Abstract:
Supermassive black holes, harbored in the nuclei of almost all galaxies, can significantly impact their surroundings. How these black holes accrete gas, grow, and feedback mass, momentum, and energy into their environments remain crucial unsolved problems. We present three-dimensional hydrodynamic simulations of the fueling of supermassive black holes in elliptical galaxies from a turbulent medium on galactic scales, taking M87* as a typical case. The simulations use a new GPU-accelerated version of the Athena++ code, AthenaK, and span more than 6 orders of magnitude in radius, reaching scales similar to the black hole horizon. We find that the accretion flow takes the form of multiphase gas at radii less than about a kpc. The cold gas accretion includes two dynamically distinct stages: the typical disk stage in which the cold gas resides in a rotationally supported disk and relatively rare chaotic stages in which the cold gas inflows via chaotic streams. Most of the time, the accretion rate scales with radius as r^0.5 when hot gas dominates and we obtain ~10^-4 to 10^-3 Msun yr^-1 near the event horizon. We propose a subgrid model for accretion in lower-resolution simulations in which the hot gas accretion rate is suppressed relative to the Bondi rate by ~ (r_g/r_Bondi)^0.5. I will also briefly discuss our recent results from MHD and GRMHD modelling and the implication to observations.
