Dynamical evolution of dense clusters of compact stars

We present results of multicomponent Fokker-Planck simulations of the dynamical evolution of dense clusters of compact stars (neutron stars or black holes). The dominant physical process is the dissipative formation of binaries through gravitational radiation emission and their subsequent merger. Our simulations predict a rapid buildup of massive black holes in the cluster core resulting from successive binary mergers and mass segregation. Starting with a cluster of ~ 10⁸^ stellar-mass compact stars, we can follow the evolution until black holes of mass m >~ 100 Mₛun_ have formed. We stop the simulation when the cluster core has shrunk so much that the Fokker-Planck equation is no longer valid. The binary systems that form are promising sources of gravitational radiation for detection by ground-based laser interferometers. The ultimate fate of the cluster is discussed. We also discuss the possibility of large mass loss due to explosions during the evolution of neutron-star binaries, and the effect that this would have on the cluster evolution. In an appendix we compare three methods of including binary formation and stellar mergers in the Fokker-Planck equation; two of the methods are approximate, and the third is exact. Fokker-Planck simulations using the three methods give results that are in close agreement; our new approximate method is considerably faster than the other two and should be adequate for most applications.