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The microwave radiometer on board the Juno spacecraft provided a measurement of the water abundance found to range between ∼1 and 5.1 times the protosolar abundance of oxygen in the near-equatorial region of Jupiter. Here, we aim to combine this up-to-date oxygen determination, which is likely to be more representative of the bulk abundance than the Galileo probe subsolar value, with the other known measurements of elemental abundances in Jupiter, to derive the formation conditions and initial composition of the building blocks agglomerated by the growing planet, and that determine the heavy element composition of its envelope. We investigate several cases of formation of icy solids in the protosolar nebula (PSN), from the condensation of pure ices to the crystallization of mixtures of pure condensates and clathrates in various proportions. Each of these cases corresponds to a distinct solid composition whose amount is adjusted in the envelope of Jupiter to match the O abundance measured by Juno. The volatile enrichments can be matched by a wide range of planetesimal compositions, from solids exclusively formed from pure condensates or from nearly exclusively clathrates, the latter case providing a slightly better fit. The total mass of volatiles needed in the envelope of Jupiter to match the observed enrichments is within the ∼4.3–39 M_⊕ range, depending on the crystallization scenario considered in the PSN. A wide range of masses of heavy elements derived from our fits is found to be compatible with the envelope's metallicity calculated from current interior models.

With our new Ca-CN-CH-NH photometry, we revisit the globular cluster (GC) M5. We find that M5 is a mono-metallic GC with a small metallicity dispersion. Our carbon abundances show that the σ[C/Fe] of the M5 CN-s population, with depleted carbon and enhanced nitrogen abundances, is significantly large for a single stellar population. Our new analysis reveals that the M5 CN-s population is well described by the two stellar populations: the CN-s_I, being the major CN-s component, with the intermediate carbon and nitrogen abundance and the CN-s_E with the most carbon-poor and nitrogen-rich abundance. We find that the CN-s_E is significantly more centrally concentrated than the others, while CN-w and CN-s_I have similar cumulative radial distributions. The red giant branch bump V magnitude, the helium abundance barometer in mono-metallic populations, of individual populations appears to be correlated with their mean carbon abundance, indicating that carbon abundances are anticorrelated with helium abundances. We propose that the CN-s_E formed out of gas that experienced proton-capture processes at high temperatures in the innermost region of the proto-GC of M5 that resided in a dense ambient density environment. Shortly after, the CN-s_I formed out of gas diluted from the pristine gas in the more spatially extended region, consistent with the current development of numerical simulations by others.

All-sky imaging surveys have identified several dozen isolated planetary-mass objects (IPMOs) far away from any star. Here we examine the prospects for detecting transiting moons around these objects. We expect transiting moons to be common, occurring around 10%–15% of IPMOs, given that close-orbiting moons have a high geometric transit probability and are expected to be a common outcome of giant planet formation. The IPMOs offer an advantage over other directly imaged planets in that high-contrast imaging is not necessary to detect the photometric transit signal. For at least 30 (>50%) of the currently known IPMOs, observations of a single transit with the James Webb Space Telescope would have low enough forecast noise levels to allow for the detection of an Io- or Titan-like moon. The intrinsic variability of the IPMOs will be an obstacle. Using archival time-series photometry of IPMOs with the Spitzer Space Telescope as a proof of concept, we found evidence for a fading event of 2MASS J1119–1137 AB that might have been caused by intrinsic variability but is also consistent with a single transit of a habitable-zone 1.7 R_⊕ exomoon. Although the interpretation of this particular event is inconclusive, the characteristics of the data and the candidate signal suggest that Earth-sized habitable-zone exomoons around IPMOs are detectable with existing instrumentation.

