Astrophysics of Galaxies
Little Red Dots on FIRE: The Ability of Bursty Galaxies to Host an Abundant Population of High-Redshift AGN
Andrew Marszewski, Claude-André Faucher-Giguère, Guochao Sun et al. (+5 more)
The James Webb Space
Telescope has unveiled an abundant population of potential active
galactic nuclei (AGN) at high
redshift ($z\gtrsim4$) known as little red dots (LRDs), which are likely hosted in relatively low-mass
galaxies. However, previous theoretical models have highlighted the difficulty in continuously feeding massive black holes in the central regions of bursty, high-
redshift galaxies because of repeated gas evacuation by
stellar feedback. We analyze
galaxies in high-
redshift FIRE-2 simulations to understand whether they are capable of hosting the observed abundant population of high-
redshift AGN. We use a gravitational torque-driven
accretion (GTDA) model and a simple free-fall
accretion model to derive black hole
accretion rates and construct predicted AGN bolometric luminosity functions for $z=5-7$. The GTDA model and the free-fall model with black holes accreting $\lesssim 1$ percent of their central gas supply ($<100 \rm \ pc$) per free-fall time predict AGN abundances that are more than sufficient to explain the most recent LRD observations. The fiducial models, in fact, overpredict the number of low-luminosity AGN as compared with observations. We explore possible resolutions of this tension. A plausible, though likely not unique, scenario for alleviating the AGN overpredictions and which also provides a good match to the host-
galaxy UV luminosity distribution suggests that LRDs are super Eddington-accreting, Eddington luminosity-limited, $M_{\rm BH}\gtrsim 2\times10^5 \ \rm M_\odot$ black holes residing in $M_\star\gtrsim 2\times10^7 \ \rm M_\odot$
galaxies. We show that, under simple assumptions, mock observations of such sources can reproduce key observed LRD characteristics.
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All authors Andrew Marszewski, Claude-André Faucher-Giguère, Guochao Sun, Daniel Anglés-Alcázar, Robert Feldmann, Kung-Yi Su, Tim B. Miller, Niranjan Chandra Roy
Cosmology and Nongalactic Astrophysics
Cosmological Equivalence of Scalar-Tensor-Vector Modified Gravity and Cold Dark Matter
John W. Moffat
We show that Scalar-Tensor-Vector
Gravity (STVG-MOG) is observationally equivalent to the standard model $\Lambda$CDM cosmological model for all probes that depend on isotropic and linear gravitational dynamics, including
galaxy rotation curves, cluster
lensing, the linear matter power spectrum P(k), $\sigma_8$,
baryon acoustic oscillations, and the
cosmic microwave background (CMB). This degeneracy arises from the scale-dependent effective gravitational coupling $G_{\mathrm{eff}}$, which ensures identical background
evolution, transfer functions, and linear growth. Consequently, all early-universe, low and intermediate scale cosmological observables are equally well described by STVG-MOG without invoking non-baryonic dark matter. We argue that the equivalence implies that isotropic cosmological data alone cannot establish the physical existence of dark matter. The degeneracy is broken only by observables sensitive to large-scale, anisotropic gravitational response. In particular, recent measurements of enhanced
radio-
galaxy and
quasar number-count dipoles at gigaparsec scales probe a regime where $G_{\mathrm{eff}}$ departs from its $\Lambda$CDM limit, allowing STVG-MOG to generate anisotropic bulk flows, while preserving consistency with all isotropic constraints. These observations provide a concrete pathway for empirically distinguishing modified
gravity from particle dark matter.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Optimal cross-correlation technique to search for strongly lensed gravitational waves
Anirban Kopty, Sanjit Mitra and Anupreeta More
As the number of detected gravitational wave (GW) events increases with the improved sensitivity of the observatories, detecting strongly lensed pairs of events is becoming a real possibility. Identifying such lensed pairs, however, remains challenging due to the computational cost and/or the reliance on prior knowledge of source parameters in existing methods. This study investigates a novel approach, Optimal Cross-Correlation Analysis for Multiplets (OCCAM), applied to strain data from one or more detectors for Compact Binary Coalescence (CBC) events identified by GW searches, using an optimal, mildly model-dependent, low computation cost approach to identify strongly lensed candidates. This technique efficiently narrows the search space, allowing for more sensitive, but (much) higher latency,
algorithms to refine the results further. We demonstrate that our method performs significantly better than other computationally inexpensive methods. In particular, we achieve 97 percent (80 percent) lensed event detection at a pairwise false positive probability of approximately 13 percent (7 percent) for a single detector with LIGO design sensitivity, assuming an SNR greater than or equal to 10 astrophysically motivated lensed and unlensed populations. Thus, this method, using a network of detectors and in conjunction with sky-localisation information, can enormously reduce the false positive probability, making it highly viable to efficiently and quickly search for
lensing pairs among thousands of events, including the sub-threshold candidates.
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Earth and Planetary Astrophysics
Densities of small planets around the M dwarfs TOI-4336 A and TOI-4342 with ESPRESSO: Three sub-Neptunes, one super-Earth, and a Neptune-mass candidate
Léna Parc, Charles Cadieux, Nolan Grieves et al. (+27 more)
We present the characterization of two planetary systems orbiting the M
dwarfs TOI-4336 A (M3.5V) and TOI-4342 (M0V), each hosting two transiting
planets previously validated with TESS and ground-based observations. We refined the photometry of the TOI-4342 system using TESS and LCOGT data, and characterized the host
stars with NIRPS and ESPRESSO spectroscopy. High-precision ESPRESSO radial velocities allowed us to constrain the planetary masses and investigate their potential compositions. The TOI-4336 A system is composed of a sub-Neptune with a period of 16.34 days, a radius of $2.14 \pm 0.08$ Re, and a mass of $3.33 \pm 0.36$ Me, along with an inner super-Earth on a 7.59-day orbit with a radius of $1.25 \pm 0.07$ Re and a mass of $1.55 \pm 0.13$ Me. The TOI-4342 system hosts two sub-Neptunes of similar sizes ($2.33 \pm 0.09$ Re and $2.35 \pm 0.09$ Re), with periods of 5.54 and 10.69 days. Their masses are measured to be $7.3 \pm 1.3$ Me and $4.8 \pm 1.4$ Me, respectively. The RVs also reveal a
planet candidate around TOI-4342, likely non-transiting, with a period of 47.5 days and a minimum mass of $17.8 \pm 3.0$ Me. With precise radii and masses, we derived bulk densities and explored possible compositions. The TOI-4336 A sub-Neptune and super-Earth have densities of $1.87 \pm 0.30$ and $4.35 \pm 0.79$ g cm$^{-3}$, while the two similar-sized sub-Neptunes in TOI-4342 show distinct densities of $3.18 \pm 0.67$ and $2.01 \pm 0.63$ g cm$^{-3}$. All four
planets are excellent targets for future atmospheric characterization with JWST, and their multi-
planet nature makes them especially interesting for comparative planetology. Notably, TOI-4336 A b stands out as one of the best-known targets in its size and temperature regime, with a TSM of 138, comparable to
benchmark planets such as K2-18 b and LHS 1140 b.
