escaped. It also predicts a deposited layer averaging 2 metres thick, with a minimum thickness of half a metre, suggesting that debris covered the entire surface but only partly buried boulders larger than 1 metre. Another model prediction suggests that estimates of Dimorphos's mass and average density may need to increase. These predictions will help scientists interpret observations from ESA's Hera spacecraft, scheduled to arrive in late 2026; they are not yet direct measurements of the post-impact surface.

Young explorerNASA flew a spacecraft into a little asteroid called Dimorphos to try a way of nudging asteroids. Scientists saw that its path changed, and so did the path it shares with its bigger companion around the Sun. Now they have used a math model to work out what might have happened to the pieces thrown up by the crash. The model suggests that some pieces escaped and others fell back, covering the little asteroid like a blanket while leaving big rocks partly sticking out. Those are predictions, not things scientists have seen up close yet. A spacecraft called Hera is due to arrive in late 2026 to study what the crash left behind.

Detecting space objects with Earth-observation radar satellites

Juha Vierinen, Laura-Kristin Scholtz, Ulrik Noer+3 more

• Instrumentation and Methods for Astrophysics
• Space Physics

AstronomerAnalysis of openly available Sentinel-1 radar voltages from six calendar days demonstrates space-object detection with an existing Earth-observation radar. Catalogue-assisted processing yielded 76 manually validated objects at ranges of 41.7–492.9 km, including satellites, rocket bodies and debris fragments. A blind search recovered two selected debris transits without orbital predictions during detection, and a short debris encounter demonstrated catalogue-orbit refinement using precise range and Doppler measurements. Ground scatter was the principal sensitivity limitation in Earth-looking observations. An ideal receiver-noise comparison predicts detectable conducting-sphere diameters of approximately 3.4 mm for Sentinel-1 and 0.6 mm for EarthCARE at 10 km, assuming coherent integration limited by beam transit time and capped at 10 ms; these are predictions, not observed detection limits. The results motivate statistical debris surveys and targeted orbit refinement after collision warnings. Looking away from Earth and adapting receive windows to nearby objects are proposed routes to improved small-debris sensitivity.

PublicSmall pieces of orbiting debris threaten spacecraft, but their numbers are hard to measure. Researchers examined six days of existing Sentinel-1 radar recordings and, using an orbital catalogue, identified and manually checked 76 objects, including satellites, rocket bodies and debris fragments. They also detected two selected debris passages without using predicted orbits during the search and showed how a brief encounter could improve a catalogued orbit. Nearby objects produce much stronger radar echoes, but reflections from the ground were the main obstacle in these Earth-facing observations. Idealized calculations suggest that at 10 km, Sentinel-1 could detect a conducting sphere about 3.4 mm across and EarthCARE one about 0.6 mm across under specified assumptions; the study did not demonstrate detections at those sizes. The work supports developing debris surveys with existing space radars, while looking away from Earth and changing when echoes are recorded could improve sensitivity.

Young explorerLittle bits of space junk can hurt spacecraft, and they are hard to count. Scientists looked at recordings from a radar in space, which sends out signals and listens for echoes. They checked 76 things, including satellites and pieces of junk. They also found two chosen pieces without using guesses about their paths to help with the search. Echoes from the ground made tiny things harder to spot. The scientists calculated that space radars might find much tinier pieces nearby under ideal conditions, but they have not shown that yet. Pointing away from Earth might help.

ALMA detection of continuum emission from GQ Lup B

Pietro Pirola, Stefano Facchini, Gabriele Cugno+9 more

AstronomerALMA band 7 observations detect 0.89-mm continuum at GQ Lup B at 5.8σ, with peak intensity 54.5 ± 9.4 μJy per beam and a position consistent with GRAVITY astrometry. The authors associate the emission with the companion's previously detected mid-infrared disk, making it the third reported millimeter disk detection around a companion in the planetary-to-brown-dwarf mass range. The source is unresolved, limiting its radius to less than 2.3 au. Assuming optically thin thermal emission from millimeter-sized grains gives a dust mass of 0.0032 Earth masses; the optically thick limit instead implies an emission radius of 0.2 au. With an assumed gas-to-dust ratio of 100, the inferred disk-mass-to-accretion-rate ratio is approximately 10,000 years. GQ Lup B has an estimated mass of 10–40 Jupiter masses and a projected separation of about 110 au; its roughly 63° inclined orbit crosses the primary's gas disk twice per orbit. The authors propose that these crossings could replenish the companion's disk, explaining sustained accretion despite its small inferred reservoir.

PublicAstronomers used ALMA to detect millimeter-wavelength emission at GQ Lup B, a young companion estimated to have 10–40 times Jupiter's mass. They interpret the signal as coming from a dusty disk around the companion, previously seen in infrared light. The disk is too small for these observations to resolve, but its radius must be less than 2.3 times the Earth–Sun distance. Its inferred material content depends on assumptions about how readily the dust lets radiation escape: one model gives a dust mass of 0.0032 Earth masses. Assuming a gas-to-dust mass ratio of 100, the disk's estimated mass divided by its accretion rate corresponds to only about 10,000 years. The authors suggest a possible source of fresh material: the companion's tilted orbit takes it through its star's gas disk twice each orbit. Those crossings could replenish its own disk, but this explanation is not established by the detection.

Young explorerA young star has a very big companion traveling around it. Astronomers found a faint glow that they think comes from a little disk of dust around that companion. The disk looks too tiny for their telescope to show its shape. The companion also passes through a bigger disk of gas around the star. The scientists think it might pick up fresh gas on those trips to refill its little disk, but they have not shown that this happens.

Long-term average collision frequencies between two bodies undergoing Lidov-Kozai evolution

Youpeng Liang, Xiaodong Liu

AstronomerThe authors extend the Öpik-type collision-frequency framework of Liang and Liu to a case in which both projectile and target undergo Lidov-Kozai (LK) evolution. A doubly averaged quadrupole model describes both bodies’ secular dynamics, allowing the target’s orbital evolution to enter the collision contribution of each orbital intersection configuration rather than fixing its eccentricity and inclination and prescribing uniform precession. In one numerical example, the predicted projectile survival curve has an overall decay trend close to that from direct REBOUND N-body simulations. The analysis also predicts independence of the long-term mean collision frequency from initial states, at fixed semimajor axes, Kozai constants, and closed Hamiltonian level curves, provided the relative-state parameters are jointly equidistributed at successive projectile LK-cycle starts. Numerical cases with different initial states support this conditional conclusion.

PublicThis study develops a way to calculate how often two orbiting bodies might collide when both undergo long-term changes in orbital shape and tilt called Lidov-Kozai evolution. The earlier framework included these changes for the incoming body but treated the target’s orbit more restrictively. In one numerical example, the new calculation predicted a decline in the fraction of projectiles avoiding collision that broadly matched direct computer simulations. The authors also find theoretically that, with certain orbital properties held fixed, the long-term average collision frequency should not depend on the bodies’ starting states if their relative configurations sample the allowed possibilities evenly at specified points in the orbital cycles. Numerical tests support that conditional prediction; these are modeling results, not observations of collisions.

Young explorerImagine two things going around in space, with paths that slowly change shape and tip. Scientists made a better way to work out how often they might bump into each other when both paths change. In one computer test, their calculation gave roughly the same pattern of things avoiding bumps as a more direct simulation did. They also worked out that different starting positions might give the same average number of bumps over a long time, but only under special conditions. These were calculations and computer tests, not bumps watched in space.

Kinematic Signatures of Stellar Flybys in Protoplanetary Discs

Vasundhara Prasad, Cristiano Longarini, Carolin N. Kimmig+1 more

AstronomerObserved large-scale departures from Keplerian gas motions in protoplanetary discs have been interpreted as warps, but that interpretation is not unique. This study uses 3D smoothed particle hydrodynamics simulations of inclined and coplanar stellar flybys to examine disc evolution several thousand years after closest approach. Inclined encounters initially produce warping and twisting, which damp on a viscosity-dependent timescale. Synthetic ALMA CO observations nevertheless retain complex spiral velocity residuals after the geometric warp relaxes, and also show such residuals for coplanar encounters that never induce a warp. Fitting these residuals with a simple warped-disc model systematically overestimates the warping. The simulations therefore indicate that velocity residuals alone cannot establish a warp. The study also identifies scattered-light spiral arms and lateral asymmetries as an independent diagnostic.

PublicGas in some planet-forming discs has been observed moving in patterns that differ from those expected for ordinary orbits around a star. These patterns could indicate a bent or warped disc, but the study shows why that explanation is not unique. In computer simulations, a passing star can both bend a disc and disturb its gas motions. The bending gradually fades at a rate controlled by the disc’s viscosity, yet simulated telescope observations still show spiral patterns in the gas motions long afterward. Similar patterns also appear when the passing star never bends the disc at all. A simple model that treats these motions as evidence of a warp consequently exaggerates the bending. The findings mean that gas motions alone are not enough to establish a warp; the study also identifies spiral arms and side-to-side differences in scattered-light images as an independent diagnostic.

Young explorerA young star can have a big disc of gas around it. Astronomers have seen gas moving in unusual ways and wondered whether the disc is bent. In computer experiments, the researchers let another star pass nearby. Sometimes it bent the disc, but the gas kept moving in swirly patterns even after the bend faded. The passing star could also make those patterns without bending the disc at all. So strange gas movements do not prove that a disc is bent. Pictures made from light scattered by the disc offer another way to look for clues.

The Neptunian ridge depends on the choice of linear or logarithmic period

Kaiming Cui, David J. Armstrong

AstronomerThis study reassesses the reported Neptunian ridge, an apparent excess of planets with radii approximately 5–8 Earth radii and periods approximately 3–6 days. The authors attribute the excess to expressing occurrence per unit period rather than per unit logarithmic period, the standard demographic convention. Because the comparison savanna interval spans twice the period width, a population uniform in logarithmic period naturally yields a twofold contrast in the former representation. Converting published TESS and Kepler ridge-to-savanna contrasts to logarithmic-period density reduces them from 1.6–2.2 to 0.8–1.2, consistent with unity. A simulated population containing a desert but no intrinsic ridge reproduces the apparent excess. Reanalysis of TESS-SPOC occurrence rates for 5.5–8.5 Earth-radius planets around FGK stars gives a logarithmic-period ridge-to-savanna ratio of 0.91, with uncertainties of +0.21 and −0.16. These tests support a scale-choice explanation rather than a definitive overdensity in the observed population.