We report the detection of X-ray pulsations from the rotation-powered millisecond-period pulsars PSR J0740+6620 and PSR J1614−2230, two of the most massive neutron stars known, using observations with the Neutron Star Interior Composition Explorer (NICER). We also analyze X-ray Multi-Mirror Mission (XMM-Newton) data for both pulsars to obtain their time-averaged fluxes and study their respective X-ray fields. PSR J0740+6620 exhibits a broad double-peaked profile with a separation of ∼0.4 in phase. PSR J1614−2230, on the other hand, has a broad single-peak profile. We show the NICER detections of X-ray pulsations for both pulsars and also discuss the phase relationship to their radio pulsations. The XMM-Newton X-ray spectra of both pulsars shows they are thermally dominated but in the case of PSR J1614−2230 a weak nonthermal high energy tail appears to be present in the spectrum. The thermally dominated spectra along with broad modulations for both pulsars are indicative of thermal radiation from one or more small regions of the stellar surface. For PSR J0740+6620, this paper documents the data reduction performed to obtain the pulsation detection and prepare for pulse light curve modeling analysis.

We report on Bayesian estimation of the radius, mass, and hot surface regions of the massive millisecond pulsar PSR J0740+6620, conditional on pulse-profile modeling of Neutron Star Interior Composition Explorer X-ray Timing Instrument event data. We condition on informative pulsar mass, distance, and orbital inclination priors derived from the joint North American Nanohertz Observatory for Gravitational Waves and Canadian Hydrogen Intensity Mapping Experiment/Pulsar wideband radio timing measurements of Fonseca et al. We use XMM-Newton European Photon Imaging Camera spectroscopic event data to inform our X-ray likelihood function. The prior support of the pulsar radius is truncated at 16 km to ensure coverage of current dense matter models. We assume conservative priors on instrument calibration uncertainty. We constrain the equatorial radius and mass of PSR J0740+6620 to be ${12.39}_{-0.98}^{+1.30}$ km and ${2.072}_{-0.066}^{+0.067}$M_⊙ respectively, each reported as the posterior credible interval bounded by the 16% and 84% quantiles, conditional on surface hot regions that are non-overlapping spherical caps of fully ionized hydrogen atmosphere with uniform effective temperature; a posteriori, the temperature is ${\mathrm{log}}_{10}(T\,[{\rm{K}}])={5.99}_{-0.06}^{+0.05}$ for each hot region. All software for the X-ray modeling framework is open-source and all data, model, and sample information is publicly available, including analysis notebooks and model modules in the Python language. Our marginal likelihood function of mass and equatorial radius is proportional to the marginal joint posterior density of those parameters (within the prior support) and can thus be computed from the posterior samples.

PSR J0740+6620 has a gravitational mass of 2.08 ± 0.07 M_⊙, which is the highest reliably determined mass of any neutron star. As a result, a measurement of its radius will provide unique insight into the properties of neutron star core matter at high densities. Here we report a radius measurement based on fits of rotating hot spot patterns to Neutron Star Interior Composition Explorer (NICER) and X-ray Multi-Mirror (XMM-Newton) X-ray observations. We find that the equatorial circumferential radius of PSR J0740+6620 is ${13.7}_{-1.5}^{+2.6}$ km (68%). We apply our measurement, combined with the previous NICER mass and radius measurement of PSR J0030+0451, the masses of two other ∼2 M_⊙ pulsars, and the tidal deformability constraints from two gravitational wave events, to three different frameworks for equation-of-state modeling, and find consistent results at ∼1.5–5 times nuclear saturation density. For a given framework, when all measurements are included, the radius of a 1.4 M_⊙ neutron star is known to ±4% (68% credibility) and the radius of a 2.08 M_⊙ neutron star is known to ±5%. The full radius range that spans the ±1σ credible intervals of all the radius estimates in the three frameworks is 12.45 ± 0.65 km for a 1.4 M_⊙ neutron star and 12.35 ± 0.75 km for a 2.08 M_⊙ neutron star.

