 Shakura--Sunyaev thin disk

The Shakura--Sunyaev thin disk combines a thin disk, large optical depth, efficient local radiative cooling and an alpha disk stress prescription. At each radius, orbital-energy dissipation is balanced by radiation escaping vertically. The model predicts a radial sequence of effective temperatures and therefore a broad spectrum. It is useful when vertical adjustment and cooling are faster than radial evolution; strong inward heat transport, winds or large thickness require a different approximation.^[ref]