Sazuna/UAT_keywords huggingface dataset:
Spin─Orbit Alignment in Merging Binary Black Holes Following Collisions with Massive Stars. Merging binary black holes (BBHs) formed dynamically in dense star clusters are expected to have uncorrelated spin─orbit orientations since they are assembled through many random interactions. However, measured effective spins in BBHs detected by LIGO/Virgo/KAGRA hint at additional physical processes that may introduce anisotropy. Here we address this question by exploring the impact of stellar collisions and accretion of collision debris on the spin─orbit alignment in merging BBHs formed in dense star clusters. Through hydrodynamic simulations, we study the regime where the disruption of a massive star by a BBH causes the stellar debris to form individual accretion disks bound to each black hole (BH). We show that these disks, which are randomly oriented relative to the binary orbital plane after the initial disruption of the star, can be reoriented by strong tidal torques in the binary near pericenter passages. Following accretion by the BHs on longer timescales, BBHs with small but preferentially positive effective spin parameters (χeff ≲ 0.2) are formed. Our results indicate that BBH collisions in young massive star clusters could contribute to the observed trend toward small positive χeff, and we suggest that the standard assumption often made that dynamically assembled BBHs should have isotropically distributed BH spins is not always justified.

Keywords: Black holes, Gravitational wave sources
Observational Constraints of Radial Migration in the Galactic Disk Driven by the Slowing Bar. Radial migration is an important dynamical effect that has reshaped the Galactic disk, but its origin has yet to be elucidated. In this work, we present evidence that resonant dragging by the corotation of a decelerating bar could be the main driver of radial migration in the Milky Way disk. Using a test particle simulation, we demonstrate this scenario explains the two distinct age–metallicity sequences observed in the solar vicinity: the plateauing upper sequence is interpreted as stars dragged outward by the expanding corotation of the decelerating bar and the steeper lower sequence as stars formed locally around the solar circle. The upper migrated sequence dominates at guiding radii around the current corotation radius of the bar, R ∼ 7 kpc, but rapidly dies away beyond this where the mechanism cannot operate. This behavior naturally explains the radial dependence of the [α/Fe]-bimodality, in particular the truncation of the high-[α/Fe] disk beyond the solar circle. Under our proposed radial migration scenario, we constrain the Milky Way bar's pattern speed evolution using the age–metallicity distribution of stars currently trapped at corotation. We find the bar likely formed with an initial pattern speed of 60‑100 km s‑1 kpc‑1 and began decelerating 6‑8 Gyr ago at a rate of   (where the quoted ranges include systematic uncertainties).

Keywords: Milky Way dynamics, Milky Way disk, Galaxy evolution, Milky Way evolution, Galactic bar
Evidence for Environmental Effects in the z = 4.3 Protocluster Core SPT2349─56. We present Atacama Large Millimeter/submillimeter Array observations of the [C I] 492 and 806 GHz fine-structure lines in 25 dusty star-forming galaxies (DSFGs) at z = 4.3 in the core of the SPT2349─56 protocluster. The protocluster galaxies exhibit a median   ratio of 0.94, with an interquartile range of 0.81─1.24. These ratios are markedly different to those observed in DSFGs in the field (across a comparable redshift and 850 μm flux density range), where the median is 0.55, with an interquartile range of 0.50─0.76, and we show that this difference is driven by an excess of [C I](2─1) in the protocluster galaxies for a given 850 μm flux density. Assuming local thermal equilibrium, we estimate gas excitation temperatures of  K for our protocluster sample and  K for the field sample. Our main interpretation of this result is that the protocluster galaxies have had their cold gas driven to their cores via close-by interactions within the dense environment, leading to an overall increase in the average gas density and excitation temperature, as well as an elevated [C I](2─1) luminosity-to-far-infrared-luminosity ratio.

