How Black Holes Get Their Kicks: Gravitational Radiation Recoil Revisited

Gravitational waves from the coalescence of binary black holes carry awaylinear momentum, causing center of mass recoil. This "radiation rocket" effecthas important implications for systems with escape speeds of order the recoilvelocity. We revisit this problem using black hole perturbation theory,treating the binary as a test mass spiraling into a spinning hole. For extrememass ratios (q = m1/m2 << 1) we compute the recoil for the slow inspiral epochof binary coalescence very accurately; these results can be extrapolated to q ~0.4 with modest accuracy. Although the recoil from the final plunge contributessignificantly to the final recoil, we are only able to make crude estimates ofits magnitude. We find that the recoil can easily reach ~ 100-200 km/s, butmost likely does not exceed ~ 500 km/s. Though much lower than previousestimates, this recoil is large enough to have important astrophysicalconsequences. These include the ejection of black holes from globular clusters,dwarf galaxies, and high-redshift dark matter halos.Comment: 4 pages, 2 figures, emulateapj style; minor changes made; accepted to ApJ Letter