Astrophysics of Galaxies
Yongseok Jo, Minyong Jung, Greg L. Bryan et al. (+3 more)
Nuclear Star Clusters (NSCs) are dense
stellar systems located at the centers of
galaxies. Employing Enzo-Abyss, which integrates hydrodynamics with a direct N-body solver, we introduce a simulation capable of resolving the
evolution of NSCs within a live
galaxy. This includes live dark matter, gaseous dynamics,
star formation and feedback, collisional dynamics for
star clusters. The
evolution of NSCs is typically shaped by two main processes: mergers of
star clusters and in-situ
star formation. Our simulation enables investigation of the contributions of these mechanisms to the growth of NSCs. This work focuses on the impact of
stellar physics and gas content on the growth of NSCs within a
dwarf galaxy. To this end, we carry out four simulations, a fiducial simulation, one without
supernova feedback, one with low
star formation efficiency, and one with higher
galactic gas content. This study shows a likelihood that both mergers and in-situ
star formation contribute to NSC
evolution comparably. In addition, mergers result in disruption of dense gas clumps within
star clusters, indicating that in-situ
star formation is suppressed when mergers occur. However, the limitations – such as the lack of individual
star physics and limited spatial/particle mass resolution – hinder drawing a definite conclusion. Nevertheless, with further development, our simulations will serve as a cornerstone that untangles the complex interplay between mergers and in-situ
star formation in shaping the structure and mass of NSCs, thereby providing insights into their formation and
evolution.
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All authors Yongseok Jo, Minyong Jung, Greg L. Bryan, Seoyoung Kim, Ji-hoon Kim, Ahram Lee
Cosmology and Nongalactic Astrophysics
Beyond Linear Bias Expansions for AbacusSummit Halos at z = 8
Kyle K. Boone and Daniel J. Eisenstein
We study the non-Gaussianity of the large-scale clustering of high-
redshift halos, seeking to assess which terms of standard bias expansions are needed to understand these highly biased populations. We find that the clustering can be well modeled with only linear and quadratic bias parameters while assuming a Gaussian underlying matter field. Our analysis focuses on AbacusSummit
halos at
redshift $z=8$. We work with
halos of mass at least $1\times10^{11}h^{-1}M_\odot$ in boxes of side length $2h^{-1}$Gpc. Measurements of bias coefficients are made by fitting bias expansions to the
halo power spectrum and bispectrum.
Tidal bias is not detected with only a ~$0.1\sigma$ deviation from $0$, but we see a $17\sigma$ level detection for a bias term of the form $\delta^2$. A bias term of the form $\delta^3$ is weakly detected at the $1.3\sigma$ level. Nonlinear matter is also detected at a $1.3\sigma$ level. To test how bias evolves, we run one test at $z=5$. We use a mass threshold for
halos that gives the same variance in the
halo field as our $z=8$ sample. Bias is smaller at $z=5$ and a
tidal bias is detected at the $1\sigma$ level. Bias coefficients at $z=5$ match a linear
evolution of the $z=8$ bias coefficients to within $10\%$.
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Earth and Planetary Astrophysics
TOI-4552 b: A new ultra-short period rocky world revealed by NIRPS and TESS
Avidaan Srivastava, René Doyon, François Bouchy et al. (+57 more)
A particularly intriguing subclass of rocky
exoplanets are the ultra-short period (USP) worlds that orbit their host
stars in less than a day. These
planets are particularly rare around M
dwarf stars, with so far only ten that have a constrained mass and radius. We present the validation and characterization of the ultra-short period (0.3-days), Earth-sized
planet TOI-4552b orbiting a nearby (27.26-pc away) M4.5V
dwarf. Complementing the TESS photometry, ground-based transit observations from LCO, ExTrA and SPECULOOS validated the planetary radius and cleared the field of any contaminants. Speckle imaging with Zorro (Gemini-S) rules out false positive scenarios caused by eclipsing binary sources. Spectroscopic observations with NIRPS and HARPS were used to obtain
stellar abundances, constrain the planetary mass, and, in conjunction with the transit observations, estimate the orbital parameters. TOI-4552 is a quiet
star exhibiting no short-term
stellar variations seen in photometric or radial velocity data that can be associated to
stellar rotation. TOI-4552b ($M_p=1.83\pm0.47\,M_e$, $R_p=1.11\pm0.04\,R_e$) lies between the Earth-like and iron-rich composition tracks on the Mass-Radius diagram. The EXOPIE interior structure model, without constraints from refractory abundance ratio, yields a core mass fraction (CMF) of 0.54 and a bulk density of 7.74g/cm$^3$. Since the CMF spans a wide range due to the large uncertainty on the mass, the definitive interior composition cannot be determined with the current
dataset. TOI-4552b hints as being marginally more iron-rich compared to the Earth but confirmation of its status requires additional, precise radial velocity measurements. Combined with its high emission spectroscopic metric (ESM=19.5), negligible
stellar activity and short orbital period, TOI-4552b emerges as a compelling target for atmospheric and surface composition studies with JWST.
