CAPTURE OF STELLAR MASS COMPACT OBJECTS BY MASSIVE BLACK-HOLES IN GALACTIC CUSPS

A significant fraction of the stellar population in the cusps around c entral black holes of galaxies consists of compact remnants of evolved stars, such as white dwarfs, neutron stars and stellar mass black hol es. We estimate the rate of capture of compact objects by massive cent ral black holes, assuming that most spiral galaxies have a central bla ck hole of modest mass (similar to 10(6) M.), and a cuspy spheroid. It is likely that the total capture rate is dominated by nucleated spira ls. We estimate the flux of gravitational wave radiation from such coa lescences, and the estimated detectable source count for proposed spac e-based gravitational wave observatories such as LISA. About one event per year should be detectable within 1 Gpc, given very conservative e stimates of the black hole masses and central galactic densities. We e xpect 10(2)-10(3) detectable sources at lower frequencies (10(-4) Hz) 'en route' to capture. If stellar mass black holes are ubiquitous, the signal may be dominated by stellar mass black holes coalescing with m assive black holes. The rate of white dwarf-white dwarf mergers in the cores of nucleated spirals is estimated at similar to 10(-6) per year per galaxy.