Binary Black Hole Accretion Flows From a Misaligned Circumbinary Disk
  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.
