Beyond Shakura-Sunyaev: First-Principles Physics of Accretion Disks in Active Galactic Nuclei

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

AST-0307657 Blaes The mechanism responsible for the prodigious power output of quasars and active galactic nuclei is almost certainly the accretion of plasma onto super-massive black holes, probably in the form of a rotationally supported accretion disk. The standard model of accretion disks has been based on an ad hoc phenomenological prescription for turbulent angular momentum transport and energy dissipation, introduced by Shakura & Sunyaev some thirty years ago. The current research will create local, radiation-magnetohydrodynamical simulations of this accretion flow, for the first time with no ad-hoc assumptions, which should finally lift the long-standing uncertainties in the standard model. The power and sophistication of modern numerical techniques will be used to determine whether there is an achievable thermally stable equilibrium state, how much turbulent stress is present in radiation-pressure-dominated flows, the average vertical distribution in the flow, and the rates of heat and energy transport. The work will also consider compressibility, density inhomogeneities, and the nonlinear development of photon-bubble and magnetoacoustic-wave instabilities. Snapshots of the turbulent state at different locations in the flow will be made available for scientists everywhere, to add other physics or consider additional effects. Some tests will be possible for the first time because the models will be based on physics and not phenomenological prescriptions. Graduate and undergraduate students will be involved in the research. Animations of the simulation results will be effective as part of the investigators' public talks about the interesting complexity of black hole astrophysics, which continues to fascinate.