Heating of stellar systems by binary collisions

Results from numerical integrations of random binary–binary encounters have been used to study the heating and mass loss of dense stellar systems by binary collisions. We used the obtained distributions and cross-sections to simulate binary collisions in a system with nearly Maxwellian velocity distribution. The loss of kinetic energy and mass by escape of reaction results was taken into account and thus a realistic estimate for the effect of these interactions was obtained. These results confirm the earlier estimates by other authors that in equal mass systems binaries must be rather numerous in order to be dynamically important. However, it is demonstrated that with increasing binary masses the importance of binary–binary reactions grows rapidly. A simple comparison of the heating rates due to binary–single star and binary–binary encounters shows that typically these are comparable or the latter dominates. It is concluded that collisions between binaries may contribute much to the dynamics of dense stellar systems provided the binaries are suitably massive.