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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 16 March

Solar and Stellar Astrophysics

Evolution of wide O star binaries through their LBV stage. Population synthesis with mass-ejection-driven orbital evolution

Xiao-Tian Xu, Philipp Podsiadlowski, Norbert Langer et al. (+6 more)

Context. Long-period Wolf-Rayet (WR) star binaries produced by mass transfer are predicted to be abundant, but are observationally rare. This yields constraints on the evolution of initially wide O star binaries, including those potentially leading to the formation of gravitational-wave sources through the Common Envelope Channel. Aims. We investigate this issue in the light of a new type of orbital evolution for initially wide O star binaries, which is driven by mass ejection at periastron passage during the Luminous Blue Variable (LBV) phase. Methods. The assumption that the mass ejection occurs instantly at periastron passage allows us to analytically describe the orbital evolution. This approach is motivated by our understanding of an Eddington-limit driven LBV phase. We perform population synthesis calculations for the WR stars in the Small Magellanic Cloud (SMC), and compare them to the observed SMC WR star population. Results. Different from mass transfer, our mass ejection scenario leads to increased orbital periods and eccentricities. The Galactic system WR 140 (orbital period 2895 d, eccentricity 0.9) could be a typical result of this evolution scenario. Our models predict measurable binary space velocities, and allow for the disruption of the binary. Our SMC population synthesis model predicts statistically 5.3 close, 3.7 long-period, and further 2 runaway single WR stars. With largely increased orbital periods and eccentricities, such WR+O star binaries may not be ruled out by past radial-velocity searches. Applying our scenario to the Gaia BH1 and BH2 systems, we find that it provides viable progenitor evolution models. Conclusions. The mass-ejection-driven orbital evolution could explain why so few wide WR binaries are observed, and why some of the apparently single WR stars have high space velocities. We discuss implications for gravitational-wave sources.
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All authors Xiao-Tian Xu, Philipp Podsiadlowski, Norbert Langer, Xue-Feng Wang, Xiang-Dong Li, Alexander Heger, Jonathan Mackey, Götz Gräfener, Harim Jin

Earth and Planetary Astrophysics

Coupled Space Weathering: Nanophase Iron Formation by Micrometeoroid Impact and Solar Wind Sputtering

Ziyu Huang and Masatoshi Hirabayashi

Understanding the interplay between micrometeoroid impacts and solar wind irradiation is crucial for interpreting lunar surface evolution. Using reactive molecular dynamics simulations and surface binding energy (SBE) analyses, this study investigates the coupled effects of these two dominant space weathering processes on lunar regolith composed of Fe$_2$SiO$_4$. Our simulations reveal that micrometeoroid impacts significantly modify the lunar surface, creating structurally heterogeneous zones with varying SBEs across microcrater morphologies. Specifically, microcrater floors exhibit enhanced surface cohesion due to high-density compaction, whereas microcrater walls and ejecta show weakened structures. Applying Sigmund's sputtering theory with these SBEs indicates differential sputtering yields for Fe, Si, and O suggesting preferential retention of heavier elements like Fe. This selective sputtering mechanism supports the formation and growth of nanophase metallic iron (npFe$^0$) clusters, influencing the optical and compositional maturation of the lunar surface. These findings advance our understanding of lunar space weathering processes.
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High Energy Astrophysical Phenomena

Constraining Spin and Inclination Angle of XTE J2012+381 using AstroSat and NICER

Vaibhav Sharma, Ranjeev Misra, Shivani Chaudhary et al. (+2 more)

We present a spectral analysis of a black hole X-ray binary XTE J2012+381 during its 2022 outburst, using data from NICER and AstroSat. Combining data from NICER, LAXPC20, and SXT, we extract energy spectra covering the 0.7-10.0 keV range. We model the energy spectra using a series of physical models and find that a reflection-Comptonization model provides the best fit. Given the uncertainties in the black hole mass and source distance, we investigate the stability of the inferred spectral parameters by systematically varying the black hole mass (7.26, 11, and 16.5 M$_\odot$), source distance (3.3, 5.4, and 7.5 kpc), and spectral hardening factor (1.5, 1.7, and 1.9). We find that, across most combinations of these parameters, the spin solutions consistently lie in the high-spin regime, spanning values between $\sim$0.67 and $\sim$0.998, with only a limited subset of configurations favoring lower spins. In contrast, the disk inclination angle remains well constrained over the majority of the explored parameter space, typically ranging between $\sim$50{\deg} and $\sim$65{\deg}. Only a few parameter combinations yield higher inclination values.
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All authors Vaibhav Sharma, Ranjeev Misra, Shivani Chaudhary, J S Yadav, Pankaj Jain

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Cosmological angular momentum from quantum rotation

Bo-Qiang Lu

The origin of cosmic angular momentum is a fundamental question in structure formation. We propose a novel mechanism that generates spatial angular momentum directly from quantum fluctuations during inflation. A spectator complex scalar field with global U(1) symmetry stores internal angular momentum via field-space rotation. Inflationary perturbations create spatial gradients that, upon horizon re-entry, couple to the background charge density and source a bulk momentum flow. During nonspherical gravitational collapse, this flow converts into net angular momentum. For primordial black holes forming from such collapse, the dimensionless spin can reach \(\chi\sim 0.1-1\) when the small-scale power spectrum is enhanced to produce detectable abundances-far exceeding tidal torque theory predictions. This establishes a testable link between inflation, primordial perturbations, and black hole spin distributions accessible to gravitational-wave observations.
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High Energy Astrophysical Phenomena

Cosmic ray mass composition measurement in the energy range from $10^{16.5}$ eV to $10^{18.5}$ eV observed with the TALE hybrid detector

Telescope Array Collaboration: R.U. Abbasi, T. Abu-Zayyad, M. Allen et al. (+126 more)

