Table of contents

We present a measurement of the Hubble constant made using geometric distance measurements to megamaser-hosting galaxies. We have applied an improved approach for fitting maser data and obtained better distance estimates for four galaxies previously published by the Megamaser Cosmology Project: UGC 3789, NGC 6264, NGC 6323, and NGC 5765b. Combining these updated distance measurements with those for the maser galaxies CGCG 074-064 and NGC 4258, and assuming a fixed velocity uncertainty of 250 km s⁻¹ associated with peculiar motions, we constrain the Hubble constant to be H₀ = 73.9 ± 3.0 km s⁻¹ Mpc⁻¹ independent of distance ladders and the cosmic microwave background. This best value relies solely on maser-based distance and velocity measurements, and it does not use any peculiar velocity corrections. Different approaches for correcting peculiar velocities do not modify H₀ by more than ±1σ, with the full range of best-fit Hubble constant values spanning 71.8–76.9 km s⁻¹ Mpc⁻¹. We corroborate prior indications that the local value of H₀ exceeds the early-universe value, with a confidence level varying from 95% to 99% for different treatments of the peculiar velocities.

Recent near-Sun solar-wind observations from Parker Solar Probe have found a highly dynamic magnetic environment, permeated by abrupt radial-field reversals, or "switchbacks." We show that many features of the observed turbulence are reproduced by a spectrum of Alfvénic fluctuations advected by a radially expanding flow. Starting from simple superpositions of low-amplitude outward-propagating waves, our expanding-box compressible magnetohydrodynamic simulations naturally develop switchbacks because (i) the normalized amplitude of waves grows due to expansion and (ii) fluctuations evolve toward spherical polarization (i.e., nearly constant field strength). These results suggest that switchbacks form in situ in the expanding solar wind and are not indicative of impulsive processes in the chromosphere or corona.

Stellar occultations have been used to search for Kuiper Belt and Oort Cloud objects. We propose a search for interstellar objects based on the characteristic durations (∼0.1 s) of their stellar occultation signals and high inclination relative to the ecliptic plane. An all-sky monitoring program of all ∼7 × 10⁶ stars with R ≲ 12.5 using 1-m telescopes with 0.1 s cadences is predicted to discover ∼1 interstellar object per year.

In astronomy, long-exposure observations are one of the important ways to improve signal-to-noise ratios (S/Ns). In this Letter, we apply a deep-learning model to de-noise solar magnetograms. This model is based on a deep convolutional generative adversarial network with a conditional loss for image-to-image translation from a single magnetogram (input) to a stacked magnetogram (target). For the input magnetogram, we use Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) line-of-sight magnetograms at the center of the solar disk. For the target magnetogram, we make 21-frame-stacked magnetograms, taking into account solar rotation at the same position. We train a model using 7004 pairs of the input and target magnetograms from 2013 January to 2013 October. We then validate the model using 707 pairs from 2013 November and test the model using 736 pairs from 2013 December. Our results from this study are as follows. First, our model successfully de-noises SDO/HMI magnetograms, and the de-noised magnetograms from our model are mostly consistent with the target magnetograms. Second, the average noise level of the de-noised magnetograms is greatly reduced from 8.66 to 3.21 G, and it is consistent with that of the target magnetograms, 3.21 G. Third, the average pixel-to-pixel correlation coefficient value increases from 0.88 (input) to 0.94 (de-noised), which means that the de-noised magnetograms are more consistent with the target ones than the input ones. Our results can be applied to many scientific fields in which the integration of many frames (or long-exposure observations) are used to improve the S/N.

GW190425 is the second neutron star merger event detected by the Advanced LIGO/Virgo detectors. If interpreted as a double neutron star merger, the total gravitational mass is substantially larger than that of the binary systems identified in the Galaxy. In this work we analyze the gravitational-wave data within the neutron star–black hole merger scenario. For the black hole, we yield a mass of ${2.40}_{-0.32}^{+0.36}{M}_{\odot }$ and an aligned spin of ${0.141}_{-0.064}^{+0.067}$. As for the neutron star we find a mass of ${1.15}_{-0.13}^{+0.15}{M}_{\odot }$ and the dimensionless tidal deformability of ${1.4}_{-1.2}^{+3.8}\times {10}^{3}$. These parameter ranges are for 90% credibility. The inferred masses of the neutron star and the black hole are not in tension with current observations and we suggest that GW190425 is a viable candidate of a neutron star–black hole merger event. Benefitting from the continual enhancement of the sensitivities of the advanced gravitational detectors and the increase of the number of the observatories, similar events are anticipated to be much more precisely measured in the future and the presence of black holes below the so-called mass gap will be unambiguously clarified. If confirmed, the mergers of neutron stars with (quickly rotating) low-mass black holes are likely important production sites of the heaviest r-process elements.

