Sazuna/UAT_keywords huggingface dataset:
Early Warning for Lensed Gravitational Wave Counterparts from Time Delays of Their Host Galaxies Observed in the Optical. Gravitational lensing of gravitational waves can be leveraged to provide early-warning times of  O(hours)  to  O(days)  before the merger of binary neutron stars (BNSs) and neutron star black holes (NSBHs). This in turn could enable electromagnetic (EM) telescopes to capture emissions surrounding the time of the merger. In this work, we assess the practicability of lensing-driven early warning by analysing optical images of the lensed host galaxy to predict the arrival time of subsequent BNS/NSBH signals following the observation of the first signal. We produce mock lenses with image quality and resolution similar to images taken with the Hubble Space Telescope (HST) and the ground-based Hyper Suprime-Cam (HSC) on the Subaru telescope. We compare the time delay uncertainties between these two cases for typical lensed image configurations and multiplicity. These include doubles and quads and, among quads, the fold, cusp, and cross-image configurations. We find that time delay uncertainties for doubles are comparable for both HST and HSC mocks. On the other hand, quads tend to provide accurate time-delay predictions (typical relative error ∼0.1) with HST. Analysis of a real lens led to a difference in time-delay estimates of  O(days)  between the predictions derived from HST and HSC data. Our work therefore strongly advocates the need for high-resolution EM observations of lensed host galaxies to feasibly enable lensing-driven early-warning.

Keywords: Gravitational lensing, Gravitational waves
Formation Channels of Magnetars. The formation channels of magnetars remain an open question. Although core-collapse supernovae of isolated massive stars are important, binary interactions—such as tidal interaction, common envelope evolution, and stellar mergers—may also play a significant role in making magnetars. Understanding the relative contributions of these channels is crucial for linking magnetars to their observed properties and host environments. In this paper, we investigate potential magnetar formation channels using population synthesis simulations, considering both single-star and isolated binary system evolution. By conducting simulations with different parameters, we compare the effects of various evolution processes on magnetar formation. Additionally, we study the delay times and kick velocities across all formation channels, and analyze the orbital properties and companion types of surviving magnetar binaries. We find that the majority of magnetars are observed as single objects (≥90%), although a large fraction of them were originally in binary systems and experienced either a kick disruption or merger. Surviving binaries are most likely to host main-sequence companions and exhibit different distributions of eccentricities due to different supernova mechanisms. These findings show the critical role of binary evolution in magnetar formation and provide predictions for the properties of magnetar populations that can be tested with future observations.

Keywords: Magnetars, Binary stars, Stellar evolution
High-resolution Observations of "Dark" Neutral Hydrogen Clouds in the Virgo Cluster with the Very Large Array. We have observed six "dark" neutral hydrogen (H I) clouds discovered in the Virgo Cluster by the Arecibo Galaxy Environment Survey (AGES) with the Karl G. Jansky Very Large Array (VLA), giving higher angular and velocity resolution than the original AGES observations. We detected compact H I emission in two of the sources, AGESVC1 231 and AGESVC1 274, allowing us to firmly associate them with faint (mg &gt; 18.5), blue (g − i &lt; 0.1) optical counterparts with high MH I/Lg ratios. In a further two sources, we detected low-column-density extended H I emission, consistent with these being dispersing clouds from ram pressure stripping or tidal interactions. The final two sources were not detected with the VLA, allowing us to set low column-density limits on the H I detected by AGES that are consistent with these clouds also being formed from H I that is dispersing into the intracluster medium. The four H I sources not associated with optical counterparts thus appear likely to be relatively short-lived objects. No evidence was found for either pressure-supported turbulent spheres or stable dark galaxies.

Keywords: Virgo Cluster, Dwarf galaxies, Neutral hydrogen clouds
The Radial Velocity Curve for He II Emission Cannot Be Used for Component Mass Determination in SS 433. More than 150 measurements of the He II 4686 Å emission line in spectra of SS 433 were obtained during 388 nights in 2020─2025 with the Transient Double-beam Spectrograph on the 2.5 m telescope of Caucasian Mountain Observatory of Sternberg Astronomical Institute. We found that the He II emission line formation region is not eclipsed and is significantly larger than both the donor star and the photosphere of the supercritical accretion disk. The He II radial velocity curve was found to be independent of the precessional phase and inconsistent with the photometric curve. These findings suggest that the He II line does not reflect the orbital motion of the compact object. Therefore, spectroscopic estimates of the masses of the components in SS 433 based on the He II emission line can be unrealistic.

