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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 6 October

Astrophysics of Galaxies

Early galactic heavy element production - a phenomenological approach

B. Wehmeyer, D. Blaschke, F.K. Röpke et al. (+1 more)

The high abundances of heavy elements in early, extremely metal-poor stars is still an unsolved issue in Galactic Chemical Evolution (GCE). Standard approaches, such as mergers of neutron stars, have several difficulties, and several non-merger production channels are under discussion. Here, we suggest that pre-enriched inflow might explain the heavy elements seen in low metallicity stars in the Galaxy. To characterize the conditions of the origin of such a pre-enriched infall, we apply a heavy-element freeze-out approach. We characterize the initial distribution by Lagrange parameters which are nonequilibrium generalizations of temperature and chemical potentials. We then speculate about the origin of such a pre-enriched infall: The required nonequilibrium conditions might be found in cosmological fluctuations in the early Universe, and might be connected to the formation of primordial black holes.
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All authors B. Wehmeyer, D. Blaschke, F.K. Röpke, G. Röpke

Cosmology and Nongalactic Astrophysics

Probing beyond the Cosmic Horizon

Tarun Souradeep

There are reasons to believe that the region of uniform curvature that we observe within our horizon is perhaps a tiny patch, much smaller than the length scales of inhomogeneity and global connectivity of an extremely complicated manifold. However, the recent supernova (SN) results suggest that the horizon scale could be comparable to or even much larger than curvature radius. Non trivial global structure too tends to be of the order of the local curvature scale. Probing (slightly) beyond the cosmic horizon can potentially reveal nontrivial global structure lurking around or just beyond the horizon scale. The cosmic microwave background (CMB) anisotropy is a sensitive probe of the universe on length scales up to and somewhats beyond the horizon scale and is perhaps poised to detect or put interesting limits on nontrivial features the global structure. This point is exemplified by high CMB anisotropy signal of the Elliptical topology in a large fraction of the revised parameter space of the closed FRW universe (spherical geometry) currently preferred by SN observations.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Axion Pyramid

Chan-Gyung Park, Dahee Lee, Hyerim Noh et al. (+1 more)

A pronounced pyramid-shaped enhancement in the axion density power spectrum induced by the QCD phase transition is identified. The enhancement occurs near the horizon scale at the transition, with a characteristic comoving length scale comparable to the size of the Solar System, and amplifies the axion density perturbation by factors exceeding $3.5 \times 10^{13}$ relative to the CDM case. Under the hilltop initial condition, coupling to radiation triggers this enhancement. The initial condition is related to the axion mass, suggesting that observation of the axion pyramid in cosmology may constrain the QCD axion mass.
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All authors Chan-Gyung Park, Dahee Lee, Hyerim Noh, Jai-chan Hwang

Earth and Planetary Astrophysics

HD 715 b, a Warm Jupiter Orbiting a Massive Subgiant Discovered from a Single TESS Transit

Alexander Venner, Robert A. Wittenmyer, Andrew Vanderburg et al. (+23 more)

Transiting Warm Jupiters orbiting bright stars are scarcely known, but a substantial number of these planets have been uncovered by the TESS mission. In this work we report the discovery and confirmation of a transiting Warm Jupiter orbiting the bright ($V$ = 8.70) subgiant star HD 715 (TOI-6893). HD 715 b was originally identified from a single transit event in TESS Sector 70. We acquired two seasons of radial velocity follow-up using the PFS, TRES, and MINERVA-Australis spectrographs, which clearly detect the planetary orbit. At $M_*=1.60\pm0.04 M_\odot$, HD 715 thus becomes one of the most massive stars known to host a transiting Warm Jupiter. From a joint fit to the TESS transit and our RVs, we find that HD 715 b has a $56.40^{+0.19}_{-0.23}$ day orbital period and measure a precise mass and radius of $0.635\pm0.056 M_J$ and $1.07\pm0.04 R_J$, rendering it a relatively typical member of the Warm Jupiter population. The moderate orbital eccentricity of $0.21^{+0.07}_{-0.08}$ contrasts with the higher eccentricities of other similar Warm Jupiters orbiting evolved stars, indicating a greater diversity in orbital eccentricities than previously known. The absence of additional transits in preceding TESS observations in Sectors 42 and 43 allows us to further refine the range of possible orbital periods to $[56.01, 56.35]$ days. Though the ephemeris uncertainty remains substantial, future photometric observations may nonetheless allow for recovery of the transit of HD 715 b.
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All authors Alexander Venner, Robert A. Wittenmyer, Andrew Vanderburg, Karen A. Collins, David W. Latham, Allyson Bieryla, Tyler R. Fairnington, Chelsea X. Huang, Timothy R. Bedding, Samuel Grunblatt, Sydney Jenkins, R. Paul Butler, Jeffrey D. Crane, Jhon Yana Galarza, Jonathan Horner, Steve B. Howell, Marc Huten, Stephen R. Kane, David Osip, Marcelo Said Tala Pinto, Samuel N. Quinn, Johanna Teske, Steve Shectman, Shreyas Vissapragada, Duncan Wright, George Zhou

Cosmology and Nongalactic Astrophysics

Third-order scalar induced gravitational waves during a matter-dominated era: secular growth and implications for primordial black hole domination

Jing-Zhi Zhou

We investigate scalar induced gravitational waves (SIGWs) at third-order during a matter-dominated (MD) era. We classify the sources into four parts—built from three first-order scalars, and from a first-order scalar times the second-order tensor, vector, and scalar perturbations—and obtain all four kernel functions analytically in closed form. Unlike their radiation-dominated counterparts, the MD kernel functions grow secularly, translating into a rapid growth of the spectrum, $\Omega^{(3)}_{\mathrm{GW}}\propto x^{6}$ versus $\Omega^{(2)}_{\mathrm{GW}}\propto x^{2}$ at $x\equiv k\eta\gg1$. We derive the third-order power spectrum as a five-fold integral for a general primordial spectrum, and evaluate it numerically for a monochromatic one, where all contributions from the second-order vector source vanish identically. As an application, we consider the early MD era driven by primordial black holes (PBHs) before their evaporation. Requiring that the induced gravitational waves do not backreact on the cosmological perturbations, $\int\mathrm{d}\ln k\, \Omega^{\mathrm{tot}}_{\mathrm{GW}}<1$ then bounds the initial PBH abundance as $\Omega_{\mathrm{PBH},f}\lesssim4.6\times10^{-7}\, (m_{\mathrm{PBH}}/10^{7}\,\mathrm{g})^{-0.48}$, about three orders of magnitude stronger than the second-order-only bound. Our results indicate that higher-order SIGWs inevitably become nonperturbative during a sufficiently long MD era, with important implications for scenarios involving an early matter domination.
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Solar and Stellar Astrophysics

