Betelgeuse, the iconic red star of the Orion constellation, has been the subject of much talk in recent years due to its atypical behavior. Its episodes of dimming and brightening have puzzled the scientific community. However, an explanation is gradually beginning to take shape thanks to recent observational progress.
The confirmation in 2025 of a companion star, named Siwarha, moving within Betelgeuse's extended atmosphere, marked a significant milestone. This discovery helps define an explanatory framework for the observed fluctuations.
Artist's impression of the red supergiant star Betelgeuse with its companion Siwarha in orbit. The companion generates a wake of dense gas as it traverses Betelgeuse's extended atmosphere.
Credit: NASA, ESA, Elizabeth Wheatley (STScI); Science: Andrea Dupree (CfA) Data collected by the Hubble Space Telescope and ground-based observatories have recently revealed the wake left by Siwarha. This phenomenon, comparable to the wake of a ship cutting through water, consists of an area of gas denser than the surrounding stellar environment. Andrea Dupree, an astronomer at the Center for Astrophysics, notes that these observations constitute direct proof of the stellar companion's existence, allowing for a better understanding of the mechanisms at work.
Furthermore, the visibility of this wake follows a cycle, becoming particularly detectable every six years when Siwarha aligns precisely between Betelgeuse and Earth. This configuration then alters the light spectrum emitted by the star, making the structure apparent. This regularity offers researchers the ability to predict and analyze these events with great precision, thereby strengthening astrophysical models.
Hubble Space Telescope data showing light variations linked to the wake of the companion star Siwarha around Betelgeuse.
Credit: NASA, ESA, Elizabeth Wheatley (STScI); Science: Andrea Dupree (CfA)
Understanding Siwarha's influence on Betelgeuse helps clarify certain stellar evolution processes. Supergiants like Betelgeuse gradually expel matter before exploding as supernovae. The existence of a companion can accelerate or alter these mechanisms.
The next steps are already planned, with new observation campaigns scheduled for 2027, when Siwarha will once again be in an optimal position. This work aims to refine our knowledge of the end of life of massive stars and their interactions within binary systems.