Supermassive black hole spin-flip during the inspiral

László Gergely (1, 2) , Peter L Biermann (3, 4, 5, 6, 7) , Laurent ¸iu , I Caramete (8)

1 Department of Theoretical Physics
2 Department of Experimental Physics
3 Max Planck Institute for Radio Astronomy
4 BCGS - Bonn-Cologne Graduate School of Physics and Astronomy
5 Department of Physics and Astronomy [Tuscaloosa)
6 Physics Department [Huntsville]
7 FZ Karlsruhe, and Physics Department
8 ISS - Institute of Space Science [Bucharest-Măgurele]

During post-Newtonian evolution of a compact binary, a mass ratio ν different from one 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, then to establish a logarithmically even probability in ν of the mass 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 a mechanism 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 happens, 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 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.

Mots clés: Physical Sciences

László Gergely, Peter L Biermann, Laurent ¸iu, I Caramete. Supermassive black hole spin-flip during the inspiral. Classical and Quantum Gravity, 2010, 27 (19), pp.194009. ⟨10.1088/0264-9381/27/19/194009⟩. ⟨hal-00629991⟩