Keywords: Protoclusters, High-redshift galaxies, Galaxy environments
Primordial Origin of Methane on Eris and Makemake Supported by D/H Ratios. Deuterium, a heavy isotope of hydrogen, is a key tracer of the formation of the solar system. Recent James Webb Space Telescope observations have expanded the data set of deuterium-to-hydrogen (D/H) ratios in methane on the KBOs Eris and Makemake, providing new insights into their origins. This study examines the elevated D/H ratios in methane on these KBOs in the context of protosolar nebula (PSN) dynamics and chemistry, proposing a primordial origin for the methane, in contrast to previous hypotheses suggesting abiotic production by internal heating. A time-dependent disk model coupled with a deuterium chemistry module was used to simulate the isotopic exchange between methane and hydrogen. Observational constraints, including the D/H ratio measured in methane in comet 67P/Churyumov–Gerasimenko, were used to refine the primordial D/H abundance. The simulations show that the observed D/H ratios in methane on Eris and Makemake are consistent with a primordial origin. The results suggest that the methane on these Kuiper Belt Objects likely originated from the PSN, similar to cometary methane, and was sequestered in solid form—either as pure condensates or clathrates—within its building blocks prior to accretion. These results provide a simple explanation for the high D/H ratios in methane on Eris and Makemake, without the need to invoke internal production mechanisms.

Keywords: Solar system formation, Cosmochemistry, Astrobiology, Protoplanetary disks, Trans-Neptunian objects
Eclipse Mapping with MIRI: 2D Map of HD 189733b from 8 μm JWST MIRI LRS Observations. Observations and models of transiting hot Jupiter exoplanets indicate that atmospheric circulation features may cause large spatial flux contrasts across their daysides. Previous studies have mapped these spatial flux variations through inversion of secondary eclipse data. Though eclipse mapping requires high signal-to-noise data, the first successful eclipse map—made for HD 189733b using 8 μm Spitzer IRAC data—showed the promise of the method. JWST eclipse observations provide the requisite data quality to access the unique advantages of eclipse mapping. Using two JWST MIRI low-resolution spectroscopy eclipse observations centered on 8 μm to mimic the Spitzer bandpass used in previous studies, combined with the Spitzer IRAC 8 μm eclipses and partial phase curve (necessitated to disentangle map and systematic signals), we present a two-dimensional dayside temperature map. Our best-fit model is a two-component fifth-degree harmonic model with an unprecedentedly constrained eastward hotspot offset of   deg. We rule out a strong hemispheric latitudinal hotspot offset, as three + component maps providing latitudinal degrees of freedom are strongly disfavored. As in previous studies, we find some model dependence in longitudinal hotspot offset; when we explore and combine a range of proximal models to avoid an overly constrained confidence region, we find an eastward hotspot offset of   deg, indicating the presence of a strong eastward zonal jet. Our map is consistent with some previous eclipse maps of HD 189733b, though it indicates a higher longitudinal offset from others. It is largely consistent with predictions from general circulation models at the 115 mbar level near the 8 μm photosphere.

Keywords: Exoplanet atmospheric dynamics
Betatron Cooling of Halo and Strahl Electrons in the Solar Wind. It is widely recognized that adiabatic acceleration plays an essential role in the dynamics of the solar wind electron distribution. Nevertheless, the role of electron adiabatic cooling remains poorly understood, at least from an observational standpoint. Even the betatron cooling has never been verified in the solar wind. Here, we present a distinct event of simultaneous betatron cooling of halo and strahl electrons in a small-scale magnetic structure, probably due to a local expansion (weakening of magnetic field strength). The betatron cooling results in the drop of electron differential fluxes, which peaks in the quasi-perpendicular direction and smoothly decreases toward the field-aligned direction. The cooling processes of halo and strahl electrons via the betatron mechanism are well reproduced using an ideal adiabatic acceleration/cooling model.

Keywords: Interplanetary particle acceleration, Solar wind, Interplanetary physics
A Possible Four Month Periodicity in the Activity of FRB 20240209A. Fast radio bursts (FRBs) are millisecond-duration radio transients from distant galaxies. While most FRBs are singular events, repeaters emit multiple bursts, with only two—FRB 121102 and FRB 180916B—showing periodic activity (160 and 16 days, respectively). FRB 20240209A, discovered by CHIME-FRB, is localized to the outskirts of a quiescent elliptical galaxy (z = 0.1384). We discovered a periodicity of ∼126 days in the activity of the FRB 20240209A, potentially adding to the list of extremely rare periodic repeating FRBs. We used autocorrelation and Lomb–Scargle periodogram analyses, validated with randomized control samples, to confirm the periodicity. The FRB's location in an old stellar population disfavors young progenitor models, instead pointing to scenarios involving globular clusters, late-stage magnetars, or low-mass X-ray binaries. Though deep X-ray or polarimetric observations are not available, the localization of the FRB and a possible periodicity point to progenitors likely to be a binary involving a compact object and a stellar companion or a precessing/rotating old neutron star.

