Dynamics of star associations in an SMBH-IMBH system: The case of IRS13 in the Galactic centre

TL;DR

This study uses high-precision N-body simulations to investigate the dynamics of star clusters near the Galactic centre, concluding that the IRS13 clump is likely a transient feature caused by tidal forces, not an IMBH-hosting cluster.

Contribution

The paper provides the first detailed numerical analysis of IRS13-like star clusters, demonstrating that an IMBH is not necessary to explain observed velocity dispersions.

Findings

IRS13-like clusters cannot remain bound if they contain an IMBH of thousands of solar masses.

Velocity dispersion in IRS13 can be explained solely by tidal forces from the SMBH.

IRS13 is likely a transient stellar clump, not a bound star cluster with an IMBH.

Abstract

Context: The existence of intermediate-mass black holes (IMBHs) still poses challenges to theoretical and observational astronomers. Several candidates have been proposed, including the one in the IRS13 cluster in the Galactic centre, where the evidence is based on the velocity dispersion of its members, however, none have been confirmed to date. Aims: We aim to gain insights into the presence of an IMBH in the Galactic centre by a numerical study of the dynamical interplay between an IMBH and star clusters (SCs) in the vicinity of a supermassive black hole (SMBH). Methods: We use high-precision N-body models of IRS13-like SCs in the Galactic centre, and of more massive SCs that fall into the centre of the Galaxy from larger distances. Results: We find that at IRS13's physical distance of 0.4 pc, an IRS13-size SC cannot remain gravitationally bound even if it contains an IMBH of thousands $M_\odot$. Thus, IRS13 appears to be an incidental present-day clumping of stars. Furthermore, we show that the velocity dispersion of tidally disrupted SCs (the likely origin of IRS13) can be fully accounted for by the tidal forces of the central SMBH; the IMBH's influence is not essential.