Interacting supernovae from photoionization-confined shells around red supergiant stars

Understand

Betelgeuse, a nearby red supergiant, is a runaway star with a powerful stellar wind that drives a bow shock into its surroundings.

• This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force.
• The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium.
• Here we report that a model in which Betelgeuse's wind is photoionized by radiation from external sources can explain the static shell without requiring a new understanding of the bow shock.