Nuclear star clusters (NSCs) are dense stellar clusters observed in galactic nuclei, that occasionally host a central black hole. They may form out of the inspiral of multiple star clusters. Here we test the possibility that the constituent clusters host intermediate mass black holes (IMBHs). Using an N-body code we examine the dynamics of the IMBHs and their effects on the NSC formation and evolution. We find that IMBHs inspiral to the core of the newly formed NSC and segregate there. Although the IMBH scatter each other and the stars, none is ejected from the NSC. The IMBHs are excited to high eccentricities and their radial density profile develops a steep power-law cusp. The stars also develop a power-law cusp (instead of the central core that forms in their absence), but with a shallower slope. The relaxation rate of the NSC accelerates due to the presence of IMBHs as massive-perturbers. This in turn fills the loss-cone and boosts the tidal disruption rate of stars both by the MBH and the IMBHs to a value excluded by observations. The observed lower rate provides a cumulative constraint on the existence of IMBHs in NSCs.
A. Mastrobuono-Battisti, H. Perets and A. Loeb
Fri, 14 Mar 14