Does Diffusive Shock Acceleration Reach Steady State? Insights from a Near-Sun Shock Observed by Parker Solar Probe

Immanuel Christopher Jebaraj, Mikhail Malkov, Nicolas Wijsen et al. (+7 more)

Collisionless shocks accelerate particles at a rate set by the diffusion coefficient of those particles in waves they themselves generate. Theory fixes that coefficient only in steady state, and no measurement has tested whether an evolving shock ever reaches that state. We report Parker Solar Probe observations of a fast, near-parallel interplanetary shock at 0.24 au, encountered four hours after eruption, with the upstream waves and the protons they scatter recorded on the same magnetic field line. From the wave spectra alone we derive the parallel mean free path of 0.05-30 MeV protons, resolved in energy and in distance from the shock. The mirror force of the measured compressive fluctuations supplies the scattering through the pitch angles that gyroresonance cannot reach. The mean free path grows with distance nearly as the steady self-generated solution requires, yet the steady balance holds at one energy only, near 1.3 MeV. The intensity profiles are a factor of two shallower than the measured coefficient predicts, because the waves are still growing. Confinement fails between 2.3 and 6 MeV, beginning a factor of two below what the age of the shock allows. The growth of the waves its own particles drive, rather than its age or its size, limits the energy an evolving shock confines.
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All authors Immanuel Christopher Jebaraj, Mikhail Malkov, Nicolas Wijsen, Oleksiy Agapitov, Athanasios Kouloumvakos, Alexandr Afanasiev, Federico Fraschetti, Edin Husidic, Christina Cohen, Rami Vainio

Cosmology and Nongalactic Astrophysics

Fast and accurate differentiable code of the galaxy power spectrum based on Eulerian and Lagrangian one-loop perturbation theories

Yosuke Kobayashi and Kazuyuki Akitsu

This paper presents a JAX-Python implementation of the galaxy power spectrum up to one-loop order in the effective field theory of large-scale structure, based on both the Eulerian and Lagrangian perturbation theories. The code uses JAX to enable automatic differentiation with respect to parameters such as cosmology, galaxy bias, or counterterm coefficients. This facilitates applications such as parameter inference using the gradient of the posterior, e.g., Hamiltonian Monte Carlo sampling. The code can compute both the EPT and LPT power spectra in a few milliseconds on a GPU, after just-in-time compilation. We also identify the various sources of numerical errors associated with discretization, and design the numerical implementation to minimize them, achieving relative errors of order $0.01\%$ at scales $k \lesssim 1\, h\, \mathrm{Mpc}^{-1}$, compared with brute-force numerical integration. Notably, this is the first auto-differentiable implementation of the one-loop galaxy power spectrum based on LPT. The natural resummation of the long-wavelength displacements in LPT further makes the code well suited for applications involving features in the power spectrum beyond the standard BAO feature, including primordial features. Our code, elf, is publicly available.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Time-Frequency Analysis for LISA: Galactic Foreground Modulation

Sudhi Mathur and Neil J. Cornish

Observations by the Laser Interferometer Space Antenna (LISA) will contain time-varying, cyclostationary confusion noise from the Galaxy, which is naturally handled using time-frequency analysis methods. We present a fast, forward model that maps the parameterized Galactic gravitational-wave luminosity density onto the annually modulated, unresolved confusion foreground in the complete set of time-delay interferometry channels. The line-of-sight luminosity integral is evaluated on a HEALPix grid and decomposed into spherical harmonics, while the detector response is decomposed analytically, independent of the Galaxy model, such that a new Galactic model costs a single map evaluation, transformation, and contraction. We compute the modulated covariance beyond the standard low-frequency limit, expanding the LISA response to second order in finite armlength corrections, and to first order in the unequal-arm corrections. These effects change the normalized modulation curves by up to $\sim\!0.23\%$ and $0.64\%$ for finite armlength corrections at $3$ and $5$ mHz respectively, and by $\sim\!0.074\%$ and $0.71\%$ for unequal-arm corrections in the self and cross channels respectively. Using the fast, forward model and a notional disk-and-bulge Galaxy model, we construct a Fisher matrix from the time-dependent channel covariance and forecast that one year of observation constrains the disk scale width and scale height relative to the distance to the Galactic center at the $8\%$ and $12\%$ levels respectively, and leaves the strongly correlated bulge fraction and bulge radius individually unconstrained.
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High Energy Astrophysical Phenomena

Scalable and sequential inference of the neutron star equation of state with the Einstein Telescope

Thibeau Wouters, Thomas C. K. Ng, Hauke Koehn et al. (+4 more)

Future gravitational-wave observatories such as the Einstein Telescope will detect tens of thousands of binary neutron star mergers per year, making gravitational waves a dominant probe of the neutron-star equation of state in the coming decades. However, extracting this information requires hierarchical inference across a rapidly growing catalog of events, and existing methods must restart from scratch whenever a new event arrives, making them impractical at this scale. In this Letter, we introduce a hybrid sequential Monte Carlo algorithm that combines data and likelihood tempering to adaptively update the equation-of-state posterior in batches, reusing previous inference results instead of restarting from a wide prior. Accelerated by GPU hardware, our method infers the equation of state from a simulated month of around 1500 binary neutron star mergers in a few hours on a single GPU, and we project that a full year of detections could be processed in a few days on current hardware. This establishes sequential Monte Carlo as a practical route for real-time hierarchical inference with future gravitational-wave detectors.
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All authors Thibeau Wouters, Thomas C. K. Ng, Hauke Koehn, Fabian Gittins, Peter T. H. Pang, Tim Dietrich, Chris Van Den Broeck

Instrumentation and Methods for Astrophysics

Optimizing Laguerre-Gaussian Mode Interferometry in Gravitational-Wave Detectors through Modal Degeneracy Breaking

