Sazuna/UAT_keywords huggingface dataset:
Imaging and Radio Signatures of Shock–Plasmoid Interaction. Understanding how shocks interact with coronal structures is crucial for understanding the mechanisms of particle acceleration in the solar corona and inner heliosphere. Using simultaneous radio and white-light observations, we investigate the interaction between a coronal mass ejection (CME)-driven shock and a plasmoid. LASCO and STEREO-A COR-2 white-light images are analyzed to track the evolution of the plasmoid, CME, and its associated shock, while the Wind/WAVES and STEREO/WAVES dynamic spectra provide complementary radio signatures of the shock–plasmoid interaction at ≈7 R⊙. An interplanetary type II radio burst was detected as the shock propagated through the plasmoid. The merging of the plasmoid into the CME was accompanied by interplanetary type III radio bursts, suggesting escaping electron beams during the reconnection process. These observations clearly demonstrate that shock–plasmoid interactions can enhance the efficiency of particle acceleration associated with CMEs, with implications for electron acceleration in flare and heliospheric current sheets as well.

Keywords: Solar coronal mass ejection shocks, Solar radio emission, Solar flares, Solar magnetic reconnection
Explaining the Weak Evolution of the High-redshift Mass–Metallicity Relation with Galaxy Burst Cycles. Recent observations suggest a nearly constant gas-phase mass–metallicity relation (MZR) at z ≳ 5, in agreement with many theoretical predictions. This lack of evolution contrasts with observations at z ≲ 3, which find an increasing normalization of the MZR with decreasing redshift. We analyze a high-redshift suite of FIRE-2 cosmological zoom-in simulations to identify the physical drivers of the MZR. Previous studies have explained the weak evolution of the high-redshift MZR in terms of weakly evolving or saturated gas fractions, but we find that this alone does not explain the evolution in FIRE-2. Instead, stellar feedback following intense bursts of star formation drives enriched gas out of galaxies, resetting their interstellar medium and separating their histories into distinct "burst cycles." We develop the "reduced burst model," a simplified gas-regulator model that successfully reproduces the simulated MZR and identifies the dominant drivers of its evolution. As redshift decreases, the metallicity of inflows within burst cycles increases at fixed stellar mass due to increased wind recycling of enriched gas. Meanwhile, the metal mass produced by stars per inflowing gas mass within these cycles decreases because of decreased star formation per gas mass inflowing into the galaxy. The effects of these two processes on the median metallicity largely cancel, holding the MZR constant for z = 5–12. At fixed stellar mass, the simulations predict lower gas metallicities at higher Hα-derived star formation rates, in qualitative agreement with the fundamental metallicity relation, but this effect is reduced in rest UV-selected samples.

Keywords: Starburst galaxies, Metallicity, Early universe, Hydrodynamical simulations, Galaxy chemical evolution, Chemical enrichment, High-redshift galaxies, Galaxies
Jet Collimation in a Spiral-hosted Active Galactic Nucleus: A Parabolic Jet Profile in 0313–192. Double-lobed active galactic nuclei (DRAGNs) are typically found in elliptical galaxies, while supermassive black holes (SMBHs) in disk galaxies rarely produce powerful kiloparsec-scale jets. However, the growing number of spiral- and disk-hosted DRAGNs challenges this classical dichotomy. We present a study of the jet collimation profile for one such source, 0313–192, using Very Long Base Line Array and Very Large Array data, tracing the jet morphology across nearly 5 orders of magnitude in scale—from ∼a few pc to ∼100 kpc (projected). We find that the jet exhibits a parabolic expansion up to ∼610 pc (∼7.9 × 106 Schwarzschild radii), followed by a transition to a nearly conical shape, assuming kiloparsec-scale emission primarily originates from the jet rather than the lobe. This structural evolution closely resembles those in active galactic nuclei (AGNs) hosted by elliptical galaxies and provides an explanation for how the jet in this system could extend to large distances by magnetohydrodynamic collimation and acceleration. However, this collimation break occurs beyond the sphere of gravitational influence of the SMBH (∼7.3 × 105RS), and no extended X-ray halos or dense molecular gas structures are detected to provide the necessary external pressure. Therefore, we suggest that jet confinement in 0313–192 is mediated by contributions from nonthermal components, such as ram and magnetic pressure from magnetized disk winds. These mechanisms may enable jet collimation even in the absence of dense ambient gas. Our results highlight how large-scale jets can arise in disk galaxies under rare conditions and demonstrate the need to broaden studies of AGN jet formation beyond traditional models.

