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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 21 May

Earth and Planetary Astrophysics · Cross-listed from physics.space-ph

Aurora Hunter: A Two-Stage Framework for Probabilistic Visibility Forecasting

Zongyuan Ge, Chenwaner Zhang, Haoyang Li et al. (+4 more)

Aurora visibility at a given location requires two physically distinct conditions to hold at once: aurora occurring overhead, governed by solar wind-magnetosphere coupling, and observing conditions that permit detection, governed by cloud cover and moonlight. Approaches that conflate the two weaken the space-weather signal and limit cross-site generalizability. We develop Aurora Hunter, a two-stage cascade that separates occurrence prediction from observing-condition assessment. Stage 1 uses 43 physics-driven features to predict P(aurora identifiable in all-sky images) via gradient-boosted trees trained on joint Tromso+Kiruna data (about 16,600 hours, 2015-2023). Stage 2 models P(unobscured image class | identifiable) with logistic regression on 15 observing-condition features, trained on hours with identifiable aurora. The cascade P(visible) = P(identifiable) x P(unobscured | identifiable) achieves retrospective ROC-AUC of 0.958 (Tromso test, 2019-2020) and 0.933 (independent Kiruna, 2024), improving on the occurrence stage used alone by +0.095 and +0.097. Transfer to Skibotn, the one station withheld entirely (2022-2025), is limited. SHAP analysis identifies magnetic local time, the Kp x nightside interaction and the three-hour mean Kp as the dominant features (44% of attribution), consistent with auroral oval physics. Hemisphere-wide occurrence maps combine the Stage 1 amplitude, on a clear-sky basis, with the Feldstein oval parameterization. By providing location-specific visibility probabilities with measured reliability rather than coarse geomagnetic indices, the framework links space weather research to practical observation planning. An operational proof of concept is available at https://aurora-hunter.onrender.com
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All authors Zongyuan Ge, Chenwaner Zhang, Haoyang Li, Hantai Zhang, Wei Zhou, Wenxin Gu, Zhaoming Wang

High Energy Astrophysical Phenomena

Constraining the Photon Intensity of Extragalactic Background Light with the HAWC Observatory for the Blazar Mrk 421

R. Alfaro, C. Alvarez, A. Andrés et al. (+79 more)

The blazar Mrk 421 exhibits rapid variability over a wide range of timescales. Spectral differences have been observed during the different emission states of Mrk 421. During the high emission states, tests to constraint the Hubble constant and the photon intensity of Extragalactic Background Light (EBL) can be performed. The HAWC observatory provides an exceptionally long term monitoring of the source at TeV energies. We selected periods of high emission state and low emission state in data with total observation time of 2460 transits from the HAWC observatory using the All-sky Root around in an Unbiased way methodology. We report on evidence of a cutoff in the spectrum of Mrk 421 during high emission states. An Exponential Cutoff Power Law is preferred over a Simple Power Law at a $3.8\,\sigma$ level. In the Exponential Cutoff Power Law, the cutoff is found at $13\pm3~\text{TeV}$. Using this result, we provide upper limits on the specific intensity of EBL photons. Moreover, the value of the energy cutoff found in our analysis is different from the cutoff expected by the interaction of gamma-rays with EBL photons. This result indicates that the cutoff is intrinsic to the source.
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All authors R. Alfaro, C. Alvarez, A. Andrés, E. Anita-Rangel, M. Araya, J.C. Arteaga-Velázquez, D. Avila Rojas, R. Babu, P. Bangale, E. Belmont-Moreno, A. Bernal, T. Capistrán, A. Carramiñana, F. Carreón, A.L. Colmenero-Cesar, U. Cotti, J. Cotzomi, S. Coutiño de León, N. Di Lalla, R. Diaz Hernandez, B.L. Dingus, M.A. DuVernois, T. Ergin, C. Espinoza, N. Fraija, S. Fraija, J.A. García-González, F. Garfias, J.A. González, N. Ghosh, A. Gonzalez Muñoz, M.M. González, J.A. Goodman, S. Groetsch, J. Gyeong, S. Hernández-Cadena, I. Herzog, F. Hueyotl-Zahuantitla, D. Huang, A. Iriarte, S. Kaufmann, D. Kieda, H. León Vargas, A.L. Longinotti, G. Luis-Raya, K. Malone, O. Martinez, J. Martínez-Castro, H. Martínez-Huerta, P. Miranda-Romagnoli, P.E. Mirón-Enriquez, E. Moreno, M. Mostafá, M. Najafi, L. Nellen, M.U. Nisa, R. Noriega-Papaqui, M. Osorio-Archila, E. Ponce, Y. Pérez Araujo, E.G. Pérez-Pérez, A. Pratts, C.D. Rho, D. Rosa-González, M. Roth, A. Sandoval, M. Shin, A.J. Smith, Y. Son, R.W. Springer, O. Tibolla, I. Torres, R. Torres-Escobedo, E. Varela, L. Villaseñor, X. Wang, I.J. Watson, H. Wu, S. Yu, X. Zhang, H. Zhou, C. de León

High Energy Astrophysical Phenomena

A Strongly Parametrized Mass Ratio Model for the Stable Mass Transfer Channel: a Case Study of the $10 \, \rm{M}_{\odot}$ Peak

Jaxen Godfrey, Lieke van Son and Ben Farr

The mass ratio of merging binary black holes (BBHs) carries information about their formation history, yet has received less attention than masses, spins and eccentricities as a channel discriminator. We derive a strongly parametrized analytical model for the mass-ratio distribution expected from the stable mass transfer (SMT) channel. The model maps mass-transfer stability and accretion efficiency onto the observed mass-ratio distribution, and naturally produces two qualitatively distinct subpopulations: a non-mass-ratio-reversed and a mass-ratio-reversed subpopulation whose distinct shapes depend on the binary-evolution parameters in a traceable way. We embed this model in a hierarchical population analysis and apply it to the $\sim 10\, \rm{M}_{\odot}$ peak in the GWTC-4 BBH catalog. We find that the data favor little to no mass-ratio reversal in this peak, and infer SMT parameters in an astrophysically plausible range. This work demonstrates how data-driven models can be used in mixtures to study singular features in BBH population data and serves as a proof of concept for how a measurement of the BBH mass-ratio distribution within a subpopulation can be translated into direct constraints on the binary-evolution physics that produced it.
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Astrophysics of Galaxies

