SCYON Abstract

Received on May 18 2001

A new Monte Carlo code for star cluster simulations: I.~Relaxation

AuthorsMarc Freitag (1, 2), Willy Benz (2)
Affiliation(1) Observatoire de Genève, CH-1290 Sauverny, Switzerland
(2) Physikalisches Institut, Universität Bern, CH-3012 Bern, Switzerland
Accepted byAstronomy & Astrophysics


We have developed a new simulation code aimed at studying the stellar dynamics of a galactic central star cluster surrounding a massive black hole. In order to include all the relevant physical ingredients (2-body relaxation, stellar mass spectrum, collisions, tidal disruption, ...), we chose to revive a numerical scheme pioneered by Hénon in the 70's. It is basically a Monte Carlo resolution of the Fokker-Planck equation. It can cope with any stellar mass spectrum or velocity distribution. Being a particle-based method, it also allows one to take stellar collisions into account in a very realistic way. This first paper covers the basic version of our code which treats the relaxation-driven evolution of a stellar cluster without a central BH. A technical description of the code is presented, as well as the results of test computations. Thanks to the use of a binary tree to store potential and rank information and of variable time steps, cluster models with up to 2 x 106 particles can be simulated on a standard personal computer and the CPU time required scales as Np ln(Np) with the particle number Np. Furthermore, the number of simulated stars needs not be equal to Np but can be arbitrarily larger. A companion paper will treat further physical elements, mostly relevant to galactic nuclei.