Henize 2-10: the ongoing formation of a nuclear star cluster around a massive black hole

The central region of the galaxy Henize 2-10 hosts a black hole (BH) candidate with a mass Log (MBH=M⊙) = 6:3 +/- 1:1. While this putative black hole does not appear to coincide with any central stellar overdensity, it is surrounded by 11 young massive clusters with masses above 10^5 M⊙. The availability of high quality data on the structure of the galaxy and the age and mass of the clusters provides excellent initial conditions for studying the dynamical evolution of Henize 2-10's nucleus. Here we present a set of N-body simulations in which we model the future evolution of the central clusters and the black hole to understand whether and how they will merge to form a nuclear star cluster. Nuclear star clusters (NSCs) are present in a majority of galaxies with stellar mass similar to Henize 2-10. While the results depend on the choice of initial conditions, we find that a NSC with mass MNSC ≃ 4 - 6 x 10^6 M⊙ and effective radius rNSC ≃ 2:6 - 4:1 pc will form within 0:2 Gyr. This work is the first showing, in a realistic realization of the host galaxy and its star cluster system, that the formation of a bright nucleus is a process that can happen after the formation of a central massive BH leading to a composite NSC+BH central system. The cluster merging process does not significantly affect the kinematics of the BH; its position changes by ≲ 1 pc and its velocity by < 2 km/s.