PublicAstronomers previously reported an unusually crowded group of planets about five to eight times Earth's radius, taking roughly three to six days to orbit their stars. This study argues that the apparent crowding comes from how the planet counts were compared. Counting planets in equal-sized ranges of orbital time can give a different impression from counting them in ranges with equal proportional changes in orbital time. Using the latter approach, which is standard for studying planet populations, the authors find no convincing excess in the published Kepler and TESS results. Their new TESS analysis likewise does not support the claimed crowding. A computer simulation with no built-in excess also creates an apparent ridge under the original counting method. Together, these findings suggest that the reported ridge reflects the choice of scale rather than an established feature of the planets themselves.

Young explorerScientists thought there was an extra-crowded group of planets that go around their stars quickly. But how you sort and count planets can make a group look more crowded than it really is. These researchers counted in a different way and did not find clear signs of extra planets in that group. They also made pretend planets on a computer and showed that the old counting method could make a crowd seem to appear. So the crowd may be a counting trick, not a real extra bunch of planets.

The compositional link between rocky exoplanets and their host stars is consistent with Earth-like devolatilization

Yared Reinarz, Lorena Acuña-Aguirre, Haiyang S. Wang

AstronomerThe authors reassess core mass fractions and elemental molar ratios for 14 rocky exoplanets spanning 0.5–10 Earth masses, using mass–radius interior retrievals with the independent Marseille Super-Earth Interior model and pyExoInt, alongside published host-star Fe, Si, Mg, O and S abundances. Eight planets show an inferred Earth-like devolatilization trend, whereas only one shows a 1:1 correspondence between planetary and stellar abundances. Both models recover the trend, supporting devolatilization as a plausible alternative to iron enrichment for explaining previously reported elevated planetary Fe/Si ratios relative to host stars. These compositions are model-derived rather than direct abundance measurements. The small sample with constrained stellar abundances and its limited orbital-distance range restrict the conclusions. PLATO is expected to extend the characterized sample to orbital periods of up to one year. The diversity of inferred refractory-element trends may reflect differences in bulk composition, outgassing and mantle properties relevant to habitability.

PublicRocky planets do not necessarily have the same elemental proportions as their parent stars. Earlier work found higher iron-to-silicon ratios in these planets, usually interpreted as extra iron. This study explores another explanation: preferential loss of more easily vaporized elements, such as oxygen and sulfur, relative to elements such as iron and magnesium. Using two models of planetary interiors, researchers inferred compositions from the masses and sizes of 14 rocky planets and compared them with their stars’ measured elemental abundances. Eight planets showed a pattern resembling Earth’s depletion of more easily vaporized elements; only one matched its star’s elemental proportions one-for-one. Agreement between the models supports this explanation, but does not prove how the planets acquired their compositions. The sample is small and covers a limited range of orbital distances. The authors expect PLATO to broaden the sample, helping test whether these patterns point to varied planetary interiors and gas release.

Young explorerA rocky planet is made from different ingredients, and its star has ingredients too. Scientists used measurements of how heavy and big 14 planets are, plus two computer models, to work out what might be inside them. Eight planets seemed to have a pattern like Earth’s: less of some ingredients that turn into gas more easily. Only one seemed to have the same ingredient mix as its star. Both models found the same pattern, so losing some ingredients could help explain the differences. But scientists have studied only a small group this way, and they cannot yet be sure.

The Swift/UVOT Observation Campaign of Comet C/2013 US₁₀ (Catalina) and Near-nucleus UV Excess

Shawn Oset, Zexi Xing, John Wm. Noonan+2 more

AstronomerExtended Swift/UVOT monitoring followed the dynamically new long-period comet C/2013 US10 (Catalina) from 5.8 AU inbound to 5 AU outbound. The study introduces its analysis pipeline and derives water production rates, active areas, and the dust proxy A(θ)fρ, using a Bayesian treatment of the unknown dust spectral gradient needed for continuum subtraction. The comet exhibited significant hyperactivity: water production approached 2.5 × 10^29 s−1, with a greatly elevated inferred active area before perihelion that settled to approximately 50 km² afterward. A quantified near-nucleus UV excess above vectorial-model predictions, termed the Pale Blue Spot, has an uncertain species identification. If attributed to OH (A–X) fluorescence, it may indicate a secondary source of slow-moving OH operating even beyond the water snow line.

PublicResearchers used the Swift spacecraft to follow comet Catalina as it approached and then receded from the Sun. Their analysis indicates unusually strong water release, approaching 2.5 × 10^29 molecules per second. The estimated area supplying that water was especially large before the comet’s closest approach to the Sun and settled to about 50 square kilometres afterward. The team also detected extra ultraviolet light near the comet’s nucleus that their model did not account for, naming it the Pale Blue Spot. Its source remains uncertain. If the light comes from hydroxyl radicals, it could reveal an additional process releasing these particles slowly, even beyond the water snow line. The analysis also accounts for uncertainty in the colour of the comet’s dust, which affects how its light is separated from gas emissions.

Young explorerScientists watched a comet called Catalina with a telescope in space as it came closer to the Sun and went away again. They worked out that it was letting out lots of water as gas. They also found extra ultraviolet light, a kind of light our eyes cannot see, near the comet’s middle. They named it the Pale Blue Spot. They do not yet know what makes it shine. One idea is that tiny particles called hydroxyl are being let out slowly, even when the comet is far from the Sun.

Testing Models of Disk Formation and Gravito-Viscous Evolution Against Observations of Young Protoplanetary Disks

Fabiola Antonietta Gerosa, Paola Pinilla, Eduard I. Vorobyov+1 more

AstronomerObservations of substructure in protoplanetary disks younger than one million years suggest that planet formation may start early, but the processes governing early disk evolution remain poorly understood. This study presents two-dimensional thin-disk hydrodynamical simulations of cloud collapse and disk evolution, including self-gravity and turbulent viscosity alone, for a range of initial cloud masses. Comparisons with surveys across evolutionary stages show that the models broadly reproduce Class 0 millimeter fluxes and later-stage dust disk radii. They account for the most massive observed Class I and II disks but fail to reproduce the least massive disks in gas and dust. The authors suggest that including the star-forming environment in simulations might resolve this discrepancy; this possibility is not demonstrated here.

PublicStructures observed in disks of gas and dust less than a million years old suggest that planets may begin forming earlier than previously thought. To investigate how these young disks evolve, the researchers simulated clouds collapsing into disks, including only the disks’ own gravity and a model of turbulent friction. The simulations broadly match the millimeter-wave brightness of the youngest disks and the sizes of dust disks at later stages. However, although they can account for the most massive disks seen at later stages, they do not explain the least massive ones. The authors suggest that effects from the surrounding star-forming environment may need to be included in future simulations to explain the mismatch.

Young explorerBaby stars have spinning disks of gas and dust around them, where planets can grow. Scientists made computer models to see how these disks form and change. The models matched some things seen in real disks, but they could not explain disks with very little gas and dust. The scientists think the disks’ surroundings might help explain the difference, but they have not tested that idea here.

MarsNet: Learning the Martian Atmosphere from Observations Alone

Sebastian Mengwall, J. Michael Battalio

• Atmospheric and Oceanic Physics

AstronomerMarsNet is an observation-trained model of the Martian atmosphere that jointly learns a two-hour forecast and an observation-assimilation update. Learning is constrained by a physical-unit state, fixed-form tendencies with learned strengths, and a bounded Kalman update. Reanalyses are used only for evaluation, not training. Trained on MY24–31, MarsNet matches or improves on three reanalyses over the lowest three scale heights in three seasons of MGS radio-occultation temperatures assimilated by none of the datasets: near-surface RMSE is 4.2 K versus 4.4–5.4 K, although performance is poorer aloft. Against Curiosity surface pressures in MY32, its RMSE is 10 Pa versus 20–46 Pa for the reanalyses. Withheld MY32 Mars Climate Sounder profiles show temperature skill over observed climatology and persistence, including ten-sol forecasts without new observations, with nearly calibrated uncertainty. Importantly, much temperature skill exists before training and appears attributable to the imposed structure and observation-fitted tables; training chiefly improves surface pressure, with some degradation in dust performance. Stable cycling through nine Mars years, traceable observation influence, and computational speed support its use for observing-record experiments and as an independent reference for GCMs and reanalyses.

PublicMarsNet uses observations to learn how Mars’s atmosphere changes, alternating two-hour forecasts with updates from new measurements. Unlike existing reconstructions that blend observations with general circulation models, it does not train on those reconstructions. It still relies on a fixed physical structure to keep learning constrained because observations are sparse. Independent tests found temperatures near the surface comparable to or better than three existing reconstructions, and the most accurate surface pressures among the four products. Temperatures higher in the atmosphere were less accurate than in the reconstructions. It also outperformed simple temperature baselines in forecasts lasting ten Martian days without new observations. A key caution is that much of its temperature skill was already present before training, apparently thanks to its structure and tables fitted to observations. Training mainly improved surface pressure while somewhat worsening dust performance. The model offers a fast, independent way to examine Mars’s weather record and compare atmospheric models.

Young explorerScientists made a computer helper called MarsNet to work out what the air on Mars is doing. It uses measurements and rules about how air behaves. In tests, it did well with temperatures near the ground and with how hard the air presses down, but it was not as good higher up. Much of its temperature skill came from its setup, even before it learned from examples.

Simulation of a Jovian Planet Undergoing Gas Accretion

Fabian Menezes

AstronomerThis numerical study examines planet–disk interactions and orbital migration using FARGO3D. Five simulations model a planet with twice Jupiter’s mass, varying only its initial radial position in the protoplanetary disk. Within these simulations, the authors find that the starting radius strongly influences the planet’s interaction with disk gas and the formation of gas gaps. The abstract does not specify migration directions, rates, or gap properties, and the findings are simulation-based rather than observational.

PublicResearchers used five computer simulations to study how a forming planet interacts with the gas disk around a star. Each simulation included a planet twice as massive as Jupiter; only its starting distance from the star changed. In these models, the starting distance made an important difference to the planet’s interaction with the gas and the formation of gaps in the disk. The study explores how planets change their orbits, but the abstract does not report how fast or in which direction they moved.

Young explorerScientists made five computer models of a young planet in a disk of gas around a star. They used the same big planet each time but started it at a different distance from the star. In their models, where the planet started made a big difference to how it interacted with the gas and how gaps formed in the disk. These were computer experiments, not pictures of a real planet.

