Tonight’s sky of new research

Poisson Clustering and Seed Effect of PBHs: Implications for Microlensing, Gravitational Waves, Little Red Dots and Ultra-Faint Dwarf Galaxies

Bernard Carr, Sebastien Clesse, Juan Garcia-Bellido+2 more

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

AstronomerThe authors examine how primordial black holes (PBHs) with an extended mass function could affect structure formation through seed and Poisson fluctuations, predicting dark, gravitationally bound PBH clusters with more massive central black holes. Their analysis combines small-scale binding, dilution by dynamical heating of clusters below roughly 10^6 solar masses, and cluster survival in the outer Galactic halo versus destruction in the central halo. Clustering at the expected masses and radii is unlikely to weaken microlensing constraints, but a declining Galactic rotation curve might allow a large dark-matter fraction in solar-mass PBHs formed at the quantum chromodynamics transition. They argue that merger-rate estimates require revision: binaries formed in clusters could dominate and might remain compatible with LIGO-Virgo-KAGRA limits even if PBHs supply the dark matter. Seed and Poisson effects are also proposed as possible origins of Ultra-Faint Dwarf Galaxies and Little Red Dots. These are conditional theoretical conclusions, not a detection of PBHs; stronger clustering from primordial fluctuations with exponential non-Gaussian tails could change them.

PublicCould black holes formed in the early universe account for much of the invisible matter called dark matter? This study explores that possibility rather than reporting a discovery. The authors consider how these primordial black holes might gather into dark clusters containing larger black holes at their centers, and how gravitational interactions could spread out or destroy those clusters. The expected clustering probably would not weaken limits from searches for the temporary magnification of background stars. However, a decline in the Milky Way's rotation curve might loosen those limits enough to permit much of its dark matter to consist of primordial black holes with masses similar to the Sun's. The authors also argue that black-hole mergers inside clusters could be important and might be consistent with gravitational-wave limits. They suggest that the same clustering processes could help explain Ultra-Faint Dwarf Galaxies and Little Red Dots. The conclusions depend on how primordial black holes formed and how strongly they clustered.

Young explorerSome scientists wonder whether black holes made when the universe was very young could be much of its hidden matter. This paper asks what would happen if those black holes gathered in groups, sometimes with a bigger black hole in the middle. Gravity could pull the groups together, spread them out, or break them apart. The scientists think some versions of this idea might still fit what astronomers have measured, but other versions have trouble. They also suggest these groups might help explain some small galaxies and objects called Little Red Dots. This is an idea being studied, not a discovery that these ancient black holes are really there.

Gravothermal Evolution of Self-Interacting Dark Matter Halos across Knudsen Numbers

James Gurian, Suroor Seher Gandhi, Neal Dalal+1 more

AstronomerFor dark matter with elastic self-interactions mediated by a light particle, the cross section scales as v^-4 above a particle-physics-dependent velocity scale w, potentially allowing very large cross sections in low-mass halos. The authors use KiSS-SIDM kinetic simulations of isolated halos spanning masses, concentrations, and cross sections of 50–250,000 cm²/g, including velocity-dependent and anisotropic scattering. For idealized NFW halos, they find that the collapse time can be predicted from the Knudsen number at the scale radius. Halo cutouts drawn from cosmological simulations with collisionless N-body or strongly collisional SPH dynamics yield collapse times differing from the idealized cases by up to a factor of a few. A hydrostatic fluid model calibrated against these simulations predicts late-stage convection for velocity-independent cross sections. Fluid and kinetic collapse times agree well, especially for velocity-independent scattering; density profiles agree well in some cases, including all velocity-dependent runs. These are simulation results and fluid-model predictions, not observational findings.

PublicThis study uses computer simulations to explore how dark matter halos collapse if dark matter particles can scatter off one another. The proposed particle interaction could make scattering especially strong in low-mass halos. In simplified halos, the researchers find a way to predict collapse times from a quantity describing how readily particles travel between collisions. Halos taken from cosmological simulations collapse on timescales that differ from the simplified cases by up to a factor of a few. A simpler fluid model reproduces the simulated collapse times well, though agreement in density profiles is less universal. That model also predicts that a region with convection develops late in collapse when scattering does not depend on speed. The study does not establish that real dark matter behaves this way.

Young explorerScientists used computers to study big clumps of dark matter. They asked what might happen if its tiny pieces bumped into each other. Their computer clumps could shrink, and a simpler model often predicted how long that took. These are pretend clumps in computers, not proof that real dark matter acts this way.

Constraints on Reionization from Planck Low-ℓ EE Polarization and the Lyman-Series Forests

Garett Lopez, Anson D'Aloisio, Christopher Cain

• Astrophysics of Galaxies

AstronomerThe study combines full Planck likelihoods with Lyman-series forest constraints to reduce degeneracies in reionization histories allowed by the CMB optical depth, tau_es. Forest inputs include dark-pixel upper limits on the neutral fraction at approximately z = 4.9–6.9 and a lower limit at z = 5.8 inferred from damping-wing-like features near long dark gaps in stacked spectra. Neither changing between parametric and non-parametric histories nor changing forest-data combinations significantly shifts tau_es or other cosmological parameters; the main effect is to redistribute the optical-depth contribution across redshift. Combining CMB, dark-pixel, and damping-wing-like constraints gives z50 = 7.7 (+0.7, −0.8) and a 95% upper limit on duration of Delta z90 < 11.4, while the asymmetry Az remains poorly constrained. Adding mean IGM photoionization-rate measurements yields tighter but more model-dependent constraints. With a new semi-analytic model, the inferred values are z50 = 7.4 (+0.2, −0.3), Delta z90 = 6.0 (+0.8, −1.0), and Az = 2.4 (+0.3, −0.7). The analysis also finds evidence for declining ionizing emissivity after the epoch at z = 7–8; reduced escape fractions or feedback are possible interpretations, not established causes. The results motivate forest likelihood products and fast forward models of transmission statistics.

PublicReionization was the period when radiation stripped electrons from gas between galaxies. Measurements of the cosmic microwave background constrain its overall effect but still allow many different timelines. This study combines those measurements with constraints from patterns of absorption in distant spectra. The added information narrows when reionization could have happened without significantly changing the inferred overall scattering of background light or other cosmological parameters. The combined analysis places the midpoint near redshift 7.7, but the history’s asymmetry remains uncertain. A more detailed model, using additional measurements of the gas’s ionization rate, gives tighter estimates, though these depend more strongly on the modeling assumptions. The researchers also find evidence that the production of escaping ionizing radiation declined after the epoch at redshift 7–8. Why it declined remains uncertain.

Young explorerLong ago, light changed the gas between galaxies by knocking tiny electrons off its atoms. Scientists put together clues from very old light and from light passing through the gas to work out when this happened. The clues help narrow the answer, but they do not tell the whole story. A more detailed model gives a tighter answer, but it depends more on the scientists’ assumptions.

Spherization of the velocity field of cosmological perturbations near density extrema

Anton N. Baushev

AstronomerThis theoretical study considers a mechanism that drives the velocity field of linear cosmological perturbations toward spherical symmetry near density maxima and minima. The analysis finds that the mechanism begins operating at the onset of nonrelativistic matter domination, at z < z_eq ≈ 3600, and rather quickly makes the local velocity distribution nearly isotropic. This isotropy need not persist: if the initial perturbation has a noticeably aspherical density profile, its gravitational field subsequently destroys it.

PublicThe study theoretically examines how motions near unusually dense or sparse regions of the early Universe could become nearly the same in every direction. The proposed mechanism starts working when nonrelativistic matter begins to dominate the Universe and is found in the analysis to act relatively quickly. But the symmetry can be temporary: if the region initially has a noticeably nonspherical distribution of matter, its gravity later makes the motions uneven across directions again. These are theoretical findings, not reported observations.

Young explorerImagine a place in the young Universe with more stuff, or less stuff, than nearby places. The researchers' calculations say that the way things move near its middle can soon become almost the same in every direction. But if the stuff starts out in a shape that is not very round, its gravity can later make those motions uneven again. This is an idea studied with calculations, not something the researchers report seeing.

Not so Fast: Revised Calibration of SIDM Core Collapse

Frank C. van den Bosch, Yarone M. Tokayer

• Astrophysics of Galaxies

AstronomerThis numerical study recalibrates SIDM gravothermal evolution using SphDSMC, a spherical Direct Simulation Monte Carlo code that avoids force softening and reaches substantially higher central densities than standard N-body simulations. N-body calculations converge to SphDSMC only with softening lengths significantly below those typically used for collisionless simulations; appropriately implemented multiple scatterings per particle per time step introduce no significant errors. Comparisons with one-dimensional gravothermal fluid models reveal inaccuracies in the usual harmonic interpolation between long- and short-mean-free-path conductivities. A gentler transition reproduces the spherical NFW halo calculations across a range of concentrations and truncation radii using one long-mean-free-path conductivity parameter. The revised long-mean-free-path collapse time is somewhat shorter than previous estimates, but collapse slows dramatically after the core becomes optically thick. The authors supply late-time fitting functions and argue that SIDM black-hole seed formation generally takes longer than previously estimated, making it unlikely to explain the massive high-redshift black holes inferred from JWST observations without additional physics.

PublicThe researchers used computer simulations to study how dark matter that interacts with itself might form increasingly dense centers inside spherical halos. Their new simulation method follows these centers to much higher densities than standard simulations. The comparisons show that standard simulations need finer settings than commonly used, and that a widely used mathematical description of heat transport needs revision. Although the revised model predicts somewhat faster collapse during an earlier stage, collapse slows dramatically once particles have difficulty traveling through the core without interacting. The authors therefore argue that forming black-hole seeds this way generally takes longer than previously estimated. Without additional physics, they consider this process unlikely to explain the massive black holes inferred from JWST observations of the early universe. These conclusions come from simulations and modeling, not direct observations of dark matter collapsing.

Young explorerScientists used computers to imagine round clumps of dark matter whose tiny bits can bump into each other. They studied how the middle gets denser and found that the squeezing slows a lot when bumps become very common. They think making a baby black hole this way takes longer than people thought—probably too long to explain some huge black holes in the young universe without something else helping. They did not watch dark matter do this in space.

νGundam: a unified framework for point-redshift and PDF-aware spatial correlation functions

E. Donoso, C. A. Lopez Cortez, U. Sureshkumar+1 more

AstronomerνGundam propagates radial redshift PDFs through pair counts using exact empirical-PDF integration, Gaussian-mixture compression, Monte Carlo sampling, or quantile compression, with a common resolved (r_p, π) grid for reconstructing ξ and projected clustering. Validation uses DESI galaxies and CosmoDC2 mocks. The PDF-aware modes yield nearly indistinguishable line-of-sight redistribution kernels; under practical settings, the three approximate modes reproduce exact integration with fractional RMS residuals below 5%. Radial uncertainty primarily shifts clustering signal to larger line-of-sight separations, with the projection depth needed for recovery scaling with pairwise radial dispersion. In DESI Bright Galaxy Survey samples, Monte Carlo sampling recovers spectroscopic clustering shapes and relative amplitudes at r_p ≳ 0.8 h⁻¹ Mpc, using recovery depths of approximately 400 and 180 h⁻¹ Mpc for red and blue galaxies, respectively. These findings support treating integration depth as a sample-dependent part of the measurement definition, rather than a universal fixed choice.

PublicUncertain galaxy distances can blur measurements of how galaxies cluster together. The researchers present νGundam, software that carries the full range of possible distances into calculations of galaxy pairs, rather than assigning each galaxy just one estimated distance. They tested it with DESI galaxy data and simulated galaxies from CosmoDC2. Three faster methods reproduced the exact calculation with fractional root-mean-square differences below 5% in the practical settings tested. In DESI samples, one of these methods also recovered the shapes and relative strengths of clustering measured using spectroscopic distances, over the reported range of transverse separations. The key finding is that distance uncertainty largely spreads the clustering signal along our viewing direction rather than simply erasing it. Recovering that signal requires including a sufficiently deep range of possible separations, and the necessary depth differs between galaxy samples.

Young explorerImagine trying to find groups of galaxies when you are not sure how far away each one is. Giving every galaxy just one guessed distance can make the groups look blurry. The researchers made a computer tool that uses many possible distances instead. They tested it with real galaxy information and pretend galaxies made in a computer. Their quicker ways of doing the counting gave answers close to the more exact way. To find the groups well, the tool needs to count galaxies across a wide enough range of distances—and different groups need different ranges.

Parity-odd CMB Correlations induced by a Chiral Gravitational Wave Background

Baoyu Xu, Yun-Long Zhang

• General Relativity and Quantum Cosmology

AstronomerThe authors propose weak lensing by a chiral gravitational-wave background as a mechanism for parity-odd CMB correlations. Including both photon deflection and polarization rotation, they derive the induced EB and TB angular power spectra. For representative gravitational-wave energy-density spectra, some parameter choices fit existing measurements well. This is a proposed probe of chiral gravitational-wave backgrounds, not a reported detection.

PublicThe study explores whether a background of gravitational waves with a preferred handedness could leave distinctive patterns in the cosmic microwave background, the ancient light filling the universe. The calculations account for both bending the light’s path and rotating its polarization, or orientation. Some choices of the model’s parameters fit existing measurements well, but this does not establish that such a gravitational-wave background has been detected. The effect could offer a way to search for it.

Young explorerScientists worked out how tiny ripples in space that favor one kind of twist might bend very old light and turn the direction it wiggles. Their idea can match some patterns people have measured, but that does not mean they have found these ripples. It might give them a new way to look.

Magnetic monopoles produced by first-order phase transition

Yuefeng Di, Ligong Bian, Rong-Gen Cai

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

AstronomerThe authors report the first 3D lattice simulations of monopole production in a first-order phase transition using the Press-Ryden-Spergel method, following annihilation and entry into a scaling regime in an expanding universe. They quantify the relationship between the initial bubble number and residual monopole abundance and calculate magnetic-field and gravitational-wave power spectra from monopole dynamics. The simulated magnetic spectrum declines as k^-5 at scales smaller than the monopole size w_M. The gravitational-wave spectrum peaks at the mean monopole-separation scale d_M, with k^3 and k^-3 behavior below and above the peak, respectively. The authors conclude that the resulting magnetic-field strength is excluded by blazar observations, ruling out this monopole mechanism as the origin of primordial cosmic magnetic fields. They derive monopole-mass upper limits of approximately 2.18 × 10^11 GeV from the Parker bound and 1.58 × 10^12 GeV from the dark-matter abundance constraint.

PublicThis study uses three-dimensional computer simulations, rather than a detection of magnetic monopoles, to explore how these hypothetical objects could form during a sudden phase change in an expanding universe. The simulations follow their formation, mutual annihilation, and later evolution, linking the initial number of phase-transition bubbles to the number of monopoles left behind. They also predict patterns in magnetic fields and gravitational waves: the magnetic signal falls sharply on scales smaller than a monopole, while the gravitational-wave signal peaks at a scale set by the average distance between monopoles. Comparing the predicted magnetic-field strength with constraints from blazar observations, the authors conclude that this mechanism cannot explain primordial cosmic magnetic fields. They also calculate upper limits on monopole mass using two existing constraints.

Young explorerScientists made a computer model of an expanding universe to study tiny, imagined magnets called monopoles. They watched these magnets appear, some disappear together, and others remain. The model showed what magnetic fields and ripples in space they could make. But the magnetic fields did not fit limits from real observations, so the scientists say this idea cannot explain the universe’s early magnetic fields. This was a computer experiment, not the discovery of real monopoles.

Cosmology of self-interacting ultralight dark matter: simultaneous shifts in the Hubble constant and structure growth

Seokcheon Lee, Jae-Weon Lee

AstronomerThe authors implement background evolution and linear perturbations for mixed cold and self-interacting ultralight dark matter in CLASS. The scalar evolves from Hubble-frozen behavior through a quartic-dominated, radiation-like phase to a quadratic, matter-like phase. The intermediate phase increases pre-recombination expansion and reduces the sound horizon, while the late phase permits a dark-matter contribution. For m = 10^-22 eV and tilde m ≈ 1 eV, increasing the ultralight fraction raises H0 at fixed θ*, lowers late-time clustering, strengthens scale-dependent matter-power suppression, and yields a smooth CMB-temperature residual reaching about 9% at the largest fraction studied. These theoretical shifts have directions relevant to the Hubble and structure-growth tensions, but whether they improve a joint observational fit remains untested and requires a likelihood-level analysis.

PublicThis study calculates how a proposed form of very light, self-interacting dark matter could affect cosmic expansion and the growth of structure. In the model, a field first remains nearly frozen, then behaves like radiation, and finally behaves like matter. Its radiation-like stage speeds up early expansion and reduces the distance sound can travel before the early universe becomes transparent. For the parameters studied, adding more of this dark-matter component raises the calculated present-day expansion rate when the apparent angular size of that sound scale is held fixed, while reducing later clustering. It also changes the predicted cosmic microwave background temperature pattern, with a difference reaching about 9% in the largest-fraction case studied. These are model predictions, not observational findings. They move in directions relevant to existing disagreements about expansion and structure growth, but a joint comparison with observations is still needed to establish whether the model helps.

Young explorerScientists used a computer to explore an idea about dark matter, the invisible stuff in space. In their model, one kind of dark matter changes how it acts as the universe grows. Adding more of it can make the universe expand faster today and make matter gather into clumps less strongly. Those changes might help with some puzzles about the universe, but the scientists still need to check the idea against observations to see whether it really helps.

HETDEX [OII] galaxies at z ≤0.48: Growth of structures from power spectrum multipoles

Jeongin Moon, Eiichiro Komatsu, Robin Ciardullo+9 more

• Astrophysics of Galaxies

AstronomerThe authors constrain structure growth at z ≤ 0.48 using the monopole and quadrupole power spectra of [O II]-emitting galaxies in HETDEX Public Data Release 1, interpreted with a model based on the Mucho-Uchuu-1G N-body simulation. The best-fit model reproduces the observed spectra up to k_max = 0.7 h Mpc⁻¹, and goodness-of-fit tests find consistency with Planck flat ΛCDM. With Alcock–Paczyński parameters fixed to fiducial values, the inferred linear growth index is γ = 0.55 ± 0.05, consistent with the GR prediction of approximately 0.55. Allowing those parameters to vary yields γ = 0.60 ± 0.07, consistent with both GR and the suppressed growth reported by Nguyen (2023), rather than distinguishing between them. The results support this galaxy sample as an independent low-redshift growth probe and motivate future full cosmological inference.

PublicResearchers studied how galaxies emitting light from singly ionized oxygen cluster together in the HETDEX survey to test how cosmic structures grow. A model built from a computer simulation closely matches the observed clustering, which is consistent with the Planck version of the standard cosmological model. The inferred growth index agrees with general relativity: it is 0.55 ± 0.05 when parameters describing how distances are inferred are fixed, and 0.60 ± 0.07 when those parameters can vary. The latter result also allows a previously reported slower growth rate, so this study does not settle that distinction. It supports using these galaxies as an independent way to study cosmic growth.

Young explorerGalaxies make big groups in space. Scientists looked at how some galaxies are grouped and compared what they saw with a computer model. The model matched the galaxy patterns well. Their results fit what Einstein’s gravity theory says about how these groups grow, but they also leave room for a slower-growing picture reported before. The study does not yet tell us which of those pictures is right.

Alleviating CMB-BAO tension with a large cosmic birefringence angle during reionization induced by energy injection to axion-like particles

Salvatore Samuele Sirletti, Toshiya Namikawa, Blake D. Sherwin

AstronomerRecent DESI BAO measurements show mild tension with CMB observations within ΛCDM, while analyses of Planck polarization have been interpreted as hints of cosmic birefringence. The paper explores a proposed ALP mechanism linking these issues: energy transfer from matter to ALPs before reionization produces a much larger polarization rotation during reionization than during recombination. This rotation suppresses the EE reionization signal, permitting higher optical depth τ and potentially alleviating the CMB–BAO tension. Using Planck low-ℓ EE, BB, and EB data, the authors identify parameter regions with energy injection at approximately 10 ≤ z ≤ 100 where τ ≈ 0.08–0.10 is compatible with the data. This establishes compatibility within the explored scenario, not a detection of ALPs or confirmation of the proposed energy transfer.

PublicMeasurements of large-scale patterns in the distribution of matter from DESI disagree mildly with observations of the universe’s oldest light when interpreted using the standard cosmological model. Separately, analyses of Planck data have hinted that the polarization of this ancient light may have rotated during its journey. The researchers explore whether hypothetical axion-like particles could help explain both clues. In their scenario, matter transfers energy to these particles before the era when cosmic gas became ionized again. A stronger polarization rotation during that later era could weaken one polarization signal, allowing a higher inferred optical depth—a measure related to how often the ancient light scattered—and easing the disagreement. Their analysis finds that some versions of this scenario fit Planck polarization data with optical depths around 0.08–0.10. The study does not establish that the particles or energy transfer actually exist.

Young explorerScientists have two ways to learn about the universe that do not quite agree, and they have a hint that some very old light may have had its wiggle direction twisted. They tried an idea with tiny particles that have not been discovered. In the idea, these particles get energy from matter and twist the light more during a later part of the universe’s story. That could help the two ways agree better. Some versions of the idea fit the light measurements, but that does not mean the particles are really there.

Cosmological Gravitational Wave Collider Physics

Sukannya Bhattacharya, Matteo Fasiello, Anish Ghoshal+1 more

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

AstronomerThis theoretical study computes primordial tensor signatures in an effective field theory where the massless graviton mixes with the helicity-two mode of a massive spin-two field with cubic self-interactions. For constant sound speed, the authors obtain new analytical expressions for the leading tensor power-spectrum correction and tree-level bispectrum. For m_sigma > 3H/2, the squeezed bispectrum contains a nonanalytic contribution proportional to (k_L/k_S)^(3/2 ± i mu), with mu = sqrt(m_sigma^2/H^2 − 9/4), producing logarithmic oscillations whose frequency depends on the mass. Polarisation contractions set relative amplitudes among graviton helicity configurations. The authors also derive an associated quadrupolar modulation of short-scale tensor power, relate its amplitude to model parameters, and explore modifications from slowly varying sound speed. These are model-based predictions connecting two-point, three-point, and quadrupolar tensor signatures, not observational detections.

PublicCould primordial gravitational waves reveal massive particles that existed during inflation? This theoretical study examines a model in which gravitational waves interact with an additional massive field of spin two. The calculations predict linked changes in the waves’ strength and in correlations among three wave modes. When the extra field is sufficiently massive, correlations involving one long-wavelength mode and two short-wavelength modes contain oscillations whose frequency depends on the field’s mass. The model also predicts a direction-dependent pattern in the strength of short-wavelength waves. The researchers connect these effects to the model’s parameters and explore how a slowly changing propagation speed alters the oscillatory signal. The study offers possible signatures of such a field, rather than evidence that it has been observed.

Young explorerScientists used math to imagine how tiny ripples in space might have behaved when the universe was very young. They asked what would happen if those ripples interacted with another kind of particle. In their model, that particle could leave a special pattern in how big and small ripples go together. The pattern would depend on how heavy the particle was. This is a prediction from their math, not something they have seen.

Testing Dynamical Dark-Energy Model with Standard Sirens

Yuanmin Mao, Wen Zhao

AstronomerThis forecasting study tests whether future Einstein Telescope bright standard sirens could constrain dynamical dark energy, assuming the DESI DR2-inspired best-fitting 29-bin equation of state as the fiducial cosmology. Mock catalogs contain 100, 500, 1000, or 3000 binary-neutron-star events with known host redshifts. Reconstructions constrain effectively about 4–5 modes with GW data alone and 5–6 when combined with DESI DR2 BAO, BBN, and a compressed CMB constraint; information remains concentrated in a few correlated modes. The 3000-event GW-only reconstruction departs from ΛCDM at more than 5σ, while combined analyses attain similar significance with roughly 1000 events. Separately, comparisons of flat ΛCDM with its Chevallier–Polarski–Linder extension yield significances of 3.3σ and 6.3σ for 1000 and 3000 GW events, increasing to 7.7σ and 11.0σ with external data. These are conditional forecasts under the adopted dynamical-dark-energy cosmology, not detections from ET observations.

PublicCould future gravitational-wave measurements reveal whether dark energy changes over cosmic history? This study explores that possibility using simulated Einstein Telescope observations of merging neutron-star pairs whose host-galaxy redshifts are known. The simulations assume a particular changing-dark-energy model inspired by DESI DR2, rather than the constant-dark-energy model ΛCDM. In that simulated universe, 3000 events could reveal a departure from ΛCDM at a statistical significance above 5σ; combining the simulated signals with other cosmological data could reach similar significance with roughly 1000 events. However, the measurements constrain only a few combinations of the model’s many components. The results show potential sensitivity under the assumed model, not observational evidence that dark energy actually changes.

Young explorerScientists want to learn whether something called dark energy stays the same as the universe grows. They made pretend signals from pairs of stars called neutron stars coming together, to see what a future telescope could learn. In their pretend universe, dark energy changes, and a few thousand signals could help show that. This is a test of what future measurements might tell us—not a discovery that dark energy really changes.

Constraining Dynamical Dark Energy with Tomographic Galaxy and CMB Weak Lensing Through Higher-Order Statistics

Shu-Fan Chen, J. Colin Hill, Zoltán Haiman

AstronomerThis simulation-based study forecasts the information in non-Gaussian summaries of tomographic galaxy and CMB lensing convergence beyond the power spectrum. Using DDELenS ray-traced N-body simulations, the authors construct Gaussian-process emulators for the power spectrum and five non-Gaussian statistics, varying Ωm, σ8, w0, and wa. For Rubin-like galaxy lensing and Simons Observatory-like CMB lensing over 15,000 square degrees, combining all five non-Gaussian summaries across the modeled source planes forecasts uncertainty reductions of 24.3% in w0, 28.0% in wa, 41.9% in Ωm, and 45.8% in σ8 relative to the power-spectrum-only baseline. The forecast w0 and wa uncertainties are 34.7% and 48.7% smaller than current DESI+DES constraints. If the DESI+DES best-fit values persist, a Gaussian posterior and unchanged w0–wa correlation would imply a 5.2σ departure from ΛCDM, versus 3.8σ using the power spectrum alone and the current 3.0σ; this is conditional, not a detection. Minkowski functionals and moments offer comparable constraining power, with all summaries together performing best. Broad galaxy-source redshift coverage is particularly important for dynamical dark energy, and CMB lensing adds complementary information. Validation includes a withheld fiducial cosmology, analytical power-spectrum forecasts, and Gaussian random-field null tests. Important simplifications are the omission of baryonic effects and intrinsic alignments and the use of discrete galaxy-source redshift planes.

PublicThe researchers use computer simulations to forecast how much future measurements of gravitational lensing—the distortion of light by gravity—could tell us about dark energy that changes over time. They model galaxy-light and cosmic microwave background lensing surveys and compare several ways of measuring patterns in the resulting maps. Combining five additional pattern statistics is forecast to reduce uncertainty in two dark-energy parameters by about 24% and 28% compared with using the lensing power spectrum alone. Galaxy sources spanning a broad range of distances are especially helpful, while the microwave background supplies complementary information. These are forecasts, not new observations or a discovery of changing dark energy. If current DESI+DES best-fit values remain the same, the forecast precision could raise the statistical significance of a departure from the standard cosmological model from 3.0σ to 5.2σ, but only under specified assumptions about the uncertainty distribution and parameter correlation. The modeling also leaves out effects of ordinary matter and intrinsic galaxy alignments and simplifies the distribution of source distances.

Young explorerGravity bends light as it travels through space. Scientists made pretend universes on computers to see whether studying more shapes and patterns in that bent light could help them understand dark energy and whether it changes over time. In their computer tests, using several kinds of patterns together gave more precise clues than using just one kind. Looking at light from many distances helped, too. This is a prediction about what future studies might learn, not a discovery that dark energy changes. The pretend universes also leave out some things that could affect real measurements.

Optimal galaxy magnification: generalized fundamental-plane residuals and number counts are all you need

Kun Xu, Ravi K. Sheth

• Astrophysics of Galaxies

AstronomerThis theoretical analysis derives optimal weak-lensing magnification statistics from galaxy properties, decomposing the measurement into an optimal mean statistic and total number counts. The mean statistic is constructed from the residual distribution of a generalized fundamental plane that predicts galaxy size, or equivalently flux, using surface brightness and other lensing-invariant properties. Its functional form is flexible: reducing intrinsic scatter improves magnification precision. For Gaussian residuals, the optimal mean statistic becomes the inverse-variance-weighted residual, or the residual itself when scatter is constant. Under Poisson statistics, combining this statistic with total counts retains all magnification Fisher information and matches full-likelihood precision, without requiring a model of the potentially high-dimensional galaxy-property distribution. These are analytical results, not a reported survey measurement.

PublicWeak gravitational lensing changes galaxies’ apparent brightness, size, and number counts, offering information complementary to measurements of their distorted shapes. This paper derives a way to compress that magnification information into two ingredients: galaxy counts and a statistic based on how much galaxy sizes or brightnesses differ from predictions using properties unchanged by lensing. Better predictions, with less natural scatter among galaxies, can improve precision. The authors show that, under a Poisson statistical assumption, this combination preserves all the magnification information quantified by their analysis and can be as precise as using the full likelihood. The work presents a mathematical method rather than a new observational measurement.

Young explorerGravity can act a little like a magnifying glass, making faraway galaxies look bigger or brighter. The researchers worked out a way to study this by counting galaxies and checking how different their sizes or brightnesses are from what is expected. Their math shows that, when its counting rule applies, these two clues together can work as well as a much more complicated calculation. They worked out the method; they did not report a new measurement of the sky.

The variance of the CMB temperature gradient: a dependence on the spatial orientation and anisotropy of a multiply connected Universe

Ralf Aurich, Martin J France, Frank Steiner

• General Relativity and Quantum Cosmology

AstronomerThe authors develop a method described as model-independent that combines rho-statistics with sweeping a mask through 768 orientations to characterize CMB temperature anisotropy and geometry. In ensembles of maps with 3-torus topology, they find faint, persistent geometric and periodic patterns whose layouts match those expected for circles-in-the-sky. They also recover a linear relation between cubic-torus size L and rho, the standard deviation of the normalized variance of the CMB temperature gradient, reporting little sensitivity to the weak statistical-isotropy violation. Under a toroidal interpretation, they infer a universe size of approximately three Hubble lengths; this is a topology-dependent inference, not an independently established measurement of cosmic size. They argue that rho can probe spatial finiteness and size while mask-sweeping reveals anisotropy patterns.

PublicThe researchers introduce a way to search the cosmic microwave background, the sky's background temperature map, for very faint geometric patterns. Their method moves a mask through 768 orientations and tracks a statistic describing variations in temperature gradients. Tests on collections of maps representing a universe with a wraparound, torus-like shape reveal repeating patterns arranged like the circles expected in that geometry. The authors also connect their statistic to the size of such a universe and infer approximately three Hubble lengths under that interpretation. The size and shape inference depends on the toroidal picture; the pattern tests do not independently establish that our Universe has this shape.

Young explorerScientists studied pretend maps of the Universe's leftover warmth. They looked for tiny repeating patterns in a universe where going far enough could bring you back around. Their new pattern-finding trick worked on those maps. They also used that idea to suggest how big our Universe might be, if it really wraps around that way.

Impact of cosmic evolution on the gravitational wave spectrum from cosmic strings

Xi-He Hu, Danny Marfatia, Ye-Ling Zhou

• High Energy Physics - Phenomenology

AstronomerThis theoretical study investigates how nonstandard epochs during the radiation era modify cosmic string network evolution, loop production, and the resulting stochastic gravitational-wave spectrum. The authors find that kination enhances the predicted signal, while extra relativistic degrees of freedom, early matter domination, and intermediate vacuum domination suppress it to varying degrees. They also find that late-time dynamical dark energy has a negligible effect on the spectrum. These are predictions for cosmic string signals, not reported detections.

PublicCosmic strings could leave a background of gravitational waves, and this study explores how different possible stages in the Universe’s history would change that signal. The calculations predict a stronger signal after a stage called kination, but weaker signals with extra fast-moving particles or early periods dominated by matter or vacuum energy. Changes in dark energy at late times are found to have almost no effect. The study concerns theoretical signals, not an observed discovery of cosmic strings.

Young explorerScientists studied how tiny ripples in space might come from things called cosmic strings, if those strings exist. They worked out how different chapters in the young Universe’s story could make the ripples stronger or weaker. One possible chapter made them stronger, while the others made them weaker. This was a study of what might happen, not a report of finding the ripples.

Testing the statistical compatibility of data sets with a common prior

Pilar Coloma, Michele Maltoni, Thomas Schwetz

• High Energy Physics - Phenomenology
• High Energy Physics - Experiment
• Data Analysis, Statistics and Probability
• Methodology

AstronomerThis methodological work extends the Parameter Goodness-of-fit (PG) test for assessing data-set compatibility within a specified theoretical model when shared auxiliary data, termed a prior, constrain some model parameters. Applying the same prior to all data sets breaks the statistical independence assumed by the original test. The authors show that, under a Gaussian approximation, the prior-constrained PG statistic follows a generalised chi-squared distribution, enabling calculation of p-values. In the strong-prior approximation, it approaches the standard PG test applied to the unconstrained model parameters.

PublicThe paper proposes a way to check whether different sets of data are compatible with the same theoretical model when they all use shared supporting information. That shared information makes the data sets statistically dependent, violating an assumption of the original Parameter Goodness-of-fit test. Under a Gaussian approximation, the authors derive the statistical distribution needed to calculate p-values for the extended test. When the supporting information constrains some model parameters very strongly, the method approaches the original test applied to the parameters left unconstrained.

Young explorerImagine checking whether several groups of clues fit the same explanation. If every group uses the same extra clue, the check needs to account for that shared clue. The researchers propose a math rule to do this and show how it works when a simplifying assumption is a good fit. If the extra clue pins down some parts of the explanation very tightly, the rule becomes like the old check for the parts still free to change.

Gravitational Waves from New Inflation

Naoya Kitajima, Kamil Mudrunka, Kazunori Nakayama

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

AstronomerThe paper presents what the authors describe as the first comprehensive prediction of the complete gravitational-wave spectrum for new inflation, a prototypical small-field inflation scenario, incorporating all known classical and quantum production mechanisms. The motivation is that the high-frequency spectrum can probe inflaton properties and post-inflationary dynamics, helping discriminate among inflationary models. This is a theoretical prediction, not a reported detection; the abstract gives no quantitative spectral results.

PublicGravitational waves could help scientists distinguish between models of inflation, an early period of cosmic expansion. Their high-frequency patterns can carry clues about the field driving inflation and what happened afterward. This paper predicts the full gravitational-wave pattern for a model called new inflation, including all known classical and quantum ways of producing these waves. The authors describe the prediction as the first comprehensive one for this model; the abstract reports no detection.

Young explorerScientists have ideas about how the universe grew very early on. Those ideas can make different patterns of ripples in space. This paper predicts the ripple pattern for one idea called new inflation, including all the ways scientists know those ripples could be made. It is a prediction, not a report of finding the ripples.

On Particle Production from Bubble Collisions in the Non-runaway Regime

Fayez Abu-Ajamieh, Amine Ahriche, Sagar Modak+1 more

• High Energy Physics - Phenomenology

AstronomerThis theoretical and numerical study extends particle-production calculations for bubble collisions during first-order phase transitions beyond the runaway-wall limit to arbitrary wall velocities v_w < 1. The authors generalize the analytical trapping-equation treatment to finite-thickness boosted kink profiles for elastic and inelastic collisions, then solve the full Klein-Gordon equation without imposing SO(1,1) symmetry or thin walls. Across the parameter grid studied, the generalized analytical treatment underestimates the numerical efficiency factor by orders of magnitude away from the runaway limit. New semi-analytic fits combining a power-law continuum and a resonance peak reproduce the main numerical spectral features. In a toy dark-sector model, production falls strongly as wall velocity decreases and is enhanced for lighter produced particles; the oscillatory peak's relative contribution also differs from earlier runaway-regime estimates. The authors discuss limitations of both the trapping equation and the off-shell effective-action truncation underlying the formalism. These are modeling results, not observational detections.

PublicColliding bubbles during a first-order phase transition could produce particles, a mechanism studied in connection with the origin of matter and dark matter. Earlier calculations assumed bubble walls moving almost at the speed of light. This study develops calculations for slower walls and compares analytical approximations with numerical simulations. Away from the near-light-speed limit, the analytical approximation predicts particle-production efficiencies orders of magnitude below the numerical results. The authors provide improved formulas that capture the simulations' main features. In a simplified dark-sector model, slower walls produce far fewer particles, while lighter particles are produced more readily. These theoretical findings do not establish that this mechanism made dark matter, and the calculation framework still has limitations.

Young explorerScientists used math and computer simulations to study bubbles that might make tiny particles when they bump together. In a simple model, slower bubble edges made fewer particles, and lighter particles were easier to make. An older math shortcut missed much of the effect, so they made better formulas. This was a computer study, not something they watched happen in space.

Ridged Lagrangian Perturbation Theory (RLPT)

Francisco-Shu Kitaura, Francesco Sinigaglia

AstronomerThe authors introduce Ridged Lagrangian Perturbation Theory (RLPT), an inexpensive two-step forward model intended to improve nonlinear morphology at fixed force resolution while preserving the large-scale solution. Standard LPT/ALPT transport is followed by one Eulerian ridging update, reconstructing a short-range, curl-free displacement from the realised density through smooth scale separation and a Poisson inversion. In tests against particle-mesh and N-body references, the additional step systematically improves nonlinear power and field-level agreement over 2LPT/ALPT baselines. A small parameter set controls the short-range response. The authors also demonstrate ridging as a deterministic subgrid relocation model for tuning tracer clustering beyond nominal mesh resolution, even when the underlying dark-matter field is only approximately adequate. This offers a tool for mock-galaxy production and close-pair-sensitive observational systematics; the reported findings concern computational models, not new astronomical observations.

PublicFast computer models used for galaxy surveys can make the cosmic web’s filaments and dense knots too diffuse and underestimate clustering on small scales. The authors introduce a method called RLPT that adds one inexpensive adjustment to an existing model, sharpening small-scale structure while preserving its large-scale pattern. In comparisons with reference simulations, this extra step improves both the predicted clustering and agreement in the spatial density pattern. The authors also show how the adjustment can tune the clustering of objects representing galaxies below the model’s nominal resolution. That could help produce simulated galaxy catalogues and study observational effects involving close pairs, but this tuning is not a demonstration that all unresolved structure has been accurately recovered.

Young explorerScientists use computers to make pretend maps of where galaxies might be. Fast maps can look too blurry. This team added an extra step that makes little clumps and strands clearer without changing the big pattern. Their maps matched other computer simulations better. These are computer tests, not new pictures of real galaxies.

Calibrating optical galaxy cluster projection effects with sparse spectroscopic samples: A clustering redshift approach

Lei Yang, Hao-Yi Wu, Tesla Jeltema+3 more

AstronomerThe authors develop a clustering-redshift method to calibrate line-of-sight projection contamination in optically selected galaxy clusters by cross-correlating candidate members with sparse spectroscopic samples not targeted at clusters. In the Cardinal simulation, the method recovers the correct spectroscopic redshift distribution and projection-effect parameters for members selected by the red-sequence Matched-filter Probabilistic Percolation algorithm. The authors report that the approach is insensitive to spectroscopic-sample selection. This is a simulation validation, not a demonstrated calibration of observed clusters; application to upcoming Legacy Survey of Space and Time cluster samples using DESI and Roman spectroscopy is prospective.