Keywords: Jets, Spiral galaxies, Disk galaxies, Radio galaxies, Radio continuum emission
A Radially Resolved Magnetic Field Threading the Disk of TW Hya. We present a new approach to detecting and characterizing a magnetic field in protoplanetary disks through the differential broadening of unpolarized molecular emission from CN. To demonstrate this technique, we apply it to new Atacama Large Millimeter/submillimeter Array observations of the full complement of hyperfine components from the N = 1─0 transition, achieving a spatial and spectral resolution of  ≍0.″5  and 80 m s−1, respectively. By fitting a model that incorporates the velocity structure of the disk, the potential non-LTE excitation of the molecule, and the Zeeman effect, we recover a radially resolved magnetic field with a strength of ∼10 mG between 60 and 120 au. The morphology of the field is also inferred through azimuthal variations in the line broadening, revealing a predominantly poloidal field at 60 au, sharply transitioning to one within the disk plane outside of the gap at 82 au. The signal-to-noise ratio of the data meant that the planar component was unable to be decomposed into toroidal and radial components. Lower limits on the local gas density (n(H2) ≳ 108 cm−3) from the excitation analysis of the CN emission correspond to a lower limit between 0.1 and 0.01 for the plasma β.

Keywords: Radio interferometry, Magnetic fields, Protoplanetary disks
A Magnetic White Dwarf Formed through a Binary Merger within 35 Million Yr. White dwarfs (WDs) represent the final evolutionary stage of most stars, typically originating from progenitor stars with masses below approximately 8─10 M⊙. Formation through single-star evolution generally requires at least 25 Myr, with the youngest WDs often near the Chandrasekhar limit of 1.4 M⊙. In contrast, WDs formed via binary channels, such as mergers or mass transfer, can develop smaller masses in a shorter timescale and may exhibit unique characteristics, including strong surface magnetic fields and rapid rotation. Accurately determining the ages of these WDs is essential for understanding their formation. A valuable method involves studying WDs in star clusters, where member stars share the same age and chemical composition, allowing for precise constraints on the formation times and metallicities of the WDs' progenitors. Here we report a WD found in the open cluster RSG 5, which is only 35 Myr old. The WD's mass is lower than 1.05 M⊙, indicating it may not have formed through single-star evolution. The WD possesses an exceptionally strong surface magnetic field (≥200 MG), a short rotational period (∼6.5 minutes), and, most notably, a corotating half-ring of ionized circumstellar debris. This distinctive feature provides evidence for a binary merger origin, a scenario further substantiated by our stellar evolution models.

Keywords: Open star clusters, White dwarf stars, Binary stars
The Detection of Teraelectronvolt Radiation from a Flat-spectrum Radio Quasar. The very high-energy (VHE; &gt;100 GeV) radiation carries the signatures of the matter–energy interaction in some of the most extreme astrophysical environments. Considering broad emission line blazars, i.e., flat-spectrum radio quasars (FSRQs), the dense photon fields surrounding the relativistic jet can prohibit the particle population from accelerating to very high energies and producing VHE radiation. They can also possibly make the environment opaque for the VHE γ rays due to γγ pair production, thus explaining the paucity of VHE-detected FSRQs and nondetection of TeV radiation (&gt;1 TeV) from them. Here we report, for the first time, a &gt;7σ detection of an FSRQ, S5 1027+74 (z = 0.123), in the VHE band, including the first ever detection of TeV emission from an object of this class, using the Fermi Large Area Telescope observations. Its γ-ray spectrum covering the 100 MeV–2 TeV band revealed a prominent spectral break with a flat, rising shape above ∼10 GeV, a feature never detected from other VHE-detected FSRQs. The radio-to-γ-ray spectral energy distribution of S5 1027+74 provides strong evidence of a third bump peaking at multi-TeV energies. These enigmatic findings imply that FSRQ jets can accelerate particles to extremely high energies and provide tantalizing clues about the complex radiative environment of relativistic jets.