We report on the cosmic ray mass composition measured by the Telescope Array Low-energy Extension (TALE) hybrid detector. The TALE detector consists of a fluorescence detector (FD) station with 10 FD telescopes located at the Telescope Array (TA) Middle Drum FD Station (itself made up of 14 FD telescopes), and a surface detector (SD) array of scintillators. The array consists of 40 SDs with 400 m spacing and 40 SDs with 600 m spacing. In this paper, we present results on the measurement of the depth of shower maxima ($X_\mathrm{max}$) in the energy range from $10^{16.5}$ eV to $10^{18.5}$ eV collected over five years of the TALE hybrid detector. The $X_\mathrm{max}$ distributions were analyzed and compared with Monte Carlo simulations of proton, helium, nitrogen, and iron primaries, using the QGSJet II-04 hadronic interaction model. Our results indicate that the elongation rate of the mean $X_\mathrm{max}$, which is defined as the slope of $\langle X_\mathrm{max} \rangle$ versus cosmic ray energy, exhibits a break around $10^{17}$ eV. Up to this energy, the composition becomes increasingly heavy, characterized by a growing dominance of heavy nuclei and a steadily decreasing fraction of light primaries. Beyond this energy, the proton fraction increases significantly with energy. These findings suggest a transition from Galactic to extra-Galactic cosmic ray sources around the so-called second knee.
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All authors Telescope Array Collaboration: R.U. Abbasi, T. Abu-Zayyad, M. Allen, J.W. Belz, D.R. Bergman, F. Bradfield, I. Buckland, W. Campbell, B.G. Cheon, K. Endo, A. Fedynitch, T. Fujii, K. Fujisue, K. Fujita, M. Fukushima, G. Furlich, A. Gálvez Ureña, Z. Gerber, N. Globus, T. Hanaoka, W. Hanlon, N. Hayashida, H. He, K. Hibino, R. Higuchi, D. Ikeda, D. Ivanov, S. Jeong, C.C.H. Jui, K. Kadota, F. Kakimoto, O. Kalashev, K. Kasahara, Y. Kawachi, K. Kawata, I. Kharuk, E. Kido, H.B. Kim, J.H. Kim, J.H. Kim, S.W. Kim, R. Kobo, I. Komae, K. Komatsu, K. Komori, A. Korochkin, C. Koyama, M. Kudenko, M. Kuroiwa, Y. Kusumori, M. Kuznetsov, Y.J. Kwon, K.H. Lee, M.J. Lee, B. Lubsandorzhiev, J.P. Lundquist, H. Matsushita, A. Matsuzawa, J.A. Matthews, J.N. Matthews, K. Mizuno, M. Mori, S. Nagataki, K. Nakagawa, M. Nakahara, H. Nakamura, T. Nakamura, T. Nakayama, Y. Nakayama, K. Nakazawa, T. Nonaka, S. Ogio, H. Ohoka, N. Okazaki, M. Onishi, A. Oshima, H. Oshima, S. Ozawa, I.H. Park, K.Y. Park, M. Potts, M. Przybylak, M.S. Pshirkov, J. Remington, C. Rott, G.I. Rubtsov, D. Ryu, H. Sagawa, N. Sakaki, R. Sakamoto, T. Sako, N. Sakurai, S. Sakurai, D. Sato, K. Sekino, T. Shibata, J. Shikita, H. Shimodaira, H.S. Shin, K. Shinozaki, J.D. Smith, P. Sokolsky, B.T. Stokes, T.A. Stroman, H. Tachibana, K. Takahashi, M. Takeda, R. Takeishi, A. Taketa, M. Takita, Y. Tameda, K. Tanaka, M. Tanaka, M. Teramoto, S.B. Thomas, G.B. Thomson, P. Tinyakov, I. Tkachev, T. Tomida, S. Troitsky, Y. Tsunesada, S. Udo, F.R. Urban, M. Vrábel, D. Warren, K. Yamazaki, Y. Zhezher, Z. Zundel, J. Zvirzdin

Cosmology and Nongalactic Astrophysics

CosmoDS: A Python toolkit for constraining cosmological models via dynamical systems analysis with Cobaya

Nandan Roy and Prasanta Sahoo

We present a toolkit, CosmoDS, designed to study cosmological models at the background level using dynamical system analysis within the Cobaya framework. Dynamical system analysis is a powerful mathematical approach for studying nonlinear systems and is widely used in cosmology to investigate the stability and evolution of different cosmological models, particularly those involving dark energy. In this code, we provide a framework for constraining cosmological models using a dynamical system formulation. Most importantly, the toolkit is directly integrated with the Cobaya interface, allowing users to take advantage of the sophisticated statistical and inference tools already implemented in Cobaya for cosmological parameter estimation and model analysis.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Dark Matter Induced Scalarization as a Possible Solution to the Hyperon Puzzle

Suchana Adhikari and Teruaki Suyama

We investigate the properties of neutron stars when a massive scalar field, which could comprise all dark matter, is non-minimally coupled to the Ricci scalar. This coupling generates additional contributions to the field's effective mass, leading to tachyonic instabilities inside neutron stars and giving rise to rich phenomenology. Within this framework, we obtain neutron-star configurations with maximum masses exceeding 2 $M_\odot$, even when hyperons, which typically soften the equation of state and significantly lower the maximum mass, are included. Furthermore, we find that larger coupling strengths lead to multiple solutions for the scalar-field configuration. We analyze the structure of the corresponding effective potential responsible for this behavior. We also investigate how the inclusion of a scalar self-interaction term, in addition to the non-minimal coupling, modifies the resulting neutron-star properties.
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Solar and Stellar Astrophysics

Dynamics of the Upwind Heliosphere Due to Data-Driven, Solar Wind and Magnetic Field Variations and Implications for Wave Propagation into the Very Local Interstellar Medium

Chika Onubogu, M. Opher, E. Powell et al. (+4 more)

We introduce an updated, time-dependent treatment to the split-tail ("croissant-like") heliosphere model with data-driven solar wind conditions at 1 au, to study the evolution of the heliosphere with solar-cycle variations in plasma speed, plasma density, and magnetic field intensity. The model produces a sub-Alfvénic and low beta region, not observed by the Voyagers, ~15 au ahead of the heliopause. The simulated magnetic field and radial flow depart from Voyager observations in this region, indicating that time-dependent effects alone are not sufficient to understand this regime of the heliosheath. We decompose fast and slow magnetosonic wave modes from time-dependent plasma pulse structures in the heliosheath, using a linear Riemann variable analysis, for the first time. Fast mode waves can both reflect at the heliopause and transmit into the interstellar medium, and their speeds are unaffected by the low beta plasma regime in front of the heliopause. The model reproduces the pf2 jump in the magnetic field at ~2020 in the interstellar medium and we attribute the source of pressure fronts observed by Voyager 1 in the interstellar medium, and pressure pulses observed by Voyager 2 in the heliosheath, to fast mode waves that are commonly recurring solar-cycle features. The presence of fast mode waves drive a highly variable termination shock, with average radial speeds of 6.05 au yr$^{-1}$ $\pm$ 5.37 au yr$^{-1}$ in the New Horizons direction. We find that the termination shock has a sinusoidal-like oscillatory motion in the rising phase of the solar cycle, and broad inward motions during the declining phase.
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All authors Chika Onubogu, M. Opher, E. Powell, S. Du, J. M. Sokół, J. D. Richardson, B. Van Der Holst