Liu Tao, Eleonora Capocasa and Matteo Barsuglia

Higher-order Laguerre-Gaussian modes can reduce test-mass thermal noise in gravitational-wave interferometers, but their implementation is limited by degeneracy-induced coupling losses in realistic high-finesse cavities. We mitigate these losses by optimizing the mirror curvature to break modal degeneracy. We develop a general framework for designing an axisymmetric corrective test-mass surface profile that lifts the degeneracy of the sixth-order Laguerre-Gaussian subspace while preserving an injected donut-shaped $\mathrm{LG}_{0,6}$ mode. Expanded in a Fourier-Bessel basis, the profile is optimized to maximize the frequency splitting from the nearest unwanted mode while minimizing target-mode loss. For a Virgo-like Fabry-Perot arm cavity, the optimized profile separates the $\mathrm{LG}_{0,6}$ resonance from the nearest same-order resonance, $\mathrm{LG}_{1,4}$, by 2.04% of the free spectral range, reducing unwanted-mode gains below unity at the target-mode resonance and suppressing their resonant enhancement. The profile introduces negligible target-mode loss and improves robustness against astigmatism and realistic mirror surface distortions. Monte Carlo simulations with realistic mirror imperfections yield an average contrast defect of 368 ppm and an average reflected optical loss of 979 ppm, equivalent to a round-trip loss of approximately 3.5 ppm for the modeled cavity. These results substantially improve upon the central anti-reflective mirror mask approach based on selective loss engineering, bringing reflected optical loss within a factor of two of that obtained with the fundamental Gaussian mode under the same simulation conditions. This approach offers a route toward robust donut-shaped Laguerre-Gaussian modes in future precision interferometers with realistic imperfections.
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Astrophysics of Galaxies

Chaotic accretion can (still) explain early supermassive black hole growth

Kastytis Zubovas and Matas Tartėnas

The origin of supermassive black holes (SMBHs) is still debated, with hypotheses ranging from massive seeds to super-Eddington growth to chaotic accretion. Recent discoveries of very high redshift SMBHs constrain their possible origin and growth scenarios. We investigate whether the chaotic accretion scenario can explain the most extreme high-redshift SMBH masses. We predicted the exponential growth timescale of black holes accreting chaotically in a slowly-spinning dark matter halo, in which uncorrelated gas inflows maintain a low spin and hence a low radiative efficiency. We compared this prediction against the growth timescales and seed masses implied by a compilation of all known SMBH mass estimates at $z>7$ and against the feeding and feedback conditions expected in such haloes. We found that in the period $7.6 < z < 10.6$, the most massive SMBHs likely grew very efficiently, with an exponential growth timescale $\tau \sim 32$~Myr, which is consistent with chaotic accretion predictions provided that growth was almost continuous. All high-redshift SMBHs with virial mass estimates could have grown from seeds with $M_{\rm seed} \lesssim 100 \, \msun$. We describe the evolution of the mass reservoir feeding such a black hole, suggesting that wind-driven feedback eventually removes most of the gas and changes the growth mode of black holes at $z \sim 7.5$. We make several predictions regarding the spins, host-galaxy correlations, and observable counterparts of high-redshift SMBHs that distinguish our model from its alternatives. These predictions will be testable in the near future. Chaotic accretion from stellar-mass seeds remains a viable origin for the earliest known SMBHs, without invoking massive seeds or super-Eddington growth.
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Cosmology and Nongalactic Astrophysics

Stochastic Bubble Completion in de Sitter Space: Power Spectrum, Bispectrum, and Infrared Moment Hierarchies

Hyukjung Kim, Alp Kagan Ozmen and Heeseung Zoe

Stochastic bubble nucleation makes the local completion time of a first-order phase transition a random spatial field. We study its power spectrum and equilateral bispectrum in Minkowski and de Sitter backgrounds, with particular emphasis on the infrared consequences of a finite transition duration. In an eternally extended de Sitter history, rare bubbles nucleated in the remote past generate an ancient-bubble tail that produces a hierarchy of infrared-sensitive spatial moments. For the two-point function, the first finite-$k$ correction becomes tail sensitive at $H/\beta=1/5$, while the leading moment becomes singular at $H/\beta=1/3$. The corresponding three-point thresholds are $H/\beta=1/8$ and $1/6$, showing that the bispectrum is more infrared sensitive than the power spectrum. For any finite starting time, however, the ancient-bubble tail is cut off, all spatial moments remain finite, and the strict infrared spectra recover the analytic white-noise limits ${\cal P}_\tau\propto k^3$ and ${\cal B}^{\rm eq}_\tau\propto k^6$. The eternal-background thresholds instead control the duration dependence of the moment coefficients and the crossover into an intermediate tail-sensitive regime, in agreement with our numerical calculations. We further show that temporal localization of the nucleation history provides a smooth regulator of the ancient-bubble tail and restores the same analytic infrared limits. These results establish a general first-arrival framework for completion-time fluctuations and clarify how de Sitter expansion can generate distinct power-spectrum and bispectrum infrared hierarchies relevant to curvature perturbations and non-Gaussianity.
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Astrophysics of Galaxies

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS): I. Overview of the ALMA Large Program

J. K. Jørgensen, A. Coutens, M. N. Drozdovskaya et al. (+27 more)

It remains a fundamental research question in astrochemistry to characterize the inventory of complex organic molecules formed during the early stages of star formation, which may affect the eventual chemical composition of protoplanetary disks and potentially planets. The Atacama Large Millimeter/submillimeter Array (ALMA) provides the angular resolution and sensitivity to zoom in on the hot (T > 100 K) gas surrounding embedded solar-type protostars and chart their molecular inventories with high accuracy. The ALMA Large Program Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) aims to provide comprehensive inventories of the molecular content of a sample of protostellar sources to understand the chemical impact of their environments and evolutionary stages. COMPASS is an unbiased spectral survey of 11 line-rich Class 0 and I protostellar sources in the spectral range from 279.0 to 311.7 GHz at 0.15-0.5" angular resolution with ALMA, corresponding to the inner ~100 au (radius) around the targeted sources. This paper provides an overview of the COMPASS program and the adopted strategy in terms of observational setups and targeted sources. We also present a qualitative comparison of the spatial distributions of selected molecules and the relative strengths of the line fluxes of selected complex organics. The qualitative comparisons suggest that chemical differences between sources may be present, for example, between the abundances of groups of oxygen- and nitrogen-bearing species, but also that such variations occur at levels smaller than an order of magnitude. Quantitative comparisons of abundances at these levels require the large bandwidth of the survey, as well as a careful analysis of the excitation and strengths of the several thousands of lines detected toward each source in the survey, as will be explored in forthcoming papers.
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All authors J. K. Jørgensen, A. Coutens, M. N. Drozdovskaya, J.-E. Lee, A. L. Plunkett, S. Maret, A. Belloche, D. Harsono, Z. Telkamp, F. Cruz-Sáenz de Miera, M. L. R. van 't Hoff, Á Kóspál, M. Rao, J. Bergner, J.-H. Jeong, S. Spezzano, B. A. McGuire, P. Nazari, Y.-L. Yang, H.-S. Yun, A. Andreu, J. Ferrer Asensio, C.-H. Kim, N. F. W. Ligterink, Y. Lin, S.-Y. Liu, M. Lützen, P. Marchand, C. Xue, S. Zeng

Astrophysics of Galaxies

COSMOS-3D: Spectro-photometric Confirmation of Shabgard, a Cool, Metal-poor Brown Dwarf in the COSMOS Field