We report on the discovery and analysis of bursts from nine new repeating fast radio burst (FRB) sources found using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. These sources span a dispersion measure (DM) range of 195–1380 pc cm⁻³. We detect two bursts from three of the new sources, three bursts from four of the new sources, four bursts from one new source, and five bursts from one new source. We determine sky coordinates of all sources with uncertainties of ∼10'. We detect Faraday rotation measures (RMs) for two sources, with values −20(1) and −499.8(7) rad m⁻², that are substantially lower than the RM derived from bursts emitted by FRB 121102. We find that the DM distribution of our events, combined with the nine other repeaters discovered by CHIME/FRB, is indistinguishable from that of thus far non-repeating CHIME/FRB events. However, as previously reported, the burst widths appear statistically significantly larger than the thus far non-repeating CHIME/FRB events, further supporting the notion of inherently different emission mechanisms and/or local environments. These results are consistent with previous work, though are now derived from 18 repeating sources discovered by CHIME/FRB during its first year of operation. We identify candidate galaxies that may contain FRB 190303.J1353+48 (DM = 222.4 pc cm⁻³).

Exoplanets orbiting M-dwarfs present a valuable opportunity for their detection and atmospheric characterization. This is evident from recent inferences of H₂O in such atmospheres, including that of the habitable-zone exoplanet K2-18b. With a bulk density between Earth and Neptune, K2-18b may be expected to possess a H/He envelope. However, the extent of such an envelope and the thermodynamic conditions of the interior remain unexplored. In the present work, we investigate the atmospheric and interior properties of K2-18b based on its bulk properties and its atmospheric transmission spectrum. We constrain the atmosphere to be H₂-rich with a H₂O volume mixing ratio of 0.02%–14.8%, consistent with previous studies, and find a depletion of CH₄ and NH₃, indicating chemical disequilibrium. We do not conclusively detect clouds/hazes in the observable atmosphere. We use the bulk parameters and retrieved atmospheric properties to constrain the internal structure and thermodynamic conditions in the planet. The constraints on the interior allow multiple scenarios between rocky worlds with massive H/He envelopes and water worlds with thin envelopes. We constrain the mass fraction of the H/He envelope to be ≲6%; spanning ≲10⁻⁵ for a predominantly water world to ∼6% for a pure iron interior. The thermodynamic conditions at the surface of the H₂O layer range from the supercritical to liquid phases, with a range of solutions allowing for habitable conditions on K2-18b. Our results demonstrate that the potential for habitable conditions is not necessarily restricted to Earth-like rocky exoplanets.

In the past few years, the ALMA radio telescope has become available for solar observations. ALMA diagnostics of the solar atmosphere are of high interest because of the theoretically expected linear relationship between the brightness temperature at millimeter wavelengths and the local gas temperature in the solar atmosphere. Key for the interpretation of solar ALMA observations is understanding where in the solar atmosphere the ALMA emission originates. Recent theoretical studies have suggested that ALMA bands at 1.2 (band 6) and 3 mm (band 3) form in the middle and upper chromosphere at significantly different heights. We study the formation of ALMA diagnostics using a 2.5D radiative MHD model that includes the effects of ion–neutral interactions (ambipolar diffusion) and nonequilibrium ionization of hydrogen and helium. Our results suggest that in active regions and network regions, observations at both wavelengths most often originate from similar heights in the upper chromosphere, contrary to previous results. Nonequilibrium ionization increases the opacity in the chromosphere so that ALMA mostly observes spicules and fibrils along the canopy fields. We combine these modeling results with observations from IRIS, SDO, and ALMA to suggest a new interpretation for the recently reported "dark chromospheric holes," regions of very low temperatures in the chromosphere.

