Ion viscosity in hot accretion disks.

Cygnus X-1 and nuclei of Seyfert galaxies are known to radiate mostly in hard X-rays. The source of this radiation may be a very hot accretion disk around a black hole. In this paper the ion viscosity is estimated for ion temperature up to 1 trillion K. It is shown that ordinary ion viscosity due to Coulomb and strong interactions between the protons is capable of driving disk accretion at a rate up to a few percent of the critical (Eddington) value. The model requires preheating of gas up to 'ignition' temperature, and it is valid when there is no magnetic field.