Elementary processes in astrophysics (NAST024)

Shakura-Sunyaev model of disc accretion

Model of disc accretion presented in this section is one of the first models of accretion onto compact objects that was able to explain properties of quasars discovered several years before. Later on, a broad variety of models of disc-like accertion was formulated, nevertheless, the Shakura-Sunyaev solution is still viable and considered to be valid in many astrophysical systems.

Derivation of the "standard" solution is in Sections 4.3 and 4.4 of the textbook by Vladimir Karas. Some steps can be found in my hand-notes in a bit more detail. Derivations presented in these texts (as well as in many other textbooks) are based on somewhat heurisitc approach to derivation of the angular momentum transfer. Also the equation (4.25) which is the azimuthal component of the Euler equation is actually not derived from the basic form of the Euler equation. For more rigorous derivation of the hydrodynamic equations governing evolution of the standard accretion disc see another set of my hand notes which shows that these equations can be derived under the classical Naviere-Stokes approximation in cylindrical coordinates.

What to concentrate on: