Sazuna/UAT_keywords huggingface dataset:
The Stability Boundary of the Distant Scattered Disk. The distant scattered disk is a vast population of trans-Neptunian minor bodies that orbit the Sun on highly elongated, long-period orbits. The orbital stability of scattered-disk objects (SDOs) is primarily controlled by a single parameter-their perihelion distance. While the existence of a perihelion boundary that separates chaotic and regular motion of long-period orbits is well established through numerical experiments, its theoretical basis as well as its semimajor axis dependence remain poorly understood. In this work, we outline an analytical model for the dynamics of distant trans-Neptunian objects and show that the orbital architecture of the scattered disk is shaped by an infinite chain of exterior 2:j resonances with Neptune. The widths of these resonances increase as the perihelion distance approaches Neptune's semimajor axis, and their overlap drives chaotic motion. Within the context of this theoretical picture, we derive an analytic criterion for instability of long-period orbits, and demonstrate that rapid dynamical chaos ensues when the perihelion drops below a critical value, given by ${q}_{\mathrm{crit}}={a}_{{\rm{N}}}{\left(\mathrm{ln}(({24}^{2}/5)({m}_{{\rm{N}}}/{M}_{\odot }){\left(a/{a}_{{\rm{N}}}\right)}^{5/2})\right)}^{1/2}$ . This expression constitutes an analytic boundary between the "detached" and actively "scattering" subpopulations of distant trans-Neptunian minor bodies. Additionally, we find that within the stochastic layer, the Lyapunov time of SDOs approaches the orbital period, and show that the semimajor axis diffusion coefficient is approximated by ${{ \mathcal D }}_{a}\,\sim (8/(5\pi ))({m}_{{\rm{N}}}/{M}_{\odot })\sqrt{{ \mathcal G }{M}_{\odot }{a}_{{\rm{N}}}}\,\exp \left[-{\left(q/{a}_{{\rm{N}}}\right)}^{2}/2\right]$ . We confirm our results with direct N-body simulations and highlight the connections between scattered-disk dynamics and the Chirikov Standard Map. Implications of our results for the long-term evolution of minor bodies in the distant solar system are discussed.

Keywords: Orbits, Perturbation methods, Scattered disk objects
Photometry and Kinematics of Self-gravitating Eccentric Nuclear Disks. The Andromeda galaxy hosts an elongated nucleus with (at least) two distinct brightness peaks. The double nucleus can be explained by the projection of a thick, apsidally aligned eccentric nuclear disk of stars in orbit about the central black hole. Several nearby early-type galaxies have similar asymmetric nuclear features, indicating the possible presence of eccentric nuclear disks. We create simulated photometric (surface density) and kinematic (line-of-sight velocity) maps of eccentric nuclear disks using N-body simulations. We image our simulations from various lines of sight in order to classify them as double nuclei, offset nuclei, and centered nuclei. We explore the effects of mass segregation on the photometric maps, finding that heavier stars are concentrated in the brighter peak. The average line-of-sight velocity values are lower in an eccentric nuclear disk than for a circular ring about the supermassive black hole. The velocity dispersion values are higher and peak at the position of the supermassive black hole, which does not typically match the peak in photometry.

Keywords: Galaxies, Galaxy nuclei
The Impact of Powerful Jets on the Far-infrared Emission of an Extreme Radio Quasar at z ∼  6. The interactions between radio jets and the interstellar medium play a defining role for the coevolution of central supermassive black holes and their host galaxies, but observational constraints on these feedback processes are still very limited at redshifts z &gt; 2. We investigate the radio-loud quasar PSO J352.4034-15.3373 at z ∼ 6 at the edge of the Epoch of Reionization. This quasar is among the most powerful radio emitters and the first one with direct evidence of extended radio jets (∼1.6 kpc) at these high redshifts. We analyze NOrthern Extended Millimeter Array and Atacama Large Millimeter/submillimeter Array millimeter data targeting the CO (6-5) and [C II] far-infrared (FIR) emission lines, respectively, and the underlying continuum. The broad 440 ± 80 km s-1 and marginally resolved [C II] emission line yields a systemic redshift of z = 5.832 ± 0.001. Additionally, we report a strong 215 MHz radio continuum detection, 88 ± 7 mJy, using the Giant Metrewave Radio Telescope. This measurement significantly improves the constraints at the low-frequency end of the spectral energy distribution of this quasar. In contrast to what is typically observed in high-redshift radio-quiet quasars, we show that cold dust emission alone cannot reproduce the millimeter continuum measurements. This is evidence that the strong synchrotron emission from the quasar contributes substantially to the emission even at millimeter (FIR in the rest-frame) wavelengths. This quasar is an ideal system to probe the effects of radio jets during the formation of a massive galaxy within the first gigayear of the universe.

