Understand
I discuss the possibility that accreting supermassive black hole (SMBH) binaries with sub-parsec separations produce periodically recurring luminous outbursts that interrupt periods of relative quiescence.
- This hypothesis is motivated by two characteristics found generically in simulations of binaries embedded in prograde accretion discs: (i) the formation of a central, low-density cavity around the binary, and (ii) the leakage of gas into this cavity, occurring once per orbit via discrete streams on nearly radial trajectories.
- The first feature would reduce the emergent optical/UV flux of the system relative to active galactic nuclei powered by single SMBHs, while the second can trigger quasiperiodic fluctuations in luminosity.
- I argue that the quasiperiodic accretion signature may be much more dramatic than previously thought, because the infalling gas streams can strongly shock-heat via self-collision and tidal compression, thereby enhancing viscous accretion.