STATISTICS OF N-BODY SIMULATIONS .2. EQUAL MASSES AFTER CORE COLLAPSE

This paper presents and analyses statistical results from a large number of N-body simulations of isolated systems with equal masses, in which 250 less than or equal to N less than or equal to 2000. It concentrates on the phase starting around the end of core collapse. Binaries play a crucial role, and we find that the total energy of bound pairs is in line with theoretical expectations. Interpretation of the total number is complicated by the presence of a number of binaries on the hard/soft threshold. Interactions of hard binaries are consistent with the Spitzer cross-section. The spatial evolution of the half-mass radius after core collapse nearly follows classical theory, and, by comparison with Fokker-Planck and gas models, allows a redetermination of the effective thermal conductivity and the argument of the Coulomb logarithm in the expression for the relaxation time. The evolution of the inner parts of the system around the time of core bounce is consistent with these simplified models, provided that the continuous production of energy, as is usually assumed, is replaced by a model of stochastic energy production. Similarly, postcollapse evolution of the core requires a modest recalibration of the coefficient of energy generation, especially for small N. These remarks refer to the behaviour averaged over many models; individual cases show alternate and irregular phases of expansion and recollapse. The distributions of velocity dispersion and anisotropy become remarkably homologous soon after core bounce. The bound mass of the systems very nearly follows a power law with time. A small number of escapers, presumed to be those associated with binary activity, dominate the energy that is carried off: the distribution of energies of escapers changes abruptly at the end of core collapse. The 'internal' energy of escaping binaries is consistent with theoretical expectations, and again supports Spitzer's reaction cross-section for hard binaries.