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All authors Léna Parc, Charles Cadieux, Nolan Grieves, François Bouchy, Alexandrine L'Heureux, Caroline Dorn, Marie-Luise Steinmeyer, Elisa Delgado-Mena, René Doyon, Yolanda G.C. Frensch, Romain Allart, Etienne Artigau, Nicola Astudillo-Defru, Xavier Bonfils, Yann Carteret, Ryan Cloutier, Marion Cointepas, Karen A. Collins, Jose Renan De Medeiros, Xavier Delfosse, Xavier Dumusque, Tianjun Gan, Jonay I. González Hernández, Ravit Helled, Monika Lendl, Lucile Mignon, Angelica Psaridi, Nuno C. Santos, Richard P. Schwarz, Julia Venturini
Cosmology and Nongalactic Astrophysics
Probing the Sound Speed of Dark Energy with a Lunar Laser Interferometer
Alfredo Gurrola, Robert J. Scherrer and Oem Trivedi
The sound speed of dark energy encodes fundamental information about the microphysics underlying
cosmic acceleration, yet remains essentially unconstrained by existing observations. We demonstrate that a lunar-based
laser interferometer, such as the proposed
Laser Interferometer Lunar
Antenna (LILA), can directly probe the sound speed of dark energy by measuring the real-time
evolution of horizon-scale gravitational potentials. Operating in the ultra-low-frequency gravitational band inaccessible from Earth, LILA is sensitive to scalar metric perturbations sourced by dark energy dynamics. Using both fluid and effective field theory descriptions, we develop a complete framework linking dark energy sound speed to observable strain signatures. We construct a likelihood pipeline and Fisher forecasts, showing that LILA can either detect clustering dark energy or exclude broad classes of models with unprecedented sensitivity. This establishes lunar interferometry as a novel and powerful probe of the physics driving
cosmic acceleration.
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Solar and Stellar Astrophysics
BE Lyncis is not a Black Hole Binary: Lessons From Gaia and Hipparcos Astrometry
Pranav Nagarajan, Kareem El-Badry, Thomas J. Maccarone et al. (+3 more)
BE Lyncis (BE Lyn) is a well-studied high-amplitude $\delta$ Scuti variable
star (HADS). Recently, Niu et al. (2026) analyzed a 39-year baseline of times of maximum light of BE Lyn, reporting that it is the most eccentric binary known ($e \approx 0.9989$) and hosts the nearest black hole (BH) known to date. We analyze Hipparcos and
Gaia astrometry of BE Lyn, predicting what the observed proper motion anomaly (PMA) over the 25 year baseline between the two missions would be were the companion really a $\gtrsim 17.5\,M_{\odot}$ BH. We find that the predicted PMA is at least an order of magnitude larger than the observed value of $\approx 1.7 \pm 0.8$ mas yr$^{-1}$, regardless of the assumed orientation of the orbit. We predict the expected
Gaia DR3 RUWE for different orientations of the putative BH binary, finding that it ranges from $\approx 2.5$-$4.0$, much larger than the reported value of $1.073$. The observed value is instead consistent with a low-mass secondary or a single
star. We find that BE Lyncis would have received a 7-parameter acceleration solution if it were a BH binary, in contradiction with its absence from the
Gaia DR3 non-single
star catalogs. Finally, we show that the reported orbit is impossible because the luminous
star would overflow its Roche lobe at periastron, irrespective of inclination. We recommend caution in interpreting light-travel time effect (LTTE) models that require very high eccentricities, face-on inclinations, or large companion masses. The observed pulsation timing variations are most likely simply a result of red noise or pulsation phase
evolution.
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All authors Pranav Nagarajan, Kareem El-Badry, Thomas J. Maccarone, Giuliano Iorio, Sara Rastello, Johanna Müller-Horn
Astrophysics of Galaxies
Mapping the Extended Lyman-Alpha Emission within the Circumgalactic Medium of Quasars Hosted by Dusty Starbursts with CubeCarve
Kevin Hall and Hai Fu
We present a study of extended Ly$\alpha$ emission around four
quasars hosted by dusty starbursts, which are composite systems thought to represent a transitional stage in
quasar evolution. To extract faint CGM emission in the presence of bright point sources, we introduce CubeCarve, a dual-channel deconvolution
algorithm that separates unresolved
quasar emission from spatially extended structure. This approach enables reliable recovery of \Lya\ emission projected onto the
quasar position without introducing subtraction artifacts. Using CubeCarve, we find that the \Lya\ surface brightness profiles of these systems are, on average, fainter and shallower than those of
quasars of similar bolometric luminosities. We also find that the total integrated \Lya\ luminosities of the nebulae are lower in systems whose host
galaxies exhibit brighter far-infrared emission. These results suggest that the CGM conditions in composite systems differ from those in the broader
quasar population. Our study highlights both the physical diversity of
quasar CGM environments and the effectiveness of CubeCarve for recovering diffuse emission in modern IFU
datasets.