Cosmology and Nongalactic Astrophysics

Background-level reconstruction of scalar-field potentials from dark-energy histories and comparison with analytic potential families

Shahnawaz A. Adil, Miguel A. Zapata, Özgür Akarsu et al. (+1 more)

We present a unified background-level framework that maps a prescribed late-time dark-energy density history $\rho_{\rm de}(z)$ onto an effective scalar-field description in a spatially flat FLRW universe. Working directly with $\rho_{\rm de}(z)$, we reconstruct the associated field trajectory $\phi(z)$, and field-space potential $V(\phi)$, together with a null energy condition (NEC) consistency check. We apply the method to three benchmark histories: (i) the Chevallier–Polarski–Linder (CPL) form; (ii) a smooth mirror AdS$\rightarrow$dS sign-switching profile in which $\rho_{\rm de}$ crosses zero at $z_\dagger$, interpolating between a positive late-time plateau and a negative high-$z$ plateau ($\Lambda_{\rm s}$CDM-like at the background level); and (iii) a shifted-$\tanh$ emergent profile that remains positive definite and approaches $\rho_{\rm de}\to 0^{+}$ at high redshift. Finally, treating the reconstructed potential, $V_{\rm tar}(\phi)$, as a target, we perform Bayesian model comparison directly in potential space and rank representative analytic potential families by their Bayesian evidence. For CPL (restricting to the single-valued phantom branch for the potential-space comparison), the exponential potential has the highest evidence in the baseline analysis, while the shifted-$\tanh$ and hilltop quartic forms remain close competitors; for the sign-switching $\tanh$ target, the shifted-$\tanh$ potential is strongly preferred, and the emergent profile yields the same qualitative ranking. These results provide a practical dictionary between phenomenological expansion histories and the scalar-field potential shapes required to reproduce them at the background level.
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All authors Shahnawaz A. Adil, Miguel A. Zapata, Özgür Akarsu, J. Alberto Vazquez

Instrumentation and Methods for Astrophysics

The TOLIMAN mission: A low-cost space telescope for high precision narrow-angle astrometry

Peter Tuthill, Christopher Betters, Max Charles et al. (+29 more)

The TOLIMAN project is engaged with the construction, launch and operation of a low-cost space telescope of unorthodox optical design. Its primary science goal targets an exhaustive search for temperate-orbit rocky planets around either star in the alpha Centauri AB binary within our nearest-neighbor star system. Despite their favorable proximity and brightness, the detection of terrestrial exoplanets around such nearby Sun-like stars remains problematic for contemporary instrumental approaches. By performing narrow-angle astrometric monitoring of binary stars at extreme precision, any exoplanets will betray their presence by way of gravitationally-induced perturbations on the binary orbit. Recovery of this signal is challenging for it amounts to only a few microarcseconds of angular deflection (at best), and so is normally thought to require a large (meter-class) instrument. By implementing an innovative optical and signal encoding architecture, the TOLIMAN space telescope aims to recover such signals with a telescope aperture of only 12.5cm. This paper gives an overview of key features of the mission; in particular the concepts underlying the optics to enable image registration at the extreme levels of precision required. An outline is also provided, sketching further mission components and systems incorporated into the 16U CubeSat spacecraft bus in which the science payload is housed - all of which are now under construction.
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All authors Peter Tuthill, Christopher Betters, Max Charles, Fred Crous, Donald G. Dansereau, Conaire Deagan, Louis Desdoigts, Mark George, Thomas Holland, Connor J. Langford, Milo Langker, Kieran Larkin, Clarissa Luk, Jack Nelson, Benjamin Pope, Grace Piroscia, Angus Rutherford, David Sweeney, Adam Taras, Karel Valenta, Tim White, Alison Wong, Eduardo Bendek, David Doelman, Kyran Grattan, Olivier Guyon, Peter Klupar, Benjamin T. Montet, Jeffrey Smith, Douglas Caldwell, Frans Snik, Simon P. Worden

Astrophysics of Galaxies

Revisiting candidate high-velocity stars associated with the Sagittarius dwarf spheroidal galaxy

Jian Zhang, Cuihua Du, Mingji Deng et al. (+2 more)

Hypervelocity stars (HVSs) are valuable tracers of extreme dynamical processes. The Sagittarius dwarf spheroidal galaxy (Sgr dSph), currently undergoing tidal disruption, offers a unique environment to search for such stars. We aim to identify candidate HVSs dynamically linked to the Sgr dSph and to assess their possible origins. Using Gaia DR3, DESI DR1, and LAMOST DR12, we selected stars with galactocentric velocities above 400 km\,s$^{-1}$ and traced their orbits in a realistic Galactic potential including the Sgr dSph and the Large Magellanic Cloud. We then tested three scenarios for their origin: the Hills mechanism, tidal disruption, and random halo star encounters. We identified 95 candidates passing within 2.5 half-mass radii of the Sgr dSph. Their kinematics are inconsistent with production by the Hills mechanism or tidal disruption but are well reproduced by halo stars that naturally cross the Sgr orbit. Furthermore, their metallicity distribution is consistent with that of the Milky Way halo rather than the Sgr stream or Sgr dSph. Our results suggest that our candidates and those in previous studies are most likely halo stars rather than genuine Sgr-origin HVSs. This highlights the need to account for the halo population when inferring stellar origins from orbital analysis and that chemical abundances will be a valuable constraint in the future. While we detect no unbound Sgr HVSs, such a discovery would directly imply extreme dynamical processes. Our results serve as a basis for future studies with upcoming surveys.
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All authors Jian Zhang, Cuihua Du, Mingji Deng, Haoyang Liu, Zhongcheng Li

