Showing new listings for Wednesday, 15 April 2026

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Keyword list: ['star formation', 'star-forming', 'molecular cloud', 'interstellar medium', 'cloud', 'clump', 'core', 'filament', 'atomic gas', 'N-PDF']

Excluded: ['galaxies', 'galaxy cluster', ' AGN ', 'standard candle', 'X-ray binar', 'solar corona']

Today: 17papers

Finite temperature effects on g-modes of inviscid neutron stars

• Authors: David Morales-Zapien, Prashanth Jaikumar, Thomas Klähn

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)

• Arxiv link: https://arxiv.org/abs/2604.11815

• Pdf link: https://arxiv.org/pdf/2604.11815

• Abstract We study the effect of temperature on secular, compositional $g$-modes in the core of inviscid neutron stars. Using a chiral $SU(2)_f$ sigma model, we construct isentropic temperature profiles for hot and dense matter and find that the frequency of the global core $g$-mode's dependence on temperature is governed by the nuclear symmetry energy slope parameter $L$. As a result, the $g$-mode frequency of a warm neutron star can be either higher or lower than that of its cold counterpart, depending on $L$. Our results highlight the interplay of thermal effects and composition gradients, and demonstrate the potential of neutron star $g$-mode observations to constrain the density dependence of the symmetry energy.

JWST Observations of Starbursts: Dust Processing in the M82 Superwind

• Authors: Serena A. Cronin, Alberto D. Bolatto, Helena M. Richie, Grant P. Donnelly, Rebecca C. Levy, Karl D. Gordon, Elizabeth Tarantino, Martha L. Boyer, Lee Armus, Patricia A. Arens, Leindert A. Boogaard, Daniel A. Dale, Keaton Donaghue, Bruce T. Draine, Sara E. Duval, Kimberly Emig, Deanne B. Fisher, Simon C. O. Glover, Brandon S. Hensley, Rodrigo Herrera-Camus, Ralf S. Klessen, Thomas S.-Y. Lai, Laura Lenkić, Adam K. Leroy, Ashley E. Lieber, Ilse De Looze, Sebastian Lopez, David S. Meier, Elisabeth A.C. Mills, Karin M. Sandstrom, Evan Schneider, Kaitlyn E. Sheriff, Utsav Siwakoti, Evan D. Skillman, J.D.T. Smith, Yu-Hsuan Teng, Todd A. Thompson, Alexander G.G.M. Tielens, Sylvain Veilleux, Vicente Villanueva, Fabian Walter, Paul P. van der Werf

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2604.11873

• Pdf link: https://arxiv.org/pdf/2604.11873

• Abstract We present JWST MIRI and NIRCam imaging of the inner ~5 kpc of the M82 superwind at 0.05-0.375'' (~0.9-6.5 pc) resolution. Targeted filters probe emission from polycyclic aromatic hydrocarbons (PAHs; F335M, F360M, F770W, F1130W) and continuum (F250M, F360M). The images reveal a network of cool wind filaments traced by PAHs. PAH surface brightness declines with the inverse square of distance to the midplane, suggesting that the incident radiation field from the starburst drives the observed PAH intensity out to 2.5 kpc. The 3.3/11.3 and 3.3/7.7 band ratios show uniformity with distance from the starburst, though comparisons with mid-IR dust emission models indicate a modest shift toward larger PAHs. Outside the disk, 11.3/7.7 increases moderately, reflecting that PAHs become more neutral with distance from the starburst as they are exposed to a declining radiation field and ionization parameter. Overall, PAHs in the wind are consistent with standard-to-large sizes and standard-to-high ionization states. Including Spitzer and Herschel data, PAH abundance (qPAH) is set at ~1% in the starburst and remains unchanging out to 5 kpc off the disk. This flat qPAH profile suggests that PAHs are shielded from the hot wind, perhaps residing in the surface layers of cool clouds, with possible replenishment from cloud interiors and enrichment of the halo from previous bursts. In this picture, clouds are not dense enough to promote PAH growth, and they likely undergo radiative cooling and mixing with the hot phase to survive the gauntlet for at least ~20 Myr.

