Title: Accretion Disk Outbursts: MHD Simulations (Finally) Confront Reality 

Speaker: Omer Blaes (UC Santa Barbara)  

Time & Place: Thursday, 3:00pm, September 4th, Lecture Hall, 3rd floor  

Abstract:  Accretion disks around compact objects are responsible for some of the most powerful phenomena that we observe in the universe, from gamma-ray bursts to quasars. Stresses in the flow that transport angular momentum outward and allow gravitational binding energy to be released are central to the physics of these flows. For over twenty years, the dominant theoretical paradigm for these stresses is turbulence driven by an instability of weak magnetic fields embedded in the flow. Numerical simulations of this turbulence have revealed much about how these stresses might work, but until recently, they have not successfully explained (never mind predicted) the most significant quantitative observational constraints: the outburst time scales of dwarf novae and low mass X-ray binaries. I will describe recent progress on understanding the behaviour of these systems through simulations that incorporate the physics that is essential for exploring the physics of these phenomena.

Biog: Omer Blaes was born in the US, but grew up in Europe from age 12 onward. He obtained his PhD from SISSA, Trieste in 1985 under Marek Abramowicz and went on to postdoc positions at Caltech and CITA. In 1993 he joined the physics faculty at University of California, Santa Barbara in 1993. He works in the area of theoretical astrophysics, with a focus on compact objects.