Abstract
We present the results of high-resolution numerical simulations of gas clouds falling onto binary supermassive black holes to form circumbinary accretion discs, with both prograde and retrograde cloud orbits. We explore a range of clouds masses and cooling rates. We find that for low mass discs that cool fast enough to fragment, prograde discs are significantly shorter-lived than similar discs orbiting retrograde with respect to the binary. For fragmenting discs of all masses, we also find that prograde discs fragment across a narrower radial region. If the cooling is slow enough that the disc enters a self-regulating gravitoturbulent regime, we find that alignment between the disc and binary planes occurs on a timescale primarily dictated by the disc thickness. We estimate realistic cooling times for such discs, and find that in the majority of cases we expect fragmentation to occur. The longer lifetime of low-mass fragmenting retrograde discs allows them to drive significant binary evolution, and may provide a mechanism for solving the 'last parsec problem'.
Highlights
Most, if not all, large galaxies host super-massive black holes (SMBHs) at their centres
We present the results of high-resolution numerical simulations of gas clouds falling onto binary supermassive black holes to form circumbinary accretion discs, with both prograde and retrograde cloud orbits
We have performed a suite of high-resolution smoothed-particle hydrodynamics (SPH) simulations of an initially turbulent cloud falling onto a SMBH binary1
Summary
If not all, large galaxies host super-massive black holes (SMBHs) at their centres. It has been shown that accretion from misaligned or counter-rotating gas discs is a possible mechanism for coalescing such binaries, as a circumbinary disc rotating in a retrograde direction (with respect to the binary orbit) reduces the binary separation much more rapidly than an otherwise identical prograde disc (Nixon et al 2011; Nixon, King, & Pringle 2011; Nixon, King, & Price 2013). This is because resonant torques from the binary act to hold disc material away from the SMBHs in prograde discs, and accretion proceeds only through low-density tidal streams.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
