Self-consistent realignment during differential accretion

Construct live-binary simulations that follow a sustained nonzero mass-ratio evolution to determine whether a locked circumbinary disk realigns as the initially designated secondary becomes the more massive black hole, and to establish how this realignment affects the binary’s eventual mass ratio and observable signatures.

Background

The simulations find that nominally equal-mass binaries at eccentricities $e_b=0.2$ and $0.3$ can accrete preferentially onto the black hole initially labeled as the secondary, causing the mass ratio to drift away from unity. In the $e_b=0.2$ case, the locked disk is oriented toward that component, so a change in which black hole is more massive may require the disk to realign or reverse its association with the primary and secondary.

The paper hypothesizes that this realignment may occur on the disk’s apsidal-precession timescale, potentially much faster than gas-driven mass-ratio evolution, but does not test the process with evolving binary masses and orbit. The authors explicitly leave its confirmation to simulations that evolve the live binary through a sustained phase of nonzero mass-ratio change.