Keywords: Radio bursts, Time domain astronomy, Radio transient sources
Time–Frequency Correlation of Repeating Fast Radio Bursts: Correlated Aftershocks Tend to Exhibit Downward Frequency Drifts. The production mechanism of fast radio bursts (FRBs)—mysterious, bright, millisecond-duration radio flashes from cosmological distances—remains unknown. Understanding potential correlations between burst occurrence times and various burst properties may offer important clues about their origins. Among these properties, the spectral peak frequency of an individual burst (the frequency at which its emission is strongest) is particularly important because it may encode direct information about the physical conditions and environment at the emission site. Analyzing over 4000 bursts from the three most active sources—FRB 20121102A, FRB 20201124A, and FRB 20220912A—we measure the two-point correlation function ξ(Δt, Δνpeak) in the two-dimensional space of time separation Δt and peak frequency shift Δνpeak between burst pairs. We find a universal trend of asymmetry about Δνpeak at high statistical significance; ξ(Δνpeak) decreases as Δνpeak increases from negative to positive values in the region of short time separation (Δt ≲ 0.3 s), where physically correlated aftershock events produce a strong time correlation signal. This indicates that aftershocks tend to exhibit systematically lower peak frequencies than mainshocks, with this tendency becoming stronger at shorter Δt. We argue that the "sad trombone effect"—the downward frequency drift observed among subpulses within a single event—is not confined within a single event but manifests as a statistical nature that extends continuously to independent yet physically correlated aftershocks with time separations up to Δt ∼ 0.3 s. This discovery provides new insights into underlying physical processes of repeater FRBs.

Keywords: Two-point correlation function, Radio transient sources
The Importance of Berry Phase in Solar Acoustic Modes. An analytic expression for the frequencies of standing waves in stars, applicable to any radial order n, is derived from ray-tracing equations by the mean of Wigner–Weyl calculus. A correction to previous formulas currently employed in asteroseismology is identified as the Berry phase, which accounts for the vectorial nature of wave propagation in stars. Accounting for this quantity significantly improves upon previous laws for low n modes of the Sun, and we show that the Berry phase is indeed present in the available observational data of solar modes. This phase is due to inhomogeneities of the medium.

Keywords: Helioseismology, Solar physics, Solar oscillations, Stellar oscillations, Asteroseismology
Embers of Active Galactic Nuclei: Tidal Disruption Events and Quasiperiodic Eruptions. Recent observations have confirmed the direct association between tidal disruption events (TDEs) and quasiperiodic eruptions (QPEs). In addition, TDE hosts and QPE hosts are statistically found to be similar in their morphological properties and in the strong overrepresentation of poststarburst galaxies. Particularly, both of them show an intriguing preference for extending emission line regions, which are indicative of recently faded active galactic nuclei (AGNs). This further suggests that QPEs might be produced following TDEs involving supermassive black holes at a particular stage, when the AGN activity has recently ceased. Moreover, in the framework of the "QPEs = extreme mass ratio inspiral (EMRI) + accretion disk" model, a large fraction of QPE EMRIs are inferred to be quasi-circular from the QPE timing, indicating that they are wet EMRIs that were formed in the AGN disk during a previous AGN phase. Based on these facts, we propose a unified scenario that connects these three phenomena: AGN activities boost both the TDE rate and the formation rate of low-eccentricity EMRIs; consequently, TDEs are preferentially found in recently faded AGNs instead of in ongoing AGNs due to selection effects; and QPEs are also preferentially found in recently faded AGNs where TDEs frequently feed a misaligned accretion disk to the EMRI.