Keywords: Gamma-ray astronomy, Relativistic jets, Flat-spectrum radio quasars, Blazars
Three-dimensional Dynamics of Strongly Magnetized Ion–Electron Relativistic Reconnection. We present 3D simulations of semirelativistic collisionless magnetic reconnection, where upstream ions are subrelativistic while electrons are ultrarelativistic. We employ the realistic proton-to-electron mass ratio and explore a range of upstream ion magnetizations spanning 2 orders of magnitude, with our highest-magnetization run achieving unprecedentedly large domain sizes. Through a parameter scan, we find that as the system transitions from mildly to trans- and ultrarelativistic regimes, the qualitative behavior of reconnection becomes strongly influenced by 3D effects mediated by drift-kink and flux-rope kink dynamics. As a result, magnetic-energy dissipation at high magnetizations, and the subsequent nonthermal particle acceleration, can become less efficient, contrary to general expectations for 3D relativistic reconnection. Our results have important implications for understanding reconnection in magnetized astrophysical scenarios, such as the surroundings of black holes and neutron stars.

Keywords: High energy astrophysics, Plasma physics, Plasma astrophysics, Active galactic nuclei, Magnetic fields, Astrophysical black holes
A Confirmed Deficit of Hot and Cold Dust Emission in the Most Luminous Little Red Dots. Luminous broad Hα emission and red rest-optical spectral energy distributions (SEDs) are the hallmark of compact little red dots (LRDs), implying highly attenuated dusty starbursts and/or obscured active galactic nuclei (AGN). However, the lack of observed far-infrared (FIR) emission has proved difficult to reconcile with the implied attenuated luminosity in these models. Here, we utilize deep new Atacama Large Millimeter/submillimeter Array imaging, new and existing JWST/MIRI imaging, and archival Spitzer/Herschel imaging of two of the rest-optically brightest LRDs (z = 3.1 and z = 4.47) to place the strongest constraints on the IR luminosity in LRDs to date. The detections at λrest = 1─4 μm imply flat slopes in the rest-IR, ruling out a contribution from hot (T ≳ 500 K) dust. Similarly, FIR nondetections rule out any appreciable cold (T ≲ 75 K) dust component. Assuming energy balance, these observations are inconsistent with the typical FIR dust emission of dusty starbursts and quasar tori, which usually show a mixture of cold and hot dust. Additionally, our [C II] nondetections rule out typical dusty starbursts. We compute empirical maximum IR SEDs and find that both LRDs must have  log(LIR/L⊙)≲12.2  at the 3σ level. These limits are in tension with the predictions of rest-optical spectrophotometric fits, be they galaxy-only, AGN-only, or composite. It is unlikely that LRDs are highly dust-reddened intrinsically blue sources with a dust temperature distribution that conspires to avoid current observing facilities. Rather, we favor an intrinsically redder LRD SED model that alleviates the need for strong dust attenuation.

Keywords: Galaxy evolution, Active galactic nuclei, High-redshift galaxies, Far infrared astronomy
Born Dry or Born Wet? A Palette of Water Growth Histories in TRAPPIST-1 Analogs and Compact Planetary Systems. It is still unclear whether exoplanets in compact multiplanet systems such as TRAPPIST-1 are able to accrete large quantities of volatiles, grow to sufficient mass, and maintain robust atmospheres and hydrospheres. Previous estimates of water content in M-dwarf systems have largely relied on population synthesis or atmosphere–interior evolution models, often treating impacts and atmospheric loss in isolation. In this work, we combined impact delivery, impact erosion, and mantle-atmosphere exchange within a unified framework that tracks volatile evolution through stochastic collision histories. By explicitly including both planetesimal accretion and the prolonged luminous pre-main-sequence phase of M dwarfs, we find systematically lower water inventories for the inner TRAPPIST-1 analogs (b–e), spanning only 10‑4 and 1% of Earth's ocean mass across a wide range of disk structures and impact scenarios. By contrast, the outer planets (f–h analogs) frequently retain water inventories exceeding an Earth ocean mass. This volatile gradient provides a physically motivated explanation for JWST's nondetections of atmospheres on TRAPPIST-1 b and c, suggesting an origin rooted in rocky planet formation. Our results suggest that many rocky planets in compact M-dwarf systems may form already depleted in volatile compounds, fundamentally limiting their capacity to sustain atmospheres or surface oceans. More broadly, our multistage framework for volatile tracking can help interpret future observations of compact system and set more realistic initial conditions for exoplanet interior compositions and atmospheric models.