Above the Sun's luminous photosphere lies the solar chromosphere, where the temperature increases from below 4000 K to over 1 million K. Though physicists do not understand the origin of these increases, they know it powers the solar wind with enormous consequences for the entire solar system. This report describes a set of simulations and analytical theory showing that solar atmospheric flows originating in the photosphere will frequently drive a previously unidentified thermal plasma instability that rapidly develops into turbulence. Though this turbulence is small scale (centimeters to a few meters), it will modify the conductivity, temperatures, and energy flows through much of the chromosphere. Incorporating the effects of this turbulence, and other small-scale turbulence, into large-scale models of solar and stellar atmospheres will improve physicists' ability to model energy flows with important consequences for the predicted temperatures and radiation patterns.

While most of the intergalactic medium (IGM) today is permeated by ionized hydrogen, it was largely filled with neutral hydrogen for the first 700 million years after the big bang. The process that ionized the IGM (cosmic reionization) is expected to be spatially inhomogeneous, with fainter galaxies likely playing a significant role. However, we still have only a few direct constraints on the reionization process. Here we report spectroscopic confirmation of two galaxies and very likely a third galaxy in a group (hereafter EGS77) at redshift z = 7.7, merely 680 Myr after the big bang. The physical separation among the three members is <0.7 Mpc. We estimate the radius of ionized bubble of the brightest galaxy to be about 1.02 Mpc, and show that the individual ionized bubbles formed by all three galaxies likely overlap significantly, forming a large yet localized ionized region, indicative of inhomogeneity in the reionization process. It is striking that two of three galaxies in EGS77 are quite faint in the continuum, thanks to our selection using their Lyα line emission in the narrowband filter. Indeed, one is the faintest spectroscopically confirmed galaxy yet discovered at such high redshifts. Our observations provide direct constraints on the process of cosmic reionization, and allow us to investigate the properties of sources responsible for reionizing the universe.

The right-hand resonant instability (RHI) is one of several electromagnetic ion/ion beam instabilities responsible for the formation of parallel magnetized collisionless shocks and the generation of ultra-low frequency (ULF) waves in their foreshocks. This instability has been observed for the first time under foreshock-relevant conditions in the laboratory through the repeatable interaction of a pre-formed magnetized background plasma and a super-Alfvénic laser-produced plasma. This platform has enabled unprecedented volumetric measurements of waves generated by the RHI, revealing filamentary current structures in the transverse plane. These measurements are made in the plasma rest frame with both high spatial and temporal resolution, providing a perspective that is complementary to spacecraft observations. Direct comparison of data from both the experiment and the Wind spacecraft to 2D hybrid simulations demonstrates that the waves produced are analogous to the ULF waves observed upstream of the terrestrial bow shock.

2014 MU69 (named Arrokoth), targeted by New Horizons, has a unique bilobate shape. Research suggested that there is a large circular depression feature with a diameter of ∼7 km on the smaller lobe of this object. This feature, called Maryland, is surrounded by topographically high regions and faces perpendicular to the shortest axis of this object. Here, following the interpretation by earlier work that Maryland is formed by an impact, we investigate how the Maryland impact affects the structure of a neck of this object. We find that to avoid a structural breakup driven by this impact, MU69 needs high cohesive strength, at least tens of kilopascals depending on the bulk density. The cohesive strength at this level is much higher than that of other small bodies observed at high resolution, which is usually reported to be a few hundred pascals. It may be possible that MU69 actually has such a high cohesive strength, which may challenge the current knowledge about the cohesive strength of small bodies. Alternatively, we hypothesize a scenario that the Maryland impact actually broke the neck structure and made the shape settle into the current configuration. Considering this scenario, we obtain that the bulk density of MU69 should be between 300 and 500 kg m⁻³.