Spectral index evolution of the limb-brightened jet in 3C 84

• Authors: L. C. Debbrecht, G. F. Paraschos, E. Ros, T. P. Krichbaum, U. Bach, M. A. Gurwell, J. A. Hodgson, M. Janssen, J.-Y. Kim, M. M. Lisakov, N. R. MacDonald, D. G. Nair, J. Oh, J. A. Zensus

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2604.11875

• Pdf link: https://arxiv.org/pdf/2604.11875

• Abstract Relativistic jets launched by active galactic nuclei are fundamental for understanding the physics of accreting supermassive black holes and their immediate environment, yet the mechanisms driving jet launching remain uncertain. In this study, we investigate the sub-parsec jet of 3C 84 using multi-epoch, multi-frequency, very long baseline interferometry (VLBI) observations with the European VLBI Network and the Very Long Baseline Array at 22 and 43 GHz. We analyse the evolution of the spectral index gradient in the core region to relate the observed structure to physical interpretations and to discriminate between competing jet launching models. Furthermore, we examine the impact of the ambient medium and magnetic field configuration on jet morphology and dynamics over time, and explore their connection to a coinciding $\gamma$-ray flare. Our spectral analysis reveals significant changes across three epochs, indicating dynamic activity between filamentary structures on sub-parsec scales, evolving magnetic fields, and a complex interaction with the surrounding medium, all of which shape the innermost jet and may influence its high-energy emission.

Beyond the Diffusion Coefficient: Propagators and Memory in Cosmic Ray Transport

• Authors: Naixin Liang, S. Peng Oh

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

• Arxiv link: https://arxiv.org/abs/2604.11898

• Pdf link: https://arxiv.org/pdf/2604.11898

• Abstract Cosmic ray (CR) transport is usually modeled with a single diffusion coefficient, but this description captures only the growth of the variance and not the full transport process. Distinct transport mechanisms can share the same effective diffusion coefficient while producing different particle distributions and approaches to the diffusive limit. This limitation is especially relevant in realistic multiphase, structured, and time-dependent media, and is also reflected in observed environmental variations in CR transport near pulsar wind nebulae, supernova remnants, and molecular clouds. Particle-tracing studies also show clear departures from standard diffusion, including both superdiffusion and subdiffusion. We therefore develop a propagator-based framework centered on $P(x,t)$, the probability distribution of particle positions, or equivalently its Fourier-Laplace transform $P(k,s)$. This object is compact and statistically complete, and naturally exposes memory: the CR flux can depend on earlier gradients when unresolved trapping or phase changes are coarse-grained away. Using the Montroll-Weiss formalism, we show how to measure $P(k,s)$ directly from trajectories, how to recover the associated memory kernel, and how to represent broad kernels efficiently with a Prony expansion. Applied to a multiphase medium, the framework shows that slow regions can regulate escape without dominating the total residence-time budget. We also introduce an accelerated Monte Carlo method for coarse-grained transport, and show that if trapping structures evolve while particles are still sampling them, the static long-time limit need not be reached. This paper provides the foundation for future observational applications, particle-tracing measurements, and CR-MHD closures.

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

• Authors: Łukasz Tychoniec, Logan Francis, Maria Gabriela Navarro, Jakobus M. Vorster, Ewine F. van Dishoeck, Alessio Caratti o Garatti, Korash Assani, Valentin J. M. Le Gouellec, Benoît Tabone, Pamela Klaassen, Adriaan G. M. Janssen, Kay Justtanont, Daniel Harsono, Pooneh Nazari, Simon Reyes, Katerina Slavicinska, Caroline Gieser, Tyler Bourke, Yao-Lun Yang, Brunella Nisini, Teresa Giannini, Henrik Beuther, R. Devaraj, Thomas P. Ray, Nashanty G. C. Brunken, Yuan Chen, Martijn L. van Gelder

