Current date: 2026-10-20
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Datestamp limit: 2026-10-20 (0 days ago)
Created/updated limit: 2026-10-13 (7 days ago)
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Suggested sets: physics, physics:astro-ph, physics:gr-qc, physics:physics
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Scoring abstracts
Number of records retrieved: 1298
Keyword score statistics
score 9 -- 1 abstracts
score 8 -- 1 abstracts
score 7 -- 2 abstracts
score 6 -- 3 abstracts
score 5 -- 1 abstracts
score 4 -- 8 abstracts
score 3 -- 8 abstracts
score 2 -- 34 abstracts
in total -- 58 abstracts
Articles that appeared on 2026-10-20
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[abstract 1 / 58] Wow! (score: 9)
- Title: Tidal Disruption Events in Active Galactic Nuclei: Thermal Radiation and JetsAuthors: Nimrod Tripto, Tsvi Piran, Julian Krolik,Comments: 16 figures, 1 table. Submitted to ApJSubjects: astro-ph.HECreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
Over the past decade, dozens of Tidal Disruption Events (TDEs) have been identified, with many more expected from upcoming surveys. A small subset has been observed to launch transient, highly luminous RELATIVISTIC JETs, for which the origin of the requisite MAGNETic flux has not been identified. A non-negligible fraction of TDEs are expected in Active Galactic Nuclei (AGNs), where a MAGNETized accretion flow is already present. As shown first by Chan et al. (2019), the collision of a TDE debris stream with this flow can substantially alter both disk and debris dynamics, leading to a possibly Eddington-limited flare. Here, we use the Athena++ radiation MAGNETohydrodynamic (RMHD) code to simulate the time near peak fallback rate of a TDE in an AGN, studying the debris-disk interaction, the radiation emitted, and the accumulation of MAGNETic flux near the horizon. In the example simulated, the accretion rate climbs to $\sim 12\,\dot{M}_{ \rm Edd}$, while the escaping solid angle-integrated luminosity approaches $\sim L_{ \rm Edd}$. The photon luminosity is strongly asymmetric, brighter in the hemisphere from which the debris strikes the disk and dimmer in the hemisphere toward which the debris travels. The photon spectrum peaks in the EUV. The polar MAGNETic flux grows $\sim 33$-fold, enough to raise the Blandford--Znajek luminosity by a factor $\sim 10^3$, reaching a level sufficient to power observed TDE JETs. The polar MAGNETic flux is also asymmetric, likely making any JET similarly asymmetric, but in the opposite sense to the photon flux.
[abstract 2 / 58] Wow! (score: 8) - Title: Detection Forecasting for Blazars at MeV Energies with FERMI-LAT SWIFT-BAT Cross MatchAuthors: Timothy Wessling-Resnick, Naomi Tsuji, Tsuguo Aramaki, Paolo Coppi, Manel Errando, Yoshiyuki Inoue, Reshmi Mukherjee, Svanik Tandon, Jiancheng Zeng,Comments: Initial Arxiv submission. 25 pages, 7 figuresSubjects: astro-ph.HECreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
Over the past two decades, the lack of an MeV $γ$-ray all-sky instrument has left an observational gap in BLAZAR broadband emission. Recently, a new suite of MeV $γ$-ray instruments with sensitivity in the $10^{-11}$ to $10^{-12}$ $\mathrm{erg/cm^{2}/s}$ range has been proposed, with the potential to far surpass the capabilities of previous all-sky MeV instruments. In this work, we forecast the capabilities of future MeV $γ$-ray instruments including COSI, GRAMS, newASTROGAM, and AMEGO-X to observe BLAZARs. We pair total source count estimates of BLAZAR luminosity functions with SED-modeled flux estimates of 76 BLAZARs selected from a sample of 115 BLAZARs cross-matched between the latest FERMI-LAT and SWIFT-BAT catalogs. We forecast that an instrument with a sensitivity limit of $10^{-11}$ $\mathrm{erg/cm^{2}/s}$ could detect 61 of the 76 SED-modeled BLAZARs, and expect a total population of a few tens to a few hundreds of Flat-Spectrum Radio Quasars (FSRQs), as well as a few hundred BL Lacs (BLLs). An instrument with a sensitivity limit of $10^{-12}$ $\mathrm{erg/cm^{2}/s}$ could detect all 76 of the SED-modeled BLAZARs, and we expect a total population of a few hundred to one thousand FSRQs and roughly one thousand BLLs. As MeV BLAZARs have been observed to be extremely luminous and MeV $γ$-rays are minimally attenuated by the extragalactic background light, we use luminosity functions to estimate that BLAZARs could be detected out to $z\approx6$. Lastly, we demonstrate detectability for BLAZARs that have been proposed as neutrino-emitting candidates, as the MeV regime could provide a window into resolving lepto-hadronic degeneracies.
[abstract 3 / 58] Wow! (score: 7) - Title: Re-interpreting the GRS 1915+105 observations within the variable TADAF scenarioAuthors: Chun Xu,Comments: preprint, 11 pages, 1 figure. Corrected a type in Abstract QSO to QPO that could cause misunderstandingSubjects: astro-ph.HECreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
The Galactic microQUASAR GRS 1915+105 is one of the most interesting X-ray binary systems, exhibiting an exceptionally diverse range of observational phenomena. It displays the most complicated and variable X-ray light curves and carries superluminal radio JETs. Its X-ray and radio fluxes change on very different timescales, from seconds to minutes to days and even longer. In recent years, its JET has also displayed large position angle shifts. We find that most of the observational phenomena can be well explained within our newly developed variable turbulent ADAF (TADAF) model. The accretion disk is composed of an outer thin disk and an unstable inner TADAF torus whose size is variable. The previously suggested 'disappearance' and regain of the inner disk is understood as the transition between the thick TADAF and the thin disk. Some types of QPOs are understood in terms of the radius change of the TADAF torus. The JET position angle shift is understood as the direct sideways frame-dragging on the JET by the Lense-Thirring effect from a tilted, spinning BLACK HOLE. The slower the outshooting JET, the larger the angle shift. We note that such an effect also applies to other sources, such as V404 Cygni and the AGN M87. This mechanism may also be applicable to the famous 'precessing' JET in SS 433.
[abstract 4 / 58] Wow! (score: 7) - Title: The evolution of 3C 306 in the galaxy cluster RXCJ1454.4+1622: linking spectral ageing, ICM conditions, and JET dynamics through MHD simulationsAuthors: A. S. R. Antas, A. Caproni, L. Loinard, G. S. Souza, T. F. Laganá,Comments: 22 pages. Published in Monthly Notices of the Royal Astronomical SocietySubjects: astro-ph.HE astro-ph.GACreated: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20
We present a methodology for analysing radio sources in galaxy clusters by combining multi-frequency radio observations, X-ray analysis of the intracluster medium (ICM), and three-dimensional MAGNETohydrodynamic (MHD) simulations, and apply it to the galaxy cluster RXCJ1454.4+1622 and its associated FR II RADIO GALAXy 3C 306 (IC 4516). The radio emission exhibits a curved structure connecting the lobes, likely indicating a complex dynamical evolution influenced by environmental effects. Spectral index and break-frequency maps reveal a relatively homogeneous radiative ageing distribution, with characteristic spectral ages of $\sim220$ Myr and a smooth spatial gradient. From equipartition arguments, we estimate an equivalent JET MAGNETic field of $2.1 \pm 0.3\,μ$G, consistent with values observed in FR II RADIO GALAXies. These observational constraints are used to initialise non-RELATIVISTIC MHD simulations exploring three scenarios: JET precession, bulk motion of the source through the ICM, and a combined model including both effects. Neither pure precession nor pure source motion alone fully reproduces the observed morphology, whereas the combined model provides a more consistent representation of the JET curvature and lobe asymmetries. Nevertheless, the simulations indicate that source motion is the dominant mechanism shaping the large-scale radio morphology, with JET precession playing a secondary role. The inferred source velocity ($\sim280$ km s$^{-1}$) and precession timescale ($\sim250$ Myr) are compatible with the spectral ageing constraints. These results suggest that the morphology of 3C 306 is influenced by the interplay between JET precession and dynamical interaction with the ICM, highlighting the role of environmental effects in radio-galaxy evolution in clusters.
[abstract 5 / 58] Yes (score: 6) - Title: Modeling Multi-band Active Galactic Nuclei Lightcurves Using an Self-supervised Attentive Neural Process NetworkAuthors: Tzuken Shen, Chengcheng Xin, Joshua Fagin, Ashley Villar, Matthew J. Graham, K. E. Saavik Ford,Comments:Subjects: astro-ph.HE astro-ph.GACreated: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20
With the the Legacy Survey of Space and Time (LSST), observations of tens of millions of QUASARs are expected. We present a machine-learning framework based on an attentive neural process (ANP) that models stochastic QUASAR variability and jointly performs two tasks: (i) probabilistic reconstruction of QUASAR light curves in all six LSST bands, and (ii) inference of physical parameters of the AGN system --- BLACK HOLE mass, Eddington ratio, and intrinsic variability timescale --- with joint, full-covariance posteriors. The model processes all six bands within a single masked attention mechanism, so that observations in any band constrain the shared driving process, and natively handles irregularly and asynchronously sampled light curves with realistic heteroscedastic noise. We train and evaluate on full ten-year light curves simulated with a RELATIVISTIC accretion-disk reprocessing model, observed through the fielded Rubin baseline cadence with per-visit photometric noise. The light-curve model is trained with self-supervised, learning from the sparse noisy observations alone and never accessing the underlying noiseless light curves. On a held-out test set, we show that our ANP model reach comparable performances to that of the near-optimal baseline Gaussian process model, while exceeding it in power spectrum reconstruction and damped-random walk timescale estimation. The compact learned latent representation supports future downstream applications, and the fully observation-driven training objective enables direct fine-tuning on real LSST light curves.
[abstract 6 / 58] Yes (score: 6) - Title: The accretion flow and JET of M87: broadband modelling across spatial scalesAuthors: Eduardo M. Gutiérrez, Santiago del Palacio, Tomás Tobías Mazzei,Comments: 15 pages, 7 figures, submitted to journalSubjects: astro-ph.HE astro-ph.GACreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
The nearby RADIO GALAXy M87 is an ideal laboratory for studying accretion flows and RELATIVISTIC JET emission. The EHT collaboration conducted the most comprehensive multi-wavelength observational campaign of M87, in which radio instruments with resolutions ranging from tens of microarcseconds to about an arcsecond sampled different portions of the outflow. We model these data using a radiatively inefficient accretion flow (RIAF) with winds and a new multi-zone JET model, initially MAGNETically dominated, in which we solve the transport equation for the non-thermal electrons as they are injected, advected, and cooled along the JET. We then compare each radio flux with the JET emission within an effective aperture set by the angular scale of the corresponding observation. The comparison across spatial scales favours a scenario in which the RIAF, rather than the JET, produces the compact $230~{\rm GHz}$ emission, while the JET dominates the lower-frequency radio, optical/UV and X-ray emission, but cannot produce the observed $γ$-rays. The RIAF connects the Bondi-scale gas supply to an accretion rate at the horizon of $1.1\times 10^{-5}$ of the Eddington rate, consistent with EHT polarimetry, and the two JETs carry about a quarter of the accretion power, $1.2\times10^{43}~{\rm erg~s}^{-1}$ each. The framework presented in this work provides a simple way to disentangle the accretion-flow and JET contributions to the emission from nearby RADIO GALAXies.
