Hidden star plows through the outer atmosphere of Betelgeuse

Astronomers studying the massive red supergiant star Betelgeuse have found new evidence that a nearby companion star, named Siwarha, is traveling directly through its vast outer atmosphere. By combining data gathered between 2021 and 2026 from large radio telescope networks, researchers tracked subtle changes in the star’s shape and temperature.

Probing the layers of a giant star

The research team used multiple radio frequencies to examine different depths within Betelgeuse’s atmosphere. Their measurements confirmed the existence of a cool region of molecular gas known as the MOLsphere, located between the visible surface and the higher atmospheric layer. While the star experienced a dramatic drop in brightness a few years ago, the new data shows that its outer atmosphere has largely returned to normal temperatures.

Tracking an invisible companion

Siwarha orbits extremely close to Betelgeuse, passing right through its extended gas layers. Although the companion star is too faint to be seen directly with these radio telescopes, scientists detected its presence by observing how it alters the giant star’s shape. Betelgeuse appears more elongated when the companion is at its greatest apparent separation, behaving much like a boat cutting through water and leaving a wake.