Table of contents

In binary black hole mergers from isolated binary-star evolution, both black holes are from progenitor stars that have lost their hydrogen-rich envelopes by binary mass transfer. Envelope stripping is known to affect the pre-supernova core structures of such binary-stripped stars and thereby their final fates and compact remnant masses. In this paper, we show that binary-stripped stars give rise to a bimodal black hole mass spectrum with characteristic black hole masses of about 9 M_⊙ and 16 M_⊙ across a large range of metallicities. The bimodality is linked to carbon and neon burning becoming neutrino dominated, which results in interior structures that are difficult to explode and likely lead to black hole formation. The characteristic black hole masses from binary-stripped stars have corresponding features in the chirp-mass distribution of binary black hole mergers: peaks at about 8 and 14 M_⊙ and a dearth in between these masses. Current gravitational-wave observations of binary black hole mergers show evidence for a gap at 10–12 M_⊙ and peaks at 8 and 14 M_⊙ in the chirp-mass distribution. These features are in agreement with our models of binary-stripped stars. In the future, they may be used to constrain the physics of late stellar evolution and supernova explosions and may even help measure the cosmological expansion of the universe.

The community agrees that Type Ia supernovae arise from carbon/oxygen white dwarfs undergoing thermonuclear runaway. However, the full progenitor system and the process that prompts the white dwarf to explode remain unknown. Most current models suggest that the white dwarf explodes because of interaction with a binary companion that may survive the process and remain within the resulting remnant of the exploded star. Furthermore, both the pre-supernova interaction process and the explosion of the primary are expected to imprint a significant departure from ordinary stellar radii and temperatures onto the secondary, making the star identifiable against the unrelated stellar population. Identification of a surviving companion inside an SN Ia remnant might confirm a specific corresponding SN Ia progenitor channel based on the identity of the companion. We conducted a surviving companion search of the Type Ia remnant SNR 0509−67.5 based in the Large Magellanic Cloud. The well-constrained distance to and foreground extinction of the Large Magellanic Cloud allow for Bayesian inference of stellar parameters with low correlation and uncertainties. We present a deep catalog of fully characterized stars interior to SNR 0509−67.5 with radii, effective temperatures, and metallicities inferred using combined Hubble Space Telescope photometric observations across multiple visits. We then compile a list of surviving companion models appropriate for the age of the remnant (roughly 400 yr after the explosion). We compare these predictions with the inferred stellar parameters and conclude that none of the stars are consistent with the predicted signatures of a surviving companion.

To understand the global-scale physical processes behind coronal mass ejection (CME)–driven geomagnetic storms and predict their intensity as a space weather forecasting measure, we develop an interplanetary CME flux rope–magnetosphere interaction module using 3D magnetohydrodynamics. The simulations adequately describe CME-forced dynamics of the magnetosphere including the imposed magnetotail torsion. These interactions also result in induced currents, which are used to calculate the geomagnetic perturbation. Through a suitable calibration, we estimate a proxy of geoeffectiveness—the Storm Intensity index (STORMI)—that compares well with the Dst/SYM-H index. Simulated impacts of two contrasting CMEs quantified by the STORMI index exhibit a high linear correlation with the corresponding Dst and SYM-H indices. Our approach is relatively simple, has fewer parameters to be fine-tuned, and is time efficient compared to complex fluid-kinetic methods. Furthermore, we demonstrate that flux rope erosion does not significantly affect our results. Thus our method has the potential to significantly extend the time window for predictability—an outstanding challenge in geospace environment forecasting—if early predictions of near-Earth CME flux rope structures based on near-Sun observations are available as inputs. This study paves the way for early warnings based on operational predictions of CME-driven geomagnetic storms.

We develop a tool, which we name Protoplanetary Disk Operator Network (PPDONet), that can predict the solution of disk–planet interactions in protoplanetary disks in real time. We base our tool on Deep Operator Networks, a class of neural networks capable of learning nonlinear operators to represent deterministic and stochastic differential equations. With PPDONet we map three scalar parameters in a disk–planet system—the Shakura–Sunyaev viscosity α, the disk aspect ratio h₀, and the planet–star mass ratio q—to steady-state solutions of the disk surface density, radial velocity, and azimuthal velocity. We demonstrate the accuracy of the PPDONet solutions using a comprehensive set of tests. Our tool is able to predict the outcome of disk–planet interaction for one system in less than a second on a laptop. A public implementation of PPDONet is available at https://github.com/smao-astro/PPDONet.