Sunday 15 March

Solar and Stellar Astrophysics

A modest change in magnetic braking at the fully convective boundary explains cataclysmic variable evolution

Joaquín A. Barraza-Jorquera, Matthias R. Schreiber, Stuart Littlefair et al. (+2 more)

Context. For decades, reproducing the orbital period distribution of non-magnetic Cataclysmic Variables (CVs) seemed to require a drastic decrease, usually termed disruption, of angular momentum loss through magnetic braking at the fully convective boundary, which argued for a change in the dynamo mechanism operating in fully and partially convective stars. However, recent studies showed that the magnetic braking prescription traditionally used in CV evolution theory is clearly outdated as saturation, that is, a weak period dependence for rapidly rotating stars, is not included. Aims. Here we test an updated version of a saturated magnetic braking prescription that has been developed to explain the spin-down of single stars in the context of CV evolution. This prescription contains a boosting and a disruption parameter that represent the change in the strength of magnetic braking at the fully convective boundary. Methods. We performed state of the art MESA simulations for CVs with the revised saturated magnetic braking prescription. Results. As in previous studies, we found that magnetic braking needs to be stronger in close binaries than in single stars and that, in contrast to what is observed in single stars, magnetic braking needs to be reduced at the fully convective boundary. However, in contrast to previous studies of CV evolution, only a moderate disruption by a factor of 2 - 3 is sufficient to explain key features of the CV orbital period distribution and the measured mass-radius relation for CV donors. Conclusions. The relatively small decrease of the efficiency of magnetic braking at the fully convective boundary might have implications for our understanding of dynamo models for fully and partially convective stars.
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All authors Joaquín A. Barraza-Jorquera, Matthias R. Schreiber, Stuart Littlefair, Diogo Belloni, Axel D. Schwope

Earth and Planetary Astrophysics

Constraining Small Planet Compositions for Future Missions

Larissa Palethorpe, Annelies Mortier, Jo Ann Egger et al. (+14 more)

Accurate mass and radius measurements of small transiting exoplanets are essential for probing their compositions, formation histories, and potential habitability. We present a uniform analysis of six planetary systems (each hosting at least one small transiting planet): K2-79, K2-106, K2-111, K2-222, K2-263, and TOI-1634. Our study combines new CHEOPS transit observations with archival photometry from K2, TESS, and ground-based facilities, alongside new and archival radial velocity data from HARPS-N, HIRES, ESPRESSO, and others. For each system, we perform joint transit and RV modelling, achieving typical precisions better than 15% and 5% for mass and radius, respectively, and thus enabling precise bulk density determinations. These reveal a range of compositions, including rocky planets near the radius valley (e.g. K2-106 b, TOI-1634 b), intermediate-density planets requiring steam-rich or mixed volatile envelopes (e.g. K2-111 b, K2-263 b), and low-density regimes, consistent with gas dwarfs or water-worlds (e.g. K2-79 b, K2-222 b). Several systems show evidence of additional companions detectable via RVs but not seen in transit. The results highlight the value of coordinated CHEOPS and HARPS-N observations in delivering some of the most precise bulk densities for small planets to date and support the preparation for future atmospheric characterisation missions.
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All authors Larissa Palethorpe, Annelies Mortier, Jo Ann Egger, Ken Rice, Thomas G. Wilson, Andrew Vanderburg, Aldo S. Bonomo, Walter Boschin, Andrew Collier Cameron, Yoshi Nike Emilia Eschen, Avet Harutyunyan, Luca Malavolta, Aldo F. Martínez Fiorenzano, Alessandro Sozzetti, Manu Stalport, Vincent Van Eylen, Christopher Allan Watson

Solar and Stellar Astrophysics

Phosphorus in cool stars of various metallicities: The non-local thermodynamic equilibrium consideration

S.M. Andrievsky and S.A. Korotin

The phosphorus abundance distribution in field stars as a function of metallicity reveals a complex pattern. The LTE data for [P/Fe] in the low-metallicity range are sparse and scattered around [P/Fe]~ 0 dex. Near [Fe/H]~ -2 dex, the relative abundance [P/Fe] increases and reaches a maximum value of around [Fe/H]~ -1 dex. In this domain, P-rich stars and (super)phosphorus-rich stars are observed; the [P/Fe] value can exceed 1 dex. Until now, no attempts have been made to study the NLTE effects on the ultraviolet and infrared phosphorus lines in spectra of cool stars to test the robustness of the observed LTE phosphorus abundance distribution. We developed an atomic model of P I that can be used to analyze phosphorus lines in the spectra of cool dwarfs and giants in the NLTE approximation. The model was tested using the solar flux and intensity spectra, as well as the spectra of Procyon and sigma Boo. Profiles of 14 phosphorus lines in the infrared regions and equivalent widths were analyzed. Our NLTE phosphorus abundance in the Sun is (P/H)=5.35+/-0.04 dex. Using our NLTE model, we selected 12 ultraviolet and infrared phosphorus lines and calculated a grid of NLTE corrections for the following parameter ranges: Teff from 4000 to 6750 K, step 250 K; log g from 1 to 5 dex, step 1 dex; and Vt = 2 km/s, [Fe/H] from -3 to +0.5 dex, step 0.5 dex. The NLTE corrections were calculated for phosphorus abundance ratios of [P/Fe]=-0.4, 0.0, +0.4 dex. For the Sun, the NLTE correction is -0.08 dex. The grid of the NLTE corrections, as well as the direct line profile synthesis, were used to refine the literature data on the phosphorus abundance in metal-poor, intermediate-deficient, and solar-metallicity stars. NLTE corrections do not qualitatively alter the overall phosphorus abundance distribution over a wide metallicity range, and do not change the characteristic pattern of phosphorus-rich stars.
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Cosmology and Nongalactic Astrophysics