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Cosmology and Nongalactic Astrophysics
A null test of the Hubble tension
Gerasimos Kouniatalis and Emmanuel N. Saridakis
The origin of the Hubble tension remains one of the central open problems in modern cosmology, with competing explanations invoking either early-Universe physics, late-time modifications of
cosmic expansion, or unresolved observational systematics. In this Letter we propose a new, purely
geometric null test of the late-time expansion history that is exactly independent of the Hubble constant. By combining strong-
lensing time-delay distances with gravitational-wave standard-siren luminosity distances, we construct a dimensionless ratio that depends only on the
redshift dependence of the expansion rate and can be both predicted from early-Universe data and measured directly at late times, without relying on the
cosmic distance ladder or the sound horizon. We show that the comparison between the early- and late-time determinations of this ratio provides a transparent consistency test of the standard cosmological expansion. When combined with an independent standard-siren measurement of $H_{0}$, this framework allows one to unambiguously distinguish between early- and late-time origins of the Hubble tension. With the forthcoming detection of lensed gravitational-wave standard sirens, the proposed test provides a timely and robust framework for probing this long-standing cosmological puzzle.
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Earth and Planetary Astrophysics
The Volatile Inventory of 3I/ATLAS as seen with JWST/MIRI
Matthew Belyakov, Ian Wong, Bryce T. Bolin et al. (+4 more)
We present the first spectroscopic characterization of an interstellar object at mid-infrared wavelengths. Post-perihelion observations of 3I/ATLAS using the JWST/MIRI medium-resolution spectrometer were obtained on 2025 December 15–16 and 27 when the object was at heliocentric distances of 2.20 and 2.54 au, respectively. Our 5–28 micron spectra exhibit fluorescence features from several gaseous species, including the $\nu_2$ band of water at 5.8–7.0 microns. the primary $\nu_2$ and associated hot bands of carbon dioxide around 15 microns, and a forbidden transition of atomic nickel at 7.507 microns. We also report the first direct detection of methane in an interstellar object. The delayed onset of methane production relative to water suggests past depletion from the outermost layers, with the observed methane emerging from unprocessed subsurface material. Comparison of the volatile production rates measured during the two epochs indicate a significant reduction in overall outgassing over 12 days, with the measured water activity level dropping more steeply than other species. As shown through near-
nucleus coma mapping, 3I continues to display an extended source of water production from icy grains entrained within the coma. Our production rate measurements confirm that 3I exhibits a strongly enhanced CO$_2$:H$_2$O mixing ratio relative to typical
solar system comets, as well as a somewhat enriched CH$_4$:H$_2$O value.
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All authors Matthew Belyakov, Ian Wong, Bryce T. Bolin, M. Ryleigh Davis, Steven J. Bromley, Carey M. Lisse, Michael E. Brown
Solar and Stellar Astrophysics
Inclination Bias in Techniques Used to Identify Be Star Candidates
B. D. Lailey and T. A. A. Sigut
Several methods for identifying Be
star candidates are reviewed for observational bias with respect to system inclination, that is the angle between the
stellar/disk rotation axis and the observer's line of sight, with focus on two photometric methods that leverage narrow-band filters centred on H$\alpha$ and a spectroscopic method using a H$\alpha$ peak-finding
algorithm. Tests for bias were performed using a sample of 20,000 synthetic Be
stars drawn from a Salpeter initial mass function and computed libraries of spectral energy distributions and H$\alpha$ profiles. The spectroscopic method showed substantial bias against high inclinations ($i > 80^\circ$). Both photometric methods were biased against low inclinations, with one also biased against inclinations above $80^\circ$, resulting in a surplus in the Be
star candidate detection rate for moderate inclinations ($ 50^\circ < i < 80^\circ$). Inclination probability distributions, including the random $\sin i$ factor, are given for the three methods that can be applied to observational samples.
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High Energy Astrophysical Phenomena
Constraining Black Hole Parameters from Shadow and Inner-Shadow Morphology Considering Effects from Thick Disk Accretion Flows
Julien A. Kearns, Dominic O. Chang, Daniel C. M. Palumbo et al. (+1 more)
We study the effects of emission geometry on the capability to constrain black hole parameters from measurements of the shadow and inner-shadow of a Reissner-Nordström black hole. We investigate the capability to constrain mass, charge, observer inclination, and emission co-latitude from images of black hole
accretion flows that would arise from thick and thin
accretion disks. We confirm previous studies that have shown that independent radii measurements of the shadow and inner-shadow can constrain black hole parameters if the viewing inclination is known, but find that it is only possible if the true emission geometry is also assumed. We study the constraining capabilities of the shadow and inner-shadow observations of M87* and Sgr A* like systems within the context of the BHEX and NgEHT future observatories.
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All authors Julien A. Kearns, Dominic O. Chang, Daniel C. M. Palumbo, Shane W. Davis
Astrophysics of Galaxies
Stellar Populations in the Extreme Outer Halo of the Spiral Galaxy M96
J. Christopher Mihos, Patrick R. Durrell, Brian Malkan et al. (+1 more)
We use deep Hubble Space
Telescope imaging to study
stellar populations in the outer
halo of the spiral
galaxy M96, located in the dynamically active Leo I
galaxy group. Our imaging targets two fields at a projected distance of 50 kpc from the
galaxy's center, with a 50% photometric completeness limit of F814W = 28.0, nearly two magnitudes below the tip of the red
giant branch. In both fields we find a clear detection of red
giant stars in M96's
halo, with a space density that corresponds to an equivalent broadband surface brightness of $\mu_V \approx $ 31.7 mag arcsec$^{-2}$. We find little evidence for any difference in the spatial density or color of the RGB
stars in the two fields. Using isochrone matching we derive a median
metallicity for the red
giants of [M/H] = -1.36 with an interquartile spread of $\pm$0.75 dex. Adopting a power-law radial density profile, we also derive a total
halo mass of $M_h = 7.8^{+17.4}_{-4.9}\times10^9$ M$_\odot$, implying a
stellar halo mass fraction of $M_{*,halo}/M_{*,tot} = 15^{+33}_{-9}$%, on the high end for spiral
galaxies, but with significant uncertainty. Finally, we find that M96 appears offset from the
stellar halo mass-
metallicity relationship for spirals, with a
halo that is distinctly metal-poor for its
halo mass. While a variety of systematic effects could have conspired to drive M96 off this relationship, if confirmed our results may argue for a markedly different
accretion history for M96 compared to other spirals in the nearby universe.