Bahareh S. Salmasi, Priyanka Jalan, Tomotsugu Goto et al. (+19 more)

Brown dwarfs are unique laboratories for studying cool atmospheres, the low-mass end of star formation, and the transition between stars and giant planets. Identifying and characterizing the coldest brown dwarfs remains challenging, particularly at faint magnitudes in deep extragalactic surveys. We investigate COSMOS2025 ID639188, hereafter Shabgard, a compact source previously selected as a brown-dwarf candidate from COSMOS-Web photometry. We use serendipitous JWST/NIRCam F444W wide-field slitless spectroscopy from COSMOS-3D, combined with COSMOS2025 NIRCam photometry and multi-epoch imaging. We extract a local-background-subtracted, profile-weighted $4.05$-$4.85\mu{\rm m}$ spectrum and compare the data with six atmosphere-model families. The LOWZ atmosphere-grid fit, using PCA interpolation and MCMC sampling, gives $T_{\rm eff}=718.6^{+10.6}_{-10.2}$ K and $[{\rm M/H}]=-1.00^{+0.07}_{-0.08}$, favoring a cool, subsolar-metallicity atmosphere near the late-T/Y transition. A fixed-atmosphere molecular-opacity test strongly favors a contribution from CH$_4$ to the observed $4$-$5 \mu{\rm m}$ spectral shape, although the restricted wavelength coverage prevents a molecule-by-molecule abundance determination. Model-dependent physical estimates span approximately $23$-$52 {\rm M_{\rm Jup}}$ and $140$-$180$ pc. We measure a proper motion of $|\mu|=89.2\pm0.4$ mas yr$^{-1}$, while the LOWZ MCMC flux scaling gives a distance of $176.2^{+18.4}_{-17.8}$pc. Together, these results support the classification of Shabgard as a cool, metal-poor Galactic brown dwarf and demonstrate the ability of JWST deep-field surveys to discover and characterize faint substellar objects.
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All authors Bahareh S. Salmasi, Priyanka Jalan, Tomotsugu Goto, Tetsuya Hashimoto, Feige Wang, Tayyaba Zafar, Koki Kakiichi, Ece Kilerci, Srivardini Ayyappan, Romain A. Meyer, Anilkumar Mailvaganam, Tamal Mukherjee, Xuanyi Lyu, Imam Uzma Aalia, Arihant Raidani, Samuel Carlson, Jose Luis Carrillo Martinez, Andreas L. Faisst, Marko Shuntov, Hollis B. Akins, Zihao Li, the COSMOS-3D Collaboration

Astrophysics of Galaxies

A Graph Attention Network Framework for Simultaneous Prediction of Galaxy and Dark Matter Halo Properties in GAMA DR4

Sandeep Aashish, Abhay V Hegde, Aditya Prakash Gupta et al. (+4 more)

We develop a graph-based deep learning model, GAMANet, to predict galaxy and halo properties using the GAMA DR4 dataset. Multiple catalogues are combined to construct a unified sample of 19,469 galaxies and derive a set of photometric, spectroscopic, morphological, and environmental features. The galaxy sample is represented as a graph, with galaxies as nodes and physically motivated connections based on spatial proximity and group membership as edges. A Graph Attention Network with GATv2 layers is then used to learn information from the galaxy neighbourhood while assigning different weights to neighbouring galaxies. The model simultaneously predicts halo mass, stellar mass, and a specific star formation rate proxy. On the test set, GAMANet achieves $R^2 = 0.958$, $0.985$, and $0.982$ for halo mass, stellar mass, and SSFR proxy, respectively, with an RMSE of $0.237$ dex for halo mass. These results demonstrate that graph-based learning can extract useful information about galaxy and halo properties directly from observational data while incorporating the environmental relationships encoded in the galaxy graph.
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All authors Sandeep Aashish, Abhay V Hegde, Aditya Prakash Gupta, Ashmit Verma, Md Saif, Nishanth Kumaran, Shivang Rayat

Instrumentation and Methods for Astrophysics

Very Long Baseline Interferometry with the SKA Observatory

J. F. Radcliffe, J. Yang, Z. Paragi et al. (+131 more)

Very Long Baseline Interferometry (VLBI) is a fundamental technique that combines signals from telescopes separated by thousands of kilometres to obtain some of the highest-resolution images in astronomy. The Square Kilometre Array Observatory (SKAO) will provide sensitive elements to current VLBI arrays, enabling deep VLBI observations (including the first low-frequency VLBI capability in the Southern Hemisphere). This summary chapter outlines the science that the SKAO, when participating in a VLBI array, will achieve (such as AGN physics, explosive transient localisation, Galactic structure, and gravitational waves), and the current understanding of how VLBI with the SKAO will operate. Given that VLBI requires partnerships with other instruments, the chapter concludes with outstanding issues and considerations for the community needed to maximise the scientific return on investment in SKA-VLBI.
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All authors J. F. Radcliffe, J. Yang, Z. Paragi, O. Bayandina, C. Reynolds, C. García-Miró, T. An, M. Abada-Simon, J. N. H. S. Aditya, I. Agudo, T. Akahori, A. Alberdi, S. Anton, P. Atri, A.-K. Baczko, S. Belladitta, E. K. Bempong-Manful, R. Beswick, M. Bhardwaj, E. Bonnassieux, A. Brunthaler, C.-S. Chang, P. Charlot, S. Chen, W. Chen, X. Cheng, A. Chhipa, J. O. Chibueze, I. Cho, J. B. Climent, L. Cui, S. Curiel, F. D'Ammando, J. R. Dawson, A. Deller, H. Ding, R. Dodson, J. Drevon, F. Eppel, S. Frey, M. Garrett, M. Gawroński, J. Geng, S. Giarratana, M. Giroletti, S. Gulyaev, L. I. Gurvits, C. Hao, T. Hirota, A. J. Hedge, H. Hu, H. Imai, P. Jiang, J. de Jong, M. Kadler, B. Karimi, P. Kharb, R. Khatun, J.-Y. Kim, J. Kim, J. Kim, F. Kirsten, H. R. Klöckner, H. Kobayashi, Y. Y. Kovalev, M. Kunert-Bajraszewska, A. Kutkin, H. J. van Langevelde, J. Li, Y. Li, Y. Li, Z. Lin, D. Liu, H. Liu, K. Liu, A. Lobanov, R.-S. Lu, V. Mahatma, B. Marcote, M. Mezcua, J. Moldón, L. K. Morabito, S. E. Motta, S. Murthy, I. Natarajan, A. Njeri, J. Oh, M. Orienti, A. Osetrova, M. Pandey-Pommier, F. Panessa, J. Park, M. Pérez-Torres, L. Petrov, J. C. S. Pierce, C. Phillips, L. Ricci, M. Rioja, H. Ro, J. Röder, E. Ros, M. Rupen, K. L. J. Rygl, R. Santra, S. Silpa, T. Savolainen, G. A. S. Sundaram, P. Shastri, X. Shu, A. Słowikowska, B. W. Sohn, C. Spingola, F. Sweijen, K. Takahashi, R. Timmerman, F. Ubertosi, L. Uscanga, E. Varenius, M. Verkouter, T. Vernstrom, S. Wagner, D. Williams-Baldwin, J. Wongphechauxsorn, X. Wu, M. Xu, Y. Xu, M. K. Y{\i}ld{\i}z, Z. Yan, A. Yang, X. Yang, S. Yao, W. Yu, B. Zhang, P. van Zyl