Joint Gaia-Hipparcos astrometry, RV, and Imaging posteriors from the G23H Hipparcos sample

William Thompson, Dori Blakely, Alexandre Bouchard-Côté+17 more

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

AstronomerThe study provides consistently derived posteriors for the presence or absence of stellar and planetary companions around 100,000 Hipparcos and Gaia stars. Using the G23H catalog, the model combines absolute astrometry from Hipparcos and Gaia DR2/DR3 with Gaia DR3 photometry, excess radial-velocity variability, and information on the presence or absence of common-proper-motion companions. The authors highlight examples involving known companions and new candidates, along with companion detection rates across the HR diagram. The posteriors support companion searches, RV and imaging follow-up selection, and demographic analyses; new candidates are not presented as confirmed companions. Results are available through a machine-readable catalog and website. The modelling approach is also applicable to Gaia DR4 epoch astrometry and RVs.

PublicResearchers have assessed 100,000 stars for evidence of companion stars or planets. Their model combines measurements from Hipparcos and Gaia, including stellar positions and motions, brightness, changes in motion toward or away from us, and whether nearby stars share the same motion across the sky. Rather than simply declaring each star to have a companion or not, the catalog reports probabilities based on the available evidence. The team highlights known companions and new candidates, which should not be confused with confirmed discoveries. The publicly accessible results can help astronomers choose targets for further observations and study how common companions are among different kinds of stars.

Young explorerSome stars have another star or a planet as a neighbor. Scientists looked at information about 100,000 stars to find clues that they have these companions. They used how the stars move and how bright they are to work out which ones might have company. They found clues for some possible new companions, but those clues do not mean they are sure yet. They shared their list so other scientists can decide where to look more closely.

The Tierras Observatory: Ultra-Precise Photometry for Characterizing Exoplanets and Their Host Stars

Juliana García-Mejía, Patrick Tamburo, David Charbonneau+9 more

• Instrumentation and Methods for Astrophysics

AstronomerTierras is a fully robotic 1.3-m telescope at the Fred Lawrence Whipple Observatory in southern Arizona, designed for precision photometry of nearby mid-to-late M dwarfs. The authors describe the facility, instrument, photometric pipeline, and on-sky performance, reporting sub-part-per-thousand precision both within nights and from night to night across an observing season. They present what they identify as the first ground-based light curves with sub-ppt precision over months. This performance supports transit detection and characterization and monitoring of host-star variability. Measuring stellar rotation periods, detecting long-period transits, and discovering additional terrestrial planets in known M dwarf systems are enabled science applications, not discoveries reported in this abstract.

PublicThe fully robotic Tierras telescope in southern Arizona measures the brightness of nearby small, cool stars with precision better than one part in a thousand, both within a night and across months. The researchers describe the telescope and its data-processing methods and report what they identify as the first ground-based records of stellar brightness to maintain this precision over months. Such measurements can help reveal the small dips in starlight caused by planets passing in front of their stars and track how the stars themselves change. The work establishes the telescope’s performance; it does not report new planet discoveries, but could support searches for planets with long orbits and additional rocky planets in systems already known to contain planets.

Young explorerA robot telescope called Tierras watches nearby small stars very carefully. The team showed that it can measure tiny changes in their light, both during one night and over many months. A planet passing in front of a star can make the star look a little dimmer, but stars can change their light too. These careful measurements could help scientists find planets and learn about their stars. This report shows how well the telescope works, rather than announcing a newly found planet.

The Brown Dwarf Desert is a Mass-Ratio Desert: Astrometric Demographics of 63,254 Stars

William Thompson, Alexandre Bouchard-Côté, Dori Blakely+19 more

• Solar and Stellar Astrophysics

AstronomerJoint modelling of Hipparcos and Gaia DR2/DR3 astrometry for 63,254 stars measures planetary and stellar companion occurrence on 3–94-year orbits, approximately 2–20 au, across M- to B-type hosts. The sample is 1–2 orders of magnitude larger than previous wide-orbit demographic samples. The analysis finds a strong companion deficit near mass ratio q ≈ 0.02 across this host-mass range and excludes a desert at fixed companion mass. Occurrence increases with metallicity below the mass-ratio desert but decreases above it. The authors interpret these trends as evidence for two populations that scale with host mass, plausibly reflecting distinct formation channels rather than demonstrating them directly. Illustratively, the lightest stellar-like companions of K stars are about 13 Jupiter masses, while the heaviest planet-like companions of B stars reach about 27 Jupiter masses, beyond the deuterium-burning limit. The authors therefore argue for mass ratio, rather than companion mass, as the physically meaningful planet–stellar-like boundary.

PublicBrown dwarfs are unusually scarce as close companions to stars, a pattern called the brown dwarf desert. Researchers analysed position measurements from Hipparcos and Gaia for 63,254 stars, studying companions with orbital periods of 3–94 years. They found that the shortage follows a companion’s mass relative to its star: companions are scarce at about 2% of the star’s mass, across stars ranging from M dwarfs to B stars. The shortage does not occur at one fixed companion mass. Companions below and above this dividing region also show opposite relationships with their stars’ metallicity. The authors interpret this as evidence for two populations, possibly formed in different ways. Their conclusion is that relative mass is a more meaningful dividing line between planet-like and stellar-like companions than companion mass alone.

Young explorerStars can have smaller companions going around them. Scientists studied lots of stars and found that companions of one particular relative size are hard to find: ones about two hundredths as heavy as their star. This pattern showed up around both smaller and bigger stars. The scientists think companions on either side of this gap might be made in different ways, but that part is not yet certain.

Exploring tidal dissipation in rubble pile binary secondaries using a discrete element model

Ethan R. Burnett, Iosto Fodde, John Wimarsson+2 more

AstronomerThe study simulates rubble-pile binary secondaries in several spin states in a system comparable in size and scale to Didymos–Dimorphos. Using the Chrono-based N-body code GRAINS, it models gravity, contact, and friction among thousands of nonspherical elements, allowing tidal dissipation to emerge from granular interactions. The simulations exhibit tidal deformation, phase lag, secular spin-down from super-synchronous rotation to synchronous libration, and energy and angular-momentum exchange between spin and orbit. Spectral and topographical analyses identify the semidiurnal tidal response. Energy- and torque-based estimates give Q/k₂ of order 10², near the low end of earlier predictions spanning 10² to 10⁶. Whether this reflects genuinely enhanced dissipation or material and modeling assumptions remains unresolved. These are numerical findings, not measurements of the actual Didymos–Dimorphos system.

PublicComputer simulations explore how a small asteroid made of loose rubble changes its spin while orbiting a larger companion. The modeled system is similar in size and scale to Didymos–Dimorphos, but the findings are not observations of those asteroids. By tracking gravity, collisions, and friction among thousands of irregular pieces, the researchers find that tidal deformation and internal friction dissipate energy. In the simulations, the smaller body slows from spinning faster than it orbits to keeping roughly the same face toward its companion while rocking back and forth. Energy and angular momentum also pass between its spin and orbit. The calculated tidal response suggests relatively strong energy dissipation compared with much of the previously predicted range, but the researchers cannot yet tell whether this reflects real rubble-pile behavior or assumptions in their model.

Young explorerScientists used a computer to make a pretend space rock built from lots of smaller rocks, going around a bigger one. In the computer, gravity pulls the little rock out of shape, and its pieces rub and bump together. Its spinning slows until it mostly keeps the same side facing the bigger rock, with a little rocking back and forth. This happened in the computer, not in a space rock they watched. Scientists still need to check how well their pretend rocks act like real ones.

The Maximum Initial Mass in low-thrust spacecraft trajectory design

Dario Izzo, Giacomo Acciarini

• Instrumentation and Methods for Astrophysics

AstronomerThis theoretical trajectory-design study formulates low-thrust transfer optimization as maximizing initial spacecraft mass for fixed transfer time and endpoint states. Within Pontryagin’s framework, the necessary conditions imply full-throttle operation in the nondegenerate case and standard primer-vector steering. The authors establish correspondence between this formulation’s extremals and those of minimum- and maximum-time problems: the terminal dynamics-only Hamiltonian’s sign distinguishes the normal representations, while its zero value admits an abnormal representation. They also clarify free-time transversality versus costate normalization. The formulation provides a unified initial-mass threshold for reachability analysis and extended homotopy continuation paths between solution branches. In a multiple-revolution GTO-to-GEO benchmark, it recovers the best known minimum-time solution and identifies previously unreported extremals. A constant-initial-mass contour shows a funnel-like arrangement of transfer-time minima and maxima, including a previously reported trajectory classified as a local maximum rather than a minimum. These are mathematical and benchmark findings, not observations of spacecraft flights; extremals need not be minima.

PublicThe researchers introduce a mathematical way to plan spacecraft journeys using low thrust. Instead of directly seeking the shortest or longest journey, they fix the travel time and starting and ending conditions, then maximize the spacecraft’s starting mass. They show how candidate solutions to this problem connect to both minimum-time and maximum-time transfers. The approach can simplify checks of whether a journey is possible and help optimization methods explore additional families of routes. In a benchmark orbit-transfer problem, it reproduced the best known shortest-time solution and found previously unreported mathematical candidates. It also showed that one previously reported route was a local travel-time maximum, not a minimum: nearby alternatives take less time. The work concerns mathematical planning and a benchmark application, not a demonstrated spacecraft flight.

Young explorerImagine planning a spaceship trip with a gentle engine. The researchers made a math puzzle: if the ship must arrive at a set time, how heavy can it be when it starts? This helps them look for trips that take less time or more time. In a test problem, their method found the best known fastest trip and some other possible paths. They also found that one old path took longer, not less time, than nearby choices. This was a math test, not a real spaceship flight.