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All authors J. Christopher Mihos, Patrick R. Durrell, Brian Malkan, Aaron E. Watkins
High Energy Astrophysical Phenomena
Spectroscopic Variability of the Broad H$\beta$ Emission Line in Sloan Digital Sky Survey Quasars
Collin M. Dabbieri, Jessie C. Runnoe, Michael Eracleous et al. (+3 more)
We present a catalog of broad H$\beta$ variability properties for all spectra of
quasars with $z<0.8$ and at least two observations included in the Sloan Digital Sky Survey (SDSS) Data Release 16
quasar catalog. For each spectrum, we perform a spectral decomposition to isolate the broad H$\beta$ emission. We measure the luminosity, FWHM, equivalent width, centroid, and Pearson skewness coefficient of broad H$\beta$ and provide derived physical properties such as the single-epoch black hole mass and the bolometric luminosity. For each pair of spectra in the sample, we calculate the change in radial velocity of the centroid of broad H$\beta$ emission ($\Delta v_{rad}$) as well as other derived properties related to broad H$\beta$ shape variability. We use forward-modeling methods to estimate the uncertainty in our measurements and discuss an improved method for estimating the uncertainty in $\Delta v_{rad}$ in the case where a spectral decomposition is used to isolate the broad H$\beta$ emission. We find that $\Delta v_{rad}$ is not normally distributed and that the shape of the distribution depends on the interval between observations. We discuss the effect of the predominance of the Reverberation Mapping subsample in the sample of pairs of spectra in SDSS.
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All authors Collin M. Dabbieri, Jessie C. Runnoe, Michael Eracleous, Mary E. Kaldor, Mary Ogborn, Niana N. Mohammed
Instrumentation and Methods for Astrophysics
Critical Evaluation of Studies Alleging Evidence for Technosignatures in the POSS1-E Photographic Plates
Wesley Andrés Watters, Laura Dominé, Sarah Little et al. (+3 more)
Recent studies by B. Villarroel et al. have assembled and analysed
datasets of unidentified features measured from digital scans of pre-Sputnik photographic plates. We have examined the claims in these papers using two previously published
datasets that are closely related to those used in the Villarroel et al. studies. For these
datasets, the assumption of a spatially uniform-random background distribution of features, essential to the Earth shadow analysis, is shown to be false. After finding the null distribution of feature count deviations from the background, we find no statistically significant deficit in the shadow. We find that the reported correlation between the timing of feature observations and
nuclear tests becomes insignificant after properly normalizing by the relevant number of observation days, and is almost completely determined by the observation schedule of the Palomar
telescope. We uncover important inconsistencies in the definitions of the
datasets used in these studies, as well as the use of unvalidated
datasets containing catalogue
stars, scan artefacts, and plate defects. We find an overall gradual increase in number density of features toward the corners and edges of plates, as well as examples of (i) empty north-south strips that span multiple plates; (ii) clusters and voids having
geometric shapes; and (iii) amorphous clusters. We also highlight a circular argument used in these studies, that leverages the results of an inferential analysis to justify conclusions about the origin of the features as well as the validity of the measurements. Finally, we also review the literature concerning historical searches for optical transients in photographic plates corresponding to gamma ray bursts (GRBs); following decades of work, researchers were unable to make a confident identification of a GRB-associated optical transient.
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All authors Wesley Andrés Watters, Laura Dominé, Sarah Little, Cameron Pratt, Kevin H. Knuth, Matthew Szenher
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
$f$-Mode oscillations and the gravitational response of compact stars with analytic equations of state
Kilar Zhang, Alessandro Parisi, C. Vásquez Flores et al. (+2 more)
We use a simple
holographic model to study the property of cold and dense
neutron stars (NSs) and deconfined QCD matter. With the aim of investigating the global properties of compact
stars, such as the total gravitational mass and radius, the equation of states (EOS) of
neutron stars and
quark stars (QSs) are used to solve the Tolman-Oppenheimer-Volkov (TOV) equations for
stellar structure. Additionally, we investigate the
tidal deformabilities and $f$-mode oscillation for these two different compact
stars. Our main conclusion is that, by using a
holographic equation of state, it is possible to obtain
neutron matter and
quark matter properties and that it is also possible to extend the procedure to astrophysical applications.
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All authors Kilar Zhang, Alessandro Parisi, C. Vásquez Flores, C.Henrique Lenzi, Chian-Shu Chen
Astrophysics of Galaxies
Orbital decomposition of the nuclear regions in the early-type galaxy FCC 47: Unveiling the nuclear cluster origin
Julia Lamprecht, Anja Feldmeier-Krause, Mariya Lyubenova et al. (+8 more)
Nuclear star clusters (NSCs) are among the densest
stellar systems in the Universe and often coexist with supermassive black holes (SMBHs) at
galaxy centres. While SMBH formation histories are essentially lost, NSCs preserve evolutionary imprints through their
stellar populations and
stellar kinematics, reflecting the cumulative effects of mergers,
accretion, and internal dynamical
evolution. We aim to investigate the orbital structure of the unusually large NSC in FCC 47 (NGC 1336) by decomposing its
stellar orbits into dynamically distinct components. We extract
stellar kinematics, and in particular the line-of-sight velocity distributions (LOSVDs), from VLT/MUSE integral-field spectroscopy using the non-parametric Bayes-LOSVD approach, and apply triaxial Schwarzschild orbit-superposition modelling with the DYNAMITE software. We decompose the orbit library into hot, warm, cold, and counter-rotating components. We detect triple-peaked LOSVDs in the
nucleus, indicating a complex orbital structure. The NSC forms a counter-rotating, kinematically decoupled component. A hot pressure-supported component, a warm counter-rotating structure and a counter-rotating cold disk in the centre suggest hierarchical assembly via early
star cluster
accretion and later in situ
star formation. Our orbital decomposition of FCC 47 supports a hybrid formation scenario for this NSC. Dynamically distinct substructures reflect the interplay of
accretion and in situ
star formation during
galaxy evolution.
