Towards the million body problem on the computer - no news since the three-body problem?

Abstract

Astrophysical Challenges which demand the solution of the one million (or more) gravitating body problem are briefly discussed for the fields of cosmology, galactic nuclei and globular star clusters. Results from the classical three-body problem are to be combined with methods of statistical mechanics or thermodynamics in order to provide a reasonable model for astrophysically relevant particle numbers of the order 10**4-10**8. For high-precision modelling of star clusters and galactic nuclei over the required hundreds and thousands of crossing times specially tailored ``brute-force'' N-body integration methods are used together with special purpose hardware. A recent implementation of such code on a general purpose parallel computer is presented. After a comparison of the relevance of different N-body algorithms a new concept for a more flexible customized special purpose computer based on a combination of GRAPE and FPGA is proposed. It is an ideal machine for all kinds of N-body simulations using neighbour schemes, as the Ahmad-Cohen direct N-body codes and smoothed particle hydrodynamics (SPH) for systems including interstellar gas dynamics.