Wednesday, November 17, 3:00 pm (note unusual date and time)

"How Black Hole Disks Stay Cool"

Neal Turner

Jet Propulsion Laboratory

Abstract:  Black hole accretion is a key problem in astrophysics as it powers active galactic nuclei, gamma-ray bursts and X-ray binary systems that are the endpoints of the evolution of high-mass stars. For accretion rates greater than 1% of the Eddington limit, gas near the black hole forms an opaque, rotating disk in which radiation pressure is greater than gas pressure. A fundamental unresolved issue is the nature of the cooling mechanism that determines the internal gas temperature and the disk thickness. I will discuss 2-D and 3-D numerical radiation-MHD calculations of patches of disk, showing that photon bubble instability leads to radiation forces driving shocks through the disk gas. The flow cools as photons escape between the shocks.