Gradual approach to coalescence for compact stars orbiting massive black holes

Abstract

We consider roughly 10<SUP>6</SUP> to 10<SUP>7</SUP> solar mass black holes (MBHs) in galactic nuclei. As such objects grow by accretion, some fraction of the accreted mass is in the form of compact stars. If the approach to coalescence proceeds gradually, many orbital revolutions will occur, and substantial amounts of gravitational radiation will be emitted. We estimate the cosmological rate of such events, assuming MBHs are quite common in galaxies. Despite large uncertainties about the conditions in galactic nuclei, particularly during the early growth phase, the event rates are encouraging. The chances of such signals being observable with a laser gravitational radiation antenna in space appear to be good.