Keywords: Observational astronomy, AGN host galaxies, Quasars, Extragalactic radio sources, Radio loud quasars, Active galactic nuclei, High-redshift galaxies
Spin Dynamics of Extrasolar Giant Planets in Planet-Planet Scattering. Planet-planet scattering best explains the eccentricity distribution of extrasolar giant planets, and past literature showed that the orbits of planets evolve due to planet-planet scattering. This work studies the spin evolution of planets in planet-planet scattering in two-planet systems. Spin can evolve dramatically due to spin-orbit coupling made possible by the evolving spin and orbital precession during the planet-planet scattering phase. The main source of torque to planet spin is the stellar torque, and the planet-planet torque contribution is negligible. As a consequence of the evolution of the spin, planets can end up with appreciable obliquities (the angle between a planet's own orbit normal and spin axis), with the obliquity distribution peaking at about 10°, and extending to much larger values.

Keywords: Planetary dynamics, Exoplanets
Variable Stars in Local Group Galaxies. VI. The Isolated Dwarfs VV 124 and KKr 25. We present the discovery of variable stars in two isolated dwarf galaxies in the outskirts of the Local Group, VV 124 and KKr 25, using observations with the Hubble Space Telescope. VV 124 hosts stellar populations with a wide range of ages (&gt;10 Gyr until the present) and therefore we find all types of classical pulsators. In VV 124, we detect a total of 771 variable stars, including 78 classical Cepheids, 10 anomalous Cepheids, one Type II Cepheid, 678 RR Lyrae stars, and four eclipsing binaries. In KKr 25, we find 25 anomalous Cepheids, 46 RR Lyrae stars, and no classical Cepheids, thus the galaxy does not have a strong young population. A comparison of the variables with evolutionary tracks suggests that both galaxies may contain an intrinsic spread in metallicity, but overall are fairly metal-poor. We also present detailed simulations, which have been designed to estimate the completeness of our variable catalog. Particularly in the cases for which the observations are not deep enough to reach the main-sequence turnoff, such as the more distant Local Group dwarf galaxies, the techniques developed here can be used together with relatively shallow color-magnitude diagrams to inform on the nature of galactic populations over the full range of ages.

Keywords: Pulsating variable stars, Anomalous Cepheid variable stars, Population II Cepheid variable stars, Dwarf galaxies, RR Lyrae variable stars, Cepheid variable stars, Dwarf spheroidal galaxies
Similar Scale-invariant Behaviors between Soft Gamma-Ray Repeaters and an Extreme Epoch from FRB 121102. The recent discovery of a Galactic fast radio burst (FRB) associated with a hard X-ray burst from the soft gamma-ray repeater (SGR) J1935+2154 has established the magnetar origin of at least some FRBs. In this work, we study the statistical properties of soft gamma-ray/hard X-ray bursts from SGRs 1806-20 and J1935+2154 and of radio bursts from the repeating FRB 121102. For SGRs, we show that the probability density functions for the differences of fluences, fluxes, and durations at different times have fat tails with a q-Gaussian form. The q values in the q-Gaussian distributions are approximately steady and independent of the temporal interval scale adopted, implying a scale-invariant structure of SGRs. These features indicate that SGR bursts may be governed by a self-organizing criticality (SOC) process, confirming previous findings. Very recently, 1652 independent bursts from FRB 121102 have been detected by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Here we also investigate the scale-invariant structure of FRB 121102 based on the latest observations of FAST, and show that FRB 121102 and SGRs share similar statistical properties. Given the bimodal energy distribution of FRB 121102 bursts, we separately explore the scale-invariant behaviors of low- and high-energy bursts of FRB 121102. We find that the q values of low- and high-energy bursts are different, which further strengthens the evidence of the bimodality of the energy distribution. Scale invariance in both the high-energy component of FRB 121102 and SGRs can be well explained within the same physical framework of fractal-diffusive SOC systems.

