Supermassive binary black hole mergers

TL;DR

This paper discusses how supermassive black hole mergers, driven by galaxy collisions, lead to spin reorientation or spin-flip phenomena observable through radio jet reorientation, modeled using post-Newtonian techniques.

Contribution

It demonstrates that the spin-flip occurs during the inspiral phase of black hole mergers and can be effectively modeled with post-Newtonian methods.

Findings

Spin-flip occurs during the inspiral phase.

Typical galaxy encounters involve mass ratios of 1:3 to 1:30.

Reoriented jets are evidenced by X-shaped radio galaxies.

Abstract

When galaxies collide, dynamical friction drives their central supermassive black holes close enought to each other such that gravitational radiation becomes the leading dissipative effect. Gravitational radiation takes away energy, momentum and angular momentum from the compact binary, such that the black holes finally merge. In the process, the spin of the dominant black hole is reoriented. On observational level, the spins are directly related to the jets, which can be seen at radio frequencies. Images of the X-shaped radio galaxies together with evidence on the age of the jets illustrate that the jets are reoriented, a phenomenon known as spin-flip. Based on the galaxy luminosity statistics we argue here that the typical galaxy encounters involve mass ratios between 1:3 to 1:30 for the central black holes. Based on the spin-orbit precession and gravitational radiation we also argue that for this typical mass ratio in the inspiral phase of the merger the initially dominant orbital angular momentum will become smaller than the spin, which will be reoriented. We prove here that the spin-flip phenomenon typically occurs already in the inspiral phase, and as such is describable by post-Newtonian techniques.