Keywords: Habitable zone, Planetary atmospheres, Habitable planets, Planet formation
Neutron-quark Stars: Discerning Viable Alternatives for the Higher-density Part of the Equation of State of Compact Stars. We investigate binary neutron star (BNS) mergers using general-relativistic numerical simulations with hadronic and hybrid equations of state (EOSs), incorporating the latest observations and theoretical constraints. We address two viable scenarios for the transition to quark matter: a quark-hadron crossover (QHC) or a strong first-order phase transition (1PT). To distinguish between different models, we define neutron-quark stars (NQSs) as configurations where quark effects emerge at masses below the lowest observed neutron-star mass. While traditional "hybrid stars" may be distinguished by purely hadronic configurations through mass–radius measurements, the mass–radius relations of NQSs resemble those of purely hadronic models, with no sharp boundary between hadrons and quarks. The name NQS effectively captures the absence of a phase boundary between hadrons and quarks in QHC scenarios. Our results indicate that QHC models can be distinguished from hadronic ones if both the inspiral and postmerger gravitational waves (GWs) are observed. In particular, the dominant postmerger frequency (f2) tends to be lower than in hadronic models with the same tidal deformability (Λ). We also present the first general-relativistic simulations of BNS mergers where the stars already contain quark matter before merging. These involve a strong 1PT at 1.8 times nuclear saturation density, followed by a stiff quark EOS. Finally, we identify a robust linear correlation between the total GW energy emitted after the merger and the f2 frequency. Remarkably, this relation holds regardless of the quark presence.

Keywords: Neutron stars, Hydrodynamical simulations, Neutron star cores, Compact binary stars, Nuclear astrophysics, Gravitational waves
Zeeman Doppler Imaging of τ Ceti: The Weakest Magnetic Field Detected in a Sun-like Star. For nearly a decade, observations have shown that many older Sun-like stars spin faster than predicted, a phenomenon known as weakened magnetic braking (WMB). The leading hypothesis for WMB is a weakening of the large-scale dipole field, which leads to a less efficient angular momentum loss. To test this hypothesis on a star known to be in the WMB regime, we present the first Zeeman Doppler imaging (ZDI) map of the Sun-like star τ Ceti, reconstructed using spectropolarimetric data from the Canada–France–Hawai'i Telescope. Our ZDI analysis reveals a remarkably simple, stable, and weak ( = 0.17 G) magnetic field, characterized by a predominantly dipolar (∼92% magnetic energy contained in l = 1 modes), and highly axisymmetric (∼88% magnetic energy contained in m &lt; l/2 modes) morphology. We infer a dipole field strength of Bdip = 0.31 G, nearly an order of magnitude weaker than standard braking model predictions, providing direct confirmation of the weakened large-scale dipole predicted by the WMB hypothesis. This work establishes a new benchmark for ZDI, demonstrating that even extremely quiet stars in the WMB regime are accessible to this technique.

Keywords: Stellar rotation, Spectropolarimetry, Stellar magnetic fields, Stellar evolution
On the Search for a Generation Mechanism for the Ion Acoustic Waves Observed by the Parker Solar Probe. The solar wind plasma is strongly accelerated near the Sun—this acceleration and heating remain beyond 1 au, which contradicts cooling by adiabatic expansion. Wave–particle interaction has been recognized as one of the key mechanisms for particle acceleration and heating in the solar wind. In this context, it is relevant to analyze the origin of the ion acoustic waves (IAWs) observed by the Parker Solar Probe (PSP) and their possible role in solar wind acceleration and heating. PSP has recorded various phenomena during its close encounters with the Sun, including IAWs, current sheets, ion velocity streams, and reconnection exhausts. The origin of the observed IAWs remains unknown. This study investigates the temporal correlation between IAWs, current sheets, ion speed streams, and reconnection exhausts as possible sources of ion beams. Our analysis reveals that current sheets and ion speed streams exhibit a statistically significant temporal proximity with IAWs and also between them, while reconnection exhausts did not show a statistical association with IAWs. These results suggest that current sheets may be associated with proton beams, which then excite IAWs.

