Two-body tidal dissipation in large N-body systems

Abstract

The dynamical influence of two-body tidal dissipation on the evolution of large N-body systems is considered. We suggest that in sufficiently evolved systems an important process for the formation of ''hard'' binaries (i.e., binaries with binding energies exceeding the mean kinetic energy in the core) may be the dissipative tightening of ''soft'' binaries following tidal interactions between the two stars. The rate of hard binary formation by this mechanism is calculated and compared with previously determined binary formation rates involving the tidal capture of unbound stars and (nondissipative) three-body gravitational encounters. The energy dissipation rate in a cluster due to all two-body tidal processes is calculated. It is shown that such dissipation may accelerate the rate of core collapse above the rate given by stellar evaporation alone. Dissipation-dominated core collapse drives the core to a high-density ''singular'' state before all of the stars have evaporated. Tidal dissipation may thus promote the formation of supermassive objects (e.g., supermassive stars and/or black holes), following stellar collisions and coalescence in the core during the final stages of core collapse.