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All authors Avidaan Srivastava, René Doyon, François Bouchy, Étienne Artigau, Charles Cadieux, Nicole Gromek, Elisa Delgado-Mena, Yuri S. Messias, Xavier Bonfils, Roseane de Lima Gomes, Susana C. C. Barros, Björn Benneke, Marta Bryan, Ryan Cloutier, Nicolas B. Cowan, Eduardo Cristo, Xavier Delfosse, Xavier Dumusque, David Ehrenreich, Jonay I. González Hernández, David Lafrenière, Izan de Castro Leão, Christophe Lovis, Alejandro Suárez Mascareño, Bruno L. Canto Martins, Jose Renan De Medeiros, Lucile Mignon, Christoph Mordasini, Francesco Pepe, Rafael Rebolo, Jason Rowe, Nuno C. Santos, Damien Ségransan, Stéphane Udry, Diana Valencia, Gregg Wade, Jose Manuel Almenara, Karen A. Collins, Dennis M. Conti, George Dransfield, Elsa Ducrot, Zahra Essack, Dasaev O. Fontinele, Thierry Forveille, Marziye Jafariyazani, Pierrot Lamontagne, Alexandrine L'Heureux, Khaled Al Moulla, Ares Osborn, Léna Parc, David R. Rodriguez, Richard P. Schwartz, Madison G. Scott, Avi Shporer, Atanas K. Stefanov, Mathilde Timmermans, Amaury H.M.J. Triaud, Joost P. Wardenier, Drew Weisserman, Sebastián Zúñiga-Fernández
Cosmology and Nongalactic Astrophysics
Gamma-Ray Bursts as an Independent High-Redshift Probe of Dark Energy
Maria Giovanna Dainotti, Aleksander Łukasz Lenart, Biagio De Simone et al. (+6 more)
Testing the $\Lambda$CDM model requires cosmological probes spanning the wide
redshift interval between Type Ia
Supernovae (SNe Ia, $z\lesssim2.9$) and the
Cosmic Microwave Background (CMB, $z\approx1100$). Gamma-Ray Bursts (GRBs), observed up to
redshift $z=9.2$, offer the opportunity to explore this regime. Here, we investigate how many GRBs are needed to become a useful cosmological probe capable of independently testing deviations from $\Lambda$CDM suggested by the recent DESI BAO observations. We develop forecasts based on the two-dimensional X-ray and optical Dainotti relations, between the luminosity at the end of the plateau phase and its rest-frame duration. Using simulated GRB samples constructed from the observed population, we evaluate the constraining power of GRBs on cosmological parameters within the $w$CDM and $w_0w_a$CDM models, both independently and in combination with CMB observations. Our results show that GRB samples containing several tens to hundreds of well-characterized plateau can already approach the precision currently achieved by CMB measurements on the Dark Energy (DE) equation-of-state parameter $w$. Particularly, a sample of $\sim66$ optical GRBs can reach a precision $\sigma_w \approx 0.47$, comparable to that obtained from Planck within the $w$CDM framework. Such sample sizes are already attainable through Machine Learning techniques that double the number of GRBs using inferred
redshifts. These forecasts indicate that future GRB observations, when combined with next-generation transient missions and improved statistical techniques, will provide an independent high-
redshift probe of
cosmic expansion and will play an important role in testing the robustness of potential Dynamical DE signals suggested by other cosmological
datasets.
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All authors Maria Giovanna Dainotti, Aleksander Łukasz Lenart, Biagio De Simone, William Giarè, Eleonora Di Valentino, Dieter H. Hartmann, Nissim Fraija, Kazunari Iwasaki, Gaetano Lambiase
High Energy Astrophysical Phenomena
Neutrinos and gamma rays from Seyfert galaxies constrain the properties of coronal turbulence
Federico Testagrossa, Damiano F. G. Fiorillo, Luca Comisso et al. (+3 more)
The TeV
neutrino signal observed by IceCube from the active
galactic nucleus (AGN) NGC 1068 can probe its innermost coronal regions. If these
neutrinos originate from
hadrons accelerated within a magnetized turbulent corona, their intensity and spectrum depend on the turbulent
magnetic field strength and
turbulence coherence scale. The gamma rays accompanying
neutrino production are absorbed in this optically thick environment, in a way that depends sensitively on the size of the corona. By a joint fit of the IceCube and
Fermi-LAT observations, we translate the multimessenger signal from NGC 1068 and the tentative signal from NGC 7469 into quantitative constraints on coronal properties. NGC 1068, with a significant TeV
neutrino excess, favors a compact, strongly magnetized corona with a large
turbulence coherence length relative to the coronal size. NGC 7469, with two $\sim 100$ TeV
neutrino events, points instead to a somewhat larger corona with much smaller coherence length and high magnetization, but a very small fraction of energy in non-thermal
protons. We obtain the diffuse flux from a population of Seyfert
galaxies identical to either NGC 1068 or NGC 7469. Finally, we consider a third scenario, motivated by the spectral break observed in the diffuse
neutrino flux at tens of TeV, with coronal properties intermediate between the two point-source-inspired models. To enable detailed comparisons with the IceCube and electromagnetic observations, we release our model predictions in a GitHub repository.
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All authors Federico Testagrossa, Damiano F. G. Fiorillo, Luca Comisso, Enrico Peretti, Maria Petropoulou, Lorenzo Sironi
Earth and Planetary Astrophysics
Proton Irradiation of Primitive Atmospheres of Young Exoplanets and early Earth: $N_{\mathrm{2}}O$ Greenhouse Warming and Prebiotic Synthesis
Kensei Kobayashi, Vladimir S. Airapetian, Takumi Udo et al. (+8 more)
The emergence of habitable conditions on the early Earth and on rocky
exoplanets requires persistent energy sources that can drive both prebiotic chemistry and
climate warming under magnetically active young G to M
stars. To quantify the contribution of
stellar energetic particle (StEP) events associated with superflares to the atmospheric chemistry of young
planets with primitive atmospheres, we carried out a suite of laboratory
proton irradiation experiments on mildly reduced gas mixtures. We present first
proton irradiation experiments of $N_{\mathrm{2}}$/$CO_{\mathrm{2}}$ rich gas mixtures that yield abundant nitrous
oxide ($N_{\mathrm{2}}O$) at mixing ratios up to 1000 ppmv, together with amino acid precursors including glycine, corresponding to global production rates of order $2\times10^{10}$ kg/yr on the early Earth. Our photochemical modeling of StEP driven
proton irradiation reproduces the experimentally inferred $N_{\mathrm{2}}O$ production rates and provides self-consistent atmospheric $N_{\mathrm{2}}O$ profiles. We then use these profiles of $N_{\mathrm{2}}O$ as input to a 3D global
climate model to evaluate the radiative and climatic impact of StEP generated $N_{\mathrm{2}}O$ in primitive atmospheres representative of the early Earth and young rocky
exoplanets. Our results show that frequent StEP events can help alleviate the faint young Sun paradox on the early Earth and can maintain temperate surface conditions on young rocky
exoplanets beyond the outer edges of habitable zone, while simultaneously enhancing the buildup of prebiotic molecules. Together, these processes may constitute a robust pathway toward early planetary habitability.