SDSS+JWST Census of Stellar and Nebular Dust Attenuation at $z \sim 0$-7: Mass Dependence and Redshift Evolution

Jie Song, Masami Ouchi, Tomokazu Kiyota et al. (+3 more)

We present the demography of dust attenuation, including its mass dependence and redshift evolution, using spectroscopic samples of 34,182 SDSS galaxies at $z\sim0.1$ and 863 JWST/JADES galaxies at $z\sim1.5$–$7$. We find that, on average, ${\rm H\alpha}/{\rm H\beta}$ ratios are comparable to the Case B recombination value at $M_\ast \lesssim 10^9 M_\odot$, and increase beyond $M_\ast \sim 10^9 M_\odot$ both at $z\sim0.1$ and $1.5$–$7$. We derive the nebular attenuation $A_{\rm V, nebular}$ from Balmer decrements and the stellar attenuation $A_{\rm V, stellar}$ from rest-frame UV–optical spectra with supplementary GALEX data, via comparisons with stellar-population models and multiple attenuation curves in a consistent manner across cosmic time. We find no significant redshift evolution of $A_{\rm V, nebular}$ and $A_{\rm V, stellar}$ at fixed $M_\ast$ over $z\sim0$–$7$, forming a universal extinction relation, and both rise from $0.2$–$0.4$ at $M_\ast \lesssim 10^9 M_\odot$ to $\sim1$ at $M_\ast \sim 10^{11} M_\odot$. Interestingly, at $M_\ast \gtrsim 10^9 M_\odot$, $A_{\rm V, nebular}$ rises more steeply than $A_{\rm V, stellar}$. This correlation holds within an uncertainty of $\sim\pm0.2$ for various combinations of attenuation curves (Calzetti, SMC, and Milky Way). These results indicate that $M_\ast \sim 10^9 M_\odot$ is a transition mass in dust attenuation, whose low-mass behavior reflects dust widely distributed by feedbacks. These mass-dependent extinction results address the long-standing issue of appropriate choice of the stellar-to-nebular color excess ratio, $f\equiv E(B-V)_{\rm stellar}/E(B-V)_{\rm nebular}=1.0$ or $0.44$, and suggest that galaxy $M_\ast$ determines $f$ from $\sim1.0$ to $\sim0.44$ across low- to high-mass galaxies.
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All authors Jie Song, Masami Ouchi, Tomokazu Kiyota, Chenghao Zhu, Xu Kong, Yurina Nakazato

Earth and Planetary Astrophysics

JWST reveals anomalously enhanced methane outgassing from below Chiron's water ice and carbon dioxide bearing surface

Ian Wong, Silvia Protopapa, Aurélie Guilbert-Lepoutre et al. (+7 more)

Centaurs are inward-scattered Kuiper belt objects, with some exhibiting comet-like activity. The physical mechanisms powering this activity remain poorly understood, with carbon monoxide (CO) sublimation or the crystallization of amorphous water ice commonly invoked as the dominant drivers. Here we present high-resolution JWST spectroscopy of 2060 Chiron, one of the largest known Centaurs, revealing methane and carbon dioxide gas emission with distinct coma spatial morphologies and production rates of $Q_{\rm CH_4}=(1.55\pm0.04)\times10^{27}$ molecules s$^{-1}$ and $Q_{\rm CO_2}=(1.01\pm0.06)\times10^{26}$ molecules s$^{-1}$. The surface spectrum displays spectral signatures attributed to water ice, carbon dioxide, CO, and refractory organic-rich material, while lacking detectable methane ice absorption bands. These findings suggest that carbon dioxide production is sustained by direct surface sublimation, whereas methane originates from the subsurface. The absence of measurable CO emission despite the presence of solid-state CO implies that any surviving primordial CO reservoir remains thermally inaccessible at greater depth below the methane, while irradiation-produced near-surface CO may be inefficiently released from the surface matrix. This inferred volatile stratification may result from long-term thermal evolution or potentially partial differentiation. Chiron differs markedly from other active small bodies, where CO production typically dominates over methane, indicating that Centaur activity may be driven by a broader range of volatile and thermophysical processes than predicted by canonical models.
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All authors Ian Wong, Silvia Protopapa, Aurélie Guilbert-Lepoutre, Geronimo L. Villanueva, Bryan Holler, Rosario Brunetto, Joshua P. Emery, Noemí Pinilla-Alonso, Ana Carolina de Souza Feliciano, Estela Fernández-Valenzuela

Earth and Planetary Astrophysics

Gaia Exoplanet Orbits, Demographics, and Evolution Survey (GEODES): Characteristics of Three Long-Period Companions Accelerating their Host Stars

Judah Van Zandt, Brendan Bowler, Erik Petigura et al. (+12 more)

The upcoming release of $Gaia$ DR4 will yield thousands of giant planet candidates, eventually enabling studies of giant planet eccentricities, masses, and occurrence rates across a broad range of stellar host masses, metallicities, and ages. However, some of these planet candidates are expected to be false positives, and even genuine detections will require additional observations to precisely determine their orbits and masses. We present here the first results of the $Gaia$ Exoplanet Orbits, Demographics, and Evolution Survey (GEODES), an observational campaign to identify the most promising planet candidate hosts for pre-DR4 vetting and post-DR4 validation and characterization. In this paper we showcase three systems from our broader sample exhibiting both tangential and radial accelerations, each representing a distinct outcome of our survey strategy. We combine $Hipparcos$, $Hipparcos$-$Gaia$, $Gaia$ DR2, and $Gaia$ DR3 absolute astrometry with adaptive optics (AO) imaging and precision RVs to constrain companion masses and orbits. HIP 18512, a nearby (15.3 pc) K4V dwarf, hosts a low-mass stellar companion at 10.87" $\pm$ 0.07" (166 AU) which produces significant RV and astrometric accelerations on its host star. The RV trend and astrometric acceleration of the nearby (24.2 pc) K4V star HIP 45839, together with an AO imaging non-detection, constrain the companion to $a$ = 17.9^{+4.8}_{-2.7} AU ($P$ = 70–127 years) and $M$ = 45.2^{+10.5}_{-12.7} $M_{Jup}$. In the case of HIP 81991 (43.8 pc, G5V), the astrometric and RV data indicate that the companion has a separation of 6.4^{+0.6}_{-0.3} AU ($P$ = 14.4–17.7 years) and a mass of 9.5^{+5.4}_{-2.2} $M_{Jup}$, and is more likely a planet (65%) than a brown dwarf (35%).
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All authors Judah Van Zandt, Brendan Bowler, Erik Petigura, Kyle Franson, Jerry Xuan, Marvin Morgan, Lauren Biddle, Rocio Kiman, Jingwen Zhang, Howard Isaacson, B.J. Fulton, Andrew Howard, Justin Crepp, William Thompson, Dori Blakely