A Sulfur-Rich Atmosphere for the Young Jupiter Analog AF Lep b Reveals Significant Solid Accretion

Jerry W. Xuan, William O. Balmer, Yayaati Chachan+25 more

• Solar and Stellar Astrophysics

AstronomerJWST/NIRSpec spectroscopy of AF Lep b, a 3–4-Jupiter-mass planet with a semi-major axis of 9 AU, detects CO2, H2S, CH4, 12CO, 13CO, and H2O over 2.85–5.3 micrometers at R ≈ 3000. Complementary NIRCam imaging constrains the 4.0–4.7-micrometer continuum. Retrievals combining these data with VLTI/GRAVITY and VLT/SPHERE spectra include clouds and disequilibrium chemistry and independently vary C, O, and S abundances. They yield C/H, O/H, and S/H enrichments of 2.9 ± 0.5, 3.7 ± 0.6, and 4.7 ± 0.7 times solar and stellar values, respectively. Slightly sub-solar C/O and C/S are consistent with formation near the current orbit and disfavor formation beyond the CO snowline. The authors interpret the sulfur enrichment as evidence for substantial disk-solid accretion and estimate a solids inventory of 56 ± 7 Earth masses. Similarities to Jupiter and HR 8799 bcde, and between these imaged planets’ atmospheric enrichments and transiting giants’ bulk enrichments above roughly one Jupiter mass, suggest—but do not establish—weak dependence of metal-accretion processes and efficiency on orbital distance or planet mass.

PublicObservations with the James Webb Space Telescope reveal water, methane, carbon dioxide, hydrogen sulfide, and two forms of carbon monoxide in the atmosphere of AF Lep b, a planet with three to four times Jupiter’s mass. Combining these observations with ground-based spectra, the researchers use atmospheric models to infer that carbon, oxygen, and sulfur are about three to five times as abundant relative to hydrogen as in the Sun and the planet’s star. The inferred element ratios favor formation near the planet’s present orbit over formation beyond the disk region where carbon monoxide freezes. Sulfur enrichment points to substantial capture of solid material during formation; the researchers estimate that the planet contains 56 ± 7 Earth masses of solids. Comparisons with other giant planets suggest that the efficiency of gathering heavy elements may not depend strongly on planet mass or orbital distance, although this is an interpretation rather than a demonstrated rule.

Young explorerAstronomers studied light from a giant planet called AF Lep b and found signs of water and several gases in its air. Their models suggest its air has more carbon, oxygen, and sulfur compared with hydrogen than the Sun does. These clues suggest the planet gathered lots of solid bits while growing, perhaps near where it is now. Scientists are still working out its story.

Composition gradients in sub-Neptunes: K2-18 b and TOI-270 d as case studies

Luca Morf, Ravit Helled

AstronomerThis modeling study compares purely adiabatic, compositionally homogeneous layered interiors with interiors containing composition gradients and stable non-convective regions for K2-18 b and TOI-270 d. Both model classes admit solutions consistent with observed masses, radii, and atmospheric boundary conditions, but composition gradients substantially broaden the allowed structures and bulk compositions, even at fixed mass and radius. Relative to the adiabatic models, the maximum allowed H-He mass fraction for K2-18 b increases by about threefold at a 1 bar temperature of 300 K and tenfold at 600 K; for TOI-270 d, it generally increases by more than an order of magnitude. The Spearman correlation between H-He and iron abundances falls from approximately 0.7 to 0.3 for both planets, with similar weakening for H-He abundance versus rock-to-iron mass ratio. Other correlations, including that with water-to-rock mass ratio, persist or strengthen. The authors conclude that purely adiabatic models understate compositional uncertainty and overstate the constraining power of improved measurements, atmospheric models, and host-star constraints. They recommend routinely including composition gradients and non-convective regions; the analysis does not establish that either planet actually has these interior features.

PublicDifferent interiors can fit the same measured planet. Researchers modeled K2-18 b and TOI-270 d to test how assumptions about their hidden interiors affect estimates of their composition. Standard models assume separate layers with uniform composition and purely adiabatic interiors. Allowing composition to change gradually, along with stable regions that do not mix by convection, produced a much wider range of possibilities consistent with the planets’ observed masses, sizes, and atmospheric boundary conditions. In these models, the maximum permitted hydrogen-and-helium share could rise severalfold or more than tenfold, depending on the planet and assumed conditions. Some relationships between possible ingredients became weaker, but others remained important. These are modeling results, not observations of the interiors themselves. The authors argue that simpler models can make composition estimates look more certain than they are and can exaggerate how much better data alone will resolve the uncertainty.

Young explorerScientists know how heavy and how big two faraway planets are, but they cannot tell exactly what is inside. They tried computer models, like trying different recipes that could make the same planet. When they let the ingredients change gradually inside, and let some places stay without mixing, many more recipes worked. That does not mean the planets really are made that way. It means scientists should try more kinds of recipes before deciding what is inside.

A CNN search for ultra-short-period planets in TESS: blends among real false positives and an independent validation of TOI-6662 b

Juan F. Pagés Navarrete

• Instrumentation and Methods for Astrophysics

AstronomerA simple convolutional neural network using only phase-folded global TESS light curves was initially trained on synthetic trapezoidal transits and eclipsing binaries. Its ROC AUC drops from 0.97 against catalogued eclipsing binaries to 0.50 when the same planets are tested against real false positives rejected by the TESS Follow-up Observing Program. This illustrates the known risk of overly optimistic binary-based benchmarks, rather than a limitation established for leading classifiers trained on vetted false positives. Pixel-level examination of 145 real false positives finds that at least 42% are blends with contaminants more than one TESS pixel away. Assuming these blends are indistinguishable from transits in the light curve gives a heuristic light-curve-only AUC bound of about 0.79. Fine-tuning the network on real false positives yields 0.80 +/- 0.06, consistent with but not a strong test of that bound; the figures characterise this detector and do not limit classifiers using richer inputs. The authors combine the network with difference-image centroid analysis, scene modelling, high-resolution imaging and Gaia astrometry in CASCADE-USP, which prioritises candidates and records missing evidence rather than issuing verdicts. Of 435 unresolved TESS candidates, the pipeline isolates 20: 19 prove false positives from causes invisible in TESS photometry, while TOI-6662 b is validated as a 0.94 +/- 0.03 Earth-radius planet orbiting an M dwarf every 7.05 hours, in agreement with an independent concurrent validation.

PublicAn AI system that looked highly successful in one test proved unable to distinguish planets from realistic impostors in another. Trained initially on artificial brightness dips, it scored 0.97 on a discrimination measure when tested against catalogued eclipsing binaries, but only 0.50 when those comparison objects were replaced with real rejected planet candidates. Examining the image pixels helped explain the difficulty: at least 42% of 145 false positives involved light mixed in from a source more than one TESS pixel away. An estimated performance ceiling based on these blends depends on assuming their brightness patterns cannot be distinguished from planetary transits; it is not a demonstrated limit for systems using additional information. The researchers therefore built CASCADE-USP to combine the AI with image analysis, high-resolution images and Gaia position measurements. It ranks candidates and identifies evidence still needed, rather than declaring them planets. Among 435 unresolved TESS candidates, it singled out 20. Nineteen proved to be false alarms caused by effects not apparent in the TESS brightness data. The remaining object, TOI-6662 b, was validated as a planet about Earth's size, orbiting a small star every 7.05 hours. An independent team reached an agreeing validation at the same time.

Young explorerA planet passing in front of a star can make the star look a little dimmer. But other things can make a similar little dip and fool a computer. The scientists found that their computer did much worse when they tested it with real tricky examples instead of simpler ones. So they built a tool that also checks pictures and information about where stars are. It helps scientists decide what to check next, but it cannot give the final answer by itself. From 435 possible planets, it picked 20 for closer checking. Nineteen were false alarms. The last one, called TOI-6662 b, was checked and found to be a planet about as wide as Earth. It goes around its star once every 7.05 hours!

Low-Thrust Trajectory Optimization for Cubesat Lunar Mission: HORYU-VI

Omer Burak Iskender, Keck Voon Ling, Mengu Cho+2 more

• Systems and Control
• Instrumentation and Methods for Astrophysics

AstronomerA GMAT trajectory simulation investigates three low-thrust phases for the HORYU-VI CubeSat lunar mission: pre-flyby deceleration, lunar capture, and circularization. Impulsive reference trajectories initialize finite-burn targeting. The archived propagation assumes a constant 12 kg spacecraft mass and 1.08 mN effective thrust, with mass depletion disabled. The first reported bound lunar state occurs at day 184.1; at the end of the 381.3-day record, the osculating lunar orbit has a semi-major axis of 3,862 km and eccentricity of 0.0867. Integration of the reported thrust state gives an estimated velocity increment of 839.8 m/s over 108.00 thrusting days. At the configured specific impulse of 2800 s, the ideal rocket-equation propellant equivalent is 0.361 kg, not a propagated fuel consumption. The simulation demonstrates capture and partial circularization, but does not complete the intended 100 km science orbit. Mass-depleting propagation and uncertainty analysis are also needed to assess operational feasibility.

PublicA computer simulation explores how the HORYU-VI CubeSat could use a small, sustained thrust to slow down before passing the Moon, enter lunar orbit, and make that orbit more circular. In the simulated record, the spacecraft first becomes bound to the Moon at day 184.1. By the end of 381.3 days, it is in a nearly circular but still elliptical lunar orbit, rather than the intended 100 km science orbit. The model includes 108 days of thrusting and keeps the spacecraft's mass fixed at 12 kg. A separate ideal calculation gives a propellant equivalent of 0.361 kg, but the simulation does not account for the spacecraft losing mass as fuel is used. These are simulated results, not a report of a completed flight. Reaching the intended orbit, modeling fuel-related mass loss, and testing uncertainties remain necessary before the plan's operational feasibility can be assessed.

Young explorerResearchers used a computer to try out a trip to the Moon for a tiny spacecraft called HORYU-VI. In the computer test, gentle pushes helped it slow down and start going around the Moon. More pushes made its path rounder, but it did not reach the planned path close to the Moon. This was a pretend trip in a computer, not a real flight. The researchers still need to check what happens as the spacecraft uses up fuel and whether the plan works when things do not go exactly as expected.

g4chargeit: Geant4-based kinetic Monte Carlo simulations of charging in dielectric materials

Kush P. Gandhi, Advik D. Vira, William M. Farrell+5 more

• Applied Physics
• Materials Science

AstronomerThe authors present g4chargeit, an openly available Geant4-based kinetic Monte Carlo framework for time-dependent dielectric charging. It couples stochastic particle transport and scattering, using validated Geant4 cross-sections, to self-consistent evolution of the electric potential and field. Applied to regolith grains under average lunar dayside conditions, the simulations show charge accumulation in intergrain micro-cavities and resulting repulsive electrostatic forces consistent with experimental observations. These are simulation findings, not new lunar measurements. The framework links microscopic scattering to the surface-charge continuity equation and macroscopic charge patches in complex grain geometries, addressing geometric and interaction simplifications in earlier analytical treatments. Its applicability beyond planetary regolith is presented as a general capability, rather than demonstrated here.