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All authors Kensei Kobayashi, Vladimir S. Airapetian, Takumi Udo, Shunsuke Mouri, Yoko Kebukawa, Hitoshi Fukuda, Yoshiyuki Oguri, Naoto Hagura, M.J. Way, Guillaume Gronoff, Eric T. Wolf
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Stellar Bounds on a Model with Photon-Photino Oscillation
Bernard Teles de Menezes and José Abdalla Helayël-Neto
In this paper, we pursue an investigation of the consequences of a mixing between supersymmetric partners - the
photon and photino - analogous to the so-called Primakoff effect, but induced by a Lorentz-
symmetry violating (LSV) fermionic-condensate background. In our framework, the LSV parameters are introduced as members of a non-dynamical superfield. As a consequence, we show that naturally there appears a mixing term between the gauge
boson and the gaugino, which can be readily seen in the superspace/superfield approach. We inspect the kinetic
photon-photino mixing
matrix in the scenario of
stellar physics which we apply our results to. Bounds on the strength of the fermionic LSV background are can be set by invoking the energy loss argument and the
solar data we adopt.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Axions at the meV Crossroads: Theory, Cosmology, Astrophysics, and Experiments
Michele Cicoli, Francesco D'Eramo, Luca Di Luzio et al. (+18 more)
The meV mass range has emerged as a focal point in
axion physics, where advances in theory, cosmology, astrophysics, and experimental techniques converge.
Axions in this mass range are theoretically well motivated, can arise in ultraviolet-complete models, and can have significant cosmological impacts as dark matter or dark radiation. In parallel, their efficient production in
stellar and
supernova environments provides powerful astrophysical probes. Here, we provide a comprehensive overview of meV
axions across these domains, highlighting both established results and open questions. We discuss the theoretical underpinnings of meV
axions, their cosmological and astrophysical signatures, and the diverse experimental strategies – ranging from helioscopes and haloscopes to quasiparticle systems and large-volume Cherenkov detectors – that aim to explore this regime. The convergence of these approaches emphasizes the pivotal role of the meV mass range for
axion discovery in the coming years, identifying meV
axions as a key probe for testing beyond-Standard-Model physics. This review document is the direct outcome of the discussions at the dedicated workshop "The meV Mass
Axion Frontier: Challenges and Opportunities", held at Laboratori Nazionali di Frascati (IT) on 27–28 October 2025, and organized by the EU funded COST Action "
Cosmic WISPers in the Dark Universe: Theory, astrophysics, and experiments" (CA21106, https://www.cost.eu/actions/CA21106). Its aim is to provide an overview of current efforts in meV
axion research, their motivations, and the research goals that animate the community involved in this search.
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All authors Michele Cicoli, Francesco D'Eramo, Luca Di Luzio, Damiano F. G. Fiorillo, Maurizio Giannotti, Alicia Gomez, Diego Guadagnoli, Mathieu Kaltschmidt, Bradley J. Kavanagh, Alessandro Lella, Giuseppe Lucente, David J. E. Marsh, Federico Mescia, Alessandro Mirizzi, Javier Redondo, Nicole Righi, Jaime Ruz, Ken'ichi Saikawa, Elisa Todarello, Edoardo Vitagliano, Su-Yang Xu
Cosmology and Nongalactic Astrophysics
TUNeS: Neural Emulation of Large-Scale Structure Across Redshifts
Yuqi Kang, Hu Bin, Dongxing Li et al. (+1 more)
In this work, we introduce TUNeS (Temporal UNet emulator for Structure formation), a neural network framework for accelerating N-body simulations by predicting the nonlinear
evolution of the matter density field from an initial particle distribution. TUNeS employs a two-stage modeling strategy, combining particle-based inference with a density-field refinement on a regular grid, enabling accurate reconstruction of both large- and small-scale structures. The model is designed to operate across
redshift, taking particle snapshots at arbitrary input
redshifts and predicting density fields at arbitrary target
redshifts. In this work, we evaluate its performance using simulations initialized at $z=100$, with predictions generated at multiple lower
redshifts. Trained on only eight N-body simulations, TUNeS reproduces reference results with good agreement in both Gaussian and non-Gaussian statistics, including two-point correlations, one-point distributions, peak counts, and three-dimensional Minkowski functionals. In particular, at $k \simeq 1\,h\,\mathrm{Mpc}^{-1}$, the power spectrum error remains at the few-percent level. End-to-end inference from $256^3$ particles to a $256^3$ density grid can be completed in $\sim25\,\mathrm{second}$ on a single GPU. Thanks to its architectural design, the model naturally scales to larger particle numbers and larger volumes through particle batching and window-based refinement.
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All authors Yuqi Kang, Hu Bin, Dongxing Li, Jan Hamann
Earth and Planetary Astrophysics
JWST Edge-on Disk Ice (JEDIce): Program overview and ice survey results
Jennifer B. Bergner, Nicole Arulanantham, Emmanuel Dartois et al. (+21 more)
The icy material within protoplanetary disks plays a central role in
planet formation, yet remains poorly characterized by observations. We present 1.6-28$\mu$m spectra of five disks obtained as part of the JWST Edge-on Disk Ice (JEDIce) program, representing the largest survey of disk ices to date. The major ice species H$_2$O, CO$_2$, and CO are detected towards all disks, and exhibit a wide range of absolute optical depths and optical depth ratios across the sample. This is suggestive of a range of ice abundances and compositions, but quantitative constraints will require radiative transfer modeling. All disks exhibit ice features across the entire spatial region where the IR continuum is detected; vertically elevated ice grains therefore seem to be ubiquitous in disks. The CO ice is consistently dominated by apolar CO:CO$_2$ mixtures, implying that the disk ice compositions are neither completely reset nor pristinely inherited from the protostellar stage. The presence of these mixtures also suggests that entrapment may be important in shaping the spatial distribution of CO within the disks. Small molecules commonly seen in protostellar ices (CH$_4$, CH$_3$OH, NH$_3$) are generally not detected in our sample, though tracers of ammonium salts (OCN$^-$ and the 6.85 $\mu$m band) are common, potentially reflecting an
evolution towards comet-like ice compositions. The spectra also contain a wealth of information about the micron-sized
dust, atomic and molecular gas, and PAH content, which together with the ice constraints will provide a comprehensive picture of the chemical, physical, and dynamical state of these systems.