• Subjects: Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2604.11904

• Pdf link: https://arxiv.org/pdf/2604.11904

• Abstract Protostellar winds can theoretically lift solids from the planet-forming disks, but direct evidence for launched dust has been scarce so far. Numerous atomic lines that are unique to mid-infrared (IR) wavelengths reveal refractories eroded from dust grains and provide information on wind properties in the earliest stages of the star formation process. We present JWST/MIRI-MRS spectral imaging of the inner 2000 au of the BHR71-IRS1 blueshifted side of the outflow. Atomic line intensities are compared to shock models to constrain the physical conditions and elemental abundances of the outflowing gas. Dust continuum maps are constructed from PSF-subtracted cubes, and the dust spectral energy distribution is analyzed. The ionized central jet of BHR71-IRS1 is spatially resolved and imaged for the first time, revealing a unique inventory of refractory, volatile, and noble-gas fine-structure lines (Fe, Ni, Co, Cl, S, Ne, Ar). The emission is concentrated along four bright knots that wiggle along the jet axis. PSF-subtracted continuum maps reveal extended mid-IR continuum emission co-spatial with the jet bullets and within the H$_2$-traced outflow cone. Spectral energy distributions along the jet are fit together with the extinction, revealing a warm (200-400 K) and a cold (70-90 K) dust component. Shock modeling constrained by the mid-IR lines indicates a decline in shock velocity from 70 to 35 km s$^{-1}$ and pre-shock density from $>$10$^5$ to $ 4\times 10^4$ cm$^{-3}$ with distance from the protostar. Gas-phase Fe and Ni are measurably depleted relative to Solar abundances, consistent with a substantial fraction of refractories remaining locked in grains in spite of the shocks. These JWST observations provide direct evidence that dust is launched in a Class 0 jet and at least partly survives shock processing.

No Country for Old Stars -Spectroscopic confirmation of the first intermediate-age RR Lyrae in the open cluster Trumpler 5

• Authors: Valentina D'Orazi, Cecilia Mateu, Giuliano Iorio, Alexey Bobrick, Zdenek Prudil, Ricardo Salinas, Angela Bragaglia, Lyudmila Mashonkina, Raffaele Gratton, Ilya Ilyn, Natalia Alvarez Baena, Vittorio F. Braga, Antonino Nunnari, Venu Kalari, Felice Cusano, Silvia Tosi

• Subjects: Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2604.11955

• Pdf link: https://arxiv.org/pdf/2604.11955

• Abstract RR Lyrae stars are widely considered tracers of ancient (greater than 10 Gyr), metal-poor stellar populations. However, recent kinematic and photometric studies suggest the existence of a metal-rich RRL sub-population associated with the thin disc and intermediate ages (approximately 2-5 Gyr), challenging canonical evolutionary models. We aim to provide the first spectroscopic confirmation of a member of this elusive population. Specifically, we target a metal-rich RRL candidate recently identified photometrically as a member of the intermediate-age open cluster Trumpler 5. We obtained high-resolution spectroscopy using PEPSI at the LBT and GHOST at Gemini-South Telescope. We measured radial velocities from multiple epochs to constrain cluster membership and derived detailed chemical abundances (Mg, Ca, Sc, Ti, Mn, Fe, Cu, Zn, Y, and Ba) to compare the RRL's composition with that of red clump stars in the cluster. The RRL's systemic velocity Vgamma = 50.57 +0.78/-0.36 km/s is in excellent agreement with the cluster mean V = 50.76 +/- 0.49 km/s. Combining RVs, proper motions, and parallax, the probability of the star being a background interloper is negligible (approximately 0.002%, better than 4 sigma). We derived a metallicity of [Fe/H] = -0.40 +/- 0.05, matching the cluster value. While most abundance ratios (Mg, Ti, Mn, Cu, and Zn) align with cluster members, the RRL exhibits significant depletion in Ca, Sc, Y, and Ba. Notably, [Sc/Fe] is under-abundant by approximately 0.6 dex relative to the cluster stars, following trends seen in field metal-rich RRLs. We provide strong constraints on the membership status between an RRL variable and an intermediate-age open cluster [...]

