Sazuna/UAT_keywords huggingface dataset:
Ionized Envelopes Around Protoplanets and the Role of Radiative Feedback in Gas Accretion. Planetary growth within protoplanetary disks involves the accreting of material from their surroundings, yet the underlying mechanisms and physical conditions of the accreting gas remain debated. This study aims to investigate the dynamics and thermodynamic properties of accreting gas giants, and to characterize the envelope that forms near the planet during accretion. We employ 3D hydrodynamical simulations of a Jupiter-mass planet embedded in a viscous gaseous disk. Our models incorporate a nonisothermal energy equation to compute gas and radiation energy diffusion and include radiative feedback from the planet. The results indicate that gas accretion occurs supersonically toward the planet. The ionized envelope extends from the planetary surface up to 0.2 times the Hill radius in the no-feedback model, and up to 0.4 times the Hill radius in the feedback model. The envelope's radius, or ionization radius, acts as a boundary halting supersonic gas inflow and is pivotal for estimating accretion rates and Hα emission luminosities. Including radiative feedback increases the accretion rates, especially within the ionization radius and from areas to the right of the planet when the star is positioned to the left. The accretion luminosities calculated at the ionization radius are substantially lower than those calculated at the Hill radius, highlighting potential misinterpretations in the nondetection of Hα emissions as indicators of ongoing planet formation.

Keywords: Shocks, Protoplanetary disks, Planet formation, Radiative processes
Observations of Turbulence and Particle Transport at Interplanetary Shocks: Transition of Transport Regimes. The transport of energetic particles is intimately related to the properties of plasma turbulence, a ubiquitous dynamic process that transfers energy across a broad range of spatial and temporal scales. However, the mechanisms governing the interactions between plasma turbulence and energetic particles are not completely understood. Here we present comprehensive observations from the upstream region of a quasi-perpendicular interplanetary (IP) shock on 2004 January 22, using data from four Cluster spacecraft to investigate the interplay between turbulence dynamics and energetic particle transport. Our observations reveal a transition in energetic proton fluxes from exponential to power-law decay with increasing distance from the IP shock. This result provides possible observational evidence of a shift in transport behavior from normal diffusion to superdiffusion. This transition correlates with an increase in the time ratio from τs/τc &lt; 1 to τs/τc ≫ 1, where τs is the proton isotropization time, and τc is the turbulence correlation time. Additionally, the frequency–wavenumber distributions of magnetic energy in the power-law decay zone indicate that energetic particles excite linear Alfvén-like harmonic waves through gyroresonance, thereby modulating the original turbulence structure. These findings provide valuable insights for future studies on the propagation and acceleration of energetic particles in turbulent astrophysical and space plasma systems.

Keywords: Interplanetary turbulence, Particle astrophysics, Interplanetary shocks, Solar energetic particles
The Impact of Local Stellar Radiation on Dwarf Galaxy Formation around Milky Way Analogs across Cosmic Reionization. We explore the effect of local stellar radiation on the formation and evolution of dwarf galaxies around Milky Way (MW) analogs. Using five simulations from the Auriga project, both with and without local stellar radiation, we find that local stellar radiation, as a pre-reionization source, is highly effective at photoionizing and heating the gas around the proto-MW analogs. As a result, the formation of surrounding dwarf galaxies in dark matter halos with masses below approximately 109.5 M⊙ is significantly suppressed. After reionization, the intensity of local stellar radiation eventually becomes comparable to the ultraviolet background. Consequently, the impact of local stellar radiation on the surrounding dwarf galaxy formation decreases with decreasing redshift and nearly vanishes after redshift z = 4. At present day, the bright satellite population in the simulations with and without local stellar radiation is nearly identical. While our simulations do not have sufficient resolution to resolve the faintest satellite galaxies that are most prone to the local stellar radiation, we use the accreted galaxy mass function to assess the impact and find that the reduction in the faintest satellite is around 13% in the presence of local stellar radiation, but this difference is within ∼2σ of the Poisson uncertainty and thus not statistically significant.