PublicGalaxies that appear close together in sky images can actually lie at very different distances, making some galaxy clusters look as though they contain unrelated galaxies. Checking every apparent member with detailed light measurements cannot keep up with growing cluster catalogs. The researchers developed a statistical method that compares apparent cluster members with galaxies measured by other spectroscopic surveys, even when those measurements are sparse around clusters. In a simulated universe, the method correctly recovered the members’ distance-related distribution and the parameters describing this contamination. The authors propose using it with DESI and Roman measurements to help calibrate future Legacy Survey of Space and Time cluster catalogs; that application has not yet been demonstrated here.

Young explorerSome galaxies look like they belong to the same group, even when they are far apart. Scientists made a new way to help spot these mix-ups using clues from other galaxies. It worked in a computer-made pretend universe. They hope to use it to check future pictures of the real sky, too.

Signals from the early Universe: a comprehensive search for primordial features in Planck CMB datasets

Antonio Raffaelli, Mario Ballardini, Nicola Barbieri

AstronomerThe study searches for primordial oscillatory features in CMB anisotropies using phenomenological templates, comparing Planck PR3 legacy and PR4 NPIPE products and likelihood choices. Unbinned likelihoods enhance sensitivity to rapidly varying signals. Several previously reported hints persist, but some earlier anomalies weaken substantially with updated CamSpec likelihoods using PR4 products. Across the templates, a few frequencies at ω ∼ 10–100 improve the fit relative to a featureless reference by Δχ² ≃ −10 to −15. These improvements do not translate into Bayesian support: the three or four extra parameters incur an Occam penalty. After accounting for the look-elsewhere effect, global significance is at most 2.6σ, with no globally significant detection. Forecasts suggest that combined SO and LiteBIRD measurements could improve feature-amplitude upper bounds or uncertainties by more than an order of magnitude, with next-generation polarisation data crucial for distinguishing primordial signals from fluctuations and modelling systematics.

PublicResearchers searched Planck measurements of the cosmic microwave background for oscillating patterns that might trace the early universe. They compared different versions of the data and analysis methods. Some previously reported hints remained, while others became much weaker with updated analyses. Adding oscillations improved how closely some models matched the data, but those models also required extra adjustable parameters. A Bayesian comparison did not favour them over a model without the features. After allowing for the many possible oscillation frequencies searched, the strongest hint reached at most 2.6 sigma—not a statistically significant detection overall. Forecasts suggest that future polarisation measurements combining SO and LiteBIRD could tighten limits or uncertainties on the strength of these patterns by more than tenfold, helping distinguish genuine early-universe signals from chance fluctuations and modelling problems.

Young explorerScientists looked at the universe’s oldest light to see whether it has tiny repeating wiggles. Some possible wiggles still showed up when they checked the data in different ways, but others became much less convincing. Because they tried lots of possible wiggles, a few could look promising just by chance. They have not found clear proof that the wiggles are real. They predict that future measurements could check much more carefully.

Ultralight dark matter mixed with primordial black holes

Xing-Yu Yang

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

AstronomerThis theoretical study separates primordial black holes’ effects on mixed ultralight-dark-matter halos into a continuum contribution to the averaged Schrödinger-Poisson background and a discrete shot-noise perturbation driving eigenmode transitions and soliton heating. Continuum effects scale with PBH fraction, while perturbative transition rates scale with PBH fraction times individual PBH mass. For a fiducial halo with ULDM particle mass 10^-22 eV, virial mass approximately 10^10 solar masses, and 1% PBHs, the continuum component changes the background density, potential, and low-lying eigenvalues by less than 1%, yet changes radial mode participation in the coherent soliton region by about 20%. For solar-mass PBHs, the fastest low-lying multiplet transition takes approximately 10^9 Gyr. Thus, in the studied regime, the continuum response dominates and PBH discreteness is dynamically negligible on galactic timescales; these are model results, not observational findings.

PublicThe researchers calculated how a dark matter halo might behave if it mixed ultralight dark matter with primordial black holes. They separated the black holes’ averaged gravitational influence from the fluctuations caused by their being individual objects. In an example model where black holes make up 1% of the halo, their averaged influence changes several overall halo properties by less than 1%, but changes how radial wave patterns contribute within the coherent dark matter region by about 20%. By contrast, fluctuations from individual stellar-mass black holes drive changes far too slowly to matter on galactic timescales in this model. The study therefore predicts that the averaged influence matters more than individual black-hole fluctuations in the regime examined; it does not report an observed mixture of these dark matter candidates.

Young explorerScientists used math to imagine dark matter that acts like waves mixed with black holes. In their example, the black holes’ pull together changed the wave patterns more than the tiny bumps from separate black holes did. Those bumps worked much too slowly to matter. This was a calculation, not something they saw in space.

Impact of numerical stability in Bayesian noise wave calibration on global 21-cm experiments

Saswata Dasgupta, Adarsh Kumar Dash, Dominic Anstey+3 more

• Instrumentation and Methods for Astrophysics

AstronomerThe authors identify a numerical instability in REACH’s Bayesian noise-wave calibration, which jointly fits five frequency-dependent low-noise amplifier parameters. The posterior covariance condition number reaches approximately 10^9–10^11, producing solutions that vary across computing environments. Singular value decomposition traces the instability to near-collinearity between the excess-noise-source and load-temperature design-matrix columns. Their Chebyshev-basis mitigation first fixes the noise-source temperature to a scalar, reducing the condition number to about 60, then restores its frequency dependence by recovering it directly from the hot-load calibration measurement. Tests on mock data retain the reduced model’s stability with comparable calibration accuracy. Masking narrow channels near cable standing-wave degeneracies removes additional local design-matrix artefacts. The authors argue that the underlying degeneracy is inherent to the noise-wave formalism, making the approach relevant to other global 21-cm experiments; the abstract does not report a cosmological signal detection.

PublicREACH aims to detect a faint radio signal from the early universe, but doing so requires extremely precise calibration beneath much stronger foreground emission. This study identifies a numerical problem in its calibration calculations: two contributions to the receiver model are so similar mathematically that the answers can change between computing environments. The researchers develop a two-step fix, first simplifying one temperature parameter and then recovering its variation with frequency from a calibration measurement. On simulated data, the method makes the calculations stable while maintaining comparable calibration accuracy. Excluding narrow frequency channels affected by cable standing waves removes further numerical artefacts. The approach could help other experiments using the same receiver-modeling framework, but this study is a calibration advance, not a detection of the early-universe signal.

Young explorerScientists want to hear a very quiet radio whisper from when the universe was young. First, they need to check their listening machine very carefully. They found that two parts of the computer’s math looked so alike that the computer could get mixed up and give different answers. They made a way to separate those parts. When they tried it with pretend data, the answers stayed steady and were about as accurate as before. This helps them get ready to listen; it does not mean they have heard the whisper yet.

Searching for signatures of self-interacting dark matter in halos from full physics simulations: From 3D structure to projected observables

Giovanni Y. Ferron, Antonio Ragagnin, Lorenzo Pizzuti+1 more

• High Energy Physics - Phenomenology

AstronomerThis simulation study examines self-interacting dark matter (SIDM) signatures in galaxy groups and clusters. Baryonic effects and line-of-sight projection substantially suppress SIDM core formation in mass and density profiles, leaving deviations of ≲5% from collisionless dark matter. In the most massive simulated halos, however, SIDM instead tends to enhance central density. Comparisons with observed dark matter profiles of MACS J1206 and Abell S1063 suggest potentially detectable core signatures given the small uncertainties of current kinematic mass measurements; they do not establish an SIDM detection. Under idealized control of systematics, weak-lensing shear profiles show deviations up to approximately 20% for halos with M200 ≳ 10^13 solar masses, whereas the projected concentration–mass relation changes only slightly. The authors discuss simulation-resolution effects and other limitations, presenting these results as a baseline for future lensing and kinematic constraints rather than an observational confirmation.

PublicSimulations suggest ways to test whether dark matter particles interact with one another rather than behaving as collisionless matter. In simulated groups and clusters of galaxies, ordinary matter and the overlapping material seen along our line of sight largely hide the expected spreading-out of central dark matter, leaving differences of about 5% or less in mass and density profiles. The most massive simulated systems behave differently: their centers tend to become denser. Comparisons with measurements of two real clusters suggest that such central changes might be detectable, but do not demonstrate dark matter interactions. Weak gravitational lensing—the distortion of background galaxy images by intervening mass—also looks promising: predicted distortions differ by up to about 20% if systematic measurement effects can be controlled. These findings depend on simulations with resolution limits and other caveats, and offer possible tests for future observations.

Young explorerDark matter is invisible stuff in space. Scientists used computer models to ask what might happen if bits of dark matter could bump into each other. In many model groups of galaxies, the difference was mostly hidden by ordinary matter and by things overlapping when we look at them. But the biggest model groups tended to pack more dark matter into their middles. Scientists think that watching how these groups bend light, or how things move inside them, might help test the idea. They have not shown that real dark matter bumps into itself, and the computer models are not perfect.

Sensitivity of calibration-free DESI DR2 BAO--supernova constraints to a distance-duality tilt

Mikel Artola, Stéphane Fay, Leandros Perivolaropoulos

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

AstronomerThe authors test whether the moderate DESI BAO preference for dynamical dark energy could instead reflect a mismatch between BAO and SN distance relations. They parameterize departures from cosmic distance duality as η(z) = D_L/[(1+z)^2 D_A] = α(1+z)^ε. With DESI DR2 and uncalibrated Pantheon+, DES-Dovekie, Union3, and Union3.1 SN data, freeing ε reduces the preference for CPL over ΛCDM more than allowing spatial curvature, except that Union3.1 gives comparable reductions. The reduction persists with alternative η(z) parameterizations. Pantheon+ η(z) constraints are stable against BAO-tracer removal and low-redshift cuts, whereas the DES-Dovekie preference largely disappears after excluding SNe at z < 0.1. A separate calibrated analysis using illustrative Planck sound-horizon and SH0ES absolute-magnitude priors yields α ≃ 0.942 ± 0.014, a normalization mismatch conditional on those assumptions. These fits do not establish a physical violation of distance duality. Ordinary positive opacity cannot explain the negative central ε values in a ΛCDM background, and local gravity tests strongly constrain the illustrative unscreened varying-G interpretation.

PublicRecent DESI measurements moderately favor dark energy that changes over time rather than the constant dark energy of the standard cosmological model. This study asks whether that preference could instead arise from a mismatch between distances inferred from galaxy patterns and from exploding stars. When the researchers allow the usual relationship between two kinds of cosmic distance to vary, the preference for changing dark energy weakens—generally more than it does when they allow space to be curved. The reduction survives alternative mathematical descriptions, but some findings depend on the supernova sample: removing nearby supernovae largely erases the DES-Dovekie preference. A separate analysis finds a distance-normalization mismatch under specific calibration assumptions. None of this proves that the usual distance relationship fails. The authors also find that ordinary light loss cannot explain one feature of their fits, while local gravity tests strongly restrict an illustrative explanation involving changing gravitational strength.

Young explorerScientists use different clues to work out how far away things in space are. Those clues do not quite agree, and that might make it look as though the mysterious dark energy is changing. When researchers let the usual rule connecting the distance clues change, there was less reason to think dark energy changes. But they have not proved which explanation is right, and the clues they choose matter.

Anatomy of RHN DM relic in the vanilla scotogenic neutrino mass model

Sujit Kumar Sahoo, Narendra Sahu, Vicky Singh Thounaojam

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

AstronomerThis theoretical study revisits the minimal scotogenic model, in which light neutrino masses arise radiatively and an imposed Z2 symmetry makes the lightest loop particle a dark matter candidate. The authors examine the relic abundance of right-handed neutrino dark matter, including self-annihilation, co-annihilation, conversion-driven processes, and freeze-in production. Applying constraints from direct detection, collider searches, the muon anomalous magnetic moment, charged-lepton flavor violation, and neutrino oscillation data, they find viable lightest-right-handed-neutrino dark matter masses of approximately Mh/2–2000 GeV for thermal production and 0.1–1000 GeV for non-thermal production, where Mh is the Standard Model Higgs mass. These are model-dependent viability ranges, not detections. The study also identifies displaced-vertex signatures from long-lived particles that could be probed at future colliders.

PublicThe researchers investigate a theoretical model that could connect the small masses of neutrinos with dark matter. In this model, a new type of neutrino, called a right-handed neutrino, could be the dark matter particle. They calculate how different processes in the early universe could leave behind such particles and check the model against existing experimental constraints. Their analysis finds allowed mass ranges that depend on how the particles were produced; it does not establish that these particles exist or make up dark matter. The model also offers a possible future test: long-lived particles could travel some distance before decaying, leaving a distinctive signal at future particle colliders.

Young explorerScientists are trying out a math idea that might help explain both tiny particles called neutrinos and invisible matter in space. Their idea includes a new kind of particle that might be the invisible matter. They checked which versions of the idea still fit what experiments tell us. They have not found this new particle. Future experiments might look for clues from other particles in the idea that travel a little way before changing into different particles.

Impact of non-standard neutrino-electron interactions on Big Bang Nucleosynthesis

Julien Froustey, Stefano Gariazzo, Jaume Moncho+2 more

• High Energy Physics - Phenomenology

AstronomerThis theoretical and cosmological analysis updates neutrino decoupling calculations with non-standard neutrino–electron interactions (NSI), extending the parameter space and evaluating effects on primordial light-element abundances. Accurate helium-4 predictions require tracking NSI-induced changes in the neutrino distributions; a change in N_eff alone is insufficient. Big Bang nucleosynthesis thus supplies observables complementary to N_eff. Constraints derived using different dataset combinations on non-universal and flavour-changing NSI parameters are significantly weaker than terrestrial bounds, but offer an independent probe of early-universe neutrino interactions.

PublicSome theories predict that neutrinos could interact with electrons in ways beyond those normally considered. The researchers calculated how these hypothetical interactions would affect neutrinos as they stopped exchanging energy efficiently with the hot early universe, and how this would change the production of light elements. They found that predicting helium-4 accurately requires following changes in the neutrinos’ energy distributions, rather than changing only a quantity called N_eff that describes their contribution to cosmic radiation. Comparing cosmological predictions with different combinations of data places limits on these possible interactions. Those limits are much weaker than limits from experiments on Earth, but provide an independent test; they do not establish that the interactions occur.

Young explorerWhen the universe was very young and hot, tiny particles called neutrinos helped shape how much helium was made. Scientists used calculations to ask what would happen if neutrinos interacted with electrons in extra ways that some theories suggest. To work out the helium correctly, they had to keep track of how the neutrinos’ energies changed. Clues from the universe can help check these ideas, though experiments on Earth give tighter limits. This study does not show that the extra interactions really happen.

Primordial black hole formation in bulk-viscous cosmology

Zi-Yan Yuwen, Cristian Joana, Shao-Jiang Wang+1 more

• General Relativity and Quantum Cosmology

AstronomerNumerical simulations investigate primordial black hole formation in a cosmological background with bulk viscosity. The collapse threshold μ_c retains a dependence on the equation-of-state parameter w similar to the inviscid case, but increases by an amount comparable to the bulk-viscosity strength ε; at fixed w, this increase is approximately linear in ε. Fits to the standard critical-scaling law for near-threshold collapse also indicate an enhancement of the resulting PBH mass. These simulation results suggest that bulk viscosity can systematically modify both the formation threshold and the PBH mass scaling law.

PublicComputer simulations explore how bulk viscosity, a resistance to compression or expansion in cosmic matter, could affect black hole formation in the early Universe. In the simulations, stronger bulk viscosity raises the threshold needed for collapse, making black holes harder to form. It also increases the resulting black hole mass in the studied cases close to that threshold. These are theoretical simulation findings, not observations of early-Universe black holes.

Young explorerScientists used computers to explore how black holes might have formed when the Universe was very young. They tested what happens when the stuff filling space resists being squeezed. In their computer experiments, it took a bigger squeeze to make a black hole. For squeezes just strong enough to work, the black holes also ended up heavier. This is what their computer models showed, not something they saw in the sky.

Measuring Ultralight-Axion Coherence with Galaxy Polarization Correlations

Yasuo Doi

• High Energy Physics - Phenomenology

AstronomerThe authors propose measuring the three-dimensional two-point correlation of galaxy polarization-rotation angles to constrain an ultralight axion-like particle (ALP) birefringence field. For nonrelativistic ALPs with an isotropic Gaussian velocity distribution, the equal-time correlation has a physical e-folding scale L_G = sqrt(6)/(m_a v_a), where v_a is the three-dimensional rms velocity dispersion. A detected correlation turnover would constrain the momentum scale m_a v_a, while the amplitude would constrain g_aγ sqrt(Ω_a/Ω_DM), rather than the coupling alone. For an assumed survey of one million polarized galaxies covering a quarter of the sky to z = 2, with 10° effective per-galaxy scatter, the forecast gives 5σ sensitivity to sub-degree correlated rotations over m_a(10^-3 c/v_a) ≈ 10^-29–10^-27 eV. For detected signals across much of this range, the forecast uncertainty in log10(m_a v_a) is at most about 0.1. This is a proposed late-time geometric probe complementary to CMB birefringence and structure-formation constraints, not a reported detection.

PublicHypothetical ultralight particles called axion-like particles could rotate the polarization—the orientation of light’s oscillations—from distant galaxies. The authors propose comparing these rotations between pairs of galaxies at different three-dimensional separations. How the similarity changes with separation could reveal a combination of the particles’ mass and typical speed, while the strength of the pattern could constrain their interaction with light together with their share of dark matter. Under specific assumptions about particle velocities, a forecast for a survey of one million galaxies suggests that correlated rotations smaller than one degree could be detectable. No detection is reported; this is a proposed way to test these particles alongside existing cosmological approaches.

Young explorerLight has an orientation, a little like an arrow pointing sideways. Scientists think tiny particles that we have not found might turn that arrow as light travels from faraway galaxies. They suggest checking whether light from nearby galaxies gets turned in similar ways. The pattern could give clues about the particles. This is an idea for a test, not a discovery.

Seesaw Cosmology

Nicolás Bernal, Chee Sheng Fong, Óscar Zapata

• High Energy Physics - Phenomenology

AstronomerThis theoretical study models perturbative reheating through right-handed neutrinos (RHNs) that generate light-neutrino masses via the type-I seesaw. If produced relativistically and sufficiently long lived, RHNs yield successive inflaton-, relativistic-RHN-, nonrelativistic-RHN-, and Standard Model radiation-dominated eras. The Boltzmann treatment retains the production-time dependence of the nonthermal RHN distribution and its relativistic-to-nonrelativistic transition. The calculated Standard Model temperature rapidly approaches a plateau during inflaton domination, then scales as a^(-1/4) and a^(-3/8) during the two RHN-dominated eras. Relative to conventional reheating, direct dark-matter production through inflaton decay can be enhanced by a factor of order m_phi/(2m_N). Ultraviolet freeze-in has critical temperature powers p = 12 and 20, allowing potentially large contributions before final radiation domination. These model results connect neutrino-mass generation to the pre-BBN thermal history, with implications for dark-matter production and possible connections to baryogenesis; they are not observational findings.

PublicThe researchers calculate a possible history of the early universe in which the inflaton transfers its energy to ordinary particles through hypothetical right-handed neutrinos. These neutrinos also provide a proposed explanation for why familiar neutrinos have mass. If the right-handed neutrinos begin moving relativistically and survive long enough, they can temporarily dominate the universe's energy budget, first while relativistic and then after slowing down. In the calculations, this changes how the ordinary-particle temperature evolves and can substantially increase some routes to producing dark matter before the final radiation-dominated era. The work links a possible origin of neutrino mass with early-universe heating and dark-matter production, but does not establish that this history actually occurred.

Young explorerScientists used math to explore how the very young universe might have warmed up. In their idea, energy passes through tiny particles that have not been discovered before reaching ordinary particles. If those tiny particles last long enough, they could change how the universe cools and how much dark matter gets made. This is a possible story from calculations, not something scientists have seen happen.

Chemical abundance patterns at z=1-7: Carbon, Nitrogen, Neon, Sulphur, and Argon abundances from JWST spectroscopy

E. Cataldi, F. Belfiore, M. Curti+22 more

AstronomerUsing ultra-deep JWST/NIRSpec MARTA observations and archival spectroscopy, the study measures chemical abundance patterns in star-forming galaxies at z=1–7. It derives direct electron-temperature-based abundances for 244 galaxies with [OIII]4363 detections and extends the analysis to 514 additional galaxies using new empirical strong-line calibrations. Median N/O is enhanced by 0.18 dex relative to local galaxies, with a larger enhancement at low metallicity. Direct measurements show declining S/O and Ar/O with increasing metallicity, whereas strong-line estimates suggest flattening at higher metallicity, especially for S/O. Lower-mass galaxies have lower O/Ar at fixed Ar/H, consistent with differences in star-formation efficiency and delayed Type Ia supernova enrichment, though this interpretation is not uniquely established. Ne/O is approximately constant up to 12+log(O/H)=8.2, rises mildly above that threshold, and shows no significant redshift evolution. C/O tentatively rises with metallicity along a broadly local relation. Forward modeling indicates that selection mainly limits the metallicity range sampled for Ne/O and Ar/O but preferentially selects enhanced N/O at low metallicity, with a weaker analogous effect for S/O. These selection effects must be considered when interpreting the abundance trends.

PublicThe mix of chemical elements in a galaxy’s gas holds clues to its history of star formation and enrichment. Combining deep James Webb Space Telescope observations with archival data, researchers studied these mixtures in distant star-forming galaxies. They measured abundances directly in 244 galaxies and used newly calibrated methods to study 514 more. Compared with nearby galaxies, the distant sample has more nitrogen relative to oxygen on average, particularly where the overall abundance of heavier elements is low. Sulfur and argon relative to oxygen generally decline as heavy-element abundance rises, although the two measurement methods suggest different behavior at the high-abundance end. Neon relative to oxygen changes little over much of the range, while evidence for increasing carbon relative to oxygen remains tentative. Differences associated with galaxy mass may reflect how efficiently galaxies form stars and when supernovae add elements. Crucially, a model of observational selection shows that galaxies with unusually high nitrogen relative to oxygen are easier to include at low heavy-element abundance. The observed patterns therefore cannot all be read straightforwardly as differences in galaxies’ chemical histories.

Young explorerGalaxies have gas with different ingredients, like oxygen, nitrogen, and carbon. Scientists studied light from faraway galaxies to learn how much of each ingredient their gas contains. They found that these galaxies often have more nitrogen compared with oxygen than nearby galaxies do. That can give clues about how stars have changed the gas. But there is a catch: some kinds of galaxies are easier to spot than others. The scientists used a model to check this, so they would not mistake the easiest galaxies to see for what all galaxies are like.

The Balmer Absorber Strength Problem of Little Red Dots

Hanpu Liu, Eliot Quataert, Bingjie Wang+2 more

AstronomerSome observed Little Red Dot spectra show weaker H-alpha than H-beta absorption, apparently conflicting with atomic physics under standard attenuation models. The authors propose that emission from the absorbing medium, neglected in those models, can fill in optically thick H-alpha absorption and reduce its equivalent width. Proof-of-concept photoionization models indicate that the H-alpha source function could systematically exceed that of H-beta: radiative trapping preferentially populates neutral hydrogen's n=3 level when the medium is optically thick to H-alpha but not very optically thick to Paschen-alpha. These line-dependent source functions could selectively weaken H-alpha absorption, consistent with observations. The quantitative correction depends on the absorber's distance and internal structure, potentially providing an environmental diagnostic. Estimating the central engine's mass remains a possible avenue for future absorber modeling, not a demonstrated result.

PublicLittle Red Dots commonly show dips in their spectra where hydrogen absorbs light. In some observations, the H-alpha dip is weaker than the H-beta dip, contrary to expectations from standard models. This study proposes that the absorbing gas also emits light, partly filling the H-alpha dip. Preliminary computer models show how trapped radiation could make this filling-in effect stronger for H-alpha than for H-beta under particular conditions. The explanation is consistent with the observations, but the size of the effect depends on the gas's location and internal structure. Modeling it could help researchers investigate the surroundings of Little Red Dots; using it to estimate the mass of their central engine is a possibility for future work.

Young explorerScientists see dark marks in the light from space objects called Little Red Dots. Some marks are weaker than expected. The scientists suggest that gas blocking the light might also glow, filling in one mark more than another. Their computer models show this could happen, but they still need to learn more about the gas.

Arepo-CD: Coupling Collisional N-Body Dynamics with Moving-Mesh Magnetohydrodynamics

Chuizheng Kong, Hui Li, Long Wang+2 more

• Instrumentation and Methods for Astrophysics

AstronomerArepo-CD couples star-by-star collisional N-body dynamics to Arepo’s moving-mesh MHD, using unsoftened star-star gravity while retaining softening for interactions involving gas or collisionless components. Compact stellar subsystems are identified dynamically and integrated with a fourth-order forward symplectic method and slow-down algorithmic regularization within Arepo’s timestep hierarchy. Benchmarks against PeTar show good agreement in core collapse and subsequent expansion, radial density profiles, and stellar velocity distributions. With the Rigel star formation and feedback model, the framework is applied to radiation-MHD simulations of a turbulent molecular cloud of 100,000 solar masses. In the fiducial comparison, collisional and softened-gravity runs have similar star formation histories and integrated efficiencies. However, close encounters during the embedded phase generate a substantial runaway population with a velocity tail beyond 100 km/s. Ejected massive stars redistribute radiative feedback into lower-density surroundings, extending the heated-gas distribution. These are simulation results, with the star formation comparison limited to the fiducial setup described.

PublicThe researchers present Arepo-CD, a computer-simulation framework that models close gravitational encounters between individual stars while also following the gas, magnetic fields, and radiation involved in star formation. Tests agree well with a separate stellar-dynamics code. In simulations of a turbulent gas cloud containing 100,000 times the Sun’s mass, including close encounters produced a similar overall star formation history and fraction of gas converted into stars as a comparison that smoothed stellar gravity. But the encounters flung out a substantial population of stars, with some exceeding 100 kilometres per second. Escaping massive stars spread radiation into less-dense surroundings, creating a more extended region of heated gas. These findings come from simulations, not observations, and the comparison describes one reference cloud setup.

Young explorerScientists made a computer model of stars being born in a big cloud of gas. It lets stars pull strongly on each other when they get very close. In the model, these close meetings sent many stars racing away. Some big stars carried their light into thinner gas farther out, spreading the warming. About as much gas became stars as in the comparison model. This happened in a computer, not in a cloud the scientists watched.

Discovery of a Broad-Line Active Galactic Nucleus at z = 9.98

Xingyao Cai, Akio K. Inoue, Masafusa Onoue+12 more

AstronomerA systematic search of public JWST/NIRSpec PRISM spectra identifies MoM-BL-z10 at z = 9.9837 ± 0.0009 as the highest-redshift broad-line AGN reported to date. A narrow-plus-broad Gaussian fit to Hβ gives a broad-component detection at S/N = 3.87, with FWHM = 3480 (+2040/−950) km/s and luminosity = 1.25 (+0.33/−0.31) × 10^42 erg/s. [Ne III] emission and high [Ne III]/[O II] and [O III]/Hβ ratios further support the AGN interpretation. Continuum slopes, compact NIRCam morphology, and a tentative MIRI F770W detection suggest similarities to Little Red Dots. The authors present the first virial SMBH mass estimate at z ≈ 10: standard single-epoch calibration and a quasar bolometric correction yield a mass of 3.6 (+5.8/−1.7) × 10^7 solar masses and an Eddington ratio of 0.11 (+0.10/−0.07). An alternative calculation using an LRD-specific bolometric correction and an assumed Eddington ratio of unity yields 2.1 (+0.6/−0.5) × 10^6 solar masses. These assumption-dependent estimates at a cosmic age of 470 million years challenge rapid-growth scenarios and suggest either super-Eddington accretion from a stellar-mass seed or a more massive seed; they do not establish a particular growth history.

PublicJWST observations have revealed MoM-BL-z10, an object seen when the Universe was only 470 million years old. The researchers identify it as the most distant broad-line active galactic nucleus reported so far: a galaxy center apparently powered by a feeding black hole. A broadened hydrogen emission line, detected with a signal-to-noise ratio of 3.87, and other emission-line evidence support that interpretation. Its appearance and light also suggest similarities to objects called Little Red Dots, although one relevant infrared detection is tentative. Using a standard method, the team estimates a black hole mass of about 36 million Suns, with substantial uncertainty. A different calculation, using assumptions tailored to Little Red Dots and assuming the black hole feeds at its Eddington limit, gives about 2.1 million Suns. Neither estimate is a direct measurement of the mass. Such a large black hole so early raises questions about how it grew: unusually rapid feeding or a larger starting seed are possible explanations, not demonstrated histories.

Young explorerA space telescope called JWST saw light from a faraway galaxy when the Universe was very young. The light has clues that a huge black hole may be eating material in the galaxy’s middle. Scientists used those clues to estimate how big the black hole is, but the answer depends on their assumptions. Even the smaller estimate is about as heavy as two million Suns! They do not yet know how it became so big so early. It might have eaten very quickly or started out bigger.

A combined HST and JWST analysis of the stellar population in Draco II

Axelle C. Raffin, Giacomo Cordoni, Helmut Jerjen+5 more

• Solar and Stellar Astrophysics

AstronomerDeep HST and JWST photometry of Draco II, with membership selected using proper motions and photometric quality, strengthens its classification as an ultra-faint dwarf galaxy rather than an extended globular cluster. The combined optical–infrared catalogue reaches 50% completeness at F814W = 26.5 mag (absolute magnitude 10.1). Colour–magnitude analysis gives an age of 13.5 Gyr with uncertainties of −1.5/+1.7 Gyr and a distance of 19.2 ± 0.9 kpc. The population is alpha-enhanced, with mean [Fe/H]CaHK = −2.38 ± 0.17 dex and an intrinsic metallicity dispersion of 0.85 ± 0.13 dex. Ten unresolved main-sequence binaries with q > 0.5 and primary masses of 0.43–0.71 solar masses imply a binary fraction of 0.21 ± 0.07 within those limits, higher than typical globular-cluster values and near the upper range for open clusters. A single power law best models the stellar mass function, with slope 1.53 ± 0.26 over 0.13–0.77 solar masses. No evidence of mass segregation is found, and independent JWST-catalogue results are consistent. Together these findings strongly favour, but do not definitively establish, the dwarf-galaxy interpretation.

PublicDraco II is an extremely faint companion of the Milky Way whose identity has been debated: is it a tiny galaxy or an extended star cluster? Researchers combined Hubble and James Webb space telescope observations to study its stars. They find an ancient population, about 13.5 billion years old, roughly 19.2 kiloparsecs away. Its stars contain very little iron on average, but their inferred iron abundances vary substantially. The team also identified ten pairs of stars too close together to appear separately. Within the studied mass and companion-size limits, the estimated proportion of such pairs is higher than is typical in globular clusters. They found no evidence that heavier stars are more concentrated toward the centre than lighter stars. Taken together, the measurements strongly support Draco II being an ultra-faint dwarf galaxy, although the classification is not definitive.

Young explorerDraco II is a very faint group of old stars near our Milky Way. Scientists used two space telescopes to learn about its stars. They found that the stars have different amounts of iron, and some come in close pairs. These clues suggest Draco II is a tiny galaxy rather than just a star cluster, but scientists are not completely sure.

Unveiling the correlation between the UV 2175 Å dust attenuation bump, PAH emission, and gas-phase metallicity at cosmic noon

L. Arriscado, I. Shivaei, L. A. Boogaard+17 more

AstronomerA systematic study of 49 galaxies at cosmic noon (1.5 < z < 2.7) finds a positive correlation between the 2175 Å attenuation-bump amplitude and the PAH-to-dust mass fraction, q_PAH (Spearman rho = 0.60). Bump amplitudes are measured with VLT/MUSE spectroscopy, while q_PAH and other galaxy properties are inferred through Prospector SED fitting incorporating JWST/NIRCam and MIRI photometry. Strong-line oxygen abundances are available for 19 galaxies. Bumps are rarely detected at low q_PAH, supporting, but not establishing, PAHs as their primary carriers. Both bump amplitude and q_PAH correlate positively with stellar mass, oxygen abundance, and V-band optical depth, and negatively with specific SFR. These trends are consistent with PAH destruction under limited dust shielding and/or strong radiation fields, rather than directly demonstrating that mechanism. A principal component analysis of bump amplitude, q_PAH, optical depth, specific SFR, and oxygen abundance explains 97% of the variance and suggests that previously reported stellar-mass correlations reflect an underlying metallicity dependence. At high q_PAH, bump amplitudes span 0–0.5 mag; variations in dust geometry are proposed as a possible explanation.

PublicDust in galaxies blocks some ultraviolet wavelengths especially strongly, creating a distinctive feature whose origin remains uncertain. Researchers studied 49 distant galaxies and found that this feature tends to be stronger in galaxies with a larger estimated fraction of their dust in molecules called polycyclic aromatic hydrocarbons, or PAHs. The feature is rarely detected when the PAH fraction is low. This supports PAHs as its main source, but does not prove the connection. Both the feature and the PAH fraction tend to be stronger in galaxies with more stars, more oxygen, and greater dust obscuration, and weaker in galaxies forming stars faster relative to their stellar mass. The authors interpret these patterns as consistent with PAHs being destroyed where dust offers little protection or radiation is strong. Their statistical analysis suggests that chemical enrichment may underlie the link with stellar mass. Different arrangements of dust could explain why galaxies rich in PAHs still show widely differing feature strengths.

Young explorerDust in faraway galaxies blocks some kinds of invisible light more than others. Scientists looked at 49 galaxies and found that a special kind of light-blocking usually goes along with more of certain tiny molecules in the dust. That is a clue that these molecules do the blocking, but it is not proof. The scientists think strong light might break the molecules apart, and the way dust is spread around might matter too.

Ammonia Fitting of Multiple Velocity Components in High-Mass Star-Forming Regions

T. Withers, S. Sadavoy, M. Chen+19 more

• Solar and Stellar Astrophysics

AstronomerThe authors analyze NH3 emission from the Green Bank Telescope KEYSTONE survey of 11 giant molecular clouds at distances of 0.7–2.7 kpc, extending radiative-transfer fitting codes to fit up to three velocity components simultaneously in NH3 (1,1). Multiple components are detected in 13% of pixels with detected and fitted NH3 emission, primarily clustered in cloud interiors. In these pixels, the median fitted linewidth is smaller by a factor of 1.4 than in equivalent single-component fits, with significant cloud-to-cloud variation. Multiple-component regions preferentially coincide with the densest gas and high-mass star formation sites, suggesting overlapping filaments, cores, or complex motions associated with massive-star formation rather than establishing a unique physical explanation. The resulting centroid-velocity and velocity-dispersion maps enable future quantitative studies of coherent motions such as infall and outflow; those motions are not established here. Multi-component data products are available through the CADC.

PublicResearchers studied ammonia gas in 11 giant clouds using the Green Bank Telescope, separating signals from gas moving at different speeds along the same line of sight. They found multiple velocity components in 13% of the map pixels where ammonia emission was detected and successfully fitted, mostly in dense cloud interiors and places where massive stars form. Treating these components separately reduced the typical measured width of each gas signal by a factor of 1.4 compared with treating it as a single component, although the effect varied substantially between clouds. The patterns may reflect multiple gas filaments, compact cores, or complicated motions linked to massive-star formation. The maps and publicly available data will support future tests of gas falling inward or flowing outward, but this study does not establish those motions.

Young explorerScientists used a telescope to study gas in 11 huge space clouds. In some parts, they found gas moving at different speeds even though it looked like it was in the same spot. These mixed signals often came from crowded places where very big stars are forming. Separating the signals helped them get a clearer picture of how the gas moves. There might be several strands or clumps of gas there. Scientists still need to study the maps more to find out whether gas is moving inward or outward.

Link between the properties of circumgalactic outflows and the recent star formation history of their host galaxies

Ismael Pessa, Lutz Wisotzki, Constanza Muñoz López+8 more

AstronomerUsing outflow properties inferred from modeling extended Mg II emission observed with VLT/MUSE, the authors examine their dependence on recent star formation history (SFH). Non-parametric SFHs fitted to spectroscopy and photometry yield SFRs and specific SFRs that correlate moderately with maximum outflow velocity and radial acceleration rate. These correlations are not recovered with [O II] luminosity-based SFRs or parametric SFHs, emphasizing sensitivity to bursty star formation over timescales comparable to gas travel into the circumgalactic medium. SFRs averaged over timescales estimated from Mg II halo extent and kinematics correlate with maximum velocity, but not significantly more strongly than fixed-timescale averages. The authors interpret this as evidence that multiple star formation events shape the halos rather than a single dominant burst. Galaxies with recent star formation concentrated into one or a few episodes have faster inferred outflows than those with more evenly distributed star formation. The findings support interpreting the circumgalactic medium as a dynamical record of recent star formation and provide an observational constraint on feedback models.

PublicThe study connects the timing of star formation in galaxies with the motion of gas flowing outward into their surroundings. The researchers reconstructed recent star formation histories from galaxy spectra and brightness measurements, then compared them with gas motions inferred by modeling extended magnesium emission. They found moderate links between recent star formation rates and both the fastest outflow speeds and how outflow speed changes with distance. These links did not appear when they used two alternative methods for estimating star formation. Galaxies that formed stars in one or a few concentrated recent episodes had faster outflows than galaxies whose star formation was spread more evenly over time. Estimating when the gas began its outward journey did not produce a significantly stronger correlation than averaging star formation over fixed periods. The authors therefore suggest that the surrounding gas records several star-forming events, rather than just one major burst; the correlations do not establish a simple one-event explanation.

Young explorerGalaxies make stars, and some gas moves outward from them. Scientists studied light to work out when galaxies made stars and how fast the gas was moving. They found that galaxies that made stars in a few busy spells tended to have faster-moving gas than galaxies that made stars more steadily. The match was not perfect. The scientists think the gas around a galaxy may hold clues about several busy spells from its past, not just one.

The MIni-Halos in MIni-Clusters (MIMIC) project: New insights into the origin of mini-halos from a LOFAR, uGMRT, and MeerKAT study of diffuse radio emission in Abell 496 and ZwCl 235

F. Ubertosi, S. Giacintucci, A. Botteon+18 more

AstronomerThis MIMIC pilot study detects radio mini-halos in the central 100 kpc of the low-mass, relaxed clusters Abell 496 and ZwCl 235, using LOFAR, uGMRT, MeerKAT, and Chandra data. Both sources are confined within X-ray cold fronts attributed to gas sloshing. Their 1.4 GHz powers are (2.2 ± 0.2) × 10^22 W/Hz and (1.3 ± 0.3) × 10^22 W/Hz, respectively, making them the least powerful mini-halos known to date. Their spectra are steep, with spectral indices from −1.9 to −1.4; Abell 496 also shows outward spectral steepening. Radio and X-ray surface brightness correlate across both sources, with frequency-dependent sub-linear or nearly linear slopes. These observations suggest contributions from fossil plasma transported from the central radio galaxy and possible turbulent re-acceleration, rather than uniquely establishing that mechanism. The systems extend mini-halo scaling relations to lower powers and support a strong relation between radio power and cool-core X-ray luminosity, P_1.4 ∝ L_X,70^(1.5 ± 0.2). Evidence that steeper-spectrum mini-halos preferentially have lower core X-ray luminosities and radio powers remains tentative. The study also characterizes two extended, greater-than-200-kpc tailed radio galaxies in these clusters.

