MOCCA survey data base - I. Dissolution of tidally filling star clusters harbouring black hole subsystems

Abstract

We investigate the dissolution process for dynamically evolving star clusters embedded in an external tidal field by exploring the MOCCA survey data base I, with focus on the presence and evolution of a stellar-mass black hole subsystem. We argue that the presence of a black hole subsystem can lead to the dissolution of tidally filling star clusters and this can be regarded as a third type of cluster dissolution mechanism (in addition to well-known mechanisms connected with strong mass-loss due to stellar evolution and mass-loss connected with the relaxation process). This third process is characterized by abrupt cluster dissolution connected with the loss of dynamical equilibrium. The abrupt dissolution is powered by strong energy generation from a stellar-mass black hole subsystem accompanied by tidal stripping. Additionally, we argue that such a mechanism should also work for even tidally underfilling clusters with topheavy initial mass function. Observationally, star clusters which undergo dissolution powered by the third mechanism would look as a 'dark cluster' i.e. composed of stellarmass black holes surrounded by an expanding halo of luminous stars, and they should be different from 'dark clusters' harbouring intermediate mass black holes as discussed by Askar et al. An additional observational consequence of an operation of the third dissolution mechanism should be a larger than expected abundance of free floating black holes in the Galactic halo.