Does IRS13 require an intermediate-mass black hole?

Abstract

We investigate whether the Galactic-centre association IRS13 requires an intermediate-mass black hole (IMBH) to remain bound. Using high-precision $N$-body calculations of IRS13-like systems orbiting the Milky Way supermassive black hole (SMBH), as well as simulations of more massive infalling clusters, we find that an IRS13-sized cluster dissolves on a very short timescale even when an IMBH of $4\times 10^4{M}_{\odot }$ is present. The observed velocity dispersion can arise naturally from the tidal field of Sgr A* and the infall event itself; therefore, it need not imply a central IMBH. In the infalling-cluster runs, tidal stripping produces transient disks, spiral-like structures, and ring-like overdensities. These features suggest a broader interpretation: IRS13 is best viewed as a temporary phase-space overdensity, analogous in mechanism (though not in scale) to phase-wrapped shells and streams in disrupted galaxies.

4 pages, 3 figures, to appear in Proceedings of IAU Symposium No. 405 "Traversing the Galactic Center in Space and Time"