PublicAstronomers have detected faint, extended radio glows around the centers of two relatively low-mass galaxy clusters, Abell 496 and ZwCl 235. These glows qualify as radio mini-halos and are the least powerful examples known to date. In both clusters, the radio emission fills the central region, about 100 kiloparsecs across in extent, and stays inside boundaries seen in X-rays that are associated with sloshing gas. The radio signals fade strongly toward higher frequencies, and the radio and X-ray brightness patterns are related. These findings suggest that old radio-emitting material from the central galaxy may be carried through the cluster gas and re-energized by turbulent motions, but this explanation is not established conclusively. The discoveries extend a strong link between mini-halo radio power and central X-ray luminosity to fainter systems. A possible tendency for lower-power mini-halos to have more steeply declining radio spectra is still tentative.

Young explorerAstronomers found faint radio glows in the middles of two big groups of galaxies. Our eyes cannot see these glows, but radio telescopes can. They are the faintest known glows of this particular kind. The glows stay inside edges in hot gas that seems to be sloshing around. The scientists think that this moving gas might help give old material from a galaxy fresh energy to glow, but they are not sure yet.

PIANISTpy: A JAX-based Python package for velocity-anisotropic astrophysical equilibrium models

Barry T. Chiang, Frank C. van den Bosch, Hsi-Yu Schive

• Cosmology and Nongalactic Astrophysics
• Instrumentation and Methods for Astrophysics
• High Energy Physics - Phenomenology

AstronomerCosmological simulations produce velocity anisotropy through mergers and direction-dependent accretion, yet idealised dynamical simulations commonly assume isotropy. The authors present an analytical phase-space truncation framework for constructing finite, self-consistent anisotropic systems, with separate approaches that guarantee either distribution-function monotonicity or identical truncated density profiles. Their open-source, JAX-based, GPU-accelerated package PIANISTpy constructs spherical, non-rotating initial conditions with arbitrary double-power-law analytical radial density profiles and a library of analytical anisotropy profiles. Linear combinations of these anisotropy models also allow non-analytical profiles. Differentiable outputs include three-dimensional velocity profiles and line-of-sight-integrated observables for gradient-based Monte Carlo inference, plus local dark matter velocity distributions beyond the Maxwell–Boltzmann approximation used in terrestrial detection experiments. In numerical demonstrations, the authors report orders-of-magnitude higher solver accuracy and superior dynamical stability relative to existing tools, including galpy and AGAMA. These are methodological and simulation results, not observational measurements.

PublicComputer simulations suggest that mergers and uneven flows of matter leave galaxies and dark matter haloes with motions that differ by direction. Yet simplified simulations often assume that motion is the same in every direction, partly because constructing physically consistent models with finite boundaries is difficult. This work introduces a mathematical framework and open-source software, PIANISTpy, to build spherical, non-rotating models with direction-dependent motions and self-consistent boundaries. The software also calculates quantities that can be compared with observations and local dark matter velocity distributions relevant to detection experiments. In numerical tests, the authors report substantially better solver accuracy and more stable simulated systems than existing tools. The work provides modelling capabilities rather than a new observation or a dark matter detection.

Young explorerScientists use computers to make pretend galaxies and dark matter clouds. In these models, things can move more in some directions than in others. The researchers made a new tool to build round models that do not spin, with carefully designed edges. Their computer tests showed that the tool calculates more accurately and makes models that stay more stable than older tools. They did not discover a new galaxy or detect dark matter.

KROME-X: a GPU-ready library for chemistry and microphysics in astrophysical simulations

Alessandro Lupi, Tommaso Grassi, Stefano Bovino

• Instrumentation and Methods for Astrophysics

AstronomerKROME-X is a modern C++ rewrite of KROME for astrochemical kinetics and microphysics. It generates network-specific rates, right-hand sides, analytic Jacobians, thermal terms, and tables, integrated by a header-only runtime using a C++ port of CVODE’s backward differentiation formula method. Validation against legacy KROME and independent references finds agreement within solver accuracy where the physics is unchanged; legacy benchmarks show speedups of up to 13.5 at equal tolerance. NVIDIA A100 GPU acceleration becomes advantageous relative to its share of a computing node from a few thousand cells per call, with highest throughput at 100,000 cells per batch. Networks containing hundreds of species remain faster on CPUs because of limited GPU memory. Physics updates include coupled photon-field and chemistry evolution with exact photon conservation, absorption-specific secondary ionizations, grain size and temperature evolution with a grain energy equation, and revised line cooling incorporating optical thickness. These are software validation and benchmark results, not astronomical observations; the framework is intended for future hydrodynamic simulations.

PublicThe researchers introduce KROME-X, a rewritten tool for calculating chemical reactions and heating and cooling in computer simulations of space. In tests where the underlying physics was unchanged, it matched the earlier KROME program within numerical accuracy and ran up to 13.5 times faster at the same error tolerance. Graphics processors helped when many simulation cells were processed together, but networks with hundreds of chemical species still ran faster on conventional processors because of graphics-memory limits. The update also improves calculations involving light, dust, and cooling. These results test simulation software rather than report new observations of space.

Young explorerScientists made a new computer tool to help pretend space worlds follow chemistry rules. It keeps track of chemicals, light, and tiny dust grains. In tests, it could work faster than the old tool while giving matching answers when the rules were the same. Which computer works best depends on the job.

The H IX galaxy survey IV: What does the molecular gas reveal in HI eXtreme galaxies

V. A. Capa, H. Dénes, K. A. Lutz+1 more

AstronomerALMA CO(1–0) observations of five HI-eXtreme (HIX) galaxies reveal compact molecular discs with normal H2 masses relative to stellar mass, despite their massive, extended HI discs and normal or low star formation rates. 3DBarolo dynamical modelling finds kinematic consistency between the atomic and molecular gas; both phases have elevated velocity dispersions, indicating enhanced turbulence relative to regular late-type galaxies. Component-specific angular momentum estimates and the global stability parameter q support an interpretation in which the HI discs hold most of the systems’ angular momentum and are globally stable against collapse. Extremely long HI depletion times, alongside typical H2 depletion times, point to inhibited atomic-to-molecular conversion as the star formation bottleneck. Past gas accretion or recent tidal interactions are proposed origins of the high angular momentum and HI excess, with extended HI structures and positive tidal indices providing particular support in ESO378-G003 and ESO381-G005.

PublicWhy do some galaxies have enormous supplies of gas but form stars at only normal or low rates? Observations of five such galaxies show that their extended reservoirs of atomic hydrogen surround compact discs containing ordinary amounts of molecular hydrogen relative to their stellar mass. The researchers interpret the results as evidence that the atomic gas carries enough angular momentum to remain stable against collapse, limiting its conversion into molecular gas. The atomic reservoirs would take exceptionally long to deplete, while the molecular gas has typical depletion times. This suggests the bottleneck is making molecular gas, rather than using it to form stars. The excess gas and high angular momentum may come from earlier gas acquisition or recent gravitational encounters with other galaxies, but their origin is not established.

Young explorerAstronomers studied five galaxies with lots of gas but no extra star-making. They think much of the gas stays spread out as it spins, making it hard to gather into the kind of gas that forms stars. The galaxies do have normal amounts of that star-making gas. So having lots of gas does not always mean making lots of stars.

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

Zhiyuan Yao, Avishai Dekel, Romain Teyssier+5 more

AstronomerMAGE comprises eleven RAMSES cosmological zoom-in simulations at approximately 10 pc resolution, evolved to z ≃ 9, with stellar masses of approximately 2 × 10^8–3 × 10^10 solar masses. Stellar half-mass radius rises steeply with mass at low masses, turns over near 5 × 10^9 solar masses, and depends weakly on redshift. Intrinsic UV sizes overlap the compact end of observed distributions, including compact strong-line systems, but miss the extended population at z > 9; dust, PSF-limited measurements, and the simulations’ overdense environments may contribute to the discrepancy. Above approximately 5 × 10^8 solar masses, stars dominate within the half-mass radius and central circular speeds exceed a characteristic stellar-feedback scale. Increasing outflow retention is consistent with galaxy-scale gas recycling sustaining central supply and compaction-like buildup. The size turnover coincides with rapidly increasing rotational support, reaching v/σ ≃ 1.5–3 in star-forming gas and stars younger than 10 Myr, as central circular speed exceeds halo virial speed. Low subsequent central gas fractions, declining central star formation, and younger outskirts suggest, rather than establish, the onset of inside-out quenching.

PublicEleven computer simulations explore how galaxies in the early universe grew and developed rotating disks. Smaller simulated galaxies become larger as their stellar mass increases, but that trend turns over at higher masses, alongside a rapid increase in ordered rotation. The simulations suggest that stronger central gravity increasingly keeps expelled gas inside galaxies, allowing it to feed dense central regions again. Later, reduced central gas and star formation, together with younger stars farther out, hint that star formation may begin shutting down from the center outward. These are simulation findings and interpretations, not direct observations of that process. The modeled galaxies match compact observed galaxies but not the more extended ones; dust, limits on measuring apparent sizes, and the dense environments modeled could partly explain the mismatch.

Young explorerScientists made eleven computer versions of young galaxies, huge groups of stars and gas. In these models, gas could stay nearby and help build crowded centers, while stars and gas began moving more like a spinning disk. Later, the centers made fewer new stars. That might mean star-making starts slowing in the middle first. The models match some real galaxies’ sizes, but not all.

NGC 3227 Blinks: An Extreme Changing-Look Event in a Seyfert Galaxy

Kaiwen Zhang, Michael S. Brotherton, Pu Du+10 more

• High Energy Astrophysical Phenomena

AstronomerNGC 3227 underwent a rapid optical changing-look event: its optical continuum faded by more than 70% and broad H-beta nearly disappeared within weeks, followed by recovery within two months. Damped random walk simulations calibrated to normal source variability assign such a decline a probability of p = 0.002, disfavoring ordinary stochastic accretion fluctuations. Simultaneous Swift observations show X-ray spectral hardening, interpreted as enhanced line-of-sight absorption. A persistent 6–8 day continuum-to-broad-H-beta reverberation lag during the dim state indicates that the broad-line region remained responsive and places the inferred obscurer interior to it. Photoionization calculations require a fully ionized, Compton-thick column of N_H approximately 1.5 × 10^24 cm^-2 to reproduce the optical suppression. The observations and modeling support compact, high-column-density obscuration inside the broad-line region as a mechanism for week-timescale changing-look behavior.

PublicThe bright center of the galaxy NGC 3227 dimmed dramatically within weeks: its visible-light continuum dropped by more than 70%, and a broad hydrogen emission feature almost vanished. It recovered within two months. Simulations suggest that a decline this large is unlikely to come from the galaxy center’s usual random brightness fluctuations. At the same time, changes in the X-ray spectrum pointed to more material blocking our view. The hydrogen-emitting gas still responded to brightness changes after a delay of 6–8 days, indicating that it remained active and placing the inferred blocking material closer to the center than this gas. Calculations suggest that a compact, very dense layer of fully ionized gas could explain the fading; its required properties come from modeling rather than a direct measurement.

Young explorerThe middle of a galaxy called NGC 3227 grew much dimmer in just a few weeks, then brightened again within two months. Gas around the middle still answered its changing light with a delayed glow, like an echo. The clues suggest that something closer to the middle blocked our view, rather than the glowing gas going away. Computer calculations suggest that a small, thick patch of gas could do this.

Unveiling Accretion-Disk Reverberation Beneath BLR Contamination with TILDE

Sungho Jung, Jong-Hak Woo

AstronomerTILDE is a two-stage Bayesian framework for decomposing multi-band AGN light curves into underlying accretion-disk variability and delayed broad-line region (BLR) contamination, inferring lags for both components. Tests on synthetic data recover the known disk and BLR delays. Applied to the Seoul National University AGN Monitoring Project sample, the inferred BLR light curves match observed Hβ light curves, with lags consistent with reported Hβ measurements. After correcting the lag spectrum for BLR contamination, inferred disk sizes are broadly consistent with the standard thin-disk model. This suggests that BLR contamination can significantly bias disk sizes estimated through cross-correlation of broad-band photometry.

PublicThe light from an active galaxy mixes signals from its glowing disk and a surrounding region of gas, making the disk’s size difficult to estimate. The researchers developed TILDE, a statistical method that separates these signals using brightness changes measured in several color bands. It recovered the correct light-travel delays in simulated data. In observations, its reconstructed gas-region signals agreed with independently observed hydrogen emission. After accounting for the gas contribution, the estimated disk sizes were broadly consistent with a standard model of thin disks. The findings suggest that mixing these signals can substantially distort disk-size estimates made with a common analysis method.

Young explorerA bright galaxy’s middle has a glowing disk and glowing gas. Their light gets mixed together, and some changes arrive later than others. Scientists made a new way to untangle the changing light. It worked on pretend data where they already knew the answers. With real galaxy data, the gas signal it found matched other observations. After separating the light, the disk sizes roughly matched what a standard model says they should be.

B-fields In STar-forming Region Observations (BISTRO): Technical Foundations for Quantitative 450/850 μm JCMT SCUBA-2/POL-2 Polarimetry

Ray S. Furuya, David Berry, Pierre Bastien+59 more

• Instrumentation and Methods for Astrophysics

AstronomerFive technical validations assess JCMT SCUBA-2/POL-2 polarimetry at 450 and 850 μm using 174 archival fields in 69 molecular-cloud regions, with test-specific subsets. Extended-source calibration avoids the deterministic Δβ = −1.05 bias that peak-brightness calibration would introduce into the dust emissivity index for extended emission. A Stokes I noise model includes additive and signal-dependent terms; the measured median 450/850 μm surface-brightness noise ratio is 25. Independent Q/U tests support approximately equal additive variances and weak error correlations. Field-specific corrections reduce 450 μm Q/U zero-level offsets of order 1 mJy arcsec⁻², leaving a median combined residual amplitude of 0.07 mJy arcsec⁻² after three-step regression. Independent SOFIA/HAWC+ comparisons at 154 and 214 μm support the correction in strongly affected fields. Matching the 450 μm maps to the modeled 850 μm beam and a common 12.6–300 arcsec angular-scale range improves agreement among reductions of the same observations across 30 sources: the median over sources of each source’s median angular residual relative to the final product falls from 6.3° to 4.7°, with 29 sources below 10° after matching. These are inter-reduction residuals, not absolute angle-accuracy measurements. The study also quantifies propagation of residual Q/U offsets into polarization-fraction ratios, spectral-index differences, and polarization angles, providing procedures and quantitative references for multiwavelength interpretation.

PublicThis study checks how reliably archived James Clerk Maxwell Telescope observations measure polarization—the orientation of light waves—from molecular clouds at two wavelengths. Using different subsets of 174 fields in 69 cloud regions, the researchers tested calibration, noise, unwanted baseline offsets, and how maps should be matched before comparison. They show that an unsuitable calibration would systematically shift an inferred dust property. Their corrections substantially reduce baseline offsets, with independent observations supporting the correction in strongly affected fields. Matching the maps’ resolution and range of angular scales also improves agreement between processing versions: a typical angular discrepancy decreases from 6.3° to 4.7°. This measures agreement between versions, not accuracy against a known true angle. The work provides practical checks and uncertainty estimates for interpreting these measurements and combining them with observations at other wavelengths.

Young explorerScientists checked telescope pictures of big clouds in space. They studied which way the light waves line up. Tiny unwanted signals and differences in picture sharpness can make the pictures disagree. Fixing some of these problems helped the pictures match better, but that does not mean every measurement is perfect.

B-fields In STar-forming Region Observations (BISTRO): Dual-Wavelength Constraints on Size-Dependent Grain Alignment in Star-Forming Regions

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

• Instrumentation and Methods for Astrophysics

AstronomerJCMT POL-2 observations at 450 and 850 μm, compared at 12.6-arcsecond resolution, show a median absolute polarization-angle difference of 6.7° across 21 regions. Defining I ∝ ν^α and PI ∝ ν^γ, 24–27 of 35 regions have γ < α when 3σ limits on weak polarized intensities are included. The median γ − α is −0.51, with a limit-dependent range of −0.57 to −0.45. The polarization-fraction ratio is P450/P850 = 0.69 ± 0.02 (systematic) ± 0.03 (statistical), with no detected dependence on angle difference. The authors suggest grain-size-dependent alignment as the simplest explanation, rather than establishing it observationally. For optically thin temperature mixtures sharing a polarization angle and opacity law, reproducing the median requires lower effective polarization efficiency in warm dust; cold dust at ≥10 K and warm dust at ≤40 K require a warm-to-cold efficiency ratio r ≲ 0.18. Tests in four fields used β = 2, Herschel dust temperatures, and Green Bank Ammonia Survey kinetic temperatures, assuming equal gas and dust temperatures and ammonia tracing cold gas. With cold dust at 3–20 K and warm dust at 25–40 K carrying at most half the mass, temperature-matched models cannot reproduce γ − α within 1σ in three fields, including OMC 2 tentatively, even at r = 0. Expanding warm-dust temperatures to 10–100 K and its mass fraction to 95% permits solutions only for r ≤ 0.041. Temperature mixing therefore requires broader model ranges and a strong efficiency contrast in these fields; the contrast’s origin remains undetermined.

PublicObservations with the James Clerk Maxwell Telescope compared dust emission at wavelengths of 450 and 850 micrometres. The preferred directions of polarization were generally similar, but the fraction of emission that was polarized was lower at 450 micrometres: its ratio to the 850-micrometre fraction was 0.69, with small reported uncertainties. The researchers suggest that dust grains of different sizes align differently, but this explanation is not proven. They also tested whether mixing warm and cold dust could explain the findings. Under their model assumptions, this works only if warm dust produces polarization much less efficiently than cold dust. In three of four fields, including one tentative case, models constrained by measured temperatures could not match the polarization measurements within the stated uncertainty using the initial temperature and mass ranges. Broader ranges allowed matches, but only with an especially strong difference in polarization efficiency. What causes that difference remains unknown.

Young explorerSpace dust gives off light. Scientists compared two kinds of that light and found that one had less of a special pattern called polarization, though the pattern usually pointed nearly the same way. They think dust pieces of different sizes might line up differently. They also tried models mixing warm and cold dust, but those needed the warm dust to make much less of the pattern. They do not yet know why.

Ballistic mixing: stellar mergers drive internal mixing in extremely massive stars, with implications for proto-globular cluster pollution

J. Roman-Garza, C. Charbonnel, A. Rantala+3 more

• Solar and Stellar Astrophysics

AstronomerThis modeling study tests merger-formed extremely massive stars as candidate sources of the chemical enrichment associated with globular-cluster multiple populations. The authors follow the formation of a roughly 6,700-solar-mass star through 253 mergers drawn from a direct N-body simulation of a cluster resembling the densest clusters observed at redshift about 10. They evolve individual stars with 1D stellar models and construct merger products using mixing and shock-heating prescriptions calibrated to 3D simulations of parabolic collisions. In the models, entropy-based mixing carries nuclear-processed material from the convective core into the envelope, while merger heating promotes chemical homogenization. The resulting surface enrichment in hydrogen-burning products yields abundance patterns consistent with those observed in globular-cluster multiple populations. These simulated results support, but do not establish, merger-formed extremely massive stars as early enrichment sources under proto-globular-cluster-like conditions.

PublicSome globular star clusters contain groups of stars with different chemical compositions. One proposed explanation is that exceptionally massive stars supplied chemically processed material early in the clusters' history. Researchers tested part of this idea by modeling a star that grew to about 6,700 times the Sun's mass through 253 stellar mergers in a simulated dense cluster. Their calculations indicate that the mergers mix material altered by nuclear reactions in the star's core toward its surface, with collision heating helping to spread that material throughout the star. The modeled surface composition resembles chemical patterns observed in globular clusters. This supports the proposed role of merger-built giant stars in early chemical enrichment, but it does not show that they actually supplied the material in observed clusters.

Young explorerSome big groups of stars have stars made with different mixes of ingredients. Scientists used a computer to see what might happen when many stars join together to make one enormous star. In their model, the crashes helped bring ingredients made deep inside the star up to its outside. That outside mix looked like mixes seen in some real groups of stars. This is a clue that enormous stars might help explain those mixes, but it is not proof.

FEAST: Spatially Resolved Star Formation History of the NGC 4485/NGC 4490 System and its Tidal Bridge from JWST/NIRCam Color Magnitude Diagrams

Giacomo Bortolini, Matteo Correnti, Angela Adamo+19 more

AstronomerDeep JWST/NIRCam imaging from FEAST is used to reconstruct the spatially resolved star formation history of the interacting, low-mass, gas-rich pair NGC 4485/NGC 4490, including its tidal bridge, through near-infrared resolved-star CMD fitting with SFERA 2.0. Recent star formation is widespread beyond the main galaxy bodies, with a significant fraction in NGC 4485 occurring outside its central region. All major regions show enhanced activity around 0.5–1 Gyr and 10–30 Myr ago; the bridge exhibits the largest increase relative to its own average star formation rate. These reconstructed peaks follow the first and second pericenter passages predicted by independent dynamical models by a few hundred million years. This timing supports, but does not establish, an interpretation in which repeated tidal encounters redistributed and compressed gas, triggering spatially extended bursts.

PublicAstronomers used deep James Webb Space Telescope images of individual stars to reconstruct when and where stars formed in the interacting galaxies NGC 4485 and NGC 4490. They found recent star formation throughout the pair, including the bridge between them and areas away from their centers. All major regions show two periods of increased star formation, roughly 500 million to 1 billion years ago and 10–30 million years ago. The bridge had the strongest increase compared with its own usual rate. Separate models predict that the galaxies made close passes a few hundred million years before these bursts. The timing supports the idea that repeated encounters moved and squeezed gas into forming stars, although it does not prove that explanation.

Young explorerTwo galaxies called NGC 4485 and NGC 4490 are tugging on each other. Scientists used pictures from the James Webb Space Telescope to work out when their stars were born. They found two times when many more stars formed, including in a bridge between the galaxies. Other models suggest the galaxies passed close together before those busy times. Their tugging may have moved and squeezed the gas that makes stars, but scientists have not proved that this caused the bursts.

Euclid Quick Data Release (Q1). Data processing for intracluster light measurements

Euclid Collaboration, S. P. Bamford, H. Gao+97 more

AstronomerThe authors present post-processing and measurement procedures for Euclid intracluster light (ICL) studies that substantially reduce background variations without small-scale background subtraction. Tests injecting simulated clusters into real images show that the approach preserves faint, extended outskirts. On scales of several arcminutes, they report reliable detection around 27.5 mag arcsec⁻² in Y_E, J_E, and H_E, and 29 mag arcsec⁻² in I_E. They conclude that the method enables accurate ICL measurements in individual clusters from the local Universe to z ≈ 0.8, with uncertainties of order 10% in surface brightness, 10° in position angle, and 0.1 in ellipticity. The preservation test uses simulated sources rather than independently established profiles of real clusters.

PublicEuclid images can reveal the very faint light spread between galaxies in galaxy clusters, but uneven image backgrounds can obscure it. The researchers describe a way to reduce those background variations without using a small-scale subtraction that could remove genuine diffuse light. They tested the method by adding simulated clusters to real images and found that it preserved their faint outer regions. They report sensitivity to extremely faint light over areas several arcminutes across and say the method enables measurements in individual clusters from the nearby Universe out to a redshift of about 0.8. The stated measurement uncertainties are roughly 10% for surface brightness, 10 degrees for orientation, and 0.1 for a measure of shape. The work establishes measurement capabilities; its broader impact on understanding this light remains an expectation.

Young explorerThere is a very faint glow between galaxies in big groups. Pictures from Euclid can help us see it, but an uneven background makes it tricky. The scientists made the background smoother while trying not to erase the glow. To check, they put pretend galaxy groups into real pictures, and their method kept the faint outer parts. They say this will help them measure the real glow, though the measurements will not be perfect.

Euclid Quick Data Release (Q1). The shape of cluster haloes revealed by intracluster light

Euclid Collaboration, T. Kolcu, N. A. Hatch+97 more

AstronomerUsing Euclid Q1 imaging, the authors measured intracluster light (ICL) morphology in 205 eROSITA- and DES-selected clusters at 0.1 ≤ z ≤ 0.8. Shape parameters agree across five bands, with H_E reaching the largest cluster-centric distances in individual profiles, about 0.1R200c (~100 kpc). The ellipticity distribution, defined by e = 1 − b/a, peaks at 0.5, consistent with halo ellipticities inferred from lensing; this supports, rather than directly establishes, ICL as a tracer of cluster halo structure. BCG-dominated cores have e ~ 0.2, rising to ~0.5 at 0.1R200c. ICL position angles align more closely with BCGs (87% within 30°) than with satellite distributions (61%); robust position angles are measurable for 63% of the sample using ICL versus 30% using satellites. Redshift-bin stacks extend surface-brightness measurements to 0.6–0.8R200c and ellipticity measurements beyond 0.3–0.4R200c (300–400 kpc), revealing an ellipticity plateau beyond 0.1R200c. The measurements demonstrate Euclid's statistical capability for ICL morphology and offer a route to constraints on halo structure and redshift evolution; an evolutionary trend is not reported here.

PublicResearchers used Euclid images to study the faint intracluster light spread through 205 galaxy clusters. They found that the central regions, where the brightest cluster galaxy dominates the light, are relatively round, while the surrounding light becomes more stretched out farther from the center. Combining images of multiple clusters showed that this stretching levels off at larger distances. The diffuse light usually points in the same direction as the brightest central galaxy, but matches the arrangement of satellite galaxies less closely. It also provides a reliable orientation measurement for a larger fraction of clusters than the satellite galaxies do. Its measured shapes resemble cluster halo shapes inferred from gravitational lensing, suggesting that this faint glow can help map halo structure, though the resemblance is not direct proof. The study demonstrates Euclid's ability to measure these shapes and could help future studies investigate how cluster structure changes over time.

Young explorerScientists looked at pictures of 205 big groups of galaxies. They studied a faint glow spread through each group. Near the middle, the light looks fairly round. Farther out, it looks more stretched, and it often points the same way as the brightest galaxy in the middle. When the scientists put many pictures together, they found that the glow stops getting more stretched farther out. This faint light may help them work out the shapes of the much bigger groups around it.

Euclid Quick Data Release (Q1). A systematic study of the intracluster light fraction at 0.2 < z < 1.5

Euclid Collaboration, H. Gully, N. A. Hatch+97 more

AstronomerA homogeneous analysis of approximately 300 clusters at 0.2 < z < 1.5 combines South Pole Telescope Sunyaev–Zeldovich-selected and Euclid optically selected samples, with comparison to Hydrangea simulations. BCG light is measured within elliptical isophotes of semi-major axis 50 kpc and ICL between 50 and 200 kpc. Euclid Wide detects ICL in individual massive clusters with M500 ≳ 10^14.2 solar masses out to at least z ≈ 1.5, with detection rates of 70–80%. At fixed cluster mass, ICL accounts for approximately 40% of combined BCG-plus-ICL light and 20% of total cluster stellar light, with both fractions approximately constant across the sampled redshift range. The authors interpret this as evidence that the relative stellar-mass partition among BCG, ICL, and satellites was largely established by z ≈ 1.5. However, the sample is not an evolutionary sequence, so individual clusters may still evolve. The findings are consistent with, rather than proof of, joint BCG–ICL assembly through accretion, stripping, and merging of the same massive-galaxy population above 10^10 solar masses. Inferred ICL fractions depend systematically on wavelength but are largely insensitive to outer integration radii of 200–600 kpc.

PublicResearchers measured the faint, spread-out starlight in about 300 galaxy clusters spanning a broad range of cosmic history and compared their findings with computer simulations. They found that Euclid Wide can detect this intracluster light in 70–80% of sufficiently massive clusters, even out to a redshift of about 1.5. The diffuse light contributes about 20% of all cluster starlight, or about 40% when counting only it and the brightest central galaxy. For clusters of comparable mass, these proportions remain roughly constant across the period studied. This suggests that the balance of stars among central galaxies, diffuse surroundings, and other cluster galaxies was established relatively early. It does not mean that individual clusters stopped changing: the study compares different clusters rather than following the same ones through time. The results fit an explanation in which central galaxies and diffuse stellar surroundings grow together as massive galaxies arrive, lose stars, and merge. The measured diffuse-light fraction also depends on the wavelength observed.

Young explorerGalaxies gather in big groups, and faint starlight spreads around the galaxies. Scientists looked at about 300 of these groups. In groups of similar size, this soft glow made up about the same share of all the starlight, whether the groups were seen earlier or later in the universe’s story. That hints that this balance was set early. But the scientists looked at different groups, not one group growing up, so each group could still change. One possible explanation is that galaxies lose stars and join together, helping both the biggest galaxy and the soft glow grow.

Euclid Quick Data Release (Q1). The metallicity of the intracluster light

Euclid Collaboration, J. B. Golden-Marx, N. A. Hatch+97 more

AstronomerUsing Euclid Q1 imaging, the authors stack elliptical-annulus light profiles of the brightest central galaxy (BCG) and intracluster light (ICL) in 168 DES redMaPPer clusters at 0.1 < z < 0.75 with M_200m > 10^14.05 solar masses/h. They measure radial colours reliably to approximately 300 kpc, finding a gradient in which the ICL becomes bluer than the BCG out to approximately 150 kpc. Stellar population synthesis models indicate that the near-infrared colours are sensitive to metallicity but not age, enabling what the authors report as the first statistical BCG–ICL metallicity profile extending to 300 kpc. They infer super-solar BCG metallicity, log10(Z/Z_sun) > 0.1, and metal-poor ICL, log10(Z/Z_sun) approximately -0.5. The colour and metallicity gradients are robust, but the inferred metallicity values depend on the adopted synthesis model and colour. The findings support, rather than directly establish, BCG growth through mergers with massive galaxies or satellite cores and ICL growth through tidal stripping of lower-metallicity stars from massive satellites’ outskirts.

PublicAstronomers combined measurements of 168 galaxy clusters to study how the colour of their central galaxies compares with the faint, diffuse light spread through the clusters. They measured this light’s colour out to about 300 kiloparsecs and found that it becomes bluer than the central galaxy out to about 150 kiloparsecs. Models of stellar populations connect these near-infrared colours mainly to the abundance of elements heavier than helium, rather than stellar age. The models suggest that the central galaxies’ stars are richer in these elements than the Sun, while the diffuse stars are poorer. The colour trend is robust, but the inferred element abundances depend on which model and colour are used. The results support a picture in which central galaxies grow by mergers, while the diffuse light grows as gravitational forces pull stars from the outer regions of massive companion galaxies.

Young explorerGalaxies live in big groups, with a faint glow spread around them. Scientists combined pictures of 168 groups and found that this glow gets bluer compared with the big galaxy in the middle. Using models of stars, they think the glowing stars have fewer heavy ingredients than stars in the middle galaxy. The exact amounts depend on the model they use. This fits the idea that some stars were pulled away from the edges of nearby galaxies, but it does not prove that is how they got there.

Evaluating Zero-Shot Anomaly Detection for Identifying Unusual Galaxy Morphologies in CEERS and NGDEEP

T. B. Surakan, J. S. Kartaltepe, R. Pattnaik+7 more

AstronomerThe study applies AdaCLIP, a CLIP-based zero-shot anomaly-detection model adapted using non-astronomical datasets, to 38,853 galaxies in CEERS and NGDEEP without galaxy-specific anomaly-detection training or morphological labels. It extracts anomaly scores and 768-dimensional feature embeddings and compares the scores with GALFIT and statmorph measurements. The embeddings show structure associated with both galaxy morphology and observational properties. Anomaly scores exhibit modest trends with asymmetry, concentration, M20, and size, but weaker or less consistent trends with Sérsic index, axis ratio, smoothness, and Gini coefficient. These findings suggest potential for scalable searches for unusual morphologies, including in future Roman surveys, rather than establishing anomaly scores as definitive morphological classifications.

PublicResearchers tested an artificial-intelligence tool on images of 38,853 galaxies from the CEERS and NGDEEP surveys to help identify unusual galaxy shapes. The tool had been adapted using non-astronomical examples, without training specifically on unusual galaxies or using galaxy-shape labels. Its scores showed modest relationships with some established measurements of galaxy structure, such as asymmetry and size, but weaker or less consistent relationships with others. The patterns it extracted also reflected observational properties, not just galaxy shapes. The results suggest the approach could help search large image collections, including future Roman Space Telescope surveys, but do not establish that a high score reliably identifies an unusual galaxy.

Young explorerGalaxies can have many different shapes. Scientists tried a computer helper on pictures of nearly 39,000 galaxies to look for shapes that stand out. The helper had learned from things that were not galaxies. Its scores matched some ways scientists measure galaxy shapes a little, but matched other ways less well. How the pictures were taken mattered too. The helper might make searching lots of galaxy pictures easier, but its scores are not a sure answer.

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

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

AstronomerJWST/NIRSpec medium-resolution spectroscopy of COLA1 at z=6.6 reveals a blue UV continuum, strong NIV] emission, stellar P Cygni profiles, and broad HeII, alongside a redder rest-optical continuum and broad Balmer emission with absorption resembling Little Red Dot (LRD) spectra. UV population fits statistically favor models including very massive stars, with an adopted upper mass limit of 300 solar masses; the best fit has a stellar mass of approximately 10^8 solar masses and an age of 2.4 ± 0.8 Myr. Evolving this model predicts 1–2 magnitudes of UV fading in roughly 5 Myr, potentially yielding a typical V-shaped LRD spectrum. Inferred abundances are log10(N/O) = −0.07 ± 0.05 and log10(C/O) = −0.64 ± 0.11. Independent NIV] and CIII] density diagnostics require distinct zones with electron densities ≳10^6.5 and ≲10^3.5 cm−3, respectively. The dense-zone estimate log10(N/C) > 1.3 at 2σ calls for extreme enrichment, with rapidly rotating very massive stars, tidal disruption events, or supermassive stars suggested as possible mechanisms. Runaway stellar collisions seeding an intermediate-mass black hole are a speculative interpretation, not a demonstrated outcome.

PublicNew JWST observations of the distant galaxy COLA1 bring together several unusual features: bright ultraviolet light, exceptionally nitrogen-rich gas, and visible-light spectral features resembling those of objects called Little Red Dots. Models of the ultraviolet spectrum favor a very young stellar population containing stars more than 100 times the Sun’s mass, although this is a model-based inference rather than a direct count of such stars. The best-fitting population is about 2.4 million years old. Gas diagnostics indicate both a very dense region and a much less dense one, with especially extreme nitrogen enrichment relative to carbon inferred in the dense region. Several possible sources of this enrichment are proposed, but none is established. The stellar model predicts that COLA1’s ultraviolet light could fade substantially over about five million years, making its spectrum look like a typical Little Red Dot. The authors also speculate that repeated stellar collisions might have helped form a black hole; the observations do not demonstrate that this happened.

Young explorerAstronomers used the JWST telescope to study a very faraway galaxy called COLA1. Its light gives clues that it has very young, giant stars and gas with an unusually large amount of nitrogen compared with carbon. Some gas is packed much more tightly than other gas. A computer model suggests the galaxy’s ultraviolet light could grow dimmer over millions of years, making it look like galaxies nicknamed Little Red Dots. The scientists wonder if stars crashing together could have helped make a black hole, but they have not shown that this happened.

The Structural Anatomy of Galaxies: Environmental Dependence of Morphological and Quenching Evolution at 0.1 < z < 0.5

Can Xu, John D. Silverman, Qiusheng Gu+12 more

AstronomerUsing HSC-SSP imaging and DESI DR1 spectroscopy, this observational study compares spectroscopically confirmed satellites in X-ray-selected eROSITA clusters at 0.1<z<0.5 with stellar-mass- and redshift-matched field galaxies. It measures dust-corrected Hα SFRs, light-weighted effective radii, bulge-to-total light ratios, and Dn4000. UVJ-star-forming galaxies are divided at log(sSFR_Hα) = −10.5 yr−1 into active and Hα-low, or green-valley, populations. Cluster star-forming galaxies show modest SFR suppression and weak structural offsets. The strongest joint differences occur in low-mass green-valley satellites at projected R<0.5R500: lower SFRs, smaller light-weighted sizes, higher B/T, and higher Dn4000 than matched field counterparts. Quiescent galaxies have weaker structural offsets but positive Dn4000 residuals. A Mahalanobis statistic using matched residuals and a field–field reference covariance confirms that the multivariate offset peaks for low-mass green-valley galaxies and decreases with projected radius. SFR suppression extends farther radially than the structural offsets, suggesting a broader environmental reach for star-formation suppression. These comparisons indicate the strongest coupling between quenching and structural differences in the Hα-low transition population, rather than directly tracking individual galaxies through transformation.

PublicThis study compares galaxies in clusters with galaxies of similar stellar mass and redshift outside clusters, asking how their surroundings relate to star formation and visible structure. The clearest differences appear in lower-mass cluster galaxies that still have star-forming colors but are forming relatively few stars according to their hydrogen emission. Especially near cluster centers in projection, these galaxies form stars more slowly, look more compact, and have a larger fraction of their light in a central bulge than comparable galaxies outside clusters. Their spectra also show differences in their stellar populations. More actively star-forming cluster galaxies show modestly reduced star formation but little structural difference. Reduced star formation is seen over a wider range of distances from cluster centers than the structural differences. This suggests that cluster environments can affect star formation more widely than galaxy structure. The observations link the strongest combined changes to a transitional population, but do not directly follow individual galaxies changing over time.

Young explorerGalaxies are huge groups of stars. Some live in crowded groups called clusters. Astronomers compared them with similar galaxies outside those crowds. Some smaller galaxies near the middle of a cluster were making fewer new stars, looked more compact, and had more of their light coming from the middle. The differences were clearest in galaxies that seemed to be slowing down their star-making. This hints that living in a crowded place can matter, but the astronomers did not watch each galaxy change.

Simulation-Informed High-Velocity Dark Matter in the Effective Theory of Direct Detection

Xiuyuan Zhang, Gonzalo Herrera, Andreas Thoyas+1 more

• High Energy Physics - Phenomenology

AstronomerThe study constructs a local dark matter velocity distribution by combining an empirically motivated Milky Way reconstruction based on Gaia stellar kinematics with the best Large Magellanic Cloud analogue in the FIRE-2 simulations. This combined model contains no local dark matter faster than approximately 900 km/s, compared with debris reaching approximately 950 km/s in the commonly used Au-25 simulation. The authors compare their distribution with Au-25 and the Standard Halo Model across all non-relativistic effective-field-theory operators for elastic and inelastic dark matter–nucleon scattering. As an illustrative application, interpreting the high-energy event observed in the LUX-ZEPLIN extended search as inelastic dark matter, while requiring compatibility with the absence of signal in adjacent energy sidebands, yields inferred mass splittings that differ by up to approximately 130 keV between assumed velocity distributions. This is not a dark matter detection claim; it demonstrates sensitivity to the modeled high-velocity tail and motivates higher-resolution simulations for future signal interpretation and robust limits.

PublicHow fast nearby dark matter moves can strongly affect what underground searches could detect, especially when a collision needs extra energy. The researchers used Gaia measurements of stellar motions to reconstruct a model of the Milky Way’s dark matter, then added a simulated contribution associated with a Large Magellanic Cloud analogue. Their combined model has no nearby dark matter moving faster than about 900 kilometers per second; this is a modeling result, not a direct measurement of dark matter speeds. They compared its implications with two commonly used models. In an illustrative interpretation of a high-energy event observed by LUX-ZEPLIN, the assumed speeds changed the inferred energy gap between dark matter states by as much as about 130 kiloelectronvolts, while still requiring consistency with the lack of signals at neighboring energies. The event is not established here as dark matter. The study argues that more detailed simulations are needed to interpret possible future signals reliably.

