Table of contents

The spin evolution of stellar-mass black holes (sBHs) embedded in AGN accretion disks is an important process relevant to the production of gravitational waves from binary BH (BBH) merger events through the AGN channel. Because embedded sBHs are surrounded by circumstellar disks (CSDs), the rotation of CSD gas flows determines the direction of the angular momentum it accretes. In this Letter, we use global 2D hydrodynamic simulations to show that while a disk-embedded sBH on a circular orbit transforms the initial retrograde Keplerian shear of the background accretion disk into a prograde CSD flow, as in the classical picture of companion-disk interaction theory, moderate orbital eccentricity could disrupt the steady-state tidal perturbation and preserve a retrograde CSD flow around the sBH. This switch in CSD orientation occurs at a transition eccentricity that scales nearly proportional to the local sound speed. This bifurcation in the CSD flow and thereafter spin-up direction of SBHs leads to the formation of a population of nearly antialigned sBHs and should be incorporated in future population models of sBH and BBH evolutions.

We study the magnetic field to density (B–ρ) relation in turbulent molecular clouds with dynamically important magnetic fields using nonideal three-dimensional magnetohydrodynamic simulations. Our simulations show that there is a distinguishable break density ρ_T between the relatively flat low-density regime and a power-law regime at higher densities. We present an analytic theory for ρ_T based on the interplay of the magnetic field, turbulence, and gravity. The break density ρ_T scales with the strength of the initial Alfvén Mach number ${{ \mathcal M }}_{{\rm{A}}0}$ for sub-Alfvénic (${{ \mathcal M }}_{{\rm{A}}0}\lt 1$) and trans-Alfvénic (${{ \mathcal M }}_{{\rm{A}}0}\sim 1$) clouds. We fit the variation of ρ_T for model clouds as a function of ${{ \mathcal M }}_{{\rm{A}}0}$, set by different values of initial sonic Mach number ${{ \mathcal M }}_{0}$ and the initial ratio of gas pressure to magnetic pressure β₀. This implies that ρ_T, which denotes the transition in mass-to-flux ratio from the subcritical to the supercritical regime, is set by the initial turbulent compression of the molecular cloud.

We present ALMA high-angular-resolution (∼50 au) observations of the Class I binary system SVS13-A. We report images of SVS13-A in numerous interstellar complex organic molecules: CH₃OH, ¹³CH₃OH, CH₃CHO, CH₃OCH₃, and NH₂CHO. Two hot corinos at different velocities are imaged in VLA4A (V_sys = +7.7 km s⁻¹) and VLA4B (V_sys = +8.5 km s⁻¹). From a non-LTE analysis of methanol lines, we derive a gas density of 3 × 10⁸ cm⁻³ and gas temperatures of 140 and 170 K for VLA4A and VLA4B, respectively. For the other species, the column densities are derived from an LTE analysis. Formamide, which is the only N-bearing species detected in our observations, is more prominent around VLA4A, while dimethyl ether, methanol, and acetaldehyde are associated with both VLA4A and VLA4B. We derive in the two hot corinos abundance ratios of ∼1 for CH₃OH, ¹³CH₃OH, and CH₃OCH₃; ∼2 for CH₃CHO; and ∼4 for NH₂CHO. The present data set supports chemical segregation between the different species inside the binary system. The emerging picture is that of an onion-like structure of the two SVS13-A hot corinos, caused by the different binding energies of the species, also supported by ad hoc quantum chemistry calculations. In addition, the comparison between molecular and dust maps suggests that the interstellar complex organic molecules emission originates from slow shocks produced by accretion streamers impacting the VLA4A and VLA4B disks and enriching the gas-phase component.

We analyze the stellar ages obtained from a combination of Lick indices in Borghi et al. for 140 massive and passive galaxies selected in the LEGA-C survey at 0.6 < z < 0.9. From their median age–redshift relation, we derive a new direct measurement of H(z) without any cosmological model assumption using the cosmic chronometer approach. We thoroughly study the main systematics involved in this analysis: the choice of the Lick indices combination, the binning method, the assumed stellar population model, and the adopted star formation history; these effects are included in the total error budget. We obtain H(z = 0.75) = 98.8 ± 33.6 km s⁻¹ Mpc⁻¹. In parallel, we also propose a simple framework based on a cosmological model to describe the age–redshift relations in the context of galaxy downsizing. This allows us to derive constraints on the Hubble constant H₀ and the typical galaxy formation time. This new H(z) measurement, whose accuracy is currently limited by the scarcity of the sample analyzed, paves the road for the joint study of the stellar populations of individual passive galaxies and the expansion history of the universe in light of future spectroscopic surveys.

