Berkeley Fluids Seminar
University of California, Berkeley
Bring your lunch and enjoy learning about fluids!
Friday, April 3, 2015
3110 Etcheverry Hall, 12:00-13:00
Dr. Alexander Tchekhovskoy (Astrophysics, Berkeley)
Getting the Most out of a Black Hole
As black holes accrete surrounding gas, they often produce relativistic, collimated outflows, or jets. Since jets form near a black hole, they can be powerful probes of strong-field gravity. However, how jet properties (e.g., jet power) connect to those of the accretion flow (e.g., mass accretion rate) and the black hole (e.g., black hole spin) remains an area of active research. This is because what sets the strength of large-scale magnetic flux threading the black hole and the jet power is not understood. Recently, using first-principles general relativistic magnetohydrodynamics (GRMHD) computer simulations, I demonstrated that accretion disks can accumulate large-scale magnetic flux on the black hole until the flux becomes so strong that it obstructs gas infall and leads to a magnetically-arrested disk (MAD). In MADs, both the black hole magnetic flux and jet power are at their maximum, well-defined values. I will review the emerging observational evidence for MADs in radio-loud active galactic nuclei, jetted tidal disruptions, and gamma-ray bursts. The abundance of MADs opens up a new vista in the measurements of black hole masses and spins and in quantitative tests of black accretion and jet theory. I will finish by describing the ongoing effort at developing the next-generation GRMHD codes that will enable us to compute detailed radiative signatures of accreting black holes and make a more realistic than ever connection to observations.