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All authors Jennifer B. Bergner, Nicole Arulanantham, Emmanuel Dartois, Maria N. Drozdovskaya, Daniel Harsono, Melissa McClure, Jennifer A. Noble, Karin I. Öberg, Klaus M. Pontoppidan, Yao-Lun Yang, Korash Assani, Zhi-Yun Li, Julia C. Santos, Will E. Thompson, Lukas Welzel, Elizabeth S. Yunerman, Aditya M. Arabhavi, Alice S. Booth, Charles Mentzer, Mayank Narang, Thomas Henning, Inga Kamp, Giulia Perotti, Alice Somigliana
High Energy Astrophysical Phenomena
Supermassive Black Hole Winds in X-rays: SUBWAYS V. Properties of hot coronae in quasars at intermediate redshift
S. Peluso, G. Lanzuisi, A. Comastri et al. (+25 more)
We present the X-ray analysis of coronal properties in a statistically representative sample of 23 mostly
radio-quiet AGN from the SUBWAYS campaign (SUpermassive Black holes Winds in XrAYs), focusing on
quasars at
redshifts $0.1 < z < 0.4 $ and bolometric luminosities $2 \times 10^{44} <L_{bol}(erg/s) < 2 \times 10^{46}$. The main aim of this work is to investigate the properties of the hot corona through the study of the hard X-ray band emission, including a proper treatment of the soft X-ray band. High-quality X-ray spectra from XMM-Newton, complemented by NuSTAR data extending up to 30-40 keV in the rest frame, are available for this sample. The soft X-ray band (0.3-2 keV) spectrum is best fitted by a warm corona model with a median temperature of 0.40 keV, and an optical depth in the range $\tau$=20 - 40, consistent with previous results on lower luminosity sources. The hard X-ray band is well described using a hot corona model, with a median high-energy cut-off of 87 keV, at the lower end of the distribution of typical values found in Seyfert
galaxies (100 - 200 keV). The derived median value of the optical depth ($\tau$ = 1 - 5) suggests the presence of a moderately optically thick corona. Combining the SUBWAYS results with literature samples at low and high
redshift, we assemble the largest sample to date of AGN with E$_{cut}$ and
accretion parameter measurements, finding a significant anticorrelation of E$_{cut}$ with both $\lambda_{Edd}$ and $L_{bol}$ with the median E$_{cut}$ decreasing from 250 - 300 keV at low
accretion rates and luminosities to 90 - 100 keV at high
accretion rates and luminosities - consistent with enhanced coronal cooling, possibly driven by pair-production. These results favor cooler, optically thicker coronae in luminous AGN compared to those in lower-luminosity Seyfert
galaxies.
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All authors S. Peluso, G. Lanzuisi, A. Comastri, M. Brusa, M. Giustini, G. Miniutti, S. Bianchi, V. E. Gianolli, R.Middei, P-O. Petrucci, L. Borrelli, E. Amenta, E. Bertola, B. De Marco, A. De Rosa, S. Kraemer, G.Kriss, Y. Krongold, S. Mathur, A. Merloni, E. Nardini, F. Panessa, E. Piconcelli, G. Ponti, F. Ricci, A. Tortosa, L. Zappacosta, R. Serafinelli
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
High-Frequency Gravitational Waves from Phase Transitions in Nascent Neutron Stars
Katarina Bleau, Joachim Kopp, Jiheon Lee et al. (+1 more)
Tentative evidence suggests that the cores of massive
neutron stars consist of deconfined
quark matter. We argue that the formation of such a
quark matter core during a
galactic supernova could be accompanied by the emission of gravitational waves in the MHz band. These signals constitute a new target for high-frequency gravitational wave detectors, demonstrating that such detectors may offer unique opportunities for testing
quantum chromodynamics in an otherwise inaccessible regime.
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All authors Katarina Bleau, Joachim Kopp, Jiheon Lee, Jorinde van de Vis
Solar and Stellar Astrophysics
Mining the Kepler Field: Atmospheric Parameters, Bolometric Corrections, and Luminosities
Diego Godoy-Rivera, Desmond H. Grossmann, Tyler Richey-Yowell et al. (+3 more)
The ~ 200,000
stars observed by the Kepler mission have provided unprecedented constraints across astrophysics. With the advent of modern spectroscopic and photometric surveys, new limits in
stellar characterizations are within reach. In this work, we report a compilation of atmospheric parameters (Teff, logg, and [M/H]) for the Kepler
stars by crossmatching with several spectroscopic and spectro-photometric surveys. We use these to calculate bolometric corrections, which combined with color-magnitude diagram (CMD) information from
Gaia yield self-consistent luminosities on a survey-by-survey basis. These properties will aid in future explorations of Kepler data towards new astrophysical insights. We make our catalog publicly available online in Zenodo (doi:10.5281/zenodo.18620911).
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All authors Diego Godoy-Rivera, Desmond H. Grossmann, Tyler Richey-Yowell, Angela R. G. Santos, Savita Mathur, Rafael A. Garcia
Astrophysics of Galaxies
The Spectroscopic and Photometric Study of a Star Cluster Sample in Andromeda Halo
Hongrui Gu, Zhou Fan, Bingqiu Chen et al. (+18 more)
Halo star clusters serve as vital tracers for the formation and
evolution of the Andromeda
galaxy. In this work, we present physical parameters for 29 M31
halo star clusters, derived from a combination of spectroscopic and photometric data. Low-resolution spectra were acquired using the BFOSC spectrograph on the NAOC Xinglong 2.16-m
telescope. For the photometric analysis, we utilized uSC and vSAGE bands from the SAGE survey, complemented by archival data from GALEX(NUV, FUV), PAN-STARRS(grizy) and the 2MASS(JHK). Ages and
metallicities were determined via ULySS (Vazdekis et al. and pegase-hr) SSP model and the Bruzual & Charlot (2003) (BC03)
stellar population synthesis models. The derived parameters show good agreement with literature values. Notably, for three of these clusters, this study represents the first combined photometric and spectroscopic analysis.
