Behavior of dynamical ejecta from black hole-neutron star binaries near neutron star disruption limit

Black hole–neutron star (BHNS) binaries are important sources of gravitational waves (GWs) and are also a proposed mechanism for UV/optical/infrared kilonova signals. In order for a BHNS merger to produce a kilonova signal, the spin of the black hole must be sufficiently high, creating a tidal field strong enough to disrupt the neutron star. With spins above this threshold, a disrupting BHNS binary will usually eject a few percent of a solar mass of matter, leading to observable kilonovae driven by radioactive decays in the ejecta which may be used as a counterpart to GW observations of BHNS systems. Below this spin limit, the neutron star may plunge into the black hole in its entirety. In this talk, I summarize preliminary results from simulations of BHNS binaries with black hole spins just above and below the predicted spin limit. These simulations serve as an exploration into the behavior of dynamical ejecta close to this threshold and were run with the Spectral Einstein Code (SpEC).