Gravitational Radiation from Intermediate‐Mass Black Holes

Recent X-ray observations of galaxies with ROSAT, ASCA, and Chandra haverevealed numerous bright off-center point sources which, if isotropic emitters,are likely to be intermediate-mass black holes, with hundreds to thousands ofsolar masses. The origin of these objects is under debate, but observationssuggest that a significant number of them currently reside in younghigh-density stellar clusters. There is also growing evidence that someGalactic globular clusters harbor black holes of similar mass, fromobservations of stellar kinematics. In such high-density stellar environments,the interactions of intermediate-mass black holes are promising sources ofgravitational waves for ground-based and space-based detectors. Here we explorethe signal strengths of binaries containing intermediate-mass black holes orstellar-mass black holes in dense stellar clusters. We estimate that a few totens per year of these objects will be detectable during the last phase oftheir inspiral with the advanced LIGO detector, and up to tens per year will beseen during merger, depending on the spins of the black holes. We also findthat if these objects reside in globular clusters then tens of sources will bedetectable with LISA from the Galactic globular system in a five yearintegration, and similar numbers will be detectable from more distant galaxies.The signal strength depends on the eccentricity distribution, but we show thatthere is promise for strong detection of pericenter precession andLense-Thirring precession of the orbital plane. We conclude by discussing whatcould be learned about binaries, dense stellar systems, and strong gravity ifsuch signals are detected.Comment: Minor changes, accepted by ApJ (December 10, 2002