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All authors Hongrui Gu, Zhou Fan, Bingqiu Chen, Xiaoying Pang, Juanjuan Ren, Ruizheng Jiang, Song Wang, Kefeng Tan, Nan Song, Chun Li, Jie Zheng, Gang Zhao, Wei Wang, Yuqin Chen, Jingkun Zhao, Haining Li, Yihan Song, Haibo Yuan, Ali Luo, Yujuan Liu, Yaqian Wu
High Energy Astrophysical Phenomena
Spectral Hardness as the Primary Discriminator: Unveiling the Collapsar–Merger Boundary with a Gold-Standard Gamma-Ray Burst Sample
Xue Zhang, Yan-Kun Qu, Shuang-Xi Yi et al. (+4 more)
In this Letter, we establish a robust, physically motivated classification method using a Support Vector Machine (SVM) trained on a "gold-standard" sample of 24 GRBs with spectroscopically confirmed progenitors (associated SNe or KNe). By isolating the
prompt main spike to excise contamination from extended emission, we derive a quantitative classification index, I_SVM = 5.01 log_10 E_p,i - 1.25 log_10 E_iso - 0.34 log_10 T_90,z - 12.90 (units: keV, 10^52 erg, s). Events with I_SVM > 0 are classified as mergers. Analysis of the standardized classification weights reveals that the discriminative power of E_p,i is approximately 5 times that of T_90,z, while E_iso contributes a weight comparable to E_p,i. This quantitatively demonstrates that spectral hardness and energetics, rather than duration, are the primary physical signatures distinguishing mergers from collapsars. The derived boundary implies a stringent hardness ceiling for collapsars, while mergers are identified as outliers with excessive hardness relative to their energy budget. The classifier successfully identifies the nature of historic test cases, including the ultra-long GRB 111209A (collapsar) and the short GRB 050709 (merger), independent of instrumental eras. This tool paves the way for cleaning archival and future high-
redshift GRB samples for precision cosmology.
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All authors Xue Zhang, Yan-Kun Qu, Shuang-Xi Yi, Yu-Peng Yang, Fen Lyu, Fa-Yin Wang, Zhong-Xiao Man
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Branching Universes
Anamaria Hell and Tatsuya Daniel
We propose the idea that our Universe is a realization among different possible branches, which can be observationally tested through the modified dispersion relation of the gravitational waves. We achieve this through a framework of spatially constrained vector fields. We show that the simplest realizations of such theories in flat and cosmological spacetimes do not introduce new propagating modes, but they give rise to tensor perturbations that differ from those of standard general relativity. As a result, they avoid the strong coupling issues or ghost modes that otherwise easily appear in vector-field models. We further show that such theories admit stealth black hole solutions, and we recover weak gravitational potentials, thus passing the
solar system experiments. Finally, we discuss the implications of such theories and propose further generalizations.
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Instrumentation and Methods for Astrophysics
Setting SAIL: Leveraging Scientist-AI-Loops for Rigorous Visualization Tools
Nico Schuster, Andrés N. Salcedo, Simon Bouchard et al. (+8 more)
Scientists across all disciplines share a common challenge: the divide between their theoretical knowledge and the specialized skills and time needed to build interactive tools to communicate this expertise. While large
language models (LLMs) offer unparalleled acceleration in code generation, they frequently prioritize functional syntax over scientific accuracy, risking visually convincing but scientifically invalid results. This work advocates the Scientist-AI-Loop (SAIL), a framework designed to harness this speed without compromising rigor. By separating domain logic from code syntax, SAIL enables researchers to maintain strict oversight of scientific concepts and constraints while delegating code implementation to AI. We illustrate this approach through two open-source, browser-based astrophysics tools: an interactive gravitational
lensing visualization and a large-scale structure formation sandbox, both publicly available. Our methodology condensed development to mere days while maintaining scientific integrity. We specifically address failure modes where AI-generated code neglects phenomenological boundaries or scientific validity. While cautioning that research-grade code requires stringent protocols, we demonstrate through two examples that SAIL provides an effective code generation workflow for outreach, teaching, professional presentations, and early-stage research prototyping. This framework contributes to a foundation for the further development of AI-assisted scientific software.
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All authors Nico Schuster, Andrés N. Salcedo, Simon Bouchard, Dennis Frei, Alice Pisani, Julian E. Bautista, Julien Zoubian, Stephanie Escoffier, Wei Liu, Georgios Valogiannis, Pauline Zarrouk
Solar and Stellar Astrophysics
Interferometric Images of the Starspot Evolution of $\zeta$ Andromedae
Rachael M. Roettenbacher, John D. Monnier, Heidi Korhonen et al. (+21 more)
The
evolution of starspots of the
giant primaries of RS CVn systems is typically detected indirectly with photometric and spectroscopic monitoring. These observations suggest slowly-evolving
stellar surfaces and can constrain differential rotation as starspots move with respect to one another. However, starspot latitudes are difficult to constrain without resolved images of the
stellar surfaces from which the unambiguous locations of starspots are determined. We imaged the active RS CVn primary $\zeta$ And with the 330-m-baseline Center for High Angular Resolution Astronomy Array for three epochs over approximately six rotations of the
star. The resultant images show a more complicated picture of
stellar activity than expected from the contemporaneous photometry and earlier Doppler images. The spot structures change on the timescale of rotation, making differential rotation difficult to study. Our observations show changes in the polar spot, growing over time. We do not detect the secondary
star in the interferometric data, though the observations are sensitive to the predicted 0.75 $M_\odot$ main-sequence
star, and we suggest the companion may be a white
dwarf.