On the possibility of chemically driven convection in red giants. Implications for the He-core flash and mixing above the Red Giant Branch Bump

• Authors: M. Miguel Ocampo, Marcelo M. Miller Bertolami

• Subjects: Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Fluid Dynamics (physics.flu-dyn)

• Arxiv link: https://arxiv.org/abs/2604.12117

• Pdf link: https://arxiv.org/pdf/2604.12117

• Abstract Turbulent mixing remains one of the primary uncertainties in the modeling of stellar interiors. In stellar evolution simulations, regions where mixing occurs are typically identified using instability criteria. A particularly interesting situation arises when nuclear reactions produce inversions in the mean molecular weight within stellar interiors. Under these conditions, the material can become unstable to either thermohaline or a Rayleigh-Taylor instabilities. We demonstrate that the standard criterion adopted in stellar evolution calculations does not accurately distinguish between these two regimes. We derive an alternative criterion and show that chemically driven convection in stellar interiors might be viable under much smaller mean molecular weight inversions than it is normally assumed. We investigate whether inversions in the mean molecular weight can trigger chemically driven convection above the red giant branch bump (RGBB) or during the helium core flash. We find that the inversion at the base of the convective envelope above the RGBB is too weak and short-lived to sustain steady-state convection. In contrast, rapid carbon production at the base of the He-flash-driven convective zone can maintain a steady chemically driven convective region. This process could significantly alter our understanding of the He-core flash and warrants further study.

Inspecting Cloudy Substellar Atmospheres with JWST MIRI Synthetic Magnitudes from Spitzer Mid-infrared Spectra

• Authors: Jolie LHeureux (1 and 2), Genaro Suárez (3), Johanna M. Vos (4), Stanimir Metchev (5 and 6), Jacqueline K. Faherty (3), Sherelyn Alejandro Merchan (1 and 3), Kelle L. Cruz (1, 3, and 7) ((1) Department of Physics, Graduate Center, City University of New York, New York, USA, (2) Department of Astronomy, Columbia University, New York, USA, (3) Department of Astrophysics, American Museum of Natural History, New York, USA, (4) School of Physics, Trinity College Dublin, Dublin, Ireland, (5) Department of Physics and Astronomy, Western University, London, Canada, (6) Institute for Earth and Space Exploration, Western University, London, Canada, (7) Department of Physics and Astronomy, Hunter College, City University of New York, New York, USA)

• Subjects: Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

• Arxiv link: https://arxiv.org/abs/2604.12132

• Pdf link: https://arxiv.org/pdf/2604.12132

• Abstract We examine the positions of substellar objects in mid-infrared color-magnitude and color-color diagrams to distinguish between cloudy and cloud-free atmospheres. Using Spitzer mid-infrared spectra of 113 M5-T9 ultracool dwarfs, we derive synthetic photometry for the JWST MIRI F560W, E'770W, F1000W, and F 1280W filters, which cover key absorption features including the ~9 um silicate signa-ture. We find that diagrams involving F770W and F1000W best separate L-type objects with silicate clouds in their photospheres. L dwarfs with mE77ow - mF1000w < 0.03 mag are seven times more likely to host cloudy atmospheres. Diagrams using F1000W and F1280W are less informative due to the lower signal of the spectra at long wavelengths. Current model predictions struggle to reproduce the positions of cloudy, warm brown dwarfs, likely because atmospheric models underestimate the ~9 um silicate feature. Cloudy Sonora Diamondback models better match the observed trends, although this may reflect improvements capturing indirect effects of clouds on the 6.25 um water absorption feature rather than accurately modeling the silicate feature itself. Our analysis indicates that JWST MIRI photometry can efficiently identify new cloudy extrasolar atmospheres for targeted spectroscopic follow-up, optimizing the use of telescope time.

A First Principles Approach to the 100,000-year Problem

• Authors: Liam Wheen

• Subjects: Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Chaotic Dynamics (nlin.CD); Atmospheric and Oceanic Physics (physics.ao-ph)