[abstract 7 / 58] Yes (score: 6) - Title: Deep X-ray Observations of the Gamma-ray Bright Pulsar Wind Nebula HESS J1303-631Authors: Seth Gagnon, Oleg Kargaltsev, Yichao Lin, Jeremy Hare, Jordan Eagle,Comments: Submitted to ApJ, 10 pages, 7 figures, 2 tablesSubjects: astro-ph.HECreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
HESS J1303$-$631 is an evolved, TeV-bright pulsar wind nebula (PWN) powered by the energetic radio pulsar PSR~J1301$-$6305, offset by $\approx7'$ northwest of the TeV centroid, with an energy-dependent gamma-ray morphology. We present new, deep joint Chandra (108 ks) and XMM-Newton (102 ks) observations of this field. High-resolution Chandra ACIS imaging resolves the pulsar from a neighboring point source that XMM-Newton cannot separate. The pulsar's 2-10 keV spectrum is well described by an absorbed power law with $Γ=2.02\pm1.04$ and an unabsorbed luminosity of $3.44\times10^{31}\,{\rm erg\,s^{-1}}$ at $d=4.7$ kpc. Chandra also reveals faint diffuse emission east of the pulsar: a clumpy compact nebula on arcsecond scales ($Γ=2.98\pm0.53$, $L_X=4.15\times10^{31}\,{\rm erg\,s^{-1}}$) and a fainter extended nebula on arcminute scales ($Γ=1.20\pm1.25$, $L=4.36\times10^{31}\,{\rm erg\,s^{-1}}$). This morphology, the hard GeV counterpart, and the energy-dependent TeV emission together support an evolved, SYNCHROTRON-underluminous PWN whose X-ray nebula is far more compact than its TeV nebula. We also serendipitously discovered a transient X-ray source, CXOU~J130131.0$-$625919, in one of the nine new Chandra observations. Its hard spectrum ($Γ=1.4\pm0.3$) and 0.5-7\,keV luminosity of $3.34\times10^{32}\,{\rm erg\,s^{-1}}$ at a fiducial distance of 3 kpc, together with a plausible near-infrared counterpart, most closely match a flare from a young pre-main-sequence star, though an active binary or compact-object binary is not excluded. Its large offset from HESS J1303$-$631 makes association with the TeV source unlikely.
[abstract 8 / 58] Yes (score: 5) - Title: Destinies of Plasmoids Formed from the Magnetic Reconnection Occurring within the Ergo Region of a Rotating Black HoleAuthors: Ho-Yun YuChih, Ye Shen,Comments: 10 pages, 6 figures, accepted for publication in Phys. Rev. DSubjects: gr-qc astro-ph.HECreated: 2026-10-18; Updated: 2026-10-20; Datestamp: 2026-10-20
It is widely accepted that MAGNETic RECONNECTions occur successively in BLACK HOLE accretion flows, especially on the equatorial plane, owing to the formation of the equatorial current sheet. When MAGNETic RECONNECTion takes place within the ergosphere of a rotating BLACK HOLE, one of the ejected plasmoids (denoted as $p_-$) may acquire negative energy-at-infinity density, while the companion plasmoid (denoted as $p_+$) correspondingly carries the energy extracted from the BLACK HOLE. This mechanism, known as the Comisso-Asenjo process, provides a viable astrophysical pathway for extracting energy from a rotating BLACK HOLE. Generally speaking, two conditions have to be satisfied for successful energy extraction. First, $p_-$ is generated via MAGNETic RECONNECTion with negative energy-at-infinity density. Second, the associated $p_+$, which carries the extracted energy, must escape to infinity. Though a number of studies have promoted the theory of the Comisso-Asenjo process, the escape of $p_+$ lacks consideration. In this work, we adopt geodesic approach to systematically examine the destinies of $p_+$ after ejection, thereby establishing the complete conditions for energy extraction from a rotating BLACK HOLE via MAGNETic RECONNECTion. We redefine the covering factor, for which only escaping $p_+$ are counted. This quantity reflects how probable the successful energy extraction occurs in an accretion system. Through analysis of this revised covering factor, we identify a lower bound on the BLACK HOLE spin, $a=0.8005$, below which energy extraction via MAGNETic RECONNECTion can never succeed, no matter how high the MAGNETization of the bulk plasma is. This limit suggests that the spin-down of a BLACK HOLE caused by successive MAGNETic RECONNECTions would terminate once the spin decreases to approximately 0.8005.
[abstract 9 / 58] Yes (score: 4) - Title: A 4200-hour HyperFlash and ÉCLAT campaign on the hyperactive FRB 20240114A: constraining energetics with the most brilliant burstsAuthors: O. S. Ould-Boukattine, A. J. Cooper, A. M. Cook, J. W. T. Hessels, D. M. Hewitt, J. Huang, I. Cognard, T. J. Dijkema, M. P. Gawroński, W. Herrmann, F. Kirsten, A. Moroianu, Z. Pleunis, W. Puchalska, S. Ranguin, M. P. Snelders, T. Telkamp,Comments: Accepted for publication in MNRAS, see https:www.doi.org/10.1093/mnras/stag1957Subjects: astro-ph.HECreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
Hyperactive repeaters provide a unique window into the evolving environments and energy budgets of fast radio burst (FRB) sources, though they may not be representative of the FRB population in general. High-cadence observations are key to capturing the rarest and most energetic bursts, which occur only once per hundreds to thousands of hours. Here we present an unprecedented $4{,}200$-hour observing campaign targeting FRB 20240114A as part of the HyperFlash and ÉCLAT FRB monitoring programs. Over $806$ days, we detected $178$ high-energy ($\sim$$10^{40-42}$ erg) bursts with HyperFlash, which together amount to $4.4 \times 10^{42}$ erg of released radio energy (assuming isotropic emission and 1-GHz emission bandwidth). The cumulative energy of the HyperFlash bursts is about twice that of $\sim$$11{,}000$ lower-energy bursts detected with FAST, emphasising the significant role that the highest-energy bursts play in depleting the central engine's stored energy. In fact, the single most brilliant burst from our sample, which we term the STROOP, contributes roughly $1/3$ of all the energy we measure, and is at the maximum energy seen in studies of both repeating and apparently one-off FRBs alike. We also find a break in the burst energy distribution at $\sim$$2\times10^{40}$ erg and a linear dispersion measure (DM) increase of $+0.96 \pm 0.06$ pc cm$^{-3}$ over a period of $318$ days. We discuss these findings in the context of a MAGNETar source model and highlight comparisons with the energetics of intermediate and giant X-ray/$γ$-ray flares from Galactic sources.
[abstract 10 / 58] Yes (score: 4) - Title: The Structure in the Structure Function of Black Hole Light CurvesAuthors: Daniel C. M. Palumbo, Alejandro Cárdenas-Avendaño, Lena Murchikova,Comments: 10 pages, 5 figures, accepted in ApJL. V2: Version to match the published versionSubjects: astro-ph.HECreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
Of the two BLACK HOLEs, M87$^\ast$ and Sgr~A$^\ast$, for which event-horizon-scale imaging is currently achievable, only Sgr~A$^\ast$ at our Galactic Center exhibits sub-hour variability, making light curve observations of the inner accretion flow especially valuable for time-domain studies of the spacetime and the surrounding plasma. Observed light curves are often sampled with variable cadence, so a structure function is often used to quantify their variability properties. In this work, we assemble a heterogeneous Sgr~A$^\ast$ light curve data set from discrete observations acquired over $\sim12$ years at 230 GHz, with different instruments, durations, and cadences, and study its structure function in three frameworks. First, we consider analytic predictions for the features of structure functions of stationary random processes with Fourier spectra dictated by the Matérn covariance. We then study the structure functions resulting from lensed movies of synthetic optically thin accretion flows approximated with Matérn covariance in both space and time, and identify which features in the structure function can be attributed to the black-hole geometry. Lastly, we examine the structure functions of a library of $72$ general RELATIVISTIC MAGNETohydrodynamic simulations. We find that, in general, MAGNETically arrested disk (MAD) models produce smoother structure functions with steeper slopes than standard and normal evolution (SANE) counterparts. On time scales of $5-15$ minutes, the observed structure function slope of Sgr~A$^\ast$ more closely aligns with the MAD trend, while both simulation types are generally more variable than the data on all sub-hour timescales.
[abstract 11 / 58] Yes (score: 4) - Title: Neutrino production at the extreme vicinity of supermassive BLACK HOLE in NGC 1068Authors: Zhi-Peng Ma, Kai Wang,Comments: Accepted for publication in Physical Review DSubjects: astro-ph.HECreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
The identification of NGC~1068 as an extragalactic high-energy neutrino source raises the question of the physical conditions required for neutrino production. Motivated by the newly updated IceCube data (down to $\sim 0.2 \,\rm TeV$) for NGC 1068, we present a statistical, model-independent inference primarily constrained by the multi-messenger observations. We calculate neutrino production from hadronic channels (including hadronuclear and photomeson processes) and the accompanying cascade gamma rays, and then employ the Latin hypercube sampling (LHS) method to explore the parameter space comprehensively, constrained by observational data. According to our results, the emission region is tightly limited: $R \gtrsim 10\,R_{\rm s}$ is excluded at $\sim 5σ$, and $R \gtrsim 6\,R_{\rm s}$ at $\sim 3σ$, where $R_{\rm s}$ is Schwarzschild radius of supermassive BLACK HOLE (SMBH). Furthermore, reproducing $\gtrsim 80\%$ of the observed neutrino flux further restricts the emission to $R \lesssim 3R_{\rm s}$. Finally, we explore the possible particle acceleration mechanisms and find that stochastic acceleration naturally satisfies all constraints, whereas alternative mechanisms require extreme, fine-tuning parameters. We therefore identify stochastic acceleration as the most viable origin of the neutrino emission from NGC~1068.
[abstract 12 / 58] Yes (score: 4) - Title: Multiline Spectropolarimetric Evidence for Photospheric Reconnection in Ellerman Bombs from DKISTAuthors: Rahul Yadav, Maria D. Kazachenko, Viggo Hansteen,Comments: accepted for publication in The Astrophysical Journal LettersSubjects: astro-ph.SRCreated: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20
Ellerman bombs (EBs) are compact, transient brightenings observed in the wings of Balmer lines and are believed to result from MAGNETic RECONNECTion in the lower solar atmosphere. However, their signatures have rarely been observed simultaneously in multiple spectral lines sensitive to the lower atmosphere. We present novel high-resolution multiline spectropolarimetric observations of EBs obtained with the Visible Spectro-Polarimeter (ViSP) on the Daniel K. Inouye Solar Telescope (DKIST). Simultaneous observations reveal remarkable H$β$ wing enhancements extending up to $\sim$4~Å from the line core and intensity enhancements in the \ion{Na}{1}~D1 and \ion{Fe}{1}~6302 lines. Using multiline non-LTE inversion of the \ion{Na}{1} and \ion{Fe}{1} lines, we infer localized photospheric heating of up to $ΔT\sim$800~K, accompanied by weak upflows and downflows at EB locations. Comparing with synthetic observables from Bifrost radiative-MHD simulations, we find that synthetic spectra reproduce the observed H$β$ and \ion{Na}{1}~D wing enhancements and yield atmospheric stratification broadly consistent with those inferred from the non-LTE inversion. This study provides strong evidence that EBs are driven by photospheric MAGNETic RECONNECTion below the temperature-minimum region, and places new constraints on the realistic EB models and small-scale energy release in the lower solar atmosphere.
[abstract 13 / 58] Yes (score: 4) - Title: Effect of induced frame dragging on energy extraction from axially symmetric MAGNETized Reissner-Nordström BH and observational benchmarksAuthors: Ikhtiyor Eshtursunov, Chen Zhou, Sanjar Shaymatov, Pankaj Sheoran, Chengxun Yuan,Comments: 17 pages, 10 captioned figuresSubjects: gr-qcCreated: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20
In this paper, we probe the effect of induced frame dragging on the energy extraction process via MAGNETic RECONNECTion in axially symmetric MAGNETized Reissner-Nordström BLACK HOLE (MRNBH) spacetime and show the influence of BH charge $Q$ and the MAGNETic field $B$ parameters, respectively. We start by analyzing the metric and present the distinction between the geometrical and induced ergospheres. We argue that the induced ergosphere, unlike the geometric ergosphere, is not a property of the spacetime metric but rather a particle-dependent negative energy region that changes as the charge on the particle varies. We find the region where MAGNETic RECONNECTion can extract energy from the axially symmetric MRNBH and determine the conditions required for this process. We further examine the energies of the accelerated and decelerated plasma outflows and the corresponding MAGNETic RECONNECTion efficiency. We show that within the parameter ranges considered, the extraction efficiency increases with the MRNBH charge $Q$ and the MAGNETic field parameter $B$. For sufficiently large $B$, it reaches the efficiency comparable to that of an extremal Kerr BH case. Our results therefore show that electroMAGNETically induced frame dragging can support energy extraction efficiencies similar to those associated with rotation parameter. To connect with observations, we evaluate the RECONNECTion power directly from the decelerated-plasma energy at infinity and compare it with the observed power scales of M87* and Sgr~A*. For $Q=M$, RECONNECTion extraction appears in our scan only for $|B|M\gtrsim0.2$ ($B\sim10^{9}\,\mathrm{G}$ for M87*, $\sim10^{12}\,\mathrm{G}$ for Sgr~A*), where $P_{\mathrm{ext}}\sim10^{53}$--$10^{57}\,\mathrm{erg\,s^{-1}}$ exceeds the observed power scales by many orders of magnitude.
