Betelgeuse’s Hidden Partner: Tracing a Stellar Wake Inside a Supergiant Atmosphere

This paper argues that Betelgeuse’s long secondary period is caused by a companion star orbiting within its extended atmosphere. Optical and ultraviolet spectra show repeating changes in absorption and outflow that match the companion’s six-year orbit. These signatures are best explained by a dense, expanding wake of gas trailing behind the companion as it moves through the star’s chromosphere.