High-resolution spectroscopy of stars on the red giant branch (RGB) of the globular cluster M15 has revealed a large (∼1 dex) dispersion in the abundances of r-process elements such as Ba and Eu. Neutron star mergers (NSMs) have been proposed as a major source of the r-process. However, most NSM models predict a delay time longer than the timescale for cluster formation. One possibility is that a NSM polluted the surfaces of stars in M15 long after the cluster finished forming. In this case, the abundances of the polluting elements would decrease in the first dredge-up as stars turn on to the RGB. We present Keck/DEIMOS abundances of Ba in 66 stars along the entire RGB and the top of the main sequence. The Ba abundances have no trend with stellar luminosity (evolutionary phase). Therefore, the stars were born with the Ba that they have today, and Ba did not originate in a source with a delay time longer than the timescale for cluster formation. In particular, if the source of Ba was a NSM, it would have had a very short delay time. Alternatively, if Ba enrichment took place before the formation of the cluster, an inhomogeneity of a factor of 30 in Ba abundance needs to be able to persist over the length scale of the gas cloud that formed M15, which is unlikely.

The discovery of planetary systems outside of the solar system has challenged some of the tenets of planetary formation. Among the difficult-to-explain observations are systems with a giant planet orbiting a very low mass star, such as the recently discovered GJ 3512b planetary system, where a Jupiter-like planet orbits an M star in a tight and eccentric orbit. Systems such as this one are not predicted by the core accretion theory of planet formation. Here we suggest a novel mechanism, in which the giant planet is born around a more typical Sun-like star (${M}_{* ,1}$), but is subsequently exchanged during a dynamical interaction with a flyby low-mass star (${M}_{* ,2}$). We perform state-of-the-art N-body simulations with ${M}_{* ,1}=1{M}_{\odot }$ and ${M}_{* ,2}=0.1{M}_{\odot }$ to study the statistical outcomes of this interaction, and show that exchanges result in high eccentricities for the new orbit around the low-mass star, while about half of the outcomes result in tighter orbits than the planet had around its birth star. We numerically compute the cross section for planet exchange, and show that an upper limit for the probability per planetary system to have undergone such an event is ${\rm{\Gamma }}\sim 4.4{({M}_{{\rm{c}}}/100{M}_{\odot })}^{-2}{({a}_{{\rm{p}}}/\mathrm{au})(\sigma /1\mathrm{km}{{\rm{s}}}^{-1})}^{5}$ Gyr⁻¹, where a_p is the planet semimajor axis around the birth star, σ the velocity dispersion of the star cluster, and M_c the total mass of the star cluster. Hence these planet exchanges could be relatively common for stars born in open clusters and groups, should already be observed in the exoplanet database, and provide new avenues to create unexpected planetary architectures.

Two components of jets associated with the afterglow of the gamma-ray burst (GRB) 160623A were observed with multifrequency observations including long-term monitoring in a submillimeter range (230 GHz) using the Submillimeter Array. The observed light curves with temporal breaks suggest on the basis of the standard forward-shock synchrotron-radiation model that the X-ray radiation is narrowly collimated with an opening angle ${\theta }_{n,j}\lt \sim 6^\circ$, whereas the radio radiation originated from wider jets (∼27°). The temporal and spectral evolutions of the radio afterglow agree with those expected from a synchrotron-radiation modeling with typical physical parameters, except for the fact that the observed wide jet opening angle for the radio emission is significantly larger than the theoretical maximum opening angle. By contrast, the opening angle of the X-ray afterglow is consistent with the typical value of GRB jets. Since the theory of the relativistic cocoon afterglow emission is similar to that of a regular afterglow with an opening angle of ∼30°, the observed radio emission can be interpreted as the shocked jet cocoon emission. This result therefore indicates that the two components of the jets observed in the GRB 160623A afterglow are caused by the jet and the shocked jet cocoon afterglows.

The atmospheric composition of giant planets carries the information of their formation history. Superstellar C/H ratios are seen in atmospheres of Jupiter, Saturn, and various giant exoplanets. Also, giant exoplanets show a wide range of C/O ratio. To explain these ratios, one hypothesis is that protoplanets accrete carbon-enriched gas when a large number of icy pebbles drift across the CO snowline. Here we report the first direct evidence of an elevated C/H ratio in disk gas. We use two thermo-chemical codes to model the ¹³C¹⁸O, C¹⁷O, and C¹⁸O (2−1) line spectra of the HD 163296 disk. We show that the gas inside the CO snowline (∼70 au) has a C/H ratio that is 1–2 times higher than the stellar value. This ratio exceeds the expected value substantially, as only 25%–60% of the carbon should be in gas at these radii. Although we cannot rule out the case of a normal C/H ratio inside 70 au, the most probable solution is an elevated C/H ratio that is 2–8 times higher than the expectation. Our model also shows that the gas outside 70 au has a C/H ratio that is 0.1× the stellar value. This picture of enriched C/H gas at the inner region and depleted gas at the outer region is consistent with numerical simulations of icy pebble growth and drift in protoplanetary disks. Our results demonstrate that the large-scale drift of icy pebble can occur in disks and may significantly change the disk gas composition for planet formation.