• Arxiv link: https://arxiv.org/abs/2604.12143

• Pdf link: https://arxiv.org/pdf/2604.12143

• Abstract The 100,000-year problem concerns the dominant period of glacial-interglacial cycles over the past 800,000 years and their correlation with Earth's orbital eccentricity, despite eccentricity's weak influence on solar radiation. Two theories compete: the astronomical theory, in which orbital forcing drives the cycles with amplification from Earth system feedbacks, and the geochemical theory, in which internal dynamics dominate with orbital forcing synchronising oscillations. We investigate these theories using conceptual models. Augmentations to the Budyko energy balance model fail to reproduce the 100,000-year period, revealing formulation limitations. Linearised versions of existing non-linear ice volume models perform comparably to their full counterparts, indicating the data does not necessitate non-linear dynamics. We develop two simple linear models: a feedforward model aligned with the astronomical theory and a feedback model aligned with the geochemical theory. The feedforward model reproduces the ice volume record well and offers a novel explanation for the absence of eccentricity's 400,000-year period, arising from oceanic heat storage and tropospheric energy responding with differing phase lags. Conservative estimates show bulk ocean temperature variation can be explained by eccentricity alone, challenging the geochemical theory's core assumption. We also show that widespread use of Q65 may bias models towards geochemical explanations by underrepresenting eccentricity. The feedback model's improvement is concentrated around Marine Isotope Stage 11, suggesting this anomalous interglacial reflects Earth-based events rather than a general requirement for feedback mechanisms. We conclude that 800,000 years of glacial cycles can be largely reproduced by a linear astronomical model, emphasising the importance of parsimony when interpreting palaeoclimate data.

Probing Collapsed Dark Matter Halos with Fast Radio Bursts

• Authors: Yuxuan He, Weiyang Wang, Chen Zhang, Yi-Ming Zhong

• Subjects: Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

• Arxiv link: https://arxiv.org/abs/2604.12189

• Pdf link: https://arxiv.org/pdf/2604.12189

• Abstract Observations of ultra-dense substructures in strong lensing systems challenge the standard cosmological model at small scales. Self-interacting dark matter (SIDM), as an alternative to the cold and collisionless dark matter (CDM) of the standard cosmological model, provides a natural mechanism for forming such structures via gravothermal core collapse. We show that strong gravitational lensing of fast radio bursts (FRBs) provides an effective approach to detecting these substructures and probing dark matter self-interactions. Core-collapsed SIDM halos exhibit steeper central density profiles than CDM halos, enhancing the lensing cross section and producing longer time delays between FRB images. We compute lensing properties of core-collapsed subhalos and host halos, including maximal impact parameters and time-delay distributions. We demonstrate that future all-sky monitors, such as BURSTT, SKA2-Low, and SKA2-Mid, which are expected to detect $10^{5}$--$10^{7}$ FRBs over a decade, can measure time-delay distributions with high statistical significance. Modeling collapsed halos with a cored power-law density profile with inner slope $\gamma=3$ and assuming no excess beyond the singular isothermal sphere lens model, we show that our strategy can probe self-interaction cross section strengths of $\sigma_{\text{SI}}/m \gtrsim \min{18,, 40\lambda_{\text{sub}}},\text{cm}^2/\text{g}$, where $\lambda_{\text{sub}}$ parameterizes the collapse time of a subhalo relative to that of the isolated case.

POLARIS: A Sparse Radial Neutrino Telescope Design for the Pacific Ocean

• Authors: Karolin Hymon, Alexander Chen, Meng-Xue (Mark)Tsai, Wan-Ting Hseu, Tzu-Hsuan (Shane)Su, Anatoli Fedynitch

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

• Arxiv link: https://arxiv.org/abs/2604.12521

• Pdf link: https://arxiv.org/pdf/2604.12521

• Abstract The cubic-kilometer neutrino telescopes have opened neutrino astronomy as an observational discipline. The recent detection of KM3-230213A, the highest-energy neutrino ever observed at ~220 PeV, as a near-horizontal muon track underscores that the ultra-high-energy frontier is accessed through horizontal directions where the Earth's opacity above ~100 TeV confines the observable sky to a narrow band around and above the horizon. Yet extending general-purpose detector architectures into this regime requires disproportionate increases in instrumentation, cost, and logistical complexity. A compelling alternative is to deploy specialized detectors that target this natural geometry. POLARIS (Pacific Ocean Large Area Radial Instrumented Sparse array) is a sparse planar deep-water Cherenkov array optimized for neutrino-induced muon tracks from horizontal directions in the multi-TeV to PeV regime. By rotating the conventional vertical string layout into a radial planar configuration, the detector presents maximal cross-section to horizontal tracks while naturally suppressing the down-going atmospheric background. With only 1100 optical modules, the five-arm design reaches point source and diffuse flux sensitivities at PeV energies competitive with detectors deploying several times more instrumentation. As a dedicated $\nu_\mu$ track detector, POLARIS provides the muon-flavor channel that tau-optimized experiments such as TAMBO and Trinity do not cover, enabling full flavor composition measurements from astrophysical sources. Using the Prometheus simulation framework, this study demonstrates that targeted sparse geometries can open new discovery space at the high-energy frontier at a fraction of the cost of general-purpose arrays.

