Numerical simulations of axisymmetric hydrodynamical Bondi-Hoyle accretion on to a compact object

Abstract

Bondi-Hoyle accretion configurations occur as soon as a gravitating body is immersed in an ambient medium with a supersonic relative velocity. From wind-accreting X-ray binaries to runaway neutron stars, such a regime has been witnessed many times and is believed to account for shock formation, the properties of which can be only marginally derived analytically. In this paper, we present the first results of the numerical characterization of the stationary flow structure of Bondi-Hoyle accretion on to a compact object, from the large-scale accretion radius down to the vicinity of the compact body. For different Mach numbers, we study the associated bow shock. It turns out that those simulations confirm the analytical prediction by Foglizzo & Ruffert concerning the topology of the inner sonic surface with an adiabatic index of 5/3. They also enable us to derive the related mass accretion rates, the position and the temperature of the bow shock, as function of the flow parameters, along with the transverse density and temperature profiles in the wake.