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All authors Julia Lamprecht, Anja Feldmeier-Krause, Mariya Lyubenova, Katja Fahrion, Sabine Thater, Prashin Jethwa, Stefanie Reiter, Jesus Falcón-Barroso, Thomas I. Maindl, Giulia Santucci, Iris Breda
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Numerical simulations of primordial black hole formation via delayed first-order phase transitions
Zhuan Ning, Xiang-Xi Zeng, Rong-Gen Cai et al. (+1 more)
We perform fully nonlinear, spherically symmetric numerical simulations of superhorizon false-
vacuum-domain (FVD) collapse in a coupled
gravity-scalar-fluid system to study
primordial black hole (PBH) formation during delayed first-order phase transitions (FOPTs). Using adaptive mesh refinement to resolve the bubble wall, we identify three dynamical outcomes: type B (supercritical) PBHs with an interior baby universe and a bifurcating trapping horizon, type A (subcritical) PBHs with an apparent horizon formed by direct wall collapse, and dispersal with no PBH formation. To separate these three cases, we evaluate two commonly used PBH-formation criteria: the time scale ratio $t_\mathrm{H}/t_\mathrm{V}$ (horizon crossing time versus
vacuum-energy domination time) and the local density contrast $\delta(t_\mathrm{H})$ at horizon crossing. For the parameter space explored, we find that $t_\mathrm{H}/t_\mathrm{V}$ is a more robust predictor of outcome: type B PBHs form when $t_\mathrm{H}/t_\mathrm{V} \gtrsim 1$ (critical range $\sim 1.1 - 1.6$ in our survey), type A PBHs arise when $t_\mathrm{H}/t_\mathrm{V}$ is below this threshold but remains above a lower bound (typical range $\sim 0.35 - 0.7$), and no-PBH dispersal occurs when $t_\mathrm{H}/t_\mathrm{V}$ falls below this lower bound. When a clear thin-wall FVD boundary exists, $\delta(t_\mathrm{H})$ can correspondingly distinguish different outcomes (roughly $\delta_c(t_\mathrm{H}) \sim 1 - 1.7$ for type B and $\delta_c(t_\mathrm{H}) \sim 0.35 - 0.5$ for type A), but is highly sensitive to wall structure and model details and thus less universal. These results offer new insights into the dynamics of FVD collapse, quantify practical PBH-formation thresholds, and pave the way for precise predictions of PBH abundance from delayed FOPTs.
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All authors Zhuan Ning, Xiang-Xi Zeng, Rong-Gen Cai, Shao-Jiang Wang
High Energy Astrophysical Phenomena
Extreme-Value Distribution Analysis of the Second CHIME/FRB Catalog: Assessing the Rarity of the One-off FRB 20250316A
Wen-Long Zhang and Jun-Jie Wei
We present a statistical analysis of the extremely bright, apparently non-repeating fast
radio burst FRB 20250316A, detected by the Canadian Hydrogen Intensity Mapping Experiment (CHIME), to assess its rarity. Using a model-agnostic framework based on the Generalized Extreme Value (GEV) distribution and the second CHIME/FRB catalog, we perform
Bayesian fits to the block-maxima of its peak flux and fluence. Our analysis confirms FRB 20250316A as a pronounced statistical outlier in both quantities. For the peak flux, the best-fit GEV model follows an unbounded, heavy-tailed Fréchet-type distribution, yielding return periods of approximately $802$ years at the $68\%$ confidence level (CL), $81$ years at the $95\%$ CL, and $30$ years at the $99\%$ CL. The fluence distribution exhibits greater complexity: while the full sample is consistent with a Fréchet-type distribution (return period of approximately $55$, $15$, and $8$ years at the $68\%$, $95\%$ and $99\%$ CLs, respectively), removing three other conspicuous outliers reveals a light-tailed Weibull-type distribution with a finite upper bound that is far exceeded by the fluence of FRB 20250316A. Although its inferred recurrence time is shorter than that of the “Brightest Of All Time” (BOAT) gamma-ray burst GRB 221009A, FRB 20250316A represents a similarly exceptional event (a potential FRB “BOAT”) within the relatively short observational baseline of wide-field
radio surveys. This work affirms the existence of rare, extremely luminous events at the extreme upper end of the FRB luminosity distribution, which may delineate a distinct physical channel or the extreme tail of a complex luminosity function.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Compact Stars Sourced by Perfect Fluid Dark Matter Halos
Yuan Yue and Yong-Qiang Wang
Recent studies have shown that dark matter
halos can support regular black holes or compact
stars by assuming an anisotropic energy-momentum tensor. In this paper, we extend the analysis to the dark matter
halo as an isotropic perfect fluid. By employing
galactic dark matter profiles-specifically the Einasto and Dehnen models-as the mass-energy density source, we numerically solve the Einstein field equations and find a class of non-singular, horizonless compact
star solutions. Moreover, these configurations remain stable against axial perturbations while satisfying the dominant energy condition.
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Astrophysics of Galaxies
A UV-Luminous Galaxy at z=11 with Surprisingly Weak Star Formation Activity
Yuichi Harikane, Pablo G. Perez-Gonzalez, Javier Alvarez-Marquez et al. (+8 more)
One of the major discoveries by the James Webb Space
Telescope (JWST) is the identification of a large population of luminous
galaxies at $z>10$, challenging theoretical models for early
galaxy formation. The unexpectedly high number density of these systems has triggered intense debate about potential differences in the physical properties of
galaxies at such extreme
redshifts and those at lower
redshift. However, progress has been limited by the lack of rest-frame optical diagnostics, which are critical for constraining the key properties. Here we present deep JWST/MIRI observations of a UV-luminous
galaxy at $z=11.04$, CEERS2-588, only 400 Myr after the Big Bang. CEERS2-588 is detected in the MIRI F560W and F770W bands, while deep MIRI/MRS spectroscopy yields no detection of H$\alpha$ or [OIII]$\lambda5007$ line, revealing a prominent Balmer break detected for the first time at $z>10$. Spectral energy distribution (SED) fitting indicates an extended
star formation history possibly reaching $z>15$, followed by rapid quenching within the recent $\sim10$ Myr, in stark contrast to other $z>10$
galaxies. The MIRI detections also significantly improve our
stellar mass estimate to $\mathrm{log}(M_*/M_\odot)=9.1^{+0.1}_{-0.1}$, making CEERS2-588 the most massive
galaxy securely confirmed at $z>10$. Remarkably, the inferred gas-phase
metallicity is near
solar, exceeding predictions from current theoretical models. These results suggest that efficient starbursts play a key role in producing the abundant luminous
galaxy population in the early universe.