Cosmological peculiar velocities in general relativity

Chris Clarkson and Roy Maartens

We reconsider the late-time evolution of galaxy peculiar velocities in the 1+3 covariant approach to cosmological perturbation theory. It has recently been claimed that this approach predicts substantially stronger growth of peculiar velocities than standard metric-based perturbation theory – on the grounds that the covariant treatment is fully relativistic whereas standard treatments are effectively Newtonian. We show that this is not the case. When the covariant equations are applied consistently, the $1+3$ approach reproduces exactly the standard perturbative result for peculiar-velocity growth. The stronger growth laws claimed in recent work arise from an inconsistent treatment of the coupled covariant system, in which terms constrained by the field equations are treated as if they were independent sources. Further claims are made that the stronger bulk flows can mimic accelerated expansion in a dust universe. We argue that these claims rest on a confusion between the kinematics of an arbitrarily chosen observer congruence and the physical expansion of the matter congruence traced by galaxies. We conclude that the standard treatment of peculiar velocities is correct and fully relativistic~– and does not lead to anomalous bulk flows or to apparent accelerated expansion.
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Cosmology and Nongalactic Astrophysics · Cross-listed from cs.CV

Mapping Dark-Matter Clusters via Physics-Guided Diffusion Models

Diego Royo, Brandon Zhao, Adolfo Muñoz et al. (+2 more)

Galaxy clusters are powerful probes of astrophysics and cosmology through gravitational lensing: the clusters' mass, dominated by 85% dark matter, distorts background light. Yet, mass reconstruction lacks the scalability and large-scale benchmarks to process the hundreds of thousands of clusters expected from forthcoming wide-field surveys. We introduce a fully automated method to reconstruct cluster surface mass density from photometry and gravitational lensing observables. Central to our approach is DarkClusters-15k, our new dataset of 15,000 simulated clusters with paired mass and photometry maps, the largest benchmark to date, spanning multiple redshifts and simulation frameworks. We train a plug-and-play diffusion prior on DarkClusters-15k that learns the statistical relationship between mass and light, and draw posterior samples constrained by weak- and strong-lensing observables; this yields principled reconstructions driven by explicit physics, alongside well-calibrated uncertainties. Our approach requires no expert tuning, runs in minutes rather than hours, achieves higher accuracy, and matches expertly-tuned reconstructions of the MACS 1206 cluster. We release our method and DarkClusters-15k to support development and benchmarking for upcoming wide-field cosmological surveys.
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All authors Diego Royo, Brandon Zhao, Adolfo Muñoz, Diego Gutierrez, Katherine L. Bouman

Instrumentation and Methods for Astrophysics

Compact and Physically Interpretable Feature Models for Photometric Type Ia Supernova Classification

Anurag Garg

Photometric classification of Type Ia supernovae is essential for modern time-domain surveys, where spectroscopic confirmation is not always feasible for the full transient sample. We investigate a compact and physically interpretable feature representation derived from multi-band light curves and evaluate its performance using gradient-boosted decision trees on the Supernova Photometric Classification Challenge (SPCC) dataset. The compact representation is derived from an initial pool of 31 light-curve features, reduced to 30 after removing redundant variables and further optimized to a 16-feature model through systematic ablation analysis. The final compact model achieves an F1-score of 0.844 on the held-out test set, consistent with k-fold cross-validation results (0.841 +/- 0.006). The precision-recall area under the curve (PR-AUC) is 0.928, with similarly low variance across folds. Ablation experiments show that temporal evolution provides the dominant classification signal, while brightness, color, and variability features contribute complementary information. A reduced core of approximately ten physically meaningful features retains most of the performance of the compact model, with only a small decrease in F1-score, indicating that reliable classification does not require large high-dimensional feature spaces. These results demonstrate that interpretable feature-based models can capture the essential astrophysical information needed for Type Ia photometric classification, with implications for survey cadence, filter coverage, and the design of transparent and efficient machine-learning pipelines for time-domain surveys.
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Cosmology and Nongalactic Astrophysics

A possible detection of gas rotation in galaxy groups via the kinetic Sunyaev-Zeldovich effect

Tianyi Yang, Yan-Chuan Cai, Weiguang Cui et al. (+5 more)

We utilise the kinetic Sunyaev-Zeldovich effect (kSZ) to measure the rotation of ionised gas within galaxy groups defined in the SDSS-DR7 galaxy sample, via their dipolar imprint on the cosmic microwave background (CMB). We estimate the direction of the projected angular momentum for each of our selected fast-rotating groups by measuring the redshift dipole of satellite galaxies around their group centres. We find a clear redshift dipole in the stacked data for the selected SDSS groups. We then perform oriented stacking of the Planck CMB temperature map using the group centres and directions of angular momenta. We report a $2.3\sigma$ tentative detection of the dipolar rotational kSZ effect (rkSZ) within the virial radii of our fast-rotating groups from SDSS with an average mass of $10^{14}h^{-1} \rm M_{\odot}$ (corresponding to a null-hypothesis probability of 0.96%). We estimate the averaged rotational velocity of the sample to be $\sim 100-200 ~\rm km ~s^{-1}$, reaching a maximum value of $158.8\pm13.6 ~\rm km ~s^{-1}$. Our results are consistent within the errors with predictions based on the ELUCID constrained realisation simulation, with the predicted amplitude of the rkSZ signal being slightly lower near the centre. We also identify a systematic bias when estimating rotational velocities using the observed redshifts of galaxies, but find it to be subdominant for our analysis.
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All authors Tianyi Yang, Yan-Chuan Cai, Weiguang Cui, John A. Peacock, Romeel Davé, Houjun Mo, Huiyuan Wang, Xiaohu Yang

Astrophysics of Galaxies

Hidden in Plain Sight: Searching for Globular Clusters Within JWST Observations of the PLCK G165.7+67.0 Galaxy Cluster

Tyler R. Hinrichs, Patrick S. Kamieneski, Rogier A. Windhorst et al. (+21 more)