Keywords: Space plasmas, Heliosphere, Plasma physics, Solar wind, Interplanetary particle acceleration
Pinching of ICME Flux Rope: Unprecedented Multipoint Observations of Internal Magnetic Reconnection during Gannon's Superstorm. The extreme solar storm of 2024 May 10, during the 25th solar cycle, which recorded a symmetric H component index (Sym-H) reaching ‑500 nT, was the strongest since the 2003 Halloween storm. This event offered a unique opportunity for unprecedented multipoint observation of the complex interaction of interplanetary coronal mass ejections (ICMEs) from different vantage points. Utilizing NASA's Wind, ACE, DSCOVR, THEMIS-C, STEREO-A, MMS, and ISRO's recently launched Aditya-L1 spacecraft, we comprehensively investigated the spatiotemporal variations in interplanetary plasma and magnetic field parameters. Our study reveals large-scale quasi-steady magnetic reconnection within the interior of the ICME flux rope, possibly triggered by interactions between multiple ICMEs. A current sheet (CS) forms within the flux rope, enabling internal magnetic reconnection between concentric magnetic surfaces, which leads to a sharp reversal of the interplanetary magnetic field (IMF) By component, as observed at the L1 point. Concurrently, reconnection exhaust and enhanced electron and ion fluxes were detected with the CS, extending over 200 RE (1.3 million kilometers) along the geocentric solar ecliptic y-direction. This finding sheds new light on the role of internal reconnection in ICME evolution, highlighting its pivotal role in modifying the morphology of the ICME magnetic structure and exerting severe space weather effects on Earth.

Keywords: Solar storm, Space weather, Solar coronal mass ejections
Sub-Neptunes Are Drier than They Seem: Rethinking the Origins of Water-rich Worlds. Recent claims of biosignature gases in sub-Neptune atmospheres have renewed interest in water-rich sub-Neptunes with surface oceans, often referred to as Hycean planets. These planets are hypothesized to form beyond the snow line, accreting large amounts of H2O (&gt;10 wt%) before migrating inward. However, current interior models often neglect chemical equilibration between primordial atmospheres and molten interiors. Here, we compute global chemical equilibrium states for a synthetic population of sub-Neptunes with magma oceans. Although many initially accrete 5–30 wt% water, interior–atmosphere interactions destroy most of it, reducing final H2O mass fractions to below 1.5 wt%. As a result, none meet the threshold for Hycean planets. Despite that, we find H2O-dominated atmospheres exclusively on planets that accreted the least ice. These planets form inside the snow line, are depleted in carbon and hydrogen, and develop small envelopes with envelope mass fractions below 1%, dominated by endogenic water. In contrast, planets formed beyond the snow line accrete more volatiles, but their water is largely converted to H2 gas or sequestered into the interior, resulting in low atmospheric H2O mass fractions. Most H2O-rich envelopes are also fully miscible with H2, making a separate water layer unlikely. Our results challenge the conventional link between ice accretion and water-rich atmospheres, showing instead that H2O-dominated envelopes emerge through chemical equilibration in hydrogen-poor planets formed inside the snow line.

Keywords: Exoplanet structure, Exoplanet atmospheric composition , Exoplanet atmospheric structure
Weakened Magnetic Braking Signals the Collapse of the Global Stellar Dynamo. Weakened magnetic braking (WMB) was originally proposed in 2016 to explain anomalously rapid rotation in old field stars observed by the Kepler mission. The proximate cause was suggested to be a transition in magnetic morphology from larger to smaller spatial scales. In a series of papers over the past 5 yr, we have collected spectropolarimetric measurements to constrain the large-scale magnetic fields for a sample of stars spanning this transition, including a range of spectral types from late F to early K. During this time, we gradually improved our methods for estimating the wind braking torque in each of our targets, and for evaluating the associated uncertainties. Here, we reanalyze the entire sample with a focus on uniformity for the relevant observational inputs. We supplement the sample with two additional active stars to provide more context for the evolution of wind braking torque with stellar Rossby number (Ro). The results demonstrate unambiguously that standard spin-down models can reproduce the evolution of wind braking torque for active stars, but WMB is required to explain the subsequent abrupt decrease in torque as Ro approaches a critical value for dynamo excitation. This transition is seen in both the large-scale magnetic field and the X-ray luminosity, indicating weakened coronal heating. We interpret these transitions as evidence of a rotational threshold for the influence of Coriolis forces on global convective patterns and the resulting inefficiency of the global stellar dynamo.

Keywords: Stellar magnetic fields, Solar dynamo, Stellar winds, Stellar rotation, Stellar evolution