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Spin Variations of Black Hole Binaries in AGN Disks

Presentation #300.04 in the session Compact Object Binaries I: AGN Disk Environments.

Published onApr 25, 2022
Spin Variations of Black Hole Binaries in AGN Disks

The spin-orbit misalignment of stellar-mass black hole binaries (BHB) provide important constraints on the formation channels of merging BHBs. Here, we study the spin evolution of a black-hole component in a BHB around a supermassive BH (SMBH) in an AGN disk. We consider the BH’s spin-precession due to the J2 moment introduced by a circum-BH disk within the warping/breaking radius of the disk. We find that the BH’s spin-orbit misalignment (obliquity) can be excited via spin-orbit resonance between the BHB’s orbital nodal precession and the BH spin-precession driven by the circum-BH disk. Assuming a 107 M SMBH, this typically occurs at a distance of 102–4 AU to the SMBH or 103–5 GMSMBH/c2. In many cases, spin-orbit resonance leads to a high BH obliquity, and a broad distribution of the binary components’ obliquities and effective spin parameters.

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