Sazuna/UAT_keywords huggingface dataset:
Outer Solar System Spacecraft to Probe the μHz Gravitational-wave Frontier. The microhertz frequency band of gravitational waves probes the merger of supermassive black holes, as well as many other gravitational-wave phenomena. However, space-interferometry methods that use test masses would require further development of test-mass isolation systems to detect anticipated astrophysical events. We propose an approach that avoids onboard inertial test masses by situating spacecraft in the low-acceleration environment of the outer solar system. We show that, for Earth─spacecraft and interspacecraft distances of ≳10 au, the accelerations on the spacecraft would be sufficiently small to potentially achieve gravitational-wave sensitivities determined by stochastic gravitational-wave backgrounds. We further argue, for arm lengths of 10−30 au and ∼10 W transmissions, that stable phase locks could be achieved with 20 cm mirrors or 5 m radio dishes. We discuss designs that send both laser beams and radio waves between the spacecraft, finding that, despite the ∼ 104× longer wavelengths, even a design with radio transmissions could reach stochastic background-limited sensitivities at ≲0.3 × 10−4 Hz. Operating in the radio significantly reduces many spacecraft design tolerances. Our baseline concepts require two arms to do interferometry. However, if one spacecraft carries a clock with Allan deviations at 104 s of 10−17, a comparable sensitivity could be achieved with a single arm. Finally, we discuss the feasibility of achieving similar gravitational-wave sensitivities in a "Doppler tracking" configuration where the single arm is anchored to Earth.

Keywords: Supermassive black holes, Gravitational wave detectors, Gravitational waves
Gas Pressure Driven Screening Forces and Pebble Aggregation: A Pathway for Growth in Planet Formation. The formation of planetesimals from centimeter-sized pebbles in protoplanetary disks faces significant barriers, including fragmentation and radial drift. We identify a previously unaccounted screening force, arising from mutual shielding of thermal gas particles between pebbles when their separation falls below the gas mean free path. This force facilitates pebble binding, overcoming key growth barriers under turbulent disk conditions. Unlike conventional mechanisms, screening forces operate independently of surface adhesion and complement streaming instability and pressure traps by enhancing aggregation in high-density regions. Our analysis predicts that screening interactions are most effective in the middle disk regions (∼0.3 to a few astronomical units), consistent with Atacama Large Millimeter/submillimeter Array observations (e.g., TW Hya) of enhanced dust concentrations. Furthermore, we find that screening-induced pebble growth from centimeter to kilometer scales can occur on timescales significantly shorter than the disk lifetime (∼105 yr). Importantly, this growth naturally terminates when particles smaller than the local gas mean free path are depleted, thereby avoiding runaway accretion. Beyond planetary science, the screening forces have potential implications for high-energy astrophysics, dusty plasmas, confined particle suspensions, and other relevant areas, suggesting a broader fundamental significance.

Keywords: Planet formation, Planetesimals
Rigorous Analytic Solution to the Gravitational-wave Overlapping Event Rates. In the era of the next-generation gravitational-wave detectors, signal overlaps will become prevalent due to the high detection rate and long signal duration, posing significant challenges to data analysis. While effective algorithms are being developed, there still lacks an integrated understanding of the statistical properties for the population of overlapping compact binary coalescence signals. For the first time, in order to aid rapid and robust estimation, we rigorously derive and establish analytical expressions for the expectation and variance for the number of overlapping events. This framework is highly extensible, allowing analytical calculation for more complicated scenarios, such as multi-signal overlaps, overlaps between different types of sources, and source-dependent thresholds. We also mathematically prove that the time difference between events in a single observation run is described by the beta distribution, offering an analytical prior reference for Bayesian analysis.