[abstract 14 / 58] Yes (score: 4) - Title: Clumpy Outflows from Super-Eddington Accreting Black Holes. II. Conditions for Clump FormationAuthors: Haojie Hu, Yuta Asahina, Shogo Yoshioka, Hiroyuki R. Takahashi, Ken Ohsuga,Comments: submittedSubjects: astro-ph.HE astro-ph.GACreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
Active galactic nuclei (AGNs) commonly exhibit ultra-fast outflows (UFOs) with velocities of $0.03$--$0.3~c$. Recent high-resolution X-ray observations with XRISM/Resolve suggest that UFOs may have a clumpy structure. However, the formation and evolution of these clumpy outflows remain poorly understood. In the first paper of this series, we investigated the formation of clumpy outflows using numerical simulations and find that sufficiently high spatial resolution is required to reproduce clumpy structures numerically. In this second paper, we perform a series of numerical experiments to identify the key physical processes governing clump formation. We find that spatial fluctuations of physical quantities at the disk surface are essential for the formation of clumpy outflows, whereas spatial and temporal fluctuations at the inner boundary have only a minor effect. Furthermore, density structure-function analysis suggests that the high-density regions have an elongated morphology with characteristic transverse widths of several tens of $R_{\rm g}$, possibly produced by radiation Rayleigh--Taylor instability. A more comprehensive investigation of the instability in general-RELATIVISTIC radiation MAGNETohydrodynamic simulations, where accretion disk structures emerge self-consistently, is expected to provide deeper insights into the physical origin of clumpy outflows.
[abstract 15 / 58] Yes (score: 4) - Title: Pulsars as natural launchers of interstellar probesAuthors: Zaza N. Osmanov,Comments: 7 pages, 4 figuresSubjects: physics.pop-phCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
In this study, we investigate the feasibility of accelerating small probes up to RELATIVISTIC energies via MAGNETocentrifugal acceleration by pulsars. Specifically, we consider a broad range of pulsars and examine probes with radii ranging from $10$ to $1000$ nm. We show that the probes may attain Lorentz factors of up to approximately $25$. Furthermore, we investigate the detectability of such probe swarms and demonstrate that, if a highly advanced civilization deploys probes with a total mass of approximately one billion tonnes for acceleration, their collective SYNCHROTRON emission could be detectable by the FAST radio telescope at a distance of 1 kpc. The study also discusses the potential resemblance between the emission from such probe swarms and fast radio bursts (FRBs), and outlines directions for future research.
[abstract 16 / 58] Yes (score: 4) - Title: X-ray Comptonization in an Accreting Kerr Black Hole System with a Tilted Disc and Thermal Corona; A General-Relativistic Monte Carlo Simulation: I. Model, Radiative Transfer and Spectral-Timing PropertiesAuthors: Mainak Chatterjee, Dipankar Bhattacharya,Comments:Subjects: astro-ph.HECreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
Quasi-periodic oscillations (QPOs) in the X-ray emission of accreting BLACK HOLE binaries are commonly attributed to the RELATIVISTIC Lense--Thirring precession of the inner accretion flow, in which a hot inner flow, tilted with respect to the BLACK HOLE spin axis, precesses as a solid body while a cooler outer disc remains at its own, different tilt -- a warped, Bardeen--Petterson-type geometry. Testing this picture requires a radiative-transfer model that self-consistently follows photons through such a system: from emission near the innermost stable circular orbit (ISCO), through Compton scattering in a hot corona, to possible reflection off the misaligned outer disc, all under the full effects of light bending in Kerr spacetime. In this first paper of a two-part series, we present a general-RELATIVISTIC Monte Carlo (GRMC) radiative-transfer model of a misaligned, warped, two-zone accretion system around a Kerr BLACK HOLE. We describe the disc--corona geometry, the seed-photon prescription, the photon-transport engine -- including the geodesic integration scheme, the coronal Compton-scattering module and the outer-disc reflection treatment -- and the observer pipeline used to construct energy spectra, photon path-length and arrival-time distributions. We present the resulting energy spectra, light curves and spectral lags as functions of the BLACK HOLE mass, corona size, outer-disc geometry, reflection albedo, photon-injection radius and observer inclination, and show how gravitational light bending systematically lengthens the path-length and arrival-time distributions of the escaping radiation. This model and its spectral-timing predictions form the foundation for Paper II, which extends the framework to track the full photon POLARIZATION state and presents the resulting energy- and precession-phase-resolved polarimetric signatures.
[abstract 17 / 58] (score: 3) - Title: A High Incidence of Mid-infrared Variability in Local Ultraluminous Infrared GalaxiesAuthors: Shun Hatano, Masatoshi Imanishi, Takanobu Kirihara, Takashi Yamamoto, Yuxing Zhong, Chenghao Zhu,Comments: 14 pages, 10 figures. Published in PASJSubjects: astro-ph.GA astro-ph.HECreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
We explore mid-infrared (MIR) variability in local ultraluminous infrared galaxies (ULIRGs; infrared luminsoity $L_{\rm IR}>10^{12}\ L_\odot$) utilizing the $\sim$11 years of photometry from the NEOWISE multi-epoch catalog of {\it Wide-field Infrared Survey Explorer} ({\it WISE}). We identify 30 variable ULIRGs with statistically significant MIR variability. The variability is observed on timescales of a few years, implying that the MIR-emitting regions are compact ($\lesssim 1$ pc). The difference between maximum and minimum $W2$ (4.6 ${\rm μ}$m) band luminosity ($ΔL_{\rm W2}$) of the 30 variable ULIRGs range from $ΔL_{W2}$ = $7\times10^{42}$ to $5\times 10^{44}$ erg s$^{-1}$. The $ΔL_{W2}$ of 25 variable ULIRGs out of 30 are greater than $ΔL_{W2}$ = $1\times10^{43}$ erg s$^{-1}$, surpassing the MIR luminosity {range} observed in known SUPERNOVAe (SNe; $L_{\rm 3.6\ {\rm μm}}$ and $L_{\rm 4.5\ {\rm μm}}$ < 10$^{42.3}$ erg s$^{-1}$). Therefore, the MIR variabilities in these 25 ULIRGs are most likely driven by tidal disruption events (TDEs) or intrinsic changes in their ACTIVE GALACTIC NUCLEi (AGN) torus emission. Our sample includes hard X-ray detected AGNs (e.g., UGC 05101) and previously reported TDE candidates (IRAS F01004-2237, IRAS 05189-2524). All 25 also exhibit at least one AGN signature(s) besides the MIR variability, suggesting that even if the MIR variability originates from TDEs, the BLACK HOLEs responsible are likely AGNs. Our results suggest that MIR variability is an effective tool for detecting buried AGNs and highlights the intense nuclear activity in ULIRGs.
[abstract 18 / 58] (score: 3) - Title: Probing an Intermediate-Mass Black Hole Companion of Sagittarius A* with Pulsar TimingAuthors: Zexin Hu, Lijing Shao,Comments: 12 pages, 14 figuresSubjects: astro-ph.HE astro-ph.GA gr-qcCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
An intermediate-mass BLACK HOLE (IMBH) hidden in our Galactic Center (GC) may explain the puzzling observations of the stellar distribution around Sagittarius A* (Sgr A*), the supermassive BLACK HOLE (SMBH) in the GC. Future observations with the next-generation radio telescopes, such as the SKA, are promising to discover pulsars orbiting around Sgr A*, and thus provide the possibility of constraining the hidden IMBH with pulsar timing. We study the detectability of a third-body, the IMBH, in the pulsar-SMBH system based on radio timing observation. We find that the pulsar-SMBH system is very sensitive to such a third-body perturbation and can be used to put stringent constraints on the existence of the IMBH. Even under strong perturbations caused by the complex GC astrophysical environments, timing observation will still complement the existing observational constraints.
[abstract 19 / 58] (score: 3) - Title: A deep learning algorithm for BLACK HOLE spin estimation using hot-spot secondary imagesAuthors: Aristomenis I. Yfantis, Rami Al-Belmpeisi,Comments:Subjects: astro-ph.HE astro-ph.IMCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
Sagittarius A* exhibits frequent flaring activity across the electroMAGNETic spectrum that is often associated with a localized region of strong emission known as a hot spot. We aim to train a deep learning model to provide a link between key parameters of this phenomenon - hot-spot emission radius, and BLACK HOLE inclination and spin - to the observed angle difference between the primary and secondary image ($ΔPA$) that present and future interferometric arrays could resolve. Using the general RELATIVISTIC radiative transfer code IPOLE, we generated a library of $\sim100.000$ models with varying system parameters and computed the position angle difference on the image plane between the primary and secondary images of the hot spot. We explore equatorial and non-equatorial circular orbits and evaluate our models against approximate observational constraints, including partial-orbit visibility and observational errors. Our algorithm STIHOS shows remarkable accuracy in calculating spin and inclination from the majority of the observational tests we perform ($σ_{a_*}=0.04,\,σ_i=2^{\circ}$), even in extreme conditions where only half of the orbit is visible. The off-equatorial estimation provides softer constraints in the absence of prior information. Our results demonstrate the importance of hot-spot observations for spacetime estimations. Given the increasing efforts to detect the photon-ring, our framework could prove valuable in interpreting the first observations of lensed emission.
[abstract 20 / 58] (score: 3) - Title: Axial Mode Stability and Quasinormal Modes of Charged Kiselev Black Holes in Rastall GravityAuthors: Yan Wang, Yun-tao Gu, Wen-Di Guo,Comments: 40 pages,6 figures,4 tablesSubjects: gr-qcCreated: 2026-10-18; Updated: 2026-10-20; Datestamp: 2026-10-20
We investigate axial gravitoelectroMAGNETic perturbations of charged BLACK HOLEs surrounded by dust-like Kiselev-type anisotropic matter in Rastall gravity. We derive the axial matter compatibility condition and construct a compatible response by holding the covariant anisotropy-direction vector unperturbed. The resulting gravitational and electroMAGNETic perturbations obey two coupled Schrodinger-type master equations. An r-independent algebraic decoupling exists in the Reissner-Nordstrom and general-RELATIVISTIC dust-like limits; additional radial structure obstructs it in generic charged Rastall backgrounds with nonzero surrounding matter. We prove axial mode stability under the adopted closure for every nonextremal background satisfying the stated exterior conditions, covering all physical axial multipoles. A matrix S-deformation excludes exponentially growing coupled modes for l >= 2, while the physical electroMAGNETic dipole has a positive effective potential. A Chebyshev pseudospectral calculation, validated against the Reissner-Nordstrom spectrum and spectral convergence, determines the fundamental frequencies. In the parameter ranges examined, increasing the Rastall coupling lowers both the oscillation frequency and the damping rate in the small-coupling region; in the large-coupling region, the oscillation frequency rises while the damping rate varies nonmonotonically. A larger charge generally raises the oscillation frequency, whereas stronger surrounding-matter contributions produce longer-lived modes.
[abstract 21 / 58] (score: 3) - Title: Critical MAGNETic Reynolds number of the weakly-collisional turbulent dynamo in supersonic plasmasAuthors: Radhika Achikanath Chirakkara, Christoph Federrath,Comments: 10 pages, 5 figures, submitted to MNRASSubjects: astro-ph.CO physics.plasm-phCreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
Weakly-collisional plasmas are found in several turbulent astrophysical environments, such as the Intra-galaxy-cluster medium (ICM) and the solar wind, where MAGNETic fields can be amplified by the turbulent dynamo. The onset of dynamo action is determined by the critical MAGNETic Reynolds number, ${\rm Rm}_{\rm crit}$, above which turbulent motions amplify MAGNETic energy. Although ${\rm Rm}_{\rm crit}$ has been studied extensively in collisional MAGNETohydrodynamic (MHD) turbulence, its value in supersonic weakly-collisional plasmas remains unknown. Here we determine ${\rm Rm}_{\rm crit}$ using three-dimensional hybrid particle-in-cell (HPIC) simulations of solenoidally driven turbulence with a sonic Mach number $\approx 2$. We vary the MAGNETic Reynolds number over ${\rm Rm}\approx31$-$1000$ and consider two initial plasma MAGNETisations, characterised by initial Larmor ratios $r_{\rm Larmor, 0}/L_{\rm box}=1$ and $100$. We find that the MAGNETic energy grows exponentially at sufficiently large ${\rm Rm}$ and decays when MAGNETic diffusion dominates at low ${\rm Rm}$. By fitting the MAGNETic-energy growth rate as a function of ${\rm Rm}$, we measure ${\rm Rm}_{\rm crit}=190^{+21}_{-17}$ and $198^{+16}_{-18}$ for the initially MAGNETised and unMAGNETised plasma, respectively. These values are the same within their uncertainties, indicating that the initial plasma MAGNETisation does not significantly affect ${\rm Rm}_{\rm crit}$ in the supersonic regime. The measured values are higher than those previously obtained for the subsonic weakly-collisional dynamo, showing that increasing compressibility makes weakly-collisional turbulent dynamo action more difficult to excite. The measured values are also approximately 1.5 times higher than the ${\rm Rm}_{\rm crit}$ value reported for supersonic MHD turbulence.