Keywords: Stellar accretion disks, Stellar mass black holes, Hz Herculis x-ray binary stars
Is the Milky Way Gravitationally Stable? A TNG50 View from the Cosmic Noon to the Present Day. We investigate the stability of Milky Way analogs (MWAs) in the TNG50 simulation against the growth of local axisymmetric instabilities, tracing their evolution from cosmic noon (z = 2.5) to the present day (z = 0). Using a two-component stability criterion that accounts for stars, gas, and the force field of the dark matter halo, we compute the net stability parameter (QT), the critical gas surface density (Σc), and the instability timescale (τ) for 10 barred and 10 unbarred MWAs. We find that these galaxies remain stable to axisymmetric instabilities at all epochs, with  QTmin&gt;2 . The stability levels increase toward higher redshift, where enhanced gas velocity dispersion counterbalances the destabilizing effect of larger gas fractions. Furthermore, the barred MWAs consistently show lower  QTmin  than unbarred ones. The gas density remains subcritical (Σg &lt; Σc) across radii and epochs, implying that local axisymmetric instabilities are not the primary channel for star formation. Growth timescales are short (a few Myr) in central regions but increase exponentially to several Gyr in the outer disk, naturally explaining the concentration of star formation toward galactic centers. We study the effect of gas dissipation and turbulence in ISM and find that while MWAs are stable against axisymmetric instabilities (QT &gt; 1), a combination of gas dissipation and turbulence in ISM can destabilize the disk at small scales, even when QT &gt; 1.

Keywords: Gravitational instability
Digging into the Interior of Hot Cores with ALMA (DIHCA). VII. Disk Candidates around High-mass Stars and Evidence of Anisotropic Infall. We study the kinematics of condensations in 30 fields forming high-mass stars with the Atacama Large Millimeter/submillimeter Array at a high resolution of  ∼0.″08  on average (∼230 au). The presence of disks is important for feeding high-mass stars without feedback halting growth as their masses increase. In the search for velocity gradients resembling rotation that can reveal the presence of disks, we analyze the emission of gas tracers in 49 objects using CH3OH, CH3CN, and tentative detections of HNCO and cis-HCOOH. Most of the velocity distributions show velocity gradients indicative of rotation. We reveal a total of 32 disk candidates, the largest sample to date that has been uniformly analyzed at a few hundred astronomical unit scales in the high-mass regime. Their position─velocity maps are generally asymmetric with one side brighter than the opposite. We successfully fit a power law to the position─velocity maps of the disk candidates and find indices between −0.5 (Keplerian rotation) and −1 (rotation under specific angular momentum conservation) with a median of −0.7. Under Keplerian rotation assumption, we estimate central masses, uncorrected for inclination, ranging between 7 and 45 M⊙. Excluding outliers, the disk candidates are relatively more compact (&lt;200 au) and less massive (&lt;5 M⊙) than previous results at coarser angular resolution. We calculate an average Toomre-Q parameter and find that most are gravitationally unstable (median of 0.5). We conclude that these observations offer the first opportunity to separate the disk and envelope components of hot cores on a statistically significant sample, and confirm that anisotropic collapse plays a role in feeding high-mass (proto)stars.

Keywords: Massive stars, Star forming regions, Star formation
Low-metallicity Gas on the Outskirts of the Local Group: The Circumgalactic Medium of Sextans B. We present a UV absorption-line analysis of the circumgalactic medium (CGM) of Sextans B, a dwarf irregular galaxy at 1.3 Mpc distance on the outer frontier of the Local Group (LG). Using Hubble Space Telescope Cosmic Origins Spectrograph spectroscopy of two active galactic nucleus sight lines passing through the Sextans B CGM at small impact parameters of 4 and 8 kpc (≍0.04─0.08R200), we detect the CGM in Si II, Si III, Si IV, and C II absorption. All four ions show a column-density profile that declines with radius. The profiles fall below the average CGM profiles of other nearby dwarfs (by ≍0.3─0.6 dex, depending on the ion), likely due to the low halo mass and low metallicity of Sextans B. Using Cloudy photoionization models and interferometric measurements of the H I column density, we find gas-phase silicon and carbon abundances in the Sextans B CGM of [Si/H] = −1.7 ± 0.2 and [C/H] = −2.1 ± 0.2, respectively, among the lowest gas-phase abundances anywhere in the LG. We calculate a cool CGM gas mass within 8 kpc of ≍4 × 107 M⊙, comparable to the H I mass and the stellar mass of Sextans B. *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program 17209.