Keywords: Hydrodynamical simulations, Galaxy formation, Dwarf galaxies, Galaxy evolution
Multiwavelength Long-term Studies of Radio Galaxy NGC 1275. It is widely considered that the processes of an interaction between the energy and radiation, which are generated in the active galactic nuclei (AGN) by accretion onto their central massive black hole with the gas in the host galaxy, take a great part in the evolution of the galaxies at all development stages. Such "feedback" of the galaxy environment by AGN including the role of their jetted outbursts generally has no evidence through the multiwavelength observations. Only a few objects are suitable for these purposes. The Perseus cluster of galaxies with the central galaxy NGC 1275 is a perfect laboratory for studying both the physics of AGN's relativistic jets and the feedback role of the central galaxy. Here, the most complete long-term observations across the electromagnetic spectrum from radio up to very-high-energy gamma rays are collected. The multiwavelength light curve provides evidence for the variability of NGC 1275 on decade timescales in the whole energy range and points to the connection of the observed activity with the launch of the features of the relativistic jets from the NGC 1275 core. The relation of multiwavelength emission components is demonstrated with spectral energy distribution and emission maps of the central part of the Perseus cluster. The evidence of the interaction of cosmic rays and magnetic fields generated in the jets at the galactic center with the gas of the Perseus cluster is obtained.

Keywords: Galaxy clusters, Seyfert galaxies, Galaxy jets
Mahakala: A Python-based Modular Ray-tracing and Radiative Transfer Algorithm for Curved Spacetimes. We introduce Mahakala, a Python-based, modular, radiative ray-tracing code for curved spacetimes. We employ Google's JAX framework for accelerated automatic differentiation, which can efficiently compute Christoffel symbols directly from the metric, allowing the user to easily and quickly simulate photon trajectories through non-Kerr spacetimes. JAX also enables Mahakala to run in parallel on both CPUs and GPUs. Mahakala natively uses the Cartesian Kerr–Schild coordinate system, which avoids numerical issues caused by the pole in spherical coordinate systems. We demonstrate Mahakala's capabilities by simulating 1.3 mm wavelength images (the wavelength of Event Horizon Telescope observations) of general relativistic magnetohydrodynamic simulations of low-accretion rate supermassive black holes. The modular nature of Mahakala allows us to quantitatively explore how different regions of the flow influence different image features. We show that most of the emission seen in 1.3 mm images originates close to the black hole and peaks near the photon orbit. We also quantify the relative contribution of the disk, forward jet, and counterjet to 1.3 mm images.

Keywords: Supermassive black holes, Black holes, Astronomical simulations, Computational methods, Radiative transfer, Radiative transfer simulations, Astrophysical black holes
Accessing a New Population of Supermassive Black Holes with Extensions to the Event Horizon Telescope. The Event Horizon Telescope (EHT) has produced resolved images of the supermassive black holes (SMBHs) Sgr A* and M87*, which present the largest shadows on the sky. In the next decade, technological improvements and extensions to the array will enable access to a greater number of sources, unlocking studies of a larger population of SMBHs through direct imaging. In this paper, we identify 12 of the most promising sources beyond Sgr A* and M87* based on their angular size and millimeter flux density. For each of these sources, we make theoretical predictions for their observable properties by ray tracing general relativistic magnetohydrodynamic models appropriately scaled to each target's mass, distance, and flux density. We predict that these sources would have somewhat higher Eddington ratios than M87*, which may result in larger optical and Faraday depths than previous EHT targets. Despite this, we find that visibility amplitude size constraints can plausibly recover masses within a factor of 2, although the unknown jet contribution remains a significant uncertainty. We find that the linearly polarized structure evolves substantially with the Eddington ratio, with greater evolution at larger inclinations, complicating potential spin inferences for inclined sources. We discuss the importance of 345 GHz observations, milli-Jansky baseline sensitivity, and independent inclination constraints for future observations with upgrades to the EHT through ground updates with the next-generation EHT program and extensions to space through the black hole Explorer.