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All authors Yuichi Harikane, Pablo G. Perez-Gonzalez, Javier Alvarez-Marquez, Masami Ouchi, Yurina Nakazato, Yoshiaki Ono, Kimihiko Nakajima, Hiroya Umeda, Yuki Isobe, Yi Xu, Yechi Zhang
High Energy Astrophysical Phenomena
Late-time X-ray afterglows of GRBs: Implications for particle acceleration at relativistic shocks
Zhi-Qiu Huang, Om Sharan Salafia, Lara Nava et al. (+2 more)
Particle-in-
cell (PIC) numerical simulations are currently among the most advanced tools to investigate particle acceleration at relativistic shocks. Still, they come with limitations imposed by finite computing power, whose impact is not straightforward to evaluate a priori. Observational features are hence required as verification. energy electrons accelerated at external shocks, provides a testbed for such predictions. Current numerical studies suggest that in GRB afterglows the maximum synchrotron
photon energy, which corresponds to the limit of electron acceleration, may fall within the $\sim$ 0.1–10 keV X-ray energy band at late times, $t\gtrsim 10^6 - 10^7$ s. To test this prediction, we analyzed the X-ray spectra of six GRBs with Swift/XRT detections beyond $10^7$ s: our analysis reveals no clear evidence of a spectral cutoff. Using a model that accounts for the effect of the finite opening angle of the shock on the observed maximum synchrotron
photon energy, we show that these observations are incompatible with PIC simulation predictions, unless one or more physical afterglow parameters attain values at odds with those typically inferred from afterglow modeling (small radiative efficiency, low ambient density, large equipartition fraction $\epsilon_{\rm B}$ of the
magnetic field). These findings challenge existing numerical simulation results and imply a more efficient acceleration of electrons to high-energies than seen in PIC simulations, with important implications for our understanding of particle acceleration in relativistic shocks.
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All authors Zhi-Qiu Huang, Om Sharan Salafia, Lara Nava, Annalisa Celotti, Giancarlo Ghirlanda
Cosmology and Nongalactic Astrophysics
Forecasting Constraints on Cosmology and Modified Gravitational-wave Propagation by Combining Strongly Lensed Gravitational Waves and Galaxy Surveys
Anson Chen and Jun Zhang
Gravitational
lensing of gravitational wave (GW) will become the next frontier in studying cosmology and
gravity. While time-delay cosmography using quadruply lensed GW events associated with optical images of the lens systems can provide precise measurement of the Hubble constant ($H_0$), they are considered to be much rarer than doubly lensed events. In this work, we analyze time-delay cosmography with doubly lensed GW events for the first time. We generate mock doubly lensed GW events with designed sensitivity of the LIGO-Virgo-KAGRA (LVK) O5 network, with LIGO post-O5 upgrade, and with Einstein
Telescope (ET) +
Cosmic Explorer (CE) respectively, and select the events that can be associated with future
galaxy surveys. Over 1000 realizations, we find an average of 0.2(2.4) qualified events with the LVK O5(post-O5) network. Whereas with the ET+CE network, we find an average of 73.2 qualified events over 100 realizations. Using the Singular Isothermal Sphere (SIS) lens model, we jointly estimate waveform parameters and the impact parameter with doubly lensed GW signals, and then forecast the constraints on cosmological parameters and modified GW propagation by combining time-delay cosmography and the standard siren approach. The average posterior gives a constraint on $H_0$ with a relative uncertainty of $14\%$, $10\%$ and $0.42\%$ in the $\Lambda$CDM model for the LVK O5, LVK post-O5, and ET+CE network, respectively. While the LVK network gives uninformative constraints on the $(w_0,w_a)$ dynamical dark energy model, the ET+CE network yields a moderate constraint of $w_0=-1.02^{+0.31}_{-0.22}$ and $w_a=0.48^{+0.99}_{-1.54}$. In addition, our method can provide precise constraints on modified GW propagation effects jointly with $H_0$.
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Solar and Stellar Astrophysics
EWOCS-V: Is Wd1-72 a recent post-interaction WR+O binary?
C. J. K. Larkin, J. Mackey, H. Jin et al. (+14 more)
The evolutionary origin of Wolf-Rayet (WR)
stars at
Solar metallicity is unclear. Single-
star evolution from massive O
stars, possibly via a Luminous Blue Variable phase, is challenged by binary period distributions of different WR subtypes. Wd1-72 is a WN7b+O binary embedded in the collective wind of the
Galactic young massive cluster Westerlund 1 (Wd 1). It is surrounded by highly structured nebulosity, with cometary tails pointing away from Wd 1 and quasi-spherical droplets towards it. In this letter, we demonstrate that this morphology can be qualitatively reproduced by a hydrodynamic simulation of non-conservative Roche Lobe Overflow (RLOF) mass-loss into a cluster wind. Our model is based on a detailed binary
evolution track consistent with key known properties of Wd1-72. Our work suggests Wd1-72 could be only ~10 kyr post-RLOF, and the hydrogen-free nature of Wd1-72 favours this being a second or subsequent RLOF episode. Follow-up observations could make Wd1-72 a valuable
benchmark for probing mass-loss and mass-transfer in forming gravitational-wave binary-progenitor systems.
