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

Abstract

The center of our Galaxy is known to host a massive compact object, Sgr A${}^{\ast }$, 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.

14 pages, 13 figures, 4 tables. In press in Monthly Notices of the Royal Astronomical Society

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• Formation of supermassive black holes in galactic nuclei II: retention and growth of seed intermediate-mass black holes
• Supermassive black hole formation via collisions in black hole clusters
• Study on the detectability of gravitational radiation from single-binary encounters between black holes in nuclear star cluster: the case of hyperbolic flybys
• Orbital precession of stars in the Galactic center
• Gravitational wave signals from long lasting binary-single black hole encounters
• Impact of a granular mass distribution on the orbit of S2 in the Galactic center
• Massive star clusters detected by JWST as natural birth places to form intermediate-mass black holes