High-resolution magnetohydrodynamics simulation of black hole-neutron star merger: Mass ejection and short gamma-ray burst

TL;DR

This study presents a high-resolution simulation of a black hole-neutron star merger, revealing detailed mechanisms of mass ejection, jet formation, and implications for gamma-ray bursts and nucleosynthesis.

Contribution

First self-consistent simulation demonstrating the formation of a collimated jet and wind in black hole-neutron star mergers with high resolution.

Findings

Discovery of thermally driven torus wind and funnel wall formation.

Identification of turbulence from magnetorotational and Kelvin-Helmholtz instabilities.

High resolution is crucial for accurate modeling of merger dynamics.

Abstract

We report results of a high-resolution numerical-relativity simulation for the merger of black hole-magnetized neutron star binaries on Japanese supercomputer "K". We focus on a binary that is subject to tidal disruption and subsequent formation of a massive accretion torus. We find the launch of thermally driven torus wind, subsequent formation of a funnel wall above the torus and a magnetosphere with collimated poloidal magnetic field, and high Blandford-Znajek luminosity. We show for the first time this picture in a self-consistent simulation. The turbulence-like motion induced by the non-axisymmetric magnetorotational instability as well as the Kelvin-Helmholtz instability inside the accretion torus works as an agent to drive the mass accretion and converts the accretion energy to thermal energy, which results in the generation of a strong wind. By an in-depth resolution study, we reveal that high resolution is essential to draw such a picture. We also discuss the implication for the r-process nucleosynthesis, the radioactively-powered transient emission, and short gamma-ray bursts.