Keywords: Accretion, Black hole physics, Magnetohydrodynamics, Supermassive black holes, Very long baseline interferometry, Polarimetry, Relativistic disks, Interferometry
How to Identify the Object with a Mass Range of (2.2–3) M<SUB>⊙</SUB> in the Merger of Compact Star Systems. High-frequency gravitational-wave (GW) radiation has been detected by LIGO-Virgo-KAGRA in the merger of compact stars. However, in two GW events, GW190814 and GW200210, the mass of one companion object falls into the mass region of (2.2–3) M⊙, and how to identify such an object (e.g., as a low-mass black hole (BH) or a massive neutron star (NS)) remains an open question. In this paper, we propose a method to identify the mystery compact object (MCO) with the mass region of (2.2–3) M⊙ in a binary system via the possible electromagnetic (EM) radiations before and after the mergers. A multiband EM emission can be produced with L ∝ ( ‑t)7/4 (or L ∝ ( ‑t)‑5/4) during the inspiral phase due to the BH battery (or interaction magnetospheres) mechanism, and a bright (or dark) kilonova emission is powered by radioactive decay with ejecta mass ratio q &gt; 1.7 (or q &lt; 1.7) during the postmerge state when MCO is as a low-mass BH (or massive NS) to merger with NS. Moreover, by considering the merger system between MCO and a BH when MCO is a massive NS, we find that it requires the BH with high spin (e.g., a ∼ 0.8–0.99) to make sure the tidal disruption event occurred, and a multiband precursor emission and bright kilonova emission can also be produced during the inspiral phase and postmerge state, respectively. In any case, no matter which mechanism we adopt, such precursor emissions are too weak to be detected by most current telescopes unless the distance is close enough.

Keywords: Neutron stars, Black holes, Compact objects
Basic Pattern of Three-dimensional Magnetic Reconnection within Strongly Turbulent Current Sheets. Magnetic reconnection is a fundamental mechanism of driving eruptive phenomena of different scales and may be coupled with turbulence as suggested by recent remote-sensing and in situ observations. However, the specific physics behind the complex three-dimensional (3D) turbulent reconnection remains mysterious. Here, we develop a novel methodology to identify and analyze multitudes of multiscale reconnection fragments within a strongly turbulent current sheet (CS) and apply it to a state-of-the-art numerical simulation of turbulent reconnection for solar flares. It is determined that the reconnection fragments tend to appear as quasi-2D sheets forming along local magnetic flux surfaces, and, due to strong turbulence, their reconnection flow velocities and reconnection rates are significantly broadened statistically but are scale independent. Each reconnection fragment is found to be surrounded by strongly fluctuated in/outflows and has a widely distributed reconnection rate, mainly in the range of 0.01–0.1. The results, for the first time, provide quantitative measurements of 3D magnetic reconnection in strongly turbulent flare CSs, offering insights into the cascading laws of 3D reconnection in other turbulent plasmas.

Keywords: Solar flares, Solar magnetic reconnection, Magnetohydrodynamical simulations
MUSEQuBES: The Column Density, Covering Fraction, and Mass of O VI-bearing Gas in and Around Low-redshift Galaxies. We present a study of O VI-bearing gas around 247 low-mass (median   = 8.7) galaxies at low redshifts (0.1 &lt; z &lt; 0.7) using background quasars as part of the MUSE Quasar-fields Blind Emitters Survey (MUSEQuBES). We find that the average O VI column density,  , measured within the virial radius for our sample, is significantly lower than for L* galaxies. Combining 253 star-forming galaxies (mostly more massive) from the literature with 176 star-forming galaxies from MUSEQuBES, we find that both   and the average covering fraction peak at   ≍ 9.5. The virial temperature corresponding to this stellar mass is ideal for O VI production via collisional ionization. However, we argue that photoionization and/or nonequilibrium processes are necessary to produce the O VI associated with low-mass, dwarf galaxies (  &lt; 9). The average O VI mass within the virial radius of dwarf galaxies is measured to be   M⊙. The characteristic normalized impact parameter (D/Rvir) at which the O VI covering fraction drops to half of its peak value is largest (≍1.1) for galaxies with stellar mass   ≍ 9.5. We report the presence of a highly ionized metal floor with   outside the virial radius of dwarf galaxies inferred from median spectral stacking.

