Relativistic Bondi-Hoyle-Lyttleton Accretion onto a Rotating Black-Hole: Density Gradients

TL;DR

This paper presents the first numerical study of relativistic Bondi-Hoyle-Lyttleton accretion onto a rotating black hole with density gradients, revealing steady-state flows and disk-like structures in certain conditions.

Contribution

It introduces a novel relativistic simulation of accretion with density gradients onto Kerr black holes, highlighting differences from Newtonian models.

Findings

All studied cases approach a stationary flow pattern.

Steady state is confirmed by mass and angular momentum accretion rates.

A disk-like gas configuration forms around the black hole in specific parameters.

Abstract

In this work, we present, for the first time, a numerical study of the Bondi-Hoyle accretion with density gradients in the fully relativistic regime. In this context, we consider accretion onto a Kerr Black Hole (BH) of a supersonic ideal gas, which has density gradients perpendicular to the relative motion. The set of parameters of interest in this study are the Mach number, M, the spin of the BH, a, and the density-gradient parameter of the gas, {\rho} . We show that, unlike in the Newtonian case, all the studied cases, especially those with density gradient, approach a stationary flow pattern. To illustrate that the system reaches steady state we calculate the mass and angular momentum accretion rates on a spherical surface located almost at the event horizon. In the particular case of M = 1, {\rho} = 0.5 and BH spin a = 0.5, we observe a disk-like configuration surrounding the BH. Finally, we present the gas morphology and some of its properties.