MOCCA code for star cluster simulations – IV. A new scenario for intermediate mass black hole formation in globular clusters

Abstract

We 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 discuss the necessary conditions to initiate the process of intermediate mass black hole formation and the influence of an intermediate mass black hole on the host global globular cluster properties. We discuss two scenarios for intermediate mass black hole formation. The SLOW and FAST scenarios. They occur later or earlier in the cluster evolution and require smaller or extremely large central densities, respectively. In our simulations, the formation of intermediate mass black holes is highly stochastic. In general, higher formation probabilities follow from larger cluster concentrations (i.e. central densities). We further discuss possible observational signatures of the presence of intermediate mass black holes in globular clusters that follow from our simulations. These include the spatial and kinematic structure of the host cluster, possible radio, X-ray and gravitational wave emissions due to dynamical collisions or mass-transfer and the creation of hypervelocity main sequence escapers during strong dynamical interactions between binaries and an intermediate mass black hole. All simulations discussed in this paper were performed with the MOCCA Monte Carlo code. MOCCA accurately follows most of the important physical processes that occur during the dynamical evolution of star clusters but, as with other dynamical codes, it approximates the dissipative processes connected with stellar collisions and binary mergers.

Search for intermediate mass black hole binaries in the first observing run of Advanced LIGO

“…Again, while the formation mechanisms are unknown, it is postulated that an IMBHB can be formed in a GC with a fraction of binary stars higher than ≈10% [81] or as a result of a merger of two clusters, each of which contains an IMBH [82,83]. While no direct observational evidence of IMBHBs exists, this hypothesis is supported by recent simulations of dense stellar systems [84]. Measurements of an IMBHB's components would allow us to not only constrain IMBH formation channels, but also make statements on the link between IMBHs and both ultraluminous [85] and hyperluminous [86][87][88] x-ray systems.…”

The Close Stellar Companions to Intermediate-Mass Black Holes

“…In simulation, the most accurate (but also computationally expensive) approach to treating the multiphysics sphere-ofinfluence dynamics is direct N-body evolution of the stars' orbital motion (Aarseth 2003). Companion objects to IMBHs have been mentioned in previous studies (e.g., Baumgardt et al 2004bBaumgardt et al , 2006Blecha et al 2006;Konstantinidis et al 2013;Leigh et al 2014;Giersz et al 2015). However, in this paper we present the first systematic study of IMBH companions in a dense cluster context that takes advantage of the accuracy of direct N-body integration.…”

N-body modelling of globular clusters: masses, mass-to-light ratios and intermediate-mass black holes

“…In addition, due to their high central densities and high stellar encounter rates, globular clusters are also unique environments for the creation of exotic stars like blue stragglers (Bailyn 1995;Davies, Piotto & de Angeli 2004), low-mass X-ray binaries (Verbunt 1993;Pooley et al 2003) and millisecond pulsars (Manchester et al 1991). The high stellar densities in globular cluster could also give rise to the creation of intermediate-mass black holes (Portegies Zwart & McMillan 2002;Portegies Zwart et al 2004;Giersz et al 2015), which might be the progenitors of supermassive black holes in Galactic centers. Globular clusters are finally important environments for the creation of tight black hole binaries which merge through the emission of gravitational waves (Banerjee, Baumgardt & Kroupa ⋆ E-mail: h.baumgardt@uq.edu.au 2010; Downing et al 2011;Askar et al 2016).…”