Multi-Zone Modeling of Black Hole Accretion and Feedback in 3D GRMHD: Bridging Vast Spatial and Temporal Scales

Simulating accretion and feedback from the horizon scale of supermassive black holes (SMBHs) out to galactic scales is challenging because of the vast range of scales involved. We describe and test a "multi-zone" technique which is designed to tackle this difficult problem in 3D general relativistic magnetohydrodynamic (GRMHD) simulations. We simulate accretion on a non-spinning SMBH (a_*=0) using initial conditions from a large scale galaxy simulation, and achieve steady state over 8 decades in radius. The density scales with radius as ρ∝ r^-1 inside the Bondi radius R_B, which is located at R_B=2× 10^5 r_g (≈ 60 pc for M87) where r_g is the gravitational radius of the SMBH; the plasma-β∼ unity, indicating an extended magnetically arrested state; the mass accretion rate Ṁ is ≈ 1% of the analytical Bondi accretion rate Ṁ_B; and there is continuous energy feedback out to ≈ 100R_B (or beyond > kpc) at a rate ≈ 0.02 Ṁc^2. Surprisingly, any ordered rotation in the external medium does not survive as the magnetized gas flows to smaller radii, and the final steady solution is very similar to when the exterior has no rotation. Using the multi-zone method, we simulate GRMHD accretion for a wide range of Bondi radii, R_ B∼ 10^2 - 10^7 r_ g, and find that Ṁ/Ṁ_B≈ (R_B/6 r_g)^-0.5.