Statistics of N-body simulations - III. Unequal masses

Abstract

We describe results from large numbers of N-body simulations containing from 250 to 1000 stars each. The distribution of stellar masses is a power law, and the systems are isolated. While the collapse of the core exhibits the expected segregation of different masses, we find that the post-collapse evolution is, at a first approximation, homologous. This is surprising because there is no reason for supposing that mass segregation should not continue to have a substantial effect on the evolution of the cluster. In fact, the spatial distribution of the mean stellar mass is nearly static throughout the post-collapse regime, except for the overall expansion of the systems, and this helps to explain why the post-collapse evolution is nearly self-similar. Selfsimilarity is also exhibited by the distribution of anisotropy and the profile of departures from equipartition, which show little change during the post-collapse phase. The departures from energy equipartition and isotropy are small in the core and increase with radius. During post-collapse evolution, massive stars (mainly) are removed from the system by binary activity. This effect dominates the preferential escape of low-mass stars owing to standard two-body relaxation processes.