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. |