Recent observations show that the CO gas abundance, relative to H₂, in many 1–10 Myr old protoplanetary disks may be heavily depleted by a factor of 10–100 compared to the canonical interstellar medium (ISM) value of 10⁻⁴. When and how this depletion happens can significantly affect compositions of planetesimals and atmospheres of giant planets. It is therefore important to constrain whether the depletion occurs already at the earliest protostellar disk stage. Here we present spatially resolved observations of C¹⁸O, C¹⁷O, and ¹³C¹⁸O J = 2−1 lines in three protostellar disks. We show that the C¹⁸O line emits from both the disk and the inner envelope, while C¹⁷O and ¹³C¹⁸O lines are consistent with a disk origin. The line ratios indicate that both C¹⁸O and C¹⁷O lines are optically thick in the disk region, and only the ¹³C¹⁸O line is optically thin. The line profiles of the ¹³C¹⁸O emissions are best reproduced by Keplerian gaseous disks at similar sizes as their mm-continuum emissions, suggesting small radial separations between the gas and mm-sized grains in these disks, in contrast to the large separation commonly seen in protoplanetary disks. Assuming a gas-to-dust ratio of 100, we find that the CO gas abundances in these protostellar disks are consistent with the ISM abundance within a factor of 2, nearly one order of magnitude higher than the average value of 1–10 Myr old disks. These results suggest that there is a fast, ∼1 Myr, evolution of the abundance of CO gas from the protostellar disk stage to the protoplanetary disk stage.

Terrestrial-type exoplanets orbiting nearby red dwarf stars (M dwarfs) are among the best targets for atmospheric characterization and biosignature searches in the near future. Recent evolutionary studies have suggested that terrestrial planets in the habitable zone of M dwarfs are probably tidally locked and have limited surface water inventories as a result of their host stars' high early luminosities. Several previous climate simulations of such planets have indicated that their remaining water would be transported to the planet's permanent nightside and become trapped as surface ice, leaving the dayside devoid of water. Here we use a three-dimensional general circulation model with a water cycle and accurate radiative transfer scheme to investigate the surface water evolution on slowly rotating tidally locked terrestrial planets with limited surface water inventories. We show that there is a competition for water trapping between the nightside surface and the substellar tropopause in this type of climate system. Although under some conditions the surface water remains trapped on the nightside as an ice sheet, in other cases liquid water stabilizes in a circular area in the substellar region as a wetland. Planets with 1 bar N₂ and atmospheric CO₂ levels greater than 0.1 bar retain stable dayside liquid water, even with very small surface water inventories. Our results reveal the diversity of possible climate states on terrestrial-type exoplanets and highlight the importance of surface liquid water detection techniques for future characterization efforts.

We present the first full six-dimensional panoramic portrait of the Sagittarius stream, obtained by searching for wide stellar streams in the Gaia DR2 data set with the STREAMFINDER algorithm. We use the kinematic behavior of the sample to devise a selection of Gaia RR Lyrae, providing excellent distance measurements along the stream. The proper motion data are complemented with radial velocities from public surveys. We find that the global morphological and kinematic properties of the Sagittarius stream are still reasonably well reproduced by the simple Law & Majewski model (LM10), although the model overestimates the leading arm and trailing arm distances by up to ∼15%. The sample newly reveals the leading arm of the Sagittarius stream as it passes into very crowded regions of the Galactic disk toward the Galactic anticenter direction. Fortuitously, this part of the stream is almost exactly at the diametrically opposite location from the Galactic center to the progenitor, which should allow an assessment of the influence of dynamical friction and self-gravity in a way that is nearly independent of the underlying Galactic potential model.

