The Ecology of Star Clusters and Intermediate‐Mass Black Holes in the Galactic Bulge

We simulate the inner 100pc of the Milky-Way Galaxy to study the formationand evolution of the population of star clusters and intermediate mass blackholes. For this study we perform extensive direct N-body simulations of thestar clusters which reside in the bulge, and of the inner few tenth of parsecsof the super massive black hole in the Galactic center. In our N-bodysimulations the dynamical friction of the star cluster in the tidal field ofthe bulge are taken into account via (semi)analytic soluations. The N-bodycalculations are used to calibrate a (semi)analytic model of the formation andevolution of the bulge. We find that about 10% of the clusters born within100pc of the Galactic center undergo core collapse during their inwardmigration and form intermediate-mass black holes (IMBHs) via runaway stellarmerging. After the clusters dissolve, these IMBHs continue their inward drift,carrying a few of the most massive stars with them. We predict that regionwithin about 10 parsec of the SMBH is populated by about 50IMBHs of some1000Msun. Several of these are expected to be accompanied still by some of themost massive stars from the star cluster. We also find that within a fewmilliparsec of the SMBH there is a steady population of several IMBHs. Thispopulation drives the merger rate between IMBHs and the SMBH at a rate of aboutone per 10Myr, sufficient to build the accumulate majority of mass of the SMBH.Mergers of IMBHs with SMBHs throughout the universe are detectable by LISA, ata rate of about two per week.