Deriving volume density profiles of filaments from observed surface densities

• Authors: Alexander Men'shchikov, Guo-Yin Zhang

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)

• Arxiv link: https://arxiv.org/abs/2604.12570

• Pdf link: https://arxiv.org/pdf/2604.12570

• Abstract Accurate characterization of filamentary structures in star-forming clouds is essential for understanding star formation. Traditional methods fit observed surface density profiles $\Sigma(r)$ with slope $\gamma$ and width $H$ using the Plummer function, assuming $\beta=\gamma+1$ and $h\approx H$ for the volume density slope and width. These assumptions are inconsistent with the finite nature of filaments. We present a new fitting method that explicitly accounts for finite cylindrical geometry and establishes self-consistent empirical relationships between the parameters of $\Sigma(r)$ and those of the volume density profile $\rho(r)$ with slope $\beta$ and width $h$. The method was validated on model profiles and applied to California filaments. The slope difference $\delta\equiv\beta-\gamma$ falls below unity for shallow ($\beta\lesssim 2$) and compact profiles; $h$ and $H$ can differ by over an order of magnitude for extended filaments with shallow slopes. Accurate parameter recovery requires high resolvedness $R\equiv H/O\gtrsim 10$ (where $O$ is the beam width); at lower resolvedness, slopes are severely overestimated and filaments remain unresolved even when $H\gg O$. The traditional Plummer function yields systematically overestimated slopes. Accurate deconvolution requires a priori knowledge of the true parameters, creating a fundamental circular problem whose only robust solution is obtaining sufficiently high angular resolution. Current far-infrared observations typically lack sufficient resolution, and some previously reported filament properties may require reinterpretation.

Phlegethon: a fully compressible magnetohydrodynamic code for simulations in stellar astrophysics

• Authors: G. Leidi, A. Holas, K. Vitovsky, F. Rizzuti, A. Roy, J. Reichert, K. Bayer, D. Gagnier, R. Andrassy, P. Christians, P. V. F. Edelmann, V. Varma, R. Hirschi, F. K. Röpke

• Subjects: Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Instrumentation and Methods for Astrophysics (astro-ph.IM)

• Arxiv link: https://arxiv.org/abs/2604.12672

• Pdf link: https://arxiv.org/pdf/2604.12672

• Abstract We present PHLEGETHON, a fully compressible, Eulerian magnetohydrodynamic (MHD) code designed for multidimensional simulations in stellar astrophysics. The code uses a time-explicit, second-order, finite-volume method optimized to model a wide range of dynamical processes in stars, from very low-Mach-number turbulent convection in the cores of massive stars to supersonic flows in subsurface convection zones. PHLEGETHON employs low-dissipation Riemann solvers and a well-balanced method to accurately capture slow flows arising from strongly stratified media. The induction equation is solved using a staggered constrained-transport method to ensure divergence-free evolution of the magnetic field. The MHD equations are coupled to arbitrary nuclear reaction networks solved in a time-implicit approach, together with super-time-stepping for efficient treatment of thermal diffusion. Equations of state appropriate for stellar plasmas are available, accounting for partial ionization, electron degeneracy, and electron-positron pair production. The code is implemented in a compact and user-friendly manner, and it scales to tens of thousands of CPU cores using MPI-based domain decomposition. We perform several verification tests to demonstrate the accuracy and versatility of the code, and present simulations of magnetoconvection in a core-collapse supernova progenitor star. The rich variety of physical effects and numerical methods implemented in PHLEGETHON enables the code to model diverse multidimensional processes that play a crucial role in stellar-interior dynamics, such as reactive convection, convective boundary mixing, internal-wave excitation, and magnetic-field amplification mechanisms. Within a single framework, these phenomena can be investigated across a wide range of stellar evolutionary stages, from main-sequence stars to supernova progenitors. PHLEGETHON is publicly accessible online.