High Energy Astrophysical Phenomena

calypso: a Parameter-Conditioned Stochastic Surrogate Model for Circumbinary Accretion Time-Series

Magdalena Siwek, Matt Ho and Earl Bellinger

We present calypso, a parameter-conditioned stochastic surrogate model for circumbinary accretion flows. We represent the total and individual accretion time series in a PCA basis and model the resulting coefficients as draws from a multivariate Gaussian distribution over the latent PCA coefficients. We specifically include the aleatoric uncertainty of the time series in the model, enabling the emulator to capture the inherent stochasticity of the accretion process and the long-term modulation due to disk precession. We further explore the epistemic uncertainty in the model due to limited training data and interpolation in the ($e_{\rm b}$, $q_{\rm b}$) parameter space and find that the data does not support inclusion of this added variance term. We present the properties of existing simulation suites of circumbinary accretion, and run new simulations to fill in gaps in the parameter space, as well as a set of 13 test simulations for validation of the emulator. We publish calypso as a pip-installable Python package with an open-source codebase and comprehensive documentation, and demonstrate use-cases for current and upcoming transient surveys. We additionally derive a closed-form Gaussian likelihood that enables direct inference of ($e_{\rm b}$, $q_{\rm b}$) from observed accretion-rate time series.
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Solar and Stellar Astrophysics

The Solar Dynamics Observatory in the Living With a Star Era: From Solar Observations to Predictive Heliophysics

Madhulika Guhathakurta

The Solar Dynamics Observatory (SDO), launched in 2010 as part of NASA's Living With a Star (LWS) program, represents a methodological transition in heliophysics: from identifying discrete solar events to characterizing the continuously evolving state of the solar atmosphere as the upstream boundary of a coupled Sun-heliosphere-geospace system. By providing co-registered, high-cadence, full-disk measurements via the Helioseismic and Magnetic Imager (HMI), Atmospheric Imaging Assembly (AIA), and Extreme Ultraviolet Variability Experiment (EVE), SDO has enabled the solar atmosphere to be treated as a dynamical system evolving in time. This capability has direct consequences for space-weather specification, ionospheric and thermospheric modeling, heliospheric transport, and the radiation environment relevant to human exploration beyond low Earth orbit. The mission's open-data policy has produced a uniform, continuously calibrated archive contributing to more than 8,400 peer-reviewed publications, enabling statistical, model-driven, and machine-learning approaches. The Space-weather HMI Active Region Patches (SHARPs) are used directly in operational flare probability forecasting and serve as the standard training dataset for machine-learning prediction systems. This perspective traces SDO's scientific lineage, infrastructure role, and the emerging applications of its archive to data-driven approaches and foundation models in the service of predictive heliophysics.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Cuspidal Singularities in Collapsing Domain Walls

Jose J. Blanco-Pillado, Matthew Elley, Francesc Ferrer et al. (+4 more)

Domain wall networks have attracted renewed interest, particularly in relation to the dynamics of network collapse. Accurately describing this process is challenging and typically requires large scale numerical simulations. Here we adopt a complementary approach by studying the collapse of individual closed domain walls, extending previous thin wall analyses and comparing them with adaptive mesh refinement field theory simulations. Firstly, we show that collapsing domain walls generically develop worldvolume singularities of two types: cuspidal edge singularities, consisting of one dimensional singular edges that propagate along the wall surface at the speed of light for a finite time, and cuspidal vertex singularities, which are spike like and instantaneous events where the wall moves momentarily at the speed of light. Both types of features arise generically from smooth initial conditions, and their formation and evolution follow the universal patterns of singularity theory. We show that these structures are captured both by the Nambu-Goto equations and by an eikonal like approximation valid in the relativistic regime. Furthermore, we demonstrate that the same singular structures are reproduced qualitatively in full field theory simulations, establishing that they are not artifacts of the thin wall approximation but robust features of realistic domain wall dynamics. Naturally, such focusing effects in the field theory simulations result in localized regions of high energy density. We briefly discuss possible phenomenological implications.
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All authors Jose J. Blanco-Pillado, Matthew Elley, Francesc Ferrer, Alberto García Martín-Caro, Daniel Jiménez-Aguilar, Oriol Pujolàs, Juan S. Valbuena-Bermúdez

Solar and Stellar Astrophysics

The unique capabilities of HST for stellar physics: Probing Atmospheric Structure, Chromospheres, and Mass Loss of Evolved Stars

Maryam Saberi, Graham Harper, Jacco Th. van Loon et al. (+10 more)

Evolved stars are among the primary sources of chemical enrichment and dust production in galaxies. During the giant phases, stars return a substantial fraction of their mass to the interstellar medium (ISM) through stellar winds, enriching galaxies with newly synthesized elements and dust. However, the atmospheric structure and physical processes that initiate mass loss remain poorly constrained observationally. Understanding the origin, structure, and evolution of stellar chromospheres remains a long-standing problem in stellar astrophysics. While the mechanisms responsible for chromospheric heating and atmospheric dynamics are not fully understood even in the Sun, they become more complex in evolved stars due to pulsation, shocks, convection, extended atmospheres, and possible magnetic activity. Determining the thermal, density, and velocity structure of these extended atmospheres is therefore essential for understanding atmospheric heating, the onset of mass loss, and the late stages of stellar evolution. High-resolution NUV and FUV spectroscopy (R ~ 30,000-100,000) provided by HST/STIS occupies a unique observational parameter space that cannot be replaced by existing facilities. HST/STIS therefore remains essential for understanding the atmospheric physics and mass-loss processes of evolved stars. We highlight the need to preserve and prioritize high-resolution NUV and FUV spectroscopic capabilities with HST. Such programs would provide essential benchmarks for stellar atmosphere modeling, complement ongoing ALMA and optical observations, and help define future UV-optical capabilities for the Habitable Worlds Observatory (HWO).
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All authors Maryam Saberi, Graham Harper, Jacco Th. van Loon, Andrea K. Dupree, Wouter Vlemmings, Susanne Höfner, Theo Khouri, Sven Wedemeyer, Roberta Humphreys, Donald Luttermoser, Atefeh Javadi, Pierre Kervella, Joachim Wiegert