Keywords: Galaxy evolution, Circumgalactic medium
Investigating the Recursive Short X-Ray Burst Behavior of Magnetars through Crustal Interactions. Energetic bursts from strongly magnetized neutron stars, known as magnetars, are typically detected in clusters. Once an active episode begins, anywhere from a few to thousands of hard X-ray bursts can occur over durations ranging from days to months. The temporal clustering of these recurrent bursts during an active episode suggests an underlying mechanism that triggers multiple bursts in rapid succession. These burst clusters are likely crucial for understanding the processes driving magnetar activity. In this study, we investigate the repetitive short X-ray burst behavior of magnetars through crustal interactions, employing the cellular automaton model for the magnetar crust proposed by S. K. Lander. Our simulations, based on physically motivated criteria, successfully reproduce burst clustering. Additionally, the durations and energetics of active episodes in our simulations agree well with observational data. We discuss the potential physical mechanisms underlying burst clusters observed in numerous magnetars, as well as the reactivations of an individual magnetar.

Keywords: Neutron stars, Magnetars, X-ray bursts
Variations in the Magnetic Field Strength of Pre-main-sequence Stars, Solar-type Main-sequence Stars, and the Sun. The surface magnetic fields of pre-main-sequence stars and zero-age main-sequence stars are notably strong, resulting in the generation of numerous spots and the emission of bright chromospheric lines. Rotational variations in magnetic field strength have been identified in T Tauri stars (TTSs) and young main-sequence stars using Zeeman–Doppler imaging. This study investigates the relationship between the mean values and variation amplitudes of the magnetic field strengths of TTSs, main-sequence stars, and the Sun. The findings reveal a positive correlation of over 3 orders of magnitude, suggesting that a common mechanism drives the magnetic fields of these stars. This positive correlation implies that stars with larger spot sizes experience greater variation amplitudes due to rotational modulations. For the Sun, both the mean magnetic field strength value and its variation amplitude tend to be higher during solar maximum than during solar minimum.

Keywords: Starspots, Stellar magnetic fields, Stellar activity, Stellar astronomy, Pre-main sequence stars, Solar magnetic fields
Investigation of Substructures of the Inner Halo Using the StarGO Algorithm with APOGEE DR17. We applied the Stars' Galactic Origin algorithm in 7D space (i.e., [Fe/H], [Mg/Fe], [Al/Fe], Lz, Jr, Jz, E) to analyze stars in the inner halo with APOGEE DR17. We identified some known substructures, including Gaia-Sausage/Enceladus, Sagittarius stream (Sgr), LMS-1 (Wukong), Thamnos, the metal-weak thick disk, and Aleph. Additionally, we identified an undefined metal-poor group (UDG, with [Fe/H] &lt; −0.8 dex) probably linked to a known substructure like Aleph, as well as a high α-abundance substructure (HAS) associated with both the Nyx and Nyx-2 streams. Chemical abundance of the HAS supports the argument that Nyx and Nyx-2 share a common origin. We discovered three substructures, which we refer to as new substructure candidates 1, 2, and 3 (NSTC-1, NSTC-2, NSTC-3). Despite exhibiting disk-like dynamics, these NSTCs demonstrate notably low [Mg/Fe] (&lt;0.2 dex) and [Al/Fe] (&lt;−0.15 dex), similar to the properties of dwarf galaxies. Their high orbital energy and low [α/Fe] indicate the association with recent accretion events.

Keywords: Galaxy stellar halos, Galaxy dynamics, Galaxy kinematics, Chemical abundances
Simulating Solar Neighborhood Brown Dwarfs. I. The Luminosity Function above and below the Galactic Plane. Brown dwarfs form the key, yet poorly understood, link between stellar and planetary astrophysics. These objects offer unique tests of Galactic structure, but observational limitations have inhibited their large-scale analysis to date. Major upcoming sky surveys will reveal unprecedented numbers of brown dwarfs, among even greater numbers of stellar objects, greatly enhancing the statistical study of brown dwarfs. To extract the comparatively rare brown dwarfs from these massive data sets, we must understand the parameter space they will occupy. In this work, we construct synthetic populations of brown dwarfs in the solar neighborhood to explore their evolutionary properties using Gaia-derived star formation histories alongside observational mass, metallicity, and age relationships. We apply the Sonora Bobcat, Saumon‑Marley, and Sonora Diamondback evolutionary models. From the populations, we explore the space densities and median ages by spectral type. We present the simulated luminosity function and its evolution with distance from the Galactic plane. Our simulation shows that brown dwarf population statistics are a function of height above/below the Galactic plane and sample different age distributions. Interpreting the local sample requires combining evolutionary models, the initial mass function, the star formation history, and kinematic heating. Our models are a guide to how well height-dependent samples can test these scenarios. Subpopulations of brown dwarfs farther from the Galactic plane are older and occupy a different region of parameter space than younger subpopulations closer to the Galactic plane. Therefore, fully exploring population statistics both near and far from the Galactic plane is critical to prepare for upcoming surveys.

