Bondi-Hoyle-Lyttleton accretion in the presence of small rigid bodies around a black hole

TL;DR

This study investigates how small rigid bodies around a black hole influence relativistic accretion flows, showing that even a few obstacles can significantly increase accretion rates by inducing turbulence and thermal pressure.

Contribution

It introduces a model of relativistic accretion with small rigid bodies, revealing their impact on flow dynamics and accretion rates in a black hole environment.

Findings

Small obstacles cause bow shocks, increasing thermal pressure.

Accretion rate can increase by about 50% with few obstacles.

Flow becomes turbulent and variable due to obstacle interactions.

Abstract

We study the relativistic Bondi-Hoyle-Lyttleton accretion onto a Schwarzschild black hole (BH), which is surrounded by rigid and small, randomly distributed, bodies. These bodies are idealized representations of substructure like stars passing close to the BH, bubbles created by stellar winds or cold clumps.We explore cases where the filling factor of these bodies is small. The flow is assumed to be adiabatic and move supersonically towards the black hole. The interaction with these rigid obstacles transforms ram pressure of the flow into thermal pressure through bow shocks, slowing down the flow and making the accreting gas turbulent. As a consequence, although the flow reaches a statistically-steady state, the accretion rate presents some variability. For a flow Mach number at infinity of 4, a few of these objects (5 - 10) are enough to increase the accretion rate about 50% over the accretion rate without bodies, even though the gas is adiabatic and the filling factor of the obstacles is small.