Cosmology and Nongalactic Astrophysics

Gravitational waves from cosmic strings with friction: analytical approximations and parameter space

Sergei Mukovnikov and Lara Sousa

We derive analytical approximations to describe the ultra-high-frequency secondary peak of the stochastic gravitational wave background generated by cosmic strings that is sourced by loops created in the friction-dominated era. We show that these approximations provide a very good description of the contribution of the friction-era loops over the relevant frequency range and for a broad range of cosmic string parameters, thus enabling a fast and accurate characterization of this signature. We also use these approximations to uncover the full parameter range in which this ultra-high-frequency peak should be distinguishable on the stochastic gravitational wave background spectrum and show that it should be present in a broader range of high-energy physics scenarios than originally reported in~\cite{Mukovnikov:2024zed}.
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Solar and Stellar Astrophysics

The first 3D MHD core-collapse progenitors II: Rotation, magnetic-field amplification, and magnetic topology

Adam Griffiths, Miguel-Ángel Aloy and Martin Obergaulinger

The most energetic core-collapse supernovae are thought to arise from rapidly rotating, magnetised progenitors. However, the three-dimensional pre-collapse structure of their angular momentum and magnetic fields remains poorly constrained, limiting the realism of magnetorotational core-collapse simulations. We investigate the angular-momentum distribution, magnetic-field amplification and magnetic topology of physically consistent three-dimensional magnetohydrodynamic pre-supernova progenitors. We used Aenus-Alcar to evolve two compact Wolf–Rayet progenitors, computed with the stellar-evolution codes GENEC and MESA, through the final minutes before core collapse. Our models suggest that the rotation profile near the inner core can depart from a purely shellular distribution and reorganise toward a more cylindrical structure. In convective regions, hydrodynamic Reynolds stresses drive the flow toward an approximately constant specific-angular-momentum profile, corresponding to an average rotation profile close to $\Omega\propto \varpi^{-2}$ ($\varpi$ denotes the cylindrical radius). Convective regions amplify seed magnetic fields, transported from neighbouring radiative layers, producing saturated fields with comparable toroidal and poloidal components and a topology containing substantial small-scale power. As a result, regions that are magnetically disconnected in the original one-dimensional stellar-evolution description become magnetically linked in the multidimensional models. Multidimensional evolution can substantially modify both the angular-momentum distribution and magnetic topology of pre-collapse progenitors. They provide a physically motivated basis for constructing more realistic initial conditions for magnetorotational core-collapse simulations and for improving prescriptions of magneto-convective angular-momentum transport in late stellar evolution.
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Cosmology and Nongalactic Astrophysics

The $\tau$ of Neutral Hydrogen: Increased CMB Optical Depth at Long Wavelengths

Gilbert Holder, Adrian Liu, Tzu-Ching Chang et al. (+1 more)

At wavelengths longer than 21 cm, photons from the long-wavelength tail of the cosmic microwave background (CMB) have a non-zero probability of being absorbed by distant neutral hydrogen. This provides an additional suppression of the observed CMB clustering in addition to the usual Thomson scattering. The optical depth as a function of frequency is sensitive to the 21 cm spin temperature $T_s$ of the gas as a function of cosmic time, with the excess optical depth peaking at a level of a few percent around 100 MHz. The details depend on the specifics of the heating of cosmic gas and the evolution of the neutral fraction $x_{HI}$. It is likely difficult to detect the CMB at these long radio wavelengths, but the cause is aided by the ability to cross-correlate with the already well-characterized fluctuations at cm/mm frequencies. We find that detecting CMB fluctuations at radio wavelengths corresponding to the 21 cm “dark ages” in cross-correlation with mm-wave maps may be easier than detecting the intrinsic 21 cm fluctuations. Measurement of the amplitude of CMB fluctuations as a function of radio wavelength provides a path for a new type of direct measurement of the combination $x_{HI}/T_s$ as a function of redshift.
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All authors Gilbert Holder, Adrian Liu, Tzu-Ching Chang, David Zegeye

Earth and Planetary Astrophysics

Towards Doppler eclipse mapping of hot Jupiters. An observational perspective on WASP-33 b with SPIRou

Vincent Yariv, Xavier Bonfils, Nicolas Cowan et al. (+7 more)

In the last decade, ground-based high-resolution spectroscopy (HRS) has emerged as a powerful method to probe exoplanet atmospheres both in transit and thermal emission. With HRS science now maturing to reveal these planet's thermal, compositional, and dynamical structure in three dimensions, novel strategies will be key to extracting the maximal scientific output from these rich datasets. In this article, we investigate the potential of exploiting eclipses in order to retrieve spatial constraints on exoplanet dayside atmospheres with HRS, as has been successfully applied at lower spectral resolutions with space-based facilities. To attempt this, we obtained an observations of 8 eclipses (ingress and egress) of the ultra-hot Jupiter WASP-33b with SPIRou. We analysed these data with the publicly available ATMOSPHERIX pipeline, which we combined with the starry Python package to fit the eclipse mapping signal. Additionally, we performed injection-recovery tests on archival data to evaluate the detection limits that could be reached with further observations. From our data, we obtain the first tentative detection of CO from in-eclipse data alone, validating that ingresses and egresses may be stacked coherently to boost detection limits. In combination with longer phase-coverage dayside data, our eclipses marginally improve constraints on the planetary rotation velocity. Through injection recovery tests, we show that our results are scaling according to expectations for a synchronously rotating WASP-33b, implying that a further 15 eclipses with SPIRou would be required to measure the planet's rotation using this method. Finally, we present promising detection limits for this method on the population of hot-Jupiters with next generation telescopes, and highlight remaining challenges in data processing for short time series and/or slowly accelerating planets.
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All authors Vincent Yariv, Xavier Bonfils, Nicolas Cowan, Thierry Forveille, Florian Debras, Andres Carmona, Xavier Delfosse, Adrien Masson, Vivien Parmentier, Romain Allart

Solar and Stellar Astrophysics

The first 3D MHD core-collapse progenitors I: General properties, convection and nuclear burning

