Interacting supernovae from photoionization-confined shells around red supergiant stars.

A model in which the stellar wind of the fast-moving red supergiant Betelgeuse is photoionized by radiation from external sources can explain the dense, almost static shell recently discovered around the star, and predicts both that debris from Betelgeuse’s eventual supernova explosion will violently collide with the shell and that other red supergiants should have similar, but much more massive, shells.