Keywords: Luminosity function, Brown dwarfs, Sky surveys, Stellar populations, Stellar evolutionary models, Solar neighborhood
Nonlinear Interactions in Spherically Polarized Alfvénic Turbulence. Turbulent magnetic field fluctuations observed in the solar wind often maintain a constant-magnitude magnetic field accompanied by spherically polarized velocity fluctuations; these signatures are characteristic of large-amplitude Alfvén waves. Nonlinear energy transfer in Alfvénic turbulence is typically considered in the small-amplitude limit where the constant-magnitude condition may be neglected; in contrast, nonlinear energy transfer of large-amplitude fluctuations remains relatively unstudied. We develop a method to analyze large-amplitude turbulence through studying fluctuations as constant-magnitude rotations in the de Hoffmann─Teller frame, in which the convected electric field of the fluctuations vanishes such that the frame and fluctuations are copropagating. Our analysis reveals signatures of large-amplitude effects deep into the inertial range. While the dominant fluctuations are consistent with spherically polarized large-amplitude Alfvén waves, the subdominant fluctuations are relatively compressible. Signatures of nonlinear interaction between the large-amplitude spherically polarized mode with the subdominant population reveal highly aligned transverse components. In many theoretical models of Alfvénic turbulence, alignment is thought to reduce nonlinearity; our observations suggest that the observed alignment is sufficient to either reduce shear nonlinearity such that non-Alfvénic interactions may be responsible for energy transfer in spherically polarized states, or alternatively that counterpropagating fluctuations maintain anomalous coherence, a predicted signature of reflection-driven turbulence.

Keywords: Space plasmas, Magnetohydrodynamics, Interplanetary turbulence, Solar wind, Interstellar plasma, Alfven waves
Deep Mantle–Atmosphere Coupling and Carbonaceous Bombardment: Options for Biomolecule Formation on an Oxidized Early Earth. Understanding what environmental conditions prevailed on early Earth during the Hadean eon, and how this set the stage for the origins of life, remains a challenge. Geologic processes such as serpentinization and bombardment by chondritic material during the late veneer might have been very active, shaping an atmospheric composition reducing enough to allow efficient photochemical synthesis of HCN, one of the key precursors of prebiotic molecules. HCN can rain out and accumulate in warm little ponds (WLPs), forming prebiotic molecules such as nucleobases and the sugar ribose. These molecules could condense to nucleotides, the building blocks of RNA molecules, one of the ingredients of life. Here, we perform a systematic study of potential sources of reducing gases on Hadean Earth and calculate the concentrations of prebiotic molecules in WLPs based on a comprehensive geophysical and atmospheric model. We find that in a reduced H2-dominated atmosphere, carbonaceous bombardment can produce enough HCN to reach maximum WLP concentrations of ∼1–10 mM for nucleobases and, in the absence of seepage, ∼10–100 μM for ribose. If the Hadean atmosphere was initially oxidized and CO2-rich (90%), we find serpentinization alone can reduce the atmosphere, resulting in WLP concentrations of an order of magnitude lower than the reducing carbonaceous bombardment case. In both cases, concentrations are sufficient for nucleotide synthesis, as shown in experimental studies. RNA could have appeared on Earth immediately after it became habitable (about 100 Myr after the Moon-forming impact), or it could have (re)appeared later at any time up to the beginning of the Archean.

Keywords: Chemical thermodynamics, Complex organic molecules, Computational astronomy, Earth atmosphere, Carbonaceous chondrites, Geological processes, Astrobiology, Meteorites, Interdisciplinary astronomy, Pre-biotic astrochemistry