Gravitational radiation from colliding clusters - Newtonian simulations in three dimensions

Gravitational radiation from colliding star cluster is studied using a Newtonian N-body code. Fully three-dimensional cases, which cannot yet be treated reliably with existing hydrodynamic codes for fluid stars can be handled. Comparing colliding axisymmetric star cluster to colliding axisymmetric fluid stars provides information on the importance of shock waves in the generation of gravitational waves. Comparison of axisymmetric and nonaxisymmetric star cluster scenarios then provides information on the importance of asymmetry. Numerical results are compared with simple analytic models. Two important effects reduce the radiation from extended objects relative to one's expectation from simple point-mass models: phase incoherence (destructive interference) and collisionless dissipation (violent relaxation). Because of phase incoherence, the gravitational radiation from the head-on collision of two fluid stars can actually be less than the correspondig emission from colliding clusters, despite the absence of shocks in the collisionless case. The present calculations include head-on, free-fall collisions, nonaxisymmetric parabolic encounters, hyperbolic collisions, and the tidal disruption and merger of close binary clusters. 27 refs