Adam Griffiths, Miguel-Ángel Aloy and Martin Obergaulinger

The most energetic core-collapse supernovae are thought to arise from rapidly rotating, magnetised progenitors, yet the three-dimensional structure of their pre-collapse interior remains poorly constrained, and realistic distributions of magnetic fields, angular momentum, and convective asphericities are still lacking. We construct physically consistent three-dimensional pre-supernova progenitors including rotation and magnetic fields. In this first paper, we focus on the behaviour of turbulence and nuclear burning in the shells surrounding the stellar core, and assess their deviations from one-dimensional stellar-evolution models. We used Aenus-ALCAR to perform three-dimensional magnetohydrodynamic (MHD) simulations of two compact Wolf–Rayet progenitors obtained from the stellar evolution codes GENEC and MESA. The models were mapped into the multidimensional domain several minutes before collapse and evolved until the onset of core collapse. We find that in extended oxygen-burning shells, turbulent velocities exceed the standard mixing-length-theory (MLT) predictions by approximately a factor of two. In contrast, a thin silicon-burning shell is poorly described by MLT: mixing is reduced near both shell boundaries, and the inferred effective diffusion profile departs significantly from the standard one-dimensional prescription. These differences directly affect the spatial extent and efficiency of nuclear burning. We present the first 3D MHD pre-supernova progenitors of this kind, suitable for subsequent collapse and explosion calculations, and show that multidimensional effects can significantly modify turbulent mixing and shell burning during the final stages of massive-star evolution. We propose prescriptions to account for these effects in the advanced phases of stellar evolution.
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Earth and Planetary Astrophysics

JWST-DECO: The Impact of Accretion on Mid-Infrared Observable Water in Planet-forming Disks

Jenny K. Calahan, Tarisai Dziire, Karin Öberg et al. (+13 more)

The inner few au of a protoplanetary disk hosts the majority of observed exoplanets and is the primary planet-forming zone of the disk. The mid-IR spectra of disks, with its rich forest of water lines, provides key insights into the composition of forming planets. One of the strongest trends seen with data from Spitzer and now JWST is a correlation between the increase in water line flux and accretion luminosity of a system. We set out to reproduce and understand this trend by adding an accretion module to the thermo-chemical code DALI, and explore how viscous accretion heating and the addition of accretion luminosity impacts the 2D temperature structure and the observable water reservoir. We reproduce the trend that the observed water mass increases with accretion rate, with hot, warm, and cool water being more to less strongly correlated, respectively. Our model suggests that these trends are due to an increased emitting area with accretion rate, with some of the cool and warm population becoming hidden underneath an optically thick dust surface and being constrained to a smaller disk volume. This trend is driven by the accretion-related increase in central luminosity, while viscous heating centralized to the midplane has no impact on observed water mass.
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All authors Jenny K. Calahan, Tarisai Dziire, Karin Öberg, Andrea Banzatti, L. Ilsedore Cleeves, Felipe Alarcón, Geoffrey A. Blake, María José Colmenares, Camilo González-Ruilova, Aashish Gupta, Claudio Hernández-Vera, Till Kaeufer, Sebastiaan Krijt, Charles J. Law, Tamara Molyarova, Joe Williams

Earth and Planetary Astrophysics

Star-planet interaction in the Proxima system

M. R. Zapatero Osorio, V. J. S. Béjar, A. Suárez Mascareño et al. (+14 more)

(Abridged) We search for evidence of star-planet magnetic interactions in the nearby Proxima Centauri planetary system using high-quality, high-spectral-resolution optical observations. We measure a photospheric stellar rotation period of 84.9 +/- 0.6 d and a half-rotation period of 44.3 +/- 0.2 d, consistent with previous studies. Using FeI absorption and emission lines, we find that Proxima Centauri was flaring during 4.8 +/- 4.7 % of the observing time, with significant statistical evidence (>99.8 %) of flare events likely phase-locked to the inner Mars-mass planet Proxima d. Modeling the star-planet interaction via the helicity-driven reconnection mechanism with the Poynting flux formalism, we estimate a likely polar magnetic field of -16 G for Proxima d (assuming a Mars-sized radius), with a plausible range of 3-280 G accounting for radial and dipolar stellar magnetic field configurations, planetary radii comparable to Mars and Earth, and the observed range of stellar flare intensities. This represents the first such estimate for a terrestrial exoplanet. Evidence for a potential star-planet interaction with the outer, Earth-mass Proxima b arises not from phase-locked flare clustering, but from modulation of flare intensities. Applying a prewhitening analysis to the full time series of combined chromospheric Halpha, NaI D1 and D2, and CaII H &K lines reveals peaks, in order, at half the stellar rotation period, Proxima b's orbital period, the full stellar rotation, and Proxima d's orbital period. All evidence suggests that both planets show magnetic interaction with their host star. Focusing on flaring epochs only, the periodogram of these chromospheric lines shows a peak consistent with the synodic period between half the stellar rotation and the mutual synodic period of Proxima b and d, implying prograde stellar rotation and planetary orbits.
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All authors M. R. Zapatero Osorio, V. J. S. Béjar, A. Suárez Mascareño, R. Rebolo, S. Cristiani, G. Micela, P. A. Miles-Páez, N. C. Santos, E. Pallé, J. I. González Hernández, M. Damasso, A. Castro-González, C. J. A. P. Martins, F. Pepe, A. Sozzetti, B. Lavie, J. Rodrigues

High Energy Astrophysical Phenomena

Magnetic field dynamics in isolated neutron stars with an external dipole field

Aurora Capobianco, William Cook, Sebastiano Bernuzzi et al. (+2 more)

Neutron stars can harbor extremely strong magnetic fields, yet the structure and stability of their magnetic field configuration remain poorly understood. Observations of pulsars indicate that the large-scale external field is predominantly dipolar far from the star, while the internal magnetic configurations are largely unconstrained. We investigate the dynamical stability of magnetized neutron stars through long-term numerical-relativity simulations. We explore a range of models with an initial external dipole field and mixed poloidal-toroidal internal field where the energy of the toroidal component varies up to $90\%$ of the magnetic energy. We find that the internal magnetic field relaxes toward a dynamically stable mixed poloidal-toroidal geometry, in which the toroidal component contributes to $\lesssim10\%$ of the total magnetic energy both in the exterior and in the interior. This configuration emerges within one Alfvén time following the saturation of the Tayler instabilities and also aided by gravitational-wave emission. These results suggest that long-lived neutron star magnetic fields are strongly constrained toward stable mixed configurations, with important implications for pulsar emission models, magnetar evolution, and the interpretation of gravitational-wave signals from magnetized remnants.
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All authors Aurora Capobianco, William Cook, Sebastiano Bernuzzi, Brynmor Haskell, Jacob Fields