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All authors Rachael M. Roettenbacher, John D. Monnier, Heidi Korhonen, Gregory W. Henry, Cliff Kotnik, Joshua Pepper, Bálint Seli, Krisztián Vida, Attila Bódi, Borbála Cseh, Géza Csörnyei, Máté Krezinger, Réka Könyves-Tóth, Levente Kriskovics, Krisztián Sárneczky, Ádám Sódor, Róbert Szakáts, Stefan Kraus, Narsireddy Anugu, Claire L. Davies, Tyler Gardner, Cyprien Lanthermann, Gail H. Schaefer, Benjamin R. Setterholm
Solar and Stellar Astrophysics
TESS light curves of two new magnetic cataclysmic variables: an asynchronous polar at the period minimum, and an eclipsing system with a large spin-to-orbit ratio
Colin Littlefield, Krystian Ilkiewicz, Paul A. Mason et al. (+2 more)
A recent development in the study of
magnetic cataclysmic variable
stars (mCVs) has been the identification of asynchronously spinning mCVs with orbital periods <2 h that have significantly higher white
dwarf spin-to-orbital period ratios than their longer-period counterparts. We report the discovery of two additional mCVs in this class. The first,
Gaia21akb, is a candidate asynchronous polar at the period minimum. While TESS photometry cannot, in isolation, lead to a conclusive identification of the orbital period, the probable orbital period of 1.29 h would be the second-shortest of any known polar and would result in a
spin-to-orbit ratio of 0.9879. The second system in our study, ZTF18aazmehw, is an eclipsing mCV with a 1.50 h orbital period and a
spin-to-orbit ratio of 0.867. Contrary to expectations for an asynchronous polar, ZTF18aazmehw does not show discernible evidence of pole switching and might possess a disk-like structure. The increasing number of short-period asynchronous mCVs with large
spin-to-orbit ratios lends credence to theoretical predictions that asynchronously rotating mCVs with sufficiently strong white
dwarf magnetic fields can achieve synchronization when their orbital separations have shrunk sufficiently.
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All authors Colin Littlefield, Krystian Ilkiewicz, Paul A. Mason, Peter Garnavich, Simone Scaringi
Solar and Stellar Astrophysics
Spectropolarimetric Constraints on the Maunder Minimum Analog HD 166620: Evidence for Weakened Magnetic Braking
Federica Chiti, Jennifer L. van Saders, Oleg Kochukhov et al. (+1 more)
We present the first spectropolarimetric time-series analysis of the Maunder Minimum analog HD 166620, using 12 nights of data from CFHT/SPIRou and a single epoch from CFHT/ESPaDOnS. While individual Stokes $V$ profiles exhibit no significant polarization signatures, we leverage the rotational coverage of the SPIRou
dataset to compute a grand average LSD profile. Forward modeling of the cumulative Stokes $V$ signal, assuming a purely axisymmetric dipole, yields a best-fit dipole field strength of $B_{\rm dip} = 1.10^{+0.95}_{-0.90}$G ($3\sigma$). This field strength matches simulations of the
solar dipole during the Maunder Minimum phase. Our results are consistent with independent constraints on the dipole field strength from an LBT/PEPSI snapshot and exclude the presence of strong non-axisymmetric fields potentially missed by this single-epoch observation. These findings provide direct empirical evidence that the transition to weakened
magnetic braking involves a weakening of the large-scale
magnetic field and suggest that HD 166620 represents a state comparable to the Sun near the peak activity of a grand minimum.
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All authors Federica Chiti, Jennifer L. van Saders, Oleg Kochukhov, Travis S. Metcalfe
Astrophysics of Galaxies
The MOND Depth Index and Dynamical Maturity Clock: Toward a Universal Classification of Galaxies and Star Clusters
Robin Eappen and Pavel Kroupa
Mass discrepancies in
galaxies are empirically known to appear only below a characteristic acceleration scale a0. Here we show that this behaviour is not limited to
galaxies: it extends continuously across the full hierarchy of self-gravitating
stellar systems, from gas-rich
dwarfs and spirals to massive early-type
galaxies, and further down to compact
stellar clusters. We introduce the Milgromian dynamics (MOND) depth index DM, together with dynamical maturity index T = tcross/tH, dynamical collisionality index T1 = tcross/trelax, with tcross being the crossing time, tH the Hubble time and trelax the median two-body relaxation time, and the MOND acceleration index A = abar/a0. We uncover a well-defined two-dimensional dividing surface in dynamical space. The "dark matter phenomenon" is found only in systems that are both in the deep-MOND regime (abar < a0) and collisionless (trelax > tH), while high-acceleration, collisional systems (abar > a0, trelax << tH), including globular clusters and UCDs, show no evidence for a mass discrepancy. This clean dynamical separation defines a new, physically motivated classification scheme for
stellar systems, unifying
galaxies and clusters under one framework. The observed division emerges naturally within the MOND framework and provides a useful diagnostic for examining how different gravitational paradigms account for the origin of the mass discrepancy.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Phasing out Dark Matter Isocurvature with Thermal Misalignment
Brian Batell, Akshay Ghalsasi, Subhajit Ghosh et al. (+1 more)
Thermal misalignment provides an alternative to the standard misalignment mechanism for the cosmological production of scalar dark matter. In this framework, feeble couplings to particles in the thermal bath generate a finite-temperature potential that drives the scalar towards large field values early in the radiation era, dynamically inducing the misalignment before the onset of scalar oscillations. As a result, the relic abundance is controlled primarily by particle masses and couplings rather than the initial field value. As a light spectator field, the scalar acquires inflationary fluctuations that are uncorrelated with the adiabatic
curvature mode, generically sourcing isocurvature perturbations. We show that, unlike standard misalignment, where light scalars are strongly constrained by
cosmic microwave background bounds on dark matter isocurvature for high-scale inflation, thermal misalignment can naturally suppress the isocurvature signal. This occurs through a novel late-time phase offset between the background zero mode and the superhorizon perturbations, which reduces the final dark matter density contrast. Thermal misalignment therefore provides a new and generic route to isocurvature-safe scalar dark matter.