Keywords: Magnetars, Soft gamma-ray repeaters, Radio bursts, Radio transient sources
X-Ray Superflares from Pre-main-sequence Stars: Flare Modeling. Getman et al. report the discovery, energetics, frequencies, and effects on environs of &gt;1000 X-ray superflares with X-ray energies EX ~ 1034-1038 erg from pre-main-sequence (PMS) stars identified in the Chandra MYStIX and SFiNCs surveys. Here we perform detailed plasma evolution modeling of 55 bright MYStIX/SFiNCs superflares from these events. They constitute a large sample of the most powerful stellar flares analyzed in a uniform fashion. They are compared with published X-ray superflares from young stars in the Orion Nebula Cluster, older active stars, and the Sun. Several results emerge. First, the properties of PMS X-ray superflares are independent of the presence or absence of protoplanetary disks inferred from infrared photometry, supporting the solar-type model of PMS flaring magnetic loops with both footpoints anchored in the stellar surface. Second, most PMS superflares resemble solar long-duration events that are associated with coronal mass ejections. Slow-rise PMS superflares are an interesting exception. Third, strong correlations of superflare peak emission measure and plasma temperature with the stellar mass are similar to established correlations for the PMS X-ray emission composed of numerous smaller flares. Fourth, a new correlation of loop geometry is linked to stellar mass; more massive stars appear to have thicker flaring loops. Finally, the slope of a long-standing relationship between the X-ray luminosity and magnetic flux of various solar-stellar magnetic elements appears steeper in PMS superflares than for solar events.

Keywords: Solar flares, Stellar x-ray flares, Pre-main sequence stars, Protoplanetary disks, Stellar flares, X-ray stars
The Nature of Black Hole Shadows. A distinct visual signature occurs in black holes that are surrounded by optically thin and geometrically thick emission regions. This signature is a sharp-edged dip in brightness that is coincident with the black hole's shadow, which is the projection of the black hole's unstable-photon region on the observer's sky. We highlight two key mechanisms that are responsible for producing the sharp-edged dip: (i) the reduction of intensity observed in rays that intersect the unstable-photon region, and thus the perfectly absorbing event horizon, versus rays that do not (blocking); and (ii) the increase of intensity observed in rays that travel along extended, horizon-circling paths near the boundary of the unstable-photon region (path-lengthening). We demonstrate that the black hole shadow is a distinct phenomenon from the photon ring, and that models exist in which the former may be observed but not the latter. Additionally, we show that the black hole shadow and its associated visual signature differ from the more model-dependent brightness depressions associated with thin-disk models because the blocking and path-lengthening effects are quite general for geometrically thick and optically thin emission regions. Consequentially, the black hole shadow is a robust and fairly model-independent observable for accreting black holes that are in the deep sub-Eddington regime, such as low-luminosity active galactic nuclei.