Although the James Webb Space Telescope (JWST) has received much attention for its ability to search deeper into the cosmos than ever before, it also enhances our capability to study objects closer to us in the Universe. We apply a methodology of subtracting intracluster light to the PLCK G165.7+67.0 (G165; $z$ = 0.35) cluster, revealing a population of unresolved point-like sources including globular clusters (GCs). By applying a fitting algorithm in color space used to select galaxy cluster members, we uncover over 900 globular cluster candidates from our point source sample. We also identify candidates by estimating the contribution of interlopers to the point source sample, yielding an estimate of 793$\pm$ 83 globular cluster candidates. We find the color-selected sources to be approximately correlated spatially with the intracluster light and lensing mass of the cluster. The observed luminosity function of the sources shows a turnover point fainter than the completeness limit, so we use fixed-parameter curve fitting models to predict a K-corrected turnover point between $-9.4 \leq M_{\rm F200W} \leq -10.7$ mag, although we predict the expected K-corrected turnover point should be closer to $-7.7 \leq M_{\rm F200W} \leq -8.4$ mag. We discuss the dynamical state of this disturbed galaxy cluster with a bimodal mass distribution using the spatial distribution of GC candidates and find that the radial profiles of our color-selected GC candidates are very consistent with the lensing-derived surface mass density at $>$50 kpc.
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All authors Tyler R. Hinrichs, Patrick S. Kamieneski, Rogier A. Windhorst, Seth H. Cohen, Brenda L. Frye, Timothy Carleton, Massimo Pascale, Jose M. Diego, Rolf A. Jansen, Jessica Berkheimer, Nathan J. Adams, Christopher J. Conselice, Simon P. Driver, Nicholas Foo, Nikhil Garuda, Nimish P. Hathi, Rachel Honor, Anton M. Koekemoer, Rafael Ortiz III, Marta Reina-Campos, Aaron S. G. Robotham, Jake S. Summers, Haojing Yan, William E. Harris

Earth and Planetary Astrophysics

A user-friendly package and workflow for generating effective homogeneous rheologies for the study of the long-term orbital evolution of multilayered planetary bodies

Yeva Gevorgyan

We present a user-friendly, open-source Wolfram Language package that automates the construction of an effective homogeneous generalized Voigt rheology for a spherically symmetric, incompressible layered body with Maxwell solid layers. It provides a practical bridge between layered interior models and time-domain simulations of tidal evolution. The package combines three components: (i) a forward computation of the degree-2 tidal Love number based on the propagator-matrix formulation for incompressible stratified viscoelastic bodies; (ii) numerical identification of the secular relaxation poles and residues of the layered model; and (iii) inversion of the resulting response into the compliance of an equivalent homogeneous generalized Voigt body. The implementation is based on the equivalence established for multilayer Maxwell bodies and includes an optional dominant-mode selection procedure for obtaining reduced rheological models over a prescribed frequency range. The package returns the parameters of the equivalent homogeneous model, including elastic, gravitational, viscous, and Voigt-element contributions, in a format suitable for downstream numerical applications. As a case study, we apply the package to a five-layer lunar interior model and obtain its equivalent generalized Voigt representation, together with a reduced model that preserves the tidal response over the frequency interval relevant for orbital evolution while using fewer relaxation elements. This package makes the reduction from stratified viscoelastic interiors to effective homogeneous rheologies reproducible and accessible. It allows physical tidal dissipation models to be used in long-term orbital and spin-evolution studies without having to repeatedly solve the full layered boundary-value problem.
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High Energy Astrophysical Phenomena

Energy transfer from jets to surrounding matter to form lateral lobes in SS433/W50

Hajime Inoue

We first investigate an approximate structure of the top region (TR) of a jet, sandwiched by a front shock from which the surrounding matter (SM) inflows and a rear shock from which the jet matter (JM) inflows. Since pressure in the TR is higher than that in the laterally outer space, both JM and SM flowing in the TR are pressed out from the side of the TR. Supposing a steady flow of SM and JM there, we construct a simplified two dimensional model on a structure of the TR. With help of the model, we next infer what happens when precessing jets go through the surroundings in the SS433-W50 system presuming a supernova remnant (SNR) occupies W50. If we assume reasonable density distributions of the SNR and the interstellar matter in a 10 $\sim$ 100 pc distance range, the density of the surroundings is found to be much higher than that of the jet so that the jet is largely braked in the TR and that outflowing rate of the energy from the side of the TR becomes almost identical to the intrinsic energy flow rate through the jet. The outflowing energy could spread to the ambient space in a form of a bow shock but the situation of the shock propagation in the present case could be peculiar due to the presence of the precession. Particularly, all the mass and the energy outflowing from the inner side of the precession cone is considered to be concentrated around the axis of the precession cone. As the result, mass-compressed and energy-accumulated regions are expected to appear along the precession axis, which could be the origin of the lobes laterally extending from the main sphere of W50 observed in radio and X-rays.
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Solar and Stellar Astrophysics

The eclipsing novalike cataclysmic variable CRTS SSS100505 J093417-174421

R. Baptista, A. Bruch, R. Lopes de Oliveira et al. (+3 more)

Time-resolved optical photometry, complemented by TESS data and long-term survey light curves, reveals that the transient object CRTS SSS100505 J093417-174421 is an eclipsing novalike cataclysmic variable of the VY~Scl subtype, with an orbital period of 0.16329188(8) d. An analysis of the light curves with eclipse mapping techniques and an entropy landscape procedure indicates an orbital inclination of 81.5 degrees and a mass ratio of 0.45. Eclipse maps reveal two diametrically opposed asymmetric arcs of enhanced emission in the intermediate and outer regions of an accretion disk elongated in the direction perpendicular to the line joining both stars, interpreted as tidally-induced spiral shock arms. The accretion disk is 50 per cent larger in the longer wavelength TESS data than in the optical range, in line with the expected radial temperature gradient of an opaque steady-state disk. The combination of a small optical disk radius (of 21 per cent of the orbital separation) and high orbital inclination explains the relatively faint absolute magnitude of $M_g = 7.44$ for a novalike variable.
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All authors R. Baptista, A. Bruch, R. Lopes de Oliveira, C.V. Rodrigues, A.S. Oliveira, I.J. Lima

Astrophysics of Galaxies

Hidden Connections: Tracing the BCG Stellar Mass-Halo Mass Relation in the SDSS-GalWCat19 Cluster Catalog

Mohamed H. Abdullah, Rasha M. Samir, Nouran E. Abdelhamid et al. (+5 more)