Young explorerScientists are looking for invisible stuff called dark matter. How fast it moves matters: a faster bit could give a detector a bigger bump. The researchers used measurements of moving stars and computer pretend galaxies to work out how dark matter might move near us. Different guesses about the fastest bits changed what one bump seen in a detector could mean. They do not know that dark matter made that bump. Better computer models could help them understand future clues.

Recovering 3D Magnetic Turbulence from Single-frequency Faraday Screens

Aliaksandr Melnichenka, Alex Lazarian, Dmitri Pogosyan

AstronomerUsing MHD simulations and synthetic turbulence spectra, the authors test the spectrum of polarization directions at a single frequency as a turbulence diagnostic for a distant synchrotron-emitting volume viewed through a separate turbulent Faraday-rotating screen. They compare the results with analytical expectations and with the wavelength-derivative diagnostic previously explored by Lazarian & Pogosyan. In these tests, the directional spectrum is more sensitive to turbulence in the Faraday-rotating volume. The authors also provide an observational criterion for determining whether the diagnostic samples the emitting region or the rotating screen. The work offers a route to extracting turbulence statistics from single-band radio polarimetry, rather than reporting an application to astronomical observations.

PublicTurbulent regions can leave patterns in the polarization—the orientation of the waves—of radio light. This study models light produced in one region and then passing through another turbulent region that rotates its polarization. Using simulations and artificially generated turbulence patterns, the researchers test whether polarization directions measured at just one radio frequency can reveal the turbulence. Compared with an earlier diagnostic based on how polarization changes with wavelength, their method is more sensitive to turbulence in the intervening region. They also give observers a criterion for deciding which region the method probes. The results suggest a way to use existing and future single-band radio measurements, but the abstract does not report a test on real astronomical data.

Young explorerRadio light can have a direction, a little like an arrow. When it travels through a messy, swirling place, that arrow can turn. The scientists used computer models to see whether patterns in the arrows could tell us about the swirls. Their tests showed that the patterns are especially useful for studying the place the light passes through. They also made a guide to help tell whether the patterns describe that place or the place where the light began. Astronomers could use this idea with radio measurements.

Diversity in Lyman Continuum Escape at z∼0.3 Revealed by WISE Infrared Observations

Fang-Ting Yuan, Zhen-Ya Zheng, Chunyan Jiang+1 more

AstronomerUsing WISE data, the authors examine 20 local star-forming galaxies classified as strong LyC leakers (LyC signal-to-noise >3 and escape fraction >5%) and 69 non-leakers. Eight strong leakers have mid-IR detections. IR-undetected strong leakers have higher O32 ratios, bluer UV slopes, and lower metallicities than the other subsamples. IR-detected strong leakers instead resemble non-leakers in these diagnostics, despite a median LyC escape fraction of about 12%. These observations indicate that substantial LyC escape can coexist with IR emission and need not require extreme UV or optical properties. Lyα profiles and morphology suggest, but do not establish, different escape mechanisms for the IR-detected and IR-undetected classes. The proposed considerable contribution of dusty star-forming galaxies to the reionization photon budget is an implication, not a direct measurement.

PublicRadiation escaping from star-forming galaxies helped ionize gas in the early universe. This study uses WISE infrared observations to examine nearby galaxies: 20 known to let substantial amounts of this radiation escape and 69 classified as non-leakers. Eight of the strong leakers are detected in mid-infrared light. Unlike the strong leakers not detected in infrared, these eight have ultraviolet and optical properties similar to the non-leakers, yet their median escape fraction is about 12%. The findings show that galaxies do not need the most extreme ultraviolet and optical characteristics to release substantial ionizing radiation. Their shapes and hydrogen emission-line profiles hint that radiation may escape differently in the two groups. The authors suggest that dusty galaxies could have made an important contribution to early cosmic ionization, but this study does not directly measure that contribution.

Young explorerSome galaxies let out special light that can change the gas around them. Scientists studied nearby galaxies and found that some letting this light out also shine in infrared light, which our eyes cannot see. Those galaxies did not look especially unusual in the other kinds of light the scientists checked. This means galaxies can let special light escape in more than one kind of setting. There are clues that the light may get out in different ways, but scientists are not sure yet. Dusty galaxies might also have helped change the gas in the very young universe.

ML in Astrophysical Turbulence I: Predicting Prestellar Cores in Magnetized Molecular Clouds using eXtreme Gradient Boosting

Nikhil Bisht, David C. Collins

AstronomerAn XGBoost framework trained on approximately 2.1 million tracer particles from self-gravitating, turbulent MHD simulations predicts prestellar gas trajectories and ranks susceptibility to gravitational core formation. Using instantaneous position, velocity, density, and magnetic field inputs, trajectory regression achieves R² > 0.99 over 0.25 free-fall times, approximately 0.31 Myr, while classification achieves AUC = 0.975. However, precision at absolute binary thresholds is only 37%, limiting reliable identification of individual collapsing parcels. SHAP analysis identifies density, kinetic energy, and magnetic field magnitude as dominant model inputs, with a sharp nonlinear density threshold above which stronger magnetic fields increase predicted collapse susceptibility; this describes model behavior, not an independently established physical criterion. The authors argue that point-wise inputs lack the spatial information needed to evaluate collapse-inhibiting differential terms, including pressure gradients and magnetic field curvature. The results support potential use in advective subgrid modeling, while motivating spatial architectures for absolute core-formation criteria; they are simulation-based, not observational findings.

PublicResearchers trained a machine-learning system to follow gas and predict which portions might collapse into dense cores where stars can form. Their tests used computer simulations of turbulent, magnetized clouds, not observations of real clouds. The system predicted gas motion very accurately over about 310,000 years and ranked gas well by its tendency to collapse. But ranking was much more successful than making definite yes-or-no predictions: at the tested decision thresholds, only 37% of gas labeled as forming a core actually did so in the simulations. Analysis of the model showed that density, energy of motion, and magnetic field strength strongly influenced its predictions. The key limitation is that information at a single point does not describe the surrounding pressure and magnetic structures that can prevent collapse. The approach could help make simulations more efficient, but reliable collapse decisions require models that also account for spatial surroundings.

Young explorerScientists taught a computer to follow tiny bits of gas in a pretend space cloud. It was very good at guessing where the gas would move. But it often guessed wrong about which bits would squeeze together into places where stars could form. Looking at one bit of gas is not enough: what is happening around it matters too. The scientists say future computer helpers need to look at the nearby gas as well.

The missing ultra-faint satellites of the Milky Way

Isabel M.E. Santos-Santos, Carlos S. Frenk, Julio F. Navarro

AstronomerThe study combines the high-resolution Aquarius-A N-body simulation of a roughly 10^12-solar-mass ΛCDM halo with GALFORM to model satellites of Milky Way-like galaxies. Galaxy formation is restricted to subhalos whose peak circular velocity exceeds the hydrogen-cooling threshold. The model follows unresolved “orphan” galaxies and treats dark matter and stellar tidal stripping while accounting for subhalo survival due to cuspy density profiles. It reproduces the massive end of the observed Milky Way satellite mass function and predicts no more than a few hundred satellites ever accreted, even extending to arbitrarily low luminosity. Many ultra-faint dwarfs with M_V > -5 are predicted to remain undiscovered, preferentially outside the innermost host regions, with properties overlapping recently discovered ultra-faint compact satellites. Conditional on the faintest dwarfs being initially as compact as these objects, many compact satellites are predicted to be dark matter-dominated dwarfs surviving within subhalo cusps, with velocity dispersions of 1–3 km/s and densities of 10^10–10^11 solar masses per cubic kiloparsec. These are model predictions; confirmation would support cuspy ΛCDM halos and the hydrogen-cooling threshold for galaxy formation.

PublicA computer simulation paired with a galaxy-formation model suggests that many extremely faint companion galaxies of the Milky Way remain undiscovered. The model matches the observed numbers of more massive companions and predicts that a Milky Way-like galaxy should have acquired no more than a few hundred companions over its history, even counting the faintest ones. The predicted missing galaxies tend to avoid the galaxy’s innermost regions. Some could resemble recently discovered tiny, compact satellites. If the faintest galaxies began that compact, the model suggests many of these satellites could be galaxies dominated by dark matter, protected from being pulled apart by sharply concentrated dark matter centers. This identity is not established by the simulation. Confirming the predictions would support both such dense central structures and the model’s requirement that a small dark matter halo must cross a hydrogen-cooling threshold before forming a galaxy.

Young explorerOur Milky Way has little galaxies around it. Scientists used a computer model to explore how many very faint ones might still be hiding. The model suggests many have not been found yet. Some tiny objects already discovered might be little galaxies held together mostly by dark matter, which we cannot see. If they started out very small and packed together, dense dark matter centers could have helped them survive. Scientists still need to check whether this idea is right.

Stardust Galaxies at z>9: A Dust-Origin Transition Behind the Excess of UV-Bright Galaxies

D. Burgarella, V. Buat, A.K. Inoue+9 more

• Cosmology and Nongalactic Astrophysics

AstronomerJWST observations suggest that galaxies at z > 9 may contain predominantly low-opacity, supernova-produced dust before efficient interstellar grain growth begins. The authors test whether this transition, alongside evolving star-formation efficiency, can explain very low attenuation and the abundance of UV-bright galaxies. Their attenuation framework combines extinction laws for reverse-shock-processed supernova dust, metallicity- and dust-to-metal-dependent opacity scalings, and porous radiative-transfer geometries permitting partial UV leakage. Extinction-based, gas-based, and hybrid prescriptions connect supernova-dominated and grain-growth regimes without requiring large-scale gas evacuation. The observed far-UV attenuation–stellar mass relation is best reproduced with an intrinsic dust opacity of 10^3–10^4 cm²/g, yielding very low attenuation even in gas-rich galaxies and reproducing the extremely low-attenuation galaxies that dominate observed z > 9 samples. Applied to intrinsic UV luminosity-function models, the supernova-dominated and hybrid prescriptions mainly suppress the brightest galaxies and bring predictions into agreement with JWST measurements without extreme star-formation efficiencies or dust-free interstellar media. These model results support, but do not establish, a transition in dust origin and opacity as the explanation for the UV-bright excess.

PublicJWST has found more ultraviolet-bright galaxies in the early universe than most earlier predictions expected, and many show very little dimming by dust. This study tests whether the kind of dust matters more than simply how much is present. The authors model dust made by exploding stars, before dust grains grow efficiently in interstellar gas. Their framework also allows some ultraviolet light to escape through gaps. Low-opacity dust best matches the observed relationship between ultraviolet dimming and stellar mass, allowing galaxies to remain rich in gas yet show little dimming. When applied to galaxy-brightness models, the proposed dust prescriptions bring predictions into agreement with JWST measurements without requiring unusually extreme star formation or an absence of dust. This suggests an explanation involving changing dust properties, rather than proving what the dust is made of.

Young explorerSome very young galaxies look brighter than scientists expected. Dust can dim their light, but not all dust blocks light equally well. Scientists tried a model with dust made by exploding stars and gaps that let light through. It matched what JWST sees without needing to remove the galaxies’ gas or all their dust. That is a promising explanation, but it is not proof.

A Unified HI Rotation Curve Database for 122 Dwarf and Irregular Galaxies

David C. Flynn

• Instrumentation and Methods for Astrophysics

AstronomerThis data-resource paper unifies HI rotation information for 122 dwarf and irregular galaxies from LVHIS (32), VLA-ANGST (29), LITTLE THINGS (26), and the WALLABY DR2 kinematic catalogue (35). It supplies standardised kinematic parameters, distances, morphological classifications, and rotation-curve data in documented JSON, JSONL, and CSV formats for cross-survey analysis and retrieval-augmented generation applications. Quality tiers separate 26 galaxies with published tilted-ring curves and per-point uncertainties from 96 entries based on automated pipelines, single-ring fits, or profile widths; the entries therefore do not all provide equally detailed rotation constraints. Three worked query examples include evaluation of the omega estimator for DDO 154. No new dynamical model is proposed. Corpus v1.3 incorporates corrections to LITTLE THINGS, WALLABY, and LVHIS entries and an LVHIS reference; the database and computation scripts are available on Zenodo.

PublicThe authors have brought together existing information about the rotation of 122 dwarf and irregular galaxies, using observations of neutral hydrogen gas from four survey sources. The database puts rotation data, distance estimates, galaxy classifications, and other motion-related information into consistent, computer-readable formats, making it easier to compare surveys and retrieve information. Its entries vary in detail: 26 galaxies have published rotation curves with uncertainty estimates for each point, while the other 96 have automated or less detailed rotation information. Three examples show how to query the collection, including an analysis of the galaxy DDO 154. This is a shared data resource, not a new theory of galaxy motion. The described release corrects several parts of the original collection, and the data and calculation scripts are available on Zenodo.

Young explorerGalaxies are huge groups of stars and gas that turn around. These researchers gathered information about how gas moves in 122 small or irregularly shaped galaxies and put it into one organised collection for others to use. Some galaxies have more detailed information than others, and some measurements show how uncertain they are. The team also fixed mistakes in earlier versions and showed ways to search the collection. They made a useful collection, not a new explanation for why galaxies move.

The role of major mergers in triggering super-Eddington accretion

Riccardo Caleno, Tommaso Zana, Raffaella Schneider+6 more

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena

AstronomerMotivated by JWST observations of black holes with several million solar masses at z > 8, this study tests whether a major merger can sustain super-Eddington accretion in relatively low-mass halos. High-resolution cosmological zoom-in simulations follow a merger at z ~ 11 between halos of approximately 10^9 solar masses, varying black-hole seeding and radiative and kinetic feedback prescriptions across three accretion regimes. With the adopted feedback prescription, gas accretion is efficiently suppressed and black-hole growth remains limited. Merger-driven central gas inflows do not produce sustained super-Eddington accretion or a substantial accretion-rate enhancement. Post-merger super-Eddington episodes occur only with black-hole feedback entirely disabled; the only significant super-Eddington episodes occur immediately after seeding. Kinetic feedback is the dominant regulator among the channels tested. These simulation results apply to the relatively low-mass halos and feedback prescriptions studied, rather than establishing a universal limit on merger-driven growth.

PublicJWST has revealed black holes weighing several million times as much as the Sun in the early Universe. One proposed explanation is that they grew through unusually rapid feeding. This study uses computer simulations to test whether a collision and merger between two relatively low-mass concentrations of dark matter could sustain such feeding. Although the simulated merger pushes gas toward the center, energy and outflows from the black holes suppress their gas supply, preventing substantial growth. Outflows are the strongest regulating influence among the feedback mechanisms tested. Rapid-feeding episodes after the merger appear only when black-hole feedback is completely switched off, and the only significant rapid-feeding episodes occur just after black holes are introduced into the simulation. For these simulated systems, the merger alone does not provide the proposed growth boost.

Young explorerScientists used a computer to see whether two groups of space stuff joining together could help black holes eat lots of gas and grow. In their model, gas moved inward, but energy and winds from the black holes kept them from eating very much. Joining together did not make them grow much faster. This is what happened in the computer test, not something the scientists watched happen in space.

Black hole populations and hierarchical growth across the AGN parameter space

Maria Paola Vaccaro, Michela Mapelli, Alessandro Alberto Trani+1 more

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena

AstronomerThis study models, rather than directly observes, stellar-origin binary black hole formation and evolution in AGN disks using an updated semi-analytical framework. It follows capture, migration, pairing, gas-driven hardening, binary–single encounters, and mergers, exploring supermassive black hole mass, Eddington ratio, and disk viscosity. Simulations weighted by observed low-redshift AGN properties produce an intrinsic merger population with hierarchical growth beyond the pair-instability mass gap into the intermediate-mass range. Growth is more efficient at viscosity parameter alpha = 0.01; higher viscosity suppresses massive remnants. Merger efficiency generally rises with Eddington ratio, while its dependence on central black hole mass is non-trivial. Predicted signatures include increasingly unequal component masses at high primary mass, a correlation between primary mass and effective-spin magnitude, and strong sensitivity of effective spins to the fraction of binaries born prograde versus retrograde. Modeled systems are broadly consistent with GW190521 and GW231123, without establishing their origin. The high-mass tail and spin signatures persist across the tested model variations except when gas hardening is disabled.

PublicCould gas disks around active galactic nuclei help black holes meet and merge repeatedly? This study explores that proposed pathway with a mathematical model and simulations, weighted using observed properties of nearby active galaxies. In the models, repeated mergers can build black holes beyond a mass gap associated with pair instability and into the intermediate-mass range. Less viscous disks favor this growth, while higher viscosity limits it. The predicted most massive pairs tend to have more unequal masses, and their spin patterns depend strongly on how their orbits are oriented relative to the disk. Some modeled systems broadly resemble the massive merger events GW190521 and GW231123, but this does not prove those events formed in active galactic nuclei. The main mass and spin patterns survive the tested modeling changes except when gas-driven orbital shrinking is removed.

Young explorerScientists used a computer model to ask whether black holes can meet in a swirling disk of gas and join together again and again. In their model, this could make much bigger black holes. Gas helping the pairs move closer was important for the model’s main patterns. This is a possible story for how some big black holes form, not something the study watched happen.

The Lifecycle and Emission Properties of PAHs in Cosmological Hydrodynamic Galaxy Formation Simulations

Desika Narayanan, Paul Torrey, Massimiliano Parente+16 more

AstronomerThis study models PAH evolution and mid-infrared emission in 40 cosmological zoom-in galaxies from z=6 to 0, coupling interstellar dust evolution to single-photon excitation calculations. PAHs are approximated as carbonaceous grains smaller than 13 angstroms. Assuming dust grains are large at formation, grain-grain shattering produces PAHs within the interstellar medium. In the simulations, a growing diffuse-gas mass fraction increases collision velocities and raises the PAH mass fraction, qPAH, from approximately 5 × 10^-4 at z≈4 to 10^-2 at z≈0. Enhanced production in diffuse gas also yields an inverse relationship between qPAH and molecular gas fraction. PAH luminosity per unit PAH mass scales with radiation-field intensity but anticorrelates with qPAH: galaxies with higher star-formation-rate surface densities have denser gas that suppresses shattering. Thus, qPAH and the PAH-to-far-infrared luminosity ratio need not evolve together. Simultaneous enrichment and growth of the diffuse interstellar component produce a PAH–metallicity relation that reproduces observations across z=0–2. The modeled PAH luminosity relations with star formation and molecular gas reflect both reservoir size and excitation efficiency. These simulation results suggest, rather than establish observationally, that diffuse-gas grain shattering drives cosmic PAH abundance evolution.

PublicWhy do galaxies contain different amounts of the tiny carbon-based dust particles called PAHs? This study explores that question using simulations of 40 galaxies and calculations of their infrared light. If dust grains start out large, the model allows collisions to break them into PAH-sized pieces. As the simulated galaxies evolve, more of their gas becomes diffuse, where faster grain collisions make this fragmentation more effective. The model reproduces an observed connection between PAH abundance and galaxies’ enrichment in heavier elements. It also shows why PAH brightness is not a simple measure of how much PAH material exists: stronger radiation makes each unit of PAH material shine more brightly. The results suggest that collisions in diffuse gas could be the main process controlling PAH abundance over cosmic time, but this is a model-based interpretation.

Young explorerGalaxies have tiny bits of carbon dust that can glow. Scientists made computer versions of galaxies to explore where these bits come from. If the dust starts in bigger pieces, the model shows that crashes can break it into tiny ones. Stronger light can make the tiny bits glow brighter, so brighter dust does not always mean more dust. This is an explanation from a computer model, not proof.

The Stellar "Snake"-V: the census within 3 kpc in the Solar Neighborhood

Xiang-Ming Yang, Ju-Yong Zhang, Hai-Jun Tian

• Instrumentation and Methods for Astrophysics

AstronomerThe authors present a Gaia DR3 source-level catalogue of 1,180 candidate Stellar Snake complexes within 3 kpc of the Sun, comprising 4,196 base nodes and 692,408 unique member-star entries. A Snake is defined as a coherent association of stellar overdensities with consistent positions, kinematics, orbital invariants, and ages, not as a single gravitationally bound system. The pipeline searches Gaia sources directly rather than using known open clusters as seeds, extracts statistically significant non-overlapping nodes, estimates homogeneous parameters with a PointNet regressor, and links nodes in a nine-coordinate space before FoF-topology checks and boundary resolution. Parameters are compared with external cluster catalogues and spectroscopic benchmarks. A graph-based Snake Reliability Index assigns Gold/Silver/Bronze structural-coherence grades, while a spatial-kinematic diagnostic flags candidate subdivisions. Reported population patterns include an age–metallicity relation in jointly inferred parameters, a declining upper envelope of observed member-star counts with older inferred age, and a projected association of young nodes with nearby spiral-arm loci and the Radcliffe Wave. These are catalogue-level patterns, not demonstrations of common origin, gravitational binding, or causal connections.

PublicUsing Gaia DR3 observations, the researchers assembled a catalogue of 1,180 candidate extended stellar groupings within about 3,000 parsecs of the Sun. They call these groupings “Stellar Snakes”: connected concentrations of stars with consistent locations, motions, estimated ages, and orbital properties, rather than single objects held together by gravity. Their method searches individual Gaia sources instead of starting from known star clusters, helping it recover sparse structures and stellar bridges. The catalogue contains 692,408 unique member-star entries, and the team grades how coherently each grouping fits together. The inferred properties show a pattern between age and metal content. The largest observed membership counts also decrease toward older estimated ages, and young components show a projected association with nearby spiral arms and the Radcliffe Wave. These patterns do not by themselves establish physical connections or explain how the groupings formed; the catalogue provides a basis for investigating those questions.

Young explorerThe researchers used Gaia’s star observations to make a list of 1,180 possible big star groups near our Sun. They call them “Stellar Snakes.” These are smaller bunches of stars that seem to fit together because of where they are, how they move, and how old they seem to be. They are not necessarily held together as one big group by gravity. Some young bunches appear near spiral arms in our galaxy and a feature called the Radcliffe Wave, but looking close together does not prove they are connected. The list can help scientists study how big families of stars form and change.

The Quasar Feedback Survey: Ionised Outflows in type 2 QSOs with MUSE data

M. Bianchin, C. M. Harrison, T. Costa+13 more

AstronomerThe study analyses ionised gas in 18 luminous obscured QSOs at 0.085<z<0.2 using VLT/MUSE and low- and high-resolution VLA observations. Non-parametric [O III]5007 kinematics identify outflow-dominated spaxels using a W80 threshold measured from unresolved nuclear spectra. Radio and W80 peaks generally coincide in a qualitative map comparison. Extinction-corrected [O III] fluxes provide a gas-mass proxy, with outflow properties estimated using both flux-weighted global quantities and radial-profile peaks. [Ar IV]4711,4740, detectable only in integrated r=1.5-arcsecond spectra, yields electron densities of 500–27,700 cm^-3 and inferred mass-outflow rates of 0.03–4.17 solar masses per year. The authors emphasise that accurate density determination changes inferred outflow rates and kinetic powers by about 1 dex. A positive electron-density–outflow-velocity correlation is interpreted as compression at higher velocities, but requires testing across other luminosity and redshift ranges before broader conclusions can be drawn.

PublicObservations of 18 luminous, obscured quasars reveal a link between the density and speed of gas flowing outward: faster outflows tend to have denser gas. The researchers interpret this as possible compression of the gas, rather than proof of how the relationship arises. They also find that peaks in radio emission generally line up with peaks in the spread of gas velocities. Using emission lines to estimate gas density, they infer outflow rates of 0.03–4.17 times the Sun’s mass per year. The density estimate matters greatly: it can change the inferred outflow rate and energy carried by roughly a factor of ten. The density–speed relationship still needs testing in quasars with other luminosities and at other redshifts; it could help inform future simulations.

Young explorerAstronomers looked at gas blowing away from 18 very bright objects called quasars. They found that faster-moving gas tended to be more tightly packed. They think the gas might be getting squeezed, but they need to check more quasars to learn whether that idea is right. Knowing how tightly the gas is packed also helps them work out how much gas is blowing away.

Rubin J122659.4+090236: An Extremely Low Surface Brightness Galaxy Candidate Discovered in the Rubin LSST Early Data Preview 2

Dipanjan Mitra, Kanak Saha, Sugata Kaviraj+28 more

AstronomerRubin Observatory imaging of the interacting NGC 4410 system, released through Cosmic Treasure Chest, revealed the exceptionally low-surface-brightness galaxy candidate Rubin J122659.4+090236. Two-dimensional Sérsic fits to g, r, and i images indicate a nearly round morphology, n ~ 0.4, an effective radius of ~6 arcsec, and central surface brightnesses of 27.52 ± 0.04, 27.62 ± 0.07, and 27.04 ± 0.08 mag arcsec−2, respectively. EAZY photometric-redshift fitting favours z ~ 0.3, but a restricted fit over 0 < z < 0.1 without a redshift prior also permits z ~ 0.028, consistent with NGC 4410. The unresolved distance leaves substantially different interpretations open: a diffuse dwarf-like system or an exceptionally extended background LSBG. The discovery demonstrates Rubin’s sensitivity to diffuse sources; large LSST samples and their use in galaxy-evolution studies remain prospective.

PublicAstronomers have spotted a candidate galaxy whose light is spread so thinly across the sky that it is exceptionally faint per unit area. Named Rubin J122659.4+090236, it was found in publicly released Rubin Observatory images of the interacting NGC 4410 system. Image modelling suggests it is nearly round, with a shallow brightness profile. Its distance is uncertain: fitting its light in different colour bands favours a more distant location, but a separate fit limited to nearby distances also allows it to lie with NGC 4410. Depending on which distance is correct, it could be a diffuse dwarf-like galaxy or an exceptionally extended galaxy in the background. The finding shows Rubin’s ability to detect very diffuse objects and points to the possibility that the LSST survey could discover many more.

Young explorerAstronomers found something that might be a galaxy, with its light spread out like a very faint, round smudge. They spotted it in pictures from the Rubin Observatory. They do not yet know how far away it is. One way of checking suggests it is farther away, but another check allows it to be closer. If it is closer, it could be a small, spread-out galaxy; if it is farther away, it could be much bigger. The pictures show that Rubin can spot very faint smudges like this, and astronomers hope to find many more.

Discovery of an isolated RELHIC Candidate: J1351+0039

Jin-Long Xu, Alejandro Benitez-Llambay, Ming Zhu+6 more

• Cosmology and Nongalactic Astrophysics

AstronomerJ1351+0039 is a newly identified isolated dark-galaxy candidate found in a blind FAST HI survey and examined with deep DESI Legacy Survey optical imaging. Its compact HI structure has a systemic velocity of V_LSR = 429.0 km/s and an inferred HI mass of 4.5 × 10^5 solar masses at a distance of 3.6 Mpc. No optical counterpart is detected down to a g-band surface-brightness limit of 28.1 mag arcsec^-2, corresponding to a stellar-mass limit of 1.2 × 10^5 solar masses. The estimated dynamical mass is 1.3 × 10^8 solar masses; the reported dark-to-baryonic mass ratio of 200 implies strong dark-matter dominance. Weak rotation is detected, but internal velocity dispersion dominates, indicating pressure support. The authors interpret these properties as making J1351+0039 a promising isolated Reionization-Limited HI Cloud (RELHIC) candidate, rather than an established member of that class. The optical nondetection constrains, but does not establish the complete absence of, stars.

PublicAstronomers have discovered J1351+0039, an isolated cloud of hydrogen gas that may be a galaxy with few or no stars. The FAST radio telescope detected its gas, but deep DESI Legacy Survey images reveal no visible counterpart within the images’ detection limits. At the reported distance of 3.6 megaparsecs, the hydrogen mass is inferred to be about 450,000 times the Sun’s mass. Estimates based on the gas motions suggest that dark matter overwhelmingly dominates the object’s mass. Although some rotation is detected, random internal motions provide most of its support. The researchers identify it as a promising candidate for a particular kind of gas cloud called a RELHIC. Its classification remains tentative, and stars too faint to detect are not ruled out.

Young explorerAstronomers found a little cloud of space gas using a radio telescope. They looked for stars in pictures but could not see any, though very faint stars might still be hiding there. The way the gas moves makes them think lots of invisible dark matter is there too. It might be a galaxy with few or no stars, but they are not sure yet.

SN Helios: A Multiply Imaged Type II Supernova Opening Time-Delay Cosmography beyond redshift of 3

Seiji Fujimoto, Conor Larison, Justin D. R. Pierel+63 more

• Cosmology and Nongalactic Astrophysics
• High Energy Astrophysical Phenomena

AstronomerSN Helios is a spectroscopically confirmed, strongly lensed Type II supernova at z=3.34 behind RXC J0018.5+1626, discovered in multi-epoch JWST/NIRCam imaging. NIRSpec spectroscopy reveals broad Hα emission with FWHM ≈7900 km/s and P-Cygni absorption blueshifted by 8800 km/s, alongside Hβ and He I features. Template fitting supports the Type II classification, while comparisons with local SNe II estimate a phase of 27.5±2.8 rest-frame days after B-band maximum. Independent lens models infer magnification of approximately 10–20 and predict another image in approximately 2–6 years, potentially enabling a time-delay measurement of H₀; that measurement has not yet been made. The host remains undetected in ultraviolet, optical, emission-line, and ALMA dust-continuum observations, making heavy obscuration unlikely. Its inferred de-lensed M_UV ≳ −13 supports, but does not establish, an elevated core-collapse rate per unit star formation in ultra-faint galaxies. Without multi-epoch observations, the transient could convincingly mimic a z≈16 Lyman-break galaxy, even with multiple medium bands. Its spectrum supplies an empirical template for vetting similar candidates.

PublicAstronomers have confirmed a distant exploding star, SN Helios, whose light is magnified by a foreground galaxy cluster. Its spectrum identifies it as a hydrogen-rich Type II supernova at redshift 3.34. Models of the cluster predict that another image of the explosion could appear in about two to six years. Measuring the delay could help determine the universe’s expansion rate, but this remains a future opportunity rather than a completed measurement. The star’s host galaxy has not been detected; the observations suggest it is extremely faint rather than heavily hidden by dust. This lends support to the idea that very faint galaxies produce more core-collapse supernovae per unit star formation. The discovery also highlights a pitfall: without observations at different times, this exploding star could be mistaken for a much more distant galaxy. Its measured spectrum can help astronomers check similar candidates.

Young explorerAstronomers found an exploding star called SN Helios. A big group of galaxies in front of it acts like a magnifying glass, making its light brighter. Their calculations say another view of the same explosion might arrive in two to six years. They cannot see the star’s home galaxy yet. Watching at different times helped them avoid mistaking the explosion for a galaxy much farther away.

A VLA Study of the Disturbed Massive Cluster PLCK G165.7 + 67.0 and Its Two Narrow Angle Tail Galaxies

Aurora Wilde, Eric F. Jimenez-Andrade, Brenda L. Frye+11 more

AstronomerVLA continuum observations at 15 and 6 GHz of six radio galaxies in the PLCK G165.7+67.0 cluster field resolve two cluster members into narrow-angle-tail sources. Both tails extend southwest, away from the cluster center of mass. Matched-resolution spectral-index maps show steepening along the tails, consistent with radiative aging. Measured source properties constrain two independent descriptions—a Mach cone model and a nonrelativistic hydrodynamic flow model based on Euler’s equation—which infer transverse velocities of approximately 2000 km/s for both galaxies. These are model-dependent estimates, rather than direct measurements of transverse motion. One source is the brightest cluster galaxy, with a measured radial velocity of −3300 km/s, implying an even higher three-dimensional speed when combined with its inferred transverse motion. Observation near core passage is proposed as a possible explanation for this high speed.

PublicMeasuring a distant galaxy’s sideways motion is difficult because its spectrum reveals only motion along our line of sight. This study uses bent radio jets as an indirect way to estimate sideways speeds. Radio images of six galaxies in a cluster field reveal two cluster galaxies with pairs of tails swept back toward the southwest, away from the cluster’s center of mass. Changes in the radio emission along the tails are consistent with aging of the emitting particles. Two different models of the tail shapes and gas flow estimate sideways speeds of about 2000 kilometers per second for both galaxies. These speeds are inferred from models, not directly observed. One is the cluster’s brightest galaxy and also has a large measured line-of-sight velocity. The authors suggest that its unusually high total speed might be explained if it is seen near passage through the cluster core.

Young explorerSome galaxies make long jets that can bend backward into tails as they move through gas. Scientists used radio pictures to find two galaxies with tails pointing the same way. They used two kinds of calculations to estimate how fast the galaxies move sideways. Both calculations suggested very fast motion, but this was an estimate, not a direct measurement. One galaxy might be moving so fast because it is passing near the middle of its galaxy group.

Collisional excitation of SiC₆ by helium: cross sections, rate coefficients, and astrophysical implications

Liman Tian, Ziyu Xiang, Chuangang Ning+1 more

AstronomerFollowing detections of SiC6 rotational transitions with j=26–40 in IRC+10216, this study calculates previously unavailable SiC6–He rotational excitation rates using a two-dimensional RCCSD(T)-F12 potential energy surface and the rigid-rotor approximation. Close-coupling (CC) calculations cover low rotational levels, while coupled-states (CS) rates extend to j=40 over 3–60 K. Although individual CC and CS rates differ by up to about a factor of two, particularly for transitions affected by weak coupling and resonances, they produce nearly identical excitation and brightness temperatures for the high-j transitions examined, including 19→18. This supports CS-based non-LTE modelling for the transitions tested, where CC calculations are computationally impractical. H2 collision rates are estimated by reduced-mass scaling of the He rates, rather than calculated directly. Fitting observed line fluxes while excluding heavily blended features gives best-fitting values of n(H2)=4.33×10^5 cm^-3 and N(SiC6)=8.11×10^11 cm^-2. The column density agrees with the earlier observational estimate of (7.9±1.5)×10^11 cm^-2, supporting the model’s consistency with observational constraints.

PublicSiC6 molecules have been detected through their rotational emission in IRC+10216, but interpreting that light requires knowing how collisions change the molecules’ rotation. The researchers calculated collision rates with helium and used an approximate scaling to estimate rates with molecular hydrogen. A less computationally demanding calculation produced almost the same predicted emission temperatures as a more demanding method for the transitions tested, even though some individual collision rates differed by about a factor of two. Using the estimated hydrogen rates, the team fitted the observed emission, leaving out features strongly mixed with other lines. Their best-fitting amount of SiC6 along the line of sight agrees with an earlier observational estimate. The agreement supports the modelling, although the hydrogen collision rates remain estimates rather than direct calculations.

Young explorerScientists have seen light from tiny molecules called SiC6 in a place in space called IRC+10216. To understand that light, they used calculations to work out how bumps with helium change the molecules’ spinning. Then they estimated what bumps with hydrogen would do. A quicker calculation gave almost the same light predictions as a harder calculation for the signals they checked. Their model also suggested an amount of SiC6 that matched an earlier estimate. That is a useful check, but some parts of the model are still approximate.

A Unified Model for the Gravitational Wave Background and Quasar Luminosity Functions

Cayenne Matt, Kayhan Gültekin, Ryan Hickox

AstronomerThe study fits bolometric quasar luminosity functions over 0.2 ≤ z ≤ 6.2 using posterior supermassive black hole mass functions inferred from the nanohertz gravitational wave background, constraining a double-power-law Eddington ratio distribution. Relative to a fiducial BHMF based on galaxies and a local black hole mass scaling relation, the GWB-inferred BHMFs reproduce the observed QLFs with lower Eddington fractions, without requiring significant super-Eddington accretion. Their fitted ERDFs have systematically lower break-points and marginally steeper high-Eddington-fraction slopes, and their best-fit QLFs better match the high-luminosity data. Both approaches yield significant redshift evolution in the ERDF break-point, peaking around z ∼ 2. These are model-fitting results rather than direct measurements of individual accretion rates. The GWB-based prescription is consistent with the electromagnetic and gravitational wave data considered, despite broader inconsistencies among existing BHMF estimates.

PublicDifferent ways of estimating how many supermassive black holes exist at different masses give conflicting answers. This study tests black hole populations inferred from the background of very-low-frequency gravitational waves against observations of quasar brightness. In these models, the gravitational-wave-based populations can explain the observed brightness distributions with lower relative feeding rates than a comparison model, without needing substantial feeding above the Eddington benchmark. They also fit the brightest quasars better. Both models suggest that the distribution of relative feeding rates changes over cosmic history. The findings show that one modeling approach can accommodate both light-based and gravitational-wave observations; they do not directly measure how fast individual black holes feed.

Young explorerScientists are trying to work out how many giant black holes there are and how fast they eat. They tested a model using clues from waves in space and the bright light made as black holes feed. The model could explain the light without needing the black holes to eat especially fast. That is a promising fit to the clues, not a direct look at each black hole’s meal.

Exploring the origin of slow-rotating pulsars: Emission from STARS simulated white dwarfs

Zenia Zuraiq, Banibrata Mukhopadhyay

• Solar and Stellar Astrophysics

AstronomerRecent observations include slow-rotating pulsars and long-period transients with periods of roughly 100–1000 seconds or longer. Under conventional dipole-driven neutron-star pulsar models, their periods and period derivatives imply magnetic fields above the Schwinger field. The authors explore magnetic white dwarfs as an alternative origin for some sources, noting that the observed periods are compatible with those of known white dwarfs. Using the STARS stellar evolution code, they simulate white dwarfs whose magnetic fields are enhanced by accretion after formation. They also briefly consider the more exotic possibility of super-Chandrasekhar white dwarfs. The authors interpret the expanded parameter space as providing a viable alternative explanation, not an observational identification of these sources as white dwarfs.

PublicAstronomers have observed sources whose signals repeat about every 100–1000 seconds, or even more slowly. Explaining them with conventional neutron-star pulsar models implies exceptionally strong magnetic fields. This study explores whether some could instead be magnetic white dwarfs, whose observed rotation periods are compatible with these slow signals. The researchers used computer simulations to model white dwarfs with magnetic fields strengthened by gathering material after they formed. They also briefly considered unusually massive white dwarfs. Their work offers a possible alternative explanation, but does not establish that the observed sources are white dwarfs.

Young explorerAstronomers have found things in space that send out signals with long waits between them. Scientists used a computer to explore whether some might be small stars called white dwarfs with strong magnetism. They think this could explain some signals, but they have not shown that these objects really are white dwarfs.

The (missing) gamma-ray counterparts to EP events

Maria Edvige Ravasio, Ansh Chopra, Peter G. Jonker+23 more

AstronomerA systematic gamma-ray search for 72 Einstein Probe fast X-ray transients from its first year identified counterparts for 23 events (32%), including seven sub-threshold detections; 49 (68%) had none, although most were observable. Searches used Fermi/GBM and LAT, supplemented by SVOM, Swift/BAT and Konus-Wind. Simultaneous 3-sigma flux upper limits were derived for observable events without counterparts. For counterpart events, X-ray fluxes averaged over the gamma-ray T90 exceed those averaged over the full X-ray duration, with gamma-ray-to-X-ray flux ratios of approximately 1–100, suggesting preferential gamma-ray detection during the brightest X-ray phases. For non-counterpart events, the tightest GBM limits imply E_peak below approximately 30–100 keV; for 14 events with redshifts, inferred L_iso upper limits span approximately 10^48–9 × 10^51 erg/s. If classical GRB correlations remain valid here, these energetics imply initial bulk Lorentz factors below about 100, supported in a few cases by afterglow constraints. LAT detected no significant GeV emission; GeV-to-X-ray flux-ratio limits of order 1–10 constrain a possible synchrotron self-Compton component. Many EP transients may extend the GRB population to lower spectral peak energies, luminosities and Lorentz factors, but individual origins remain uncertain.

