Astronomers analyzing fresh observations from NASA's Hubble Space Telescope and several ground-based observatories have uncovered clear signs that a recently identified companion star is shaping the environment around Betelgeuse. The study, led by researchers at the Center for Astrophysics | Harvard & Smithsonian (CfA), shows that the companion star, called Siwarha, is generating a dense stream of gas as it moves through Betelgeuse's enormous outer atmosphere. This newly observed structure helps explain the unusual and long-running changes seen in the giant star's brightness and atmospheric behavior.

The findings were announced at a news conference during the 247th meeting of the American Astronomical Society in Phoenix and have been accepted for publication in The Astrophysical Journal.

Eight Years of Observations Reveal a Stellar Wake

Researchers identified the influence of Siwarha by carefully measuring subtle changes in Betelgeuse's light over nearly eight years. These long-term observations revealed the effects of a companion star that had previously been suspected but not confirmed. As the companion moves through Betelgeuse's outer layers, it disrupts the surrounding gas, producing a trail of denser material.

This detection resolves one of the most enduring puzzles surrounding Betelgeuse. By confirming the companion's presence, astronomers can now better explain how the star behaves and changes over time. The discovery also provides valuable insight into the later stages of evolution for other massive stars approaching the ends of their lives.

Betelgeuse is located about 650 light-years from Earth in the constellation Orion. It is a red supergiant of extraordinary size, large enough to contain more than 400 million Suns. Because it is both enormous and relatively close to Earth, Betelgeuse is one of the few stars whose surface and surrounding atmosphere can be directly studied, making it a key target for understanding how giant stars grow older, lose material, and eventually explode as supernovae.

Multiple Telescopes Confirm the Companion's Impact

By combining data from Hubble with observations from the Fred Lawrence Whipple Observatory and the Roque de Los Muchachos Observatory, the team identified repeating patterns in Betelgeuse's behavior. These patterns provided strong evidence of the long-suspected companion star and revealed how it affects the red supergiant's outer atmosphere.

Scientists observed changes in the star's spectrum, meaning the specific colors of light produced by different elements, along with shifts in the motion of gas in the outer atmosphere. These changes are linked to a dense wake formed by the companion star. The wake appears shortly after the companion passes in front of Betelgeuse approximately every six years, or about 2,100 days, in agreement with earlier theoretical predictions.