In recent years our understanding of the dense matter equation of state (EOS) of neutron stars has significantly improved by analyzing multimessenger data from radio/X-ray pulsars, gravitational wave events, and from nuclear physics constraints. Here we study the additional impact on the EOS from the jointly estimated mass and radius of PSR J0740+6620, presented in Riley et al. by analyzing a combined data set from X-ray telescopes NICER and XMM-Newton. We employ two different high-density EOS parameterizations: a piecewise-polytropic (PP) model and a model based on the speed of sound in a neutron star (CS). At nuclear densities these are connected to microscopic calculations of neutron matter based on chiral effective field theory (EFT) interactions. In addition to the new NICER data for this heavy neutron star, we separately study constraints from the radio timing mass measurement of PSR J0740+6620, the gravitational wave events of binary neutron stars GW190425 and GW170817, and for the latter the associated kilonova AT2017gfo. By combining all these, and the NICER mass–radius estimate of PSR J0030+0451, we find the radius of a 1.4 M_⊙ neutron star to be constrained to the 95% credible ranges ${12.33}_{-0.81}^{+0.76}\,\mathrm{km}$ (PP model) and ${12.18}_{-0.79}^{+0.56}\,\mathrm{km}$ (CS model). In addition, we explore different chiral EFT calculations and show that the new NICER results provide tight constraints for the pressure of neutron star matter at around twice saturation density, which shows the power of these observations to constrain dense matter interactions at intermediate densities.

Gravitational waves from the distant sources are gravitationally lensed during their propagation through the intervening matter inhomogeneities before arriving at detectors. It has been proposed in the literature that the variance of the lensed waveform can be used to extract information of the matter power spectrum at very small scales and of low-mass dark halos. In this Letter, we show that the variance of the amplitude fluctuation and that of the phase fluctuation of the lensed waveform obey a simple relation irrespective of the shape of the matter power spectrum. We study conditions under which this relation can be violated and discuss some potential applications of the relation. This relation may be used to confirm the robustness of claimed observations of gravitational lensing of gravitational waves and the subsequent reconstruction of the matter power spectrum.

When binary black holes merge in dense star clusters, their remnants can pair up with other black holes in the cluster, forming heavier and heavier black holes in a process called hierarchical merger. The most important condition for hierarchical merger to occur is that remnants formed by mergers are retained by the host star cluster. Using the publicly available gravitational-wave event database, we infer the magnitudes of kick velocities imparted to the remnant black holes due to anisotropic emission of gravitational waves and use that to quantify the retention probability of each event as a function of the escape speed of the star cluster. Among the second gravitational-wave transient catalog (GWTC-2) events, GW190814 provides the tightest constraint on the kick magnitude with ${V}_{\mathrm{kick}}={74}_{-7}^{+10}$ km s⁻¹ at the 90% credible level. We find that star clusters with escape speeds of 200 km s⁻¹ can retain about 50% of the events in the GWTC-2. Using the escape speed distributions of nuclear star clusters and globular clusters, we find that ∼17 (2) remnants of GWTC-2 may be retained by the host star cluster if all GWTC-2 events occurred in nuclear (globular) clusters. Our study demonstrates the importance of folding in kick velocity inferences in future studies of hierarchical mergers.

Chemical tagging is a powerful tool to reveal the origin of stars and globular clusters (GCs), especially when dynamics alone cannot provide robust answers. So far, mostly α-elements and neutron capture elements have been used to distinguish stars born in the Milky Way (MW) from those born in external environments such as that of dwarf galaxies. Here, instead, we use iron-peak element abundances to investigate the origin of a sample of metal-rich GCs. By homogeneously analyzing high-resolution UVES spectra of giant stars belonging to four metal-rich GCs (namely NGC 5927, NGC 6388, NGC 6441, and NGC 6496), we find that while the α-elements Si and Ca have similar abundance ratios for all four GCs, and Ti and neutron capture elements (La, Ba, and Eu) only show a marginal discrepancy, a stark difference is found when considering the abundances of some iron-peak elements (Sc, V, and Zn). In particular, NGC 6388 and NGC 6441 have abundance ratios for these iron-peak elements significantly lower (by ∼0.5 dex) than those measured in NGC 5927 and NGC 6496, which are clearly identified as born in situ MW clusters through an analysis of their orbital properties. These measurements indicate that the environment in which these clusters formed is different, and they provide robust evidence supporting an accreted origin from the same progenitor for NGC 6388 and NGC 6441.