Illuminating the Local Universe: Large-Scale Structure from ZTF Type Ia Supernovae

• Authors: Antoine Gilles Lordet, Ariel Goobar, Jens Jasche, Stuart McAlpine, Jesper Sollerman, Young-Lo Kim, Mickael Rigault, Madeleine Ginolin, Umut Burgaz, Eric C. Bellm, Matthew J. Graham, Joahan Castaneda Jaimes, Frank J. Masci, Josiah Purdum, Reed Riddle

• Subjects: Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

• Arxiv link: https://arxiv.org/abs/2604.12714

• Pdf link: https://arxiv.org/pdf/2604.12714

• Abstract Within the volume-limited subsample at $z&lt;0.06$ of the Zwicky Transient Facility (ZTF) DR2 sample, we confirm a statistically significant excess of Type Ia supernovae (SNe Ia) at $z \simeq 0.02$-$0.04$, previously reported but not explained by survey selection effects. Forward simulations assuming a uniform volumetric SN Ia rate and realistic ZTF detection efficiencies fail to reproduce the feature at the $5$-$7\sigma$ level. We also detect an excess in the rates compared to our survey simulations at $z \simeq 0.08$ and $0.14$, albeit at smaller significance. To investigate the origin of these inhomogeneities, we compare the observed SN distribution to constrained reconstructions of the local matter density field from the Manticore project, based on Bayesian forward modelling of the 2M++ galaxy catalogue. While SN overdensities are spatially associated with prominent nearby structures such as the Perseus, Coma, and Hercules superclusters, the amplitude of the SN excesses significantly exceeds that expected from matter overdensities alone. By reconstructing a redshift-dependent volumetric SN Ia rate, we find that local enhancements can reach factors of two to five within specific clusters, while the sample-averaged rate remains consistent with previous low-redshift measurements. These results indicate that the SN Ia rate is not a linear tracer of the underlying matter density and suggest a strong environmental dependence in dense structures. We discuss possible physical origins and highlight the implications for low-redshift SN cosmology, including correlated peculiar velocities and additional covariance beyond standard linear corrections.

The role of accretion efficiency, natal kicks, and angular momentum transport in the formation of the Gaia black holes

• Authors: Michela Mapelli, Cecilia Sgalletta, Johanna Müller-Horn, Giuliano Iorio, Stefano Rinaldi, Christian Burt, Daniel Marín Pina, Amedeo Romagnolo

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2604.12839

• Pdf link: https://arxiv.org/pdf/2604.12839

• Abstract Gaia has the potential to deliver several tens of new dormant black holes (BHs) with low-mass stellar companions (hereafter, Gaia BHs) in the upcoming fourth data release. Three Gaia BHs are already known, but their formation pathways remain uncertain. Here, we perform a large parametric study to explore the formation of Gaia BHs from isolated binary systems with the population-synthesis code SEVN and compare our models with the properties of the three already reported Gaia BHs. Specifically, we explore the impact of accretion efficiency, mass transfer stability, natal kicks, angular momentum transport, and core-collapse supernova prescriptions. We find that models in which stable mass transfer is highly non-conservative and angular momentum is lost as a wind from the donor surface (Jeans mode) maximize the probability of forming dormant systems that match the properties of the observed Gaia BHs in terms of both orbital period and eccentricity, because such assumptions prevent the initial orbit from shrinking too much when the BH progenitor fills its Roche lobe. If we allow for common-envelope evolution, we find that models with common-envelope ejection efficiency $\alpha{} &lt; 1$ predict dormant systems with orbital periods that are too short compared to the observed Gaia BHs. The eccentricity of the observed Gaia BHs, when combined with information about orbital period and BH mass, favors relatively large natal kicks, similar to those inferred from Galactic neutron stars. Finally, models in which the natal kicks are low - e.g. because they are modulated by fallback - result in the formation of a large population of dormant BHs with long orbital periods ($P_{\rm orb}&gt;10^4$ days) and low eccentricity, which will be tested soon by the fourth Gaia data release.

