Shakura–Sunyaev alpha disk model

Summary

The Shakura–Sunyaev model describes a thin accretion disk of gas that orbits a central mass on nearly Keplerian circles. It replaces the unknown turbulent friction in the disk by a viscosity of the form $\nu = \alpha c_s H$. Here $c_s$ is the speed of sound, $H$ the thickness of the disk and $\alpha$ a dimensionless constant. With this single parameter the disk equations close. They give the mass flow, the heating and the temperature of the disk as functions of radius. It is the standard reference model for disks around young stars, white dwarfs, neutron stars and black holes.