A supermassive binary black hole with triple disks

Hierarchical structure formation hypothesis of the Universe inevitably leads to the formation of supermassive binary black holes (BBHs) with a sub-parsec separation in galactic nuclei. However, there is yet no definitive observational evidence for supermassive BBHs. In tihs letter, we study simulations of accretion flows around a supermassive BBH and propose a basic methodology for exploring them. In the simulations we consider a triple-disk system composing of two disks around each black hole and one circumbinary disk surrounding the two. When the supermassive BBH is on an eccentric orbit, the mass transfer from the circumbinary disk is shown to be periodic. We confirm the formation of a nonaxisymmetric accretion disk around each black hole. The light variations from these disks are significantly wavelength-dependent. While the UV and X-ray light curves exhibit periodic variations, the optical and IR light curves show little variation with orbital phase. Such properties are unique to supermassive BBHs with triple disks and thus provide a potential observational signature. Any supermassive BBH candidates found in this way will be finally confirmed through the detection of periodic gravitational wave events. Subject headings: black hole physics – accretion, accretion disks – binaries:general – galaxies:nuclei – 2 – 1.