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Abstract Periodic nuclear transients have been detected with increasing frequency, with one such system—ASASSN14ko—exhibiting highly regular outbursts on a timescale of 114 ± 1 days. It has been postulated that the outbursts from this source are generated by the repeated partial disruption of a star, but how the star was placed onto such a tightly bound orbit about the supermassive black hole remains unclear. Here we use analytic arguments and threebody integrations to demonstrate that the Hills mechanism, where a binary system is destroyed by the tides of the black hole, can lead to the capture of a star onmore »Free, publiclyaccessible full text available April 1, 2023

Abstract Corecollapse supernovae can display evidence of interaction with preexisting, circumstellar shells of material by rebrightening and forming spectral lines, and can even change types as hydrogen appears in previously hydrogenpoor spectra. However, a recently observed corecollapse supernova—SN 2019tsf—was found to brighten after roughly 100 days after it was first observed, suggesting that the supernova ejecta was interacting with surrounding material, but it lacked any observable emission lines and thereby challenged the standard supernovainteraction picture. We show through linear perturbation theory that delayed rebrightenings without the formation of spectral lines are generated as a consequence of the finite soundcrossing timemore »Free, publiclyaccessible full text available March 1, 2023

Abstract Tidal disruption events with tidal radius r t and pericenter distance r p are characterized by the quantity β = r t / r p , and “deep encounters” have β ≫ 1. It has been assumed that there is a critical β ≡ β c ∼ 1 that differentiates between partial and full disruption: for β < β c a fraction of the star survives the tidal interaction with the black hole, while for β > β c the star is completely destroyed, and hence all deep encounters should be full. Here we show that this assumption ismore »Free, publiclyaccessible full text available March 1, 2023

Abstract We develop a Newtonian model of a deep tidal disruption event (TDE), for which the pericenter distance of the star, r p , is well within the tidal radius of the black hole, r t , i.e., when β ≡ r t / r p ≫ 1. We find that shocks form for β ≳ 3, but they are weak (with Mach numbers ∼1) for all β , and that they reach the center of the star prior to the time of maximum adiabatic compression for β ≳ 10. The maximum density and temperature reached during the TDE followmore »Free, publiclyaccessible full text available February 1, 2023

Abstract Upon entering the tidal sphere of a supermassive black hole, a star is ripped apart by tides and transformed into a stream of debris. The ultimate fate of that debris, and the properties of the bright flare that is produced and observed, depends on a number of parameters, including the energy of the center of mass of the original star. Here we present the results of a set of smoothed particle hydrodynamics simulations in which a 1 M ⊙ , γ = 5/3 polytrope is disrupted by a 10 6 M ⊙ supermassive black hole. Each simulation has amore »Free, publiclyaccessible full text available January 1, 2023

ABSTRACT When a star passes close to a supermassive black hole (BH), the BH’s tidal forces rip it apart into a thin stream, leading to a tidal disruption event (TDE). In this work, we study the postdisruption phase of TDEs in general relativistic hydrodynamics (GRHD) using our GPUaccelerated code hamr. We carry out the first gridbased simulation of a deeppenetration TDE (β = 7) with realistic system parameters: a black holetostar mass ratio of 106, a parabolic stellar trajectory, and a nonzero BH spin. We also carry out a simulation of a tilted TDE whose stellar orbit is inclined relative tomore »Free, publiclyaccessible full text available December 30, 2022

Abstract The distribution of orbital energies imparted into stellar debris following the close encounter of a star with a supermassive black hole is the principal factor in determining the rate of return of debris to the black hole, and thus in determining the properties of the resulting lightcurves from such events. We present simulations of tidal disruption events for a range of β ≡ r t / r p where r p is the pericenter distance and r t the tidal radius. We perform these simulations at different spatial resolutions to determine the numerical convergence of our models. We comparemore »Free, publiclyaccessible full text available December 1, 2022

Abstract We present longduration numerical simulations of the tidal disruption of stars modeled with accurate stellar structures and spanning a range of pericenter distances, corresponding to cases where the stars are partially and completely disrupted. We substantiate the prediction that the latetime powerlaw index of the fallback rate n ∞ ≃ −5/3 for full disruptions, while for partial disruptions—in which the central part of the star survives the tidal encounter intact—we show that n ∞ ≃ −9/4. For the subset of simulations where the pericenter distance is close to that which delineates full from partial disruption, we find that amore »Free, publiclyaccessible full text available November 29, 2022

ABSTRACT The dissociation and ionization of hydrogen, during the formation of giant planets via core accretion, reduce the effective adiabatic index γ of the gas and could trigger dynamical instability. We generalize the analysis of Chandrasekhar, who determined that the threshold for instability of a selfgravitating hydrostatic body lies at γ = 4/3, to account for the presence of a planetary core, which we model as an incompressible fluid. We show that the dominant effect of the core is to stabilize the envelope to radial perturbations, in some cases completely (i.e. for all γ > 1). When instability is possible,more »

ABSTRACT Synchrotronemitting, nonthermal filaments (NTFs) have been observed near the Galactic centre for nearly four decades, yet their physical origin remains unclear. Here we investigate the possibility that NTFs are produced by the destruction of molecular clouds by the gravitational potential of the Galactic centre. We show that this model predicts the formation of a filamentary structure with length on the order of tens to hundreds of pc, a highly ordered magnetic field along the axis of the filament, and conditions conducive to magnetic reconnection that result in particle acceleration. This model therefore yields the observed magnetic properties of NTFsmore »