The stellar-to-halo mass (SMHM) relation of brightest cluster galaxies (BCGs) provides key insight into the connection between BCG growth and the assembly of their host halos. We analyze this relation using the spectroscopic SDSS GalWCat19 cluster catalog, selecting 996 systems with log(M200) >= 13.6, log(Mstar) >= 10.5, and 0.02 <= z <= 0.125 to limit evolutionary effects and ensure stellar-mass completeness. We fit lognormal scaling relations with a Markov Chain Monte Carlo (MCMC) framework that accounts for measurement uncertainties and intrinsic scatter. For the fiducial SMHM relation, <log Mstar | M200> = alpha + beta log(M200/Mpiv) with log(Mpiv) = 14.2, we find a shallow slope beta = 0.17 +/- 0.03, normalization alpha = 11.04 +/- 0.01, and intrinsic scatter sigma_int = 0.19 +/- 0.01 dex. Recasting the relation in normalized form reduces the scatter to 0.16 +/- 0.01 dex, while including the magnitude gap M14 further reduces it to 0.14 +/- 0.01 dex. Variations in richness, redshift, and mass thresholds produce systematic shifts that are small compared to the statistical uncertainties, indicating that our inferred relations are robust to plausible selection choices. The reduced scatter when including M14 supports a picture in which BCG stellar mass reflects both halo mass and halo assembly history.
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All authors Mohamed H. Abdullah, Rasha M. Samir, Nouran E. Abdelhamid, Shrouk Abdulshafy, Gillian Wilson, Anatoly Klypin, SH. M. Shehata, Ashraf A. Shaker

High Energy Astrophysical Phenomena

Reconnection-driven State Transitions in Flat Spectrum Radio Quasars

Agniva Roychowdhury

We extend the work of Roychowdhury (2026) on skewness variations of the logarithmic flux, driven by large GeV flares in FSRQs, to a sample of 18 FSRQs. We find that they can be categorized into three groups, one where the skewness attains a persistent lower value after a large flare, one where it increases, and those where change in skewness is not significant. To provide a theoretical ground for these results, we use the statistical plasmoid model of Fermo et al. (2010) that self-consistently produces large plasmoids through merging which, when gain energy from the reconnection event and are Doppler aligned, produce large flares. We find that a downsampling of our simulation of 1500 runs to 18 statistically reproduces the observed distribution in p-values for change in skewness. We further compute the ensemble Shannon entropy of the system and the skewness, where the entropy is found to decrease at a $3\sigma$ level in both the groups where skewness either increases or decreases, as a direct evidence of increase in order in the system caused by a flare. We find that the power spectral densities of the simulated light curves are broken-power-laws, resembling a white noise+red noise broken by the typical cooling timescale in our system, in accordance with known blazar variability. We find that our results are robust to a $200-300\%$ change in several fiducial parameters of the simulation. Our stochastic simulation of plasmoids inside a blazar jet is consistent with key observable statistical properties of blazar GeV light curves.
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Cosmology and Nongalactic Astrophysics

Do We Have Sufficient Knowledge of the Galactic Foreground Emission in Cosmic Microwave Background Science?

Jia-Rui Li, Peibo Yuan, Yi-Fu Cai et al. (+1 more)

Galactic foreground emission plays a key role in cosmic microwave background (CMB) science, particularly for detecting primordial gravitational waves. A well-known lesson is the “dust wave” identified by BICEP2 in 2014, which was ruled out through a more careful analysis of foreground emission. To date, most estimates of Galactic foreground emission have relied on the assumption that for each line of sight, only one component is considered per emission mechanism. However, the results in this work suggest that more complex modeling – particularly involving multiple components arising from either line-of-sight complexity or pixel mixing – may be necessary to fully account for Galactic foregrounds, including dust and other components. More interestingly, the only available two-component dust estimate also fails due to oversimplified emission parameters, although it is conceptually superior to single-component alternatives. These results yield three key conclusions: (1) Due to the intrinsic three-dimensional complexity of the Galactic environment, where physical conditions vary with both distance and direction, the actual radiation from Galactic foreground components cannot be accurately characterized by single-component models. (2) Consequently, CMB experiments require more frequency bands to resolve these components. (3) Spatial variations of foreground emission parameters should not be simplified, because in this work, all such simplifications are found to degrade the estimates significantly.
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All authors Jia-Rui Li, Peibo Yuan, Yi-Fu Cai, Hao Liu

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Born-Infeld AdS Black Holes Surrounded by Perfect Fluid Dark Matter

Behzad Eslam Panah, Bilel Hamil and Manuel E. Rodrigues

We obtain exact charged AdS black hole solutions in Einstein Lambda gravity including the effects of Born Infeld nonlinear electrodynamics and Perfect Fluid Dark Matter. The influence of the PFDM and BI parameters on the event horizon is analyzed. We compute the conserved and thermodynamic quantities and verify that they satisfy the first law of thermodynamics. Thermal stability is studied in the canonical ensemble using the heat capacity and Helmholtz free energy showing how PFDM and BI parameters affect local and global stability regions. We further investigate the thermodynamics in the extended phase space by treating the cosmological constant as thermodynamic pressure obtaining consistent conserved quantities and confirming the first law. The Ehrenfest equations are analytically verified demonstrating that the critical behavior corresponds to a second order phase transition. Heat engines associated with these black holes are also constructed to examine how PFDM and BI parameters influence their efficiency. Finally we analyze the geodesic structure through timelike and null trajectories using the effective potential determining conditions for stable and unstable circular orbits the innermost stable circular orbit and the photon sphere. PFDM significantly modifies the orbital structure while BI corrections are weaker.
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Saturday 14 March

High Energy Astrophysical Phenomena

Evidence for Atomic Absorption Features in the High Resolution X-ray Spectrum of the Neutron Star in Puppis A

John Groger, Frits Paerels, Slavko Bogdanov et al. (+5 more)

We present evidence for atomic absorption lines in the high-resolution 4-30 A X-ray spectrum of the neutron star RX J0822-4300 in the supernova remnant Puppis A. Comparison with model atmosphere calculations shows that features in the observed spectrum can be uniquely associated with redshifted and pressure-broadened transitions in highly ionized oxygen and neon. We also spectroscopically confirm the previously estimated strength of the surface magnetic dipole field; we detect both the linear and the quadratic Zeeman effect. We derive values for both the gravitational redshift and the acceleration of gravity at the stellar surface, yielding the first purely spectroscopic estimates for the radius and mass of a neutron star.
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All authors John Groger, Frits Paerels, Slavko Bogdanov, Eric V. Gotthelf, David J. Helfand, Ivan Hubeny, Thierry Lanz, Thomas A. Gomez