Keywords: Local Group, Irregular galaxies, Chemical abundances, Circumgalactic medium
The Milky Way Stellar Halo Is Twisted and Doubly Broken: Insights from DESI DR2 Milky Way Survey Observation. Using K giants from the second data release (DR2) of the Dark Energy Spectroscopic Instrument (DESI) Milky Way Survey, we measure the shape, orientation, radial profile, and density anisotropies of the Milky Way (MW) stellar halo over 8 kpc &lt; rGC &lt; 200 kpc. We identify a triaxial stellar halo (axis ratio 10:8:7), 43° tilted from the disk, showing two break radii at ∼16 and ∼76 kpc, likely associated with Gaia-Sausage/Enceladus and the Large Magellanic Cloud (LMC), respectively. The inner stellar halo (&lt;30 kpc) is oblate and aligned with the disk, whereas the outer stellar halo becomes prolate and perpendicular to the disk, consistent with the vast polar structure of MW satellites. The twisted halo may arise from the disk−halo angular momentum shift triggered by the infall of a massive satellite. The anisotropic density distribution of the stellar halo is also measured, with successful reidentification of the Hercules-Aquila Cloud North/South (HAC-N/S) overdensity and the Virgo overdensity (VOD). Break radii are found at 15 and 30 kpc for VOD and HAC-N/S, respectively. We identify the LMC transient density wake with a break radius at 60 kpc in the Pisces overdensity region. We also find new observational evidence of the LMC collective density wake, by showing a break radius at ∼100 kpc in the northern Galactic cap with a clear density peak at 90 kpc. In the end, we found that more metal-poor halo stars are more radially extended. Our results provide important clues to the assembly and evolution of the MW stellar halo under the standard cosmic structure formation framework.

Keywords: Milky Way stellar halo, Galaxy stellar content, Large Magellanic Cloud
Critical Metallicity of Cool Supergiant Formation. II. Physical Origin. This study investigates the physical origin of the critical metallicity required for the formation of cool supergiants, as revealed by stellar evolution models. Using grids of stellar models, we show that the terminal-age main-sequence (TAMS) radius, RTAMS, defines a threshold that determines whether a star of a given mass can evolve into the red supergiant (RSG) phase. Metallicity influences the supergiant outcome because it modifies RTAMS through its effects on opacity and nuclear energy generation, as demonstrated by our stellar models and dimensional analysis based on homology relations. The value of RTAMS sets the initial radius for post-main-sequence expansion and therefore controls the envelope radius reached at subsequent core-evolution stages. Higher-metallicity stars develop larger RTAMS and rapidly expand into the stable RSG regime during core helium burning. In contrast, lower-metallicity stars have smaller RTAMS and advance to more evolved core helium- or carbon-burning stages while retaining compact envelopes, thereby preventing expansion into the RSG regime during core helium burning. Our results explain the origin of the critical metallicity and offer insight into the evolution of metal-poor massive stars in the early Universe.

Keywords: Metallicity, Stellar evolution, Red supergiant stars, Supergiant stars
Growth of Metal-enriched Supermassive Stars by Accretion and Collisions. Supermassive stars (SMSs) are candidate progenitors of massive black hole seeds and may contribute to anomalous abundance patterns in high-redshift galaxies and globular clusters. Recent radiation-hydrodynamic simulations indicate that SMSs can form at finite metallicity, not only in metal-free direct-collapse conditions. We model SMS growth with GENEC over Z/Z⊙ = 10−5 to 10−2 using simulation-motivated accretion histories. The final masses reach ∼7.2 × 104 M⊙ at 10−5 Z⊙ and ∼2.3 × 103 M⊙ at 10−2 Z⊙. Models are evolved through the pre-main-sequence and core H-burning phases, terminating at the onset of general relativistic instability for Z ≲ 10−4 Z⊙ or at core He exhaustion for Z ≳ 10−3 Z⊙. The dominant mass growth channel transitions from collision driven to accretion driven between Z = 10−4 and 10−3. With stellar lifetimes remaining nearly constant at 1.8─2.0 Myr, collisions do not significantly rejuvenate the star, implying that collision-driven runaway collapse cannot proceed in isolation and must be supplemented and is likely dominated by gas accretion. We further compute the critical inflow rate required to keep the stellar envelope inflated,  Ṁcrit , which decreases with increasing Z and decreasing central mass fraction of hydrogen (Xc). The critical rate falls below 10−5 M⊙ yr−1 at Xc = 0.60 for 10−2 Z⊙. This indicates that SMSs with 0.01 Z⊙ are cool supergiants during most of their lifetimes, where UV photon emissivity and radiative feedback are strongly suppressed. Overall, SMS evolution remains viable up to Z ≃ 0.01 Z⊙, supporting SMS formation in proto─globular clusters and other metal-enriched dense environments.

