Binary Black Hole Accretion Flows From a Misaligned Circumbinary Disk

Abstract

We studied the basic properties of accretion flows onto binary supermassive black holes, including 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 ($e \gtrsim$ 0.3). The number of peaks in the 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.