Keywords: Astrostatistics distributions, Gravitational waves, Astrostatistics
Exploring the Masses of the Two Most Distant Gravitational Lensing Clusters at Cosmic Noon. Observations over the past decade have shown that galaxy clusters undergo the most transformative changes during the z = 1.5─2 epoch. However, challenges such as low lensing efficiency, high shape measurement uncertainty, and a scarcity of background galaxies have prevented us from characterizing their masses with weak gravitational lensing (WL) beyond redshift z ∼ 1.75. In this paper, we report the successful WL detection of JKCS 041 and XLSSC 122 at z = 1.80 and z = 1.98, respectively, utilizing deep infrared imaging data from the Hubble Space Telescope with careful removal of instrumental effects. These are the most distant clusters ever measured through WL. The mass peaks of JKCS 041 and XLSSC 122, which coincide with the X-ray peak positions of the respective clusters, are detected at the ∼3.7σ and ∼3.2σ levels, respectively. Assuming a single spherical Navarro─Frenk─White profile, we estimate that JKCS 041 has a virial mass of M200c = (5.4 ± 1.6) × 1014 M⊙, while the mass of XLSSC 122 is determined to be M200c = (3.3 ± 1.8) × 1014 M⊙. These WL masses are consistent with the estimates inferred from their X-ray observations. We conclude that although the probability of finding such massive clusters at their redshifts is certainly low, their masses can still be accommodated within the current ΛCDM paradigm.

Keywords: Galaxy clusters, Weak gravitational lensing, High-redshift galaxy clusters, Observational cosmology, Gravitational lensing, Dark matter
Orbital Period Changes of Recurrent Nova U Scorpii Demonstrate That M<SUB>ejecta</SUB> = 26 × M<SUB>accreted</SUB>, So U Sco Is Not a Type Ia Supernova Progenitor. Recurrent nova U Scorpii (U Sco) is one of the prototypes for a Type Ia supernova progenitor. The logic is that the white dwarf is near the Chandrasekhar mass and gas is accumulating onto its surface at a near-maximal accretion rate, so it will soon increase its mass to the supernova trigger. But the white dwarf loses mass every nova eruption, so the issue is balancing the mass ejected (Mejecta) against the mass accreted between eruptions (Maccreted). Measuring Maccreted can be done in several ways to usable accuracy. But the old methods for measuring Mejecta (involving the flux in hydrogen emission lines) all have real error bars of 2–3 orders of magnitude. The only solution is to measure the change of the orbital period across the nova eruption (ΔP). But this solution requires a vast photometric program of eclipse timings stretching decades. For U Sco, a program started in 1989, now reaches its culmination with measures of ΔP for the eruptions of 1999, 2010, 2016, and 2022. This paper reports on 52 new eclipse times (for a total of 218 eclipses from 1945 to 2025), plus a new theory result allowing for the confident calculation of Mejecta from ΔP. The four eruptions ejected a total of (103 ± 14) × 10‑6 M⊙, while the white dwarf accreted 4 × 10‑6 M⊙ over the four previous eruption cycles. With Mejecta = 26 × Maccreted, the U Sco white dwarf is losing large masses each eruption cycle, so U Sco can never produce a Type Ia supernova.

Keywords: Novae, Type Ia supernovae, Recurrent novae, Supernovae, Classical novae
Orbital Period Changes in Recurrent Nova T Corona Borealis Prove That It Is Not a Type Ia Supernovae Progenitor. T Corona Borealis (T CrB) is a recurrent nova and a symbiotic star that is commonly highlighted as the best case for being a progenitor of a Type Ia supernova (SN Ia) within the framework of single-degenerate models. This exemplar can be tested by measuring whether the white dwarf (WD) mass (MWD) is increasing over each eruption cycle. This is a balance between the mass ejected during each nova event (Mejecta) and the mass accreted onto the WD between the nova events (Maccreted). I have used all 206 radial velocities from 1946 to 2024 to measure the orbital period just after the 1946 eruption, which is Ppost = 227.6043 days, while the steady orbital period change ( Ṗ ) is (‑3.1 ± 1.6) × 10‑6. I have used my full 213,730 magnitude B and V light curve from 1842 to 2025 to measure the times of maximum brightness in the ellipsoidal modulations to construct the O ‑ C from 1866 to 1946. I fit the broken parabola shape to find the orbital period immediately before the 1946 eruption, which is  Ppre  = 227.4586 days. The orbital period changed by ΔP = +0.146 ± 0.019 days. With Kepler's Law, conservation of angular momentum, and the well-measured binary properties, the ejecta mass in 1946 is 0.00074 ± 0.00009 M⊙. Maccreted is reliably measured to be 1.38 × 10‑6 M⊙ from the accretion luminosity. Mejecta is larger than Maccreted by 540×, so MWD is decreasing every eruption cycle. T CrB can never become an SN Ia.