[abstract 22 / 58] (score: 3) - Title: Periodic orbits and gravitational-wave emission from extreme-mass-ratio inspirals around rotating charged BLACK HOLEs in nonlinear electrodynamicsAuthors: Xi Luo, Meirong Tang, Zhaoyi Xu,Comments: 25 pages, 10 figures, 2 tablesSubjects: gr-qcCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
Within general-RELATIVISTIC descriptions, the no-hair theorem dictates that black-hole geometries possess just three intrinsic physical quantities: mass, angular momentum, and electric charge. Black holes in nonlinear electrodynamics (NED) are equivalent to those composed of anisotropic matter and can develop "hair" structures near the event horizon, serving as ideal testbeds for modified theories of gravity. Working within Einsteinian gravitational theory, we adopt a coupling construction between gravity and NED matter, focusing explicitly on the Einstein-Euler-Heisenberg (EEH) variant with the power-index parameter fixed at s = 2. In this framework, a rotating, charged NED BLACK HOLE extends the Kerr-Newman geometry with extra correction terms. Treating spin a and NED charge q as primary control variables, we examine test-particle dynamics inside extreme-mass-ratio inspiral (EMRI) configurations. We derive equatorial timelike geodesics and the effective potential. Through numerical evaluation of marginally-bound orbits (MBO) and innermost stable circular orbits (ISCO), we explore how these parameters reshape the energy-angular-momentum (E-L) phase-space. Using the (z, w, v) integer-valued orbit taxonomy, we compute the two gravitational-wave POLARIZATION modes h+ and hx via the adiabatic approximation and quadrupole radiation prescription. Larger values for a and q drive inward contraction for bound trajectories while displacing the E-L phase-space toward smaller angular-momentum values. Periodic-orbit zoom-whirl signatures grow increasingly prominent, while larger parameter values shorten the waveform periods and enhance signal amplitudes. Our results provide theoretical support for space-borne gravitational-wave observatories including LISA and TianQin, enabling prospects for discriminating NED black-hole spacetimes and performing observational checks on the no-hair theorem.
[abstract 23 / 58] (score: 3) - Title: Disc breaking and parametric instability in warped accretion discs driven by differential precessionAuthors: Loren E. Held, Gordon I. Ogilvie,Comments: Submitted to MNRASSubjects: astro-ph.SR astro-ph.HECreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
We present the first local simulations of accretion disc breaking (or disc tearing) with differential precession. Precession can occur due to a non-spherical potential (e.g. tilted circumbinary discs), or RELATIVISTIC effects (e.g. tilted discs around spinning BLACK HOLEs). This tends to induce a twist in the disc, potentially causing it to break into rings. We extend earlier work on free (unforced) warps in Held+2026 [arXiv:2511.18655v1] to include differential precession in the shearing box, and carry out quasi-2D, isothermal, high-resolution ($N = 32$ cells per scale-height $H$) numerical simulations in which an imposed precession drives a warp in a tilted disc in either the wavelike ($α< H/r$) or diffusive ($α> H/r$) regime. Our key finding is that, at sufficiently large tilts and precession amplitudes, the disc breaks into multiple (4-5) mutually tilted rings exhibiting a rich morphology: from wide ($\sim 10H$), flat rings to compact tori of width $\sim H$. Interactions between rings occur as a result of oblique shocks that form in the gaps between them, leading to instances of disc rejoining. Smaller tilts and precession amplitudes lead instead to parametric instability of inertial waves in the disc. We develop a linear viscous theory of bending waves under the influence of an imposed precession. Finally, we present a systematic study of the effects of grid-based dissipation on tilted discs, and find that numerical dissipation damps the tilt and induces precession. This effect decreases with resolution as $\propto (1/N)^β$, $2.3 \lesssim β\lesssim 3.9$.
[abstract 24 / 58] (score: 3) - Title: Ion Heating in Pair-loaded Relativistic TurbulenceAuthors: Yusen Wang, Zhonghai Zhao, Xinyu Zhu, Xianxu Jin, Zhipeng Zhang, Bin Qiao,Comments:Subjects: physics.plasm-phCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
Pair-loaded RELATIVISTIC turbulence is expected in compact high-energy astrophysical environments and may sustain plasma heating. Using self-consistent three-dimensional radiative particle-in-cell simulations, we identify the mechanism of ion heating mediated by pair-enhanced radiative feedback in RELATIVISTIC turbulence. We derive the theoretical criterion for the transition to a regime dominated by radiative feedback and show that pair loading promotes the growth and persistence of large, connected optically thick structures. These long-lived structures sustain intense localized ion heating, repeatedly generating prominent hot-ion clumps and substantially enhancing the mean ion temperature. Our results establish a physical link between pair creation and sustained ion heating, providing a theoretical basis for investigating intermittent hot-ion production in black-hole coronae and GAMMA-RAY BURST outflows.
[abstract 25 / 58] (score: 2) - Title: SynradG4: A Geant4-Based Extension for Synchrotron Radiation Background Studies in the ePIC Detector at the Electron-Ion ColliderAuthors: Andrii Natochii,Comments: 13 pages, 9 figures, 3 tables. v4: revised reflection model (intensity Debye-Waller factor, local-frame diffuse sampling, current Synrad+ parameters), benchmark rerun, new Sec. 3.2 on the Geant4 roughness-factor conventionSubjects: physics.acc-ph physics.ins-detCreated: 2026-10-18; Updated: 2026-10-20; Datestamp: 2026-10-20
The Electron-Ion Collider (EIC) will operate at high luminosity with multi-GeV, high-current electron beams, resulting in substantial SYNCHROTRON radiation (SR) emission in the electron storage ring (ESR). A detailed understanding of SR photon transport in the complex three-dimensional interaction region (IR) geometry is critical for estimating backgrounds in the ePIC detector and for developing effective shielding and masking strategies. This paper presents SynradG4, an EIC-specific extension of Geant4 for fast photon tracking in vacuum based on established models of SR reflection and rough-surface scattering. SynradG4 integrates the specular and diffuse photon reflection models of Synrad+ into the Geant4 geometry and field framework, while disabling all bulk matter interactions to achieve high-statistics transport through the 50-m-long IR vacuum system. The absorbed photons are then passed to a second-stage DD4hep simulation, in which electroMAGNETic processes such as photoabsorption, Compton scattering, Rayleigh scattering, and fluorescence are enabled for their propagation through the beam pipe and detector materials. SynradG4 is not intended to replace general SR simulation codes; rather, it complements them by providing the workflow and geometry integration capabilities needed for EIC-specific background studies. Benchmark tests show that SynradG4 reproduces Synrad+ to within about 1% for both specular and diffuse reflection, and that it agrees well with Synrad3D and with the native Geant4 X-ray reflection model for smooth surfaces. Using the full IR geometry and machine lattice, we present the first SR background estimates for the ePIC detector and evaluate the impact of potential SR masks.
[abstract 26 / 58] (score: 2) - Title: Primordial Black Hole Abundance from ReionizationAuthors: Ziwen Yin, Hanyu Cheng, Luca Visinelli,Comments: 11 pages, 5 figuresSubjects: astro-ph.CO hep-phCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
We derive robust constraints on the initial abundance of evaporating primordial BLACK HOLEs (PBHs) using the reionization history of the Universe as a cosmological probe. We focus on PBHs that inject electroMAGNETic (EM) energy into the intergalactic medium (IGM) after recombination, in the mass range $3.2\times 10^{13}\,\mathrm{g} \lesssim M_{\rm PBH} \lesssim 5\times 10^{14}\,\mathrm{g}$. For each PBH mass, we compute the redshift-dependent energy injection from Hawking evaporation using \texttt{BlackHawk}, fully accounting for the time evolution of the PBH mass and the complete spectrum of emitted Standard Model particles and gravitons. The resulting photons and electrons are propagated through the primordial plasma using \texttt{DarkHistory}, which self-consistently models EM cascades and determines the fraction of injected energy deposited into ionization, excitation, and heating of the IGM. These modifications to the ionization and thermal histories are incorporated into a Gaussian Process reconstruction of the free-electron fraction based on low-$\ell$ CMB POLARIZATION data from the \textit{Planck} mission. This non-parametric approach allows for a statistically well-defined separation between exotic high-redshift energy injection and late-time astrophysical reionization, allowing PBH evaporation to be constrained through its contribution to the high-redshift optical depth. Requiring consistency with current CMB measurements, we obtain upper limits on the initial PBH abundance that are robust against reionization modeling uncertainties and systematically more conservative than existing bounds, reflecting the fully numerical and time-dependent treatment of Hawking evaporation and energy deposition. Our results demonstrate the power of reionization observables as a precision probe of PBH evaporation and other scenarios involving late-time energy injection.
[abstract 27 / 58] (score: 2) - Title: Effects of Viscosity on Sloshing Cold Fronts in Galaxy ClustersAuthors: Ming-Hsueh Hsieh, H. -Y. Karen Yang, John ZuHone,Comments: 10 pages, 13 figuresSubjects: astro-ph.HE astro-ph.CO astro-ph.GACreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
The viscous properties of the intracluster medium (ICM) remain poorly constrained. Cold fronts-sharp discontinuities formed during cluster mergers-offer a potential avenue to probe the effective viscosity of the ICM. Velocity shear across these fronts should generate Kelvin-Helmholtz instabilities (KHI), unless viscosity or MAGNETic tension suppresses them. We perform cluster merger simulations incorporating four ICM viscosity models: (A) inviscid, (B) isotropic Spitzer viscosity, (C) anisotropic Braginskii viscosity, and (D) Braginskii viscosity limited by microinstabilities. The isotropic Spitzer viscosity (case B) strongly suppresses KHI, producing smooth cold front surfaces, while the inviscid (A) and microinstability-limited (D) cases show prominent ripples. The Braginskii case (C) yields intermediate suppression. We also vary the plasma $β$ parameter ($β\approx$ 100 and 1600) to examine how a changing MAGNETic field strength affects the results. Stronger MAGNETic fields further suppress KHI, leading to smoother fronts and reduced differences between different viscosity models, while also widening the range of permitted pressure anisotropies when microinstability-based limiters are present. These results indicate that both viscosity and MAGNETic fields play crucial roles in stabilising sloshing cold fronts in galaxy clusters.
[abstract 28 / 58] (score: 2) - Title: Stars with Plumbing Issues: The Multi-component Ejecta of Common EnvelopesAuthors: Sarah V. Borges, Philip Chang,Comments: Will be submitted shortlySubjects: astro-ph.SRCreated: 2026-10-18; Updated: 2026-10-20; Datestamp: 2026-10-20
Common-envelope evolution (CEE) is one of the major open problems in binary stellar evolution, even though it is the primary channel for forming close binaries with at least one compact object. While CEE is often assumed to lack direct observational constraints, recent connections between CEE and the transient class, luminous red novae (LRNe), as well as the post-AGB systems known as Water Fountains (WFs), provide new opportunities to understand how this event unfolds. Collectively, these observations suggest that envelope ejection during CEE is neither spherically symmetric nor homologous, but rather produces complex ejecta, providing constraints for simulations of CEE. In this work, we present a series of three-dimensional hydrodynamical (non-MHD) simulations of CEE for a 2 Msun red-giant-branch (RGB) star and show that the event naturally produces multi-component ejecta including an extended radially expanding shell, a thick circumbinary disk (CBD), and collimated bipolar outflows. Consistent with previous works in the literature, the bipolar outflows in our simulations arise naturally through geometrical constraints imposed by the disk and do not require MAGNETic fields. While we find that the formation of the collimated outflows can be sensitive to the choice of Riemann solver, they appear across all resolutions and mass ratios tested in this work. We show that the multi-component ejecta formed during CEE simulations naturally reproduce some of the key properties of CEE observations, including the classical bipolar shape seen in some LRNe, WFs, and planetary nebulae.
