SIMULATION OF INTERACTIONS OF AN ORBITING COMPACT STAR WITH AN ACCRETION DISK BY SMOOTHED PARTICLE HYDRODYNAMICS

We simulate interaction between a thin accretion disk (two-dimensional ) around a massive black hole and an orbiting compact star, coplanar w ith the disk. We use the smoothed particle hydrodynamics technique for this purpose. We take into account the following main processes: (1) loss of energy and angular momentum of the companion due to the gravit ational wave emission and (2) gain of momentum and angular momentum of the companion due to its accretion of the disk gas in the super-Keple rian region. We choose various mass ratios and accretion rates to demo nstrate (a) formation of spiral shocks in the disk around the primary, (b) formation of a smaller disk around the secondary, and finally and most important, (c) stabilization of the orbit of the companion again st coalescence with the primary. Such a stabilization, which was until now only a theoretical possibility, is realized by supplying a suitab le amount of angular momentum from the disk to the companion to compen sate for the loss due to gravitational waves.