Solar and Stellar Astrophysics

Nebular Phase Evolution of SN 2023ixf (I): From Circumstellar Infrared Echo to the onset of in-situ Dust Formation in a Type II Supernova

Avinash Singh, S. Goto, A. Sarangi et al. (+59 more)

We present optical and near-infrared (NIR) photometric and spectroscopic observations of the Type II supernova SN 2023ixf spanning 150 to 750 days, combined with published early-time optical and infrared photometry, and JWST NIRSpec and MIRI spectroscopy, to disentangle circumstellar echo emission from newly formed internal dust. The combined dataset reveals an early infrared excess by 1.8 days, a broad secondary NIR rebrightening over about 89 to 175 days, progressive attenuation of the red wing of H-alpha from about 132 days, and CO emission detected by about 217 days. We identify the onset of H-alpha asymmetry as the first direct signature for internal dust formation, and modeling of the H-alpha profile over 140 to 418 days yields an internal silicate-equivalent dust mass of about 1.5e-6 to 6e-5 solar masses. By contrast, the early infrared evolution is best interpreted as echo-dominated: the 1.8 to 33.6 day excess is consistent with a radiative-flash infrared echo from pre-existing circumstellar dust, while the 89 to 175 day rebrightening is more naturally explained by a more extended echo arising from structured wind material. JWST spectral energy distribution modeling further reveals a multi-component infrared continuum in which a cold graphite component traces lingering echo emission, while a colder silicate-bearing component grows to about 2e-3 solar masses, providing the strongest late-time spectral energy distribution evidence that internal CDS/ejecta dust becomes substantial. SN 2023ixf therefore provides one of the clearest time-resolved case studies of dust signatures in a Type II supernova, linking early circumstellar reprocessing with increasingly important in situ dust formation.
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All authors Avinash Singh, S. Goto, A. Sarangi, J. Johansson, C. Fransson, S. Barmentloo, J. Sollerman, R. S. Teja, K. Maeda, T. Hamada, N. Sarin, M. Yamanaka, T. Nakaoka, K. S. Kawabata, S. Schulze, A. Jerkstrand, S. Rose, D. K. Sahu, A. Gangopadhyay, G. C. Anupama, T. Ahumada, S. Anand, A. Bochenek, S. J. Brennan, X. Chen, S. Covarrubias, K. K. Das, X. Du, M. Dubey, N. Dukiya, N. Earley, X. Er, L. Ferrari, C. Fremling, G. Folatelli, W. V. Jacobson-Galán, L. Galbany, K.-R. Hinds, R. Imazawa, V. Karambelkar, B. Kumar, M. Li, X. Liu, X. Liu, K. Misra, T. Nagayama, Y. Pan, D. A. Perley, Y.-J. Qin, Y. Sano, J. Wise, Y.-P. Yang, X. Zou, J. Adler, E. C. Bellm, M. W. Coughlin, M. Graham, M. M. Kasliwal, J. Purdum, B. Rusholme, A. Sasli, N. Sravan

Astrophysics of Galaxies

Rotation Curve of the Milky Way

Zi Liu

We investigate the rotation curve of the Milky Way using a multi-component mass model including a stellar disk, a gaseous disk, a bulge/bar component, and a dark-matter halo. The stellar and gas contributions are calibrated using recent observational determinations of the Galactic surface-density distribution, while the dark-matter halo is modelled with standard spherical profiles. We compute the circular-velocity contributions of the different components using a combination of spherical mass reconstruction for the bulge and halo, and thin-disk Hankel-transform methods for the disk and gas components. We first fit the stellar surface-density profile to determine a fiducial bulge-disk decomposition and then use this calibration to predict the Galactic rotation curve. We find that, although the resulting stellar mass model reproduces the observed surface-density profile reasonably well, it does not provide a fully satisfactory description of the rotation-curve data, with the largest discrepancies arising in the inner Galaxy. We then consider an alternative RC-first calibration strategy, in which the bulge and disk parameters are adjusted to improve the kinematic fit. While this significantly improves the agreement with the observed rotation curve, the corresponding stellar surface-density profile becomes inconsistent with the independently inferred baryonic distribution. Our results highlight a tension between photometric and kinematic constraints within simplified axisymmetric models and indicate that a fully consistent description of the Milky Way mass distribution likely requires a more realistic treatment of the bulge/bar structure and of baryonic systematic uncertainties.
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Earth and Planetary Astrophysics

Investigating tidal stripping of a pre-existing moon as the origin of Saturn's young icy rings

Yifei Jiao, Francis Nimmo, Jack Wisdom et al. (+1 more)

The origin of Saturn's rings has been debated for decades. Measurements from Voyager and Cassini have suggested that the rings could be as young as ~100 Myr and composed of nearly pure water ice. Several scenarios have been proposed to explain these properties. One hypothesis (Wisdom et al 2022) is that the rings formed through the recent tidal disruption of a pre-existing moon, Chrysalis, which experienced a close encounter with Saturn following its highly eccentric orbit. However, the mechanism by which this hypothesis would have formed the rings remains largely unexplored, in particular, whether Chrysalis could supply ring material of the desired mass and composition. To address these questions, we perform smoothed particle hydrodynamics simulations to investigate the tidal response of Chrysalis during close encounters with Saturn. Our results demonstrate that preferential tidal stripping of the ice mantle from a differentiated Chrysalis can produce rings with both mass and composition resembling the present rings – provided that the closest encounter occurs between the parabolic Roche limits for ice ~1.53Rs and rock ~1.07Rs – consistent with Wisdom et al 2022. Moreover, multiple close encounters can extend the effective disruption limit by spinning up the body, enhancing the tidal stripping efficiency. Following close encounters, the rocky remnant of Chrysalis would have been removed in less than few kyr, either by collision with Saturn or ejection onto a hyperbolic orbit. These findings support the hypothesis that Saturn's rings could originate from a recent lost moon, and imply a highly dynamical evolution of the Saturnian system over the past few hundred million years.
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All authors Yifei Jiao, Francis Nimmo, Jack Wisdom, Rola Dbouk