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Authors: Laszlo Gergely, Peter L. Biermann

Date: 16 Apr 2007

Abstract: Massive merging black holes will be the primary sources of powerful gravitational waves at low frequency, and will permit to test General Relativity if we identify candidate galaxies that are close to a binary black hole merger. In this paper we show that for a typical range of mass ratios of the two black holes the final stage of the merger is preceded by a rapid precession and a subsequent spin-flip of the main black hole. The latter already occurs in the inspiral phase, thus can be treated analytically by post-Newtonian techniques. We also show that the distance when gravitational radiation becomes the dominant dissipative effect (over dynamical friction) does not depend on this mass ratio. We then identify the radio galaxies with a super-disk as those in which the rapidly precessing jet produces effectively a powerful wind, which entrains the environmental gas to produce the appearance of a thick disk. These specific galaxies are thus candidates for a merger of two black holes to happen in the astronomically near future, and further observations and theoretical work may be capable of identifying which one is likely to be the next to merge, and how soon.

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