Journey to the Black Hole: Multiphase Accretion Flows From Galaxy Scales to Accretion Disk Scales

Speaker: Dr.  Yuan Li
Affiliation: University of Massachusetts Amherst
Date: October 7, 2026

Abstract:

The feeding and feedback cycles of Supermassive black holes (SMBHs) play a vital role in regulating the intra-cluster medium in cluster centers. While state-of-the-art numerical simulations effectively reproduce multiphase gas at the galaxy scale, understanding its connection to the gas at the accretion-disk scale remains challenging. My group recently conducted numerical studies to bridge this gap. We use the Athena++ code to simulate an idealized elliptical galaxy based on M87 in the center of the Virgo Cluster. Our galaxy-scale simulations include a black hole jet feedback prescription that balances cooling on large scales. We construct mesoscale simulations to model the dynamical evolution of multiphase accretion flow within the central parsecs down to tens of gravitational radii of the SMBH. We find that the average accretion rate follows a simple scaling of $\dot{M} \propto r^{1/2}$ across seven orders of magnitude in scale, consistent with what has been found in single-phase accretion flows. While the cool clouds usually appear clumpy and amorphous on galaxy scales, at the mesoscale, the multiphase accretion flow typically settles to a disk, which is often connected to a misaligned disk on even smaller scales. At its highest resolution, our simulation can effectively model the black hole variability over a year-long timescale, which allows for direct comparison with current and future observations. These simulations will ultimately provide more realistic boundary and initial conditions for future general-relativistic magneto-hydrodynamical (GRMHD) simulations of the accretion disk, as well as better subgrid models for next-generation cosmological simulations.