[abstract 29 / 58] (score: 2) - Title: Revisiting the $r_s$ expansion of the uniform electron gas in $d$ dimensions: $\log r_s$ terms from coincident Mellin polesAuthors: Fumihiro Imoto,Comments: v4: substantially rewritten and extended, with a new title. Supersedes v1-v3, which treated only the screened second-order exchange (kite) diagram in three dimensions with a single-pole or static screened line. The spin-polarized kite is now in a companion paper (ChemRxiv, doi:10.26434/chemrxiv.15008489/v1). 96 pages including the Supporting Information, 6 figuresSubjects: physics.comp-phCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
The high-density expansion of the correlation energy of the uniform electron gas contains $\log r_s$ terms, where $r_s$ is the Wigner--Seitz radius. Their form depends on the dimension $d$. Adapting the Mellin-transform analysis of Feynman integrals in RELATIVISTIC field theory, we write the energy of the ring series and of diagrams linear in one screened interaction line in $d$ dimensions as Mellin convolutions of a radial kernel, fixed by the diagram, with a scaling function. The scaling function depends on the momentum transfer only through its ratio to a density scale. In the Mellin variable $s$, screening places poles at $s=N(d-1)$ with $N=1,2,\dots$, and the diagram places a pole at $s=d+1$ for the rings and at $s=2$ for a POLARIZATION insertion. Once the factors $\log(1/q)$, with $q$ the momentum transfer, cancel between the vertex and self-energy corrections, as the Ward identity requires, a $\log r_s$ term appears where two poles coincide. This rule reproduces the known $\log r_s$ terms in two and three dimensions. In two dimensions it gives the coefficient of the next $\log r_s$ term, $r_s^2\log r_s$, in closed form, $7/π+4\log2/π-160/(9π^2)-16G/π^2=-0.17546$~Ry with $G$ Catalan's constant. In three dimensions the screened second-order exchange diagram alone has an $r_s\log^2r_s$ term at high density and an $r_s^{-1/4}$ term at low density, and the Fock self-energy corrections cancel both.
[abstract 30 / 58] (score: 2) - Title: Predictors of filament coil non-planarity in a dataset of QI stellaratorsAuthors: Andrea Pavone, Sehyun Kwak, Felix Warmer,Comments:Subjects: physics.plasm-phCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
Stellarator MAGNETic fields are often realized with non-planar modular coils with their out-of-plane bending being one of the main engineering challenges. We ask whether the non planarity of the fialment can be predicted from the equilibrium alone. We look at a dataset of coils for stellarator equilibira and find that the geodesic torsion of the MAGNETic field line is a strong and robust predictor in a wide range of coil feasibility requirements. We compare the performance of the geodesic torsion against other equilibrium and surface geometry properties and find it to be a superior predictorv hardly replaceable by other quantities we considered in this dataset. The ranking it induces also reproduces the ordering of four published configurations --- precise QA, precise QI at nfp 2 and 3, and W7-X. Our conclusions suggest that geodesic torsion of the MAGNETic field line may be considered as a cheap and robust candidate for a stage-one non-planarity proxy.
[abstract 31 / 58] (score: 2) - Title: Squid funnels time their elastic recoil to amplify pulsed JETsAuthors: Daehyun Choi, Paras Singh, Ian Bergerson, Minho Kim, Jieun Park, Halley J. Wallace, Kenny Zhang, Sandy Y. Hsieh, Aqua T. Asberry, Theodore A. Uyeno, William F. Gilly, Hyungmin Park, Daeshik Kang, Chandan Bose, Saad Bhamla,Comments: 49 pages (11 pages main text, 38 pages Supplementary Materials), 3 main figures, 28 supplementary figures, 1 table. Revised versionSubjects: physics.flu-dynCreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
Pulsed JETs propel squid across nearly four orders of magnitude in body size. Each pulse leaves through the funnel, a soft nozzle, but whether its compliance acts within a pulse is not known. We tracked chromatophores on two squid species and found that the funnel dilates and recoils, with a repeatable phase lag, while the mantle is still contracting, and that the lag persists after denervation. For inertia-dominated JETs, silicone nozzles, 3D fluid-structure simulations and a reduced-order model agree that the impulse reaches about 4$\times$ the rigid value when the nozzle response time is 0.2 to 0.4 of the JET-acceleration time, a range that overlaps the in vivo timing. The wall stores strain energy during acceleration and returns it during expulsion (akin to an elastic capacitor), which we term "superpropulsion". Synthetic nozzles tuned for superpropulsion launch JETs farther in air, disperse dye faster, and drive a boat faster at a lower cost of transport.
[abstract 32 / 58] (score: 2) - Title: Computing statistical solutions of a Mach 2000 astrophysical JETAuthors: Stephan Simonis, Gauthier Wissocq,Comments:Subjects: math.NA cs.MS cs.NA physics.comp-ph physics.flu-dynCreated: 2026-10-18; Updated: 2026-10-20; Datestamp: 2026-10-20
The multi-dimensional compressible Euler equations admit non-unique entropy solutions in turbulent regimes, and extreme-Mach astrophysical flows are a natural setting in which this breakdown of deterministic well-posedness becomes computationally visible. We compute statistical solutions of a Mach~2000 astrophysical JET, defined as the pushforward of an initial probability measure through a vectorial lattice Boltzmann method, by Monte Carlo sampling with $M=1000$ realizations on grids of up to $12.8$ million cells. Under mesh refinement the individual realizations diverge pathwise, while the statistical solution converges: Wasserstein distances of the one- and two-point marginals, the ensemble mean, and the ensemble standard deviation all exhibit stable positive convergence rates. A spatially resolved analysis along the JET axis traces this dichotomy to the structure of the one-point laws, which are numerically Dirac in the undisturbed core, skewed in the sheared turbulent regions, and intermittent two-state mixtures at the random leading front. We conclude that the computed statistical solution is non-Dirac and remains stable in the extreme compressible regime, in which no strong solution is expected to exist.
[abstract 33 / 58] (score: 2) - Title: Analysis of collisional and facility effects in a MAGNETic nozzle plasma expansionAuthors: Manuel Cortés-Hernán, Mario Merino, Diego García-Lahuerta, Eduardo Ahedo,Comments: 36 pages, 10 figuresSubjects: physics.plasm-phCreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
An axisymmetric, quasineutral three-fluid model is proposed to study the plasma expansion in a MAGNETic nozzle under the presence of neutrals coming either from the plasma source or as an homogeneous background. As a difference with other models, electron cooling in the plume is achieved by treating the electron energy flux as mainly convective and without the need to postulate any anomalous resistivity. Solutions are presented for the electron high-MAGNETization limit, in which the electron main magnitudes can be integrated along MAGNETic lines. Ionization, elastic and charge-exchange collisions with neutrals do not change the main qualitative features of the plasma expansion, known from previous collisionless models. Ionization enhances the plasma flow in the nozzle, and leads to additional electron cooling, which decreases the electric potential fall along the nozzle. The efficiency of the nozzle is quantified in terms of the gain of MAGNETic thrust and the plume divergence angle. Two types of boundary conditions are discussed for the electron flow: local current ambipolarity conditions at the nozzle throat and global current-free conditions at the outer boundary (i.e., metallic vacuum chamber walls). These last ones are shown to be physically more reliable: they introduce the influence of the chamber walls on the plasma expansion by shaping the ambipolar electric field; they permit the extrapolation to undisturbed free space conditions; and they approximate better experimental trends with the background pressure.
[abstract 34 / 58] (score: 2) - Title: Lattice Boltzmann Methods for Navier-Stokes Equations in General Orthogonal Coordinates for Efficient Flow Simulations using Nonuniform Clustered GridsAuthors: Eman Yahia, Kannan Premnath, William Schupbach,Comments: 92 pages, 24 figuresSubjects: physics.flu-dyn physics.comp-phCreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
Resolving multiscale fluid flows or boundary layers effectively requires the use of nonuniform meshes with local grid clustering. The standard lattice Boltzmann method (LBM), a kinetic theory-based approach for computational fluid dynamics, however, is restricted to the use of uniform Cartesian grids. We present new and improved formulations of the LBM that accommodate continuously varying spatial grids via coordinate transformations to simulate the Navier-Stokes equations (NSE) in the general orthogonal coordinates (GOC). They are constructed using a Chapman-Enskog analysis to specify the equilibrium moments of the distribution functions and the geometric force terms used in the collision step to be dependent on the local metric factors and their spatial derivatives, along with the density, momentum and their fluxes, and some correction terms related to the normal velocity gradients so as to accurately represent the NSE in the GOC. The resulting GOC-LBM importantly maintains the simplicity of the collide-and-stream approach and is Galilean invariant that is free of the cubic velocity artifacts. Our GOC-LBM is general and modular in that it can be used with any collision model with appropriate modifications to the equilibria and forcing terms. We present its implementation details for a variety of collision models while the central moments-based model using multiple relaxation times was found to be the most robust in practical implementations. We validate the GOC-LBM through numerical simulations for various benchmark flow problems. Moreover, we demonstrate significant computational advantages of our approach for a case study on simulating boundary layer flows efficiently that involves coupling the GOC-LBM for the NSE with a new GOC-LB scheme for solving the MAGNETic induction equation for MAGNETohydrodynamics (MHD), and for another case study involving orthogonal curvilinear grids.
[abstract 35 / 58] (score: 2) - Title: Magnetic pressure anisotropy in ultra-dense white dwarfs: Landau quantization and neutronization effectsAuthors: Edson Otoniel, Juan M. Z. Pretel, Victor B. T. Alves, César O. V. Flores, Clésio E. Mota,Comments: 14 pages, 6 figures and 2 tablesSubjects: astro-ph.SR astro-ph.HE gr-qcCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
Strong MAGNETic fields modify the thermodynamics of white dwarf (WD) matter by quantizing the transverse motion of degenerate electrons into Landau levels and splitting the pressure into components parallel and perpendicular to the MAGNETic field. We investigate how this microscopic pressure anisotropy affects ultra-dense WD sequences when Coulomb lattice contributions, electron capture thresholds, neutron drip limits, and nuclear composition are treated consistently in the equation of state (EoS). The stellar equilibrium structure is obtained by solving an anisotropic extension of the Tolman--Oppenheimer--Volkoff (TOV) equations, where $P_r = P_\parallel$ and $P_t = P_\perp$ denote the radial and tangential pressures, respectively. We compare the post-electron-capture branches with their corresponding pre-capture sequences for pure $^{12}\rm{C}$, $^{16}\rm{O}$, $^{20}\rm{Ne}$, and $^{24}\rm{Mg}$ compositions, as well as for fixed 50/50 C/O, Ne/O, and Mg/Ne mixtures. The EoS predicts $P_\perp < P_\parallel$ in density ranges where only a few Landau levels are occupied. Consequently, pressure anisotropy shifts the stellar sequences toward smaller radii, with only minor changes in the maximum masses. We also find that post-capture configurations cannot be interpreted from the mass--radius plane alone, since the corresponding $M(ρ_c)$ curves reveal unstable portions after the maximum mass is reached. Our results show that strong MAGNETic fields significantly reduce the radii of low-mass WDs, yielding better agreement with the observational data available in the Montreal White Dwarf Database and suggesting that future high-precision observations of massive MAGNETic WDs could help assess the role of MAGNETic pressure anisotropy in determining their masses and radii.
