Dynamics of star associations in an SMBH–IMBH system

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 through 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 used 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-sized SC cannot remain gravitationally bound even if it contains an IMBH of thousands of M ⊙ . 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.

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