Keywords: Accretion, Black hole physics, Radiative transfer
Infrared Excesses Around Bright White Dwarfs from Gaia and unWISE. II. Infrared excesses around white dwarf stars indicate the presence of various astrophysical objects of interest, including companions and debris disks. In this second paper of a series, we present follow-up observations of infrared excess candidates from Gaia and unWISE discussed in the first paper, Paper I. We report space-based infrared photometry at 3.6 and 4.5 micron for 174 white dwarfs from the Spitzer Space Telescope and ground-based near-infrared J, H, and K photometry of 235 white dwarfs from Gemini Observatory with significant overlap between Spitzer and Gemini observations. These data are used to confirm or rule out the observed unWISE infrared excess. From the unWISE-selected candidate sample, the most promising infrared excess sample comes from both color and flux excess, which has a Spitzer confirmation rate of 95%. We also discuss a method to distinguish infrared excess caused by stellar or sub-stellar companions from potential dust disks. In total, we confirm the infrared excess around 62 white dwarfs, 10 of which are likely to be stellar companions. The remaining 52 bright white dwarfs with infrared excess beyond two microns has the potential to double the known sample of white dwarfs with dusty exoplanetary debris disks. Follow-up high-resolution spectroscopic studies of a fraction of confirmed excess white dwarfs in this sample have discovered emission from gaseous dust disks. Additional investigations will be able to expand the parameter space from which dust disks around white dwarfs are found.

Keywords: M dwarf stars, Brown dwarfs, White dwarf stars, Infrared astronomy, Infrared excess, Stellar accretion disks, Debris disks, Near infrared astronomy
State of the Field: Binary Black Hole Natal Kicks and Prospects for Isolated Field Formation after GWTC-2. Advanced LIGO and Advanced Virgo's newly released GWTC-2 catalog of gravitational-wave detections offers unprecedented information about the spin magnitudes and orientations of merging binary black holes (BBHs). Notably, analysis of the BBH population suggests the presence of binaries whose component spins are significantly misaligned with respect to their orbital angular momenta. Significantly misaligned spins are typically predicted to be at odds with isolated field formation via standard common envelope (CE) evolution, and hence a "smoking gun" signature of dynamical binary formation inside dense stellar clusters. Here, we explore whether the LIGO/Virgo observation of spin-orbit misalignment indeed rules out the possibility that BBHs are formed entirely in the field via standard CE evolution. In particular, we seek to understand whether, by varying the natal kicks black holes receive upon formation, we can invoke the CE scenario to self-consistently explain both the observed spin distribution and merger rate of BBHs. We find that, if isolated black holes are born with small natal spins, then BBHs formed through CE require extreme natal kicks to match the observed BBH population, with a velocity dispersion $\sigma ={9.7}_{-5.9}^{+26.7}\times {10}^{2}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ and σ &gt; 260 km s-1 at 99% credibility. To avoid the need for extreme kicks, we argue that it is necessary to assume that isolated black holes are born with nonvanishing natal spins, that one or more alternative channels contribute to the observed BBH population, and/or that other unforeseen mechanisms serve to yield large spin-orbit misalignment in the field.

Keywords: Astronomy data analysis, Gravitational waves, Astrophysical black holes, Compact binary stars
Electromagnetic Proton Beam Instabilities in the Inner Heliosphere: Energy Transfer Rate, Radial Distribution, and Effective Excitation. Differential flows among different ion species are often observed in the solar wind, and such ion differential flows can provide the free energy to drive Alfvén/ion cyclotron and fast-magnetosonic/whistler instabilities. Previous works mainly focused on ion beam instability under the parameters representative of the solar wind nearby 1 au. In this paper we further study proton beam instability using the radial models of the magnetic field and plasma parameters in the inner heliosphere. We explore a comprehensive distribution of proton beam instability as functions of the heliocentric distance and the beam speed. We also perform a detailed analysis of the energy transfer between unstable waves and particles and quantify how much the free energy of the proton beam flows into unstable waves and other kinds of particle species (i.e., proton core, alpha particle, and electron). This work clarifies that both parallel and perpendicular electric fields are responsible for the excitation of oblique Alfvén/ion cyclotron and oblique fast-magnetosonic/whistler instabilities. Moreover, this work proposes an effective growth length to estimate whether the instability is efficiently excited or not. It shows that oblique Alfvén/ion cyclotron instability, oblique fast-magnetosonic/whistler instability, and oblique Alfvén/ion beam instability can be efficiently driven by proton beams drifting at the speed ~600-1300 km s-1 in the solar atmosphere. In particular, oblique Alfvén/ion cyclotron waves driven in the solar atmosphere can be significantly damped therein, leading to solar corona heating. These results are helpful for understanding proton beam dynamics in the inner heliosphere and can be verified through in situ satellite measurements.

