Astronomers have turned up new evidence that Betelgeuse, the red supergiant marking Orion's shoulder, isn't traveling alone. A team led by Lynn Matthews of the MIT Haystack Observatory has spent years tracking a subtle disturbance in the star's outer atmosphere that lines up with a long-hypothesized companion star, nicknamed Siwarha, orbiting deep inside Betelgeuse's own gas envelope.
Using the Karl G. Jansky Very Large Array and the Atacama Large Millimeter/submillimeter Array, the researchers imaged Betelgeuse at seven radio frequencies between 2021 and 2026. Because Siwarha is too faint to see directly at radio wavelengths, the team instead measured the shape of Betelgeuse's radio "atmosphere" — normally close to a sphere, but repeatedly stretched into a slightly egg-like shape at the moments a six-year orbit would put a companion closest to the star's core.
A wake, not a sighting
Matthews likened the pattern to the wake a jet boat leaves cutting across a lake: the companion itself stays hidden, but its passage disturbs the water around it. A separate dataset from NASA's Hubble Space Telescope, led by Andrea Dupree, found a dense trail of gas in Betelgeuse's far outer atmosphere, adding an independent line of evidence pointing the same way, as detailed in a recent write-up of the radio findings.
Betelgeuse has been a subject of intense scrutiny since its unexplained "Great Dimming" in 2019 and 2020, when the star briefly lost more than half its usual brightness before recovering — an episode some astronomers have linked to an orbiting companion disturbing dust and gas around the star. The new data show the star's radio-wavelength atmosphere has since returned to typical brightness temperatures at 22 and 44 gigahertz, suggesting whatever drove the dimming has passed.
Because Siwarha would sit well inside Betelgeuse's bloated outer layers — at roughly twice the supergiant's own radius — any direct image remains out of reach with current instruments, according to coverage of the work in Space.com.
Matthews' team says it plans to keep watching Betelgeuse as the proposed companion continues its roughly six-year circuit, looking for the wake to reappear on schedule — a test that, if it holds up, would turn a decades-old guess about Orion's brightest star into a settled fact.
