Radiation and Magnetic Pressure Support in Accretion Disks around Supermassive Black Holes and The Physical Origin of Soft X-ray Excess

Explore an astrophysics seminar from the Institute for Advanced Study featuring Yan-Fei Jiang from the Flatiron Institute discussing radiation and magnetic pressure support in accretion disks around supermassive black holes. Learn how the alpha disk model, while widely used, fails to explain many observed properties of Active Galactic Nuclei (AGNs), and discover alternative models where magnetic pressure dominates thermal pressure. Understand how radiation spectrum serves as the key differentiator between these models through findings from global 3D radiation magnetohydrodynamic simulations of AGN accretion disks. The presentation examines how disks become radiation or magnetic pressure dominated depending on cooling and inflow timescales, with magnetic pressure supported disks forming with or without poloidal magnetic fields at lower accretion rates. Discover how emerging spectra from these disks typically peak around 10 eV, and how at near-Eddington accretion rates, a power-law component emerges between 10 eV and 1 keV with spectral slopes comparable to radio-quiet quasars. The talk also explains how these high-energy photons are produced in optically thick regions through compressible bulk Comptonization within converging accretion flows.