PublicResearchers searched gamma-ray observations for signals accompanying 72 brief X-ray events found during Einstein Probe’s first year. They identified gamma-ray counterparts for 23 events, including seven faint signals below the usual detection threshold. The other 49 had no detected counterpart, even though most were observable. Where both signals were found, gamma rays appeared preferentially during the brightest X-ray phases. For events without gamma-ray detections, the observational limits suggest lower spectral peak energies and luminosities. If relationships established for conventional gamma-ray bursts also apply to these events, their outflows would be slower as well. No significant higher-energy gamma-ray emission was detected, limiting a possible additional emission component. Many of these X-ray events could therefore belong to a less energetic extension of the gamma-ray-burst population, but the origin of each event remains uncertain.

Young explorerA space telescope saw 72 quick flashes of X-ray light. Scientists looked for another kind of light, called gamma rays, from the same flashes. They found it for 23, but not for the other 49. Not finding that light does not mean it was completely absent: it might have been too faint to see. Many of these flashes might be gentler cousins of gamma-ray bursts, but scientists are not yet sure what made each one.

Prior volume effect inflates the gravitational-wave background in pulsar timing arrays

Biwei Dai, Matias Zaldarriaga, Yacine Ali-Ha\"ımoud

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

AstronomerAn analysis of NANOGrav 15-year data attributes a substantial fraction of the unexpectedly high nanohertz gravitational-wave background amplitude to a prior-volume effect. The amplitude is constrained mainly by pulsar auto-correlations, where the background is degenerate with intrinsic red noise. Marginalizing over standard log-uniform red-noise priors favors a stronger background, shifting the inferred amplitude more than 2σ above the maximum-likelihood estimate. Hellings–Downs cross-correlations, which isolate the background, are not yet strong enough to overcome this effect. Profile likelihood, a cross-correlation-only estimator, and red-noise priors uniform in power or informed by the pulsar population avoid or reduce the shift, yielding amplitudes consistent with supermassive black hole binary predictions. The revised priors also favor a steeper background spectrum closer to those predictions, strengthen evidence for Hellings–Downs correlations, and weaken the preference for new-physics sources over black hole binaries.

PublicPulsar timing arrays have found evidence for a background of very slow gravitational waves, with an inferred strength greater than most predictions for pairs of supermassive black holes. Reanalyzing NANOGrav’s 15-year data, the authors find that much of this apparent excess comes from statistical assumptions used to separate the shared gravitational-wave signal from noise belonging to individual pulsars. The correlations between different pulsars that isolate the gravitational-wave background are not yet strong enough to outweigh this effect. Alternative analysis methods or noise assumptions reduce the inferred strength to values consistent with black hole binary predictions. Revised noise assumptions also bring the signal’s frequency dependence closer to those predictions and strengthen evidence for the expected correlations between pulsars. These findings reduce the preference for new-physics explanations; they do not establish which sources produced the background.

Young explorerScientists study signals from space objects called pulsars to look for tiny ripples in space. The ripples seemed stronger than most predictions for pairs of huge black holes. This study says that part of the surprise comes from how scientists do the counting: it is hard to tell the ripples apart from each pulsar’s own noise. When the researchers used other ways to sort them out, the ripples seemed weaker and fit the black hole predictions better. That makes the surprise smaller, but it does not prove what made the ripples.

A Hybrid Neural Network Emulator for M1 Neutrino Reaction Rates in Binary Neutron Star Merger Simulations

Yi Qiu, David Radice, Raffaele Ferrari+1 more

AstronomerThe authors present a neural-network emulator for the computationally dominant two-dimensional reactions in bns_nurates: pair processes, bremsstrahlung, and inelastic neutrino-electron scattering. Their hybrid approach retains direct library evaluation for inexpensive one-dimensional processes. In computational tests, the emulator reproduces neutrino opacities to within a few percent across the relevant thermodynamic conditions and speeds their evaluation by roughly an order of magnitude. In a global Athenak binary neutron star merger simulation, it recovers the reference run’s remnant structure, neutrino luminosities, and ejecta composition at approximately half the overall computational cost. These are simulation comparisons, not observational results.

PublicThe researchers developed a neural-network shortcut for some of the most expensive calculations in simulations of two neutron stars merging. These calculations describe how neutrinos interact with matter; simpler calculations still use the original software library. In tests, the shortcut reproduced the relevant neutrino-interaction properties to within a few percent while evaluating them roughly ten times faster. A merger simulation using this hybrid method reproduced the remaining object's structure, neutrino output, and expelled material's composition from a reference simulation, at about half the total computational cost. The comparison is between computer simulations, not observations of a real merger.

Young explorerScientists use computers to pretend that two neutron stars crash together. Some parts of the pretend crash take a long time to calculate, especially how tiny particles called neutrinos meet the star material. The scientists made a computer helper that does the slow parts faster and leaves the easy parts to the old program. In their test, the new pretend crash gave very similar answers about what was left, the neutrinos, and the stuff thrown out, while using about half as much computer work. The helper was close, but not exact, and this was a computer test, not a real crash they watched.

Exploring PSR J0901-4046 as an ultra-slowly rotating neutron star versus a white dwarf

Banibrata Mukhopadhyay, Nirupam Roy, Zenia Zuraiq+2 more

AstronomerPSR J0901-4046 has a rotational period of approximately 75.88 s. Comparing highly magnetized white-dwarf and neutron-star interpretations, the authors find that a white dwarf with a surface field of about 10^10 G can explain several properties, including the rotational-energy budget needed to account for its luminosity. Under the neutron-star interpretation, particularly with conventional spin-down, the inferred surface field is at least about 10^14 G and can exceed 10^16 G, depending on obliquity and emission mechanism. The source also lies near the white-dwarf pulsar AR Sco in the period–period-derivative plane. The authors favor, but do not establish, a magnetic white-dwarf identity, arguing that it alleviates the pair-production difficulty associated with the extreme fields required in the neutron-star interpretation. If correct, this identification, together with AR Sco, would constrain death-line models and suggest that some extreme rotation-powered pulsars could be white dwarfs.

PublicPSR J0901-4046 takes about 76 seconds to rotate once. The authors investigate whether this unusually slow pulsar could be a highly magnetic white dwarf rather than a neutron star. Their calculations suggest that the white-dwarf interpretation can account for several of its properties, including the energy needed to explain its brightness. The neutron-star interpretation instead requires a much stronger magnetic field, with the estimated strength depending on assumptions about its orientation and how it emits. Its rotation period and rate of slowing also place it near the white-dwarf pulsar AR Sco in a comparison diagram. The authors propose that PSR J0901-4046 is a white dwarf, but this is an interpretation rather than a confirmed identification.

Young explorerThis object in space takes about 76 seconds to turn all the way around. Scientists compared two ideas about what it could be: a white dwarf or a neutron star. They think a white dwarf with a strong magnetic field could explain many things about it, including how it has enough energy to shine. That is their suggested answer, but they have not shown for sure which kind it is.

A new view of the cosmic-ray knee after LHAASO

Carmelo Evoli

AstronomerThis contribution reviews LHAASO measurements of the all-particle spectrum, mean logarithmic mass, and proton and light-component spectra across the PeV cosmic-ray knee. The proton and helium knees are approximately charge-ordered, but their spectra evolve differently. Their turnover shapes constrain possible source populations and Galactic escape mechanisms without uniquely identifying them. Extending this measurement-anchored elemental ladder to heavier nuclei will be crucial for determining the Galactic component’s reach and locating the Galactic–extragalactic transition.

PublicThis review brings together LHAASO measurements of high-energy cosmic rays around a bend in their energy distribution called the knee. The bends for protons and helium occur in an order approximately consistent with their electric charges, although their energy distributions change differently. These patterns help constrain explanations of how our galaxy accelerates particles and how they escape. Extending the measurements to heavier atomic nuclei should help establish where cosmic rays from beyond our galaxy take over; that boundary is not yet established here.

Young explorerTiny particles zip through space. Scientists measured how the mix of particles changes at very high energies. Two kinds, protons and helium, show bends in their patterns, but they do not change in quite the same way. Studying heavier kinds could help scientists learn where particles from our galaxy give way to ones from farther away.

Can we constrain the binary neutron star merger time from kilonova light curves?

Noah Jamsin, Marion Pillas, Marko Ristić+18 more

• Cosmology and Nongalactic Astrophysics
• General Relativity and Quantum Cosmology

AstronomerThis study investigates whether kilonova light curves can constrain binary neutron star merger times, helping associate electromagnetic transients with gravitational-wave events when discovery occurs after emission begins. The authors simulate and fit light curves using multiple kilonova models and inference frameworks, varying cadence and wavelength coverage with a focus on the Vera C. Rubin Observatory. Tests also include observed AT2017gfo data and several GRBs associated with possible kilonova candidates. Under simulated, realistic Rubin observing conditions, they report merger-time precision of 5.5 days (90% CI); the best-case scenario achieves 0.18-day accuracy and 0.74-day precision (90% CI). Available source redshift can improve results by about 5%, while upper limits near the merger time can narrow the timing posterior by about 60%. These are timing-recovery tests, not results from Rubin kilonova detections. Electromagnetic follow-up with other telescopes could provide further improvement.

PublicWhen two neutron stars merge, their gravitational waves and the light from an associated kilonova can reveal different parts of the event. But a kilonova may be discovered after its glow has already begun, making it harder to match it to a gravitational-wave signal. This study tests whether changes in the kilonova's brightness can reveal when the merger happened. Using simulated observations aimed at the Vera C. Rubin Observatory, the researchers report timing precision of 5.5 days for realistic observing conditions, improving to 0.74 day in the best case; both figures describe 90% uncertainty intervals. They also tested their methods on some existing observations. Knowing the source's redshift, having observations that limit its brightness near the merger, or obtaining follow-up observations with other telescopes could help. The Rubin findings are simulation-based, not measurements from newly detected mergers.

Young explorerWhen two neutron stars crash together, they can make a glow. If we notice the glow late, can we tell when the crash happened? Scientists practiced with pretend glows on computers and also tried some real observations. Their tests suggest that watching a glow change could help work out when the crash happened, but the answer would still be uncertain. More clues from telescopes could help.

A Comprehensive X-ray Characterization of the Pulsar Wind Nebula CTB 87: Evidence for Reverse-Shock Interaction from Its X-ray and Broadband Emissions

Jaegeun Park, Jason Alford, Hongjun An+4 more

AstronomerA joint analysis of new NuSTAR and archival Chandra and XMM-Newton observations reveals significant curvature in the X-ray spectrum of the pulsar wind nebula CTB 87. A broken power law gives photon indices of 1.89 ± 0.05 and 2.73 ± 0.10 below and above 5.12 ± 0.26 keV; a cutoff power law also describes the spectrum, with Γ = 1.23 ± 0.10 and a cutoff energy of 5.29 ± 0.67 keV. Spatially resolved spectroscopy confirms radial spectral softening, interpreted as significant synchrotron cooling of outward-moving electrons. An evolutionary one-zone leptonic model reproduces the broad SED features but not the detailed X-ray spectrum. In the multi-zone modeling, the hard electron distribution needed for the X-rays fails to explain the observed gamma-ray SED. These modeling limitations suggest, but do not establish, an additional electron population, possibly associated with a reverse-shock interaction.

PublicNew NuSTAR observations, combined with earlier Chandra and XMM-Newton data, show that the X-ray spectrum of CTB 87, a nebula powered by a pulsar, steepens at higher energies. The spectrum also becomes softer farther from the pulsar, which the researchers interpret as electrons losing energy as they travel outward and emit synchrotron radiation. The team tested models in which electrons produce the nebula’s emission across a broad range of energies. A model treating the nebula as one region captures the broad pattern but misses details of the X-rays. In a model with multiple regions, the electron distribution needed to explain the X-rays cannot also explain the observed gamma rays. The mismatch suggests that another population of electrons may be present, possibly linked to an interaction with a reverse shock, but this explanation is not established.

Young explorerScientists studied X-ray light from a space cloud called CTB 87, which is powered by a spinning star called a pulsar. They found that the light changes farther from the star, a clue that tiny particles called electrons are losing energy as they move away. The scientists tried computer models to explain the cloud’s light, but the models could not match everything they saw. There might be another group of electrons helping make the light, but they do not know for sure.

Probing the QPO and spectro-temporal evolution of MAXI J1750-327 with XPoSat during its first detected outburst : Constraints on black-hole mass and spin

Meghamani Haldar, Biki Ram, Shubhrangshu Ghosh+3 more

AstronomerEleven continuous XSPECT/XPoSat observations tracked the August 2026 outburst of the black hole low-mass X-ray binary candidate MAXI J1750-327. Epochs 1–2 showed prominent type-C quasi-periodic oscillations (QPOs), with systematically increasing frequency and strong low-frequency noise. A type-C to type-B transition followed, with QPOs absent after epoch 4. Broadband spectral fits showed an abrupt rise and subsequent stabilization in inner-disk temperature, together with a steep decrease in disk normalization between epochs 3 and 4. The authors interpret these changes as inward migration of the thin disk toward the ISCO, rather than a direct measurement of disk motion. A sharp decline in Comptonized flux after QPO disappearance suggests evolution from a hard to a soft state through intermediate states. The spectro-temporal correlations support, but do not establish, Lense–Thirring precession as the origin of the type-C QPOs. Bayesian modeling of their frequencies with a global precession model gives M_BH = 7.92 (+6.19/−3.72) solar masses and dimensionless spin a_* = 0.163 (+0.116/−0.056), marginalizing over distance, inclination, and diskbb-normalization uncertainties. These parameter estimates depend on the adopted model.

PublicResearchers used 11 observations from the XSPECT instrument aboard XPoSat to study an August 2026 outburst from MAXI J1750-327, a system thought to contain a black hole and a low-mass companion star. Repeating variations in its X-ray brightness became faster, changed type, and then disappeared. Models of the X-ray spectrum also showed changes in the temperature and apparent size of the inner disk of material. The researchers interpret these linked changes as evidence that the disk moved inward and the system shifted from a hard to a soft X-ray state. The findings support an explanation in which precession—a wobble associated with the black hole’s rotation—produces the initial brightness oscillations, but do not prove it. Assuming that explanation, their model estimates a black hole mass of about eight Suns and a dimensionless spin of about 0.16, both with substantial uncertainty. These are model-based estimates, and the system remains a black hole candidate.

Young explorerScientists watched X-rays from a place where they think a black hole is taking in material. The light had a repeating beat that got faster, changed, and then stopped. Other changes in the light suggest that a disk of material moved closer to the possible black hole. A wobbling motion might explain the first beat, but the scientists are not sure yet.

X-ray Comptonization in an Accreting Kerr Black Hole System with a Tilted Disc and Thermal Corona: A General-Relativistic Monte Carlo Simulation. II. Polarization Signatures

Mainak Chatterjee, Dipankar Bhattacharya

AstronomerIXPE observations challenge simple precession and Comptonization models: SwiftJ1727.8-1613 has weak or undetected QPO-phase polarization modulation, while IGRJ17091-3624 has a hard-state polarization degree of about 9%, compared with about 4% in other hard-state black hole binaries. This study extends a general-relativistic Monte Carlo model of a misaligned, warped two-zone disc and hot, optically thin corona around a Kerr black hole to include Walker-Penrose polarization transport and polarized Compton and disc scattering. The calculations explore energy- and precession-phase-dependent polarization versus coronal optical depth, outer-disc albedo, injection radius, and inclination. In the model, gravitational light bending increases mean polarization degree and modulation, while coronal scattering, outer-disc reflection, and steady outer-disc polarization weaken the signal. These competing effects offer possible explanations for SwiftJ1727.8-1613's weak modulation and IGRJ17091-3624's high polarization degree, rather than uniquely establishing their geometries. The framework yields testable predictions for IXPE, XPoSat, and eXTP.

PublicX-ray polarization—the preferred orientation of the light—can help probe material around black holes. Observations show little or no detectable polarization change during the repeating X-ray variations of SwiftJ1727.8-1613, while IGRJ17091-3624 has unusually strong polarization. Researchers extended a computer model of a warped disc and hot gas around a spinning black hole to follow polarization. In their simulations, gravity bending the light strengthens polarization and its changes as the inner flow precesses, while scattering and reflection can weaken both. The balance could explain the two observed behaviors, but these are possible explanations, not confirmed descriptions of either system. The model provides predictions that X-ray polarization observations can test.

Young explorerScientists study X-ray light from hot material around black holes. That light can have a favorite direction. In one black hole system, this direction pattern barely changes; in another, it is unusually strong. A computer model suggests that bending the light can strengthen the pattern, while bouncing it around can weaken it. This might explain what scientists see, but they still need to test the idea.

Interpreting the γ-ray emission from Westerlund 1: hadronic or leptonic?

Ben Li, Pasquale Blasi, Elena Amato

AstronomerThis modeling study tests hadronic and leptonic explanations for Westerlund 1’s gamma-ray emission, assuming particle acceleration at the cluster WTS. Numerical proton and electron transport calculations predict gamma-ray spectra and morphology, together with electron synchrotron emission, for comparison with Fermi-LAT and HESS measurements and an eROSITA X-ray upper limit. For reasonable model parameters, both scenarios reproduce the observed spectrum and gamma-ray morphology under Bohm diffusion. Under Kraichnan diffusion, described as better motivated for star clusters, only the hadronic scenario explains the observations; the leptonic model misses the highest-energy gamma-ray data. In the leptonic scenario, the X-ray upper limit constrains the magnetic field immediately downstream of the shock to at most a few microgauss. A purely hadronic explanation requires a bubble gas density of at least approximately 1.2 particles per cubic centimetre. These conclusions depend on the assumed acceleration site and transport model rather than establishing a unique emission mechanism.

PublicWesterlund 1 is a star cluster detected in high-energy gamma rays, but the particles responsible remain uncertain. This study models two possibilities: energetic protons colliding with gas, or energetic electrons boosting surrounding light to gamma-ray energies. Assuming the particles are accelerated at a shock associated with the cluster, the researchers compare their calculations with the measured gamma-ray spectrum and spatial pattern, as well as an X-ray upper limit. The answer depends on how particles spread through the cluster’s surroundings. Both explanations work for one transport model, called Bohm diffusion. With Kraichnan diffusion, which the authors consider better motivated for star clusters, only the proton explanation works; the electron model cannot reproduce the highest-energy measurements. The electron explanation also requires a weak magnetic field just beyond the shock, while a proton-only explanation requires sufficiently dense gas. The findings favor protons under particular modeling assumptions, not a definitive identification.

Young explorerA group of stars called Westerlund 1 shines in very energetic light called gamma rays. Scientists used computer models to ask what makes that light: tiny particles called protons hitting gas, or electrons giving other light a big energy boost. They assumed the particles get their energy at a shock near the star group. With one way of letting particles move around, either idea works. With another way the scientists think fits star groups better, only the proton idea works. That is a clue, but it does not settle the mystery.

Investigating a TeV-Halo Candidate around PSR J1928+1746 with HAWC

HAWC Collaboration, R. Alfaro, C. Alvarez+94 more

AstronomerAn updated analysis of 2904 days of HAWC data, using improved reconstruction and a likelihood model with six TeV source components plus Galactic diffuse emission, resolves a distinct, moderately extended source near PSR J1928+1746 in the crowded region previously linked to 3HWC J1928+178. HAWC J1928+1750 is detected from approximately 2 TeV to above 100 TeV, with Gaussian extension σ = 0.19° and a log-parabola spectrum characterized by K = 5.0 × 10^-15 TeV^-1 cm^-2 s^-1 at 12 TeV, α = 2.09, and β = 0.35. Diffusion-halo templates assuming B = 8 μG yield D(100 TeV) = 2.1 × 10^27 cm^2 s^-1, roughly 500 times below typical interstellar values, suggesting strongly suppressed transport under the TeV-halo interpretation. The spectrum is consistent with inverse-Compton emission from pulsar-injected electrons and positrons, requiring less than approximately 1% of the pulsar's characteristic spin-down energy, but an environmental hadronic contribution remains possible.

PublicUsing 2904 days of HAWC observations and an improved analysis that separates overlapping gamma-ray sources and diffuse emission, researchers identified a distinct, somewhat extended source near the pulsar PSR J1928+1746. Named HAWC J1928+1750, it emits gamma rays from about 2 trillion to more than 100 trillion electron volts. Its spectrum is consistent with electrons and positrons supplied by the pulsar boosting light to gamma-ray energies. In a halo model that assumes a particular magnetic-field strength, the inferred particle diffusion rate is about 500 times lower than typical values between stars. This suggests that particles spread unusually slowly near the pulsar if the halo interpretation is correct. The electron-and-positron explanation requires less than about 1% of the pulsar's characteristic spin-down energy, but some emission could instead come from energetic protons or other atomic nuclei in the surrounding environment.

Young explorerScientists used a detector called HAWC to study very energetic light from a crowded part of our galaxy. They found a small, spread-out glow near a spinning star called a pulsar. Tiny particles sent out by the pulsar might make the glow by giving light extra energy. If that explanation is right, the particles seem to spread much more slowly nearby than they usually do between stars. But the scientists cannot yet rule out other particles helping to make the glow.

Double-Shock Radiation in Supernova Wind Breakout and EP260321a

Zhuo Li, Rui-Ze Shi, Qiang Wang

AstronomerThe authors develop a model of supernova shock breakout in an optically thick stellar wind, where ejecta–wind interaction produces forward and reverse shocks. The reverse shock has internal energy and velocity smaller by a factor μ ≲ 1/6, favoring local thermal equilibrium and blackbody emission; the likely non-equilibrium forward shock may produce a non-blackbody component at least about six times stronger. Applied to the detected X-ray flash EP260321a associated with the type Ic-BL SN2026gzf, the model attributes the approximately 0.13 keV thermal emission to the reverse shock. Representative parameters are ejecta kinetic energy of approximately 10^52 erg, ejecta mass of approximately one solar mass, and a wind containing approximately 10^-4 solar masses within approximately 10^13 cm. In this interpretation, reverse-shock emission sets the X-ray rise time, while scattering in a distant shell-like medium with a photospheric radius of approximately 10^14 cm explains the extended duration and decline. The inferred delay of at least a few kiloseconds in the observed breakout onset allows cooling of a shocked pure carbon–oxygen envelope to explain optical emission within 30 kiloseconds. These are model-based explanations, not direct identifications of the emitting structures. The authors suggest that paired blackbody and non-blackbody components may be common in wind breakouts, offering probes of ejecta and pre-explosion mass loss.

PublicA supernova’s expanding debris can crash into a thick wind of material around the star, producing two shocks. This study proposes that the slower, reverse shock can make heat-like radiation, while the faster, forward shock may produce a stronger component with a different spectrum. The authors use this model to explain the detected X-ray flash EP260321a, associated with supernova SN2026gzf. They suggest that the reverse shock produced the thermal X-rays, while scattering through more distant surrounding material stretched out the flash. In the same interpretation, cooling material made of carbon and oxygen explains the early optical light. The observations do not directly establish these structures; they are the authors’ physical explanation of the signals. Such flashes could help reveal both the exploding star’s debris and material shed before its explosion.

Young explorerWhen a star explodes, its flying pieces can bump into a thick cloud around it and make a flash. Scientists saw an X-ray flash linked to an exploding star. They think one of two moving crash zones could have made part of the flash, and that light bouncing through material farther away could have made it last longer. This is their explanation of what they saw, not something they know for sure. Studying the flash may help them learn what was around the star before it exploded.

General Relativistic Simulations of the Nonlinear Evolution of r-modes in Rapidly Rotating Neutron Stars

Justin K. Yu, Andrew Melatos

• General Relativity and Quantum Cosmology

AstronomerGeneral relativistic simulations explore nonlinear r-modes with l = 2 and absolute value of m = 2 in a neutron star spinning at approximately 792 Hz, relaxing both the Cowling and small-amplitude approximations. The model is an idealised, unmagnetised, one-component perfect fluid with a polytropic equation of state. Although r-modes may grow or be excited to amplitudes alpha less than or approximately equal to 1, the simulations span initial amplitudes alpha_0 from 0.2 to 1.2. At alpha_0 = 0.2, the simulated r-mode frequency is 1014 Hz, and the dimensionless frequency kappa is approximately 0.7197, agreeing with a linear perturbation estimate to within 1.7%. The r-mode frequency increases quadratically with amplitude, while kappa decreases by 3.4% across the simulated amplitude range. The gravitational-wave strain calculated from the Newman-Penrose scalar is approximately 9.7 × 10^-22 at 10 kpc for alpha_0 = 0.2, agreeing with Einstein’s quadrupole formula to within 35%. The simulations also exhibit differential rotation, amplitude decay, and signatures of nonlinear mode coupling in spacetime oscillations. These are simulation findings, not an observational detection of continuous gravitational waves.

PublicWaves within a rotating neutron star could produce continuous gravitational waves. The researchers studied this possibility with general relativistic computer simulations, rather than observations of a real star. Their simplified star spins about 792 times per second and has no magnetic field; its material is treated as a single perfect fluid with a simplified pressure-density relationship. For an initial wave amplitude of 0.2, the simulated oscillation frequency is 1014 Hz. A related dimensionless frequency, approximately 0.7197, differs from a linear-theory estimate by no more than 1.7%. Across initial amplitudes from 0.2 to 1.2, the oscillation frequency rises quadratically with amplitude, while the dimensionless frequency falls by 3.4%. For amplitude 0.2, the calculated gravitational-wave strain at a distance of 10 kiloparsecs is approximately 9.7 × 10^-22, within 35% of a standard calculation using Einstein’s quadrupole formula. The simulations also show uneven rotation, weakening oscillations, and signs that different oscillations interact. These results concern an idealised model, not a detected signal.

Young explorerScientists used a computer to imagine a very fast-spinning neutron star with waves moving inside it. Those waves might make tiny ripples in space called gravitational waves. In their computer model, bigger waves moved faster, and the waves also became weaker over time. There were clues that different waves were affecting one another. But the pretend star was simpler than a real star: for example, it had no magnetic field. The scientists calculated possible ripples; they did not catch ripples from a real star.

Lasting mEMRIs: Signatures of Multiple Black Hole Extreme Mass Ratio Inspirals from AGN discs

Jordan W. N. Moncrieff, Evgeni Grishin, Fiona H. Panther+1 more

• Astrophysics of Galaxies
• General Relativity and Quantum Cosmology

AstronomerThis theoretical study considers stellar-mass black-hole pairs in mean-motion resonance within active galactic nucleus discs. Near the central supermassive black hole, gravitational-wave emission can overcome gas torques and disrupt the resonance. The authors derive a survival condition depending only on the stellar-mass black-hole mass ratio and resonance index, identifying pairs that could remain resonant and be detectable by LISA as multiple extreme-mass-ratio inspirals (mEMRIs). They present predicted strain signatures for co-migrating resonant pairs, including additional harmonics associated with orbital conjunctions. The frequency evolution and associated chirp mass are degenerate with those of isolated EMRIs with different masses; the inferred mEMRI mass ratio is quantised by resonance order and exceeds the true ratio. Individual strain amplitudes could break this degeneracy if they constrain the true mass ratio. Conditional on LISA detecting disc-driven EMRIs, the authors argue that mEMRIs should be common, estimating roughly 10 per year at z ≲ 0.2. These are theoretical predictions, not reported detections, and motivate including mEMRIs in future LISA analysis.

PublicTwo stellar-mass black holes orbiting a much larger black hole can settle into a repeating orbital rhythm within a galactic nucleus's gas disc. This theoretical study asks whether that rhythm can survive as gravitational-wave emission becomes more important than the gas's influence. The authors derive a condition for survival and predict the gravitational-wave signals such pairs could produce for LISA, including extra tones when the smaller black holes line up in their orbits. Their changing signal frequencies could mimic those of a single inspiralling black hole with a different mass. Measuring each object's signal strength might resolve that ambiguity. If LISA detects inspirals driven by these discs, the authors argue that resonant pairs should be common, estimating about 10 per year in the nearby universe. No detections are reported; the work highlights a potential complication for interpreting future signals.

Young explorerImagine two small black holes circling a much bigger one, keeping a rhythm like dancers. Scientists worked out when they might keep that rhythm as they spiral inward and send out tiny ripples in space. They predict that the pair could make extra notes in those ripples, but could sometimes sound like just one small black hole. A future detector called LISA might help tell them apart. This is a prediction, not something the scientists report seeing.

Searches for coincident Gravitational Waves and High-Energy Neutrinos from the KM3NeT and ANTARES telescopes during O3

ANTARES Collaboration, KM3NeT Collaboration, O. Adriani+97 more

AstronomerTwo multimessenger analyses combined LIGO–Virgo gravitational-wave data with ANTARES and ORCA high-energy neutrino data from the third LIGO–Virgo observing run. One used selected neutrino candidates to trigger gravitational-wave searches; the other sought spatial and temporal coincidences between subthreshold neutrino candidates and subthreshold compact-binary-coalescence gravitational-wave candidates. Neither search found significant coincidences. The analyses set upper limits on the rate of sources emitting both messengers. In particular, the joint search yielded a source rate density upper limit of 8.8 × 10^2 Gpc^-3 yr^-1 for a typical binary neutron star coalescence assuming gravitational-wave energy of 0.1 solar masses times c squared and isotropic neutrino energy of 10^51 erg. This limit is conditional on those emission assumptions, not a detection of joint emission.

PublicSome models predict that events such as neutron-star mergers or collapsing stars can produce both gravitational waves and high-energy neutrinos. Researchers searched for matching signals using LIGO and Virgo gravitational-wave data and ANTARES and ORCA neutrino data collected during LIGO–Virgo’s third observing run. One search started with neutrino candidates and looked for gravitational-wave counterparts; another looked for signals too weak to qualify on their own that matched in time and direction. Neither found a statistically significant match. The results place upper limits on how often sources emitting both signals occur. For a representative neutron-star merger with specified energy outputs in gravitational waves and neutrinos, the reported limit is 880 events per cubic gigaparsec per year; it depends on those assumed energy outputs.

Young explorerSome ideas say that when stars crash together or collapse, they can send out both ripples in space and tiny particles called neutrinos. Scientists used special detectors to look for signs of both coming from the same event. They did not find a convincing match. That does not mean these events never happen. It helps scientists put a limit on how often they could happen, if the events send out as much energy as the scientists assumed.

Domain models of turbulent magnetic fields and the spectral shape of ensemble averaged axion-photon conversion

Oleksandr Khasai, Lidiia Zadorozhna, Denys Malyshev+1 more

• Cosmology and Nongalactic Astrophysics
• High Energy Physics - Phenomenology

AstronomerThis theoretical study derives an analytic form for the ensemble-averaged spectral signature of photon mixing with axion-like particles, light pseudoscalars that are dark-matter candidates. For distant sources viewed through turbulent magnetic fields in intervening galaxy clusters, individual spectral modulations are stochastic, but averaging over an ensemble produces a smooth absorption-like feature, previously characterized only numerically. The work also connects the magnetic-field energy-spectrum index a to the domain-size distribution index β used in turbulent-field simulations: β = 3 − a for 1 < a < 2. Distributions with β < 1 instead mimic a = 2 because of the sharp domain walls. For Kolmogorov turbulence, relevant to galaxy clusters, the relation yields β = 4/3. These are analytic and modeling results, not an observational detection of axion-like particles.

PublicAxion-like particles are hypothetical particles that could make up dark matter. If they mix with light as it crosses a galaxy cluster’s turbulent magnetic field, they could leave irregular changes in a distant source’s spectrum. Earlier numerical work showed that averaging the spectra of many such sources turns those irregular changes into a smooth, absorption-like feature. This study derives a mathematical expression for that average signal. It also explains how the sizes of magnetic regions used in simulations relate to the underlying turbulence, while showing that sharp boundaries between those regions can impose their own behavior. The work provides theoretical tools for describing a possible particle signature; it does not report finding the particles.

Young explorerScientists wonder whether tiny particles we have not found could make up dark matter. If these particles can change into light and back, light passing through a galaxy cluster’s tangled magnetic field could get a bumpy pattern. Mixing together the patterns from many faraway lights could make one smooth dip instead. This study worked out the math for that dip and for how to model the tangled field. It did not find the tiny particles.

PSR J0653+0443: An Eclipsing Millisecond Pulsar in an Extremely Eccentric Double Neutron Star System

Z. L. Yang, J. L. Han, L. G. Hou+21 more

AstronomerThe authors report the discovery of the Galactic field double neutron star PSR J0653+0443, with two approximately 1.4-solar-mass components, orbital eccentricity e = 0.992387, and period 79.084 days. The system traverses true anomalies from -90 to +90 degrees in 46 minutes. An 85-second conjunction eclipse indicates a nearly edge-on orbit. Short-term variations in periastron advance produce pulse arrival-time modulation from -2.91 to +2.49 ms, at least an order of magnitude larger than observed in other DNS systems. This constrains the non-relativistic periastron advance rate to -1.5 (+0.9/-0.8) × 10^-4 degrees per year. The authors attribute the extreme eccentricity exclusively to a large natal kick during the second component's iron-core-collapse supernova. The predicted detection probability of a similar system is at most about 0.005, which they interpret as challenging current binary-evolution understanding. The system is expected to emit periodic gravitational-wave bursts with energy flux peaking at 0.357 mHz; the authors identify it as an ideal target for the future LISAmax mission, not as an existing gravitational-wave detection.

PublicAstronomers report discovering two neutron stars orbiting each other in our Galaxy in an exceptionally stretched-out orbit. Named PSR J0653+0443, the pair contains two stars each about 1.4 times the Sun's mass and completes an orbit in about 79 days. Near their closest approach, their relative speed reaches about 1.14 million metres per second. An 85-second eclipse of the pulsar indicates that we view the orbit nearly edge-on. Changes in the timing of its pulses also constrain how the orbit shifts. The authors argue that a strong kick from the supernova that formed the second neutron star caused the extreme orbit. Models predict a detection probability of no more than about 0.5% for a system like this, making the discovery a challenge for current accounts of how paired stars evolve. The pair is expected to produce repeating bursts of gravitational waves, and the authors highlight it as a target for the future LISAmax mission; they do not report detecting those waves.

Young explorerAstronomers found two stars called neutron stars going around each other on a very stretched-out path. They rush past each other when they get close. The scientists think a big kick from an exploding star made their path this way. Finding a pair like this was surprising. The stars should make tiny ripples in space, and a future space mission might be able to listen for them.

PBR sensitivity to boosted dark matter explanation for the KM3-230213A event

M. H. Reno, T. Venters, M. Abrate+97 more

• High Energy Physics - Phenomenology

AstronomerPOEMMA-Balloon with Radio (PBR), a fluorescence and optical Cherenkov telescope accompanied by a radio instrument, is planned for a super-pressure balloon flight in Spring 2028 as a POEMMA pathfinder. Its objectives include astrophysical-alert follow-up through atmospheric tau decays from Earth-skimming tau neutrinos. Motivated by KM3NeT's reported muon event with E_mu = 120 (+110/-60) PeV, the authors assess PBR's sensitivity within a specific boosted-dark-matter scenario, using that scenario and the event to set a fluence scale. The analysis predicts discovery potential above dark-matter energies of 10^9 GeV, extending down to 1.5 × 10^8 GeV for some beyond-standard-model parameter choices. These are model-dependent sensitivity forecasts, not dark-matter detections. Although evaluated for one scenario, the methodology can apply to other new physics affecting tau production in Earth.

PublicA balloon mission planned for Spring 2028 could help test an exotic explanation for an unusually energetic particle event reported by KM3NeT. The proposed instrument, PBR, would look for signals from particles called taus decaying in the atmosphere. The researchers calculate how well it could detect or constrain a particular model of extremely energetic dark matter, using the reported event to help estimate how much dark matter might arrive. They find potential for discovery at very high energies, but the reach depends on the model's assumptions. The study does not establish that the reported event came from dark matter or that PBR has detected it. Its approach could also test other proposed physics that changes how taus are produced inside Earth.

Young explorerScientists plan to send a special telescope up on a balloon. It would look for tiny flashes made when certain particles break apart in the air. Another experiment reported a particle with a huge amount of energy. Scientists wondered whether a kind of dark matter could help explain it, and worked out whether the balloon telescope might spot signs of that idea. They think it might, if their guesses about dark matter are right. They have not found dark matter this way yet.

Extended vs. thin screen approximation in astrophysical settings

Manuel Adlberger, Tobias Kramer

AstronomerThis theoretical and numerical study examines the validity of thin-screen approximations for wave propagation through extended scattering structures, with relevance to plasma propagation and gravitational lensing. The authors adapt analytical results from quantum scattering theory, present exact solutions for simple lensing geometries, including spherical waves scattered by a point source, and use numerical methods to quantify differences between thin-screen and extended-medium treatments. They report the emergence of branched flow in an intermediate regime between thin-screen physics and stochastic-medium results. The abstract gives no quantitative validity thresholds or observational tests.

PublicScientists often simplify calculations of how waves bend or scatter by treating a three-dimensional region as a thin sheet. This study uses mathematics and computer calculations to examine when that shortcut works and how it differs from modeling an extended region. The calculations show the emergence of branching wave patterns in a regime between thin-sheet behavior and the behavior described by statistical models of scattering. The work is relevant to radio waves traveling through plasma and to gravitational lensing, but it reports theoretical and numerical results, not observations.

Young explorerWaves traveling through space can bend and spread out. Scientists sometimes make the math easier by pretending the stuff changing the waves is a very thin sheet. These researchers used math and computers to compare that shortcut with a thicker region. Their calculations showed waves making branching patterns, a bit like the branches of a tree. This was a study with calculations, not something they watched in the sky.

Modeling MAD Sgr A* flares and their dependence on spin

Eleni Antonopoulou, Antonios Nathanail, Yosuke Mizuno+1 more

AstronomerThe study compares simulated flare kinematics with astrometric observations of Sgr A*, modeling a spherical hot spot ejected relativistically along a flux tube. In magnetically arrested disk (MAD) simulations, the flux tube wraps around the jet funnel opposite to the black hole's spin, imprinting a spin-dependent trajectory. The comparison favors Kerr models with larger spin magnitude; the maximally rotating case is the most promising, with a reported pass fraction exceeding 90% among the investigated flare models, rather than a measured probability for the spin. Constraints depend on the assumed disk rotation: for a counterclockwise disk, prograde models with a≥1/2 can reproduce the observed kinematics; for a clockwise disk, both high-spin prograde and retrograde models are supported. Prograde simulations yield clockwise sky motion regardless of disk rotation, whereas retrograde models require a clockwise disk to account for the July 22, 2018 observations. These are model-dependent spin constraints, not a unique spin determination.

PublicCould the path of a flare reveal how fast the Milky Way's central black hole, Sgr A*, spins? Researchers compared observations with computer models in which a hot spot is launched at relativistic speed along a tube of magnetic field. In the simulations, the tube winds opposite to the black hole's spin, linking the flare's motion to that spin. Faster-spinning models generally fit better, and the maximally rotating model was the most promising of those tested. But the interpretation depends on which way the surrounding disk turns: one assumed direction favors a black hole spinning with the disk, while the other allows rapid spin either with or against it. The study therefore favors rapid rotation within this model, without uniquely establishing the black hole's spin.