Keywords: Globular star clusters, Supermassive black holes, Red supergiant stars, Massive stars, Collision physics, Stellar accretion, Pre-main sequence, Stellar evolution
Accretion Properties of the Young Brown Dwarf 2MASS J08440915-7833457. We present Hubble Space Telescope Cosmic Origins Spectrograph far-ultraviolet (FUV) and Space Telescope Imaging Spectrometer (STIS) optical observations toward the young accreting brown dwarf 2MASS J08440915-7833457 (J0844) from the UV Legacy Library of Young Stars as Essential Standards Director's Discretionary Time program. We analyse hot FUV lines, such C IV, Si IV, and N V, as well as fluorescent emission from H2. Despite evidence for accretion, the C IV line profiles are narrower than in typical classical T Tauri stars (CTTSs), resembling weak-lined T Tauri stars more closely. Additionally, the C IV integrated line flux does not follow the level expected of an accreting object in the magnetically saturated regime. However, comparing J0844 to appropriate low-mass analogs, J0844 does show excess C IV emission characteristic of accretion, suggesting the magnetic saturation level may need to be redefined for the lowest-mass objects. The C IV/Si IV emission-line ratio is found to be 20, which is higher than for most CTTSs, with a few exceptions (e.g., TW Hya). We fit the STIS optical spectrum to calculate an accretion rate, which we find to be 4.2 × 10−11M⊙ yr−1. The accretion rate found based on the empirical LCIV─ Ṁacc  relationship is 2 orders of magnitude higher, suggesting this relationship may not hold at the lowest masses. We find the H2 emission appears to originate within the corotation radius, pointing to either disk truncation well inside the corotation radius or additional sources of H2 emission that we do not consider (e.g., from the accretion flow itself). These data provide an extension of our current understanding of accretion and inner-disk conditions to the relatively unexplored lowest-mass regime.

Keywords: Accretion, Brown dwarfs, Low mass stars
The Self-limiting Nature of Jet-modulated Thermal Conduction in Cool Core Clusters. Conduction as a mechanism for explaining the disrupted cooling-flow in galaxy clusters has been mostly discounted, as the process is inefficient at transporting heat all the way from the cluster into the core. However, thermal conduction can be strongly enhanced when materials of significantly different temperature are brought into proximity, and thus into close thermal contact. Jets of active galactic nuclei (AGNs) may act as heat pumps by bringing low-entropy gas from the cluster core into thermal contact with the hot outer atmosphere of the cluster, significantly increasing the feedback efficiency of AGNs. We test this hypothesis by running a suite of 3D magnetohydrodynamic simulations of AGNs jets in a Perseus-like cluster, including anisotropic conduction. We find that the heat pump efficiency η can reach up to 50% of the maximum possible efficiency  ηmax  if conduction operates near the Spitzer─Braginskii limit, while  η≍fspηmax  if conduction along the field lines is substantially suppressed below the Spitzer─Braginskii value by a factor fsp by kinetic effects, as recently suggested. We further find that jet-induced thermal conduction is self-limiting. Magnetic draping during the uplift results in a magnetic field orientation close to perpendicular to the induced temperature gradients, significantly reducing conduction along the ideal conductive pathways. Thus, for conservative assumptions about thermal conduction suppression by fsp ≲ 0.1, the heat pump effect leads to only marginal heat transfer and, correspondingly, to immaterial changes in the overall thermal evolution of cool core clusters beyond the isolated effects of conduction and jet-induced heating alone.

