New radio observations suggest that Siwarha, a companion star orbiting close to Betelgeuse, may be moving through the red supergiant’s extended atmosphere and disturbing its gas. Researchers found that Betelgeuse’s radio-emitting outer layers sometimes appear slightly elongated, with the changes seemingly related to where Siwarha is expected to be in its orbit.
The team, led by Lynn D. Matthews of MIT Haystack Observatory, analyzed observations collected from 2021 to 2026 using the U.S. National Science Foundation’s Very Large Array and the Atacama Large Millimeter/submillimeter Array. By observing at different radio frequencies, the researchers could examine layers at different depths, from just above Betelgeuse’s visible surface to several times the star’s radius.
Siwarha is thought to orbit only about twice Betelgeuse’s radius from the star, passing through its extended atmosphere. The companion is too faint to be detected directly in the radio observations, so the researchers looked for indirect signs of its influence. They found that Betelgeuse tends to look more elongated when Siwarha is predicted to be most separated from the giant star in the sky, and rounder when it is expected to pass in front of or behind it.
The observations also offer an update on Betelgeuse’s atmosphere following the Great Dimming of late 2019 and early 2020. Measurements indicate that the outer atmosphere has largely returned to more typical temperatures. The team also detected a cool region between the visible surface and the chromosphere, with temperatures reaching about 2,200 Kelvin—more than 1,000 degrees below the photosphere. This region corresponds to the molecular-gas layer known as the MOLsphere.
The researchers say more observations are needed to confirm the link between Siwarha’s orbit and the atmospheric distortions, especially across more of the companion’s orbital cycle. The findings were published in The Astronomical Journal.
Sources: ScienceDaily.