Characteristic scale of convection turbulence and normalization of shear stress in the radiation-dominated region of the accretion disk of black holes

The influence of radiative heat transfer on thermal convection in the radiative-dominated region of accretion disk is discussed. It is shown that convective turbulence must be small-scale; more precisely, its realistic outer length-scale ought to be by an order of magnitude smaller than the half-thickness of the disk. It is also demonstrated that, despite the possible existence of rather strong large-scale and small-scale magnetic fields in the radiative-dominated region of the disk, the angular momentum transfer outwards is determined mainly by turbulence. The scaling of shear stress is estimated by the order of magnitude (α∼10-2)