Figure 2. Evolutionary tracks for a system consisting of a star, with spin angular velocity Ωs, and a planet in a circular orbit of angular velocity n. On each track the total angular momentum J is conserved, and the direction of evolution is such as to lower the total mechanical energy. Jc and Ωc are the critical values defined in the text. Blue dots represent stable tidal equilibria.

Adapted from Ogilvie (2014).