Keywords: Supermassive black holes, High energy astrophysics, Tidal disruption, Active galactic nuclei, Time domain astronomy
Optical and Near-infrared Contemporaneous Polarimetry of C/2023 A3 (Tsuchinshan-ATLAS). We conducted contemporaneous optical and near-infrared polarimetric and spectroscopic observations of C/2023 A3 (Tsuchinshan-ATLAS, hereafter T-A) from 2024 October 16 to December 17, covering a wide range of phase angles (20°–123°) and wavelengths (0.5–2.3 μm). We paid special attention to gas contamination in the dust polarization using these data. As a result, we find the maximum polarization degree  %, 33.52% ± 0.06%, 35.12% ± 0.01%, 37.57% ± 0.01%, and 35.35% ± 0.01% in the Rc, Ic, J, H, and Ks bands, respectively. Although dust polarization shows a red slope at shorter wavelengths and can peak around 1.6 μm, the phase angle at which maximum polarization occurs exhibits less dependence on wavelength ( –95°). Although only a few historically bright comets, such as West, Halley, and Hale–Bopp, have undergone such extensive dust-polarization observations, our measurements are generally consistent with those of two comets that possibly originated from the Oort Cloud (West and Halley). From these results, we conjecture that the optical properties and growth processes of dust in the presolar nebula, which formed these cometary nuclei, were likely uniform.

Keywords: Dust physics, Spectropolarimetry, Optical astronomy, Near infrared astronomy, Infrared astronomy, Protoplanetary disks, Comets, Polarimetry, Planet formation, Coma dust
A Lower Mass Estimate for PSR J0348+0432 Based on CHIME/Pulsar Precision Timing. The binary pulsar J0348+0432 was previously shown to have a mass of approximately 2 M⊙, based on the combination of radial-velocity and model-dependent mass parameters derived from high-resolution optical spectroscopy of its white-dwarf companion. We present follow-up timing observations that combine archival observations with data acquired by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) pulsar instrument. We find that the inclusion of CHIME/Pulsar data yields an improved measurement of the variation of the orbital period ( ) that is 1.2σ consistent with the original values published by J. Antoniadis et al. while being roughly 6 times more precise due to the extended baseline. Assuming that this   is due to gravitational wave damping, and that the latter is as predicted by general relativity, we obtain new constraints on the mass of the pulsar and companion. When combined with the mass ratio determined from phase-resolved optical spectroscopy we determine a pulsar mass of 1.806(37) M⊙. For the first time for this pulsar, timing alone significantly constrains the pulsar mass. If confirmed, our mass estimates indicate that the original analysis of the optical data has overestimated the mass of the companion (and by extension the mass of the pulsar) by about 10%.

Keywords: Neutron stars, White dwarf stars, Pulsars, Companion stars, Radio pulsars
Shear–Gravity Transition Determines the Steep Velocity Dispersion–Size Relation in Molecular Clouds: Confronting Analytical Formula with Observations. The velocity dispersion–size relation (σv ∼ Rβ) is a crucial indicator of the dynamic properties of interstellar gas, where the slope is considered as β ∼ 0.5. Recent observations reveal a steep velocity dispersion–size relation with the slope β &gt; 0.6, which cannot be explained by a single mechanism with only gravity (β ∼ 0.5) or shear (β ∼ 1). We present a two-component model   to explain the steep velocity dispersion–size relation for clouds larger than several parsecs in observations from, e.g., M.-A. Miville-Deschênes et al., J.-X. Zhou et al., and Y. Sun et al. We find that, above several parsecs, the velocity dispersion of small clouds is mainly caused by self-gravity, while large clouds are primarily affected by shear, and these two regimes are linked by a gradual transition with a transition scale ∼100 pc—the scale height of the Galactic molecular gas disk. The variation of cloud velocity dispersion–size relation with the Galactocentric distance results from the variation of both cloud internal density structure and Galactic shear rate. Our two-component model captures how the dynamics of the molecular gas can be affected by both internal and external factors, and we expect it to be applied to data from galaxies with different physical conditions to reveal the physics.