2610.07743 · 6 Oct · Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366) Report-no:AASKAII/Radcliffe01. Advancing Astrophysics with the SKA II (AASKAII) outlines the transformative scientific advances that will be enabled by the SKA telescopes

Abstract PDF $TSCP ×1

Astrophysics of Galaxies

The Role of the Cosmic Web in Galaxy Evolution Across 0.4<z<4

Sina Taamoli, Bahram Mobasher, Hossein Hatamnia et al. (+12 more)

We investigate the dependence of stellar mass and star formation activity on the topology of hosting large-scale structures using mass-complete galaxy samples in four redshift bins spanning from z = 0.4 to z = 4 using the COSMOS2020 catalog. Cosmic web components (clusters, filaments, and field) are identified by applying the Multiscale Morphology Filter to galaxy density maps, and group memberships (central, satellite, isolated) are assigned to each galaxy by the Friends of Friends (FoF) algorithm. Out to z < 1, we find that stellar mass increases toward denser structures, driven primarily by central and satellite galaxies, with differences up to ~0.35 dex between field and clusters. At these redshifts, star formation rate (SFR) is suppressed by ~0.1 dex in clusters compared to field galaxies, particularly for centrals, while the SFR of star-forming galaxies shows a much weaker dependence on the type of host structure, indicating that the quenched population primarily drives the observed environmental dependence. Specific SFR (sSFR) shows the strongest decline for centrals in clusters at z<1, consistent with enhanced quenching in dense environments. At 1<z<2, star formation activity becomes largely independent of environment, suggesting a transitional regime in the role of large-scale structure. At z>2, we observe a mild increase in SFR (~+0.1 dex) and sSFR (~+0.13 dex) from field to cluster galaxies, pointing to a possible reversal of environmental trends during early cosmic epochs. These results highlight the evolving influence of environment on galaxy evolution and set the stage for deeper investigations with upcoming wide-field surveys.
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All authors Sina Taamoli, Bahram Mobasher, Hossein Hatamnia, Nima Chartab, John R. Weaver, Ghassem Gozaliasl, Anton M. Koekemoer, Caitlin M. Casey, Jeyhan S. Kartaltepe, Aryana Haghjoo, Olivier Ilbert, Henry J. McCracken, David B. Sanders, Nicholas Scoville, Sune Toft

Earth and Planetary Astrophysics

Hubble Space Telescope Observations of Active Asteroid (101955) Bennu

David jewitt, Max Mutchler and Yoonyoung Kim

Measurements from NASA's OSIRIS-REx spacecraft revealed (101955) Bennu as a member of the active asteroid class. These objects exhibit transient, comet-like activity, commonly producing particle trails best observed from a vantage point close to the projected orbit plane. Accordingly, we obtained deep, high resolution observations of Bennu at orbit plane crossing in 2023, using the Hubble Space Telescope. We find no evidence for ejected material, and place model-dependent limits to the mass loss of dM/dt < 0.12 kg/s from an analysis of the near-nucleus surface brightness profiles and dM/dt < 6e-3 kg/s from the absence of a measurable particle trail. These limits are one to two orders of magnitude smaller than rates of mass loss measured remotely in other active asteroids and raise the possibility that low activity in many or most asteroids might fall beneath the prevailing thresholds offered by remote observations. Taking a still smaller mass loss rate estimated from OSIRIS-REx data, we calculate a specific rate L = 1e-7 kg/km2/s and extrapolate to the entire main-belt asteroid population. We estimate a cumulative dust production rate 850/r_min**1/2 [kg/s], where r_min is the minimum asteroid radius in meters. For r_min > 1 m, this is <1% to 10% of the rate needed to sustain the Zodiacal cloud in steady state.
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Astrophysics of Galaxies

Radiation pressure powers quasar broad absorption line winds but fails to drive galaxy feedback

Braden Seefeldt-Gail, Lluís Mas-Ribas and Norman Murray

Most cosmological simulations invoke quasar-driven winds as the primary mechanism quenching star formation in massive galaxies, assuming wind momentum flux approaches the radiation-pressure maximum, $L/c$. Using 81,388 broad absorption line troughs from the SDSS-IV DR16 quasar catalog and detailed mock trough spectra, we detect line locking, a spectral signature of radiation-pressure-driven outflows, in 60 to 70 percent of troughs, demonstrating that radiative line driving dominates wind acceleration and ruling out alternative mechanisms. Direct measurement of the wind energy budget yields a median kinetic luminosity of only 0.01 percent of bolometric luminosity, 50 times below the level required for effective feedback. Line-driven quasar winds are therefore insufficiently powerful to quench star formation, challenging the primary physical mechanism invoked for black hole feedback in galaxy formation models.
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Earth and Planetary Astrophysics

Discovery of 2 km ultra-fast rotating asteroid in Rubin DP2 catalog via varying Fourier order method

Dmitrii E. Vavilov, Siegfried Eggl and Sarah Greenstreet

Time-resolved photometry from large surveys can yield rotation periods for huge numbers of asteroids, but only if the reliability of each period is assessed automatically, since sparse and irregular sampling produces many false periodogram minima. We present an improved method that determines asteroid rotation periods with a Fourier series whose order is chosen for each object individually. This has substantial advantages over lower order methods, especially when unique solutions for the spin period cannot be reliably determined. In such cases, the method reports the set of alternative periods together with the corresponding probability estimates. We apply the improved spin period determination method to the NSF-DOE Vera C. Rubin Observatory Data Preview 2 (DP2) catalog of solar system objects and determine reliable periods for a large sample of asteroids. Among them we find 66 super-fast rotators, which spin faster than the classical 2.2 h spin barrier. Two of them are remarkable: asteroids 491384 and 566130 are both larger than 2 km, yet they complete a full rotation in only about five minutes. To survive such a fast spin, they must have significant internal cohesion. At a diameter of about 2.5 km, asteroid 491384 is the largest ultra-fast rotator known so far.
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Astrophysics of Galaxies

