Bondi Accretion in the Presence of Vorticity

The classical Bondi-Hoyle formula gives the accretion rate onto a pointparticle of a gas with a uniform density and velocity. However, the Bondi-Hoyleproblem considers only gas with no net vorticity, while in a real astrophysicalsituation accreting gas invariably has at least a small amount of vorticity. Wetherefore consider the related case of accretion of gas with constantvorticity, for the cases of both small and large vorticity. We confirm thefindings of earlier two dimensional simulations that even a small amount ofvorticity can substantially change both the accretion rate and the morphologyof the gas flow lines. We show that in three dimensions the resulting flowfield is non-axisymmetric and time dependent. The reduction in accretion rateis due to an accumulation of circulation near the accreting particle. Using acombination of simulations and analytic treatment, we provide an approximateformula for the accretion rate of gas onto a point particle as a function ofthe vorticity of the surrounding gas.Comment: 34 pages, 10 figures, accepted for publication in Ap