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All authors Brian Batell, Akshay Ghalsasi, Subhajit Ghosh, Mudit Rai
Cosmology and Nongalactic Astrophysics
High-redshift physics from the acoustic scale
Zachary J. Weiner
We present a simplified and general description of the high-
redshift information in acoustic scale measurements from the
cosmic microwave background and large-scale structure. The transverse distance interval between
photon–
baryon decoupling and a late epoch in the matter era provides an analytically tractable summary statistic thereof and a general diagnostic of the current tension between the Dark Energy Spectroscopic Instrument and the CMB. We show that this "matter-era distance excess" is unlikely to be explained by modified dynamics at low
redshift. We then analytically derive the matter-era distance interval's sensitivity to new physics at high
redshift, including nonstandard recombination, nonminimal dark matter dynamics, and spatial
curvature; in particular, we explain how this observable represents a direct
geometric measurement of (and underlies the current incompatibility with)
neutrino masses. Finally, we demonstrate that phenomenological models of dynamical dark energy mediate the matter-era distance excess in a manner reliant on their unphysical, extrapolated behavior at high
redshift. Invoking alternative explanations of the excess removes the CMB's contribution to the evidence for these models; the residual preference of around $1.7\sigma$ mostly derives from DESI's two lowest-
redshift measurements of the Alcock–Paczynski distortion, without which it drops to $0.5 \sigma$.
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High Energy Astrophysical Phenomena
Probing Kerr black hole in a uniform Bertotti-Robinson magnetic field through astrophysical quasi-periodic oscillations
Hamza Rehman, Sanjar Shaymatov, Saddam Hussain et al. (+1 more)
In this study, the behavior of high-frequency quasi-periodic oscillations (QPOs) is investigated around a Kerr black hole immersed in a uniform Bertotti-Robinson
magnetic field. The motion of the test particle is analyzed by determining the geodesic equations and evaluating the corresponding orbital, radial, and vertical epicyclic frequencies. These fundamental frequencies are used to construct the theoretical framework of QPO models based on parametric and forced resonance mechanisms. Observational data obtained from several black hole X-ray binaries (GRO J1655-40, XTE J1550-564, XTE J1859+226, GRS 1915+105, H1743-322, M82~X-1, and Sgr~A$^{*}$) are used to constrain the black hole parameters through
Bayesian inference and Markov Chain Monte Carlo (MCMC) analyses. For the X-ray binaries GRO J1655-40, GRS 1915+105, H1743-322, and M82~X-1, nonzero values of the dimensionless parameter $b=Bm$ are obtained at the $68\%$ confidence level within the framework of the parametric resonance model, while only upper bounds at the $90\%$ confidence level are obtained for the remaining sources. In contrast, in the case of the forced resonance model, only an upper bound at the $90\%$ confidence interval is obtained for the
magnetic field parameter for all considered X-ray binary sources. The analysis indicates that the value of the
magnetic field parameter is small but not negligible, producing minor modifications to particle dynamics and epicyclic frequencies. The influence of the
magnetic field is further examined through the properties of the innermost stable circular orbit and the radiative properties of the thin
accretion disk, including the energy flux and temperature profiles, within the allowed parameter range inferred from the MCMC analysis.
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All authors Hamza Rehman, Sanjar Shaymatov, Saddam Hussain, Tao Zhu
High Energy Astrophysical Phenomena
Discovery of Bimodal Drift Rate Structure in FRB 20240114A: Evidence for Dual Emission Regions
Santosh Arron
We report the discovery of bimodal structure in the drift rate distribution of upward-drifting burst clusters from the hyperactive repeating fast
radio burst FRB 20240114A. Using unsupervised machine learning (UMAP dimensionality reduction combined with HDBSCAN density-based clustering) applied to 233 upward-drifting burst clusters from the FAST
telescope dataset, we identify a distinct subpopulation of 45 burst clusters (Cluster C1) with mean drift rates 2.5x higher than typical upward-drifting burst clusters (245.6 vs 98.1 MHz/ms). Gaussian mixture modeling reveals strong evidence for bimodality (delta-BIC = 296.6), with clearly separated modes (Ashman's D = 2.70 > 2) and a statistically significant gap in the distribution (11.3 sigma). Crucially, we demonstrate that this bimodality persists when restricting the analysis to single-component (U1) burst clusters only (delta-BIC = 19.9, Ashman's D = 2.71), confirming that the result is not an artifact of combining single- and multi-component burst clusters with different drift rate definitions. The extreme-drift subpopulation also exhibits systematically lower peak frequencies (-7%), shorter durations (-29%), and distinct clustering in multi-dimensional feature space. These findings are suggestive of two spatially separated emission regions in the magnetosphere, each producing upward-drifting burst clusters with distinct physical characteristics, although confirmation requires observations from additional epochs and sources.
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High Energy Astrophysical Phenomena
Waveforms and Fluxes of Generic Extreme-Mass-Ratio Inspirals with a Spinning Secondary
Qiuxin Cui and Wen-Biao Han
Extreme mass-ratio inspirals (EMRIs), comprising a
stellar-mass compact object (CO) orbiting a supermassive black hole (BH), are key targets for future space-based gravitational-wave (GW) observatories. Incorporating the
spin of the secondary body into waveform models not only enhances measurement precision but also offers insight into the
spin distribution of
stellar-mass COs. In this work, we construct the flux and waveform for an EMRI with a spinning secondary in a Kerr background under the linear-
spin approximation. Using the radiative prescription (half-retarded minus half-advanced field), we calculate orbit-averaged fluxes for the fundamental constants of motion, including the energy, angular momentum, and the Carter-like constant. This framework provides a tractable route to generating waveforms that incorporate the secondary
spin.