PublicA new, openly available computer model called g4chargeit simulates how electrical charge builds up in insulating materials. The researchers applied it to grains of lunar soil exposed to typical daytime conditions, where sunlight's ultraviolet radiation and the solar wind can charge the grains. Unlike simplified calculations, the model follows individual particle interactions while updating the electric field they produce. In the simulations, charge collects in tiny cavities between grains, creating electrical forces that push grains apart. This agrees with experimental observations, but it is not a new measurement on the Moon. The method connects small-scale interactions to larger patches of surface charge and is intended to help study other insulating materials as well.

Young explorerSunlight and tiny particles from the Sun can give Moon dust an electric charge. Scientists made a computer model to explore how this happens. In their pretend Moon dust, charge gathered in tiny spaces between grains and made the grains push away from each other. That fits with what experiments have seen, but the scientists did not watch real dust on the Moon do this in this study.

Orbital Networks in the Three-Body Problem

Abdullah Braik, Shane D. Ross

• Dynamical Systems
• Space Physics

AstronomerThis computational study constructs weighted orbital networks in the circular restricted three-body problem by using overlaps of finite-ΔV, finite-time-of-flight reachable sets to infer accessibility between representative periodic-orbit families on a common Jacobi energy manifold. Applied to the Earth–Moon system, the framework separates the emergence of direct reachability, graph connectedness, and feasible multileg closure. Multi-orbiter cycler families serve as the principal hubs, gateways, and relays: the (3,2)-cycler dominates much of the sampled maneuver-budget and flight-time parameter space, while the short-period (1,1)-cycler dominates at low flight times. The stable 2:1 resonant orbit remains difficult to access. Even at the largest sampled budgets, a nearly complete binary network retains strongly nonuniform weighted accessibility. Selected connections inferred from the overlap proxies are refined into concrete trajectories using differential correction; corrected costs fall below the proxy estimates in every tested case. These model-based results expose large-scale transport structure without exhaustive pairwise trajectory optimization, but trajectory refinement is demonstrated only for selected connections.

PublicThe researchers developed a computer-based way to map connections between repeating orbits in a simplified Earth–Moon gravity model. Rather than calculate every possible transfer separately, they compared the regions reachable from different orbits under limits on velocity changes and travel time. The resulting network suggests that some orbit families act as major junctions, while others remain hard to reach. Which family is most central depends on the allowed travel time and maneuver budget. Even when almost every pair appears connected, the strength of those connections varies considerably. The team converted selected estimated connections into calculated transfer trajectories, all with costs below their initial estimates. These are findings within the model, not observations of spacecraft flights, and only selected connections received this detailed check.

Young explorerImagine drawing a map of paths a spaceship could take near Earth and the Moon. The researchers used a computer model to find which looping paths might be easy to travel between. Some loops were like busy stations with lots of connections; another was hard to reach. They checked a few routes more carefully, but they did not fly a spaceship along them.

What observations are needed to advance our theoretical understanding of galaxy formation at high redshift?

H. Katz, R. S. Somerville, R. Schneider+98 more

• Astrophysics of Galaxies

AstronomerThis perspective highlights five open problems in theoretical galaxy formation and argues that addressing them requires dedicated high-redshift observations beyond the capabilities of current GO programs. The abstract does not identify the five problems individually. It emphasizes that models starting from cosmological initial conditions cannot yet accurately predict key galaxy properties a priori, including structure, size, star formation histories, chemical abundance patterns, and supermassive black hole mass. Simulations must bridge sub-AU processes near stars and black holes with Mpc-scale gas flows and environmental effects, necessitating subgrid prescriptions and approximations. The authors therefore stress observational constraints and iterative tests of model predictions rather than present new observational findings or simulation results.

PublicScientists still lack a framework that reliably predicts how galaxies form and acquire their properties, such as their sizes, shapes, star-making histories, chemical makeup, and central black hole masses. Computer simulations must connect processes on enormously different scales, so they rely on approximations for details they cannot directly model. The authors argue that progress depends on repeatedly comparing predictions with observations. They highlight five unresolved questions and call for dedicated observations of the distant, early Universe beyond what current GO observing programs can achieve. The abstract does not list those questions or report new measurements.

Young explorerScientists use computers to try to understand how galaxies grow. But tiny things near stars and black holes and huge things around galaxies all matter, and computers cannot follow every detail. Scientists have to simplify some parts and check their ideas by looking at real galaxies. The writers say we need special observations of galaxies from long ago to help answer five big questions. They do not give the answers here.

DMAJOR: A JWST Legacy Survey of Protoplanetary Disks

Benjamin Pope, Yinuo Han, Sean Andrews+36 more

• Earth and Planetary Astrophysics

AstronomerDMAJOR (Disk Motions and Architectures JWST Observational Reference survey) is a proposed infrared imaging survey of spatially resolved protoplanetary disks across a range of galactic environments. It aims to map disk structure in three dimensions across infrared wavelengths and establish a uniform benchmark sample linking disk architecture to environment. Scheduled revisits would probe variability, while JWST’s sensitivity and resolution would enable observations of disks inaccessible from the ground. Science goals include tracing small grains and ice, relating scattered-light structures to large-scale environmental features, and identifying new companions. The proposed processing uses model-based analysis, telemetry, and mutual calibration to improve data products while minimizing telescope overheads. The abstract presents survey plans and anticipated capabilities, not observational results.

PublicDMAJOR is a proposed survey using the James Webb Space Telescope to study disks of gas and dust where planets form, in different environments within our galaxy. Infrared images would help map the disks’ three-dimensional shapes, trace tiny grains and ice, and investigate how disk features relate to their surroundings. Planned repeat visits would look for changes over time, and the survey would also search for previously unidentified companions. The team plans to combine models, telescope operating information, and comparisons among observations to improve the images while limiting extra telescope time. These are the survey’s goals, not discoveries reported in the abstract.

Young explorerScientists want to use the James Webb Space Telescope to look at dusty disks where planets can grow. They hope to learn the disks’ shapes, find tiny dust grains and ice, and see how the things around them might be connected to their shapes. They also plan to look again later to check whether anything changes and search for nearby companions. This is a plan for exploring, not a report of things they have already found.

Satellite Streaks in HETDEX: Spectra, Orbital Identification, and Survey Impact

Erin Mentuch Cooper, Karl Gebhardt, Dustin Davis+10 more

AstronomerA spectroscopic catalog of satellite streaks in HETDEX PDR1 covers 6,778 observations and approximately 90 square degrees from January 2017 to July 2024. The authors detect 527 streaks in 492 observations: 7.3% of observations are contaminated, with monthly fractions exceeding 20% by 2023–2024, although streaks mask only 0.09% of the survey area. Archival orbital elements associate 475 streaks (90.1%) with cataloged objects; of these, 54% are in low Earth orbit and 46% are geostationary or highly elliptical. Only 35% were launched since 2010, a distribution the authors attribute to sensitivity to faint objects and the observing baseline. Median exposure-averaged magnitudes are similar for LEO and GEO objects, g_AB = 16.2 ± 1.1 and 16.7 ± 1.1, respectively, whereas transit-time-corrected instantaneous magnitudes differ by 5.6 mag: 7.4 versus 13.0. For 34 Starlink streaks, normalization to 550 km gives g = 5.95, consistent with the reported VisorSat mean V = 5.92 ± 0.04. Spectra are consistent with reflected sunlight, with modest slope differences attributed to signal-to-noise effects. The catalog, spectra, and code are archived.

PublicResearchers found 527 satellite streaks in 492 of 6,778 observations from the Hobby-Eberly Telescope Dark Energy Experiment, collected between January 2017 and July 2024. Streaks appeared in 7.3% of observations overall, with monthly rates exceeding 20% by 2023–2024, but covered just 0.09% of the surveyed area. About 90% of the streaks could be linked to cataloged objects. Only 35% of those identified objects were launched since 2010; the rest were older spacecraft, spent rocket bodies, or debris. The researchers interpret this mix as reflecting the survey’s ability to detect faint objects and its years of observations. Objects in low Earth orbit and geostationary orbit had similar brightness when averaged over an exposure, but correcting for how long each crossed the telescope’s view revealed a much larger brightness difference. Their spectra are consistent with reflected sunlight.

Young explorerA telescope looking at space saw moving satellites and old space junk leave streaks in its observations. The streaks showed up more often in the later years, but covered only a tiny part of all the sky the telescope studied. The team matched most streaks to known objects, and many were old rather than newly launched. The light they studied looked like sunlight bouncing off those objects.

Foreshortening of Polarizer Angles in Wide Field Polarizing Imagers

Ritesh Patel, J. Marcus Hughes, C.E. DeForest+3 more

• Solar and Stellar Astrophysics
• Optics

AstronomerPUNCH combines four fields of view into a 90-degree-diameter polarimetric image; three are supplied by Wide Field Imagers (WFIs), each with a 40-degree-diameter field. Precise linear polarimetry requires accounting for projection-induced foreshortening of the nominal −60°, 0°, and +60° polarizer orientations relative to each pixel’s line of sight. A simple geometrical calculation estimates effective-angle variations of ±2.5° for the ±60° polarizers and ±3.5° for the 0° polarizer across the WFI field. These are geometric estimates, not reported observational measurements. The study presents the resulting effects on the polarized brightness to be recorded by WFI and how optical distortion shifts the locations of the foreshortened angles, with implications for future wide-field polarimetry.

PublicPUNCH is designed to measure the polarization of light—the orientation of its vibrations—across a very broad region of sky. Its wide-field cameras face a geometrical complication: a polarizing filter’s effective angle changes depending on where light enters the image. Using a simple geometrical calculation, the authors estimate changes of up to 2.5 degrees in either direction for two filter orientations and 3.5 degrees for the third. These are calculated effects, not measurements reported from sky observations. The study examines how the angle changes affect the polarized brightness the cameras will record and how optical distortion shifts the pattern across the image. The issue also matters for future instruments measuring polarization over wide views.

Young explorerPUNCH has cameras that look at a very big patch of sky. They use special filters to tell which way light is wiggling. But a filter can seem tilted differently in different parts of such a wide picture. The scientists used geometry to work out how much that tilt could change and explored how it would affect what the cameras record. This is a calculation about the cameras, not a new discovery seen in the sky.