Young explorerA bright flare near the black hole at the middle of our galaxy followed a path across the sky. Scientists used computer make-believe to see how a little hot spot might move near a spinning black hole. Their models worked best when the black hole spun very fast. But the answer also depends on which way the stuff around it goes, so they cannot yet say for sure how it spins.

Dyonic black holes supporting nearly-black self-gravitating thin shells

Shahar Hod

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

AstronomerThis theoretical study considers dyonic spacetimes in a quasitopological nonlinear electrodynamic field theory. Earlier work identified discrete radial regions with dg_tt/dr = 0 that can support static, spherically symmetric test shells with negligible self-gravity. The paper proves that regions satisfying d[r g_tt(r)]/dr → 0 from above can instead support static, self-gravitating thin shells on the verge of becoming black holes. The allowed discrete radii of these nearly-black Dyson shells are independent of the central supporting dyonic compact object's mass. These are mathematical results within the specified theory, not observations of such shells.

PublicIn a particular mathematical theory of gravity and nonlinear electromagnetism, the authors show that a thin spherical shell of matter could remain stationary around a compact object carrying both electric and magnetic charge. Unlike shells studied previously with negligible gravity of their own, these shells have substantial self-gravity and are on the verge of becoming black holes. The theory permits them at discrete radii that do not depend on the central object's mass. The study establishes a theoretical possibility, not evidence that such shells exist in space.

Young explorerThe scientists used math to study whether a hollow ball of matter could stay still around a special object in space. In their theory, the ball's own gravity can be so strong that it is almost a black hole, yet it can still stay still at certain sizes. Those sizes do not depend on how much mass the object in the middle has. This is a math result, not something they have seen in the sky.

The renormalization-group running of neutrino mixing is undetectable

Gabriela Barenboim, Mauricio Bustamante, Qinrui Liu

• High Energy Physics - Phenomenology

AstronomerThis theoretical study challenges proposals that neutrino production or detection at momentum transfer Q directly probes the mixing matrix evolved to renormalization scale μ = Q. The authors argue that physical mixing is fixed by the neutrino’s on-shell self-energy. Choosing μ = Q is valid, but self-energy logarithms cancel the apparent running; omitting them creates a spurious process dependence. Apart from small vertex and box corrections, they conclude that all experiments measure the same mixing. They illustrate the argument in the Minimal Supersymmetric Standard Model, two seesaw models, and Standard Model effective field theory. Thus, RG running itself would not produce the proposed zero-distance flavor changes, CP-phase shifts, or anomalous flavor composition of high-energy astrophysical neutrinos. Independently, existing short-baseline data constrain a change in any one mixing angle between pion decay and detection at Q of a few GeV to below 0.7°–2.4°.

PublicNeutrinos can change between different types, a behavior described by mixing. Some researchers have proposed that experiments involving different momentum transfers could directly reveal changes in mixing caused by a mathematical effect called renormalization-group running. This paper argues that the proposed effect disappears when all relevant terms in the calculation are included. The authors conclude that experiments should measure the same underlying mixing, apart from small corrections associated with their interactions. Their theoretical argument challenges proposed signals, including unusual proportions of neutrino types arriving from astrophysical sources; it is not a report of such a signal. Separately, existing short-baseline measurements already place tight limits on certain possible differences in mixing between production and detection.

Young explorerNeutrinos are tiny particles that can change from one kind to another. Some scientists thought different experiments could reveal a special change in how this happens. This paper says that, when the math includes all the needed pieces, that change goes away. This is a calculation, not a newly seen change.

How general relativity stacks up: Testing gravity by coherently combining gravitational-wave observations

Lachlan Passenger, Nir Guttman, Paul D. Lasky+1 more

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

AstronomerThe authors propose a framework for coherently combining gravitational-wave measurements into a population-level test of general relativity in the high-curvature, high-velocity regime. It assumes deviations are strongest near merger, vary smoothly with total binary mass, and are most prominent in the mode with ell equal to the absolute value of m equal to 2. These assumptions restrict the deviations the framework can probe and are presented as a starting point for a more general approach. Applied to 28 high-signal-to-noise binary black hole mergers from LIGO-Virgo-KAGRA's Fifth Gravitational-Wave Transient Catalog, the framework finds no evidence for deviations from general relativity. It also permits reconstruction of how deviations could depend on total mass; the authors argue that such reconstructions could distinguish systematic waveform errors from genuine violations, rather than demonstrating that distinction here.

PublicResearchers propose a way to combine gravitational-wave measurements from many merging black hole pairs to test Einstein's general relativity under extreme conditions. Their method assumes that departures from the theory would be strongest near the merger, change smoothly with the pair's total mass, and appear most clearly in a particular wave component, labeled by ell equal to the absolute value of m equal to 2. These assumptions do not cover every possible departure. Applying the method to 28 mergers with strong signals in LIGO-Virgo-KAGRA's Fifth Gravitational-Wave Transient Catalog, they find no evidence against general relativity. The method can also map how possible departures change with total mass. The authors suggest that this could help separate genuine new physics from errors in predicted wave shapes, but they do not establish that separation as an observed result.

Young explorerWhen two black holes join together, they send out ripples in space. Scientists made a new way to study many of these ripple signals together and check Einstein's rules about gravity. They tried it on 28 black hole pairs with strong signals and found no sign that the rules were wrong. Their method looks for only certain kinds of differences: ones biggest near the joining, changing smoothly with how heavy the pair is, and showing up mostly in one part of the ripple called the ell equals absolute value of m equals 2 mode. Other kinds of differences could be missed. The scientists think this method could help tell a real change in gravity's rules from a mistake in their ripple predictions, but they have not shown that it does so yet.

SpinOctopus: A Versatile, User-Friendly, and Extensible Public Code for General-Relativistic Ray-Tracing in axisymmetric spacetime

Shiyang Hu, Dan Li, Chen Deng+2 more

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

AstronomerThe authors develop and release SpinOctopus, a Fortran/Python relativistic ray-tracing code with OpenMP parallelization for arbitrary axisymmetric spacetimes. Users supply the covariant metric tensor and simulation parameters in a configuration file. The code simulates timelike orbits and associated light curves, null geodesics, and black hole images with phenomenological emission models including thin and thick accretion disks, thin tilted disks, relativistic jets, spherical accretion flows, and point sources. Interfaces allow modification of source geometry and kinematics. Using a customized adaptive integration step size, the authors report approximately 800 rays per second per thread on an Intel Core i7-14700 for thick-disk image simulations; this benchmark is specific to that setup. Fe Kα fluorescent line profiles and thick tilted-disk images are planned for future releases, not current capabilities. The work presents a numerical toolkit rather than observational findings.

PublicThe authors have released SpinOctopus, software that calculates how light and matter move through curved spacetime and creates simulated images of black holes surrounded by different kinds of light-emitting material. It supports models of disks, jets, spherical flows, and individual point sources. Users specify the spacetime geometry and simulation settings, and can adjust the shapes and motions of the light sources. The software is designed for spacetimes with symmetry around an axis. In a reported test making images of a thick disk, it processed about 800 light rays per second per computing thread on an Intel Core i7-14700; performance in other setups is not established by that figure. These are computer simulations, not new telescope observations. Additional features, including simulated iron emission-line profiles and thick tilted disks, are planned for later versions.

Young explorerScientists made a computer tool called SpinOctopus that follows pretend paths of light near black holes. It can make pretend pictures showing how glowing disks and other bright things around a black hole might look. Scientists choose the rules for the space in their model and the glowing things they want to include. These pictures are made by a computer, not taken by a telescope. The team plans to add more things the tool can do later.

Rotation slows the instability of Ellis-Bronnikov wormholes

Nikita M. Shirokov, Ilya Nachevsky

• General Relativity and Quantum Cosmology

AstronomerNonlinear 3+1 simulations of rotating Ellis-Bronnikov wormholes indicate that rotation slows the static solution’s radial instability but does not simply remove it as second-order perturbation theory suggests. With perturbations supplied only by numerical truncation error, the throat switches from collapse to expansion near 30% of the extremal angular momentum. From 58% upward, no instability is detected within the simulated durations; the fastest-spin case is tested at three resolutions. This finite-time result does not establish long-term stability. Collapsing rotating throats produce axisymmetric quadrupolar gravitational-wave bursts whose energy increases with spin. The authors construct stationary drainhole solutions with equatorial rotation speeds up to 99% of light speed, validate their spectral solver against published symmetric solutions, and correct a published field equation. They also find that truncation errors intrinsic to second-order perturbative initial data trigger the instability, making those data unsuitable for stability studies. These are computational findings, not astronomical observations.

PublicComputer simulations explore whether spinning can keep a theoretical wormhole from collapsing. Faster rotation slows the instability, but near 30% of the maximum angular momentum, the simulated tunnel begins expanding instead of collapsing—not becoming stable as an earlier approximation suggested. At 58% and above, the researchers see no instability during the time simulated, although that does not prove the wormholes would remain stable indefinitely. At the fastest spin, this finding holds at three numerical resolutions. When rotating wormholes do collapse in the simulations, they release a burst of gravitational waves, with more energy at higher spin. The study also finds that errors in an approximate way of preparing the simulations can themselves trigger instability. No real wormholes were observed.

Young explorerScientists used computers to study pretend tunnels through space called wormholes. Spinning made the tunnels change more slowly. Some closed up, while others grew bigger. The fastest-spinning ones did not show trouble while the computer watched, but that does not mean they would stay safe forever. These were computer experiments, not tunnels scientists found in space.

Local tests of Schwarzschild-Bertotti-Robinson spacetime

Fatma Kutlu, Livanur Çelik, Özgür Delice

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

AstronomerThis theoretical study examines weak-field local tests of Schwarzschild-Bertotti-Robinson spacetime, describing a static black hole embedded in an external magnetic field. The authors derive analytical results for perihelion precession, light deflection, and radar-echo time delay to investigate possible magnetic-field effects. They also directly integrate the relevant geodesic equations using an exact approach, both to check the weak-field results and to extend the treatment beyond that approximation. The abstract reports no observational measurements or quantitative constraints.

PublicThe researchers use mathematics to investigate how an external magnetic field might affect motion and light around a nonrotating black hole. They consider changes in the orientation of an orbit, the bending of light, and delays in returning radar signals. They compare approximate calculations for weak gravity with a more complete mathematical treatment that also reaches beyond that limit. This is a theoretical investigation, not a report that these magnetic-field effects have been observed.

Young explorerScientists used math to study a black hole sitting in a magnetic field. They explored how things might move around it, how light might bend, and how long a radar signal might take to come back. They checked simpler math with more complete math. They did not report seeing these effects in the sky.

Modeling X-ray reflection spectra from disk returning radiation: Application to 4U 1630-47

Kostas Kourmpetis, Shafqat Riaz, Honghui Liu+6 more

AstronomerThe authors present a new reflection-spectroscopy table model that self-consistently includes returning thermal disk radiation, an effect not yet fully incorporated into XSPEC reflection models. To isolate disk self-irradiation, they adopt a standard disk-corona configuration with the corona disabled. The model fits three simultaneous NICER and NuSTAR observations of 4U 1630-47 in the soft state well, suggesting that returning disk radiation could explain the observed reflection features without establishing it as the unique explanation. The fits suggest a rapidly spinning black hole with a_* ~ 0.99, disk inclination of 43–54 degrees, accretion rate of 0.13–0.25 times the Eddington accretion rate, and distance of 7.3–11.3 kpc, broadly consistent with previous studies.

PublicLight emitted by the disk around a black hole may return to the disk and produce features in its X-ray spectrum. The researchers built a model of this process and tested it against three sets of simultaneous NICER and NuSTAR observations of the black-hole binary 4U 1630-47 during its soft state. To study the disk's own returning light alone, they switched off the surrounding corona in the model; this does not establish that the real source has no corona. The model matches the observations well, supporting returning light as a possible explanation for the reflection features rather than proving it is the only explanation. The fits favor a rapidly spinning black hole and give estimates of the disk's tilt, the rate at which matter flows inward, and the system's distance that broadly agree with earlier studies.

Young explorerA black hole has a disk of hot material around it that shines in X-rays. Some of that light may come back and shine on the disk again. Scientists made a computer model to see whether this returning light could explain patterns in observations of one black hole's disk. The model matched the observations well, so the idea might work, but that does not prove it is the only answer.

Jet Power Estimates of FSRQs PKS 1441+25 and Ton 599 from Broadband SED Modeling

Hritwik Bora, Ranjeev Misra, Rukaiya Khatoon+1 more

AstronomerBroadband SED modeling of the FSRQs PKS 1441+25 and Ton 599 used Swift-XRT/UVOT, NuSTAR, Fermi-LAT, and VERITAS observations from 2015 and 2021, respectively. The study compared broken-power-law and log-parabola particle distributions with two models featuring energy-dependent diffusion or acceleration timescales. Jet-power estimates from the intrinsically curved distributions were of the same order as those from the broken power law. This contrasts with HBLs, for which estimates can differ by nearly two orders of magnitude between models. The authors attribute the contrast to the lower electron break energies typical of FSRQs and interpret their findings as reflecting external Compton dominance and weaker sensitivity to spectral curvature. The two-source analysis suggests relative robustness of FSRQ jet-power estimates to the assumed particle distribution, rather than providing a direct measurement of jet power.

PublicResearchers modeled light observed from two powerful galactic cores, PKS 1441+25 and Ton 599, to estimate the power carried by their jets. They tested four descriptions of how the particles’ energies are distributed. Although these descriptions differ, they produced jet-power estimates of the same general size. For another class of jet-producing galactic cores, estimates can vary by almost a factor of 100 between models. The researchers suggest that the lower characteristic electron energies in these two sources’ class help explain the difference. Their results indicate that jet-power estimates may be less sensitive to this modeling choice, but the conclusion comes from modeling two objects, not directly measuring their jet power.

Young explorerSome galaxies have very bright centers that send out powerful jets. Scientists studied light from two of them and tried four different ways to describe the particles in their jets. Each way gave a roughly similar answer for how powerful the jets might be. That is a useful clue, but these are estimates from models, not direct measurements.

The Deep Newtonian Regime in Late-Time Blast Waves: Inevitable Transition and Distinct Flux Signatures

Sk. Minhajur Rahaman, Jonathan Granot, Paz Beniamini

AstronomerThis work develops a unified analytic framework for deep Newtonian (DN) synchrotron emission from single-velocity and stratified ejecta. Below a shock speed of approximately 0.2c, only a fraction of electrons are accelerated to relativistic energies. For gamma-ray burst afterglows in a uniform medium, the framework predicts t_DN ≈ 3.7 E_51^(1/3) n_0^(-1/3) yr and a decay shallower than standard Newtonian predictions by δα = 6(p−2)/5. For the modeled kilonova remnant with E_0 = 10^50.5 erg and ejecta mass 0.1 solar masses, DN evolution begins before deceleration; omitting it underestimates the coasting-phase radio flux by roughly factors of 3–5, with larger discrepancies thereafter. Magnetar-boosted remnants with E ≈ 10^52 erg are predicted to reach approximately 10–100 microjansky at 3 GHz at 40 Mpc; existing GW170817 limits already disfavor a long-lived millisecond magnetar. For core-collapse supernovae in a wind medium, the model gives constant peak luminosity during coasting and ν_pk ∝ t^−1. Application to SN 2023ixf yields an inferred density-profile index k = 1.29 ± 0.14. The typical DN ordering is ν_m < ν_sa < ν_c, with sub-GHz spectral peaks favoring LOFAR and SKA-low. The authors argue that even non-detections robustly constrain ambient density and outflow energetics.

PublicOutflows from cosmic explosions create shocks that accelerate electrons and produce radiation, including radio waves. This study develops an analytical model for a late stage when the shock slows below about one-fifth of light speed and only some electrons reach relativistic energies. Its predictions suggest that some fading explosions should remain brighter in radio waves than standard calculations imply. For one modeled remnant of a neutron-star merger, including this stage raises the predicted early radio brightness by roughly three to five times, and by more later. The study also predicts radio emission from remnants energized by a long-lived, rapidly spinning magnetar, although existing limits for GW170817 already argue against that possibility in that event. Applying the framework to supernova SN 2023ixf, the authors infer how the surrounding material’s density changes with distance. The predicted emission typically peaks below one gigahertz, making low-frequency radio searches useful; even a failure to detect it can constrain the surroundings and the outflow’s energy.

Young explorerWhen a star explodes, rushing material can push into the stuff around it and make radio waves. Scientists made a math model of what happens as that rush slows down. Their model says some explosions could stay brighter in radio waves than older calculations suggested. These are predictions, not new pictures of explosions. Listening for those radio waves—even when we hear nothing—can help scientists learn about the explosion and what surrounds it.

Spectral energy-loss bump and γ-ray pulsar halos

Kun Fang

AstronomerThe broadband Geminga halo spectrum measured by Fermi-LAT and HAWC is consistent with an age-dependent energy-loss bump expected from continuous electron injection and nonlinear radiative losses. The authors interpret the GeV-region bump as arising primarily from electrons injected at early times, allowing spectral fits to constrain the braking index n and initial spin period P0. Explaining the spectrum also requires an injection power-law index close to 1, consistent with X-ray observations of the Geminga pulsar wind nebula. No significant energy-loss bump is currently detected for Monogem; its absence yields preliminary constraints on n and P0. The analysis presents halo spectra as a route to model-based, independent estimates of intrinsic pulsar properties.

PublicThe gamma-ray glow around the Geminga pulsar may preserve clues to its early history. Researchers find that measurements from Fermi-LAT and HAWC match an expected bump in the spectrum caused by electrons losing energy. Their interpretation links this feature mainly to electrons released early in the pulsar’s life. Fitting the spectrum lets them constrain how rapidly Geminga initially spun and how its rotation slowed, as well as the energies of the electrons it released. The electron-energy distribution needed by the model is also consistent with X-ray observations of Geminga’s surrounding nebula. A second pulsar halo, Monogem, has no significant detected bump, so its corresponding constraints remain preliminary.

Young explorerA spinning star called Geminga has a glow around it that we cannot see with our eyes. Scientists measured this glow and found that its pattern fits an idea about tiny particles losing energy. They think a bump in the pattern comes mostly from particles the star sent out long ago. That could help them work out how fast the star spun when it was young. Another star, Monogem, has no clear bump in its glow, so the clues about its early spinning are still uncertain.

Signatures of Lorentz violation in the bright ring for Sgr A* images from radiatively inefficient accretion flows

Cuiyu Zhao, Songbai Chen, Jiliang Jing

• General Relativity and Quantum Cosmology

AstronomerThis study models Sgr A*’s 230 GHz thermal synchrotron image from a radiatively inefficient accretion flow around a rotating Lorentz-violating black hole in low-energy Hořava gravity. In the model, the Lorentz-violation (LV) parameter reduces the bright-ring diameter while increasing its width, luminosity, azimuthal asymmetry, and orientation angle; higher spin strengthens these effects. A thicker disk reduces the diameter and enhances its sensitivity to LV, but ring width has no systematic dependence on disk thickness. Applying EHT observations to this model yields parameter constraints, not a detection of LV. At fixed disk thickness, the allowed LV range first broadens and then contracts with increasing spin, shifting toward smaller LV values. LV also narrows the allowed spin range: negative LV values favor higher spins, while positive values favor lower spins. The peak positions and widths of the primary image and n=1 photon ring nearly always decrease with increasing LV parameter. Differences in peak position between LV values are more pronounced for purely Keplerian flows, while purely radial free-fall produces broader primary-image and photon-ring features than purely Keplerian motion.

PublicResearchers modeled how a proposed change to gravity involving Lorentz violation could affect images of Sgr A*. Their calculations predict a smaller but wider and more luminous bright ring, with greater unevenness around the ring and a changed orientation. Faster black-hole rotation strengthens these modeled effects. The thickness and motion of the surrounding gas also matter, so the ring’s appearance does not depend on gravity alone. Comparing the model with Event Horizon Telescope observations restricts which combinations of rotation and Lorentz violation are allowed. Those restrictions change with the assumed disk thickness and spin; they do not establish that Lorentz violation exists. The study also predicts changes in the positions and widths of finer image features, including a photon ring, depending on the proposed gravity change and how the gas moves.

Young explorerScientists used a model to ask how a different rule for gravity might change the glowing ring around a black hole. In their model, the ring could become smaller across but thicker and brighter. Swirling or falling gas changes the picture too. They compared their model with telescope observations, but that does not prove the different gravity rule is real.

Chana: A GPU-Accelerated Adaptive-Mesh Code for General Relativistic Magnetohydrodynamics with Multigroup M1 Neutrino Transport

Tianshu Wang

• Instrumentation and Methods for Astrophysics

AstronomerThe paper introduces Chana, a GPU-accelerated, block-structured adaptive-mesh code coupling GRMHD, multigroup M1 neutrino transport, and dynamical spacetime evolution with Z4c. Physical modules independently select spatial discretizations and ghost-zone widths; stiff radiation–matter coupling is integrated implicitly using analytically calculated Jacobians. Implemented in C++20 with MPI and Kokkos 5, the code is validated against GRMHD, radiation-transport, and dynamical-spacetime tests. In a representative core-collapse supernova configuration with three neutrino species and 12 energy groups per species, four-stage RK4 integration achieves approximately 1.1 million cell updates per GPU second on NVIDIA A100 GPUs. Reported weak-scaling efficiency exceeds 85% through 256 GPUs on Perlmutter. These are code-validation and computational-performance results, not observational findings or reported supernova discoveries.

PublicResearchers present Chana, a new simulation program for modeling magnetized matter, neutrinos, and changing spacetime under general relativity. It uses graphics processing units (GPUs) and a grid that can adapt its level of detail, with different numerical choices for different parts of the physics. The authors report checks of the program’s treatment of matter, radiation, and spacetime. For a representative setup used to simulate a collapsing stellar core, it performed about 1.1 million grid-cell updates per GPU per second on NVIDIA A100 GPUs. Its efficiency at handling proportionally larger problems stayed above 85% when scaled up to 256 GPUs on Perlmutter. The paper reports software tests and computing performance, rather than observations of an actual exploding star.

Young explorerScientists made a computer program called Chana to help pretend, using math, what happens when a star’s middle collapses. It can keep track of moving star material, tiny particles called neutrinos, and changes in space and time. They checked different parts of the program and tested how fast it worked on many computer chips. These were computer tests, not pictures or measurements of a real exploding star.

Ellis-Bronnikov Wormhole Shadows with Spherically Symmetric Accretion Flow

Mikiya M. Takahashi, Keisuke Nakashi

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

AstronomerGeneral relativistic radiative transfer simulations with synchrotron emission compare an Ellis–Bronnikov wormhole and a Schwarzschild black hole under spherically symmetric, steady-state accretion. Both produce a central shadow and a bright photon ring, but the wormhole's shadow region and ring are brighter. The authors attribute this to the absence of an event horizon, which permits emission from accreting matter around and beyond the throat to contribute. Although the simulated total fluxes and ring diameters are comparable to EHT observations of M87*, neither model reproduces the observed deep central brightness depression. The authors conclude that non-spherical accretion is required for a detailed comparison; these spherical-flow simulations do not establish an observational identification of a wormhole.

PublicThe researchers simulated what a hypothetical Ellis–Bronnikov wormhole and a Schwarzschild black hole would look like with matter flowing steadily inward in a spherical pattern. Both simulated images have a dark center surrounded by a bright ring, but the wormhole's center and ring are brighter. In the wormhole model, there is no event horizon to block contributions from glowing matter around and beyond its throat. The simulations produce overall brightnesses and ring sizes comparable to the Event Horizon Telescope's observations of M87*, but neither reproduces its deeply dark center. The authors therefore say that a less spherical flow of matter is needed for a detailed comparison. These are simulation results, not evidence that a wormhole has been observed.

Young explorerScientists used computers to make pretend pictures of a black hole and a possible space tunnel called a wormhole, with glowing stuff falling toward them from all sides. Both pictures had a dark middle and a bright ring, but the wormhole picture was brighter because more glowing stuff could add light. A real telescope picture of M87* has a much darker middle than either pretend picture. The scientists say they need to try a different way for the stuff to fall in. They did not discover a wormhole.

Direct Injection of Chemically-Enhanced Plasma into a Solar Flare Arcade

Jeffrey W. Reep, Andy S.H. To

AstronomerThe authors test the proposal that reconnection exhaust loads newly reconnected flare arcades with plasma of coronal composition, producing observed post-flare abundance patterns. Their modeling tracks the spatiotemporal evolution of low-first-ionization-potential (low-FIP) elements with material injected near loop apices. Direct injection can produce abundance enhancements similar in magnitude and spatial extent to those observed during the gradual phase of an X11.9 flare. In the model, direct chromospheric heating instead confines the enhancement to a narrow region near the injection site. The authors interpret low-FIP abundance enhancements as an explanation for bright knots commonly observed near arcade tops; the modeling demonstrates the mechanism's capability rather than establishing it as the observed cause.

PublicSolar flares rearrange magnetic fields and can send material into newly formed loops. This study models a proposed explanation for the unusual chemical makeup observed in some post-flare loops: material from the Sun's outer atmosphere is injected near the loop tops and flows downward. The modeled enrichment of certain elements can resemble the strength and spread observed during the gradual phase of an X11.9 flare. The model also shows that directly heating the Sun's lower atmospheric layer, the chromosphere, restricts this enrichment to a small area near the injection point. The authors suggest that enriched material could explain bright spots often seen near the tops of flare loops, but the simulations do not prove that this is their actual cause.

Young explorerAfter a big burst on the Sun, hot gas can follow magnetic loops. Scientists used a computer model to try putting extra gas near the tops of these loops. The model made patches rich in certain kinds of atoms, a bit like patches seen after one big solar burst. Heating gas lower down kept those patches small in the model. The scientists think the extra atoms could help explain bright spots at the loop tops, but they have not shown for sure that this is what makes them.

Rotation in the Lagoon Nebula with K2

L. M. Rebull, A. M. Cody, L. Venuti+2 more

AstronomerK2 observations of the approximately 1–2 Myr Lagoon Nebula yield reliable rotation periods for 325 stars from 414 light curves, including 124 disk-bearing and 201 disk-free stars. The sample substantially expands the available K2 rotation measurements for approximately 1–5 Myr stars. The rotation distribution is broadly consistent with expectations: mid-K stars are the slowest rotators, while stars of both lower and higher mass rotate faster on average. Evidence that disk-bearing stars rotate more slowly is weak. A few complex periodic variables are identified and appear to have surprisingly high masses relative to previously known examples. These observations provide constraints for models of star and planet formation.

PublicUsing K2 observations, researchers measured how long 325 young stars in the Lagoon Nebula take to spin once. The region is about 1–2 million years old, making it one of the youngest star clusters with rotation measurements from space. Of the stars with reliable measurements, 124 have surrounding disks and 201 do not. The slowest-spinning stars are in the mid-K stellar category; stars with either lower or higher masses tend to spin faster on average. There is only weak evidence that stars with disks spin more slowly. A few stars show complex repeating brightness changes and appear unusually massive compared with previously known examples of that kind. The measurements can help test ideas about how stars and planets form.

Young explorerScientists watched young stars in a place called the Lagoon Nebula and worked out how fast 325 of them spin. Some have disks of material around them, and some do not. The stars with disks might spin more slowly, but the clues are not strong enough to be sure. A few stars also brighten and dim in complicated repeating patterns. Learning how stars spin helps scientists study how stars and planets form.

Enhanced Mass Transfer from Extended Shock-Supported Stellar Chromospheres

Soumyadeep Bhattacharjee, Jim Fuller, Kareem El-Badry

AstronomerThe authors derive an analytic prescription for mass transfer from a shock-supported chromosphere in a binary potential and implement it in MESA. Motivated by hydrodynamic simulations suggesting that shocks can extend giant-star chromospheres to a few stellar radii, the model predicts optically thin mass-transfer rates orders of magnitude above conventional thermal-pressure-supported atmosphere estimates, especially high on the red giant and asymptotic giant branches. It permits substantial accretion before the donor’s photosphere fills its Roche lobe, in systems subsequently undergoing either stable mass transfer or common-envelope evolution. For fixed initial binary parameters, this may change predicted final periods and component masses. The prescription resembles Wind Roche-lobe Overflow but has a physical rather than empirical motivation. These are model predictions, with implications proposed for testing through population synthesis and observed binary populations. The authors also identify and correct an inaccuracy in MESA’s implementation of the optically thin Ritter 1988 prescription.

PublicA giant star in a pair may begin feeding its companion well before its visible surface reaches the boundary usually associated with strong mass transfer. Earlier models generally assumed a very thin outer atmosphere and therefore little early transfer. Motivated by simulations in which shocks produce much more extended atmospheres, the authors developed a mathematical model and added it to the MESA stellar-evolution code. Their calculations predict that some giant stars could transfer matter at rates orders of magnitude higher than earlier estimates during this early stage. The extra feeding could change the stars’ eventual masses and orbital period, whether the later interaction remains stable or develops into a shared envelope. These are predictions rather than observational findings; the authors discuss how they could be tested against populations of interacting stars. They also correct an inaccuracy in an existing MESA mass-transfer calculation.

Young explorerTwo stars can travel around each other, and one can give some of its gas to the other. Scientists made a new computer recipe to explore what happens if shocks puff up a giant star’s outer gas. The recipe says much more gas might reach the other star before the giant’s main surface gets close enough for the usual strong sharing to begin. That could change how the pair ends up. This is an idea worked out with calculations, not something this study has shown by watching stars.

simesh: A Python Framework for Quantitative Analysis of Native AMR Data from MPI-AMRVAC

Hao Wu, Jinhan Guo, Rony Keppens+1 more

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

Astronomersimesh is an independent Python framework for quantitative analysis of cell-centered fields on block-structured adaptive mesh refinement (AMR) meshes. Its current implementation supports three-dimensional Cartesian datasets from MPI-AMRVAC and compatible AGILE snapshots, retaining the native AMR hierarchy and combining Python interfaces with compiled Cython kernels. Comparisons with VTK point-data conversion and uniform-grid resampling show that data association, interpolation support, and differentiation scale affect sampled magnetic fields and derived current densities. Small differences in the primary field can be amplified in derivative-based quantities, especially near coarse-fine interfaces. Applications combine field diagnostics, tracing, regional statistics, and line-of-sight integration within the same native AMR representation. These are simulation-analysis findings, not astronomical observations.

PublicAstrophysical simulations often use a patchwork of coarse and fine grids to represent structures at different scales. The authors present simesh, a Python tool for analyzing these simulations without replacing that grid structure. In comparisons with methods that convert or resample the data, they find that the processing choices change the sampled magnetic fields and the electric current densities calculated from them. Small field differences can become more noticeable when calculating how the field changes across space, particularly where coarse and fine grids meet. The tool brings several analysis tasks into a shared, reusable workflow. Its current scope is three-dimensional Cartesian simulation data from MPI-AMRVAC and compatible AGILE snapshots; the findings concern analysis methods rather than observations of space.

Young explorerScientists make computer models of space using boxes of different sizes. A new tool called simesh helps them study those models while keeping the boxes as they are. The researchers found that changing how the model data are arranged can change the answers they calculate about magnetism. Small differences can look bigger when they work out how magnetism changes from place to place, especially where big and small boxes meet. This is about studying computer models, not finding something new in the real sky.

Stellar Loci X: Selection of Nitrogen-Rich Giants Using GALEX NUV and Synthetic SDSS Photometry

Liangyu Yu, Haibo Yuan, Baitian Tang+3 more

• Astrophysics of Galaxies

AstronomerThe study presents a photometric selection of nitrogen-rich giant candidates, motivated by their likely association with second-generation stars lost from globular clusters. Enhanced NH and CN absorption suppresses u-band flux, whereas NUV photometry is largely insensitive to nitrogen enhancement but remains sensitive to overall metallicity. Combining GALEX NUV with synthetic SDSS optical photometry, the authors model the metallicity-dependent giant locus and identify significantly redder u-g outliers. A relaxed selection ([Fe/H] <= -0.8, 2 sigma) yields 970 candidates, with estimated completeness of 64-65% and purity of 41-62%; a stricter selection ([Fe/H] <= -1.0, 3 sigma) yields 220 candidates, with 30-38% completeness and 60-91% purity. These are candidates rather than uniformly confirmed nitrogen-rich stars. Dominant contaminants have anomalous spectral energy distributions, including UV excess. Diverse candidate kinematics and dynamics suggest multiple origins. The method offers a scalable route to halo searches and is proposed as well suited to forthcoming surveys such as CSST.

PublicAstronomers have developed a way to search for nitrogen-rich stars using their ultraviolet and visible-light colors. Such stars may include former members of globular clusters, so finding them could help trace how these clusters lose stars into the Milky Way’s halo. Nitrogen-bearing molecules dim one visible-light band, while a near-ultraviolet band helps account for differences in overall metal content. A broader search identified 970 candidates; a stricter search selected 220 with a higher estimated fraction of genuinely nitrogen-rich stars, but missed more potential targets. Neither list is entirely free of unrelated stars. The candidates’ varied motions suggest they may have more than one origin. The authors argue that this approach could support larger searches with future surveys.

Young explorerSome stars may have wandered away from big groups of stars. Scientists are looking for ones with extra nitrogen by checking the colors of their light. They found many stars that might fit, but some could be look-alikes. The stars move in different ways, so they may not all have come from the same kind of place.

Coronal spectroscopy - Past, Present and Future

Jagdev Singh, R. Ramesh, V. Muthu Priyal

AstronomerThis review traces solar-coronal spectroscopy from early eclipse observations to present instruments and future observational needs. It recounts Janssen’s observation of the 5875 Å emission line during the 1868 eclipse, leading to helium’s discovery, and the 1869 discovery of a green line later measured at 5303 Å. Initially attributed to a hypothetical element, coronium, the green line was identified in 1939 with [Fe XIV], establishing a coronal temperature of about 10^6 K. High-resolution observations revealed excess emission-line widths, interpreted as evidence of non-thermal velocities. More recent spectroscopy indicates complex height dependence of emission-line parameters. The review discusses observations across the spectrum, including those with the Visible Emission Line Coronagraph aboard Aditya-L1, and the need for future spectroscopy; the abstract reports no specific new instrumental measurements.

PublicThis article reviews how studying the Sun’s outer atmosphere through its spectrum has changed our understanding of it. Eclipse observations helped reveal helium in 1868. A green emission line discovered the following year was first attributed to an unknown element called coronium, but its later identification with iron ions showed that the Sun’s outer atmosphere reaches about a million kelvin. Observed spectral lines are also broader than expected, which researchers have interpreted as evidence of motions beyond those associated with heat alone. Recent observations show that the lines’ properties vary with height in complicated ways. The article surveys past and present observations, including Aditya-L1’s coronal instrument, and discusses future observing needs rather than presenting a specific new discovery.

Young explorerThe Sun has a very hot outer layer. Scientists study its light for clues about what is there and how it moves. Long ago, one green light clue seemed to come from a mystery material, but it turned out to come from iron. This article tells the story of those discoveries and explains why scientists want to keep looking.

Neutron Star-Main-Sequence Star Collision: Formation and Long-Term Evolution of Thorne-Żytkow Objects

Yuhao Guo, Xiao-Tian Xu, Dong Lai

• High Energy Astrophysical Phenomena

AstronomerThis modeling study links dynamical formation and subsequent evolution of a Thorne–Żytkow object, a stellar envelope surrounding a compact core and powered primarily by accretion. A three-dimensional simulation of a post-supernova collision between a 1.4-solar-mass neutron star and a 10-solar-mass main-sequence star produces a bound, quasi-spherical object with the neutron star at its center; subsequent evolution is calculated with MESA. Unlike classical models initialized in equilibrium, the collision heats a substantial fraction of the star, driving widespread nuclear burning during thermal relaxation. Convection carries carbon–nitrogen-cycle-processed material to the surface, producing a potentially observable formation signature that persists after the object reaches its standard accretion-supported structure. At the simulation endpoint, the luminosity greatly exceeds the Eddington limit in the outer envelope. The authors interpret this as suggesting substantial future mass ejection and an isolated neutron-star or black-hole remnant, rather than demonstrating that outcome.

PublicComputer models explore what happens when a neutron star collides with a much larger ordinary star and settles at its center. The simulated collision creates a Thorne–Żytkow object: a star with a compact core, powered mainly by material falling onto that core. The collision heats much of the star, triggering widespread nuclear reactions as it readjusts. Churning gas then brings chemically altered material to the surface, where it could provide a detectable clue to the collision even after the star settles into its longer-term structure. This is a prediction from simulations, not an observed detection. By the end of the calculation, the outer layers are so luminous that the authors suggest substantial gas loss will follow, potentially leaving an isolated neutron star or black hole; that final outcome was not demonstrated.

Young explorerScientists used a computer to imagine a tiny, very heavy star crashing into a much bigger star. In their model, the tiny star ends up in the middle, wrapped in the bigger star’s gas. The crash heats the gas and helps change what it is made of. Mixing carries some changed gas to the outside, which might give astronomers a clue that a crash happened. The scientists think much of the gas may later blow away, leaving a neutron star or a black hole, but their model did not show that ending.

The diversity of late-time interaction in Type II supernovae

Luc Dessart, Wynn V. Jacobson-Galán, K. Azalee Bostroem

• High Energy Astrophysical Phenomena

AstronomerThe study presents about 200 radiative-transfer models of CSM-powered ejecta from binary progenitors with different degrees of hydrogen-envelope stripping, representing Type IIb, II-L, and II-P supernovae from 1.5 years to 3–6 years after explosion. Models span cold-dense shell masses of 0.1–2.0 solar masses, velocities of approximately 5,000–10,000 km/s, and shock powers of 10^39–10^41 erg/s. Lyalpha, Mg II 2800, and Halpha are typically the strongest individual predicted lines; Mg II 2800 is least sensitive to time and shell mass, while Lyalpha is strongly attenuated at higher shell mass. A forest of Fe lines substantially shapes the emerging UV and optical flux through optical-depth effects, and nitrogen enrichment strengthens nitrogen lines. Some models roughly reproduce observations of SNe 1993J, 1998S, 2013ej, and 2023ixf at 1.5–3 years, but consistent agreement across the full range remains challenging, especially where dust must be invoked. Importantly, simulated UV line profiles commonly exhibit blue-red asymmetry even without dust. Gas opacity, dust opacity, or both can suppress Lyalpha and [O III] 4958–5007 emission originating within or beneath the shell.

PublicYears after a massive star explodes, collisions between its expanding debris and surrounding material can become the main source of its light. This study uses about 200 computer models to explore how those collisions shape ultraviolet and visible light, potentially revealing how the star shed material before exploding. The models predict especially strong emission from hydrogen and magnesium, while many iron lines also strongly influence the escaping light. Some models roughly match observations of four supernovae, but reproducing the full range of observations consistently remains difficult, particularly when dust is needed. The calculations also show that unequal emission on the blue and red sides of ultraviolet spectral lines need not indicate dust: the gas itself can block light and produce such asymmetry.

Young explorerAfter a star explodes, the pieces rushing outward can bump into material around it and keep making light for years. Scientists used computer models to work out what that light might look like. Some models look a little like light measured from real exploded stars, but they do not match everything. The models also show that gas can hide some of the light, even when there is no dust.