High Energy Astrophysical Phenomena

Strong X-ray Variability of I Zwicky 1: Obscuration from Clumpy Accretion-Disk Winds

Jian Huang, Bin Luo, W. N. Brandt et al. (+2 more)

Obscuration from clumpy accretion-disk winds has been invoked to explain the extreme X-ray weakness and X-ray variability observed in a substantial fraction of super-Eddington accreting quasars. We present a comprehensive study of the strong X-ray variability of the super-Eddington accreting active galactic nucleus (AGN) I Zwicky 1 (I Zw 1), a prototypical narrow-line} Seyfert 1 galaxy (NLS1), to test the disk-wind obscuration scenario as the underlying mechanism and characterizing the disk-wind absorber properties. We focus on spectral and temporal analyses of simultaneous XMM-Newton and NuSTAR observations in 2020, and a 100-day NICER monitoring campaign in 2022. Despite strong X-ray variability by factors of $\approx3$ and $\approx6$ on short-term and long-term timescales, respectively, the XMM-Newton Optical Monitor observations do not show contemporaneous significant UV variability, and archival data reveal only mild long-term optical/infrared variability ($\approx30\%$), indicating a stable accretion process in I Zw 1. The strong X-ray variability thus likely arises from variable absorption of relatively stable coronal emission. We perform time-resolved X-ray spectroscopy utilizing a partial-covering absorption model with a stable corona and varying ionized absorbers. We identify three distinct absorbers whose variations in the column density and covering factor successfully explain the observed X-ray “flares” in 2020 and the longer-term spectral evolution in 2022. Our results support a unified scenario in which obscuration from clumpy disk winds produces the strong X-ray variability observed in super-Eddington accreting AGNs. This scenario may be applicable to other NLS1s exhibiting strong X-ray variability to better characterize the disk winds driven by super-Eddington accretion.
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All authors Jian Huang, Bin Luo, W. N. Brandt, Luis C. Ho, Qingling Ni

Solar and Stellar Astrophysics

Mg II h&k spectral line properties computed using 3D radiative transfer in an enhanced network region simulated with the MURaM-ChE code

P. Ondratschek, D. Przybylski, H.N. Smitha et al. (+3 more)

The Mg II h&k lines form in the middle to upper chromosphere and are well-suited to study the structure of the chromosphere. However, the details of their formation in the solar chromosphere are not fully understood. We aim to study the effects of 3D radiative transfer (RT) on the Mg II h&k line properties and to verify known correlations between the underlying atmosphere and spectral line features in a new model of the chromosphere. We forward model the Mg II h&k lines in 3D RT with partial frequency redistribution (PRD) in a self-consistent 3D radiative magnetohydrodynamics (rMHD) simulation with non-local-thermodynamic-equilibrium (NLTE) energy transport and non-equilibrium (NE) hydrogen ionization of an enhanced network (EN) region simulated with the chromospheric extension of MURaM (MURaM-ChE). The spatially averaged Mg II h&k spectral lines computed with 3D RT match approximately a typical IRIS observation. The peak separation is still slightly lower in the simulation. In the MURaM-ChE model, the qualitative difference between 1.5D and 3D RT results is even more pronounced than in the public Bifrost snapshot, as given in the literature. We found that this large discrepancy might partly be attributed to the horizontal velocities that are naturally included in the full 3D RT synthesis but not in typical 1.5D RT computations. We confirm that correlations between spectral line properties and the underlying atmosphere from the MURaM-ChE simulation are similar to those obtained from Bifrost, but show more scatter due to the more dynamic atmosphere. The Mg II h&k lines computed with 3D RT match the observations better in the core intensities and their distribution on the Sun compared to 1.5D computations. This underlines the importance of 3D RT in the forward modeling of Mg II h&k.
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All authors P. Ondratschek, D. Przybylski, H.N. Smitha, J. Leenaarts, R. Cameron, S.K. Solanki

Astrophysics of Galaxies

No Blue without Red: Evolutionary Properties of Super-Early Galaxies

A. Ferrara, G. Rodighiero, S. Carniani et al. (+3 more)

The discovery of numerous luminous, super-early galaxies at $z>10$ by JWST has revealed a striking diversity in their ultraviolet (UV) properties, ranging from extremely blue, dust-poor systems to a smaller population of significantly reddened sources. We investigate the physical origin of this diversity within the framework of the Attenuation-Free Model (AFM), in which radiation-driven outflows redistribute dust to large galactic radii, reducing the effective attenuation. Starting from a sample of 32 spectroscopically confirmed super-early galaxies, we apply the detailed AFM analysis to a subset of 17 systems with suitable size constraints and derive their key physical properties, including halo mass, star formation efficiency, metallicity, and outflow extent. We find that these systems reside in massive halos ($\log M/M_\odot \sim 10.7$) and exhibit moderate ($0.01 < \epsilon_* < 0.05$) star formation efficiencies, while frequently reaching super-Eddington conditions that trigger powerful outflows. Within the AFM framework, we propose a possible evolutionary sequence in which galaxies transition from a dust-obscured “Red Monster” phase to a UV-bright “Blue Monster” phase as outflows clear their central regions. The recently confirmed red galaxy EGS-z11-R0 at $z=11.45$ is naturally interpreted as a system observed during this obscured phase. Compact ($r_e < 150$ pc) sources are instead difficult to reconcile within AFM; we speculate that their emission is dominated by an AGN. Our results provide a coherent interpretation of super-early galaxy properties and highlight the key role of radiation-driven outflows in shaping galaxy evolution at cosmic dawn. Future observations with JWST and ALMA will be essential to test these predictions and further constrain the nature of the earliest galaxies.
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All authors A. Ferrara, G. Rodighiero, S. Carniani, Z. Zhang, M. Kohandel, B. Das

High Energy Astrophysical Phenomena

A Precise Measurement of the Fermi-LAT Galactic Center Excess Morphology and Spectrum