Particle Swarm Optimization Strategies for Lensed Gravitational Waves: Parameter Estimation, Source Classification, and Accelerated Sampling

Weiqing Yu, Meng Zhang, Xiaobo Zou+1 more

AstronomerThe study tests Particle Swarm Optimization (PSO) for searching, estimating parameters, and classifying strongly lensed compact-binary gravitational-wave signals in a coherent four-detector network. It uses restricted 2-PN templates and a model-independent double-image lens parameterization, testing both matched 2-PN signals and mismatched IMRPhenomD signals rather than reporting an astrophysical detection. Chirp mass, mass ratio, sky position, and lens parameters are recovered effectively in the matched case, but waveform mismatch introduces mass biases. A three-class pipeline using 12 PSO runs, majority voting, and a flux-ratio threshold achieves 86.19% accuracy for lensed signals, unlensed signals, and noise. The proposed PSO_GAUSS_MIX method builds a Gaussian-mixture prior from PSO estimates for nested sampling; tests show a 1.38-fold speedup with preserved posterior accuracy in the restricted 2-PN cases.

PublicGravity can bend gravitational waves from merging compact objects, producing multiple images of a signal and making it harder to identify and interpret. This study tests a search method called Particle Swarm Optimization on modeled signals analyzed with a four-detector network; it does not report a newly observed lensed event. The method recovers source and lens properties effectively when the signal and search template use the same waveform description, but estimates of mass become biased when those descriptions differ. A pipeline combining repeated searches and decision rules correctly classifies 86.19% of the tested cases as lensed signals, unlensed signals, or noise. The researchers also propose using the search estimates to guide a more detailed statistical analysis. In tests with the matched waveform description, this provides a 1.38-fold speedup while preserving the accuracy of the resulting probability estimates.

Young explorerWhen two very heavy things in space spiral together, they make ripples in space. Gravity can bend those ripples so they reach us along different paths, making them tricky to understand. The researchers tested a computer helper on made-up signals, not a new ripple found in space. It did well when its practice pattern matched the signal, but it could guess the masses wrong when the patterns differed. It also usually sorted bent ripples, unbent ripples, and random noise into the right groups. Another idea they tested helped a more detailed computer check run faster without losing accuracy in those tests.

Upgrade of the MITHiC testbed for phase and amplitude control in the focal plane

Anton Neisius, Élodie Choquet, Vincent Chambouleyron+1 more

AstronomerThis contribution reports progress and initial results from an ongoing upgrade of the MITHiC high-contrast imaging testbed at the Laboratoire d'Astrophysique de Marseille. A new deformable mirror for wavefront control complements the existing classic Lyot coronagraph and spatial light modulator, which provides phase and amplitude control to optimize the dark-hole region. The team also implements the Zernike wavefront sensor ZELDA to correct low-order aberrations. The work develops a platform for techniques relevant to direct exoplanet imaging, but the abstract gives no quantitative performance results or exoplanet detections.

PublicBright starlight and imperfections in light waves make planets around other stars difficult to image directly. Researchers are upgrading the MITHiC laboratory testbed in Marseille with a mirror that can change shape to help correct these imperfections. It works alongside equipment that suppresses starlight and controls the light to create a darker region where a planet could be easier to see. The team is also implementing a sensor called ZELDA to help correct some wavefront errors. The report describes upgrade progress and initial results, but does not specify how much performance improved or report a planet detection.

Young explorerSeeing a planet beside a bright star is hard because the star's light gets in the way. Scientists are improving a light-testing setup in a lab. They are adding a mirror that can change shape and a tool that helps find mistakes in how the light travels. These work with tools that block and adjust the star's light. The team reports early progress, but this is a test of tools, not a report of finding a planet.

Ångström Exponent Calculation Using Wide-Field Stellar Photometry

Shefali Negi, Jan Ebr, Sergey Karpov+1 more

AstronomerThe study extends FRAM aerosol-extinction measurements from Tycho-2-based B-band photometry to simultaneous B, V, and R analysis at 440, 540, and 620 nm using Gaia DR3 synthetic Johnson–Cousins photometry. Ångström exponents are derived from paired-filter vertical aerosol optical depths at three sites over 2021–2022. The uncorrected optical depths have an unphysical filter-dependent ordering, yielding negative exponents; none of four processing configurations resolves this, and the correct optical depth cannot currently be assigned to a particular filter. A practical intercept correction produces physically plausible exponents but does not establish which filter is correct. Corrected distributions are unimodal at Paranal, with mean B–V and B–R exponents of approximately 0.84 and 0.65 at CTAO-S0, and 0.60 and 0.41 at CTAO-S1. At CTAO-N on La Palma, the distributions are bimodal, with B–V exponents near 0.2 during episodic Saharan dust intrusions and 1.3 under clean background conditions. AERONET measurements on shared dates show the same two populations, providing qualitative support rather than a quantitative validation.

PublicResearchers used FRAM telescopes to study how airborne particles dim starlight of different colors at three observatory sites during 2021–2022. Their expanded method compares three color bands to measure how strongly this dimming changes with wavelength. However, the initial measurements showed an unexpected ordering between colors, and the team could not determine which color gave the correct amount of dimming. An added correction produced physically plausible results: the two southern Paranal sites each showed a single main group of values, while La Palma showed two groups associated with Saharan dust episodes and cleaner background conditions. A separate instrument also detected the two groups on overlapping dates, offering qualitative support, but the original measurement problem remains unresolved.

Young explorerTiny bits floating in the air can make stars look dimmer. Scientists compared three colors of starlight to learn about those bits. Their first answers did not fit what they expected, so they adjusted the calculation, though they still do not know which color gave the right dimming measurement. After the adjustment, one place showed two groups of answers: one when dust came from the Sahara and another when the air was cleaner. Another instrument saw the same two groups, which is a helpful clue, but it does not prove every answer is right.

The Physics of Interstellar Travel

Coryn A. L. Bailer-Jones

• Popular Physics
• Space Physics

AstronomerThis short, semi-popular article examines the physics and challenges of sending an uncrewed spacecraft to the nearest stars within a human lifetime. Its main topics are nuclear rockets, laser sails, impacts with interstellar dust, and communication over interstellar distances. It also raises questions about destination science and points to the author's book for fuller treatment, including navigation and onboard power. The abstract presents a discussion of challenges and possible solutions, not observational findings, simulation results, or a demonstrated mission design.

PublicCould a robotic spacecraft reach the nearest stars within a person's lifetime, survive the journey, and send information home? This article explores those questions, focusing on nuclear rockets, sails driven by lasers, collisions with dust between stars, and communication across enormous distances. It discusses challenges and possible solutions rather than reporting a successful test or showing that such a mission is ready to fly. The author's book covers these topics, navigation, and onboard power in more detail.

Young explorerCould we send a spaceship with no people inside to a nearby star before a person grows old? This article talks about ideas for moving it, like nuclear rockets or a sail pushed by laser light. It also asks how the ship could stay safe from dust and send messages home from very far away. These are hard questions and possible ideas, not a trip that has already worked.

Deep-Learning-Assisted Bayesian Inference for Extreme-Mass-Ratio Inspirals

Jian-Jun Song, Zhong-Wu Xia, Wen-Hong Ruan+3 more

• General Relativity and Quantum Cosmology
• Machine Learning

AstronomerThe authors develop a deep-learning-assisted Bayesian inference framework for extreme-mass-ratio inspirals (EMRIs), whose highly multimodal likelihoods make narrow high-likelihood regions difficult to locate. The pipeline combines neural-network-guided parameter-space localization, particle swarm optimization, and MCMC sampling. On simulated six-month EMRI signals, it recovers posterior distributions in close agreement with reference MCMC analyses initialized near the true source parameters, without needing that knowledge for its own initialization. After neural-network training, the complete pipeline takes approximately 10 hours per signal. These results demonstrate performance on simulations, not real observations.

PublicThe study tests a way to infer the properties of extreme-mass-ratio inspirals (EMRIs), signals for which many different parameter combinations can appear plausible. The method uses a neural network to identify promising regions, an optimization algorithm to search them, and statistical sampling to estimate the parameters and their uncertainty. In tests on simulated signals lasting six months, its estimates closely matched those from a reference method given a starting point near the known true values. The new method did not need that advance knowledge. Processing took about 10 hours per signal once the neural network had been trained; the abstract does not report tests on real observations.

Young explorerScientists tested a computer helper on made-up space signals. Finding the right answer is tricky because lots of answers can look good. The helper first points to promising places to look, then other computer tools search carefully and work out which answers fit. It got answers close to another method that was given a starting hint, but the new helper did not need that hint. After the helper had been trained, each signal took about 10 hours to check. These were practice signals, not real ones.

First demonstration of long-distance electron drift in liquid xenon with the Xenoscope time projection chamber

N. Angelides, M. Babicz, E. E. Barillier+14 more

• Instrumentation and Detectors
• High Energy Physics - Experiment

AstronomerXenoscope, a dual-phase xenon time projection chamber at the University of Zurich, demonstrates electron drift over 2.6 m in liquid xenon using cosmic-muon-induced ionization. External muon tagging supplies timing references for charge produced at known depths, while the endpoint of the average electroluminescence waveform probes the full drift length. Measured drift velocities are (1.320 ± 0.006) mm/μs at (80.92 ± 0.36) V/cm and (1.436 ± 0.001) mm/μs at (96.00 ± 0.42) V/cm. The measurements establish detectable meter-scale charge transport and provide an experimental benchmark for future large liquid-xenon time projection chambers, including development relevant to XLZD.

PublicResearchers at the University of Zurich have demonstrated that electrons can travel 2.6 metres through liquid xenon and still produce a detectable signal. Using the Xenoscope detector, they tracked charge released by cosmic muons. A separate muon tag supplied a timing reference, and the light signal produced by the drifting charge helped probe its travel across the detector. At two tested electric-field strengths, the measured electron speeds were about 1.32 and 1.44 millimetres per microsecond. These experimental results provide a benchmark for developing future, larger liquid-xenon detectors such as the planned XLZD observatory; they are not a demonstration of that future observatory itself.

Young explorerScientists used a detector called Xenoscope to watch tiny bits of electricity called electrons move through a liquid called xenon. Particles from space called muons knocked the electrons loose. The scientists showed that the electrons could travel 2.6 metres and still make a signal they could detect. This test can help scientists build bigger detectors in the future.

