PROFESSOR PRATEEK SHARMA

Accretion disks are ubiquitous in astrophysics, from protoplanetary disks out of which planets coalesce to the central engines of most energetic transients in the universe. Unlike stars, which are spherical and pressure-supported, accretion disks are supported by the centrifugal force. For gravitational energy to be released via accretion, matter has to quickly lose angular momentum. Turbulent transport is often invoked for efficient angular momentum transport but the cause for turbulence is only known in ionized disks. For such disks, there is a powerful local magnetohydrodynamic (MHD) instability known as the magneto-rotational instability (MRI) that grows, saturates and leads to fully developed turbulence. The speaker shall give a brief overview of this field, making analogies with various ideas in fluid dynamics. He shall also describe recent high resolution 3-D global simulations of radiatively inefficient accretion flows (RIAFs), highlighting mean and turbulent magnetic field generation. Most nearby active galactic nuclei (AGN), including the one in our Galactic center, are powered by RIAFs.