[abstract 36 / 58] (score: 2) - Title: The impact of recombination during tidal disruption eventsAuthors: Simona Pacuraru, Clément Bonnerot, Martin E. Pessah,Comments: Accepted for publication in MNRASSubjects: astro-ph.HE astro-ph.GACreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
During a tidal disruption event, the resulting debris stream cools down adiabatically due to the tidal stretching. As the temperature drops, the gas is expected to undergo chemical processes, which can release thermal energy into the stream, potentially affecting the subsequent gas evolution. For the first time, we investigate in detail this effect and its dynamical impact on the early-time evolution of the stream by making use of three dimensional hydrodynamic simulations coupled with a realistic equation of state. We find that a few days after disruption, the energy injected by hydrogen recombination and molecular hydrogen formation causes the stream thickness to grow much more rapidly. In the bound debris, this effect stops the stream's confinement by self-gravity before the gas reaches apocentre. As a result, the maximum stream thickness increases by a factor that ranges from a few, for the most bound gas, to a few tens for the near-parabolic gas, reaching $\approx 30 \, R_{\star} $ around the peak of the mass fallback rate. We discuss how this accelerated stream expansion may affect the subsequent evolution of the gas, estimate the luminosity powered by recombination in the unbound debris, and evaluate the potential influence of non-ideal MAGNETo-hydrodynamic effects. By characterizing the thermodynamic and hydrodynamic properties of the stream before its return near pericentre, our results provide physically motivated initial conditions to self-consistently model the later stages of tidal disruption events, offering a promising pathway to unveiling the physical origins of their observed emission.
[abstract 37 / 58] (score: 2) - Title: The Impact of Errors in the Shape Function of Rotating Neutron Stars in the Oblate Schwarzschild ApproximationAuthors: John Ming Ngo, Charlee Amason, Sharon M. Morsink,Comments: Accepted by Physical Review D. This revision matches the accepted versionSubjects: astro-ph.HECreated: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20
Measurements of thermal X-ray flux emitted by neutron stars can constrain their radii and the equation of state of cold dense matter. Accurate flux modeling of rapidly rotating neutron stars requires an approximation for their oblate surface shape, usually given by a shape function. We examine the accuracy of five shape functions by comparing them against numerical RELATIVISTIC stellar surfaces for seven representative equations of state over a broad range of compactness and spin. We characterize their errors in the surface radius and their derivative with respect to colatitude, test the extent of quasi-universality, and propagate these errors into the differential solid angle dΩ, a geometric factor underlying the observed flux, under the oblate Schwarzschild approximation. We find that the shape functions produce distinct error patterns associated with their forms and parameter ranges. These errors remain structured in compactness, spin, and colatitude. Simple polynomial corrections substantially reduce the radius errors of several shape functions, with most corrected errors within approximately 0.5%. We show that errors in dΩ may be understood as coming from an area contribution, which scales with twice the relative radius error, and a projection contribution controlled primarily by the error in the surface derivative. The projection contribution grows towards the limb, where small surface errors can produce much larger local errors in dΩ. We provide a set of guidelines for the construction of improved quasi-universal shape functions that can be used in future radius estimation efforts. Our recommendations include that both the shape and its derivative be modeled accurately, that more accurate predictions of the polar radius be developed, and that the shape function be calibrated over the same compactness-spin range that is to be tested.
[abstract 38 / 58] (score: 2) - Title: Screened Scalar Hair and the Weak-Lensing Separation of Black Holes from Neutron Stars in Quadratic $f(R)$ GravityAuthors: Yashmitha Kumaran, Ilídio Lopes,Comments: 9 pages, 4 figuresSubjects: gr-qcCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
Quadratic $f(R)$ gravity carries a massive scalar degree of freedom, the scalaron, whose finite range $λ$ screens its influence on the geometry outside a compact object. We show that this screening severs the exterior of a BLACK HOLE from that of a neutron star of the same mass. Correction to the Schwarzschild metric is Yukawa-suppressed, falling as $e^{-r/λ}$ in the coupling, and is thus invisible to any expansion in powers of that coupling; the exterior is moreover intrinsically isotropic, so that inverting the temporal potential alone, as one does for single-potential solutions, fails to solve the field equations. Applying the Gibbons & Werner method of the Gauss-Bonnet theorem to this geometry, we find the leading deflection angle to be exactly the general-RELATIVISTIC, ($b$: impact parameter), scalaron contributions cancelling identically in the combination that bends light. First correction carries the unfamiliar signature $λ^{-1/2}b^{-3/2}e^{-b/λ}$, screened beyond the scalaron range and confirmed against direct quadrature to around 20% at $b=4λ$, improving to 7% at $b=12λ$. What survives is the ingredients that deliver it, namely, non-analyticity in the coupling, the intrinsically isotropic gauge, the closed-form screened correction and the pressure-weighted scalar charge, are obtained within a single, self-consistent derivation here. A static BLACK HOLE carries no scalar hair, and lenses precisely as general relativity requires; a neutron star acquires a scalar charge weighted by the pressure supporting it against collapse, and does not. Weak lensing therefore closes as a discriminant of the theory, whilst the horizon, as against a material surface, remains one in principle. The observational advantage lies in the strong-field imaging of the photon sphere, and in the stellar interior, where the scalar charge is fixed by the equation of state.
[abstract 39 / 58] (score: 2) - Title: Observational properties of MAGNETized quantum Oppenheimer-Snyder BLACK HOLEsAuthors: Anuar Idrissov, Hernando Quevedo,Comments: 17 pages, 14 figures, 2 tablesSubjects: gr-qcCreated: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20
We consider a thin accretion disk around the quantum Oppenheimer-Snyder BLACK HOLE immersed in an asymptotically uniform MAGNETic field, together with the gravitational capture of test particles by the BLACK HOLE. The field is described as a Wald test field and acts only on the weakly charged matter of the disk. We find that the quantum correction affects the disk only slightly, while the MAGNETic coupling strongly increases its radiative efficiency and luminosity and suppresses the Doppler blue peak of the iron K$α$ line, which becomes a single peak below the rest frame energy. On the other hand, the quantum correction reduces all capture cross sections, while the MAGNETic field does not affect the capture of photons and confines charged particles to a finite region. Therefore, in principle, the two effects may be distinguished by combining spectral and shadow observations.
[abstract 40 / 58] (score: 2) - Title: Onset of Chaos and Orbital Instabilities around Rotating Weyl Black HolesAuthors: Shubham Kala, M. Yousaf, Pradeep Singh, Faisal Javed, Hemwati Nandan, G. Mustafa,Comments: 22 pages, 10 figures, comments are welcomeSubjects: gr-qcCreated: 2026-10-13; Updated: 2026-10-20; Datestamp: 2026-10-20
We investigate nonlinear photon motion in the vicinity of a rotating BLACK HOLE (BH) within Weyl conformal gravity (WCG) by employing Poincare sections, Lyapunov exponents, Fast Lyapunov Indicators (FLI), Kolmogorov-Sinai (KS) entropy, and Discrete Indicator of Chaos (DIG) maps. The joint influence of BH spin and higher order curvature corrections, governed by the parameters $ξ$ and $γ$, induces a transition from nearly integrable trajectories to markedly chaotic dynamics in the strong field domain. As $ξ$ and $γ$ increase, the invariant tori are increasingly deformed and eventually break up. Resonance islands and stochastic layers then form, producing large chaotic regions in phase space, especially near the extremal spin regime. Increasing Lyapunov exponents, faster FLI growth, and higher KS entropy provide quantitative measures of the enhanced dynamical instability, the increased sensitivity to initial conditions, and the corresponding rate of information production. DIG maps show shrinking regular regions and expanding chaotic domains around the photon sphere, indicating that conformal gravity corrections destabilize null circular orbits. Taken together, these findings clarify how RELATIVISTIC frame dragging and higher order curvature terms jointly control photon chaos and point to nonlinear photon dynamics as a potential probe of departures from General Relativity in the strong-gravity regime.
[abstract 41 / 58] (score: 2) - Title: Astrophysical Signatures of Charged Anisotropic Compact Star in f(R,T) Gravity via Minimal Geometric DeformationAuthors: Hira Shadab, M. Sharif, Tayyab Naseer,Comments: 38 pages, 9 figuresSubjects: gr-qcCreated: 2026-10-15; Updated: 2026-10-20; Datestamp: 2026-10-20
This work employs minimal geometric deformation to develop two new anisotropic solutions under the effects of an electroMAGNETic field in the context of $f(R,T)$ theory. Our investigation begins with a static spherical system with an anisotropic fluid as a seed source. After that, a new source is inserted to the existing fluid distribution and both the fluid distributions are assumed to be gravitationally coupled with each other. After computing the Einstein-Maxwell field equations, a radial transformation is applied which results in two different sets of equations. These systems are solved individually under different constraints, generating new solutions. To obtain the constants in our interior solutions, we match the internal geometry with the external Reissner-Nordström spacetime at the surface. We further validate our models by using the known mass and radius of a star LMC X-4. Our investigation confirms that both RELATIVISTIC stellar models satisfy all the physical requirements for the specified decoupling parametric values.
[abstract 42 / 58] (score: 2) - Title: A Two-Population von Mises--Fisher Distribution of the Magnetic Field Direction in the Young Solar WindAuthors: Gang Li, N. H. Bian, S. Y. Huang, A. Chian, R. Santos-Lima, E. L. Rempel, R. A. Miranda, B. Raphaldini, Yasmmin Tamburus,Comments: submitted to ApJLSubjects: astro-ph.SRCreated: 2026-10-16; Updated: 2026-10-20; Datestamp: 2026-10-20
The one-point distribution of the MAGNETic field direction in the young solar wind is found to be a superposition of two populations rather than a single exponential. Using Parker Solar Probe (PSP) Encounter 1 MAGNETometer data, we show that the distribution of the pitch-angle cosine mu(t) = bhat(t) . bhat_0 is well described by a two-component von Mises-Fisher (vMF) mixture: a broad, weakly confined component of concentration kappa_1 ~ 3.6 that accounts for the large-amplitude rotations and switchback tail, and a field-aligned component that reduces, in the small-angle limit, to a Gaussian in the polar angle theta of width sigma ~ 15 degrees (concentration kappa_2 ~ 14). The concentration of the field-aligned component is not a free parameter: it is set by the level of the transverse Alfvenic fluctuation through kappa_2 = 2<|B|^2>/
= 2/<1-mu^2> ~ 16.2, in agreement with the fitted value to within ~12%. The transverse fluctuations are weakly anisotropic ( / ~ 1.1), so the core is a weakly anisotropic Bingham distribution rather than a pure vMF. The broad component is exponential in mu, not in theta, confirming that switchbacks saturate toward mu = -1 rather than decaying away, consistent with the drift-diffusion framework of Bian et al. (2024, ApJ, 960, L15). This physics-based two-population framework connects macroscopic fluid parameters directly to those describing the directional statistics, offering a powerful diagnostic for probing the structural evolution of MHD turbulence and switchbacks in the inner heliosphere.
[abstract 43 / 58] (score: 2) - Title: Spiraling into the `snail' cluster MCXC J0157.4-0550Authors: Chao Geng, Chong Ge, Ming Sun, Li Ji, Guilin Liu, Zhicheng He, Haiguang Xu, John ZuHone, Paul Nulsen, Craig Sarazin, Nobuhiro Okabe,Comments: 13 pages, 5 figures, submitted to ApJSubjects: astro-ph.GA astro-ph.HECreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
We present a deep Chandra (130 ks) study of a striking, tidally induced cold front in a subcluster merging with the galaxy cluster MCXC J0157.4-0550. The subcluster, nicknamed the `snail' (J0157), displays an extensive spiral structure that extends to $\sim 260$ kpc --- one of the largest spiral cold fronts identified to date. Surface brightness and spectral analysis across four sectors reveal a consistent density jump of a factor of $\sim 3$ across the front, together with significant temperature discontinuities, and thermodynamic mapping further delineates the coherent, low-entropy structure of the stripped gas. Unlike classical sloshing cold fronts, the spiral in J0157 arises not from oscillation of a displaced cool core, but from subcluster gas that has been ram pressure stripped and tidally wound into a spiral by orbital rotation. Applying Gaussian Gradient Magnitude filtering and azimuthal surface-brightness analysis, we identify quasi-periodic corrugations along the front consistent with candidate Kelvin-Helmholtz (KH) instabilities, with a characteristic scale of $\sim 90$ kpc. The presence of these KH rolls constrains the effective ICM viscosity to $\lesssim 0.59$ times the Spitzer value and the MAGNETic field strength at the interface to $\lesssim 5.9\ μ$G. These results establish J0157 as a useful laboratory for probing macro-scale merger-induced gas dynamics and micro-scale plasma transport processes in the intracluster medium.
