Quite by chance, the other day I learned something about why variable stars are variable: it is (at least in many common cases) a consequence of a feedback loop

Quite by chance, the other day I learned something about why variable stars are variable: it is (at least in many common cases) a consequence of a feedback loop in which temperature-dependent changes to the radiative opacity of internal layers of the star influences the heat flow through it, which in turn affects the temperature. https://en.wikipedia.org/wiki/Kappa%E2%80%93mechanism https://en.wikipedia.org/wiki/Kappa%E2%80%93mechanism I'm also slightly disappointed that the term "Eddington valve" for this mechanism is falling out of use.