CRA Seminar – Lizhong Zhang, Flatiron Institute (Host Julia Speicher)

Title: Understanding the dynamics of accretion onto black holes in radiation GRMHD simulations

Abstract: Radiation and magnetic fields play crucial roles in shaping the physics of black hole accretion, especially in near- and super-Eddington regimes. To model this process, we solve the GRMHD equations coupled with angle-dependent radiation transfer, which enables us to capture the complex dynamics driven by radiation and magnetic fields in extreme environments. In the super-Eddington regime, the accretion disk thermally expands under radiative support, forming a narrow conical funnel through which radiation escapes, resulting in low radiation efficiency. In the near-Eddington regime, the disk structure strongly depends on the magnetic field topology, allowing the system to reach a steady state as either a thin disk with magnetic coronae or a magnetically elevated disk.  These simulation results align with several observational findings and provide predictive diagnostics for future observations, which I will further elaborate on in the talk.