Learning What's Real: Disentangling Signal and Measurement Artifacts in Multi-Sensor Data, with Applications to Astrophysics

Pablo Mercader-Perez, Carolina Cuesta-Lazaro, Daniel Muthukrishna+5 more

• Astrophysics of Galaxies
• Machine Learning

AstronomerThe authors propose a self-supervised deep-learning framework for separating intrinsic astrophysical signals from instrument-dependent distortions and noise. It combines overlapping observations of the same physical system, a dual-encoder architecture, and a counterfactual-generation objective. They demonstrate the approach on galaxy images from the DESI Legacy Imaging Survey and the Hyper Suprime-Cam Survey, reporting representations that separate intrinsic and sensor-specific variation. These representations support counterfactual views, parameter inference intended to avoid measurement confounding, and instrument-independent similarity searches. The abstract provides no quantitative performance metrics or limits on the separation achieved. Broader applicability to scientific and multimodal pretraining is proposed rather than demonstrated across other domains.

PublicImages of a galaxy contain both information about the galaxy and effects introduced by the instrument that observed it. The authors propose an artificial-intelligence method that learns from overlapping observations of the same objects to separate these contributions. They demonstrate the method using galaxy images from the DESI Legacy Imaging Survey and the Hyper Suprime-Cam Survey. The learned information can be used to generate alternative instrument views, infer physical properties with less interference from measurement effects, and find similar objects across instruments. The abstract reports that the approach works but does not give numerical accuracy estimates. Its use beyond this galaxy-image setting is a proposed extension.

Young explorerPictures of the same galaxy can look different because the tools taking the pictures add their own blur and noise. Researchers made a computer-learning method that compares pictures of the same galaxy and tries to tell what belongs to the galaxy and what comes from the picture-taking tool. They tried it with galaxy pictures from two sky surveys and report that it works, but this summary does not say exactly how well. They suggest that the same idea could help with other kinds of science pictures and measurements, too.

Spectro Capture: A Software System for Automated Small-Observatory Spectroscopy

Paul Luckas

• Solar and Stellar Astrophysics

AstronomerSpectro Capture is a Python-based system that automates small-observatory fibre-fed spectroscopy by integrating target selection, telescope slewing, guide-star acquisition, fibre position restoration, and calibration and science exposure sequencing. The paper reports its design and operational behaviour at Shenton Park Observatory, including unattended multi-target observing. Logs from January–May 2026 show completion of 339 of 345 attempted science target blocks in primary unattended batch runs, a 98.3% completion rate. These operational results support the practicality of reliable unattended spectroscopy at a small observatory through integrated software control; the reported metric measures target-block completion, not spectral quality.

PublicSpectro Capture is software designed to let a small observatory collect spectra—observations that separate light into its different wavelengths—without an operator attending each target. It coordinates choosing targets, pointing and guiding the telescope, positioning the light-collecting fibre, and taking calibration and science exposures. At Shenton Park Observatory, logs from January to May 2026 recorded 339 completed science target blocks out of 345 attempts in the main unattended observing runs, a success rate of 98.3%. This demonstrates reliable automated operation in that setting, although the completion rate alone does not establish the quality of the spectra.

Young explorerA program called Spectro Capture helps a small telescope look at different things in the sky and collect their light without a person helping at every step. At one observatory, its records showed that it finished 339 out of 345 planned observing jobs in its main runs without someone watching over it. That shows it usually finished those jobs, but it does not tell us how good every light measurement was.

Fast and accurate bandpass integration of complex SEDs with neural networks

L. A. Bianchi

AstronomerThe paper introduces a neural-network approach to bandpass integration of spectral energy distributions (SEDs), distributed through the Python package pyfine. The approach exploits the smoothness of the target function produced by the non-local integral operator. In computational tests with 3 and 9 free parameters, the authors report maximum relative residuals as low as 0.002% and 0.08%, respectively, within the sampled parameter regions, alongside fast evaluation and little memory overhead. For the first test, using a simple modified-blackbody SED, measured network evaluation was about 100 times faster than an optimized multithreaded direct integration. The method is especially useful when evaluating the SED itself is expensive; the reported accuracy is not established beyond the sampled regions.

PublicCalculating how much light a model source contributes within a selected wavelength range can require repeated, costly calculations. This paper presents a neural-network shortcut, available in the Python package pyfine. In two computer tests, its largest relative differences from the reference calculation were reported to be as low as 0.002% and 0.08%. In the simpler test, it ran about 100 times faster than an optimized direct calculation while requiring little extra memory. These are computational benchmarks, not observations of astronomical objects, and the reported accuracy applies within the tested ranges of model settings.

Young explorerImagine a picture showing how much light there is in each color. Adding up the light in just some colors can take a computer time. The researchers taught a computer a shortcut for doing that adding. In two tests, its answers were very close to the careful calculation, and in one test it was about 100 times faster. Those tests do not tell us how well it works for every possible light picture.

Interference Meets Inference: Bayesian Time-Series Modeling of Radio-Frequency Interference

Jade M. Ducharme, Andrei Li, Michael J. Wilensky+1 more

AstronomerThe authors formulate radio-frequency interference (RFI) detection as one-dimensional time-series anomaly detection, using a probabilistic mixture model to separate a smoothly varying astronomical background from contamination. The model assigns each time sample a posterior probability of RFI membership, providing classification confidence and enabling uncertainty propagation into downstream statistics. Applied to 2014 Murchison Widefield Array observations, it yields soft classification labels and seasonal RFI trends. A parallel analysis with the Sky-Subtracted Incoherent Noise Spectra (SSINS) pipeline produces broadly similar hard labels. The reported advantage is a complementary probabilistic description of contamination and uncertainty, rather than demonstrated superior classification accuracy.

PublicUnwanted radio signals can interfere with radio astronomy observations. This study develops a method that separates a smoothly changing astronomical background from unusual contamination and estimates how likely each moment of data is to contain interference, rather than simply marking it as contaminated or clean. Applied to Murchison Widefield Array observations collected in 2014, the method produced classifications and seasonal interference trends. Its classifications were broadly similar to those from an existing software pipeline, but the probability estimates also describe uncertainty and can help researchers examine ambiguous cases and carry uncertainty into later calculations.

Young explorerA radio telescope listens for signals from space, but unwanted radio noise can get mixed in. The researchers made a computer method that asks, for each little moment, 'How sure are we that this is unwanted noise?' They tried it on telescope recordings, and it made choices much like another computer method. The new method also says how sure or unsure it is, instead of only saying yes or no.

Optimal Design of Shaped Pupil Lyot Coronagraph for China's Large Segmented Telescope

Kaining Yang, He Sun, Bin B. Ren+7 more

AstronomerThe study optimizes a Shaped Pupil Lyot Coronagraph (SPLC) for China's planned EAST and LOT telescopes, whose segmented, centrally obscured pupils introduce contrast-limiting diffraction from segment gaps and spiders. The architecture combines a binary shaped pupil apodizer, a focal-plane occulting mask, and a Lyot stop with two-deformable-mirror adaptive optics. End-to-end simulations using Lenghu site parameters and assuming idealized extreme adaptive-optics correction yield raw contrasts of order 10^-6–10^-7 in the V, H, and K bands. These simulated results represent an upper-bound performance estimate, not an observational demonstration. They suggest that the architecture can mitigate pupil diffraction while retaining a small inner working angle and practical throughput, making it promising for future high-contrast exoplanet imaging.

PublicResearchers investigated a way to reduce the glare of stars so that China's planned EAST and LOT telescopes could image planets and disks around them. Gaps between mirror segments, the central obstruction, and support structures scatter starlight in patterns that make nearby faint objects difficult to see. The proposed design combines specially shaped masks that suppress starlight with two adjustable mirrors that correct atmospheric distortion and remaining optical errors. Computer simulations based on conditions at Lenghu suggest raw contrasts of roughly one part in a million to one part in ten million in visible and infrared bands. However, the simulations assume idealized correction of atmospheric effects, so they estimate an upper limit on performance rather than demonstrate what a working telescope has achieved.

Young explorerA bright star can make a little planet beside it hard to see. Scientists studied special masks to block the star's glare and two mirrors that can change shape to help fix blurry light for future big telescopes in China. Their computer tests suggest the idea could help reveal faint things close to stars. But the tests assumed the blur could be fixed very well, so a real telescope might not do as well.

Reproducibility, Methodological Robustness, and Synthetic-Domain Selection Properties of AFINO for TESS Stellar-Flare QPP Analysis

Marc Balboa Corominas

• Solar and Stellar Astrophysics

AstronomerThis study separates reproducibility, methodological robustness, and synthetic-ground-truth performance for a frozen public AFINO implementation used to search for quasi-periodic pulsations in TESS stellar flares. The frozen baseline reproduced five published detections in an initial cohort. A ten-event observational pilot and a catalogue-scale experiment tested prospectively specified temporal-window and processing perturbations. At catalogue scale, 51 of 61 published-QPP references failed to reproduce their frozen reference state under the F3A baseline; robustness assessments were therefore restricted to baseline-concordant references and were not treated as accuracy estimates. In a separate synthetic programme, the unchanged AFINO 0.5 rule was evaluated once on an independent held-out set, selecting 152 of 1800 positives and none of 1800 nulls, with finite Wilson uncertainty. The 156-stratum selection surface applies only within the frozen synthetic domain, and period-recovery summaries are additionally conditional on selection. These tests do not establish observational validation or a population-level correction.

PublicSearches for roughly repeating pulses in stellar flares can depend on how the data are processed and which part of a flare is analysed. The researchers tested a fixed public version of the AFINO software using TESS observations and, separately, artificial signals with known properties. An initial test reproduced five published detections, but in a larger comparison, 51 of 61 published examples did not reproduce their reference classification under the specified baseline. This limits what the observational tests can say about reliability. In an independent artificial test set, the software selected 152 of 1800 signals containing pulses and none of 1800 examples without them. Zero false selections in this test does not guarantee zero false alarms generally. The artificial tests describe performance only for the simulated conditions; they neither validate detections in real observations nor establish a correction for the wider flare population.

Young explorerStars sometimes flare up, and scientists look for little beats in their light. This study checked a computer tool that looks for those beats. It found some reported beats again, but many did not come out the same way. With made-up examples, it missed many beats and picked no examples without beats. That does not mean it can never make a mistake. These tests cannot yet tell us how well it finds real star beats.