[abstract 44 / 58] (score: 2) - Title: Prospects for submillimeter VLBI of BLACK HOLE photon rings with a stratospheric balloon-borne telescopeAuthors: Mayukh Bagchi, Dominic W. Pesce, Felix M. Thiel, Laura M. Fissel, Lindy Blackburn,Comments: 15 pages, 8 figures, 4 tables. Submitted to ApJSubjects: astro-ph.IMCreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
Submillimeter very long baseline interferometry (VLBI) achieves higher angular resolution and probes more optically thin emission near supermassive BLACK HOLEs, with less interstellar scattering toward Sgr A$^*$. Above 345 GHz, however, the atmosphere confines ground-based VLBI to a few high, dry sites. Using 2012-2022 weather, we forecast what a 2.5 m telescope floating at 35-40 km, a successor to the 22 GHz Balloon-borne VLBI Experiment (BVEX) pathfinder, would add to ground-VLBI arrays at 345-690 GHz. The balloon adds little baseline length but reaches higher frequencies, where a fixed baseline is longer in wavelengths. On an ALMA-balloon baseline, Sgr A$^*$ at 460 GHz is at the detection threshold, with ten or more 20 s detections on about half of the simulated April days. These detections lie beyond the polarimetric photon ring transition, where the $n=1$ ring dominates the polarized visibility amplitudes. M87$^*$ at 460 GHz would need frequency phase transfer from a 230 GHz reference to be detected. With phase transfer, most Sgr A$^*$ detections beyond the transition at 460 GHz are on balloon baselines, whose thermal noise meets the linear-POLARIZATION threshold within one 300 s scan. At 690 GHz such detections require phase transfer that stays coherent at three times the reference frequency. In Fisher forecasts, a 460 GHz ring-geometry constraint requires balloons but is weaker than at 345 GHz, where balloons add little improvement. High-resolution 460 GHz VLBI science would require a 32 GHz bandwidth backend, submillimeter receivers, and simultaneous 230 GHz reference recording at every station.
[abstract 45 / 58] (score: 2) - Title: Models of spectral bumps of primary COSMIC RAYs and multi-messenger testsAuthors: Qiang Yuan, Chuan Yue, Yi-Zhong Fan,Comments: 7 pages, 1 table, 6 figuresSubjects: astro-ph.HECreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
The energy spectra of individual species of COSMIC RAY nuclei by recent direct detection experiments show complicated structures with spectral hardenings and softenings rather than featureless power laws, which challenge the traditional understanding of the production, acceleration, and propagation of COSMIC RAYs. Particularly, the DAMPE measurements reveal charge-dependent softenings and reject mass-dependent softenings with a high significance. Taking into account the correlated structures at similar energies in the large-scale anisotropies of COSMIC RAYs, one of the most natural interpretations of the spectral structures is the presence of a nearby COSMIC RAY source. In this case, the softening energies correspond to the acceleration upper limits of such a source, forming the so-called Peters cycle of the spectra. Alternative models such as the injection/acceleration and propagation models may also reproduce the spectral bumps, but show difficulty to explain the anisotropies. Fluxes of secondary nuclei and $γ$ rays offer additional tests of different models. Future multi-messenger observations are expected to be able to pin down the origin of COSMIC RAYs.
[abstract 46 / 58] (score: 2) - Title: Micrometer-thin liquid sheets from single-JET impact on a sharp edge for multi-kHz LASER-plasma experimentsAuthors: Mukesh Kumar, S. Sree Harsha, Prashant Kumar Singh,Comments: 6 FiguresSubjects: physics.plasm-ph physics.flu-dynCreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
We present a simple and robust method for generating freely suspended liquid sheets by directing a single laminar liquid JET onto the sharp edge of an inclined plate. By optimizing liquid composition, impact geometry, and flow conditions, we identify a 60:40 ethylene-glycol-deionized-water volumetric mixture for stable sheet formation. The resulting sheets span 8 mm in height and 3 mm in width, with thicknesses from 1.1 to 4.8 micrometers measured by spatial and spectral interferometry. Operated in vacuum as continuously renewed plasma mirrors, these targets demonstrate stable performance from 0.5 to 10 kHz using 175-fs Yb:KGW LASER pulses, reaching a maximum S-polarized reflectivity of 66.5% at an intensity of 4 x 10^14 W/cm^2. At higher intensities using 25-fs Ti:sapphire pulses at 1 kHz, maximum S-polarized reflectivity reaches 77% at 2 x 10^16 W/cm^2. The reflected beam exhibits high temporal stability, with angular pointing fluctuations of 18.19 +/- 0.53 microradians. Our results demonstrate a tunable, continuously renewed liquid-sheet target for multi-kHz LASER-plasma experiments.
[abstract 47 / 58] (score: 2) - Title: Static tidal Love numbers of Schwarzschild and non-Schwarzschild BLACK HOLEs in quadratic gravityAuthors: Soham Bhattacharyya,Comments: 42 pages, 4 figures. Comments welcome!Subjects: gr-qc astro-ph.HECreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
We calculate the static electric quadrupolar response of BLACK HOLEs in four-dimensional quadratic gravity, with action $R-αC^2+βR^2$. The Schwarzschild solution has zero massless gravitational Love number under the stated boundary conditions. A numerical non-Schwarzschild solution instead has a nonzero negative response. At $α/r_h^2=1/2$, we find $λ_E/r_h^5\simeq-0.1224928$ and $k_2^{(r_h)}\simeq-0.1837391$, with a final outer-endpoint change in $k_2^{(r_h)}$ of about $1.60\times10^{-7}$. We explain how the background is obtained by shooting and how the tidal solution is selected by matching at an intermediate radius. The perturbations are written in Kodama--Ishibashi gauge-invariant variables. After the scalar-curvature perturbation is excluded by horizon regularity and the absence of an applied scalar tide, the remaining static sector has three coupled second-order radial equations. We define the curvature amplitudes in these equations and describe why simple attempts to separate them fail. The coupling scan shows a negative response approaching zero near the Schwarzschild intersection. We also explain why this full-theory result does not conflict with the removal of curvature-squared operators in a perturbative low-energy expansion.
[abstract 48 / 58] (score: 2) - Title: Weak Cosmic Censorship in Einstein-Born-Infeld Black Hole: A Parameter-Space AnalysisAuthors: M. L. Peñafiel, F. T. Falciano, J. C. Fabris,Comments: The version of record for this article is published in Brazilian Journal of PhysicsSubjects: gr-qcCreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
Einstein-Born-Infeld is a charged BLACK HOLE solution of general relativity with Born-Infeld nonlinear electrodynamics, which has interesting physical features. It violates Bekenstein's entropy upper bound, and it can overcharge with respect to the Reissner-Nordström BLACK HOLE. It presents an optimum situation to test the cosmic censorship conjecture, which is another important conjecture in BLACK HOLE physics. In principle, this analysis requires the calculation of the self-energy of a test particle in the vicinity of the BLACK HOLE, which, in general, is not feasible because of the electroMAGNETic nonlinearities. In this work, we propose an alternative approach that allows us to explore the whole parameter space of the Einstein-Born-Infeld BLACK HOLE and test the validity of the cosmic censorship conjecture.
[abstract 49 / 58] (score: 2) - Title: The Impact of an AGN on PAH Spectral Features in Galaxy Evolution Simulations: Continuum Dilution and Excitation of PAHsAuthors: Grant P. Donnelly, Desika Narayanan, Paul Torrey, J. -D. T. Smith, Helena M. Richie, Hui Li, Federico Marinacci,Comments: Submitted to ApJ. 13 pages, 8 figuresSubjects: astro-ph.GACreated: 2026-10-17; Updated: 2026-10-20; Datestamp: 2026-10-20
Galaxies hosting an ACTIVE GALACTIC NUCLEus (AGN) show diminished power and non-standard spectral feature ratios from polycyclic aromatic hydrocarbons (PAHs) compared with normal star-forming galaxies. Proposed mechanisms for this difference include a combination of AGN-driven PAH grain processing, differential heating from the surrounding radiation field, and continuum dilution. These potentially competing factors are difficult to disentangle observationally. In this paper, we investigate the impact of the AGN radiation field on the excitation properties and potential dilution of the mid-IR emission features via constrained numerical experiments of idealized galaxies in simulations that include a self-consistent model for the evolution of dust. We find that, for the integrated spectrum of our simulated Milky Way analog and independent of grain-processing physics, the apparent PAH emission is progressively diminished as AGN luminosity is increased. For spectra within the central half kiloparsec, PAH features are entirely obfuscated when an AGN of any sampled luminosity is present. We additionally find that the UV radiation from an AGN is capable of impacting PAH band ratios, though note that we do not yet include a model for potential photodestruction of PAHs. Our model suggests that the inferred lack of PAHs via featureless mid-IR spectra from galaxies hosting AGN may simply owe to the direct continuum from the AGN overpowering mid-IR features from PAHs in the ISM of the host galaxy. Future work will investigate the relative role of AGN continuum dilution and PAH heating vs photodestruction/ionization of PAHs.
[abstract 50 / 58] (score: 2) - Title: Moving Beyond Quasinormal Modes and Reinterpreting Direct Waves in Binary Black Hole Merger-RingdownsAuthors: Richard Dyer, Anuj Kankani, Gareth Arturo Marks, Sean T. McWilliams, Christopher J. Moore,Comments: 23 pages, 12 figuresSubjects: gr-qc astro-ph.HECreated: 2026-10-18; Updated: 2026-10-20; Datestamp: 2026-10-20
Based on black-hole perturbation-theory calculations and an effective-one-body picture of binary BLACK HOLE mergers, it has been suggested that a direct wave may be present and measurable in the ringdown. Furthermore, it has been suggested that this signal might originate from substantially inside the light ring (or photon sphere) of the remnant BLACK HOLE, perhaps even from close to the event horizon. In this paper, we present three independent strands of evidence against such claims. In the process, we show that there is indeed an early-time part of the ringdown signal that cannot be directly modeled by quasinormal modes. However, there is no evidence that this is a direct wave as it has previously been defined, and we show that the properties of this component are related to the remnant's light ring rather than its horizon.
[abstract 51 / 58] (score: 2) - Title: Lorentz-Invariance Violation with neutrinos from GAMMA-RAY BURSTs using IceCube High-Energy Starting Events 12-year datasetAuthors: Mathieu Lamoureux, José Manuel Carmona, José Luis Cortés, Ardit Gkioni, Antoine Kouchner, Maykoll A. Reyes,Comments: 11 pages, 4 figuresSubjects: hep-ph astro-ph.HE gr-qcCreated: 2026-10-18; Updated: 2026-10-20; Datestamp: 2026-10-20
High-energy astrophysical neutrinos provide a unique probe of Lorentz-invariance violation (LIV), as small energy-dependent deviations from the speed of light can produce measurable time delays over cosmological distances. We search for LIV-induced correlations between neutrinos and GAMMA-RAY BURSTs using the public 12-year IceCube High-Energy Starting Event dataset and a catalog of 746 bursts with measured redshifts. We develop a likelihood analysis accounting for neutrino directional and energy uncertainties, a possible intrinsic time offset between neutrino and gamma-ray emission, and the decay of superluminal neutrinos expected within effective field theory. For linear LIV, the data show a mild preference over the background-only hypothesis, with a $p$-value of $3.1\%$, corresponding to a one-sided Gaussian significance of approximately $1.9σ$. The best fit corresponds to a LIV scale $Λ_{\rm LIV}=5.8\times10^{17}\,\mathrm{GeV}$ and is effectively driven by the subluminal component, as superluminal neutrinos are strongly suppressed by LIV-induced decays at the analyzed energies. The preferred LIV scale and the most significant neutrino--GAMMA-RAY BURST associations are consistent with previous studies based on different statistical approaches. No evidence for quadratic LIV is found. These results motivate further searches with complementary neutrino datasets, particularly at lower energies, where the superluminal component may become observable.