Keywords: Galaxy clusters, Cooling flows, Extragalactic magnetic fields, Radio jets, Relativistic jets, Active galactic nuclei, Magnetohydrodynamical simulations
Emergence of Photon Bose─Einstein Condensation from Down-scattering in Cold Electron Media. In this study, we investigate the kinematic enhancement of photon Bose─Einstein condensation (BEC) resulting from the interaction of high-energy photons with a cold electron gas. We employ a modified form of the Kompaneets equation that incorporates higher-order kinematic recoil corrections while retaining the Thomson scattering cross-section as a semianalytical approximation. Beginning with an initial blackbody photon spectrum, we perform numerical simulations to track the evolution of the photon distribution under the influence of inverse Compton scattering. Under the assumption of a strictly conserved photon number, our results demonstrate a pronounced enhancement of photon-number density at the low-energy tail, indicative of a BEC. This phenomenon is further corroborated by an analysis of the entropy evolution. Furthermore, we discuss the role of photon-number-violating processes, such as bremsstrahlung and double Compton scattering. We find that in realistic astrophysical plasmas, these absorption mechanisms act as efficient sinks, likely suppressing the formation of the condensate. These findings clarify the competition between scattering-induced accumulation and absorption-induced dissipation in cold electron environments.

Keywords: Sunyaev-Zeldovich effect
Modeling Solitonic Cores, Stabilization of Bar, and Suppression of Bar Dissolution in DDO 168 via GPP Formalism: A Detailed Analysis of Bose─Einstein Condensate/Fuzzy Dark Matter Halo Structure and Bar Dynamics in the Dwarf Galaxy DDO 168. The cusp─core problem remains a challenge to the ΛCDM model, since dwarf galaxies often exhibit flat central density cores rather than the steep cusps (ρ ∝ r−1) predicted by collisionless N-body simulations. We model the dark-matter-dominated dwarf irregular galaxy DDO 168 within the Bose─Einstein condensate (BEC) or fuzzy dark matter (FDM) framework, in which ultralight bosons form a solitonic core governed by the Gross─Pitaevskii─Poisson (GPP) equations, with the soliton mass─radius relation enforced. We numerically validate the ground-state solution of the GPP system as a consistency check and fit the inner rotation curve of DDO 168 using SPARC data. Within this framework, the data are consistent with an axion mass  m=(1.3−0.2+0.3)×10−23eV , and yield a solitonic core with characteristic radius  Rc=2.40−0.24+0.22kpc , enclosing a mass M(&lt;2.47 kpc) ≃ (1.5 ± 0.2) × 109M⊙. The observed flat inner rotation curve is reproduced and the presence of a weak H I bar is compatible with multigigayear survival timescales, consistent with reduced Chandrasekhar dynamical friction in a shallow central potential. These results demonstrate that the BEC/FDM framework provides an internally consistent description of DDO 168, simultaneously reproducing the observed rotation curve, alleviating the cusp─core tension, and allowing long-lived weak bars under conservative dynamical assumptions.

Keywords: Dwarf irregular galaxies
Shapiro Delay Measurements from Fifteen Years of PSR J1231−1411 Radio Observations. We present 15 yr of Nançay and Green Bank radio telescope timing observations for PSR J1231−1411. This millisecond pulsar is a primary science target for the Neutron Star Interior Composition Explorer telescope (NICER, which discovered its X-ray pulsations), has accumulated near-continuous γ-ray data since the Fermi-Large Area Telescope's launch, and has been studied extensively with the Green Bank and Nançay radio telescopes. We have undertaken a campaign with the Green Bank Telescope targeting specific orbital phases designed to improve our constraint on the pulsar's mass through the detection of a relativistic Shapiro delay. Both frequentist and Bayesian techniques—the latter incorporating priors from white dwarf binary evolution models—are applied to 15 yr of radio observations, yielding relatively weak constraints on the companion and pulsar masses of  0.23−0.06+0.09  M⊙ and  1.87−0.67+1.11  M⊙, respectively (68.3% CI from Bayesian fits); however, the orbital inclination is measured to better relative precision ( 79.80−4.70+3.47 °). Restricting the maximum allowed pulsar mass to 3 M⊙ improves the constraint and lowers the measured mass to  1.71−0.56+0.70  M⊙. A fully generalized Bayesian fit that simultaneously samples the noise and timing models yields a pulsar mass in close agreement with this value. While our radio-derived inclination result has informed recent NICER X-ray studies of J1231−1411, the lessons learned from this troublesome pulsar will also bolster future high-precision mass measurement campaigns and resulting constraints on the neutron star interior equation of state.

Keywords: Neutron stars, Radio astronomy, Millisecond pulsars