Dynamics of a Superdense Cluster of Black Holes and the Formation of the Galactic SMBH

TL;DR

This study uses high-precision N-body simulations with relativistic corrections to explore how dense clusters of intermediate-mass black holes can merge and potentially grow into supermassive black holes, shedding light on galactic center formation.

Contribution

It introduces detailed relativistic N-body simulations of dense black hole clusters, revealing a pathway for black hole mergers leading to supermassive black hole formation.

Findings

Multiple black hole mergers occur, forming a single massive object.

Significant gravitational wave emission is produced during mergers.

The process may explain the growth of supermassive black holes in galactic centers.

Abstract

The center of our Galaxy is known to host a massive compact object, Sgr A$^*$, which is commonly considered as a super-massive black hole of $\sim 4\times 10^6$ M$_\odot$. It is surrounded by a dense and massive nuclear star cluster, with a half mass radius about $5$~pc and a mass larger than $10^{7}$ M$_\odot$. In this paper we studied the evolutionary fate of a very dense cluster of intermediate mass black holes, possible remnants of the dissipative orbital evolution of massive globular cluster hosts. We performed a set of high precision $N$-body simulations taking into account deviations from pure Newtonian gravitational interaction via a Post Newtonian development up to $2.5$ order, which is the one accounting for energy release by gravitational wave emission. The violent dynamics of the system leads to various successive merger events such to grow a single object containing $\sim 25$ per cent of the total cluster mass before partial dispersal of the cluster, and such to generate, in different bursts, a significant quantity of gravitational waves emission. If generalized, the present results suggest a mechanism of mass growth up to the scale of a super massive black hole.