2017MNRAS.471.3127C

We study the relativistic Bondi-Hoyle-Lyttleton accretion on to 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 BH. 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 per cent over the accretion rate without bodies, even though the gas is adiabatic and the filling factor of the obstacles is small.