Keywords: Interstellar dynamics, Galaxy dynamics, Galaxy rotation, Molecular clouds, Scaling relations, Interstellar medium, Milky Way Galaxy
A Glimpse of the New Redshift Frontier through AS1063. We report the discovery of two galaxy candidates at redshifts between 15.7 &lt; z &lt; 16.4 in James Webb Space Telescope (JWST) observations from the GLIMPSE survey. These robust sources were identified using a combination of Lyman break selection and photometric redshift estimates. The ultradeep NIRCam imaging from GLIMPSE, combined with the strong gravitational lensing of the AS1063 galaxy cluster, allows us to probe an intrinsically fainter population (down to MUV = ‑17.0 mag) than previously achievable. These galaxies have absolute magnitudes ranging from MUV = ‑17.0 to ‑17.2 mag, with blue (β ≃ ‑2.87) ultraviolet (UV) continuum slopes, consistent with young, dust-free stellar populations. The number density of these objects, log10(ϕ/[Mpc‑3 mag‑1]) =   at MUV = ‑17, is in clear tension with pre-JWST theoretical predictions, extending the overabundance of galaxies from z ∼ 10 to z ∼ 17. These results, together with the scarcity of brighter galaxies in other public surveys, suggest a steep decline in the bright end of the UV luminosity function at z ∼ 16, implying efficient star formation and possibly a close connection to the halo mass function at these redshifts. Testing a variety of star formation histories suggests that these sources are plausible progenitors of the unusually UV-bright galaxies that JWST now routinely uncovers at z = 10–14. Overall, our results indicate that the luminosity distribution of the earliest star-forming galaxies could be shifting toward fainter luminosities, implying that future surveys of cosmic dawn will need to explore this faint luminosity regime.

Keywords: Early universe, High-redshift galaxies
The Impact of Molecular Hydrogen Cooling on the Galaxy Formation Threshold. We study the impact of molecular (H2) and atomic (H I) hydrogen cooling on the galaxy formation threshold. We calculate the fraction of dark matter (DM) halos that exceeds a critical mass required for star formation, Mcrit(z), as a function of their peak mass. By convolving analytic halo mass accretion histories (MAHs) with models for Mcrit(z), we predict that halos with peak virial masses below ∼108 M⊙ can form stars before reionization through H2 cooling. These halos remain dark when only H I cooling and reionization are modeled. However, less than ≈10% of halos with peak masses below ∼107 M⊙ ever exceed Mcrit(z), even when H2 cooling is included; this threshold is primarily set by relative streaming motion between DM and baryons imprinted at recombination. We obtain similar results using subhalo MAHs from an extremely high-resolution cosmological DM-only zoom-in simulation of a Milky Way (MW) analog (particle mass 6.3 × 103 M⊙). Based on the abundance of MW satellites, these results imply that at least some known ultrafaint dwarf galaxies formed through H2 cooling. This work sharpens predictions for the galaxy formation threshold and demonstrates how its essential features emerge from the underlying distribution of halo growth histories.

Keywords: Galaxy dark matter halos, Galaxy formation, Star formation
The Extreme Faraday Effect in Fast Radio Bursts. Fast radio bursts (FRBs) are a type of highly polarized, millisecond-duration electromagnetic pulse in the radio band, which is mostly produced at cosmological distances. These properties provide a natural laboratory for testing the extreme Faraday effect, a phenomenon in which two different propagation modes of a pulse separate after passing through a dense, highly ionized, and magnetized medium. We derive the critical condition (e.g., rotation measure) for the extreme Faraday effect to occur in FRBs, which exceeds the currently observed maximum value but remains within the theoretically predicted range. Some new features of FRBs (in particular, radio bursts with much shorter durations) after undergoing the extreme Faraday effect are predicted, such as sudden sign reversals of circular polarization, conspicuous frequency drifting, and emergency of extremely high circular polarization degrees. A potential application of this effect in FRBs is that, by comparing morphological differences of the two separated twin modes, one can identify the variations of plasma properties over extremely short timescales along the propagation path. Therefore, if this effect is found with future observations, it would provide a new tool for probing dense, magnetized environments near FRB sources.

Keywords: Interstellar scattering, Radio bursts, Magnetic fields, Radio transient sources