Joint Astrophysics Colloquium

Special Astrophysics Seminar

Turbulent, Magnetized, MRI-driven Accretion Disks:
Beyond the alpha-disk

Martin Pessah

University of Arizona

The last decade has witnessed significant advances in numerical simulations of turbulent, magnetized accretion disks. However, because of the large temporal and spatial dynamical ranges involved, the study of the long-term evolution of the accretion flows and of the accreting central objects will remain beyond reach in the near future. In order to address, some of the long-standing problems in accretion physics, such as the growth of supermassive black holes, the stability of accretion disks, and the spin-orbit alignment of accreting compact objects in binaries, it is necessary for us to follow a different approach. In this talk, I will present the first dynamical, mean-field model for angular momentum transport in thin accretion disks that is physically motivated, incorporates the MRI as the main driver of the MHD turbulence, and reproduces the results of local three-dimensional numerical simulations. The model possesses several appealing characteristics: it generates turbulence only where the disk is MRI-unstable and does not suffer from causality problems across sonic points. I will discuss the implications of this model for the global structure of accretion disks and their observational signatures.