Keywords: Novae, Type Ia supernovae, Symbiotic novae, Recurrent novae, Symbiotic binary stars, Supernovae
Palladium and Silver Abundances in Extremely Metal-poor Stars. Based on the high-resolution and high signal-to-noise ratio near-ultraviolet spectra from the ESO VLT 8.2 m Kueyen telescope, we investigate the abundances of palladium (Pd) and silver (Ag) in a sample of 27 extreme metal-poor stars. The metallicity range of our sample stars is from ∼−2.2 to ∼−3.66 dex, and they are crucial for understanding the formation and evolution of weak r-process elements in our early Galaxy. The stellar atmospheric parameters, including effective temperature (Teff), surface gravity (log g), metallicity ([Fe/H]), and microturbulence (ξt) are derived using the spectroscopic method, and the nonlocal thermodynamic equilibrium effects for both Fe I and Fe II lines have been considered when determining the iron abundance. Our results show that both [Pd/Fe] and [Ag/Fe] exhibit flat trends with metallicities between −0.7 and −3.0 dex, with an increasing scatter at lower metallicities. This study also finds a clear correlation between [Ag/H] and [Pd/H], indicating that both elements likely share a similar nucleosynthetic origin.

Keywords: Fundamental parameters of stars, Galaxy chemical evolution, Chemical abundances, Nucleosynthesis
Effects of Dissipation Physics on High-frequency Quasiperiodic Oscillations in Black Hole X-Ray Binaries. We numerically investigate the effects of black hole spin and local dissipation profiles on high-frequency quasiperiodic oscillation (HFQPO) observed in black hole X-ray binaries (BHXBs). Our HFQPO power spectra arise from self-consistent calculations that do not rely on ad hoc assumptions regarding disk geometry. Our models combine radiative transfer and disk vertical structure equations with input motivated by first-principles three-dimensional simulations. We found that HFQPO power spectra may be sensitive to the spatial distribution of dissipation rates, while the quality factors are more sensitive to black hole spin. We discuss the observational implications of our results in the context of steep power-law spectra from BHXBs that are seen together with HFQPOs, and how quasiperiodic oscillation properties may be indicators of the underlying physical oscillations.

Keywords: Accretion, Black holes, Astrophysical black holes
Magnetic Field Characteristics of Moving Magnetic Features during the Sunspot Decay from the Whole Sunspot to Pore. To understand the relationship between moving magnetic features (MMFs) and the decay of the sunspot, we studied the complete decays of four α-type sunspots based on data from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, focusing on the magnetic properties of same-polarity MMFs at the moment they detach from the sunspots. The main results are as follows: (1) The area and horizontal velocity of MMFs mainly range from 0.4 to 2 MSH and 0.2 to 1.7 km s‑1, with typical values of 0.65 MSH and 0.6 km s‑1, respectively. The dominant ranges for B, Bt, Bz, and γ are 200–400 G, 75–350 G, 153–297 G, and 20°–60°, respectively. (2) Comparing the pre-pore (the stage before the sunspot transforms into the pore) and pore (after the transformation) stages, the area, horizontal velocity, and Bz show similar distribution ranges, while the mean values and ranges of B, Bt, and γ decrease significantly. (3) In the pre-pore stage, MMFs predominantly manifest as horizontal MMFs (MMFs that have a horizontal magnetic field (45° &lt; γ &lt; 90°)), whereas in the pore stage, most of them are observed as vertical MMFs (MMFs that have a vertical magnetic field (0° &lt; γ ≤ 45°)). These findings provide observational evidence for the turbulent erosion model of the sunspot decay; the mean vertical magnetic field may be an important parameter for the detachment of MMFs from the sunspots.