Mattia Di Mauro

We present a new Fermi-LAT analysis of the Galactic-center excess (GCE) designed to substantially reduce the dominant systematic uncertainties associated with interstellar-emission and source modeling in the inner Galaxy. Using an optimized multi-step fitting procedure together with an iterative source-finding pipeline, we achieve a markedly improved agreement between data and model, reducing fractional residuals to $\lesssim 10\%$ over a $40^\circ\times 40^\circ$ region centered on the Galactic center. We analyze a suite of GALPROP-based interstellar-emission models (IEMs) and complementary analysis variants (Galactic-plane masking, fits restricted to $1$-$10$ GeV, and weighted-likelihood fits) to quantify robustness. The reconstructed surface-brightness profile is strongly centrally concentrated and is well described by an approximately spherical generalized Navarro-Frenk-White morphology with inner slope $\gamma \simeq 1.15$. Bulge-tracing templates (nuclear bulge plus boxy bulge) fail to reproduce the full radial morphology, most notably for line-of-sight angles around $\theta\simeq 1^\circ$-$2^\circ$ and at $\theta \gtrsim 8^\circ$, whereas the DM-motivated component provides a good description over the full angular range. Moreover, the DM component remains highly significant across all IEMs and analysis choices, including fits that simultaneously include the bulge templates. We also provide an updated measurement of the GCE spectrum from $0.5$ to $1000$ GeV, confirming a peak at a few GeV and setting stringent constraints above tens of GeV, where we obtain only upper limits at the level $E^2\Phi \lesssim 10^{-8}$ GeV cm$^{-2}$ s$^{-1}$ sr$^{-1}$. These results deliver a sharpened and systematically controlled characterization of the GCE morphology and spectrum, enabling more incisive tests of astrophysical and dark-matter interpretations.
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Solar and Stellar Astrophysics

Mergers via failed common envelope as a route towards intermediate-mass stripped stars

Annachiara Picco, Pablo Marchant, Daniel Pauli et al. (+1 more)

Stripped stars are a common product of binary stellar systems and span a wide mass range from Wolf-Rayet stars to hot subdwarfs and helium white dwarfs. The recent discovery of intermediate-mass stripped stars, with masses between those of WRs and subdwarfs, provides a continuous evolutionary sequence and valuable test beds for binary interaction models. Population synthesis studies explain the formation of stripped products through stable mass transfer or common envelope evolution. Recently, however, a merger scenario (or, "failed common envelope") between a stripped star and a post-main sequence companion was suggested to explain the formation of the magnetic intermediate-mass stripped star HD 45166. In this Letter, we investigate this channel using detailed interacting binary simulations at Galactic metallicity and model their stripped merger products. We find that these merger products can contribute to the population of stripped stars across the Hertzsprung-Russell diagram and produce a blue-straggler effect, with merger masses spanning from 6 to 14 solar masses. These objects would be consistent with long-lived core He-burning stars retaining thin hydrogen envelopes after a partial CE ejection, and they would appear as single or members of wide binaries that were originally hierarchical triples.
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All authors Annachiara Picco, Pablo Marchant, Daniel Pauli, Hugues Sana

Cosmology and Nongalactic Astrophysics

A No-Go Theorem for the Mass-Radius Relation of Solitons

Mohammad Hossein Namjoo

We prove a no-go theorem for the mass-radius relation of localized and stable field configurations, known as solitons. Defining the mass-radius index by $\Gamma \equiv \frac{{\rm{d}}\ln M}{{\rm{d}}\ln R}$, for real scalar field theories in $d$ spatial dimensions, we show that typical non-topological, non-relativistic, and spherically symmetric solitons cannot have $\Gamma$ in the range $[0, d]$. The forces considered originate from gradient energy, self-interaction, and gravitation, with the typicality assumption excluding the fine-tuned region of the parameter space where all three forces have comparable strength. Importantly, the theorem works for an arbitrary self-interaction that, in the relativistic theory, is allowed to be non-power-law in the field, be non-analytic around the classical vacuum (where the field amplitude vanishes), or to include derivative couplings. Additionally, the theorem makes no assumptions about the explicit form of the soliton's density profile or the behavior of $\Gamma$ as a function of $R$. We also argue that the same exclusion applies to compact objects formed from self-gravitating, non-relativistic, barotropic fluids with arbitrary equations of state. As a consequence for cosmology, it is worth noting that observations favor a core in the centers of dark matter halos with $\Gamma \simeq 1.7$, which (for $d=3$) lies approximately in the middle of the excluded range. Therefore, proposals such as ultra-light or fluid-like dark matter models are essentially ruled out as natural explanations for halo cores, provided other astrophysical effects are negligible.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Gravitational Field of a Rotating Mass on an Expanding Universe

Antonio Peña Peña

We present a new exact solution to Einstein's field equations that unifies the Kerr black hole with Friedmann-Lemaître-Robertson-Walker cosmology. This metric reduces to Kerr-de Sitter in the appropriate limit and accounts for cosmological expansion dynamics both inside and outside the black hole. The model predicts a stationary mass, as well as a contracting ergosphere and event horizon with respect to the expanding cosmic rest frame. This result correctly generalises the McVittie metric to rotating masses or Kerr-de Sitter to arbitrary scale factors $a(t)$. Additionally, we find that the ergosphere tends to fade away with respect to the universe's expansion and no further interactions of dark energy with respect to the black hole's rotation.
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Astrophysics of Galaxies

From protogalaxy through thick and thin: Why did the Milky Way evolve in three kinematic phases?