High-accuracy proper motions (PMs) of M31 and other Local Group (LG) satellites have now been provided by the Gaia satellite. We revisit the timing argument to compute the total mass M of the LG from the orbit of the Milky Way and M31, allowing for the cosmological constant. We rectify a systematic effect caused by the presence of the Large Magellanic Cloud (LMC). The interaction of the LMC with the Milky Way induces a motion toward the LMC. This contribution to the measured velocity of approach of the Milky Way and M31 must be removed. We allow for cosmic bias and scatter by extracting correction factors tailored to the accretion history of the LG. The distribution of correction factors is centered around 0.63 with a scatter of ±0.2, indicating that the timing argument significantly overestimates the true mass. Adjusting for all these effects, the estimated mass of the LG is $M={3.4}_{-1.1}^{+1.4}\times {10}^{12}{M}_{\odot }$ (68% CL) when using the M31 tangential velocity, ${v}_{\tan }={82}_{-35}^{+38}\,\mathrm{km}\,{{\rm{s}}}^{-1}$. Lower tangential velocity models with ${v}_{\tan }={59}_{-38}^{+42}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ (derived from the same PM data with a flat prior on the tangential velocity) lead to an estimated mass of $M={3.1}_{-1.0}^{+1.3}\times {10}^{12}{M}_{\odot }$ (68% CL). By making an inventory of the total mass associated with the four most substantial LG members (the Milky Way, M31, M33, and the LMC), we estimate the known mass to be in the range ${3.7}_{-0.5}^{+0.5}\times {10}^{12}\,{M}_{\odot }$.

Two recent extremely fast coronal mass ejections (CMEs) are of particular interest. The first one originated from the southern hemisphere on 2021 October 28 and caused strong solar energetic particle (SEP) events over a wide longitude range from Earth, STEREO-A, to Mars. However, the other one, originating from the center of the Earth-viewed solar disk 5 days later, left weak SEP signatures in the heliosphere. Based on the white-light images of the CMEs from the Solar and Heliospheric Observatory (SOHO) and the Ahead Solar Terrestrial Relations Observatory (STEREO-A), in combination with the observations of the corresponding solar flares, radio bursts, and in situ magnetic fields and particles, we try to analyze the series of solar eruptions during October 28–November 2 as well as their correspondences with the in situ features. It is found that the difference in SEP features between the two CMEs is mainly due to (1) the seed particles probably supplied by associated flares and (2) the magnetic connection influenced by the preceding solar wind speed.

The James Webb Space Telescope's (JWST) NIRSpec instrument will unveil the nature of exoplanet atmospheres across the wealth of planet types, from temperate terrestrial worlds to ultrahot Jupiters. In particular, the 0.6–5.3 μm PRISM mode is especially well suited for efficient spectroscopic exoplanet observations spanning a number of important spectral features. We analyze a lab-measured NIRSpec PRISM mode Bright Object Time Series observation from the perspective of a JWST user to understand the instrument performance and detector properties. We create two realistic transiting exoplanet time-series observations by performing injection-recovery tests on the lab-measured data to quantify the effects of real instrument jitter, drift, intrapixel sensitivity variations, and 1/f noise on measured transmission spectra. By fitting the time-series systematics simultaneously with the injected transit, we can obtain more realistic transit-depth uncertainties that take into account noise sources that are currently not modeled by traditional exposure time calculators. We find that sources of systematic noise related to intrapixel sensitivity variations and point-spread function motions are apparent in the data at the level of a few hundred ppm but can be effectively detrended using a low-order polynomial with detector position. We recover the injected spectral features of GJ 436 b and TRAPPIST-1 d and place a 3σ upper limit on the detector noise floor of 14 ppm. We find that the noise floor is consistent with <10 ppm at the 1.7σ level, which bodes well for future observations of challenging targets with faint atmospheric signatures.