The guest star of AD 1181 is the only historical supernova of the past millennium that is without a definite counterpart. The previously proposed association with supernova remnant G130.7+3.1 (3C 58) is in strong doubt because of the inferred age of this remnant. Here we report a new identification of SN 1181 with our codiscovery of the hottest known Wolf–Rayet star of the oxygen sequence (IRAS 00500+6713 or 2MASS J00531123+6730023, here named by us as "Parker's star") and its surrounding nebula Pa 30. Our spectroscopy of the nebula shows a fast shock with extreme velocities of ≈1100 km s⁻¹. The derived expansion age of the nebula implies an explosive event ≈1000 yr ago that agrees with the 1181 event. The on-sky location also fits the historical Chinese and Japanese reports of SN 1181 to within 35. Pa 30 and Parker's star have previously been proposed to be the result of a double-degenerate merger, leading to a rare Type Iax supernova. The likely historical magnitude and the distance suggest the event was subluminous for normal supernova. This agrees with the proposed Type Iax association that would also be only the second of its kind in the Galaxy. Taken together, the age, location, event magnitude, and duration elevate Pa 30 to prime position as the counterpart of SN 1181. This source is the only Type Iax supernova where detailed studies of the remnant star and nebula are possible. It provides strong observational support for the double-degenerate merger scenario for Type Iax supernovae.

A tiny fraction of observed gamma-ray bursts (GRBs) may be lensed. The time delays induced by the gravitational lensing are milliseconds to seconds if the point lenses are intermediate-mass black holes. The prompt emission of the lensed GRBs, in principle, should have repeated pulses with identical light curves and spectra but different fluxes and slightly offset positions. In this work, we search for such candidates within the GRBs detected by Fermi/GBM, Swift/Burst Alert Telescope, and HXMT/HE and report the identification of an attractive event GRB 200716C that consists of two pulses. Both the autocorrelation analysis and the Bayesian inference of the prompt emission light curve are in favor of the gravitational-lensing scenario. Moreover, the spectral properties of the two pulses are rather similar and follow the so-called Amati relation of short GRBs rather than long-duration bursts. The measured flux ratios between the two pulses are nearly constant in all channels, as expected from gravitational lensing. We therefore suggest that the long-duration burst GRB 200716C was a short event being lensed. The redshifted mass of the lens was estimated to be ${4.25}_{-1.36}^{+2.46}\times {10}^{5}\,{M}_{\odot }$ (90% credibility). If correct, this could point toward the existence of an intermediate-mass black hole along the line of sight of GRB 200716C.

The reionization epoch concludes when ionizing photons reach every corner of the universe. Reionization has generally been assumed to be limited primarily by the rate at which galaxies produce ionizing photons, but the recent measurement of a surprisingly short ionizing photon mean free path of ${0.75}_{-0.45}^{+0.65}$ proper Mpc at z = 6 by Becker et al. suggests that absorption by residual neutral hydrogen in the otherwise ionized intergalactic medium may play a much larger role than previously expected. Here we show that consistency between this short mean free path and the coeval dark pixel fraction in the Lyα forest requires a cumulative output of ${6.1}_{-2.4}^{+11}$ ionizing photons per baryon by reionization's end, well above the typically required ∼1–3. This represents a dramatic increase in the ionizing photon budget over previous estimates, greatly exacerbating the tension with measurements of the ionizing output from galaxies at later times. Translating this constraint into the instantaneous ionizing production from galaxies in our model, we find ${\mathrm{log}}_{10}{f}_{\mathrm{esc}}{\xi }_{\mathrm{ion}}/{(\mathrm{erg}/\mathrm{Hz})}^{-1}={25.02}_{-0.21}^{+0.45}$ at z ∼ 6. Even with optimistic assumptions about the ionizing production efficiency of early stellar populations, and assuming the galaxy luminosity function extends to extremely faint sources (M_UV ≤ − 11), complete reionization requires the escape fraction of ionizing photons to exceed 20% across the galaxy population. This is far larger than observed in any galaxy population at lower redshifts, requiring rapid evolution in galaxy properties after the first billion years of cosmic time. This tension cannot be completely relieved within existing observational constraints on the hydrogen neutral fraction and mean free path.

