Monte Carlo modelling of globular star clusters - many primordial binaries, IMBH formation

TL;DR

This paper uses Monte Carlo simulations to study the evolution of star clusters with high binary fractions, comparing results to observations and proposing a new scenario for intermediate mass black hole formation through dynamical interactions.

Contribution

It introduces a detailed Monte Carlo model for star cluster evolution with high binary fractions and proposes a novel formation mechanism for intermediate mass black holes.

Findings

Simulations match observed binary fraction trends in clusters.

Rapid binary destruction explained by density-dependent processes.

Proposed formation scenario for intermediate mass black holes in dense clusters.

Abstract

We will discuss the evolution of star clusters with an large initial binary fraction, up to 95%. The initial binary population is chosen to follow the invariant orbital-parameter distributions suggested by Kroupa (1995). The Monte Carlo MOCCA simulations of star cluster evolution are compared to the observations of Milone et al. (2012) for photometric binaries. It is demonstrated that the observed dependence on cluster mass of both the binary fraction and the ratio of the binary fractions inside and outside of the half mass radius are well recovered by the MOCCA simulations. This is due to a rapid decrease in the initial binary fraction due to the strong density-dependent destruction of wide binaries described by Marks, Kroupa & Oh (2011). We also discuss a new scenario for the formation of intermediate mass black holes in dense star clusters. In this scenario, intermediate mass black holes are formed as a result of dynamical interactions of hard binaries containing a stellar mass black hole, with other stars and binaries. We will discuss the necessary conditions to initiate the process of intermediate mass black hole formation and the dependence of its mass accretion rate on the global cluster properties.