Stirred, not shaken: Dislodging $\omega$ Centauri from the Sausage galaxy through bar resonances

Axel Mannu, Chervin F. P. Laporte, Matthew D. A. Orkney et al. (+2 more)

We test the idea proposed by Laporte & Orkney that $\omega$ Centauri ($\omega$Cen) is the central nuclear star cluster of the Gaia-Sausage-Enceladus galaxy (GSE) which got dislodged by the bar. We run a series of simulations in time-evolving bar potentials with present-day pattern speeds within Portail et al's $\Omega_{b}=39\pm3.5\,\rm{km\,s^{-1}\,kpc^{-1}}$ and rate of slow-down $\dot{\Omega}_{\rm b}= 4.5 \pm 1.4 \,\rm{km \,s^{-1}\,kpc^{-1}\, Gyr^{-1}}$ to study how bar resonances modulate the angular momentum and energies of both GSE-debris and $\omega$Cen's location in $(E,L_{z})$ space. We find that the retrograde $3:2$ resonance is capable of inflicting changes of $\Delta E\approx0.4\times10^{5}\,\rm{km^{2}\, s^{-2}}$, $\Delta L_{z}\approx0.3-0.5\times10^{3}\, \rm{km \, s^{-1}\, kpc^{-1}}$ within timescales of $\Delta t\approx 0.5-1\,\rm{Gyr}$, well within the bar's lifespan $t_{\rm{bar}}\approx10-8\,\rm{Gyr}$. These results are independent of the choice of potential or modelling. We uncover a sample of N-rich stars with metallicities $-2.0<[\rm{Fe/H}]<-1.0$ and aluminium enrichments consistent with $\omega$Cen. In ($E,L_{z}$) space, the map reveals a corridor of trailing N-rich stars clustered about the region connecting $\omega$Cen to the GSE's debris centroid, matching $\omega$Cen's past predicted track. This provides the best evidence yet that $\omega$Cen is the nuclear star cluster of the GSE. Using M54 and $\omega$Cen's chemistry we show that neither first nor second generations follow general galaxy-wide scale chemical enrichment trends. This is empirical evidence that GC chemical trends are a cluster-scale physics problem, not a galaxy-wide one.
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All authors Axel Mannu, Chervin F. P. Laporte, Matthew D. A. Orkney, Yassin Rany Khalil, Benoit Famaey

Monday 5 October

Astrophysics of Galaxies

Barium and europium abundances from the Gaia-ESO Survey using The Cannon

Pradosh Barun Das, Francesca Primas, Gayandhi De Silva et al. (+3 more)

Neutron-capture element abundances encode the time-dependent interplay between slow (s-) and rapid (r-) nucleosynthetic processes and provide critical constraints on Galactic chemical evolution. In particular, barium and europium provide important tracers of s-process and r-process nucleosynthetic enrichment, respectively. Large spectroscopic surveys enable robust statistical studies of these elements; however, determining reliable elemental abundances at intermediate spectral resolution remains challenging. Our aim was to derive homogeneous and statistically well-characterised stellar parameters and chemical abundances of Ba and Eu (hereafter collectively referred to as stellar labels) for the Gaia-ESO Survey HR15N dataset. We applied The Cannon to 36,263 FLAMES/GIRAFFE HR15N spectra (R~19,200), using a model trained on 782 stars with high-quality reference stellar labels drawn from the Gaia-ESO DR5 homogenised catalogue. The model infers Teff, log g, [Fe/H], v sin i, A(Ba), and A(Eu); its reliability was quantified through multi-dimensional quality flags and detection strength of the Ba and Eu features. Our final catalogue contains stellar parameters for 36,263 spectra, with ~21,000 and ~400 reliable Ba and Eu abundances, respectively, satisfying multiple flagging criteria. We obtained median uncertainties of ~38 K in Teff, ~0.08 dex in log g, ~0.04 dex in [Fe/H], ~0.06 dex in A(Ba), and ~0.02 dex in A(Eu). External validation against the Gaia Benchmark Stars, GALAH DR4, and multiple open clusters shows good agreement across independent reference datasets. The resulting catalogue includes newly determined Ba and Eu abundances that complement those available from previous analyses, thereby enabling investigations of neutron-capture enrichment patterns in open clusters. The model framework can readily be adapted to upcoming wide-field spectroscopic surveys such as 4MOST, WEAVE, and WST.
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All authors Pradosh Barun Das, Francesca Primas, Gayandhi De Silva, Guillaume Guiglion, Daniel B. Zucker, Melissa Ness

Instrumentation and Methods for Astrophysics

The First Decade of Breakthrough Listen

David H.E. MacMahon and Daniel J Czech

Breakthrough Listen (BL), launched in July 2015 with a 10-year, \$100M commitment from the Breakthrough Prize Foundation, is the most comprehensive search for technosignatures ever conducted. This paper reviews the program's first decade from the facilities and instrumentation perspective: the digital backends and data recorders, the signal-processing pipelines, the data archive, and the observatory partnerships that made the science possible. We organize the decade into three architectural eras. In Generation 1 (2016--2019), BL deployed packetized raw-voltage wideband recorders on the 100-m Green Bank Telescope and the 64-m Parkes telescope, enabling targeted surveys of thousands of nearby stars across $\sim$0.7--8 GHz. In a network-expansion phase (2020--2023), BL extended its instrumentation to partner facilities including the Sardinia Radio Telescope and international LOFAR stations, and developed verification frameworks that proved essential when the program's highest-profile signal candidates emerged. Since 2023, BL has operated in a fully commensal era: Ethernet-based, commodity-GPU backends riding on routine observatory operations: COSMIC at the Karl G. Jansky VLA, a revived Allen Telescope Array with deployed real-time deep-learning pipelines, and an autonomous multi-beam commensal survey at MeerKAT (BLUSE; $>$1.2 million pointings since mid-2022). Over the decade, capturing data at ever higher rates forced a systematic approach to compression and archiving; the storage estate grew to $\sim$42 PB of capacity ($\sim$31 PB in use) across seven systems on four continents by March 2026. We conclude with engineering lessons (commodity hardware over bespoke hardware, open data as a first-class requirement, commensal science as backend validation, and verification frameworks built before they are needed) and with the outlook for SKA-era commensal technosignature science.
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2610.07482 · 5 Oct · Keynote paper (Rudolf Pesek Lecture), 55th IAA Symposium on the Search for Extraterrestrial Intelligence (SETI), Session A4.1 "SETI Science and Technology". Presented at the 77th International Astronautical Congress (IAC 2026), Antalya, Türkiye, 5-9 Oct 2026; to appear in the IAC proceedings. 11 pages, 2 figures, 2 tables