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

Kaili Cao, Camille Avestruz, Feige Wang

• Digital Libraries
• Information Retrieval

AstronomerMapHub uses a large language model to assess daily arXiv submissions against participant-specific research portfolios, publishing relevance scores from 0 to 100 as a community heatmap. In the authors' blind evaluation, the highest-scoring 10% of papers captured about 70% of the raters' pooled personal top 5%, compared with about one-third for a text-matching baseline. The abstract reports that, for each participant, about 6% of a day's astro-ph papers score at least 30, while one paper every three days scores at least 60. These findings concern relevance screening, not scientific quality. MapHub runs on a standard Claude subscription; usefulness across fields is a design aim rather than a demonstrated result in the abstract.

PublicMapHub is an AI tool that helps researchers find new papers related to their interests. It compares daily arXiv submissions with profiles of researchers' work and displays relevance scores in a color-coded chart. In a blind test reported by the authors, MapHub's highest-ranked tenth of papers included about 70% of the papers the raters placed in their own top 5%. A simpler text-matching method captured about one-third. The scores indicate relevance to a researcher, not whether a paper's conclusions are correct. The tool runs on a standard Claude subscription and is intended for use beyond astronomy, though the abstract does not establish its performance across fields.

Young explorerScientists have lots of new papers to look through. MapHub is an AI helper that looks at what each scientist studies and gives papers scores for how closely they match. It shows the scores in a colorful chart. In a test, its favorite small pile included many of the papers the scientists liked best, and it did better than a simpler word-matching helper. A high score means a paper might fit someone's interests, not that everything in it is right.

Distributed Acoustic Fiber Sensing for Research Campuses and Large Scientific Infrastructures -- The Hamburg WAVE proto-network

Oliver Bölt, Luigia Cristiano, Sandy Croatto+17 more

• Instrumentation and Detectors
• Accelerator Physics
• Geophysics

AstronomerThis study investigates Distributed Acoustic Sensing (DAS) for monitoring environmental vibrations at research campuses and large scientific facilities, with potential applications to gravitational-wave experiments and particle accelerators. A May 2021 Hamburg WAVE campaign probed more than 12 km of fiber across DESY, the European XFEL, PETRA III and the University of Hamburg. The prototype network detected natural, human-generated and infrastructure-related vibrations and identified how and where they coupled into different portions of the heterogeneous fiber network. A separate study at the European XFEL examined noise and motion coupling in double-redundant fiber loops. The results demonstrate vibration-monitoring capabilities and highlight implementation and operational challenges; reducing vibration impacts on precision experiments is a prospective application, not a reported experimental outcome.

PublicVibrations from nature, people and machinery can disturb highly precise scientific experiments. The researchers tested Distributed Acoustic Sensing, a technique that uses optical fibers to sense vibrations, across more than 12 km of fiber at research sites in Hamburg in May 2021. Their prototype detected several kinds of vibration and revealed where and how vibrations entered different parts of the fiber network. They also investigated noise and motion effects in fiber loops at the European XFEL. The findings support using such networks to monitor research facilities, potentially helping protect sensitive experiments, including gravitational-wave detectors. The study also identifies challenges in building and operating these networks; it does not report a demonstrated reduction in disturbance to an experiment.

Young explorerTiny shakes from nature, people and machines can bother very careful science experiments. Researchers tested long, thin fibers to see whether they could notice these shakes around science buildings in Hamburg. The fibers did notice different kinds of shaking, and the team studied how the shakes reached different parts of the fibers. They hope this could help scientists keep experiments steadier, but this study did not show that they had made an experiment shake less.

RoverDevKit: An open, physics-grounded tradespace toolkit for conceptual design of lunar micro-rovers

Jon Reifschneider

• Robotics

AstronomerRoverDevKit is an open-source toolkit for exploring lunar micro-rover design trade-offs. Its evaluator couples an analytical wheel-soil model to bottom-up mass, solar-power, thermal-survival, and traverse models, capturing feedback between mass, sinkage, power demand, and solar-array size. An NSGA-II multi-objective search completes 3,000 mission evaluations in under a minute on one laptop core. Modeled trade-offs among distance, mass, and slope capability identify mission-dependent limits: energy storage at high latitude, traction on loose highland slopes, and traverse range on mare and crater-rim terrain. Benchmarking against two independent single-wheel datasets gives drawbar-pull accuracy consistent with the 20–30% errors typical of this model class; predicted masses for published 5–50 kg rovers have a median absolute percentage error of 10.5%. Five published rover designs fall near the predicted Pareto front of best compromises. These are modeling and benchmark results, not demonstrations of rover performance on lunar missions.

PublicDesigning a small Moon rover involves a difficult loop: extra weight makes it sink farther into loose soil, which increases power needs, while a larger solar array adds still more weight. The researchers present RoverDevKit, free, open-source software that models these connections and searches for compromises between weight, travel distance, and climbing ability. Its calculations suggest that different missions face different limits, including energy storage near the poles and traction on loose highland slopes. Comparisons with existing measurements and published rover designs provide checks on the software, but not proof of lunar performance: wheel-pulling predictions have errors consistent with the 20–30% typical of similar models, and rover-mass predictions have a median percentage error of 10.5%.

Young explorerMaking a little Moon robot is tricky. A heavier robot sinks more into soft ground and needs more power to move. Bigger solar panels can help, but they add weight too! The researchers made a computer tool to help choose designs. They checked its guesses against measurements and information about other rovers. It is helpful, but its guesses are not perfect, and this was not a Moon driving test.

Post-Newtonian Global Conservation Laws in the Presence of Sensitive Bodies

Timothy Clifton, Asta Heinesen, Oliver Pitt

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study extends the PPN classification of semi-conservative and fully conservative gravity theories to compact bodies whose modeled masses depend on their local environment, as relevant to violations of the strong equivalence principle. The authors show that global conserved quantities can still exist with such sensitivities and derive their explicit forms where they do. They also identify new expressions for PPN metric coefficients in theories admitting these conserved quantities and compare the framework with known scalar-tensor results. The work develops tools for weak-field gravity tests; it does not report an observational test or establish that these environmental sensitivities occur in nature.

PublicEinstein’s theory can be tested using a mathematical framework that describes weak gravity without committing to one particular alternative theory. This paper extends that framework to cases in which the modeled masses of compact astronomical bodies depend on their surroundings, a possibility in some alternatives to Einstein’s theory. The authors show that whole-system quantities can remain conserved in some such cases and work out their mathematical forms. They also compare their approach with established results from theories involving an additional scalar field. These are theoretical findings, not observations showing that astronomical masses actually behave this way.

Young explorerScientists use math to check ideas about gravity. In this paper, they imagine that how much mass a very tightly packed space object has could depend on what is around it. They find that, in some of these math models, certain totals for the whole group of objects can still stay the same. This is a result about the math, not a discovery that real space objects change this way.

Validating direct solvers for Newton's gravitational N-body problem, and the systematic comparison between IEEE floating point and Posits

Simon Portegies Zwart

• Computational Physics
• Programming Languages
• Chaotic Dynamics

AstronomerThis computational benchmark compares floating-point formats from 16 to 128 bits and two Posit implementations against arbitrary-precision calculations for Newton’s chaotic N-body problem. In the reported tests, 16-bit arithmetic is insufficiently precise. The 32-bit formats may support statistical ensemble calculations, but produce relatively large errors in individual strong encounters. All tested 64-bit implementations encounter difficulties. Universal Posits achieve precision comparable to fp64 but run at least an order of magnitude slower, even after correction for fp64’s more efficient hardware support. CPPPosits run at comparable speed to fp64 but have errors typically about an order of magnitude larger, with excesses exceeding two orders of magnitude; the authors report systematic drift in result space and difficulty resolving close encounters. Both Posits and fp64 struggle with integration in moving reference frames, a test of Galilean invariance. The authors conclude that current Posit implementations do not appear to be an ideal fp64 replacement for chaotic or stiff ODE integration. These findings concern numerical tests, not astronomical observations, and depend on the implementations tested.

PublicWhen computers calculate how bodies move under gravity, their limited number precision can introduce errors. This study tests several ways of representing numbers against much higher-precision calculations in chaotic gravity simulations. The lowest-precision options are inadequate, while 32-bit options might be useful for studying groups of simulations statistically but can give large errors during individual close encounters. Even the tested 64-bit methods have difficulties. Two implementations of an alternative number format called Posits make different trade-offs: one is about as accurate as standard 64-bit arithmetic but much slower, while the other is similarly fast but less accurate and shows systematic drift in its results. The authors therefore find no clear replacement for standard 64-bit arithmetic in the current Posit implementations for these demanding calculations.

Young explorerScientists tested how computers work out the paths of things pulling on each other with gravity. Computers can keep only so much detail in their numbers, and small mistakes can matter. Some new ways of keeping numbers were too slow or made bigger mistakes. In these tests, they were not a better replacement for the usual way.

Trapping of nanofabricated SiO₂ high-aspect-ratio discs in an optical lattice

Shelby Klomp, Shafaq Gulzar Elahi, Scott Grudichak+13 more

• Optics
• General Relativity and Quantum Cosmology
• Quantum Physics

AstronomerThe authors describe nanofabrication and loading of lithographically patterned silicon dioxide discs, 10 μm in diameter and 400 nm thick, into an optical standing-wave trap in vacuum. They obtain center-of-mass motional spectra using combined interferometric and imaging methods. The method supports high-efficiency loading and trapping with only a few particles and accommodates customized geometries and sizes compatible with wafer-scale nanofabrication. Trapped discs are identified as promising candidates for high-frequency gravitational-wave detectors or sensitive accelerometers; the abstract does not report demonstrations of either application.

PublicResearchers fabricated tiny silicon dioxide discs, 10 micrometers across and 400 nanometers thick, and loaded them into a trap formed by a standing wave of light in a vacuum. They measured the discs’ motion using interference of light together with imaging. The method can efficiently load and trap particles even when only a few are available, and it allows tailored shapes and sizes compatible with wafer-scale fabrication. Such trapped discs may eventually help detect high-frequency gravitational waves or measure acceleration very sensitively, but those applications are not demonstrated here.

Young explorerScientists made tiny, very thin discs and held them with light in a space with the air removed. They used light and pictures to measure how the discs moved. Their method can work with just a few tiny discs. One day, discs like these might help sense tiny changes in motion or fast ripples in space, but the scientists have not shown those uses here.