CRA Seminar – Matthew Liska (GT)

Please join us this Thursday, September 7, 2023, for our next CRA seminar, given by Matthew Liska, a Hubble Fellow who has just arrived to the CRA.

• Speaker: Matthew Liska (GA Tech)
• Date: Thursday, September 7, 2023
• Time: 3:30PM – 4:30PM
• Location: CRA Visualization Lab (Boggs 1-44)
• Host: John Wise
• Title: How do the most luminous black holes accrete and expel gas?

Abstract:  

The gravitational pull of a black hole attracts gas and forms an accretion disk where the interplay between hydromagnetic processes and the warping of space-time releases gravitational energy in the form of radiation, relativistic jets, and winds. Most gas falls into supermassive black holes when the accretion rate approaches the Eddington limit (L=Ledd), at which point radiation pressure overcomes gravity.  To date, our knowledge of such `luminous’ black hole accretion disks mostly relies on semi-analytical models, supplemented by a very limited set of numerical simulations. In my talk I will discuss new insights gained from state-of-the-art radiative general relativistic magnetohydrodynamics (GRMHD) simulations of accretion near the Eddington limit. After demonstrating that magnetic fields lead to the formation of a hot corona, I will show that, when the accretion disk is misaligned with the spin axis of the black hole, accretion is driven by shocks. This challenges the current paradigm of turbulence-driven accretion. I will subsequently demonstrate that the spin of a black hole can tear misaligned disks apart, which naturally explains both low and high frequency quasi-periodic oscillations (QPOs). I will finish my talk by discussing the opportunities the next-generation of GRMHD simulations will bring in addressing accretion from event horizon scales to galaxy-scales.