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Theoretical Astrophysics and General Relativity Seminar: "Understanding Accretion Disks through Three Dimensional Radiation MHD Simulations"

Event Type
Seminar/Symposium
Sponsor
Department of Physics
Location
464 Loomis
Date
Oct 9, 2013   12:00 pm  
Speaker
Yan-Fei Jiang (Harvard University)
Originating Calendar
Physics - Astrophysics, Gravitation, and Cosmology Seminar

Structures and thermal properties of the black hole

accretion disks in the radiation pressure dominated regime will be

discussed. Angular

momentum transfer in the disk is provided by the turbulence generated by

the magneto-rotational instability (MRI), which is calculated

self-consistently

with a recently developed 3D radiation

magneto-hydrodynamics (MHD) code based on Athena.

The thermal instability of the radiation pressure

dominated disks is studied with vertically stratified shearing box

simulations. I always find that the radiation

pressure dominated disks either collapse or expand until we have to stop

the simulations. During the thermal runaway, the heating and cooling

rates from the simulations are consistent with the general criterion of

thermal instability. However, details of the thermal runaway are

different from the predictions of the standard alpha disk model. We also

identify the key reasons why previous simulations do not find the

instability. A new mechanism to generate high temperature corona above the

accretion disk is also found from these simulations.

The thermal instability has many important implications for

understanding the observations of both X-ray binaries and Active

Galactic Nuclei.

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