JWST observations of photodissociation regions. IV. Carbonaceous emission band sub-components in NGC 7023 have distinct spatial distributions

• Authors: D. Van De Putte (1 and 2), K. D. Gordon (2 and 3), K. Misselt (4), A. N. Witt (5), A. Abergel (6), A. Noriega-Crespo (2), P. Guillard (7), M. Zannese (6), M. Elyajouri (2), B. Trahin (2 and 6), P. Dell'ova (6), M. Baes (3), P. Klaassen (8) ((1) Department of Physics & Astronomy, The University of Western Ontario, (2) Space Telescope Science Institute, (3) Sterrenkundig Observatorium, Universiteit Gent, (4) Steward Observatory, University of Arizona, (5) Ritter Astrophysical Research Center, University of Toledo, (6) Institut d'Astrophysique Spatiale, Université Paris-Saclay, CNRS, (7) Sorbonne Université, CNRS, Institut d'Astrophysique de Paris, (8) United Kingdom Astronomy Technology Centre)

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2604.12860

• Pdf link: https://arxiv.org/pdf/2604.12860

• Abstract We analyze JWST spectroscopy of the northwest filament of NGC7023, where the relatively soft radiation field results in a photodissociation region with an extended atomic hydrogen region, and strongly pronounced variations of the carbonaceous emission band profiles. We focus on the 16.4 and 17.4 um bands and their relation to the main bands at 3.3, 3.4, 5.2, 5.7, 6.2, 7.7, 8.6, 11.3, and 12.7 um, and aim to identify which bands and sub-features originate from co-spatial emission carriers. We apply a PAHFIT spectral decomposition to measure the emission bands and their individual sub-components, and produce maps that spatially resolve the main dissociation front (DF1). Nearly all emission maps peak at DF1, while the relative intensity in the atomic hydrogen region (ATM) varies strongly. We classify the features into spatial distribution types based on the intensity ratio in ATM relative to DF1. Most bands are of type I (low ATM/DF1; 3.3, 3.4, 5.2, 5.7, 11.3 um) or II (medium ATM/DF1; 16.2, 7.7, 8.6, 12.7, 16.4 um), while only few are of type III (high ATM/DF1; 11.0, 17.4 um). A breakdown of the 5.7, 7.7, 11.3 and 12.7 um bands into blue and red sub-components reveals that contributions on the blue side are of type III, while those on the red side are of type I or II. These strongly differing spatial distributions reveal that at least two different populations contribute to the 16-18 um range, and that these populations are also connected to the profiles of the 5.7, 7.7, 11.3, and 12.7 um bands. The maps further indicate a continued evolution of these profiles toward the central cavity of NGC7023, where fullerene emission (C60) was previously detected. We speculate that the population of emission carriers could be in an intermediate photochemical evolution stage that precedes fullerene formation.

High-energy Processes in the Bubbles of Wolf-Rayet Stars: The case of WR 102

• Authors: L. Espinosa, M. V. del Valle

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

• Arxiv link: https://arxiv.org/abs/2604.12993

• Pdf link: https://arxiv.org/pdf/2604.12993

• Abstract Supersonic winds from massive stars carry great amounts of kinetic power and modify the surrounding interstellar medium. Through this interaction a stellar bubble is formed. Theoretical studies and recent observations suggest that the winds of massive stars could be sources of Galactic cosmic rays. The first detection of synchrotron emission from the bubble of a single star was reported, indicating the presence of relativistic electrons. Studying the non-thermal emission from a single massive star can help to better understand the acceleration of particles taking place in massive star clusters. WR 102 is the perfect case of study. In this work, we present the first high-energy model for the bubble of WR 102: G2.4+1.4. We aim at fitting the radio data and predicting gamma-ray emission. We assume that both electrons and protons are accelerated at the wind shock. We applied a classical model for the stellar bubble and adopted a one-zone model for estimating the radiation produced by the relativistic particles near the acceleration region. Additionally, we computed the expected emission from the protons that diffuse to the outer regions of the bubble. Also, we estimated the leptonic and hadronic contributions expected from cosmic rays. We fitted the observations considering that 3% of the wind kinetic power goes into relativistic electrons, and a magnetic field of 250 $\mu$G. The dominant component at high energies is produced by locally accelerated protons reaching the shell. Protons might reach PeV energies in the wind bubble, but the predicted gamma-ray flux is too low to be detectable.

by olozhika (Xing Yuchen).

2026-04-15