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Solar and Stellar Astrophysics

High-Angular-Resolution Survey of Stars within 18 pc of the Sun: Part I

F. Carolina Rojas-Galindo, Valeri G. Orlov, Rene A. Mendez et al. (+1 more)

We present the rationale, design, methodology, and observational facilities of a high-angular-resolution imaging survey of stars within 18~pc of the Sun. Our comprehensive sample consists of 2047 stars compiled from Gaia eDR3 and complementary catalogs. The main goal is to observe as many stars from this sample as possible using high-angular-resolution techniques, considering their inherent limitations, to perform astrometry of known binary systems and determine detection limits for secondary components for each observed star. This approach may also allows us to identify previously unresolved stellar companions. Observations were carried out using the 2.1-m telescope at OAN-SPM in the North and the 3.58-m NTT in the South, employing high-speed cameras for speckle imaging. We obtained observations of 703 stars with V < 14 mag at OAN-SPM, and 645 stars with I < 16 mag at the NTT, of which 140 stars were observed in both hemispheres, for a total of 1208 unique stars observed. In this paper: (1) we present the construction of the catalog of 2047 stars within 18 pc; (2) using a control sample of 70 known close binaries within 18 pc with separations 1", we show that selecting targets based on Gaia quality parameters commonly used as binarity indicators–RUWE, ipd_frac_odd_win, and ipd_frac_multi_peak–can miss a significant fraction of binaries, justifying our unbiased, volume-limited survey; and (3) we present the results of pilot observations conducted with the 2.1 m telescope at OAN-SPM in July 2022. A full analysis of the complete sample will be presented in of forthcoming papers.
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All authors F. Carolina Rojas-Galindo, Valeri G. Orlov, Rene A. Mendez, Wolfgang Brandner

Astrophysics of Galaxies

The Rogue One: A Dark Matter-Dominated Dwarf in the Trail of Dark Matter-Deficient Galaxies

Daniel Vaz, Arsen Levitskiy, Duncan Forbes et al. (+6 more)

We present the first measurement of the stellar velocity dispersion of LEDA 4014647, a compact dwarf galaxy spatially aligned with the NGC 1052 trail, a linear chain of dark matter-deficient galaxies (DMDGs) proposed to have formed in a single high-speed dwarf$-$dwarf collision $\sim 8$ Gyr ago. Using integral-field spectroscopy obtained with the Keck Cosmic Web Imager (KCWI), we measure a stellar velocity dispersion of $\sigma = 15.8 \pm 2.0$ km s$^{-1}$ within the half-light radius ($R_\mathrm{e}$). We derive a dynamical mass within the 3D half-light radius of $M_\mathrm{dyn}(<r_{1/2}) = (1.5 \pm 0.4) \times 10^8\,M_\odot$, a factor of $\sim 3$ larger than the enclosed stellar mass, implying a DM fraction of $f_\mathrm{DM} = 0.7 \pm 0.1$ at $r_{1/2}$. Full-spectrum stellar population fitting yields an old ($t \approx 13$ Gyr) and metal-poor ($[\mathrm{M/H}] \approx -1.2$ dex) stellar population, consistent with independent photometric estimates and predating the proposed collision epoch. LEDA 4014647 is therefore a DM-dominated system, and cannot have formed from the DM-free, shock-compressed gas that produced the proposed trail DMDGs DF2, DF4, and DF9. Its nature, however, remains an open question: while a chance-projection along the trail axis is a possible explanation, its old stellar population, compact morphology, and DM content are also consistent with the surviving collisionless remnant of one of the progenitor dwarfs of the dwarf$-$dwarf collision. Distinguishing between these two scenarios will ultimately require deeper spectroscopy to tighten the stellar population and DM halo constraints, and targeted $N$-body and hydrodynamical simulations tracking the post-encounter fate of the progenitors.
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All authors Daniel Vaz, Arsen Levitskiy, Duncan Forbes, Aaron J. Romanowsky, Jonah Gannon, Jean P. Brodie, Yimeng Tang, Kenji Bekki, Warrick J. Couch

Astrophysics of Galaxies

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) III. CH$_3$OH isotopic fractionation in the low-mass protostar BHR71-IRS1

A. Coutens, F. Cruz-Sáenz de Miera, J. K. Jørgensen et al. (+26 more)

[Abridged] Methanol is a complex organic molecule detected in both ice and gas toward star-forming regions. Due to its high abundance, its rarer isotopologues, including the deuterated ones, are also commonly detected. Our aim is to determine the column density and deuterium fractionation of methanol in the low-mass protostar BHR71-IRS1. We analyzed data from a large spectral survey of BHR71-IRS1 carried out as part of the ALMA Large Program Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS). We used the CASSIS software to identify the lines of the methanol isotopologues and constrain their column densities under the assumption of local thermodynamic equilibrium. We detected CH$_3$OH, $^{13}$CH$_3$OH, CH$_3$$^{18}$OH, CH$_3$OD, CH$_2$DOH, CHD$_2$OH, and CD$_3$OH at the continuum peak position. In addition, CH$_3$$^{17}$OH is tentatively detected, while CD$_3$OD is not detected, although a few faint lines could be present toward a position redshifted from the continuum peak. The column densities of the main isotopologue obtained from $^{13}$CH$_3$OH and CH$_3$$^{18}$OH are consistent, assuming nominal $^{12}$C/$^{13}$C and $^{16}$O/$^{18}$O ratios of 68 and 557, respectively. The CH$_2$DOH/CH$_3$OD column density ratio is equal to 7$\pm$2. The statistically corrected D/H ratio is higher for CH$_2$DOH (1.9$\pm$0.6 %) than for CH$_3$OD (0.8$\pm$0.2 %). The level of deuteration after statistical correction increases with the number of D atoms in the methyl group, reaching 23$\pm$5 % for CD$_3$OH/CH$_3$OH. These trends are similar to other low-mass protostars such as IRAS~16293–2422 and HOPS 373SW, but seem to differ from the eruptive young star V883-Ori. Similar studies with comparable datasets will be carried out for the other COMPASS sources to determine if factors such as environmental conditions and evolutionary states impact the deuteration of methanol.
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All authors A. Coutens, F. Cruz-Sáenz de Miera, J. K. Jørgensen, M. N. Drozdovskaya, J.-E. Lee, A. L. Plunkett, D. Harsono, S. Maret, A. Belloche, J. Ferrer Asensio, M. L. R. van't Hoff, J.-H. Jeong, Á. Kóspál, B. A. McGuire, P. Nazari, S. Spezzano, Z. Telkamp, Y.-L. Yang, H.-S. Yun, S. Zeng, A. Andreu, J. Bergner, C.-H. Kim, N. F. W. Ligterink, Y. Lin, S.-Y. Liu, M. Lützen, P. Marchand, M. Rao