Virialized halos of cold dark matter generically exhibit multistream structures of accreted dark matter within an outermost radial caustic known as the splashback radius. By tracking the particle trajectories that accrete onto the halos in cosmological N-body simulations, we count their number of apocenter passages (p) and use them to characterize the multistream structure of dark matter particles. We find that the radial density profile for each stream, classified by the number of apocenter passages, exhibits universal features and can be described by a double power-law function comprising shallow inner slopes and steep outer slopes of indices of −1 and −8, respectively. Surprisingly, these properties hold over a wide range of halo masses. The double power-law feature is persistent when dividing the sample by concentration or accretion rate. The dependence of the characteristic scale and amplitude of the profile on p cannot be replicated by known self-similar solutions, requiring consideration of complexities such as the distribution of angular momentum or mergers.

Distance duality relation (DDR) marks a fundamental difference between expanding and nonexpanding universes, as an expanding metric causes angular diameter distance smaller than luminosity distance by an extra factor of (1 + z). Here we report a test of this relation using two independent samples of ultracompact radio sources observed at 2.29 GHz and 5.0 GHz. The test with radio sources involves only geometry, so it is independent of cosmological models. Since the observed radio luminosities systematically increase with redshift, we do not assume a constant source size. Instead, we start with assuming the intensive property, luminosity density, does not evolve with redshift and then infer its evolution from the resultant DDR. We make the same assumption for both samples, and find it results in the same angular size–redshift relation. Interestingly, the resultant DDR is fully consistent with a nonexpanding universe. Imposing the DDR predicted by the expanding universe, we infer the radio luminosity density evolves as ρ_L ∝ (1 + z)³. However, the perfect agreement with a nonexpanding universe under the assumption of constant luminosity densities poses a conspiracy and fine-tuning problem: the size and luminosity density of ultracompact radio sources evolve in the way that precisely mimics a nonexpanding universe.

Recently, several studies reported a significant discrepancy between the clustering and lensing of the Baryon Oscillation Spectroscopic Survey (BOSS) galaxies in the Planck cosmology. We construct a simple yet powerful model based on the linear theory to assess whether this discrepancy points toward deviations from Planck. Focusing on scales 10 < R < 30 h⁻¹Mpc, we model the amplitudes of clustering and lensing of BOSS LOWZ galaxies using three parameters: galaxy bias b_g; galaxy-matter cross-correlation coefficient r_gm; and A, defined as the ratio between the true and Planck values of σ₈. Using the cross-correlation matrix as a diagnostic, we detect systematic uncertainties that drive spurious correlations among the low-mass galaxies. After building a clean LOWZ sample with r_gm ∼ 1, we derive a joint constraint of b_g and A from clustering+lensing, yielding ${b}_{{\rm{g}}}={2.47}_{-0.30}^{+0.36}$ and $A={0.81}_{-0.09}^{+0.10}$, i.e., a 2σ tension with Planck. However, due to the strong degeneracy between b_g and A, systematic uncertainties in b_g could masquerade as a tension with A = 1. To ascertain this possibility, we develop a new method to measure b_g from the cluster-galaxy cross correlation and cluster weak lensing using an overlapping cluster sample. By applying the independent bias measurement (b_g = 1.76 ± 0.22) as a prior, we successfully break the degeneracy and derive stringent constraints of ${b}_{{\rm{g}}}={2.02}_{-0.15}^{+0.16}$ and A = 0.96 ± 0.07. Therefore, our result suggests that the large-scale clustering and lensing of LOWZ galaxies are consistent with Planck, while the different bias estimates may be related to some observational systematics that need to be mitigated in future surveys.