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All authors C. J. K. Larkin, J. Mackey, H. Jin, A. A. C. Sander, B. Reville, K. Anastasopoulou, M. Andersen, A. Bayo, J. J. Drake, E. K. Grebel, M. G. Guarcello, T. J. Haworth, V. M. Kalari, R. R. Lefever, F. Najarro, B. W. Ritchie, E. Sabbi
Earth and Planetary Astrophysics
Composition and Space Weathering Characteristics of Tianwen-2 Mission's First Target Near-Earth Asteroid (469219) Kamo`oalewa
Minge Liu, Yazhou Yang, Yang Liu et al. (+4 more)
The near-Earth asteroid Kamo`oalewa, a quasi-satellite of the Earth and the target for sample return by China's Tianwen-2 mission, exhibits distinctive spectral characteristics. This study re-analyzes the visible and near-infrared reflectance spectrum of Kamo`oalewa published by B. N. L. Sharkey et al. (2021), obtained using the Large Binocular
Telescope, to infer its mineral composition and space weathering characteristics. Spectral similarity analysis is performed by comparing the spectrum of Kamo`oalewa to the mean spectra of various types in the Bus-DeMeo taxonomy to make a preliminary constraint on the combined characteristics of surface mineralogy and space weathering effects. To further characterize the mineral composition, a detailed analysis of the 1 {\mu}m band center is conducted based on spectral data below 1.25 {\mu}m that have higher signal-to-noise ratios. Empirical models for normalized spectra are developed to estimate the Is/FeO content. The results suggest that asteroid Kamo`oalewa has higher olivine abundance than that of typical S-type asteroids and the Moon, exhibiting an immature to submature degree of space weathering. These findings enhance our understanding of the
evolution of similar quasi-satellites and provide important implication for the future exploration of Tianwen-2 mission.
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All authors Minge Liu, Yazhou Yang, Yang Liu, Jian-Yang Li, Qing Zhang, Jiang Zhang, Yongliao Zou
Solar and Stellar Astrophysics
Progress towards a 3D Monte Carlo radiative transfer code for outflow wind modelling: II. 3-D applications
Jakub Fišák, Jiří Kubát, Nicolas Moens et al. (+1 more)
The massive hot
stars play crucial role in the dynamics of
galaxies. These
stars influence their surroundings through strong winds which are highly structured processes. The theoretical study of the non-symmetric phenomena of the
stellar winds are becoming important these days, mainly because 1-D models are not sufficient enough. We present a new version of our Monte Carlo radiative transfer code Andy Antares with improved treatment of the velocity field for arbitrary geometries. Our aim is to develop a numerical scheme that can incorporate a general velocity field defined at discrete points. Our main objective is to calculate radiative transfer in a general input hydrodynamic model. The Andy Antares code currently calculates pure radiative transfer. The input model is pre-calculated by another hydrodynamical code. The whole radiative transfer calculation is then processed in a Cartesian grid. Radiative transfer is solved using the Monte Carlo approach in 3-D regardless of the input hydrodynamical model's dimension. The velocity field at any given point is interpolated using the trilinear interpolation. The optical depth is then integrated numerically along the
photon's path. We verified the accuracy of the numerical velocity interpolation by comparison with results obtained for analytical velocity fields, achieving successful outcomes. We also tested the radiative transfer solution on a 3-D model generated from a 2-D hydrodynamic model, and obtained emergent radiation. The code is suitable for the numerical solution of radiative transfer in 3-D with arbitrary velocity fields.
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All authors Jakub Fišák, Jiří Kubát, Nicolas Moens, Brankica Kubátová
Earth and Planetary Astrophysics
Hidden Gems in TESS: sherlock finds two new rocky planets around nearby M dwarfs
M. Timmermans, M. Dévora-Pajares, F. J. Pozuelos et al. (+25 more)
The Hidden Gems project searches the TESS data for additional
planets transiting low-mass
stars in confirmed systems. Our goal is to identify
planet candidates that are below the detection threshold set by the SPOC and QLP pipelines using sherlock, a specialized pipeline for robust detection and vetting of transit signals in TESS data. We present the discovery of two inner rocky
planets in the TOI-237 and TOI-4336 A systems, confirmed with ground-based photometry from the TRAPPIST, SPECULOOS, ExTrA, and LCO facilities. TOI-237 c has a radius of 1.21 +/- 0.04Re, orbits its mid-M host
star every 1.74 days, and is close to a 3:1 mean-motion resonance with TOI-237 b. TOI-4336 A c has a radius of 1.17 +/- 0.06Re, and orbits with a period of 7.58 days an M3.5 host
star which is part of a hierarchical triple system. We performed model comparison to search for non-zero eccentricities, and found that the circular transit models are statistically favored. Dynamical simulations show that both systems are in stable configurations, and the TTVs expected for the TOI-237 system are of the order of seconds. TOI-237 c and TOI-4336 A c join the high-interest population of warm likely super-Earths below the so-called "radius valley". In particular, TOI-237 c is a good candidate for phase curve observations with JWST/MIRI thanks to the small radius of the host
star and its short period.
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All authors M. Timmermans, M. Dévora-Pajares, F. J. Pozuelos, K. Barkaoui, B. Rojas-Ayala, J. M. Almenara, S. B. Howell, A. H. M. J. Triaud, M. Gillon, M. G. Scott, Y. T. Davis, B. V. Rackham, A. J. Burgasser, X. Bonfils, K. A. Collins, B.-O. Demory, G. Dransfield, E. Ducrot, A. Fukui, M. Ghachoui, Y. Gómez Maqueo Chew, E. Jehin, N. Narita, P. P. Pedersen, R. P. Schwarz, G. Srdoc, S. Yalcinkaya, Z. Way
Astrophysics of Galaxies
AGN Variability with Rubin Observatory in the 2030s
Swayamtrupta Panda, Francisco Pozo Nuñez, Hygor Benati Gonçalves et al. (+4 more)
AGN variability offers a direct probe of
accretion physics, disk structure, and black hole growth, but progress has been limited by sample size, cadence heterogeneity, and photometric systematics. The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will deliver multi-band light curves for millions of AGN, enabling variability studies at a true population scale. We synthesize recent results from the Zwicky Transient Facility (ZTF), which demonstrate that optical variability amplitudes and timescales are primarily regulated by
accretion state, with secondary dependence on black hole mass and
redshift, and establish the feasibility of survey-driven continuum reverberation mapping. ZTF measurements reveal optical continuum-emitting region sizes that often exceed standard thin disk predictions, implicating diffuse continuum emission from the broad line region as a significant contributor to observed inter-band lags. We evaluate the implications of LSST cadence and survey strategy, particularly the deep drilling fields, for continuum and emission line reverberation mapping, changing-look AGN, extreme variability
quasars, and periodic variability searches. Key limitations of broadband photometric variability are identified, including variable emission line contamination, diffuse BLR continuum emission, and cadence-dependent lag recoverability. We argue that realizing LSST's full scientific potential requires community-scale, standardized variability metric pipelines, probabilistic classification integrated with alert brokers for follow-up triggering, and complementary medium-band photometric observations to isolate the
accretion disk continuum. Together, these elements will enable LSST to convert photometric variability into quantitative constraints on
accretion disks, BLR structure, and supermassive black hole growth across
cosmic time.
