The age of gravitational wave (GW) astronomy has begun, and black hole (BH) mergers detected by LIGO are providing novel constraints on massive star evolution. A major uncertainty in stellar theory is the angular momentum (AM) transport within the star that determines its core rotation rate and the resulting BH's spin. Internal rotation rates of low-mass stars measured from asteroseismology prove that AM transport is efficient, suggesting that massive stellar cores may rotate slower than prior expectations. We investigate AM transport via the magnetic Tayler instability, which can largely explain the rotation rates of low-mass stars and white dwarfs. Implementing an updated AM transport prescription into models of high-mass stars, we compute the spins of their BH remnants. We predict that BHs born from single stars rotate very slowly, with a ∼ 10 −2 , regardless of initial rotation rate, possibly explaining the low χ eff of most BH binaries detected by LIGO thus far. A limited set of binary models suggests slow rotation for many binary scenarios as well, although homogeneous evolution and tidal spin-up of post-common envelope helium stars can create moderate or high BH spins. We make predictions for the values of χ eff in future LIGO events, and we discuss implications for engine-powered transients.

A large fraction of known exoplanets have short orbital periods where tidal excitation of gravity waves within the host star causes the planets' orbits to decay. We study the effects of tidal resonance locking, in which the planet locks into resonance with a tidally excited stellar gravity mode. Because a star's gravity mode frequencies typically increase as the star evolves, the planet's orbital frequency increases in lockstep, potentially causing much faster orbital decay than predicted by other tidal theories. Due to nonlinear mode damping, resonance locking in Sun-like stars likely only operates for low-mass planets (M  0.1 M Jup ), but in stars with convective cores it can likely operate for all planetary masses. The orbital decay timescale with resonance locking is typically comparable to the star's main-sequence lifetime, corresponding to a wide range in effective stellar quality factor (10 3  Q′  10 9 ), depending on the planet's mass and orbital period. We make predictions for several individual systems and examine the orbital evolution resulting from both resonance locking and nonlinear wave dissipation. Our models demonstrate how short-period massive planets can be quickly destroyed by nonlinear mode damping, while shortperiod low-mass planets can survive, even though they undergo substantial inward tidal migration via resonance locking.

The internal rotational dynamics of massive stars are poorly understood. If angular momentum (AM) transport between the core and the envelope is inefficient, the large core AM upon core-collapse will produce rapidly rotating neutron stars (NSs). However, observations of low-mass stars suggest an efficient AM transport mechanism is at work, which could drastically reduce NS spin rates. Here we study the effects of the baroclinic instability and the magnetic Tayler instability in differentially rotating radiative zones. Although the baroclinic instability may occur, the Tayler instability is likely to be more effective for AM transport. We implement Tayler torques as prescribed by Fuller et al. 2019 into models of massive stars, finding they remove the vast majority of the core's AM as it contracts between the main sequence and heliumburning phases of evolution. If core AM is conserved during core-collapse, we predict natal NS rotation periods of P NS ≈ 50 − 200 ms, suggesting these torques help explain the relatively slow rotation rates of most young NSs, and the rarity of rapidly rotating engine-driven supernovae. Stochastic spin-up via waves just before core-collapse, asymmetric explosions, and various binary evolution scenarios may increase the initial rotation rates of many NSs.

Possible formation scenarios of supermassive black holes in the early universe include rapid growth from less massive seed black holes (BHs) via super-Eddington accretion or runaway mergers, yet both of these scenarios would require seed BHs to efficiently sink to and be trapped in the galactic center via dynamical friction. This may not be true for their complicated dynamics in clumpy high-z galaxies. In this work we study this “sinking problem” with state-of-the-art high-resolution cosmological simulations, combined with both direct N-body integration of seed BH trajectories and post-processing of randomly generated test particles with a newly developed dynamical friction estimator. We find that seed BHs less massive than 108 M⊙ (i.e. all but the already-supermassive seeds) cannot efficiently sink in typical high-z galaxies. We also discuss two possible solutions: dramatically increasing the number of seeds such that one seed can end up trapped in the galactic center by chance, or seed BHs being embedded in dense structures (e.g. star clusters) with effective masses above the mass threshold. We discuss the limitations of both solutions.

Sclerotinia sclerotiorum is one of the most devastating fungal plant pathogens of oilseed Brassica and is distributed worldwide. In particular, Sclerotinia stem rot has always been a serious threat to rapeseed production in Chongqing City, China. In this study, simple sequence repeat (SSR) markers and mycelial compatibility groups (MCGs) were used to characterize the population structure of 90 geographic isolates of S. sclerotiorum collected from rapeseed in nine counties of Chongqing. A total of 52 microsatellite haplotypes were identified, and a few haplotypes were found with high frequency. Gene diversity ranged from 0.1570 to 0.4700 in nine populations. A constructed unweighted pair group with arithmetic mean dendrogram based on Nei genetic distance and a STRUCTURE analysis revealed that the genetic composition of the isolates collected in the five counties located in western Chongqing are different from those collected in the two eastern counties, suggesting that breed lines should be cultivated in both the western and eastern regions to effectively evaluate resistance levels. A total of 47 MCGs were identified, and 72% of the MCGs was represented by single isolates. Seven of 13 MCGs that included at least two isolates contained isolates from only one county. SSR haplotypes were not correlated with MCGs. A subset of 34 isolates were inoculated on rapeseed stems, and the aggressiveness showed variation. This research revealed the population genetic structure and aggressiveness of this pathogen in Chongqing, and the results will help to develop disease management and resistance screening strategies.

Gravitational wave observations indicate the existence of merging black holes (BHs) with high spin (a ≳ 0.3), whose formation pathways are still an open question. A possible way to form those binaries is through the tidal spin-up of a Wolf–Rayet (WR) star by its BH companion. In this work, we investigate this scenario by directly calculating the tidal excitation of oscillation modes in WR star models, determining the tidal spin-up rate, and integrating the coupled spin–orbit evolution for WR–BH binaries. We find that, for short-period orbits and massive WR stars, the tidal interaction is mostly contributed by standing gravity modes, in contrast to Zahn’s model of traveling waves, which is frequently assumed in the literature. The standing modes are less efficiently damped than traveling waves, meaning that prior estimates of tidal spin-up may be overestimated. We show that tidal synchronization is rarely reached in WR–BH binaries, and the resulting BH spins have a ≲ 0.4 for all but the shortest-period (P orb ≲ 0.5 day) binaries. Tidal spin-up in lower-mass systems is more efficient, providing an anticorrelation between the mass and spin of the BHs, which could be tested in future gravitational wave data. Nonlinear damping processes are poorly understood but may allow for more efficient tidal spin-up. We also discuss a new class of gravito-thermal modes that appear in our calculations.

A longstanding problem in galactic simulations is to resolve the dynamical friction (DF) force acting on massive black hole particles when their masses are comparable to or less than the background simulation particles. Many sub-grid models based on the traditional Chandrasekhar DF formula have been proposed, yet they suffer from fundamental ambiguities in the definition of some terms in Chandrasekhar’s formula when applied to real galaxies, as well as difficulty in evaluating continuous quantities from (spatially) discrete simulation data. In this work we present a new sub-grid dynamical friction estimator based on the discrete nature of N-body simulations, which also avoids the ambiguously-defined quantities in Chandrasekhar’s formula. We test our estimator in the GIZMO code and find that it agrees well with high-resolution simulations where DF is fully captured, with negligible additional computational cost. We also compare it with a Chandrasekhar estimator and discuss its applications in real galactic simulations.