Merger of black hole-neutron star binaries: nonspinning black hole case

TL;DR

This study simulates the merger of a nonspinning black hole and neutron star in full general relativity, revealing that most neutron star material is swallowed, resulting in a small accretion disk, which impacts models of such mergers.

Contribution

First full general relativity simulation of nonspinning BH-NS merger showing tidal disruption and disk formation outcomes.

Findings

Approximately 80% of NS material is swallowed by the BH.

Small accretion disk of about 0.3 solar masses forms.

No large disk of around 1 solar mass is produced from nonspinning BH-NS mergers.

Abstract

We perform a simulation for merger of a black hole (BH)-neutron star (NS) binary in full general relativity preparing a quasicircular state as initial condition. The BH is modeled by a moving puncture with no spin and the NS by the $\Gamma$-law equation of state with $\Gamma=2$. Corotating velocity field is assumed for the NS. The mass of the BH and the rest-mass of the NS are chosen to be $\approx 3.2 M_{\odot}$ and $\approx 1.4 M_{\odot}$ with relatively large radius of the NS $\approx 14$ km. The NS is tidally disrupted near the innermost stable orbit but $\sim 80%$ of the material is swallowed into the BH with small disk mass $\sim 0.3M_{\odot}$ even for such small BH mass $\sim 3M_{\odot}$. The result indicates that the system of a BH and a massive disk of $\sim M_{\odot}$ is not formed from nonspinning BH-NS binaries, although a disk of mass $\sim 0.1M_{\odot}$ is a possible outcome.