Keywords: Solar photosphere, Sunspots, Solar magnetic fields
EP241021a: A Catastrophic Collapse/Merger of Compact Star Binary Leading to the Formation of a Remnant Millisecond Magnetar?. Observations of fast X-ray transients (FXRTs) with the Einstein Probe have successfully led to the discovery of some unusual extragalactic optical transients. EP241021a is a newly discovered FXRT that was featured by a significant bump at around 10 days in both optical and X-ray bands. This timescale and the exceptionally high peak bolometric luminosity up to ∼1044 erg s−1 of the optical bump make it somewhat similar to fast blue optical transients but still distinctive from them by its relatively red color. We then suggest that the multiwavelength bump of EP241021a could represent an explosion-type transient, while the underlying power-law decaying component of the optical and X-ray emission as well as the total radio emission are produced by a moderately relativistic jet. By fitting the observed multiwavelength light curves, it is found that the explosion ejecta that produce the thermal optical emission can have a mass of ∼0.03 M⊙, an expanding velocity of ∼0.25c, and an optical opacity of ∼12 cm2 g−1, which was continuously powered by a rapidly rotating and highly magnetized neutron star (NS; i.e., a magnetar). In addition to heating the explosion ejecta, the magnetar also provided the dominant contribution to the observed X-ray rebrightening through the nonthermal emission of its wind. These properties suggest that the explosion may result from a catastrophic collapse/merger of a compact star system, which led to the formation of a millisecond magnetar, and the possible progenitor could be an accreting white dwarf (WD) or a binary consisting of a double WD, a double NS, or a WD and an NS.

Keywords: Neutron stars, Magnetars, X-ray transient sources
BASS. LII. The Prevalence of Double-peaked Broad Lines at Low Accretion Rates among Hard X-Ray Selected Active Galactic Nuclei. A fraction of active galactic nuclei (AGN) have double-peaked Hα, Hβ, and Mg II broad lines attributed to emission from rotating gas in the accretion disk. Using optical spectroscopy of a flux-limited sample of AGN selected via ultrahard X-rays from the BAT AGN Spectroscopic Survey (BASS), we systematically identify 71 double-peaked emitters (DPEs) among 343 broad-line AGN with redshifts 0.004 &lt; z &lt; 0.297 and X-ray luminosities of  40&lt;logL2‑10KeV (erg s‑1) &lt; 45.7, and provide their best-fit accretion disk parameters. We find that ∼21% of X-ray-selected broad-line AGN are DPEs, consistent with rates previously reported for z &lt; 0.2 broad-line AGN selected for strong optical variability in the Zwicky Transient Facility. 11 of 71 DPEs (15%) exhibited a single-peaked Gaussian component to the broad line profile in addition to the double-peaked disk profile. In this sample, DPEs have intrinsically higher masses by ∼0.4 dex and lower Eddington ratios by ∼0.3 dex than other broad-line AGN, and have a preference for elliptical host galaxies, higher X-ray luminosities, and higher [O I] λ6302 to narrow Hα flux ratios than other broad-line AGN. We find that DPEs are not segregated from non-DPE broad-line AGN in the Lbol versus MBH relation or their X-ray to radio luminosity ratios, and do not show a preference for intermediate Seyfert types over Seyfert 1s. We do not find differences in a wide range of multiwavelength properties when comparing DPEs to non-DPE broad-line AGN, including optical and mid-IR variability levels, Wide-field Infrared Survey Explorer colors, αox, the column density of neutral obscuring material NH, and the rate of changing-look events. We discuss the two populations in the context of multicomponent disk-wind models of the AGN broad-line region and consider how unrecognized contributions of disk emission to the broad lines may introduce biases in "virial" supermassive black hole mass estimates, with consequences for the inferred MBH–M* relation.