The symbiotic X-ray binary Sct X-1 was suggested to be the first known neutron star accreting from a red supergiant companion. Although known for nearly 50 yr, detailed characterization of the donor remains lacking, particularly due to the extremely high reddening toward the source (A_V ≳ 25 mag). Here, we present (i) improved localization of the counterpart using Gaia and Chandra observations, (ii) the first broadband infrared spectrum (≈1–5 μm; R ≈ 2000) obtained with SpeX on the NASA Infrared Telescope Facility, and (iii) the J-band light curve from the Palomar Gattini-IR survey. The infrared spectrum is characterized by (i) deep water absorption features (H₂O index ≈ 40%), (ii) strong TiO, VO, and CO features, and (iii) weak/absent CN lines. We show that these features are inconsistent with known red supergiants but suggest an M8-9 III–type O-rich Mira donor star. We report the discovery of large-amplitude (ΔJ ≈ 3.5 mag) periodic photometric variability, suggesting a pulsation period of 621 ± 36 (systematic) ± 8 (statistical) days, which we use to constrain the donor to be a relatively luminous Mira (M_K = −8.6 ± 0.3 mag) at a distance of ${3.6}_{-0.7}^{+0.8}$ kpc. Comparing these characteristics to recent models, we find the donor to be consistent with a ≈3–5 M_⊙ star at an age of ≈0.1–0.3 Gyr. Together, we show that Sct X-1 was previously misclassified as an evolved high-mass X-ray binary; instead, it is an intermediate-mass system with the first confirmed Mira donor in an X-ray binary. We discuss the implications of Mira donors in symbiotic X-ray binaries and highlight the potential of wide-field infrared time-domain surveys and broadband infrared spectroscopy to unveil their demographics.

We calculated the electron–positron pair-production rate at the base of the jet of 3C 120 due to collisions of photons from the hot accretion flow using the measurement of its average soft gamma-ray spectrum by the Compton Gamma Ray Observatory. We found that this rate approximately equals the flow rate of leptons emitting the observed synchrotron radio-to-IR spectrum of the jet core, calculated using the extended jet model following Blandford & Königl. This coincidence shows the jet composition is likely to be pair dominated. We then calculated the jet power in the bulk motion of ions and found it greatly exceeds that achievable by the magnetically arrested disk scenario for the maximum black hole spin unless the jet contains mostly pairs. Next, we found that the magnetic flux through the synchrotron-emitting jet equals the maximum poloidal flux that can thread the black hole. Finally, we compared two estimates of the magnetization parameter at the onset of the synchrotron emission and found they are in agreement only if pairs dominate the jet content.

Stellar evolution models calculate convective boundaries using either the Schwarzschild or Ledoux criterion, but confusion remains regarding which criterion to use. Here we present a 3D hydrodynamical simulation of a convection zone and adjacent radiative zone, including both thermal and compositional buoyancy forces. As expected, regions that are unstable according to the Ledoux criterion are convective. Initially, the radiative zone adjacent to the convection zone is Schwarzschild unstable but Ledoux stable due to a composition gradient. Over many convective overturn timescales, the convection zone grows via entrainment. The convection zone saturates at the size originally predicted by the Schwarzschild criterion, although in this final state the Schwarzschild and Ledoux criteria agree. Therefore, the Schwarzschild criterion should be used to determine the size of stellar convection zones, except possibly during short-lived evolutionary stages in which entrainment persists.

We present [K/Fe] abundance ratios for a sample of 450 stars in ω Centauri, using high-resolution spectra acquired with the multiobject spectrograph FLAMES@VLT. Abundances for Fe, Na, and Mg were also derived. We detected intrinsic K variations in the analyzed stars. Moreover, [K/Fe] shows a significant correlation with [Na/Fe] and an anticorrelation with [Mg/Fe]. The presence of a clear-cut Mg–K anticorrelation makes ω Centauri the third stellar system, after NGC 2419 and NGC 2808, hosting a subpopulation of stars with [Mg/Fe] < 0.0 dex, K-enriched in the case of ω Centauri by ∼0.3 dex with respect to Mg-rich stars ([Mg/Fe] > 0.0 dex). The correlation/anticorrelation between K and other light elements involved in chemical anomalies supports the idea that the spread in [K/Fe] can be associated with the same self-enrichment process typical of globular clusters. We suggest that significant variations in K abundances perhaps can be found in the most massive and/or metal-poor globular clusters as a manifestation of an extreme self-enrichment process. Theoretical models face problems explaining K production in globular clusters. Indeed, models where asymptotic giant branch stars are responsible for the Mg–K anticorrelation only qualitatively agree with the observations. Finally, we discovered a peculiar star with an extraordinary K overabundance ([K/Fe] = +1.60 dex) with respect to the other stars with similar [Mg/Fe]. We suggest that this K-rich star could be formed from the pure ejecta of AGB stars before dilution with pristine material.