Monte Carlo simulations of star clusters -- III. A million body star cluster

Abstract

A revision of Stodolkiewicz's Monte Carlo code is used to simulate the evolution of million body star clusters. The new method treats each superstar as a single star and follows the evolution and motion of all individual stellar objects. A survey of the evolution of N-body systems influenced by the tidal field of a parent galaxy and by stellar evolution is presented. The process of energy generation is realized by means of appropriately modified versions of Spitzer's and Mikkola's formulae for the interaction cross section between binaries and field stars and binaries themselves. The results presented are in good agreement with theoretical expectations and the results of other methods. During the evolution, the initial mass function (IMF) changes significantly. The local mass function (LMF) around the half--mass radius closely resembles the actual global mass function (GMF). At the late stages of evolution the mass of the evolved stars inside the core can be as high as 97% of the total mass in this region. For the whole system, the evolved stars can compose up to 67% of the total mass. The evolution of cluster anisotropy strongly depends on initial cluster concentration, IMF and the strength of the tidal field. The results presented are the first step in the direction of simulating the evolution of real globular clusters by means of the Monte Carlo method.