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Earth and Planetary Astrophysics
Investigation of Venus' thermal history, crustal evolution, and core dynamics with a coupled interior-lithosphere-atmosphere model
Rodolfo Garcia, Rory Barnes, Peter E. Driscoll et al. (+2 more)
We simulate Venus'
evolution with a coupled one-dimensional
solar-atmosphere-lithosphere-mantle-core model to predict currently unobservable features and its eruptive mass flux. We identified four distinct evolutionary pathways that simultaneously match the atmospheric abundances of water and carbon dioxide as well as the lack of a core dynamo. These scenarios are characterized by I) generally monotonic cooling, II) a low mantle melt fraction in which Venus' volcanically active phase is ending, III) a small inner core, and IV) oscillations of internal properties. Through random forest classification we determined that the key parameters that distinguish these types are the initial mantle water abundance, the mantle viscosity, the dehydration stiffening strength, the eruption efficiency, and the melting point of the core. In each of the plausible histories, Venus retains at least one Earth ocean's worth of water in its mantle and remains volcanically active today. Venus' lack of a current geodynamo allows thermal histories with an initially large inner core in our parameter sweep. In 88% of plausible histories we found that Venus possessed a past
magnetic field. The results strongly disfavor recent high eruption rate estimates, but are consistent with lower estimates. Current resurfacing estimates also strongly disfavor the low melt scenario, implying that Venus is not nearly volcanically “dead.” These predictions are testable with anticipated data and the model can be applied to
exoplanets to predict their properties.
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All authors Rodolfo Garcia, Rory Barnes, Peter E. Driscoll, Victoria S. Meadows, Megan Gialluca
High Energy Astrophysical Phenomena
Self-Limited Accretion onto Embedded Binaries in a Uniform Medium
Marcus DuPont and Eliot Quataert
We study
accretion from a uniform gas at rest onto equal-mass binaries – the binary Bondi problem – as a function of adiabatic index~$\gamma$ and compactness $\xi \equiv R_B/a$, where $R_B$ is the Bondi radius of the binary and $a$ is the component separation. We present three-dimensional hydrodynamic simulations spanning $\xi = \{0.1, 1, 10\}$ at $\gamma = \{1, 4/3, 5/3\}$. Isothermal gas ($\gamma = 1$) accretes cooperatively at high compactness, with efficiency $\eta \equiv \dot{M}_{\rm binary}/\dot{M}_{\rm Bondi} \to 1$ for $\xi \gg 1$ and a stable sonic surface that screens the orbital modulation. Adiabatic gas ($\gamma > 1$) is self-limiting: the orbit drives shocks that generate
entropy, producing convective
turbulence that suppresses
accretion to $\eta \approx 0.3$ ($\gamma = 4/3$) and $\eta \approx 0.1$ ($\gamma = 5/3$), burying the orbital signature in broadband noise. We derive a stability criterion from first principles: the sonic surface is the separatrix of the Bondi saddle point, and the binary annihilates it in $N \propto (\gamma-1)^{-1}(\sqrt{\xi/\xi_m} - 1)$ orbits, where $\xi_m = 4/(5{-}3\gamma)$ is the container threshold at which the sonic surface first encloses the binary, and the $(\gamma-1)^{-1}$ divergence follows from the lack of
entropy generation at isothermal shocks. For $\gamma = 5/3$, no saddle point exists at any~$\xi$ and the neutrally stratified Bondi profile is convectively unstable by a distinct mechanism. The single comparison $t_{\rm cool}$ versus $NT$ – where $T$ is the orbital period – determines whether an embedded binary accretes cooperatively or throttles its own fuel supply; simulations confirm the analytic thresholds and scaling.
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High Energy Astrophysical Phenomena
On the Astrophysical Origin of Binary Black Hole Subpopulations: A Tale of Three Channels?
Anarya Ray, Shirsha Mukherjee, Michael Zevin et al. (+1 more)
There is increasing evidence for multiple binary black hole~(BBH) subpopulations in the cumulative gravitational wave catalog by the LIGO-Virgo-KAGRA Collaboration. The astrophysical interpretation of this complex underlying population is subject to theoretical uncertainties in treatments of binary
stellar evolution, core collapse, and host environments. In this Letter, using parametrized mixture models, we show that the BBH detection sample comprises three astrophysical subpopulations that are likely dominated by specific formation channels. In particular, we show that the $10M_{\odot}$ peak and the $35M_{\odot}$ feature in the BBH mass spectrum correspond to distinct mass-ratio,
spin alignment,
spin precession, and
redshift evolution properties. We show that mass-based transitions reported in the distribution of BBH parameters naturally emerge from our inferred distributions without explicit modeling. Our results are consistent with the current observed population arising from specific relative abundances of isolated binary
evolution, dynamical formation in globular clusters, and higher-generation BBH mergers. Under this interpretation, we constrain the relative underlying fraction of these channels to be $79.0^{+11.5}_{-10.9}\%$, $14.5^{+11.6}_{-8.0}\%$, and, $2.5^{+5.5}_{-1.8}\%$, respectively, and find these relative fractions to be evolving over
cosmic time with more than $1\sigma$ confidence. Our interpretation relies on simple theoretical predictions that are mostly robust against uncertainties in BBH formation, with more definite conclusions expected in the near future.
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All authors Anarya Ray, Shirsha Mukherjee, Michael Zevin, Vicky Kalogera
Astrophysics of Galaxies
Characterization of molecular outflows at core-scale in the massive clump AGAL G345.0029-0.224
E. Cohen Arazi, M. E. Ortega, S. Paron et al. (+3 more)
High-mass
stars, with their powerful winds and intense radiation fields, are fundamental in regulating
galactic dynamics and
evolution; however, despite their great relevance, the mechanisms involved in their formation are still not fully understood. In this context, molecular
outflows, which are essential for removing angular momentum and allowing
accretion onto the central object, are a crucial phenomenon for characterizing their formation. Previous studies reveal a discrepancy in the masses of
outflows associated with high-mass clumps between works conducted at the clump scale ($\sim$ pc) and those at the core scale ($\sim$ subpc). This suggests that the high-mass
outflow activity observed at the clump scale might be the result of the contribution from several lower-mass
outflows linked to individual molecular cores. This work presents a study of the molecular gas toward a high-mass clump associated with an Extended Green Object (EGO). EGOs are indicators of jets associated with high-mass protostars. Employing high angular resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA), the presence of several hot cores with
outflow activity was observed in the source. A characterization of the
outflows at the core scale is presented within the context of the physical parameters of the molecular clumps.
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All authors E. Cohen Arazi, M. E. Ortega, S. Paron, P. F. Velázquez, A. Rodríguez-González, E. Alquicira