Relation of Rotation and Pulsation Properties in γ Doradus Stars

Á. Sódor, E. Plachy, Zs. Bognár

AstronomerUsing new ACE spectroscopy of 124 targets and TESS light curves through sector 98, the authors investigate rotation–pulsation relations in gamma Doradus stars. Both peak-to-peak amplitude and dominant-component semi-amplitude show a decreasing upper envelope with spectroscopic v sin i: high-v sin i stars have only low amplitudes, while high-amplitude stars have low v sin i. This does not imply that every low-v sin i star has high amplitude. Dominant pulsation frequency increases with v sin i, and the highest observed amplitudes decrease toward higher dominant frequencies. Rotation- and inclination-dependent visibility modelling using GYRE Hough functions and TAR visibilities indicates that geometry alone cannot explain the trends, suggesting an intrinsic decrease in pulsation amplitude with increasing equatorial rotation speed. Because v sin i also depends on inclination, it does not uniquely determine rotation speed. Modelled suppression of zonal dipole visibility at high rotation further suggests that high-amplitude stars are slow rotators or moderate rotators viewed nearly pole-on.

PublicA study of 124 gamma Doradus stars links their pulsating brightness changes to rotation. Spectra measure rotation as projected toward our view, while TESS observations reveal the brightness variations. Stars with high projected rotation speeds show only small variations; stars with large variations have low projected speeds. Low projected speed, however, can reflect either slower rotation or a view close to the star’s rotation pole. The researchers also find that higher projected speeds tend to accompany faster pulsations, whose largest observed brightness changes are smaller. Their modelling suggests that viewing geometry alone cannot explain the patterns: faster rotation may physically weaken the pulsations. The models also suggest that the largest-amplitude stars rotate slowly, or moderately fast while viewed nearly pole-on.

Young explorerSome stars get brighter and dimmer as they pulse. Scientists studied 124 of these stars. Stars whose spinning looked fast had only small brightness changes. Big brightness changes appeared only when the spinning looked slow—but looking down a star’s spin pole can hide how fast it turns. Computer models suggest faster spinning may make the pulses weaker, though that explanation is not certain.

A Catalog of Dispersive Ionospheric and Plasmaspheric Arcs from Cislunar and Lunar-surface GNSS Radio Occultations

Francesco Fiorina, Alex Minetto, Rebecca Ghidoni+5 more

• Space Physics
• Signal Processing

AstronomerThis observational catalog contains 263 dispersive occultation arcs attributed to ionospheric and plasmaspheric effects in GNSS signals recorded by LuGRE during Blue Ghost Mission 1, in cislunar space and on the lunar surface. GPS and Galileo dual-frequency observables are processed independently to derive the total electron content rate (ROT) and ROT index (ROTI), identify ingress, egress and tangent arcs, and validate them using a tangent-point grazing-altitude criterion. Each arc is treated as a combined dispersive signature; ionospheric and plasmaspheric contributions are not separated. The HDF5 catalog supplies timing, grazing altitude, summary ROT/ROTI/ΔSTEC attributes, geomagnetic activity, and time series of leveled slant total electron content, ROT, ROTI, tangent-point position and local time. The slant total electron content is not corrected for instrumental biases. Dataset-wide metadata and per-class statistics support arc selection for statistical and targeted analyses, complementing ground-based and low Earth orbit radio-occultation data during the declining phase of solar cycle 25.

PublicResearchers have cataloged 263 episodes in which ionized material affected GPS and Galileo radio signals received by the Lunar GNSS Receiver Experiment during Blue Ghost Mission 1, both in the space between Earth and the Moon and on the lunar surface. They identified and classified these episodes using changes in the signals and checked them against the geometry of the signal paths. The catalog records when each episode occurred, where the signal path passed, and how the electron content along it changed. It does not separate the effects of the ionosphere from those of the plasmasphere, and its electron-content measurements have not been corrected for instrument-related biases. The dataset is a resource for further studies, complementing observations from the ground and low Earth orbit.

Young explorerA receiver traveling to the Moon and sitting on its surface listened to radio signals from GPS and Galileo satellites. Scientists made a list of 263 times when electrically charged material changed those signals. The list can help scientists study that material, but it does not tell them how much of each change came from two different regions around Earth.

Hybrid Stars with a Crossover Equation of State

G. A. Tsalis, Ch. C. Moustakidis

• Nuclear Theory

AstronomerThis theoretical study models the still-hypothetical transition from hadronic to deconfined quark matter using a smooth switching function, rather than the conventional Maxwell or Gibbs constructions. It investigates how symmetry energy affects transition densities and chemical potentials, and seeks physical constraints and a parametrization for the switching function’s two parameters. The authors conclude that suitable parameter choices make the phenomenological model more physically motivated and useful for studying hybrid compact objects. They also suggest that it can predict relatively low-mass, small-radius objects beyond standard neutron-star theory. The abstract gives no quantitative parameter constraints or predictions, and does not establish that the transition occurs or that observed objects contain quark matter.

PublicScientists do not yet know whether extremely dense matter can change from hadronic matter into a proposed state of deconfined quarks. This theoretical study explores a model that blends the two forms smoothly. The researchers examine how a property called symmetry energy affects where the change happens, and seek physically justified choices for the model’s two adjustable parameters. They conclude that suitable choices make the model useful for exploring compact stars containing both forms of matter. It could also predict unusually low-mass stars with small radii, but the abstract does not report observational confirmation of the model or of quark matter.

Young explorerScientists wonder whether matter squeezed very tightly inside some stars could change into a different form. They made a model that lets the change happen smoothly and studied how to choose its settings to make physical sense. It might help them imagine stars that are small and not very heavy. But they have not shown that this change really happens.

An Implicit Conservative Finite Volume Scheme with Poisson Brackets for the Steady-State Transport of Galactic Cosmic Rays

Weihao Liu, Igor V. Sokolov

• Space Physics

AstronomerThe authors present an implicit conservative finite-volume scheme for kinetic equations written with Poisson brackets. The scheme conserves particle number, is total-variation-diminishing, has second-order spatial accuracy, and remains stable at time steps far beyond the explicit stability limit. Numerical tests reach quasi-steady states using less than about one hundredth of the explicit scheme's computational time. Applied to the Parker transport equation along magnetic field lines in the background solar wind during Carrington rotation 2211, it reaches steady-state GCR distributions within 10 iterations, about 1000 times faster than the explicit scheme. The simulated 27-day-averaged proton spectrum agrees with AMS-02 measurements to within 10%. The simulation also produces a realistic radial intensity gradient and captures Forbush-decrease features associated with three stream interaction regions observed at Earth. These tests demonstrate computational gains and agreement with selected observations, rather than establishing general predictive accuracy.

PublicGalactic cosmic rays are energetic particles that pose a radiation hazard to astronauts and spacecraft. Researchers have developed a faster computer method for calculating how the solar wind and its magnetic field affect these particles. In a simulation of one solar rotation, the method reached a steady distribution about 1000 times faster than the explicit method used for comparison. Its proton spectrum, averaged over 27 days, agreed with AMS-02 measurements to within 10%. The simulation also reproduced features of temporary cosmic-ray decreases associated with three regions where solar-wind streams interacted, observed at Earth. The results support the method's usefulness for faster modeling, but do not establish how accurately it would predict every future event.

Young explorerTiny particles from space can be dangerous to astronauts and spacecraft. Scientists made a faster way for computers to work out how these particles move through the Sun's wind and magnetic field. In one test, the new way was about 1000 times faster than the older way they compared it with. Its answers were close to real measurements and showed some of the same drops in particle numbers. That is promising, but it does not mean the computer can always tell exactly what will happen next.

Asteroseismology of the High-amplitude δ Scuti Star EH Librae

Xiran Xie, Jianning Fu, Gang Meng+7 more

AstronomerGround- and space-based photometry of the high-amplitude δ Scuti star EH Lib reveals a dominant frequency f0 = 11.3105 d⁻¹, two newly detected significant frequencies, harmonics of f0, and a linear combination. An O−C analysis of 342 times of maximum light spanning more than 70 years yields a fractional period increase of (5.4 ± 0.5) × 10⁻⁹ yr⁻¹. Using literature metallicities, the authors construct MESA evolutionary models and calculate eigenmode frequencies with GYRE, selecting models that match f0, the fractional period-change rate, and luminosity within their uncertainties. These models support stellar evolution as an explanation for the observed period change and yield a mass of 1.555 ± 0.015 M☉, log(L/L☉) = 1.26 ± 0.02, and an age of 1.46 ± 0.05 Gyr. The study classifies EH Lib as a single-radial-mode HADS star on the subgiant branch, with a helium core and a hydrogen-burning shell; the additional detected frequencies are not identified in the abstract.

PublicAstronomers studied changes in the brightness of EH Lib, a star that pulses strongly, using observations from the ground and space. They measured its main pulsation frequency at 11.3105 cycles per day and detected two additional significant frequencies. Records of 342 brightness peaks over more than 70 years show that its main pulsation period is slowly increasing. Computer models matched to the observations suggest that this change can be explained by the star’s evolution. The models estimate that EH Lib has about 1.56 times the Sun’s mass and is about 1.46 billion years old. The researchers classify it as a subgiant with a helium core surrounded by a shell where hydrogen burns. Those internal properties and the explanation for its changing rhythm come from modeling, rather than direct observation of its interior.

Young explorerEH Lib is a star that gets brighter and dimmer as it pulses, a little like a beating heart. Astronomers studied its light and used records stretching back more than 70 years. They found that its main beat is getting a tiny bit slower. They also made computer models of the star. Those models suggest that the beat could be changing because the star is growing older and changing inside.

JOYS: Launch and destruction of dust in protostellar jets. The case of BHR71-IRS1 with JWST MIRI

Łukasz Tychoniec, Logan Francis, Maria Gabriela Navarro+24 more

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies

AstronomerJWST MIRI-MRS spectral imaging of the inner 2000 au of the blueshifted BHR71-IRS1 outflow spatially resolves its ionized central jet for the first time. Fine-structure emission from Fe, Ni, Co, Cl, S, Ne, and Ar is concentrated in four bright knots along a wiggling jet axis. PSF-subtracted maps reveal extended mid-infrared continuum coincident with the jet bullets and inside the H2-traced outflow cone. Joint fits of the dust spectral energy distributions and extinction indicate warm (200–400 K) and cold (70–90 K) dust components. Comparisons of atomic line intensities with shock models infer declining shock velocities, from 70 to 35 km/s, and pre-shock densities, from above 100,000 to 40,000 particles per cubic centimetre, with increasing distance from the protostar. Gas-phase Fe and Ni are depleted relative to Solar abundances, consistent with substantial refractory material remaining in grains despite shocks. The authors present these observations as direct evidence for dust launched in a Class 0 jet and surviving shock processing at least partly; the shock conditions and dust temperatures are model-derived rather than direct measurements.

PublicWinds from very young stars could carry dust away from planet-forming disks, but direct evidence has been scarce. Using JWST, researchers imaged the central jet from the young star BHR71-IRS1 and found four bright knots along its winding path. They also detected extended infrared emission from dust in the same locations as the jet knots. Fits to the dust emission indicate both warmer and colder dust components. Comparisons with shock models suggest that shocks weaken and the gas entering them becomes less dense farther from the star. Iron and nickel are less abundant in the gas than Solar abundances would suggest, consistent with much of these materials still being trapped in dust grains. The authors conclude that the observations provide direct evidence that this young stellar jet carries dust and that some of it survives shocks.

Young explorerA baby star called BHR71-IRS1 shoots out a stream of gas. Scientists used the Webb telescope to see bright spots in the stream and found dust glowing there too. They say this shows that dust gets carried along with the gas. Even when the dust goes through shocks, some of it seems to survive.

A systematic study of quiescent and outburst properties of X-ray-bright young stellar objects using XMM-Newton

Koki Sakuta, Ikuyuki Mitsuishi, Seiya Sasamata+6 more

AstronomerAn archival XMM-Newton study of 51 X-ray-bright young stellar objects combines timing analysis with phase-resolved, multi-temperature spectroscopy of quiescent and outburst emission. Both phases show multi-temperature plasma structures. Timing–spectral relationships, Neupert-like behavior, temperature and emission-measure evolution, the Rossby-number activity relation, and correlations between quiescent and outburst properties broadly support magnetic reconnection in both phases. Comparison with Gaia DR3 stellar parameters indicates that magnetospheric accretion alone has difficulty explaining most fitted temperatures, although components with kT ≲ 0.3 keV may include accretion-shock emission. Excluding these cool components reveals a clearer positive quiescent emission-measure–temperature correlation, with inferred magnetic-loop lengths distributed around 10^12 cm. The evidence favors a key role for reconnection rather than uniquely establishing it, and the sample specifically selects X-ray-bright objects.

PublicResearchers studied archived XMM-Newton observations of 51 young stars bright in X-rays, comparing their quieter periods with outbursts. They found gas at multiple temperatures in both phases. The way the X-ray brightness and gas properties vary supports the idea that magnetic fields rearranging and releasing energy help power both kinds of emission. Comparisons with stellar properties from Gaia suggest that gas falling onto the stars cannot, by itself, readily explain most of the fitted temperatures. However, shocks from that falling gas could contribute to the coolest emission. These findings favor magnetic energy release as a major source of the X-rays, without proving it is the only source.

Young explorerScientists looked at X-rays from 51 young stars, both when they were quieter and when they flared up. They found very hot gas at different temperatures. The clues suggest that the stars’ magnetic fields release energy and heat the gas. Gas falling onto the stars might help make some of the cooler X-ray glow, too.

Spectroscopic Binary Detection as Agent-Callable Tools: Detecting 40,000+ Main-Sequence Binary Candidates from SDSS DR19 APOGEE Spectra

Serat M. Saad, Yuan-Sen Ting

• Instrumentation and Methods for Astrophysics

AstronomerThe authors package the El-Badry et al. (2018b) SB2 decomposition method for APOGEE as nine Model Context Protocol tool servers plus a Skill encoding operating decisions. A fixed-driver run on 238,205 DR19 dwarfs flags 41,466 SB2 candidates, about 15 times the DR13 count, but not at matched purity. An 8.1% control false-positive rate implies nearly 40% contamination by single stars. Joint visit fitting favors two stars for 46% of candidates with multiple visits; 4,149 of these show velocity changes above 10 km/s, although 7% of flagged single stars also pass this cut. Pipeline velocities identify another 3,943 velocity variables. Among the best-sampled binaries, close twins with q > 0.95 show no significant eccentricity difference from matched non-twins, excluding an excess of the kind measured at wide separations. An ablation of two operating decisions finds that a fresh agent recovers a removed decision only when its absence leaves a measurable fit signature. The tools, Skill, candidate catalog, and multi-epoch supplement are released.

PublicWhen two stars blend together in a survey, treating their combined light as coming from one star can distort estimates of their properties. The researchers made an existing method for separating these signals reusable, packaging both software tools and instructions for operating them. Applied to 238,205 stars in an APOGEE data release, it flagged 41,466 possible pairs. This is about 15 times the number identified in an earlier release, but the lists are not equally reliable: the authors estimate that nearly 40% of the new candidates are actually single stars. Repeated observations provide additional evidence for some candidates, although even large measured velocity changes are not a foolproof test. Among the binaries with the best coverage, pairs with nearly equal masses showed no significant difference in orbital elongation from comparable pairs with less equal masses. The researchers also found that an automated agent recovered omitted operating guidance only when the omission left a measurable effect on the fit. They release the tools, instructions, and catalogs for reuse.

Young explorerTwo stars can be so close together in our view that their light looks mixed into one. Scientists used computer tools to look for signs of two stars hiding in that mixed light. They found many possible pairs, but think about four out of every ten on their list are really single stars. They shared their tools and instructions so other scientists can use them too.

Nova shells in 3D: I. A catalog of integral field spectroscopic observations

Janis B. Rodríguez-González, Edgar Santamaría, Martin A. Guerrero+1 more

• Astrophysics of Galaxies

AstronomerThe authors present what they describe as the first integral-field-spectroscopy-based 3D catalog of nova shells, compiling observations of 19 shells from VLT/MUSE with additional GTC/MEGARA and WHT/WEAVE observations. Selected emission-line visualizations reveal ellipsoidal or spherical shells, rings, bipolar features, and clumpy or irregular components, including structures obscured in 2D projections. Approximately 60% of the sample is predominantly ellipsoidal or spherical, while about 30% shows ring-like or bipolar structures. In several objects, [O III] or [N II] traces morphology and kinematic components distinct from Hα, indicating varied excitation and physical conditions within the ejecta. Integral field spectroscopy identifies a larger fraction of bipolar or toroidal shells than imaging studies. Comparing plane-of-sky and line-of-sight expansion velocities suggests low intrinsic aspect ratios, consistent with projected-shape estimates; intrinsic 3D structures nevertheless remain poorly constrained.

PublicNova eruptions occur on white dwarf stars that are collecting matter, throwing material outward into expanding shells. Researchers assembled observations of 19 nova shells and used spectroscopy to explore their three-dimensional shapes and motions, revealing features that ordinary flat images can hide. About 60% of the sample has mainly spherical or stretched-sphere shapes, while about 30% has rings or structures extending in two opposite directions. Some shells also contain clumps or irregular features. Light emitted by different elements sometimes reveals different structures and motions, pointing to varied physical conditions within the expelled material. The technique reveals a greater share of ring-shaped and two-sided shells than imaging studies do. Comparisons of expansion speeds suggest that the shells have relatively modest differences between their long and short dimensions, although their true three-dimensional structures remain uncertain.

Young explorerSome small stars called white dwarfs collect gas and have eruptions that throw it outward. The gas makes a growing shell around the star. Scientists studied light from 19 of these shells to explore their shapes, because a flat picture can hide parts of them. Many looked like balls or stretched balls. Others had rings, parts sticking out on opposite sides, or messy clumps. Different kinds of light sometimes showed different parts moving in different ways. The scientists can now see more of these hidden shapes, but they still do not know every shell’s exact shape.

Saturation Level of the Streaming Instability

Yanqin Wu, Xuqi Chen, Joshua Bromley

• Solar and Stellar Astrophysics

AstronomerThe authors estimate the strength of streaming-instability-driven turbulence in protoplanetary disks from the available free energy, obtaining alpha ~ St Pi^2 f(epsilon) for grain Stokes numbers St < 1. Here Pi is the dimensionless pressure gradient and f(epsilon) is an explicit function of the local dust-to-gas density ratio. The estimate explains results from many previous studies and is supported by additional purpose-built simulations. The authors discuss applications to a self-consistent dust scale height and the astrophysical relevance of a pressure bump. This is a theoretical and simulation-supported characterization of streaming turbulence, not an observational measurement; connecting turbulence strength to planetesimal formation remains unresolved.

PublicGas turbulence can gather dust grains in disks around forming stars, potentially helping build the small bodies that precede planets. This study estimates how strong the turbulence generated by the streaming instability should be, using the energy available to drive it. The estimate depends on how dust grains interact with gas, the disk's pressure gradient, and the local amount of dust relative to gas. It explains results from many earlier studies and is supported by new computer simulations. The authors discuss using it to estimate the vertical thickness of the dust layer and assess the importance of a local pressure bump. However, they cannot yet connect the predicted turbulence strength to whether planet-building bodies form.

Young explorerAround a young star, gas and dust make a big disk. Swirling gas can gather dust into clumps that might help make planets. The scientists used an energy estimate to work out how strong some of these swirls could be, and computer simulations supported their idea. But they still cannot tell from the strength of the swirls whether the dust will form the little bodies that can help build planets.

Systematic Uncertainties in Rocky Exoplanet Reflected Light from Incomplete Laboratory BRDF Measurements

Leonardos Gkouvelis, Michael K. Shepard, Paul Helfenstein+2 more

• Instrumentation and Methods for Astrophysics

AstronomerThis study identifies an intrinsic systematic uncertainty in rocky-exoplanet reflected-light modeling when laboratory bidirectional reflectance spectra sample only one illumination and viewing geometry. Multiple photometric parameter combinations can reproduce the same laboratory spectrum yet yield different angular scattering behavior and disk-integrated predictions. Propagating this degeneracy over 0.5–1.7 micrometers produces large uncertainties in modeled phase curves, geometric albedos, and planet-star contrast ratios, particularly at small phase angles. Isotropic-scattering assumptions can introduce additional systematic biases. Using multi-angular measurements from the Bloomsburg University Goniometer dataset, the authors show that directly constraining angular scattering sharply reduces these prediction uncertainties. These are laboratory-based modeling findings, not measurements of exoplanet surface properties, and support the need for multi-angular laboratory data for physically predictive reflected-light models, including those relevant to future missions such as HWO.

PublicTo interpret light reflected by rocky planets around other stars, scientists need laboratory measurements of how rock-like materials reflect light. This study shows that measurements made at just one lighting and viewing angle leave an important ambiguity: several models can match the same laboratory spectrum but predict very different planetary brightnesses as the viewing angle changes. The predicted differences are especially large when a planet presents a nearly fully illuminated face. Assuming that light scatters equally in every direction can add bias. Tests using laboratory measurements taken at multiple angles greatly reduced the uncertainty in the predicted signals. The work does not establish what any particular exoplanet surface is made of; it shows why better laboratory measurements are needed to interpret future reflected-light observations.

Young explorerA rock can look brighter or darker when you move a light or look at it from a different side. Scientists found that looking at a rock from just one angle is not enough to predict how a faraway rocky planet will shine. Different guesses can fit that one look but give different answers for the planet. When they used rock measurements from many angles, their predictions became much less uncertain. This helps scientists work out how to study faraway rocky worlds; it does not tell them yet what those worlds are made of.

FAUST XXXII. Chemically layered structures and ionisation in the disk and envelope of NGC 1333 IRAS 4C

Shota Notsu, Nami Sakai, Yichen Zhang+71 more

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics

AstronomerALMA FAUST molecular-line observations reveal vertical chemical stratification in the disk and envelope of the low-mass Class 0 protostar NGC 1333 IRAS 4C in Perseus. C18O and H2CO, used as gas-density tracers, are distributed around the disk midplane, while the photochemistry tracers CCH and c-C3H2 occupy low-density upper disk layers, unlike their distribution in L1527. The HCO+/CO column-density ratio inferred from H13CO+ and C18O emission suggests that both the ionisation degree and ionisation rate vary radially, with larger values in the outer disk and envelope. These observations extend investigations of chemical layering to a Class 0 system, a stage for which few objects have been studied.

PublicALMA observations show that different molecules occupy different heights in the gas surrounding the very young star NGC 1333 IRAS 4C. Some molecules are concentrated near the middle of its disk, while molecules associated with light-driven chemistry lie in the less dense upper layers. This upper-layer distribution differs from that seen in another young system, L1527. Ratios inferred from the molecular emission also suggest that gas farther out in the disk and surrounding envelope has a greater proportion of electrically charged particles and a higher rate of ionisation. Such chemical layering has been studied in only a few systems at this early stage of star formation.

Young explorerA baby star has a disk of gas around it. Scientists found different kinds of molecules in different layers: some near the disk’s middle and others higher up, where the gas is thinner. The clues also suggest that farther from the star, more gas particles have an electric charge, and particles become charged more often. Scientists have studied only a few baby-star homes this young in this way.

White dwarf pollution in wide binaries I: the effects of stellar evolution

Constanza Norambuena, Carolina Charalambous, Claudia Aguilera-Gómez

• Solar and Stellar Astrophysics

AstronomerThis simulation study tests how stellar mass-loss histories and wide-binary architecture affect rocky-material delivery to white dwarfs. REBOUND N-body integrations incorporate time-dependent stellar parameters from MESA tracks and tidal interactions, comparing two stellar-evolution models for binaries hosting a Jupiter-mass planet and a planetesimal disc. Within the explored models and architectures, the stellar-evolution prescription has little effect on planet survival but changes the timing and efficiency of planetesimal delivery during the white dwarf stage. Binary architecture is the stronger determinant of simulated pollution: wider binaries yield the highest accretion rates and longer-lived planetesimal reservoirs, enabling pollution over billions of years. The authors interpret these trends as consistent with the observed prevalence of polluted white dwarfs in wide binaries and suggest that binary architecture outweighs the tested stellar-evolution uncertainties.

PublicRocky material in a white dwarf’s atmosphere is interpreted as evidence that the stellar remnant is swallowing debris from its former planetary system. This study uses computer simulations to ask whether that delivery depends more on how the star loses mass as it evolves or on the arrangement of a widely separated companion star. The simulations compare two stellar-evolution models in systems containing a Jupiter-mass planet and a disc of smaller bodies. The choice of stellar model makes little difference to whether the planet survives, though it affects when and how efficiently debris reaches the white dwarf. The binary arrangement matters more: wider pairs produce the highest simulated accretion rates and retain debris supplies longer, potentially sustaining pollution for billions of years. These modeled trends are consistent with observations, rather than new observational measurements.

Young explorerA white dwarf is what is left after a star grows old. Scientists think rocky bits falling onto it can make its outer layer dirty. They used computer models with two far-apart stars, a big planet, and lots of little rocky pieces. In their models, how the stars were arranged mattered more for feeding rocks to the white dwarf than which of two ways the aging star lost material they used. Stars farther apart gave the biggest rock showers and kept rocky supplies around longer. This is what the computer models showed, not something the scientists watched happen.

Surface regolith model of near-Earth asteroid (3200) Phaethon

Mikko Vuori, Antti Penttilä, Karri Muinonen+6 more

AstronomerThe authors model Phaethon’s regolith to jointly reproduce previously reported spectral, polarization, and geometric albedo measurements, which have suggested possible surface heterogeneity. Their best-fit mixture comprises large olivine particles with troilite inclusions and small-scale surface roughness, together with smaller, porous troilite aggregates made of monomers resembling interplanetary dust. The model attributes differing spectral and polarization responses to variations in the size and abundance of the small, dark troilite particles. Based on the modeled troilite abundance, the authors propose CM meteorites as a preferable analogue to CY meteorites; this is a model-based interpretation rather than a direct compositional measurement.

PublicPhaethon is a near-Earth asteroid that becomes active near the Sun and is thought to be the source of the Geminid meteor shower. Earlier measurements of its reflected light hinted that its surface material may vary from place to place. The researchers built a model that matches published measurements of the light’s spectrum, polarization, and the asteroid’s reflectivity. Their best-fitting model mixes large olivine grains containing troilite, with tiny surface irregularities, and smaller, porous clumps of dark troilite particles. The model suggests that changes in the size and amount of the small dark particles could explain the different light signatures. It also leads the authors to favor CM meteorites over CY meteorites as a comparison for Phaethon’s material, but does not directly establish its composition.

Young explorerPhaethon is a space rock. Scientists studied how light bounces off it to learn what its surface might be like. They made a model with bigger grains and smaller, dark, loosely packed clumps. This model matches the light measurements and suggests that different amounts and sizes of the dark grains could make parts of the surface look different. It is a possible explanation, not proof of exactly what is on Phaethon.

Radio and high-energy variable emission from a multi-wavelength follow-up of the infant planet-hosting star V1298 Tau

M. Damasso, D. Viganò, R. Spinelli+9 more

• High Energy Astrophysical Phenomena
• Solar and Stellar Astrophysics

AstronomerA 2025–2026 campaign investigated activity-related variability in V1298 Tau, a very young, magnetically active K1V host of multiple planets, using JVLA C-band observations at 4.5–6.5 GHz, Swift X-ray and NUV monitoring, and contemporary ASAS-SN optical photometry. The 20-day Swift campaign ended one month before the radio campaign, limiting direct radio–high-energy comparisons. Radio emission was detected in 90% of visits and switched between high (≥0.1 mJy/beam) and low states over hours to days. Radio fluxes correlated moderately with the optical light curve, suggesting rotational modulation. Except during one visit, dynamic spectra showed no minute-scale variability; no circularly polarised emission was evident. Coronal gyrosynchrotron and/or cyclotron emission linked to magnetic activity can explain the radio observations, but the mechanism is not uniquely established. X-ray luminosity varied significantly over approximately 1.2–2.5 × 10^30 erg/s; the observations captured a stellar flare’s decay and showed evidence of correlation with optical flux. The authors report that V1298 Tau follows the near-linear Güdel-Benz relation.

PublicAstronomers monitored V1298 Tau, a very young, magnetically active star with several planets, to investigate how its brightness changes across different kinds of light. Radio emission appeared in 90% of observing visits, shifting between brighter and fainter states within hours or days. Its radio brightness was moderately correlated with its visible-light brightness, suggesting that the star’s rotation helps shape the changes. X-ray observations also showed substantial variability and caught the fading stage of a stellar flare. The radio signals are consistent with emission from the star’s outer atmosphere associated with magnetic activity, although the exact emission mechanism remains uncertain. Importantly, the X-ray and near-ultraviolet monitoring ended a month before the radio campaign, so these observations did not track the same events simultaneously. The authors also report that the star follows a known, nearly linear relationship between radio and X-ray emission.

Young explorerScientists watched a very young star that has planets around it. They used telescopes that see kinds of light our eyes cannot see. The star grew brighter and dimmer, and they caught a star flare fading away. Its magnetism may help explain the changes, and its turning may matter too. But the telescopes did not all watch at the same time, so scientists could not match every change.

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

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

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

PublicAstronomers discovered a planet roughly as massive as Saturn orbiting a star much less massive than the Sun. They identified the system through gravitational microlensing, in which a foreground system magnifies light from a more distant star. By modeling brightness measurements from several telescopes and using additional Keck II observations, they estimated that the planet has 105 ± 13 times Earth's mass and its host star has 13.9 ± 1.1 percent of the Sun's mass. The system is about 1,000 parsecs away, with an uncertainty of 80 parsecs. It adds to the small number of known giant planets around low-mass stars and helps constrain ideas about how planets form.

Young explorerAstronomers found a big planet going around a star much smaller than our Sun. They found it by studying how the star and planet acted like a magnifying glass for light from a star farther away. Their measurements suggest the planet is about as heavy as Saturn, though they cannot say exactly how heavy it is. Finding a big planet around such a small star helps scientists learn how planets are made.

The morphology of contact binary objects in the Solar System

Richard E. Cannon, Agata Rożek, Colin Snodgrass

AstronomerThe study characterises the morphological diversity of currently modelled contact-binary asteroids, analysing size, rotation period, neck prominence, volume distribution, lobe size and volume ratios, and relative lobe alignment. The abstract reports that contact binaries constitute 30–50% of asteroids and comets, but only 16 contact-binary shape models have been published, already showing varied lobe configurations. Detailed remote shape reconstruction is constrained by the need for rare occultations or radar observations during Earth approaches within 0.1 au. Formation simulations now generate tens to thousands of candidates per simulation, motivating systematic shape characterisation. The abstract does not report quantitative results from the analysis or establish emerging trends.

PublicContact binaries are asteroids or comets that look like two objects stuck together. The abstract says they account for 30–50% of asteroids and comets, yet only 16 detailed shape models have been published because their shapes are difficult to determine from afar. Those models already reveal different ways the two parts can fit together. This study examines the shapes of modelled asteroids, including their sizes, spin periods, connecting necks, and the relative sizes and orientations of their two parts. Computer simulations of formation produce tens to thousands of possible contact binaries at a time, adding motivation for organising this variety. The abstract describes the analysis but does not give its results or confirm any new patterns.

Young explorerSome space rocks look like two lumps stuck together. Scientists have made detailed shape models of only a few because it is hard to see their shapes from far away. This study looks at how big the lumps are, how they line up, how narrow their join is, and how fast the rocks spin. Computer pretend-worlds also make lots of possible two-lump rocks, but those are not rocks scientists have actually seen. The summary does not tell us what new patterns the study found.

Topographically Forced Stationary Waves Can Explain the Near-Surface Zonal Winds Observed by Huygens on Titan

Sooman Han, Scot Rafkin, J. Michael Battalio+2 more

• Atmospheric and Oceanic Physics

AstronomerHuygens measured prograde near-surface winds on Titan, contrary to the climatological retrograde low-latitude flow consistently simulated by general circulation models. Paired three-dimensional dry Titan Atmospheric Model simulations with and without topography show that terrain forcing can produce longitude-locked, vertically structured wind anomalies resembling the lowest few kilometers of the Huygens profile. Helmholtz and spectral analyses attribute the simulated structure to superposed low-wavenumber responses: a predominantly rotational stationary s=1 mode supplies a major eastward anomaly through the lowest 2 km, while a locally divergent s=4 response, consistent with a gravity wave, opposes it near the surface. Weaker s=2 and s=3 responses add near-surface eastward anomalies. Superposed on the retrograde zonal mean, these modes yield prograde flow below 1 km and shear toward retrograde flow aloft. The paired experiments establish a topographic origin for the simulated responses, with terrain-forcing coherence supporting phase locking; they offer a mechanism for the observed profile rather than establishing its actual cause. Weaker stationary responses simulated near the planned Dragonfly landing site provide baseline expectations for future measurements.

PublicThe Huygens probe measured winds blowing eastward near Titan’s surface, even though climate models generally predict westward winds near the equator. Researchers tested whether large-scale terrain could explain this difference by comparing dry, three-dimensional atmosphere simulations with and without topography. In the simulations, terrain generated stationary wave patterns whose effects combined to produce eastward winds in the lowest kilometer and a shift toward westward winds above, resembling key features of Huygens’s measurements. Several wave patterns contributed, sometimes reinforcing and sometimes opposing one another. This makes terrain-driven waves a possible explanation for the local winds, not proof that they caused the observed profile. The simulations also produced similar but weaker patterns near the planned Dragonfly landing site, offering a baseline for interpreting its future atmospheric measurements.

Young explorerA probe called Huygens found wind blowing east near the ground on Titan, when computer models usually expected it to blow west. Scientists tried computer versions of Titan with and without its hills and other land shapes. In the version with those shapes, waves in the air worked together to make winds that looked like the ones Huygens found. This means the shape of the land could help explain the surprise, but it does not prove that is what really happened. The computer also showed a smaller effect near the place where Dragonfly is planned to land.

Predictions for an unseen third planet in the WISPIT 2 system

Amena Faruqi, Farzana Meru, Gabriel-Dominique Marleau+4 more

AstronomerUsing the ALMA ring at 144.4 au and findings from previous hydrodynamical models, the authors predict a currently unseen planet in WISPIT 2 with a mass of approximately 0.2–1 Jupiter masses and a semi-major axis of approximately 100–120 au. They find that the VLT/SPHERE ring at 96.7 au is consistent with the mass and semi-major axis of WISPIT 2b, while ruling out WISPIT 2b as the cause of the ALMA ring. The hypothesised third planet remains unconfirmed. Future gas observations could refine the prediction, and upcoming JWST/NIRCam observations or Gaia DR4 may enable its discovery.

PublicAn observed ring in the WISPIT 2 system may point to an unseen planet. Drawing on earlier computer models, the researchers predict a planet roughly 0.2–1 times Jupiter’s mass, orbiting at about 100–120 times the Earth–Sun distance. The known planet WISPIT 2b has properties consistent with a different ring closer to the star, but the researchers conclude that it cannot explain the outer ring observed by ALMA. The proposed additional planet has not been detected. Future observations of gas could narrow the predictions, while upcoming JWST observations or Gaia data might reveal it.

Young explorerScientists have seen rings around a star. A planet they already know about fits with one ring, but cannot explain another. Using computer-model clues, they think another planet might be there, even though no one has seen it yet. Looking again could help them find out whether that planet is really there.

Diffusive Instabilities in Dusty Disks: Linear Growth and Nonlinear Breakdown

Konstantin Gerbig, Min-Kai Lin

AstronomerThis theoretical and numerical study revisits a dusty-disk instability driven by sufficiently steep decreases in dust diffusivity and/or viscosity with increasing dust density. Including an incompressible, viscous gas with azimuthal response and drag feedback leaves the small-stopping-time instability criterion approximately β_diff ≲ −2, with modest quantitative changes for parameters motivated by streaming-instability turbulence. Nonlinear calculations reproduce linear growth and selection of the fastest-growing wavenumber. However, power-law diffusivity closures with β_diff < 0 fail to saturate: steepening gradients amplify the nonlinear dust-pressure term and produce finite-time collapse into sharp spikes. Restricting the negative diffusion slope to a finite density interval prevents blowup, but peak densities are controlled by the imposed saturation scale. The authors interpret diffusive instability as a possible linear organizing mechanism in dusty turbulence, while emphasizing that realistic nonlinear saturation requires physics beyond this one-dimensional closure.

PublicThe researchers used mathematical models and computer calculations to study how dust can concentrate in dusty disks. The instability occurs when dust spreads less efficiently as its density increases. Adding a gas that reacts to the dust changes the predicted onset only modestly under the conditions studied. In the one-dimensional calculations, initially growing concentrations develop into ever-sharper spikes rather than settling into stable clumps. A modified rule that limits the density range over which spreading becomes less efficient prevents this runaway, but the resulting peak densities depend on a limit built into the model. These are modeling results, not observations: they suggest a way dust patterns could begin to form, while leaving their realistic final state unresolved.

Young explorerScientists used a computer to study dust mixed with gas in a disk. In their model, dust could pile up when crowded dust spread out less easily. But the piles kept getting sharper instead of settling down. Changing a rule stopped that, but also set how big the piles became. Scientists still need more physics to learn what real dust piles would do.

Analysis of Io's tidal response as a function of the properties of the partially molten layer

M. Paris, A. Mura, F. Zambon+11 more

AstronomerThis modeling study links Io’s tidal response to partial melting using a fluid core, viscoelastic mantle, and elastic lithosphere. The calculation includes melting onset depth, latent heat, mantle compressibility, and melt-dependent rheology. The models produce enhanced shallow-mantle tidal dissipation as melt reduces effective viscosity and increases anelasticity. Matching the observed real part of the degree-2 potential Love number k2 in these 1D models requires melt fractions below the rheologically critical threshold; including compressibility raises the real part of k2 and strengthens this upper bound. A mass-flux analysis indicates that melt-percolation capacity exceeds thermodynamic melt production, suggesting efficient drainage. The reference Andrade parameter beta strongly affects the imaginary parts of k2, h2, and l2 and the predicted libration amplitude. These model-dependent constraints favor a heterogeneous, magmatic-sponge mantle over a global magma ocean, while the melt fraction, depth, and spatial distribution of dissipation remain poorly constrained.

PublicJupiter-driven tidal forces heat Io’s interior and partially melt its mantle, but how much rock is molten and where the heat is generated remain uncertain. This study models how melting changes the interior’s response to tidal forces. In the calculations, molten material makes the upper mantle more deformable and increases tidal heating there. Matching an observed measure of Io’s tidal response requires the modeled mantle to stay below a critical melt fraction at which its mechanical behavior changes. The analysis also suggests that melt can drain faster than it is produced. Together, these model results favor a mantle resembling a sponge of rock and molten material rather than a global magma ocean. They are an interpretation of observational constraints, not a direct image of Io’s interior, and predictions remain sensitive to assumptions about mantle behavior.

Young explorerJupiter’s pull helps heat its moon Io and melt some rock inside. Scientists made a computer model to explore what that inside might be like. It suggests rock with melted bits in it, a little like a sponge, instead of one big ocean of melted rock. They still aren’t sure exactly what is inside.

A Formation-Stage Bottleneck for Exomoons around Close-in Rocky Planets

Rongxi Bi, Hongping Deng, Christian Reinhardt+2 more

AstronomerMeshless finite-mass simulations of giant impacts between differentiated rocky planets test how stellar tidal and Coriolis forces affect moon-forming disks at orbital periods of 1–300 days, compared with otherwise identical isolated collisions. In the simulations, ultra-short-period impacts leave essentially no surviving circumplanetary disk, while 10-day systems retain strongly depleted, radially truncated, dynamically compact disks. High impact velocities, expected for close-in planets, severely inhibit disk generation; retrograde impacts provide only slight compensation for disk mass depletion. These findings identify a formation-stage bottleneck that could suppress moons around close-in rocky planets and alter expectations for exomoon demographics. They are simulation results, not exomoon detections; no exomoon has been securely confirmed.

