The Standard Model of Disc Accretion
Accretion discs are powerful energy factories in our Universe. They effectively transform the potential energy of gravitational interaction to emission, thereby unraveling the physics of distant objects. This is possible due to the presence of viscosity, driven by turbulent motions in accretion discs. In this chapter, we describe the equations for disc accretion in the framework of the standard model. We outline basic elements of the theory of turbulent viscosity and the emergence of the α-parameter. We further describe the radial and vertical structure of thin stationary accretion discs, and present analytical solutions to the basic equation of the evolution of a viscous accretion disc for both an infinite disc and for a disc in a binary system. Finally, we present a numerical method to solve the equations of disc evolution and vertical structure simultaneously.