General Relativistic Magnetohydrodynamic Bondi--Hoyle Accretion

TL;DR

This study provides a comprehensive relativistic MHD simulation of Bondi--Hoyle accretion onto a moving Kerr black hole, revealing magnetic effects on accretion flow and density depletion.

Contribution

It is the first fully relativistic MHD simulation of axisymmetric Bondi--Hoyle accretion onto a Kerr black hole, highlighting magnetic pressure effects.

Findings

Magnetic fields cause matter density depletion downstream.

Accretion rates depend on flow parameters like sound speed and velocity.

Magnetic pressure influences the accretion flow structure.

Abstract

In this paper we present a fully relativistic study of axisymmetric magnetohydrodynamic Bondi--Hoyle accretion onto a moving Kerr black hole. The equations of general relativistic magnetohydrodynamics are solved using high resolution shock capturing methods. In this treatment we consider the ideal MHD limit. The parameters of interest in this study are the adiabatic constant $\Gamma$, the asymptotic speed of sound $c_{s}^{\infty}$, and the plasma beta parameter $\beta_{P}$. We focus the investigation on the parameter regime in which the flow is supersonic, or when $v_\infty \ge c_{s}^{\infty}$. In some cases, subsonic asymptotic flows are considered for comparison purposes. We study the accretion rates of the total energy and momenta, as well as the hydrodynamic energy and momentum accretion rates. The models presented in this study exhibit a matter density depletion in the downstream region of the black hole which tends to vacuum $(\rho_0=0)$ in convergence tests. This feature is due to the presence of the magnetic field, more specifically the magnetic pressure, and is not seen in previous purely hydrodynamic studies.