Magnetic fields in galaxies and galaxy clusters are believed to be the result of the amplification of intergalactic seed fields during the formation of large-scale structures in the universe. However, the origin, strength, and morphology of this intergalactic magnetic field (IGMF) remain unknown. Lower limits on (or indirect detection of) the IGMF can be obtained from observations of high-energy gamma rays from distant blazars. Gamma rays interact with the extragalactic background light to produce electron−positron pairs, which can subsequently initiate electromagnetic cascades. The gamma-ray signature of the cascade depends on the IGMF since it deflects the pairs. Here we report on a new search for this cascade emission using a combined data set from the Fermi Large Area Telescope and the High Energy Stereoscopic System. Using state-of-the-art Monte Carlo predictions for the cascade signal, our results place a lower limit on the IGMF of B > 7.1 × 10⁻¹⁶ G for a coherence length of 1 Mpc even when blazar duty cycles as short as 10 yr are assumed. This improves on previous lower limits by a factor of 2. For longer duty cycles of 10⁴ (10⁷) yr, IGMF strengths below 1.8 × 10⁻¹⁴ G (3.9 × 10⁻¹⁴ G) are excluded, which rules out specific models for IGMF generation in the early universe.

As the James Webb Space Telescope (JWST) came online last summer, we entered a new era of astronomy. This new era is supported by data products of unprecedented information content that require novel reduction and analysis techniques. Recently, Niraula et al. (N22) highlighted the need for upgraded opacity models to prevent facing a model-driven accuracy wall when interpreting exoplanet transmission spectra. Here, we follow the same approach as N22 to explore the sensitivity of inferences on the atmospheric properties of WASP-39 b to the opacity models used. We find that the retrieval of the main atmospheric properties from this first JWST exoplanet spectrum is mostly unaffected by the current state of the community's opacity models. Abundances of strong opacity sources like water and carbon dioxide are reliably constrained within ∼0.30 dex, beyond the 0.50 dex accuracy wall reported in N22. Assuming the completeness and accuracy of line lists, N22's accuracy wall is primarily driven by model uncertainties on broadening coefficients and far-wing behaviors, which we find to have marginal consequences for interpreting the transmission spectra of large, hot, high-metallicity atmospheres such as WASP-39 b, in opposition to emission spectra and climate modeling, which depend on deeper parts of a planetary atmosphere. The origin of the opacity challenge in the retrieval of metal-rich hot Jupiters via transmission spectroscopy will thus mostly stem from the incompleteness and inaccuracy of line lists.

The atomic hydrogen (H i) properties of star-forming galaxies in the local universe are known to correlate with other galaxy properties via the "H i scaling relations." The redshift evolution of these relations serves as an important constraint on models of galaxy evolution. However, until recently, there were no estimates of the H i scaling relations at cosmological distances. Using data from a deep Giant Metrewave Radio Telescope H i 21 cm survey of the Extended Groth Strip, and the technique of spectral-line stacking, we determine the scaling relation between the H i mass and the stellar mass for star-forming galaxies at z ≈ 0.35. We use this measurement, along with the main-sequence relation in galaxies, to infer the dependence of the H i depletion timescale of these galaxies on their stellar mass. We find that massive star-forming galaxies at z ≈ 0.35, with stellar mass M_* ≳ 10^9.5M_⊙, are H i-poor compared to local star-forming galaxies of a similar stellar mass. However, their characteristic H i depletion time is lower by a factor of ≈5 than that of their local analogs, indicating a higher star formation efficiency at intermediate redshifts (similar to that at z ≈ 1). While our results are based on a relatively small cosmic volume and could thus be affected by cosmic variance, the short characteristic H i depletion timescales (≲3 Gyr) of massive star-forming galaxies at z ≈ 0.35 indicate that they must have acquired a significant amount of neutral gas through accretion from the circumgalactic medium over the past 4 Gyr, to avoid quenching of their star formation activity.

We present the direct-imaging discovery of a giant planet orbiting the young star AF Lep, a 1.2 M_⊙ member of the 24 ± 3 Myr β Pic moving group. AF Lep was observed as part of our ongoing high-contrast imaging program targeting stars with astrometric accelerations between Hipparcos and Gaia that indicate the presence of substellar companions. Keck/NIRC2 observations in $L^{\prime}$ with the vector vortex coronagraph reveal a point source, AF Lep b, at ≈340 mas, which exhibits orbital motion at the 6σ level over the course of 13 months. A joint orbit fit yields precise constraints on the planet's dynamical mass of ${3.2}_{-0.6}^{+0.7}$M_Jup, semimajor axis of ${8.4}_{-1.3}^{+1.1}$ au, and eccentricity of ${0.24}_{-0.15}^{+0.27}$. AF Lep hosts a debris disk located at ∼50 au, but it is unlikely to be sculpted by AF Lep b, implying there may be additional planets in the system at wider separations. The stellar inclination (i_* = ${54}_{-9}^{{+11}^\circ}$) and orbital inclination (i_o = ${50}_{-12}^{{+9}^\circ}$) are in good agreement, which is consistent with the system having spin–orbit alignment. AF Lep b is the lowest-mass imaged planet with a dynamical mass measurement and highlights the promise of using astrometric accelerations as a tool to find and characterize long-period planets.

