Stellar Remnants in Galactic Nuclei: Mass Segregation

The study of how stars distribute themselves around a massive black hole(MBH) in the center of a galaxy is an important prerequisite for theunderstanding of many galactic-center processes. These include the observedoverabundance of point X-ray sources at the Galactic center, the prediction ofrates and characteristics of tidal disruptions of extended stars by the MBH andof inspirals of compact stars into the MBH, the latter being events of highimportance for the future space borne gravitational wave interferometer LISA.In relatively small galactic nuclei, hosting MBHs with masses in the range10^5-10^7 Msun, the single most important dynamical process is 2-bodyrelaxation. It induces the formation of a steep density cusp around the MBH andstrong mass segregation, as more massive stars lose energy to lighter ones anddrift to the central regions. Using a spherical stellar dynamical Monte-Carlocode, we simulate the long-term relaxational evolution of galactic nucleusmodels with a spectrum of stellar masses. Our focus is the concentration ofstellar black holes to the immediate vicinity of the MBH. We quantify this masssegregation for a variety of galactic nucleus models and discuss itsastrophysical implications. Special attention is given to models developed tomatch the conditions in the Milky Way nucleus; we examine the presence ofcompact objects in connection to recent high-resolution X-ray observations.Comment: 28 pages, 24 figures, ApJ accepted. Small changes to follow referee's suggestion