Olti Myrtaj, James S. Bullock, Michael Boylan-Kolchin et al. (+9 more)

APOGEE and Gaia data suggest the Milky Way's kinematic structure evolved through three distinct phases: a disordered protogalaxy, which “spun up” into a thick stellar disk, and then “cooled down” to a final cold, thin stellar disk. We use a suite of FIRE-2 cosmological zoom-in simulations of Milky Way-mass galaxies to demonstrate that the same three phases arise in simulations, and we study their physical origin. In our simulations, the early protogalaxy phase occurs when the rate of cool gas ($T \leq 10^4$ K) converting into stars is low, star formation is bursty, and the baryonic mass “sloshes” within the host potential with respect to the center of mass. The gas begins to spin coherently after sloshing ends, followed by the spin-up of young stars. The central potential is least concentrated just prior to gas spin-up. This second, thick disk phase coincides with the highest rate of cool gas converting into stars, though star formation remains bursty. The final transition to the thin disk phase occurs when the inner circumgalactic medium virializes, and is associated with steady star formation and intermediate consumption rates of cool gas converting into stars. Mergers do not appear to play a defining role in driving transitions between the three phases. The condition for thick disk formation appears to be minimal: a stable center of mass motion. Thin disk formation requires more: gas must accrete slowly enough for its angular momentum to mix and become coherent prior to joining the galaxy.
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All authors Olti Myrtaj, James S. Bullock, Michael Boylan-Kolchin, Vedant Chandra, Claude-André Faucher-Giguère, Robert Feldmann, Francisco J. Mercado, Jorge Moreno, Jonathan Stern, Andrew Wetzel, Pratik J. Gandhi, Luke Xia

Solar and Stellar Astrophysics

A very rapidly rotating white dwarf in nova YZ Reticuli

G. J. M. Luna, N. Rawat, R. Angeloni et al. (+4 more)

YZ Ret (Nova Reticuli 2020) is the first VY Scl-type nova-like variable observed to undergo a classical nova eruption. Following the outburst, timing analysis of 20-s cadence TESS data revealed a periodicity at approximately 42 s, suggesting a possible classification as a fast-spinning Intermediate Polar. To definitively identify the nature of this modulation, we performed a multi-instrument timing analysis using high-speed ground-based photometry Zorro/Gemini South (1 s cadence) and the South African Astronomical Observatory (5 s cadence) alongside TESS Sector 97 observations. Our ground-based data reveal a highly coherent period of 37.69131 +- 0.00001 s, which we identify as the true rotation period of the white dwarf. We demonstrate that the apparent 42.61 s signal in the TESS data is a Nyquist alias of this fundamental frequency. Furthermore, the signal amplitude in the TESS data is suppressed by a factor of ~0.6 relative to the Gemini observations, a result consistent with the theoretical sinc-function damping expected for a 20-s integration time. The extreme coherence and long-term stability of the 37.69131 s signal rule out transient phenomena such as dwarf nova oscillations or non-radial pulsations. We conclude that YZ Ret hosts a fast-spinning magnetic white dwarf in an Intermediate Polar configuration. This discovery implies that mass loss during the nova eruption was likely driven by a fast magnetic rotator wind and provides a physical explanation for the missing supersoft X-ray phase, suggesting that nearly the entire accreted envelope was exhausted, promptly quenching the nuclear burning.
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All authors G. J. M. Luna, N. Rawat, R. Angeloni, M. Orio, S. Scaringi, A. Dobrotka, J. Magdolen

Earth and Planetary Astrophysics

Variation of Venusian Gravity Wave Absolute Momentum Fluxes and Drag as Retrieved from the Akatsuki Mission

Erdal Yiğit and Emilia Sloan

Using temperature retrievals from Akatsuki radio occultation measurements, we characterize gravity wave activity as a function of vertical wavenumber and altitude and, for the first time, estimate the absolute horizontal momentum fluxes and the magnitude of the associated gravity wave drag (i.e., wave acceleration), which quantify the potential effects of these waves in the Venusian middle atmosphere between 40–95 km. Observed temperature perturbations, which are indicative of atmospheric gravity wave activity, reach amplitudes of approximately $\pm$10 K, and significant momentum flux (10–30 m$^2$ s$^{-2}$) and wave drag (0.003–0.03 m s$^{-2}$) are detected across all analyzed profiles. The inferred wave drag represents a lower bound on the total gravity wave-induced drag in the Venusian atmosphere. Momentum flux tends to increase exponentially with altitude below approximately 50–60 km, then peaks and attenuates at higher altitudes. Wave drag becomes prominent where momentum flux begins to decrease, which is a consequence of wave dissipation. Both quantities exhibit multiple altitude-localized maxima, which is consistent with upward wave propagation followed by dissipation at different altitudes for different vertical wavelengths. Damping due to gravity wave nonlinear interactions is likely to play the major role in limiting the growth of wave amplitudes and fluxes with height. These features are observed across a range of latitudes and local times. Overall, the results provide observational constraints on gravity wave momentum transport and dissipation in the Venusian middle atmosphere and could guide numerical models in their effort to quantify wave-mean flow interactions in Venus's atmosphere.
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Cosmology and Nongalactic Astrophysics

Primordial black holes in excursion set theory: Formation probabilities, mass functions, and window functions

Hayami Iizuka, Daiki Saito and Koki Tokeshi

We study the mass function of primordial black holes (PBHs) within the excursion-set theory, in which the response of the stochastic density contrast to the variation of the coarse-graining scale is described by colored noises. For several window functions often used in the literature, we investigate how this choice affects the formation probability as well as the resultant mass function of PBHs. It is found that the low-mass tail of the mass function differs from the one predicted from Carr's formula. The difference comes from the prevalence of correlated noises, by which degeneracy of the formation probabilities ceases to exist. Nevertheless, Carr's formula still provides a practical estimation in the vicinity of the characteristic mass scale, as long as a smooth window function in Fourier space is used.
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High Energy Astrophysical Phenomena

Generation of Quantum Turbulence by Neutrino Cooling in Neutron Stars

J. A. Sauls

The interior crust and much of the liquid core of neutron stars is believed to be a quantum liquid mixture of neutron and proton superfluids and a relativistic electron liquid. Quantized vortices in the neutron superfluid and quantized flux lines in the proton superconductor are topological defects of these hadronic condensates. I consider the formation of the superfluid state in young neutron stars under non-equilibrium conditions imposed by the neutrino cooling rate. The nonequilibrium phase transition implies that the onset of superfluidity is accompanied by the generation of quantized vortices based on the mechanism envisioned by Kibble in the context cosmic string formation in an evolutionary models of an expanding universe, and further developed by Zurek for nonequilibrium phase transitions in quantum liquids such as $^4$He. I discuss the Kibble-Zurek mechanism (KZM) and scaling relations for topological defect formation starting from the Cooper pair fluctuation propagator for temperatures approaching $T_c$. I then calculate the predicted vortex densities based on Urca and modified Urca cooling mechanisms in the cores of neutron stars for several models of the superfluid gap and transition temperature of the interior neutron superfluid. In all cases studied the KZM leads to a large density of topological defects in the condensate phase, which in 3D form a random network of vortex lines and loops, i.e. the generation of quantum turbulence.
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