Dynamics of star associations in an SMBH–IMBH system

The case of IRS13 in the Galactic centre

¹ Astronomical Institute of the Czech Academy of Sciences, Boční II 1401, 141 00 Prague 4, Czech Republic
² Department of Astronomy, Indiana University, Swain Hall West, 727 E 3 rd Street, Bloomington, IN 47405, USA
³ I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
⁴ Max Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁵ Dept. of Physics and Astronomy “A. Righi”, University of Bologna, Via Gobetti 93/2, Bologna, Italy

^★ Corresponding author; pavlik@asu.cas.cz

Received: 29 August 2024
Accepted: 18 October 2024

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 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.