Hydrodynamical studies of wind accretion onto compact objects: Two-dimensional calculations

We present the results of hydrodynamical simulations of nonaxisymmetric gas flow past a gravitating compact object in two dimensions. Calculations were performed with uniform flow as well as with transverse velocity and density gradients. We find that the flow is highly nonsteady, exhibiting the "flip-flop" behavior seen in previous studies, in which accretion disks form with alternating directions of rotation. We investigate the periodicity of the flip-flop behavior and study the effects of spatial resolution on the results. We find that the flip-flop motion creates accretion torques that, in some cases, may be large enough to explain the erratic spin behavior observed in Be-type X-ray pulsars.