Binary Black Hole Accretion Flows From a Misaligned Circumbinary Disk

TL;DR

This study uses 3D simulations to explore how misaligned circumbinary disks affect accretion flows onto binary supermassive black holes, revealing patterns in accretion rate variations and potential explanations for observed light fluctuations.

Contribution

It provides new insights into accretion dynamics in misaligned binary systems, including the effects of eccentricity and mass ratio on accretion rate variability.

Findings

Misaligned disks produce double-peaked accretion rate variations in circular binaries.

Eccentric binaries with moderate eccentricity show single-peaked accretion variations.

Less massive black holes can approach the disk more closely, influencing light curve features.

Abstract

We study the basic properties of accretion flows onto binary supermassive black holes, including the cases in which a circumbinary disk is misaligned with the binary orbital plane, by means of three-dimensional Smoothed Particle Hydrodynamics simulations. We find that a circular binary system with a misaligned circumbinary disk normally produces a double peaked mass-accretion-rate variation per binary orbit. This is because each black hole passes across the circumbinary disk plane and captures gas twice in one orbital period. Even in misaligned systems, however, a single peaked mass-accretion-rate variation per binary orbit is produced, if the orbital eccentricity is moderately large (e\lesssim0.3). The number of peaks in mass accretion rates can be understood simply in terms of the orbital phase dependence of the distance between each binary black hole and its closest inner edge of the circumbinary disk. In the cases of eccentric binary black holes having different masses, the less massive black hole can get closer to the circumbinary disk than the massive one, thus tidally splitting gas from its inner edge, but the created gas flows are comparably captured by both black holes with a short time delay. As a consequence, the combined light curve shows periodic occurrence of double-peaked flares with a short interval. This may account for the observed light variations of OJ287.