Long and short gamma-ray bursts (GRBs), canonically separated at around 2 s duration, are associated with different progenitors: the collapse of a massive star and the merger of two compact objects, respectively. GRB 191019A was a long GRB (T₉₀ ∼ 64 s). Despite the relatively small redshift z = 0.248 and Hubble Space Telescope follow-up observations, an accompanying supernova was not detected. In addition, the host galaxy did not have significant star formation activity. Here we propose that GRB 191019A was produced by a binary compact merger, whose prompt emission was stretched in time by the interaction with a dense external medium. This would be expected if the burst progenitor was located in the disk of an active galactic nucleus, as supported by the burst localization close to the center of its host galaxy. We show that the light curve of GRB 191019A can be well modeled by a burst of intrinsic duration t_eng = 1.1 s and of energy E_iso = 10⁵¹ erg seen moderately off axis, exploding in a medium of density ∼10⁷–10⁸ cm⁻³. The double-peaked light curve carries the telltale features predicted for GRBs in high-density media, where the first peak is produced by the photosphere and the second by the overlap of reverse shocks that take place before the internal shocks could happen. This would make GRB 191019A the first confirmed stellar explosion from within an accretion disk, with important implications for the formation and evolution of stars in accretion flows and for gravitational-waves source populations.

We present evidence of hitherto undiscovered global-scale oscillations in the near-surface shear layer of the Sun. These oscillations are seen as large-scale variations of radial shear in both the zonal and meridional flows relative to their mean values. The variations cover all or most of a visible hemisphere, and reverse with a timescale on the order of a solar rotation. A large annual variation in the meridional shear anomaly is understandable in terms of the tilt of the rotation axis, but the rapid oscillations of the shear anomalies in both zonal and the meridional directions appear to be modulated in a more complex, not-quite-annual way, although the latter are also strongly modulated by the projected rotational axis angle. Small-scale anomalies in the neighborhood of active regions lend support to their solar origin and physical interpretation. These results were obtained by analyzing ring-diagram fits of low-order modes in high-resolution Doppler data from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory.

The bimodality in the stellar spin of low-redshift (massive) galaxies, ubiquitously existing at all star formation levels and in diverse environments, suggests that galaxies grow and quench through two diverged evolutionary pathways. For spheroid-dominated galaxies of slow stellar rotation, the age composition and metallicity of their stellar populations are evidence of a fast quenching history with significant gas outflows. In this work, we measure the spin parameter ${\lambda }_{{R}_{{\rm{e}}}}$, i.e., the normalized specific angular momentum of stars, out of the MaNGA integral field spectroscopy for about 10,000 galaxies. Among the two-thirds with H i follow-up observations (z ≲ 0.05), we find that, compared to fast-rotating galaxies of the same stellar mass and star formation, the galaxy populations with slower rotation are generally more H i gas-poor, robust against further environmental restriction and with nondetections properly taken into account using the stacking technique. This cold gas deficit of slow-rotating galaxies is most apparent at high mass $\sim {10}^{11}{{ \mathcal M }}_{\odot }$ below the star formation main sequence, supporting the pivotal role of gas outflows in their quenching history. With hints from H i velocity distributions, we suspect that massive gas outflows among the slow-rotating population are facilitated by high ejective feedback efficiency, which is a result of extensive coupling between disturbed volume-filling cold gas and (commonly) biconical feedback from central black holes. By contrast, in fast-rotating disk galaxies the feedback energy mostly goes to the hot circumgalactic medium rather than directly impacting the dense and planar cold gas, thus making the feedback mainly preventive against further gas inflow.