The Spin-Flip Phenomenon in Supermassive Black Hole Binary Mergers

Massive merging black holes will be the primary sources of powerful gravitational waves at low frequency, and will permit us to test general relativity with candidate galaxies close to a binary black hole merger.In this paper, we identify the typical mass ratio of the two black holes but then show that the distance where gravitational radiation becomes the dominant dissipative effect (over dynamical friction) does not depend on the mass ratio; however, the dynamical evolution in the gravitational wave emission regime does.For the typical range of mass ratios the final stage of the merger is preceded by a rapid precession and a subsequent spin-flip of the main black hole.This already occurs in the inspiral phase, therefore can be described analytically by post-Newtonian techniques.We then identify the radio galaxies with a superdisk as those in which the rapidly precessing jet effectively produces a powerful wind, entraining 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.