YITP WORKSHOP ON
Quasi-Periodic Oscillations and Time Variabilities of Accretion Flows
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ABSTRACT

NAME
INSTITUTE
TITLE OF THE TALK
S. Hirose
Earth Simulator Center, Japan
Time Variability and Stability of Radiation-dominated Accretion Disks
Dynamical and thermal stability of radiation-dominated accretion disks are studied by 3D radiation MHD simulation. The local shearing box approximation with vertical gravity is used to simulate a radial slice of an accretion disk. In the simulation box, MHD turbulence driven by magneto-rotational instability fully develops near the midplane and a statistically steady state is established where dynamical and thermal equilibrium holds. Dynamical equilibrium: radiation pressure supports the vertical stratification near the midplane while magnetic pressure does in the upper region. Thermal equilibrium: most of the energy dissipated in the MHD turbulence is transfered to the disk surface by radiation diffusion while the rest is done by radiation advection that accompanies with magnetic buoyancy. The heating and cooling rates are highly time variable due to the chaotic nature of MHD turbulence and their power spectra show 1/f^a fluctuations at high frequencies, where a = 1-1.5.


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