Gravitational wave burst produced by merging of central black holes of galaxies

When galaxies merge, the central black holes rapidly sink toward the center of the system and make a binary. We found that this black hole binary merges within <~ 10^9^ yr. This merging of black holes produces an intense burst of the gravitational wave. We investigated the nature of these gravitational wave bursts and found that the dimensionless amplitude at the Earth is as high as 10^-15^ if black holes with masses of 10^8^ M_sun_ merge at the distance of 2 Gpc. The mean time between bursts is about 2 yr if the elliptical galaxies are the merger remnants of galaxies having central black holes. In previous studies, the time scale of the merging of a black hole binary was estimated to be much longer than a Hubble time (~10^10^ yr). In those studies, the orbit of the binary was assumed to be circular. We found, however, that dynamical friction makes the orbit highly eccentric. The lifetime of a binary with a highly eccentric orbit is much shorter than that of a binary with a circular orbit, because the emission of the gravitational wave is much stronger for shorter periastron distance.