Keywords: Solar wind, Plasma astrophysics, Plasma physics
Early Universe Physics Insensitive and Uncalibrated Cosmic Standards: Constraints on Ω<SUB>m</SUB> and Implications for the Hubble Tension. To further gain insight into whether pre-recombination models can resolve the Hubble tension, we explore constraints on the evolution of the cosmic background that are insensitive to early universe physics. The analysis of the CMB anisotropy has been thought to highly rely on early universe physics. However, we show that the fact that the sound horizon at recombination being close to that at the end of the drag epoch is insensitive to early universe physics. This allows us to link the absolute sizes of the two horizons and treat them as free parameters. Jointly, the CMB peak angular size, baryon acoustic oscillations, and Type Ia supernovae can be used as early universe physics insensitive and uncalibrated cosmic standards, which measure the cosmic history from recombination to today. They can set strong and robust constraints on the post-recombination cosmic background, especially the matter density parameter with Ωm = 0.302 ± 0.008 (68% C.L.), assuming a flat Λ cold dark matter universe after recombination. When we combine these with other nonlocal observations, we obtain several constraints on H0 with significantly reduced sensitivity to early universe physics. These are all more consistent with the Planck 2018 result than the local measurement results such as those based on Cepheids. This suggests a tension between the post-recombination, but nonlocal, observations, and the local measurements that cannot be resolved by modifying pre-recombination early universe physics.

Keywords: Cosmological evolution, Cosmic microwave background radiation, Cosmological parameters from large-scale structure, Hubble constant, Dark energy
Why Do M Dwarfs Have More Transiting Planets?. We propose a planet formation scenario to explain the elevated occurrence rates of transiting planets around M dwarfs compared to Sun-like stars discovered by Kepler. We use a pebble drift and accretion model to simulate the growth of planet cores inside and outside of the snow line. A smaller pebble size interior to the snow line delays the growth of super-Earths, allowing giant planet cores in the outer disk to form first. When those giant planets reach pebble isolation mass they cut off the flow of pebbles to the inner disk and prevent the formation of close-in super-Earths. We apply this model to stars with masses between 0.1 and 2 M⊙ and for a range of initial disk masses. We find that the masses of hot super-Earths and of cold giant planets are anticorrelated. The fraction of our simulations that form hot super-Earths is higher around lower-mass stars and matches the exoplanet occurrence rates from Kepler. The fraction of simulations forming cold giant planets is consistent with the stellar mass dependence from radial-velocity surveys. A key testable prediction of the pebble accretion hypothesis is that the occurrence rates of super-Earths should decrease again for M dwarfs near the substellar boundary like Trappist-1.

Keywords: Exoplanets, Planetary system formation, Protoplanetary disks, Exoplanet formation, Planet formation
Void Replenishment: How Voids Accrete Matter Over Cosmic History. Cosmic voids are underdense regions filling up most of the volume in the universe. They are expected to emerge in regions comprising negative initial density fluctuations, and subsequently expand as the matter around them collapses and forms walls, filaments, and clusters. We report results from the analysis of a cosmological simulation specially designed to accurately describe low-density regions, such as cosmic voids. Contrary to the common expectation, we find that voids also experience significant mass inflows over cosmic history. On average, 10% of the mass of voids in the sample at z ~ 0 is accreted from overdense regions, reaching values beyond 35% for a significant fraction of voids. More than half of the mass entering the voids lingers on periods of time ~10 Gyr well inside them, reaching inner radii. This would imply that part of the gas lying inside voids at a given time proceeds from overdense regions (e.g., clusters or filaments), where it could have been preprocessed, thus challenging the scenario of galaxy formation in voids, and dissenting from the idea of them being pristine environments.

Keywords: Accretion, Computational astronomy, Galaxy environments, Large-scale structure of the universe, Voids