General-relativistic hydrodynamics simulation of a neutron star–sub-solar-mass black hole merger
Ivan Markin, Anna Neuweiler, Adrian Abac, Swami Vivekanandji Chaurasia, Maximiliano Ujevic, Mattia Bulla, Tim Dietrich
Abstract
Over the last few years, there has been an increasing interest in sub-solar-mass black holes due to their potential to provide valuable information about cosmology or the black hole population. Motivated by this, we study observable phenomena connected to the merger of a sub-solar-mass black hole with a neutron star. For this purpose, we perform new numerical-relativity simulations of a binary system composed of a black hole with mass $0.5{M}_{\ensuremath{\bigodot}}$ and a neutron star with mass $1.4{M}_{\ensuremath{\bigodot}}$. We investigate the merger dynamics of this exotic system and provide information about the connected gravitational-wave and kilonova signals. Our study indicates that current gravitational-waveform models cannot adequately describe such systems and that phenomenological relations connecting the binary parameters with the ejecta and remnant properties do not apply to our system. Furthermore, we find a dependence of the kilonova signal on the azimuthal viewing angle due to the asymmetric mass ejection. This first-of-its-kind simulation opens the door for studying sub-solar-mass black hole--neutron star mergers and could serve as a testing ground for future model development.