The Effect of Mass Segregation on Gravitational Wave Sources near Massive Black Holes

Gravitational waves (GWs) from the inspiral of compact remnants (CRs) intomassive black holes (MBHs) will be observable to cosmological distances. Whilea CR spirals in, 2-body scattering by field stars may cause it to fall into theMBH before reaching a short period orbit that would give an observable signal.As a result, only CRs very near (~0.01 pc) the MBH can spiral in successfully.In a multi-mass stellar population, the heaviest objects sink to the center,where they are more likely to slowly spiral into the MBH without beingswallowed prematurely. We study how mass-segregation modifies the stellardistribution and the rate of GW events. We find that the inspiral rate pergalaxy for white dwarfs is 30 per Gyr, for neutron stars 6 per Gyr, and forstellar black holes (SBHs) 250 per Gyr. The high rate for SBHs is due to theirextremely steep density profile, n_{BH}(r)\propto r^{-2}. The GW detection ratewill be dominated by SBHs.Comment: Submitted to ApJ