[abstract 52 / 58] (score: 2) - Title: Hyperonic Direct-Urca Neutrino Emission with Lattice-QCD-Informed Form FactorsAuthors: Andreas Konstantinou,Comments:Subjects: astro-ph.HE nucl-thCreated: 2026-10-18; Updated: 2026-10-20; Datestamp: 2026-10-20
We investigate the sensitivity of direct-Urca neutrino emission in hyperonic neutron-star matter to the structure and momentum dependence of baryonic transition form factors. Using the zero-temperature FSU2H RELATIVISTIC mean-field equation of state, we derive the RELATIVISTIC emissivity for general spin-$1/2$ baryon transitions with the complete six form-factor contribution. We compare conventional static flavor-SU(3) couplings with vacuum lattice-QCD-informed form factors, using direct lattice vacuum input for $n\rightarrow p$ and $Λ\rightarrow p$ and a hybrid construction for the remaining hyperonic channels. Evaluating the latter both at $q^2=0$ and at the kinetic momentum transfer sampled at the FERMI surfaces separates changes in the zero-momentum couplings from momentum-transfer effects. The sensitivity is strongly channel dependent. The nucleonic transition probes $q^2\simeq0$ and is only weakly affected, whereas hyperonic channels can sample substantially larger momentum transfers and receive correspondingly larger corrections. These modifications propagate to the integrated neutrino luminosity of stellar configurations. Our results estimate the possible scale of the sensitivity coming from momentum transfer dependence, absent from static-coupling treatments and motivate future first-principles studies of baryonic weak currents in dense matter.
[abstract 53 / 58] (score: 2) - Title: Velocity-resolved Ionization Mapping of the Broad-line Region. II. Signatures of Eccentric Broad-line Regions from a Quantitative Photoionization-Based ModelAuthors: Jiancheng Wu, Hai-Cheng Feng, Sha-Sha Li, Qingwen Wu, Xinwu Cao,Comments: 14 pages, 5 figuresSubjects: astro-ph.GACreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
Velocity-resolved reverberation mapping (RM) is one of the most powerful tools for probing the geometry and kinematics of the broad-line region in ACTIVE GALACTIC NUCLEi. However, its interpretation may be non-unique, as similar velocity-delay signatures can arise from different combinations of BLR geometry and kinematics. To address this degeneracy, this series of studies develops velocity-resolved ionization mapping (IM) as a complementary technique. In this second paper of the series, we construct photoionization-based BLR models to quantitatively demonstrate the diagnostic power of the joint RM+IM framework. We calculate local \ha\ and \hb\ emissivities with Cloudy, couple them with disk-like BLR models, and generate synthetic velocity-dependent line fluxes, lags, and Balmer decrements. The model reproduces the observed anti-correlation between the integrated BD and the incident ionizing continuum, with scatter naturally introduced by reverberation delays. We show that a virialized elliptical BLR can produce diverse velocity-delay maps and velocity-resolved lags that mimic RM signatures commonly attributed to virialized motion, inflow, or outflow. In contrast, the velocity-resolved BD is sensitive to the symmetry of the BLR gas distribution, providing a key diagnostic for distinguishing eccentric geometry from non-virial motions. Through proof-of-concept comparisons with one double-peaked and one single-peaked AGN, we show that an elliptical-disk BLR can simultaneously reproduce the observed line profiles, velocity-resolved lags, and velocity-resolved BDs. These results provide a quantitative basis for IM, support the presence of eccentric BLR structures in AGNs, and demonstrate the potential of joint RM+IM analyses to break the BLR geometry-kinematics degeneracy.
[abstract 54 / 58] (score: 2) - Title: Constraints on the Cosmic Expansion Rate Using the DECam Local Volume Exploration Survey and the Fifth Gravitational Wave Transient CatalogAuthors: Sean Patrick MacBride, Isaac McMahon, Danny Laghi, David Sánchez-Cid, Felipe Andrade-Oliveira, Marcelle Soares-Santos, Maciej Bilicki, Sarah Ferraiuolo, Surhud More, Rachel Gray, Gergely Dálya,Comments: 9 Pages, 6 Figures, 2 Tables, Submitted to A&ASubjects: astro-ph.COCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
Gravitational-wave standard sirens provide a calibration-free measure of distances, offering important input on the long-standing tension between early- and late-Universe measurements of the Hubble constant ($H_0$). In the absence of an electroMAGNETic counterpart, the dark siren method can be employed to statistically correlate a gravitational wave event's localization with a galaxy catalog of potential hosts. We present a measurement of the Hubble constant using the DECam Local Volume Exploration Survey Data Release 3 and the fifth Gravitational-Wave Transient Catalog. Applying the dark siren method to a large, photometrically heterogeneous footprint required revised catalog-construction choices: a faint apparent-magnitude threshold ($m_r<20$) to control known photometric-redshift bias, a bright apparent-magnitude threshold ($m_r>15.5$) to exclude saturated sources, implementation of an evolving luminosity function parameterization, and de-biasing survey regions based on survey depth and photometric redshift precision. With these choices applied to DELVE, we obtain $H_0= 67.4^{+13.0}_{-11.2}\ \mathrm{km\,s^{-1}\,Mpc^{-1}}$ from dark sirens alone, and $H_0= 70.6^{+8.7}_{-7.0}\ \mathrm{km\,s^{-1}\,Mpc^{-1}}$ when combined with the bright siren GW170817. We test other galaxy catalog configuration choices, and find subdominant influence from photometric band choice and luminosity function parameterization on the final $H_0$ posterior. Our results demonstrate that extending the dark siren method to wider-area, non-uniform galaxy surveys is feasible and provides additional constraining power on $H_0$ relative to the spectral siren method, opening the door for analyses with forthcoming galaxy catalogs from LSST, Euclid, and Roman.
[abstract 55 / 58] (score: 2) - Title: Flattenicity dependence of charge and transverse-momentum balance functions in $pp$ collisions at $\sqrt{s}=13.6$ TeV with PYTHIA8Authors: Srabani Dutta Roy, Rohit Agarwala, Kalyan Dey,Comments: 22 pages, 6 figuresSubjects: hep-phCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
We study the charge balance function $B(Δη,Δϕ)$ and the charge-dependent transverse-momentum balance function $P_{2}^{\rm CD}(Δη,Δϕ)$ in proton--proton ($pp$) collisions at $\sqrt{s}=13.6$~TeV using \texttt{PYTHIA~8.315} with the Monash tune. Flattenicity is employed as an event-shape observable to probe how these correlations depend on the topology of particle production. The results are examined across different charged-particle multiplicity intervals to disentangle the effects of overall event activity and event topology on $B$ and $P_{2}^{\rm CD}$. Both observables exhibit pronounced near-side correlations around $(Δη,Δϕ)\approx(0,0)$. The near-side peaks become stronger with increasing charged-particle multiplicity, and the RMS widths of both observables decrease systematically, indicating that the correlations become more localized in relative pseudorapidity and azimuth. A clear dependence on flattenicity is also observed: JET-like events (low flattenicity) generally exhibit stronger and narrower near-side correlations than isotropic events (high flattenicity). This event-shape dependence is more pronounced for $P_{2}^{\rm CD}$ than for $B$, indicating that $P_{2}^{\rm CD}$ is more sensitive to event topology, whereas $B$ primarily probes charge-dependent particle-pair correlations. These results demonstrate the complementary nature of the two observables and the potential of flattenicity-based event selection for studying particle-production mechanisms in high-multiplicity $pp$ collisions.
[abstract 56 / 58] (score: 2) - Title: Late-time distance consistency and model-independent curvature inference with strong lensing, QUASARs, and galaxy clustersAuthors: Jian Hu, Yi Liu, Jian Ping Hu, Zhongmu Li,Comments: 18 pages, 6 figures, Accepted for publication in Research in Astronomy and Astrophysics (RAA)Subjects: astro-ph.COCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
We revisit a late-time, model-independent distance-consistency framework that combines strong gravitational lensing systems (SGLS), ultraviolet/X-ray QUASARs (QSOs), and 38 Sunyaev--Zel'dovich/X-ray galaxy-cluster angular-diameter distances. The analysis focuses on systematics rather than on presenting a competitive curvature measurement. Starting from the 158-system SGLS catalog, we exclude 30 systems that violate the lensing-geometric requirement $D_{A,ls}/D_{A,s}<1$ in the isothermal reference case $γ_{\rm lens}=2$, leaving a fixed 128-system SGLS parent sample for cross-matching with 1598 QSOs. A deterministic maximum-cardinality, minimum-mismatch one-to-one assignment yields 100 SGLS--QSO pairs at the nominal $Δd/d=5\%$ threshold. We propagate the measured X-ray flux uncertainties and the intrinsic QSO scatter, and, crucially, we include the full $38\times38$ covariance induced by using the same QSO distances in the kernel-smoothed cluster predictions. With $Ω_K\sim\mathcal{U}[-10,10]$, the joint posterior is $Ω_K=2.085^{+1.634}_{-1.103}$ (68\%; central 95\% interval $[0.269,6.028]$). We do not interpret the positive shift as evidence for an open Universe. \added{This positive posterior offset is driven by cross-probe calibration tensions, sample-assignment effects, and the cluster anchor; it cannot be attributed to the intrinsic spatial geometry of the Universe.} The SGLS+QSO data alone leave curvature essentially prior dominated, $Ω_K=0.70^{+6.33}_{-7.12}$, whereas removing only the off-diagonal cluster covariance moves the posterior to $Ω_K=5.21^{+2.46}_{-2.07}$. Thus the cluster anchor supplies most of the curvature constraining power and its covariance materially changes the posterior location.
[abstract 57 / 58] (score: 2) - Title: Experimental verification of the PRIORA Monte Carlo code for proton radiographyAuthors: Dmitry Varentsov, Martin Schanz, John Schmidt,Comments: 5 pages, 5 figures, 1 tableSubjects: physics.plasm-phCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
PRIORA (Proton Radiography Ion-Optical Ray-tracing Analysis) is a fast Monte Carlo model for high-energy proton radiography. It combines fitted proton-matter interaction tables with energy-dependent transfer maps of arbitrary order and simulates approximately $10^6$ protons/s through a complete ion-optical system on an 8-core laptop. We verify it with GSI data obtained with the Ta_bench target: fifteen precision slits in a 2 mm Ta plate between symmetric PMMA staircases. A single experimental image provides the image scale, spatial resolution as a function of chromatic load, signed focus in both planes, effective angular acceptance and multiple-scattering contrast. With identical processing of experiment and simulation and no physics adjustment, PRIORA reproduces the data obtained with 2 and 4 GeV protons. At 2 GeV, PRIORA also recovers sub-percent quadrupole trims consistent with the control-system records and determines a target-plane spatial resolution of $115\pm6\,μ$m.
[abstract 58 / 58] (score: 2) - Title: Spectroscopy as a Probe of Spacetime FoamAuthors: A. G. Kim, P. E. Nugent, L. Wang,Comments: 21 pages, 2 figures, PRD acceptedSubjects: gr-qcCreated: 2026-10-19; Updated: 2026-10-20; Datestamp: 2026-10-20
Quantum-gravitational spacetime foam varying in space and in time imprints, respectively, a transverse phase decoherence and an achromatic, stochastic arrival-time jitter on light from distant sources. We show that the jitter modifies the first-order temporal coherence $g^{(1)}(τ)$ and hence the observed spectrum, providing a spectroscopic probe of the temporal variation, complementary to existing imaging-channel constraints on the spatial variation. In the dynamical-foam limit, where the foam decorrelates within the light's coherence time, the spectrum splits into a coherent line core suppressed by $e^{-σ_ϕ^2}$, with $σ_ϕ^2$ the variance of the foam-induced phase jitter, and an incoherent pedestal, yielding a spectral shape-distortion bound on the foam exponent $α$. Three probes follow: the outright survival of broadband flux, the fractional width of a spectral line, and a chromatic deficit across a broadband continuum. Applied to the MeV emission lines of GRB\,221009A we obtain $α\gtrsim 0.63$, a weak, lever-arm-dominated floor. For the broadband CMB the foam induces an $e^{-σ_ϕ^2(ν)}$ deficit ($σ_ϕ^2 \propto ν^2$); a fit to the COBE/FIRAS monopole spectrum reaches $α\gtrsim 0.52$ ($95\%$ CL), and next-generation spectrometers reach only $α\gtrsim 0.54$--$0.55$ (forecast), limited by the foam--temperature degeneracy. The pedestal-independent line-width and CMB bounds are floors below the holographic value $α= 2/3$, consistent with and excluding no part of the imaging window reported for GRB\,221009A; only the conditional TeV survival bound ($α\gtrsim0.74$), which holds only for near-Planck-refresh foam ($τ_{\rm foam}\lesssim4\times10^{-28}$\,s), would exclude it --- and, with it, the window.
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