PublicGiant collisions are expected to create massive moons around rocky planets beyond our Solar System, but no such moon has been securely confirmed. This study uses computer simulations to ask whether a nearby star disrupts the debris disks from which moons could form. Compared with collisions modeled without the star’s influence, simulated impacts on the shortest-period orbits leave almost no disk. Planets orbiting every 10 days retain much smaller, more compact disks. Fast collisions make disk formation especially difficult, while impacts in the retrograde direction help only slightly. The simulations suggest that a star’s influence can prevent moons from forming around close-in rocky planets; they do not establish how many such moons actually exist.

Young explorerWhen rocky planets crash together, the pieces left circling a planet might make a moon. Scientists used computer models to see what happens when the planets are very close to their star. In the models, the star made it hard for enough pieces to stay around the planet. The closest planets kept almost none, and faster crashes made things worse. This suggests that planets close to their stars may have trouble making moons. It is a clue from computer models, not a moon that scientists have found.

Emission spectroscopy of KELT-2A b with Gemini-North/IGRINS-2: hints of a stellar C/O ratio and sub-stellar metallicity

Yuya Hayashi, Stevanus K. Nugroho, Shota Notsu+13 more

AstronomerHigh-resolution H- and K-band emission spectroscopy of KELT-2A b with Gemini-North/IGRINS-2 (R ≈ 45,000), obtained over five nights before and after eclipse, detects H2O at S/N = 6.57, confirming an earlier result at higher significance. A 12CO feature appears near the expected planetary velocity in the log-likelihood map, but the data do not support a definitive detection. Atmospheric retrievals favor a non-inverted temperature–pressure profile. A joint fit with archival Spitzer/IRAC photometry gives log(H2O) = −3.78 (+0.27/−0.20) under free chemistry. Assuming chemical equilibrium, the retrieval yields C/O = 0.19 (+0.12/−0.07), [C/H] = −0.81 (+0.41/−0.34), and [O/H] = −0.37 (+0.27/−0.17). C/O agrees with the stellar value; carbon and oxygen appear moderately depleted relative to the host star but remain consistent with it at approximately 2σ. If confirmed, this composition would challenge gas accretion between the H2O and CO snowlines. The authors instead interpret it as pointing to metal-depleted gas accretion beyond the CO snowline, limited planetesimal enrichment, and subsequent disk-free, high-eccentricity migration; this formation history is not established by the observations.

PublicObservations of the hot giant planet KELT-2A b clearly reveal water vapor in its atmosphere, strengthening an earlier detection. The researchers also find a possible carbon monoxide signal, but it is not strong enough to count as a definite detection. Models fitted to the new spectra and older Spitzer measurements indicate an atmosphere without a temperature inversion: temperature does not rise toward the upper layers in the retrieved profile. The models suggest that the planet’s carbon-to-oxygen ratio resembles its star’s, while its carbon and oxygen abundances may be lower. Those apparent shortages remain uncertain and are still statistically consistent with the star’s abundances. If confirmed, this chemical pattern could favor formation from gas depleted in heavier elements far out in the original planet-forming disk, followed by migration inward along a highly elongated orbit after the disk was gone. That history is an interpretation, not a directly observed result.

Young explorerAstronomers studied light from a big, hot planet called KELT-2A b and found water vapor in its air. They also saw a hint of another gas, carbon monoxide, but they are not sure it is really there. Their models suggest the planet may have less carbon and oxygen in its air than expected from its star, but that is not certain yet. If that clue turns out to be right, it could help explain whether the planet grew far from its star and later moved closer. The scientists have not proved that story.

Families of relative periodic orbits in the planar three-body problem via consecutive alignments

Joan Gimeno, Marc Jorba-Cuscó, Begoña Nicolás

• Dynamical Systems
• Mathematical Physics
• Numerical Analysis
• Classical Physics

AstronomerThis numerical study computes and continues one-parameter families of relative periodic orbits in the planar Newtonian three-body problem: motions that repeat in a uniformly rotating frame but are generally quasi-periodic in inertial coordinates. Matching positions and momenta at consecutive symmetry-compatible alignments reduces the search to a low-dimensional nonlinear problem. Linear stability is assessed using the nontrivial eigenvalues of the rotated monodromy matrix, with neutral directions removed. Applications to several mass distributions and initial configurations yield Poincaré, Hill, and binary-type families, including transitions from nearly circular to highly eccentric motion and stability changes near resonances and turning points. Rational multiples of 2π for the rotation angle give absolute periodic solutions. Hill-family continuation connects satellite and circumstellar configurations as the smallest body loses its binding to the intermediate body; binary-regime solutions include circumbinary and circumstellar configurations. These are computed motions, not observations, and offer prescribed trajectories for restricted four-body models.

PublicResearchers have developed a computer method for finding repeating patterns in the motion of three bodies pulling on one another through gravity, assuming all three move in a plane. The patterns repeat when viewed from a steadily rotating viewpoint, although they generally do not repeat exactly from a nonrotating viewpoint. By matching the bodies’ positions and motions at successive special alignments, the method finds related families of paths and tests their linear stability. The calculated families range from nearly circular to very elongated motion, with stability changing near certain orbital relationships and bends in the families. One family connects a small body orbiting an intermediate body to motion around the star as its gravitational binding to the intermediate body is lost. These are mathematical calculations rather than observed systems, and the resulting paths could serve as inputs to simplified four-body models.

Young explorerImagine three objects pulling on each other with gravity while moving on a flat playground. Scientists used computers to find dances that repeat if you watch from a seat that turns at just the right speed. Some paths are almost circles, and others are very stretched out. In one set of computer dances, the smallest object stops being held to the middle-sized one and moves around the star instead. These are patterns worked out on computers, not things the scientists watched in the sky.

Solar System Surface Technosignatures: Searching for Signs of Artificial Design on Extraterrestrial Terrain

Ana Henrique, Sofia Sheikh, Benjamin Fields

• Earth and Planetary Astrophysics
• Machine Learning

AstronomerThe authors propose extending technosignature searches beyond artificial radio emissions to intentional, non-random patterns on planetary surfaces, drawing on anthropological comparisons with enduring human-made landscapes and monuments. They suggest that artificial traces on geologically inactive bodies such as the Moon and Mars could remain visible for hundreds of millions of years. High-resolution imaging datasets, including MRO/HiRISE imagery, and machine-learning anomaly detection motivate two proposed search strategies: supervised and unsupervised models. Complementary LiDAR, ground-penetrating radar, and reflectance spectroscopy could help establish the first quantitative upper limits on surface technosignatures while benefiting planetary science. The abstract presents a search framework, not a detection or an implemented model's results.

PublicCould deliberately shaped landscapes provide clues to technology beyond Earth? The authors propose looking for intentional patterns on planetary surfaces, inspired by the lasting marks people leave on Earth through monuments and altered landscapes. They suggest that such traces might remain visible for hundreds of millions of years on geologically inactive places such as the Moon and Mars. Detailed images, including those from a camera aboard the Mars Reconnaissance Orbiter, could be searched using machine-learning methods. Additional tools could examine surface shapes, structures underground, and reflected light. This is a proposed search, not evidence that artificial patterns have been found. It could eventually place numerical limits on how common or extensive such traces might be and also help scientists study planetary surfaces.

Young explorerPeople leave marks on Earth, like buildings and big patterns in the ground. The authors suggest looking for marks on the Moon and Mars that might have been made on purpose by someone else. Such marks might last a very, very long time. Computers could help search detailed pictures for unusual patterns. This is an idea for a search—not a discovery of anyone else's marks.

Data-driven characterisation of variable source light curves with multimodal representation learning

M. Madarász, G. Marton, M. Audard

• Solar and Stellar Astrophysics

AstronomerThe authors present a label-free framework combining a Transformer on raw light curves with a convolutional network on generalised Lomb-Scargle periodograms. Joint VICReg training on randomly split temporal halves produces 64-dimensional embeddings that capture amplitude, periodicity, and asymmetry. Evaluated on 37,006 ZTF sources covering 14 variable-star classes, a linear classifier using frozen embeddings achieves 77.1% balanced accuracy for classes and 90.5% for four broad physical categories. Combining branches improves balanced accuracy by up to 14.9 percentage points over the best single branch. The authors report interpretable embedding dimensions and within-class physical substructure not resolved by reference labels. Retraining without architectural modification on ZTF g and i bands reproduces the main results; concatenated multi-band embeddings reach 86.1% balanced accuracy. Representation learning requires no labels, although classification performance is evaluated against reference labels. The framework avoids phase folding and survey-specific preprocessing; applicability to other surveys is claimed, while the reported tests use ZTF data.

PublicThis study presents an AI method that learns patterns in how stars brighten and fade without being given star-type labels during training. It combines the brightness measurements themselves with a second view that highlights repeating patterns. In tests on 37,006 stars from the Zwicky Transient Facility, the learned summaries supported a classifier with 77.1% balanced accuracy across 14 star types and 90.5% across four broader groups. These scores were checked using existing labels, even though learning the summaries did not require them. Combining the two views worked better than using either alone, and combining measurements from multiple wavelength bands improved performance further. The authors also report patterns within labelled star types that they interpret as physical substructure. They say the method can transfer to other surveys, but the reported demonstrations use ZTF data.

Young explorerSome stars get brighter and dimmer. The researchers made a computer learn their patterns without first telling it what kinds of stars they were. It looked at both the changing brightness and clues about patterns that repeat. Using both helped it do better when researchers checked it against known star groups, but it still made mistakes. The team says it could work with other sky surveys too; the tests here used one survey.

Optimization of Petal-Shaped Occulters for Exo-Earth Observation

Simon Prunet, Céline Theys, Claude Aime

• Optics

AstronomerThis study presents a shape-optimization method for formation-flying, petal-shaped occulters intended for direct exoplanet imaging, where exo-Earth planet-to-star contrast can be below 10^-10. The method represents an apodized occulter as a weighted sum of circular occulters, exploiting their analytical Fresnel diffraction amplitudes to produce destructive interference and a dark central region rather than the bright Arago spot of a circular occulter. Weights are first optimized with fixed, regularly spaced diameters by minimizing a quadratic criterion; joint optimization of weights and diameters then improves the result. The apodized profile is converted into a petal-shaped design to accommodate physical implementation constraints. The reported rejection rates are comparable to those from SISTER's different, non-parametric approach. These are design and diffraction-calculation results, not a demonstration of exoplanet observations or in-space performance.

PublicA proposed way to photograph planets around other stars is to fly a giant, petal-shaped screen in space to block the star's dazzling light. But light bends around the screen's edges, which can spoil the dark region needed to see a faint planet. This study develops a mathematical method for choosing the screen's shape so that the bent light waves largely cancel one another in the center. The researchers first adjust the contributions of circles of different sizes, then improve the design by adjusting both the sizes and their contributions, before turning the resulting profile into a petal-shaped screen. Their calculated starlight suppression is comparable to that from another design method called SISTER. The abstract reports design calculations, not a screen tested in space or a planet detected with it.

Young explorerA star can be so bright that a little planet beside it is hard to see. Scientists are designing a giant flower-shaped shade to block the star's light. Some light bends around the shade, so they used math to choose a shape that makes those light waves mostly cancel out in the middle. Their calculations worked about as well as another design method. This study does not show the shade flying in space or finding a planet.

In search of the third dimension in Compton X-ray polarimeters

Fabio Muleri, Riccardo Campana, Edoardo Borciani+22 more

AstronomerThe authors present a Compton polarimeter design that estimates the polar scattering angle using light readout at both ends of scintillator bars. Conventional two-dimensional reconstruction uses only the scattered photon’s azimuthal angle. For sources several degrees off-axis, however, the measured azimuthal response effectively convolves the azimuthal and polar scattering angles. Measuring the latter is expected to improve sensitivity and reduce systematic effects. A representative setup is being tested, and initial performance results are presented, but the abstract gives no quantitative performance or demonstrated improvement.

PublicCompton polarimeters measure light’s polarization by tracking how photons scatter inside a detector. They typically record only one of the two angles describing the scattering. When light arrives several degrees away from the detector’s central viewing direction, both angles become mixed in the recorded pattern. The authors describe a design that estimates the second angle by measuring light signals at both ends of detector bars. This could improve sensitivity and reduce systematic errors. Testing is underway with a representative setup; the abstract mentions early performance results but does not say how well the design works.

Young explorerThis detector learns about light by watching how tiny bits of light bounce. Usually, it checks only part of the bounce’s direction. If the light comes in from a little to the side, that can make things harder to understand. The team is testing bars that give off light, with a reader at each end, to learn more about the bounce. They hope this will help the detector work better, but the short description does not tell us how much better it works.

In-orbit anomaly and recovery of IXPE detector 2

Fabio Muleri, Luca Baldini, Sudip Chakraborty+18 more

• High Energy Astrophysical Phenomena

AstronomerIXPE, the joint NASA–ASI mission launched in December 2021, measures linear X-ray polarization at 2–8 keV using three identical telescopes with grazing-incidence optics and Gas Pixel Detector photoelectric polarimeters. On 14 April 2025, detector 2 experienced an anomaly that significantly changed the electrical behavior of its photoelectron-track readout ASIC. This contribution describes the resulting effects on instrumental response and the mitigation actions taken to recover scientific observations. The abstract does not specify the anomaly’s cause, quantify its impact, or state the degree of recovery achieved.

PublicThe Imaging X-ray Polarimetry Explorer (IXPE) measures polarization, a property of X-ray light from celestial sources. On 14 April 2025, one of its three detectors developed a problem that substantially changed how an electronic chip read out images used for these measurements. The report describes how the problem affected the instrument’s response and what was done to reduce its effects and recover scientific observations. The abstract does not say what caused the problem or how fully the instrument recovered.

Young explorerIXPE is a space telescope that studies a kind of light called X-rays. One of its three detectors had an electronics problem that changed how it read pictures. The report tells how the problem affected its work and what people did to help it make science observations again. This short description does not tell us how well those steps worked.

Cosmic Ray Observations using Coincident Scintillator and Radio Signals with the Beamforming Elevated Array for COsmic Neutrinos (BEACON)

Zachary Martin, Jackson Hinkel, Kira Perna+18 more

• High Energy Astrophysical Phenomena

AstronomerBEACON considers mountaintop phased radio arrays targeting 30–80 MHz upward-going geomagnetic emission associated with Earth-skimming tau neutrinos. To assess sensitivity, its prototype identifies cosmic rays through the same emission mechanism. In 2023, the instrument was upgraded from four antennas to six newly designed antennas, with an independent scintillator array added for cross-validation. Applying selections based on expected radio characteristics to a scintillator-coincidence-triggered dataset yields 22 candidate cosmic-ray events. Hybrid-instrument simulations reproduce the observed rate to within an order of magnitude, providing only a broad consistency check. The estimated background is 0.11 events, derived by applying the selections to synthetic, uncorrelated radio-scintillator pairs constructed from fixed-rate software-triggered data. Reconstructed polarization angles are consistent with pure geomagnetic emission in comparisons with several background classes. These are cosmic-ray candidates, not reported neutrino detections.

PublicBEACON is exploring whether radio antennas on mountaintops could detect signals from tau neutrinos that skim through Earth. As a step toward evaluating that approach, researchers are using cosmic rays, which produce radio signals through the same mechanism. In 2023, they upgraded the prototype to six new antennas and added a separate particle detector to check the radio signals. They report 22 candidate cosmic-ray events selected from data triggered by coincident particle-detector signals. They estimate that accidental radio–particle-detector matches would account for 0.11 events passing their selection. A computer simulation agrees with the observed event rate only to within a factor of ten. The radio signals’ polarization is consistent with emission produced through Earth’s magnetic field. The study reports cosmic-ray candidates, not a detection of neutrinos.

Young explorerTiny particles from space can make showers of more particles in the air, and those showers can send out radio signals. Scientists tested six antennas with another particle detector to help check what they heard. They found 22 signals that look like they could come from cosmic rays. Their checks suggest that accidental matches between the detectors would be rare, but these signals are still called candidates. The team is testing this idea because it hopes to use mountaintop antennas to look for signals from particles called neutrinos. This study did not report finding neutrinos.

A design concept for the High Resolution Imager on the Habitable Worlds Observatory

Vincent Van Eylen, Richard Massey, Alan Smith+15 more

AstronomerThe authors present a design concept, not an on-sky demonstration, for the Habitable Worlds Observatory’s High Resolution Imager (HRI), developed by translating science requirements into a design within NASA’s EAC-1 telescope architecture. HRI combines imaging, grism spectroscopy and intended sub-microarcsecond astrometry with fine guidance, wavefront sensing and pupil imaging. Two mirrors collimate light from a 3-by-2-arcminute field before a dichroic splits it into simultaneous 200–900 nm and 0.9–2.2 micrometre channels. Minimising reflections before the dichroic is intended to maximise throughput and stability while reducing wavefront error. Proposed selectable readout modes support full-field exposures of at least 10 seconds or windowed observations up to 1 kHz. The paper emphasises how coupled subsystems constrain design choices; these capabilities describe the concept rather than measured performance.

PublicThis paper outlines a proposed camera system for NASA’s planned Habitable Worlds Observatory, a mission designed to search for signs of life on planets around nearby stars and study other astronomical questions. The High Resolution Imager would take pictures, spread light into spectra and measure extremely small changes in objects’ positions. It would also help the observatory point steadily and monitor its optics. The design splits incoming light into two channels so ultraviolet and visible light can be observed at the same time as near-infrared light. Using fewer reflecting surfaces before the split is intended to preserve more light and improve optical stability and image quality. The proposed camera could record its whole field with exposures lasting at least 10 seconds, or read smaller regions up to 1,000 times per second. These are design capabilities, not results from a working instrument, and the authors stress that choices in one subsystem affect others.

Young explorerScientists have made a plan for a special camera for a future space telescope. The telescope is meant to look for clues of life on planets near other stars and learn more about space. The camera would look at different kinds of light at the same time, including light our eyes cannot see. It would also help the telescope keep pointing steadily. It could take pictures of a whole patch of sky or watch a smaller patch very quickly. This paper describes the plan, not pictures the camera has already taken.

The Pandora SmallSat: Target Selection and Early Science

Emily A. Gilbert, Elisa V. Quintana, Jessie L. Dotson+41 more

• Earth and Planetary Astrophysics

AstronomerPandora, a smallsat selected in NASA’s inaugural Pioneers class, aims to separate stellar-activity contamination from exoplanet transmission spectra using combined visible photometry and near-infrared spectroscopy. Its prime program plans 10 transit visits per target, each lasting 24 hours, for 20 targets around K and M dwarfs spanning a range of rotation periods and activity levels. The planets span 1.5–15 Earth radii and orbital periods of 1.7–11.5 days. Auxiliary observations scheduled into gaps in prime operations address stellar activity and young systems, transit timing variations, brown dwarf compositions, and exoplanet phase curves. The presentation will discuss target selection, scheduling, early science results, and possible extended-mission strategies. The abstract gives no specific science findings, and additional extended-mission science remains conditional on an extension.

PublicPandora is a small NASA spacecraft designed to help researchers distinguish signals from a star’s activity from those produced by a planet’s atmosphere as the planet passes in front of its star. It combines visible-light brightness measurements with near-infrared spectra. The main observing plan covers 20 targets around low-mass K and M dwarf stars, with 10 visits lasting 24 hours each per target. Other observations fill gaps in the schedule and explore topics such as young star systems, changes in planet transit times, and brown dwarf compositions. The presentation promises discussion of early science results but does not describe any specific findings in the abstract. It also considers further science that could be done if the mission is extended.

Young explorerPandora is a little spacecraft that watches stars when planets pass in front of them. It looks at different kinds of light to help scientists tell what comes from the star and what might come from the planet’s air. The plan is to watch each of 20 targets 10 times, for a whole day each time. Pandora also uses gaps in its schedule to study other things in space. The scientists plan to talk about early discoveries, but this short description does not say what they found. If Pandora gets more time to work, it could study more things.

Noisy Pipelines I: An end-to-end pipeline to perform multivariate noise inference for LISA

Ollie Burke, Joseph Bayley, Charlie Hoy+1 more

• General Relativity and Quantum Cosmology

AstronomerThe authors present lisa-noise, a JAX-based pipeline for estimating LISA noise spectra while accounting for changes introduced by filtering, downsampling, segmentation and windowing. It fits splines to the underlying secondary noises and the full 3 × 3 covariance matrix of the Michelson channels, assuming unequal, time-varying arm lengths. Averaging transfer functions over epochs within each segment captures the non-stationary drift of their zeros. Tests use 30 days of conditioned simulated data: a likelihood evaluation for a seven-day segment takes 3 ms on a current laptop, and a gradient-based fit with a tight prior recovers injected spectra in a fraction of a second. A multi-start search with broad priors spanning ±10 in log10 around the simulated truth yields a data-consistent noise estimate, checked with Bayesian techniques. The fitted covariance whitens the simulated conditioned data across all bands, including transfer-function zeros, and is directly usable by global-fit pipelines; these are simulation results, not a demonstration on observed LISA data.

PublicPreparing LISA data for analysis changes the statistical properties of its instrumental noise, so those changes must be included when estimating signals and noise together. The authors introduce lisa-noise, software that estimates the noise and its correlations across three data channels while accounting for both data preparation and unequal, changing detector arm lengths. In tests on 30 days of simulated data, the software rapidly recovered the noise spectra used to generate the simulation when given tightly constrained starting information. A broader search also found a noise estimate consistent with the data, with Bayesian checks. The resulting model successfully standardized the simulated noise across the frequency range, including frequencies where the detector response goes to zero. The demonstration uses simulated data rather than LISA observations.

Young explorerScientists made a computer tool to help understand the unwanted noise in LISA’s data. Getting the data ready to study changes that noise, so the tool has to keep track of those changes too. They tested it with pretend data made by a computer, and it found a noise pattern that matched those data. This could help scientists study LISA’s data, but this test was not done with real LISA observations.

Dual-Phase Flow Matching for Probabilistic Source Detection and Measurement in Astronomical Images

Yicun Duan, Jeffrey Regier

• Applications

AstronomerBlending makes source configurations uncertain in deep LSST images, but the cataloging pipeline commits to one configuration, potentially biasing downstream analyses. The authors approximate the posterior over configurations with a continuous-time Markov process fitted by generator matching, an extension of flow matching to non-Euclidean state spaces. Generation has separate source-detection and measurement phases. On simulated LSST-like data, this approach outperforms five posterior-approximation alternatives: two MCMC methods, two neural posterior estimators, and a version without the dual-phase structure. The MCMC methods run thousands of times more slowly at survey scales. In Rubin Data Preview 1 imaging, only the proposed method among those compared recovers small-scale galaxy clustering consistent with higher-resolution Hubble imaging, while its reported uncertainties remain calibrated against that reference as blending increases. These real-data checks support performance relative to the Hubble reference, rather than establishing exact recovery of all sources. The authors release a probabilistic catalog of the Extended Chandra Deep Field South and use it to characterize the galaxy color–magnitude distribution.

PublicRubin Observatory’s planned 10-year sky survey will record many sources whose light overlaps, making it difficult to tell how many objects are present and measure each one. A catalog that chooses just one explanation can introduce errors into later studies. The authors developed a method that represents multiple possible arrangements and their uncertainty, first detecting sources and then measuring them. In simulated Rubin-like images, it gave better results than five comparison methods; two of those alternatives were thousands of times slower at survey scales. In actual Rubin Data Preview 1 images, the new method was the only one tested to recover the clustering of galaxies on small scales in agreement with sharper Hubble images. Its uncertainty estimates also remained consistent with that reference as overlap increased. The team released a catalog with uncertainty information for the Extended Chandra Deep Field South and studied how its galaxies’ colors relate to their brightnesses.

Young explorerWhen galaxies look close together in a sky picture, their light can mix, making them hard to count. The researchers made a computer method that keeps several possible answers instead of picking just one. It worked better than five other methods on pretend sky pictures. In real Rubin pictures, its answers about how galaxies group together matched sharper Hubble pictures, and it also showed how unsure it was. The team shared a list of possible galaxies and their properties.

Orientation-dependent sensitivity of the all-sky all-frequency gravitational-wave radiometer search to continuous-wave sources

Stavros Venikoudis, Giacomo Bruno

• General Relativity and Quantum Cosmology

AstronomerThe all-sky all-frequency (ASAF) radiometer weights the two tensor polarizations equally, which is optimal for an unpolarized stochastic background but can underestimate the intrinsic strength of continuous-wave sources with non-face-on orientations. The authors derive the exact polarization-angle dependence of the known power projection factor and prove that its orientation average is 2/5, independent of sky position, detector baseline geometry, noise weighting, and frequency. They test the formalism using four simulated pulsar signals injected into the LIGO detectors during O2. A nearly edge-on injection has SNR 5.20, below the 6.19 threshold; its face-on counterpart would have SNR 31.1 ± 6.0. Bayesian strain-amplitude upper limits marginalized over orientation and calibration uncertainty are 2.7–2.9 times the face-on limits. For 505 sub-threshold O4a candidates, the upper limits increase by factors of 2.5–2.9; sources of the same strength would reach threshold only within 34.7°–50.3° of face-on. These corrections change inferred amplitude limits, not measured SNRs or candidate significances.

PublicA search for continuous gravitational waves can make a source look weaker if it is tilted rather than facing us. This study calculates how that viewing angle affects the ASAF search, which combines data from two detectors. The authors prove that, averaged over orientations, the measured power is two-fifths of the face-on value for the same intrinsic signal strength. Tests with four simulated pulsar signals injected into LIGO detectors illustrate the effect: one nearly edge-on signal fell below the search threshold, although its face-on counterpart would have exceeded it. Accounting for uncertain orientation and calibration raises the upper limits on signal strength. For 505 below-threshold candidates from O4a, those limits rise by factors of 2.5–2.9. This does not turn any candidate into a detection: each candidate’s measured signal-to-noise ratio and statistical significance remain unchanged.

Young explorerA spinning star can send out waves that stretch and squeeze space. The same star can look weaker to a wave finder when it is tilted instead of facing us. Scientists worked out how this happens and tested it with pretend star signals added to detectors. Their work changes how strong a hidden signal could be, but it does not mean they found a new star signal.

Probabilistic Machine Learning for Short-Term Atmospheric Seeing Forecasting

Mary-Joe Medlej, Rahul Srinivasan, Simon Prunet+2 more

• Machine Learning

AstronomerThis study benchmarks atmospheric-seeing forecasts up to two hours ahead using measurements from the Maunakea summit. It compares probabilistic Gaussian Processes and FloTS, a normalizing-flow-based model, with deterministic RNN and LSTM baselines, assessing both point-prediction accuracy and the quality and calibration of predictive uncertainty. LSTM and FloTS achieve the best overall predictive accuracy in these tests. Gaussian Processes offer a useful probabilistic baseline, but their predictive distributions are constrained by the Gaussian assumption. FloTS combines competitive accuracy with flexible uncertainty estimates and yields the most informative probabilistic forecasts. The reported evaluation uses Maunakea data; the abstract does not establish performance at other sites.

PublicAtmospheric turbulence can blur astronomical images and disrupt optical communication through the air. This study tests machine-learning methods for forecasting atmospheric seeing, a measure of that blurring, up to two hours ahead using measurements from Maunakea. Two methods, LSTM and FloTS, give the most accurate predictions overall in these tests. FloTS also provides the most informative forecasts of uncertainty, describing a range of possible outcomes rather than just one predicted value. Another method, Gaussian Processes, provides a useful comparison but restricts predictions to a particular mathematical distribution. These results concern tests on Maunakea measurements, not demonstrated performance everywhere.

Young explorerMoving air can make things in a telescope look blurry. Researchers used measurements from Maunakea to test computer programs that guess how blurry the view will be up to two hours later. Two programs made the best guesses in these tests. One, called FloTS, was also best at showing the different things that might happen, instead of giving just one guess. The guesses are not promises, and these tests do not tell us how well the programs would work in other places.

A Broadband Room-Temperature Design for the Einstein Telescope

Teng Zhang, Amit Singh Ubhi, Huan Yang+21 more

• General Relativity and Quantum Cosmology
• Instrumentation and Detectors

AstronomerThe paper presents an alternative to the Einstein Telescope’s baseline xylophone configuration: a single, entirely room-temperature, fully resonant interferometer. ET’s underground location is expected to reduce seismic and gravity-gradient noise, but its baseline low-frequency design faces challenges from vertical suspension thermal noise, cryocooler vibrations, and detuned optics. The authors report that their alternative design can exceed the baseline xylophone’s broadband sensitivity using mature fused-silica suspensions, recent optical-coating advances, and novel inertial isolation. They find that 4-m-long fused-silica fibres can meet the required suspension thermal-noise performance and describe how interferometer and suspension design, optical seismometers, and quantum states can control vibrations, optical rigidity, and quantum back-action noise. These are claims about an architecture and its achievable performance, not reported measurements from an operating ET detector.

PublicThe planned Einstein Telescope is expected to benefit from being underground, where some disturbances that interfere with gravitational-wave detection should be weaker. Its baseline design uses separate cold and room-temperature detectors to cover low and high frequencies. This paper presents a different approach: one detector operating entirely at room temperature. The authors argue that it could outperform the baseline across a broad frequency range while avoiding difficulties associated with cooling equipment and the baseline optical arrangement. Their design uses four-metre-long fused-silica suspension fibres, improved optical coatings, and carefully designed vibration and quantum-noise controls. The claimed improvement concerns the proposed design’s performance, rather than results from a working Einstein Telescope.

Young explorerScientists are planning an underground machine to listen for tiny ripples in space. One plan uses two detectors, including a very cold one. This paper suggests using just one detector that does not need to be kept very cold. The scientists say special glass threads and ways to quiet unwanted shaking could help it listen even better. That is what they say their design could do, not something they have shown with a finished machine.

Validation of Satellite Lifetime Predictions at Leonid Space

Scott Shambaugh

AstronomerThe authors backtest Leonid Space’s satellite lifetime prediction pipeline against 1,283 deorbited satellites spanning six decades, reconstructing their final year of flight. The pipeline combines orbit propagation, ballistic coefficients estimated from on-orbit TLE data, assimilated atmospheric density corrections, custom space weather forecasts, and Monte Carlo uncertainty analysis. Four validation stages progressively replace hindsight-based inputs with forecasts available at the time, ending in a fully predictive historical test analogous to forecasting for a satellite flying today. Scored with the continuously ranked probability score and root mean square calibration error, the reported median one-year prediction accuracy is 2.4 days (0.7%) with perfect knowledge and 35.3 days (9.7%) in the fully predictive case. Solar flux forecasts account for 75% of prediction variance. The authors describe this as, to their knowledge, the first comprehensive long-term satellite lifetime backtest reporting quantitative fully predictive results, and present a framework for evaluating solar cycle forecasts through their operational impact on satellite lifetime predictions.

PublicHow accurately can we predict when a satellite will fall out of orbit? The researchers tested Leonid Space’s forecasting system using the final year of flight of 1,283 satellites that had already left orbit, covering six decades of spaceflight. They first gave the system historical information that would not have been known in advance, then progressively replaced it with forecasts available at the time. The reported median one-year prediction accuracy was 2.4 days with hindsight-based inputs, compared with 35.3 days in the test designed to resemble a real advance forecast. The system combines orbit calculations, estimates of atmospheric effects, space weather forecasts, and many simulations to represent uncertainty. Forecasts of the Sun’s energy output accounted for 75% of the variation in its predictions. These are historical test results, not a guarantee for future satellites; the work also offers a way to judge solar cycle forecasts by how well they support satellite lifetime predictions.

Young explorerScientists tested a computer that tries to guess when a satellite will stop circling Earth and come down. They checked it using 1,283 satellites that had already come down. When the computer got information about what had really happened, its guesses were much closer. When it had to use forecasts, like it would for a satellite still flying today, its typical timing error was about 35 days for a guess made a year ahead. Guessing what the Sun would do was the biggest source of uncertainty. The test shows how well the computer worked on past satellites, but it cannot promise exactly when the next one will come down.

A Solar Optical Clock

Connor Fredrick, Ryan K. Cole, Ryan Terrien+2 more

• Earth and Planetary Astrophysics
• Solar and Stellar Astrophysics
• Optics

AstronomerThe authors demonstrate absolute frequency measurements of a single solar Fe I line at 1565 nm using techniques from quantum sensing and optical clocks. A laser is frequency-locked to the line through coupling to a single mode of the solar thermal field, then counted against an optical frequency comb referenced to the SI second. Operating at the fundamental photon-noise limit of thermal heterodyne spectroscopy, the experiment achieves line-centroid precision of one part in 10^9 of the optical frequency, equivalent to 30 cm/s in radial velocity. It recovers the Sun’s five-minute acoustic oscillations and the expected Rossiter-McLaughlin signal during a solar eclipse. This demonstrated precision remains above the less-than-10 cm/s precision cited for finding an Earth-Sun analog. The authors project that a thirty-meter-class telescope could achieve their demonstrated precision on the nearest Sun-like stars in a few hours. They further propose multiplexing absolute frequency measurements across lines with different magnetic sensitivities and formation depths to shorten averaging times and help separate stellar variability from terrestrial-planet Doppler signals.

PublicResearchers have used techniques from quantum sensors and atomic clocks to measure tiny shifts in a single feature of sunlight. They locked a laser’s frequency to an iron line in the Sun’s spectrum and measured it against a precise frequency reference tied to the SI second. The experiment reached a precision equivalent to a radial velocity of 30 centimeters per second and recovered both the Sun’s five-minute sound-wave oscillations and an expected signal during a solar eclipse. This is not yet the better-than-10-centimeters-per-second precision cited for finding an Earth-Sun counterpart. The authors suggest that a thirty-meter-class telescope could extend the demonstrated precision to nearby Sun-like stars. Measuring several spectral lines might also help distinguish changes within stars from the tiny motions caused by Earth-like planets; that application has not been demonstrated here.

Young explorerScientists used a laser and a very precise clock-like tool to watch one tiny part of the Sun’s light. They measured very small changes and picked out the Sun’s five-minute wiggles, plus an expected change during an eclipse. They hope bigger telescopes and more measurements could help find planets like Earth around other stars. This experiment did not find such a planet.

Deep Learning Search for Gravitational Waves from Compact Binary Coalescence

Lorenzo Mobilia, Tito Dal Canton, Gianluca Maria Guidi

• General Relativity and Quantum Cosmology

AstronomerThe study tests a hybrid compact-binary search combining matched-filtering concepts with convolutional neural networks, without the usual chi-squared rejection test. In simulated datasets with injected signals, it achieves detection efficiency comparable to or better than a standard matched-filtering search and greater resource efficiency when glitches affect the data or signal physics is absent from the template bank, including eccentricity, precession, and higher-order modes. However, standard binary-neutron-star and binary-black-hole searches in pure Gaussian noise show some loss of detection capability. These simulation results suggest a complementary route to reducing the computational burden of future gravitational-wave searches, rather than demonstrating performance on observational data.

PublicFinding gravitational waves from merging compact objects requires substantial computing power, and future detectors such as the Einstein Telescope will make that challenge larger. Researchers tested a search method that combines conventional signal-matching ideas with a neural network. In simulations containing brief noise disturbances or signals with features missing from the search’s reference patterns, the method found signals about as well as or better than a standard search while using computing resources more efficiently. It did lose some detection ability in simpler tests with purely Gaussian noise and standard neutron-star or black-hole binary signals. The results suggest a useful complementary tool for future searches, but they come from simulated data, not observations.

Young explorerScientists look for tiny wiggles from pairs of very small, heavy things joining together in space. They tested a new computer helper using pretend wiggles mixed with pretend noise. When the noise had sudden bumps, or the wiggles were different from the patterns the search expected, the helper found them about as well as or better than the usual way and needed less computer work. But in some simpler tests, it missed more wiggles. It might help scientists someday, but these tests used made-up data.

Do Tabular Foundation Models Know Physics? Contamination, Units, and the Deterministic Limit

Wassim Tenachi, Yashar Hezaveh, Laurence Perreault Levasseur+1 more

• Machine Learning

AstronomerThis study tests whether tabular foundation models encode useful physical knowledge in their Bayesian priors. Four models—TabPFN-3, TabICLv2, TabDPT, and Real-TabPFN-2.5—are evaluated against six baselines on datasets sampled from 316 physical equations, both in and out of domain. The TFMs outperform the baselines both out of the box and after tuning. However, their uncertainty representations struggle with noiseless deterministic mechanisms, and the tests show no evidence that they exploit physical units. The authors interpret these results as successful interpolation of physics, not yet the ability to function as physical models. The evidence comes from equation-sampled datasets rather than astronomical observations.

PublicCan AI systems trained to fill in tables learn physics along the way? Researchers tested four such systems against six comparison methods using data generated from 316 physics equations, including tests within and outside the systems’ domains. The table-based AI systems performed best, both before and after additional tuning. But important limitations remained: their estimates of uncertainty struggled to reflect exact, noise-free relationships, and the tests found no sign that they used physical units. The authors conclude that these systems can interpolate physics data, but cannot yet serve as physical models.

Young explorerResearchers tested four computer helpers that fill in missing parts of tables. They gave them number puzzles made from physics rules. The helpers did better than six other methods, but they still had trouble showing how sure they should be when a rule gives an exact answer. The tests also found no sign that they used measurement labels, like meters or seconds. Being good at filling in numbers does not yet mean they can work like a model of how nature behaves.

Frame covariance of CMBR lensing in the exact 1+3 covariant radiation hierarchy

Tim Gebbie

AstronomerThis theoretical analysis identifies the acceleration, shear and vorticity couplings with coefficients linear in multipole order ℓ in the exact 1+3 covariant CMB Boltzmann hierarchy as manifestations of the photon Liouville equation’s aberration operator. Under a threading change, the operator shifts by the along-ray generator of a Lorentz boost; acceleration couplings between ℓ and ℓ±1 and shear couplings between ℓ and ℓ±2 are related by a pointwise relabelling of direction. With emitter and observer frames fixed, the predicted sky is threading-independent at every multipole. The derivation uses covariant, gauge-invariant variables without constructing second-order gauge-invariant variables and identifies the O(ε²ℓ) terms with gravitational lensing. Linearisation about FLRW removes these couplings, so lensing must then be restored through the geodesic equation. In Newtonian threading, the authors derive both the equivalence-principle deflection contribution through aberration and the spatial-curvature contribution through free streaming. They also derive lensing efficiency from the direction derivative. For deflections statistically independent of the source, the two fourth-order-in-potential power-spectrum terms carrying ℓ² cancel where the spectrum is smooth on the deflection scale: lensing redistributes power without adding ensemble variance under these conditions.

PublicThis paper presents a mathematical analysis, not a new observation, of how gravity changes the apparent directions of light in the cosmic microwave background. It shows that several seemingly different terms in the equations describe the same underlying change of direction. Changing the intermediate reference frames used in the calculation does not change the predicted sky, provided the emitting and observing frames remain fixed. The analysis connects these terms to gravitational lensing and explains why a simplified, linear calculation drops effects that must subsequently be restored. It also derives contributions to light deflection from both aberration and spatial curvature. Finally, under specific assumptions—deflections independent of the source and a spectrum smooth over the deflection scale—certain contributions cancel, so lensing redistributes fluctuation power without adding ensemble variance.

Young explorerGravity can bend the path of very old light coming across space, changing where it seems to come from. The researchers used math to show that different ways of keeping track of that light should give the same sky picture. Their work also shows how a simpler calculation can leave out the bending and needs to have it put back in. This was a math study, not a new picture of the sky.