Observations by the Parker Solar Probe mission of the solar wind at ∼35.7 solar radii reveal the existence of whistler wave packets with frequencies below 0.1 f_ce (20–80 Hz in the spacecraft frame). These waves often coincide with local minima of the magnetic field magnitude or with sudden deflections of the magnetic field that are called switchbacks. Their sunward propagation leads to a significant Doppler frequency downshift from 200–300 to 20–80 Hz (from 0.2 to 0.5 f_ce). The polarization of these waves varies from quasi-parallel to significantly oblique with wave normal angles that are close to the resonance cone. Their peak amplitude can be as large as 2–4 nT. Such values represent approximately 10% of the background magnetic field, which is considerably more than what is observed at 1 au. Recent numerical studies show that such waves may potentially play a key role in breaking the heat flux and scattering the Strahl population of suprathermal electrons into a halo population.

We analyze ground-based chromospheric data acquired at a high temporal cadence of 2 s in wings of the H_α spectral line using the Goode Solar Telescope operating at the Big Bear Solar Observatory. We inspected a 30 minute long H_α−0.08 nm data set to find that rapid blueshifted H_α excursions (RBEs), which are a cool component of type II spicules, experience very rapid morphological changes on timescales of the order of 1 s. Unlike typical reconnection jets, RBEs very frequently appear in situ without any clear evidence of H_α material being injected from below. Their evolution includes inverted "Y," "V," "N," and parallel splitting (doubling) patterns as well as sudden formation of a diffuse region followed by branching. We also find that the same feature may undergo several splitting episodes within about a 1 minute time interval.

The importance of the activation energy of surface diffusion (E_sd) of adsorbed molecules on amorphous solid water (ASW) has been widely discussed in terms of chemical reactions on ASW at low temperatures. However, in previous work, E_sd has not been measured directly but estimated from indirect experiments. It has been assumed in chemical network calculations that E_sd is between 0.3 and 0.8 of the desorption energies of a molecule. It remains important to obtain direct measurements of E_sd. We performed in situ observations of the deposition process of CO and CO₂ on ASW using transmission electron microscopy (TEM) and deduced the E_sd of CO and CO₂ on ASW to be 350 ± 50 and 1500 ± 100 K, respectively. The value of E_sd of CO is approximately 0.3 of the total adsorption energy of CO on ASW, i.e., much smaller than assumed in chemical network calculations, where the corresponding figure is 575 K, assuming approximately 0.5 of the desorption energy. We demonstrated that TEM is very useful not only for the observation of ices but also for the measurement of some physical properties that are relevant in astrochemistry and astrophysics. Using the E_sd of CO measured in the present study (350 K), we have updated the chemical network model of Furuya et al., confirming that CO₂ could be efficiently formed by the reaction CO + OH → CO₂ + H in the initial stages of the evolution of molecular clouds.

It has long been speculated that many starburst or compact dwarf galaxies are resulted from dwarf–dwarf galaxy merging, but unequivocal evidence for this possibility has rarely been reported in the literature. We present the first study of deep optical broadband images of a gas-dominated blue compact dwarf galaxy (BCD) VCC 848 (M_⋆ ≃ 2 × 10⁸M_⊙) that hosts extended stellar shells and thus is confirmed to be a dwarf–dwarf merger. VCC 848 is located in the outskirts of the Virgo Cluster. By analyzing the stellar light distribution, we found that VCC 848 is the result of a merging between two dwarf galaxies with a primary-to-secondary mass ratio ≲5 for the stellar components and ≲2 for the presumed dark matter halos. The secondary progenitor galaxy has been almost entirely disrupted. The age–mass distribution of photometrically selected star cluster candidates in VCC 848 implies that the cluster formation rate (CFR, ∝ star formation rate) was enhanced by a factor of ∼7–10 during the past ∼1 Gyr. The merging-induced enhancement of CFR peaked near the galactic center a few hundred Myr ago and has started declining in the last few tens of Myr. The current star formation activities, as traced by the youngest clusters, mainly occur at large galactocentric distances (≳1 kpc). The fact that VCC 848 is still (atomic) gas-dominated after the period of the most violent collision suggests that gas-rich dwarf galaxy merging can result in BCD-like remnants with extended atomic gas distribution surrounding a blue compact center, in general agreement with previous numerical simulations.

