### Abstract

During post-Newtonian evolution of a compact binary, a mass ratio ν different from 1 provides a second small parameter, which can lead to unexpected results. We present a statistics of supermassive black hole candidates, which enables us first to derive their mass distribution, and then to establish a logarithmically even probability in ν of themass ratios at their encounter. In the mass ratio range ν ∈ (1/30, 1/3) of supermassive black hole mergers representing 40% of all possible cases, the combined effect of spin-orbit precession and gravitational radiation leads to a spin-flip of the dominant spin during the inspiral phase of the merger. This provides amechanism for explaining a large set of observations on X-shaped radio galaxies. In another 40% with mass ratios ν ∈ (1/30, 1/1000) a spin-flip never occurs, while in the remaining 20% of mergers with mass ratios ν ∈ (1/3, 1) it may occur during the plunge. We analyze the magnitude of the spin-flip angle occurring during the inspiral as a function of the mass ratio and original relative orientation of the spin and orbital angular momentum. We also derive a formula for the final spin at the end of the inspiral in this mass ratio range.

Original language | English |
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Article number | 194009 |

Journal | Classical and Quantum Gravity |

Volume | 27 |

Issue number | 19 |

DOIs | |

Publication status | Published - Oct 7 2010 |

### ASJC Scopus subject areas

- Physics and Astronomy (miscellaneous)

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## Cite this

*Classical and Quantum Gravity*,

*27*(19), [194009]. https://doi.org/10.1088/0264-9381/27/19/194009