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All authors Swayamtrupta Panda, Francisco Pozo Nuñez, Hygor Benati Gonçalves, Guodong Li, Bożena Czerny, Paola Marziani, Thaisa Storchi-Bergmann
Solar and Stellar Astrophysics
Asymptotic power spectra and visibilities of damped mixed modes
Jonas Müller, Quentin Coppée, Jordan Van Beeck et al. (+2 more)
Recent observational studies of red
giant stars have estimated the visibility of their mixed oscillation modes, which is a proxy of the average energy of these modes. Among other things, they demonstrated that although the damping rate of the oscillations in the core of many red
giants appears to be negligible, other red
giants exhibit high core damping rates that are sometimes consistent with the infinite value limit. Up until now, it has not been possible to link the mixed mode visibilities to core damping rates in a quantitative way. In this study, we use the progressive wave picture to derive an analytical function expressing the approximate resonance pattern of red
giants up to a proportionality factor. This function can model the influence of the damping on the oscillations, as well as take into account other effects such as mode asymmetries. In particular, this expression can be used to obtain a quantitative estimate for the visibility of mixed modes and to predict the detectability of mixed mode and multiplet signatures under different core damping rates. Here, we conduct a parameter study to investigate how the damping processes affect these aspects. We find that the visibility approaches the value expected for an infinite core damping rate already at finite values. Furthermore, we find that both the mixed mode and the multiplet signatures disappear at finite core damping rates. This implies that the observational characteristics of red
giants with finite core damping rates can appear as if their core damping rate were infinite, providing an explanation for the observed populations. Moreover, we have used our method to quantitatively estimate the core damping rates of red
giants with unusually low mixed mode amplitudes from their observed visibilities.
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All authors Jonas Müller, Quentin Coppée, Jordan Van Beeck, Tobias van Lier, Saskia Hekker
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
The reason peculiar velocities grow faster in general relativity than in Newtonian gravity
Erick Pastén and Christos Tsagas
An increasing number of surveys has been reporting large-scale peculiar motions with sizes and speeds in excess of those allowed by the concordance cosmological model. These are the so called bulk flows, the presence of which has come to be treated as a problem for the $\Lambda$CDM paradigm. However, the limits of the $\Lambda$CDM model are based on Newtonian studies, which predict the mediocre $v\propto t^{1/3}$ growth-rate for the peculiar-velocity field ($v$). Recently, a few fully relativistic treatments have appeared in the literature, arguing for a much stronger velocity growth that could explain the reported fast and deep bulk flows. What separates the Newtonian from the relativistic studies is the gravitational input of the peculiar flux, namely of the kinetic energy triggered by the moving matter. The latter has no direct gravitational contribution in Newtonian theory, but it does so in general relativity. This drastically changes the driving
agent of the peculiar-velocity field and boosts its linear growth. The aim of this work is to directly compare the two treatments, as well as identify and discuss the reasons for their different results. In the process, we also demonstrate how one could recover the relativistic growth-rate from a Newtonian setup by selectively including certain (typically ignored) source-free terms into the Poisson equation. This way, we provide a unified covariant comparison of the Newtonian, the quasi-Newtonian and the fully relativistic studies.
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Astrophysics of Galaxies
Detection of Gravitational Anomaly at Low Acceleration from a Highest-quality Sample of 36 Wide Binaries with Accurate 3D Velocities
K.-H. Chae, B.-C. Lee, X. Hernandez et al. (+4 more)
We set out to accurately measure
gravity in the low-acceleration range $(10^{-11},10^{-9})\,{\rm m}\,{\rm s}^{-2}$ from 3D motions of isolated wide binary
stars.
Gaia DR3 provides precise measurements of the four sky-plane components of the 3D relative displacement and velocity ($\mathbf{r}, \mathbf{v}$) for a system, but not comparably precise line-of-sight (radial) separation and velocity $v_{r}$. Based on our new observations and the public databases/publications, we assemble a sample of 36 nearby (distance $<150$pc) wide binaries in the low-acceleration regime with relatively accurate values of $v_r$. Kinematic contaminants such as undetected
stellar companions are well under control using various observational diagnostics such as
Gaia's ruwe parameter, the color-magnitude diagram, multi-epoch observations of radial velocities, Speckle interferometric follow-up observations, and requiring Hipparcos-
Gaia proper motion consistency. For $\Gamma \equiv \log_{10}\sqrt{\gamma}$ with $\gamma \equiv G/G_{\rm N}$ (where $G$ is a parameter generalizing Newton's constant $G_{\rm N}$), we find $\Gamma=0.102_{-0.021}^{+0.028}$ for $<10^{-9.1}\,{\rm m}\,{\rm s}^{-2}$ ($0.132_{-0.027}^{+0.035}$ for $<10^{-9.5}\,{\rm m}\,{\rm s}^{-2}$) giving a
gravity boost factor of $\gamma=1.60_{-0.14}^{+0.24}$, which rules out Newton. This strong anomaly is dominated by two systems (the pairs of HD 189739, HD 189760, and TYC 259-236-1, TYC 259-906-1) that have 3D relative velocities exceeding their estimated Newtonian escape velocities. Without them, we have $\Gamma=0.042_{-0.024}^{+0.027}$ for $<10^{-9.1}\,{\rm m}\,{\rm s}^{-2}$, $0.057_{-0.031}^{+0.035}$ for $<10^{-9.5}\,{\rm m}\,{\rm s}^{-2}$, and $0.085_{-0.045}^{+0.059}$ for $<10^{-10.1}\,{\rm m}\,{\rm s}^{-2}$. Future radial velocity monitoring and Speckle interferometric imaging for larger samples will be useful to refine the present result.
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All authors K.-H. Chae, B.-C. Lee, X. Hernandez, V. G. Orlov, D. Lim, D. A. Turnshek, Y.-W. Lee