Recent simulations show that giant planets of about 1 M_J migrate inward at a rate that differs from the type II prediction. Here we show that at higher masses, planets migrate outward. Our result differs from previous ones because of our longer simulation times, lower viscosity, and boundary conditions that allow the disk to reach a viscous steady state. We show that, for planets on circular orbits, the transition from inward to outward migration coincides with the known transition from circular to eccentric disks that occurs for planets more massive than a few Jupiters. In an eccentric disk, the torque on the outer disk weakens due to two effects: the planet launches weaker waves, and those waves travel further before damping. As a result, the torque on the inner disk dominates, and the planet pushes itself outward. Our results suggest that the many super-Jupiters observed by direct imaging at large distances from the star may have gotten there by outward migration.

We report the discovery of a new, chemically distinct population of relatively high-metallicity ([Fe/H] > −0.7) red giant stars with super-solar [N/Fe] (≳+0.75) identified within the bulge, disk, and halo of the Milky Way. This sample of stars was observed during the second phase of the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2); the spectra of these stars are part of the seventeenth Data Release (DR 17) of the Sloan Digital Sky Survey. We hypothesize that this newly identified population was formed in a variety of progenitors, and is likely made up of either fully or partially destroyed metal-rich globular clusters, which we refer to as globular cluster debris (GCD), identified by their unusual photospheric nitrogen abundances. It is likely that some of the GCD stars were probable members of the Gaia–Enceladus–Sausage accretion event, along with clusters formed in situ.

The long wait for the detection of merging black hole–neutron star (BH–NS) binaries is finally over with the announcement by the LIGO/Virgo/Kagra collaboration of GW200105 and GW200115. Remarkably, the primary of GW200115 has a negative spin projection onto the orbital angular momentum, with about 90% probability. Merging BH–NS binaries are expected to form mainly through the evolution of massive binary stars in the field, since their dynamical formation in dense star clusters is strongly suppressed by mass segregation. In this Letter, we carry out a systematic statistical study of the binary stars that evolve to form a BH–NS binary, considering different metallicities and taking into account the uncertainties on the natal-kick distributions for BHs and NSs and on the common-envelope phase of binary evolution. Under the assumption that the initial stellar spins are aligned with the binary angular momentum, we show that both large natal kicks for NSs (≳150 km s⁻¹) and high efficiencies for common-envelope ejection are required to simultaneously explain the inferred high merger rates and the large spin–orbit misalignment of GW200115.

The enigmatic class of Fanaroff–Riley type 0 (FR0) radio galaxies is emerging as the missing link between the faint yet numerous population of compact radio sources in nearby galaxies and the canonical Fanaroff–Riley classification scheme. This Letter reports the first γ-ray identification of three FR0 galaxies above 1 GeV using more than a decade of the Fermi Large Area Telescope observations. A cumulative γ-ray emission at >5σ significance was also detected from the γ-ray unresolved FR0 sources using the stacking technique, suggesting the FR0 population to be a γ-ray emitter as a whole. The multifrequency properties of the γ-ray-detected sources are similar to other FR0s, thus indicating the high-energy radiation to originate from misaligned jets. Given their large abundance, FR0 radio galaxies are proposed as plausible candidates for IceCube-detected neutrinos and the results presented in this Letter may provide crucial constraints on their γ-ray production mechanism and the origin of cosmic neutrinos.