Keywords: AGN host galaxies, Supermassive black holes, Active galaxies
Constraining Active Galactic Nucleus Jets with Spectrum and Core Shift: The Case of M87. We analytically model stationary and axisymmetric active galactic nucleus jets, assuming energy conservation along each magnetic flux tube. Using very long baseline interferometry (VLBI) observations and published general relativistic magnetohydrodynamic simulations, we constrain the evolution of the bulk Lorentz factor, the magnetization parameter, and the magnetic field strength along the jet. We then infer the electron density, emission coefficient, and absorption coefficient at each point, and integrate the radiative transfer equation to compute the spectral energy distribution (SED) and the core shift of the synchrotron emission from the relativistic jet. Applying the method to the M87 jet, we find that the hot plasmas are injected at the altitude of seven Schwarzschild radii from the black hole (BH), that the M87 jet is likely composed of a pair plasma, and that the jet flowline geometry is quasi-parabolic as reported at much greater distances. Fitting the nonthermal fraction of the leptonic jet as a function of the position, we also find that most of the radio photons are emitted within 1000 Schwarzschild radii from the BH. Although hadronic jets do not reproduce all the VLBI observations consistently in our model, we also discuss that their heavy mass allows for a stronger magnetic field within the observational constraints, leading to an inverted SED in submillimeter wavelengths by the thermal emission from the jet base. It is therefore implied that contemporaneous observations of the M87 jet with Atacama Large Millimeter/submillimeter Array and VLBI could discriminate the jet composition and its collimation within the central 100 Schwarzschild radii.

Keywords: Theoretical models, Black holes, Extragalactic radio sources, Very long baseline interferometry, Special relativity, Relativistic jets, Plasma astrophysics, Radiative transfer equation, Active galactic nuclei
A Systematic Search for Main-sequence Dipper Stars Using the Zwicky Transient Facility. Main-sequence dipper stars, characterized by irregular and often aperiodic luminosity dimming events, offer a unique opportunity to explore the variability of circumstellar material and its potential links to planet formation, debris disks, and broadly star─planet interactions. The advent of all-sky time-domain surveys has enabled the rapid discovery of these unique systems. We present the results of a large systematic search for main-sequence dipper stars, conducted across a sample of 63 million FGK main-sequence stars using data from Gaia eDR3 and the Zwicky Transient Facility survey. Using a novel light-curve scoring algorithm and a scalable workflow tailored for analyzing millions of light curves, we have identified 81 new dipper star candidates. Our sample reveals a diverse phenomenology of light-curve dimming shapes, such as skewed and symmetric dimmings with timescales spanning days to years, some of which closely resemble exaggerated versions of KIC 8462852. Our sample reveals no clear periodicity patterns in many of these dippers and no IR excess or variability. Using archival data collated for this study, we thoroughly investigate several classification scenarios and hypothesize that the mechanisms of such dimming events are either driven by circumstellar clumps or occultations by stellar/substellar companions with disks. Our study marks a significant step forward in understanding main-sequence dipper stars.

Keywords: Main sequence stars, Circumstellar dust, Sky surveys, Young stellar objects
A Study of the Dynamical Structures in a Dark Matter Halo Using UMAP. We use a dimension reduction algorithm, Uniform Manifold Approximation and Projection (UMAP), to study dynamical structures inside a dark matter halo. We use a zoom-in simulation of a Milky Way mass dark matter halo and apply UMAP to the six-dimensional phase space in the dark matter field at z = 0. We find that particles in the field are mapped to distinct clusters in the lower dimensional space in a way that is closely related to their accretion history. The largest cluster in UMAP space does not contain the entire mass of the Milky Way virial region and neatly separates the older halo from the recently accreted matter. Particles within this cluster, which only comprise ∼70% of the Milky Way particles, have had several pericenter passages and are, therefore, likely to be phase mixed, becoming dynamically uniform. The infall region and recently accreted particles and substructure, even up to splashback, form distinct components in the lower dimensional space; additionally, higher angular momentum particles also take longer times to mix. Our work shows that the current state of the Milky Way halo retains historical information, particularly about the recent accretion history, and even a relatively old structure is not dynamically uniform. We also explore UMAP as a preprocessing step to find coherent subhalos in dark matter simulations.

Keywords: Milky Way dark matter halo, Orbits, Dark matter, N-body simulations