Tidal disruption and tidal coalescence in binary stellar systems

Abstract

Tidal effects in binary stellar systems are considered. The rate of increase of the binding energy of a component and the rate of decrease of the energy of the orbital motion of the binary are estimated under the simplifying assumption that the motion of the stars in the stellar systems may be neglected in comparison with the orbital motion of the binary system. The time of disruption of a component and the time of coalescence of the pair are obtained as functions of the separation and mass ratio of the binary for distant as well as close overlapping pairs. Applications are made to globular clusters and binary galaxies. For a pair of identical galaxies the rate of coalescence of the pair is faster than that of the disruption of the components. A study of the tidal effects at the median radius indicates that a pair of contact spherical galaxies moving in circular relative orbit will merge and form a single system in a time interval less than three periods of revolution.