Astrophysics of Galaxies

Life in the Cosmic Neighbourhood: Galactic Habitable Zones in the EAGLE Simulations

Luke A. Barnes, Geraint F.Lewis, Jaime Salcido et al. (+3 more)

When and where is life most likely to form in the universe? We use the EAGLE cosmological hydrodynamical simulations to investigate the prevalence and properties of life-friendly cosmic environments on galactic scales. Our model for the occurrence of observers depends on main-sequence stars, the production and distribution of metals, and the formation of habitable planets. We also take into account five potentially life-extinguishing processes: core-collapse supernovae, Type Ia supernovae, star-star interactions, gamma ray bursts and quasars. We characterise the amount of time that the universe creates on habitable planets per unit mass of baryons and stars in the universe, as a function of galaxy mass and galactocentric distance. As expected, early universe, newly formed, high star formation rate galaxies are the most dangerous. The present-day Milky Way is typical of habitable galaxies: efficient creation of habitable time, and low probability of cosmic catastrophes.
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All authors Luke A. Barnes, Geraint F.Lewis, Jaime Salcido, Pascal Elahi, Miroslav D. Filipovic, Richard G. Bower

High Energy Astrophysical Phenomena

Adaptive proposals for nonparametric equation-of-state inference with RIFT: iterative Gaussian-process refinement in a compressed sequence representation

R. O'Shaughnessy and Z. Zhu

Nonparametric equation-of-state (EOS) inference evaluates the likelihood on a finite ensemble drawn from a prescribed functional prior. Reweighting that ensemble suffices for the binary neutron stars detected so far, and loses effective sample size only once the likelihood concentrates — which needs third-generation catalogues, or extra electromagnetic and nuclear-theory information folded into the same target. We develop and validate an adaptive-proposal procedure that leaves the base prior fixed: data-informed generations are combined by multiple importance sampling and, where that degenerates at large catalogue size, by a calibrated Gaussian projection. We implement it in two representations — a compressed principal-component parametrization of the neutron-star sequence, whose draws need no stellar-structure solve, and a sound-speed parametrization with a differentiable Tolman–Oppenheimer–Volkoff solver — both on a constrained low-density-to-pQCD bridge. Because that anchor, and not the bridge, fixes the low-density prior, we rebuild the ensemble with a crust-plus-chiral-EFT anchor in place of the wide nuclear metamodel: the maximum-mass prior is unmoved, the radius gains a hard prior ceiling at the measured NICER value. GW170817 with the specified NICER and radio factors gives the calibration-conditional $R(1.4\,M_\odot)=11.7\pm0.4$km; in a synthetic $1000$-event catalogue it reproduces the mean fixed-prior $\Lambda(1.4\,M_\odot)$ to $0.4$%, $1.5$ times wider, as the fixed archive's effective sample size falls from $\sim\!470$ to 22.
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Solar and Stellar Astrophysics

Axial-Dipole and Equatorial-Dipole Coronal Holes: Congruent Magnetic Geometry, Divergent Evolution

Olga A. Panasenco, Yi-Ming Wang, Samuel T. Badman et al. (+2 more)

While the Sun's polar fields reverse, the axial dipole is weak and low-latitude coronal holes are common. Equatorial-dipole coronal holes (EDCHs) appear when the equatorial dipole is strong, forming at its magnetic poles, similar to the axial-dipole coronal holes (ADCHs) of minimum. Not every low-latitude hole qualifies: the 2024 maximum was quadrupole-led. Parker Solar Probe found fast wind from an EDCH deeply sub-Alfvénic at $9.9\,R_\odot$, at only $60\%$ of an asymptotic speed matching polar wind, which is usually thought to accelerate faster. We ask whether coronal structure predicts this, using potential-field models of synthetic and observed fields at three cycle phases. We show that pure axial and equatorial dipoles are exactly congruent, with the same open areas and core expansion factors, so any difference must arise from orientation relative to the differential-rotation pattern or from the surrounding multipoles. We find that ADCHs are stationary, sustained by converging meridional flow, whereas EDCHs depend on an equatorial dipole that active-region emergence builds and flux transport dismantles: over $18$-day sequences the axial-dipole strength at minimum is steady to $1\%$, while the equatorial dipole varies by $21\%$ at maximum and $8\%$ in the declining phase. Most open flux in EDCHs expands less than in ADCHs, but their boundaries are pseudostreamer-dominated, with non-monotonic expansion. Despite these differences, magnetic geometry alone does not predict slower acceleration in EDCHs; we argue that any real difference points to extended heating by reflection-driven Alfvén-wave turbulence, perhaps fed differently at those boundaries, which potential-field models cannot capture.
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All authors Olga A. Panasenco, Yi-Ming Wang, Samuel T. Badman, Adam J. Finley, Yeimy J. Rivera

Astrophysics of Galaxies

BRAHMa: Bar Recognition And Hatching using Machine learning – a framework for oriented bounding box detection of galactic bars

Rajit Shrivastava, Narendra Nath Patra and Keerthi K

Galactic bars are fundamental components in studies of dark matter, galaxy evolution, and secular dynamics. However, current methods for measuring bar properties suffer from significant limitations. Manual and crowdsourced catalogs are not scalable to next-generation surveys, while recent machine learning (ML) approaches based on pixel-wise segmentation are computationally intensive and require complex post-processing to extract physical parameters. In this paper, we introduce BRAHMa (Bar Recognition And Hatching using Machine Learning), a publicly available tool based on an oriented-bounding-box YOLO11x model, designed for the rapid and objective detection of galactic bars. Our model was initially trained on synthetic data (Shrivastava 2025), validating its efficacy before training with real data. BRAHMa was trained on bar masks from the Galaxy Zoo 3D (GZ-3D) citizen science project, utilizing images from the DESI Legacy Survey. We address the inherent challenge of 'ground truth' in astronomical data by comparing GZ-3D labels with the Hoyle dataset for 586 common galaxies. This comparison yields a baseline mean absolute error of 0.99 kpc between the GZ3D-derived and Hoyle measurements for 586 common galaxies, providing an empirical reference for catalogue-to-catalogue disagreement. Our BRAHMa tool achieves an L1 error of 1.1 kpc on a large set of 3,150 galaxies from the Hoyle dataset, demonstrating performance that approaches this fundamental limit. We further validate the model's robustness by applying it to distinct datasets, proving its generalizability. BRAHMa provides a scalable and reliable method for bar extraction, enabling large-scale morphological studies. The tool is publicly available through the BRAHMa web interface. (https://brahma-bar-detector.netlify.app/)
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