We calculate the abundances of ⁷Li, ¹¹B, ⁹²Nb, ⁹⁸Tc, ¹³⁸La, and ¹⁸⁰Ta produced by neutrino (ν)-induced reactions in a core-collapse supernova explosion. We consider the modification by ν self-interaction (ν-SI) near the neutrinosphere and the Mikheyev–Smirnov–Wolfenstein (MSW) effect in the outer layers based on time-dependent neutrino energy spectra. Abundances of ⁷Li and the heavy isotopes ⁹²Nb, ⁹⁸Tc, and ¹³⁸La are reduced by a factor of 1.5–2.0 by the ν-SI. In contrast, ¹¹B is relatively insensitive to the ν-SI. We find that the abundance ratio of heavy to light nuclei, ¹³⁸La/¹¹B, is sensitive to the neutrino mass hierarchy, and the normal mass hierarchy is more likely to be consistent with the solar meteoritic abundances.

In plasmas with a large ratio of plasma frequency to gyrofrequency (ω_pe/Ω_ce), energetic electrons characterized by $\partial f/\partial {v}_{\perp }\gt 0$ can excite electron cyclotron maser instability (ECMI), generating waves of upper hybrid (UH), Z, and W modes. It has been presumed that these ECMI waves can somehow convert to escaping X–O modes as fundamental (F) or harmonic (H) plasma emission. Here we perform a fully kinetic, electromagnetic particle-in-cell simulation to investigate the proposed radiation process. ECMI is driven by energetic electrons with a Dory–Guest–Harris distribution representative of a double-sided loss cone, and ω_pe/Ω_ce is set to be 10. We find that the electrostatic UH mode is the fastest-growing mode. Around the time when its energy starts to decline, the W mode grows to be dominant. During this stage, we observe significant F and H plasma emission. The F emission is in the O mode with a bandwidth around 0.1–0.2 Ω_ce, and the H emission is contributed by both X and O modes with a narrower bandwidth. We suggest that the O–F emission is caused by coalescence of almost counterpropagating Z and W modes, while the H emission arises from coalescence of an almost counterpropagating UH mode at relatively large wave number. Thus the plasma emission investigated here is induced by a combination of wave growth due to ECMI and further nonlinear wave-coupling processes. The result is relevant to understanding solar radio bursts as well as other astronomical radio sources that are excited by energetic electrons trapped within certain magnetic structures.

An interplanetary (IP) shock wave was recorded crossing the Magnetospheric Multiscale constellation on 2018 January 8. Plasma measurements upstream of the shock indicate efficient proton acceleration in the IP shock ramp: 2–7 keV protons are observed upstream for about three minutes (∼8000 km) ahead of the IP shock ramp, outrunning the upstream waves. The differential energy flux of 2–7 keV protons decays slowly with distance from the ramp toward the upstream region (dropping by about half within 8 Earth radii from the ramp) and is lessened by a factor of about four in the downstream compared to the ramp (within a distance comparable to the gyroradius of ∼keV protons). Comparison with test-particle simulations has confirmed that the mechanism accelerating the solar wind protons and injecting them upstream is classical Shock Drift Acceleration (SDA). This example of observed proton acceleration by a low-Mach, quasi-perpendicular shock may be applicable to astrophysical contexts, such as supernova remnants or the acceleration of cosmic rays.

We examine the relationship between individual black hole (BH) masses in merging binary black hole (BBH) systems. Analyzing the 10 BBH detections from LIGO/Virgo's first two observing runs, we find that the masses of the component BHs comprising each binary are unlikely to be randomly drawn from the same underlying distribution. Instead, the two BHs of a given binary prefer to be of comparable mass. We show that it is ∼5 times more likely that the component BHs in a given binary are always equal (to within 5%) than that they are randomly paired. If we assume that the probability of a merger between two BHs scales with the mass ratio q as q^β, so that β = 0 corresponds to random pairings, we find β > 0 is favored at credibility 0.987. By modeling the mass distribution, we find that the median mass ratio is ${q}_{50 \% }={0.91}_{-0.17}^{+0.05}$ at 90% credibility. While the pairing between BHs depends on their mass ratio, we find no evidence that it depends on the total mass of the system. We predict that 99% of BBHs detected by LIGO/Virgo will have mass ratios q > 0.5. We conclude that merging black holes do not form random pairings; instead they are selective about their partners, preferring to mate with black holes of a similar mass. The details of these selective pairings provide insight into the underlying formation channels of merging binaries.