Betelgeuse’s companion star leaves detectable wake

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NASA published this original article on January 5, 2026. Edits by EarthSky.

Astronomers detect ‘wake’ of Betelgeuse’s companion star

Astronomers have tracked the influence of a recently discovered companion star, Siwarha, on the gas around Betelgeuse.

The research, from scientists at the Center for Astrophysics | Harvard & Smithsonian (CfA), reveals a trail of dense gas swirling through Betelgeuse’s vast, extended atmosphere. And this could shed light on why the giant star’s brightness and atmosphere have changed in strange and unusual ways.

The team detected Siwarha’s wake by carefully tracking changes in the star’s light over nearly eight years. These changes show the effects of Betelgeuse’s companion as it plows through the outer atmosphere of Betelgeuse.

Notably, this discovery resolves one of the biggest mysteries about the giant star. It’s helping scientists to explain how it behaves and evolves while opening new doors to understanding other massive stars nearing the end of their lives.

The researchers presented the results of the new study on January 5, 2026, at the 247th meeting of the American Astronomical Society in Phoenix, Arizona. The study will be published in The Astrophysical Journal.

Betelgeuse’s companion revealed

Located roughly 650 light-years away from Earth in the constellation Orion, Betelgeuse is a red supergiant star so large that more than 400 million suns could fit inside.

Because of its enormous size and proximity, Betelgeuse is one of the few stars whose surface and surrounding atmosphere can be directly observed by astronomers. That makes it an important and accessible laboratory for studying how giant stars age, lose mass and eventually explode as supernovae.

Using NASA’s Hubble Space Telescope and ground-based telescopes at the Fred Lawrence Whipple Observatory and Roque de Los Muchachos Observatory, the team was able to see a pattern of changes in Betelgeuse. This provided clear evidence of the long-suspected companion star and its impact on the red supergiant’s outer atmosphere.

That includes changes in the star’s spectrum – the specific colors of light given off by different elements – and the speed and direction of gases in the outer atmosphere due to a trail of denser material, or wake. This trail appears just after the companion crosses in front of Betelgeuse every six years, or about 2,190 days, confirming theoretical models.

Andrea Dupree, an astronomer at the CfA and the lead study author, said:

It’s a bit like a boat moving through water. The companion star creates a ripple effect in Betelgeuse’s atmosphere that we can actually see in the data. For the first time, we’re seeing direct signs of this wake, or trail of gas, confirming that Betelgeuse really does have a hidden companion shaping its appearance and behavior.

The Betelgeuse mystery

For decades, astronomers have tracked changes in Betelgeuse’s brightness and surface features, in hopes of figuring out why the star behaves the way it does. Indeed, curiosity intensified after the giant star appeared to “sneeze” and became unexpectedly faint in 2020.

More specifically, two distinct periods of variation in the star were especially puzzling for scientists. A short 400-day cycle, recently attributed to pulsations within the star itself, and the long, 2,100-day secondary period.

Until now, scientists have considered everything from large convection cells and clouds of dust to magnetic activity and the possibility of a hidden companion star. Recent studies concluded, however, that the long secondary period was best explained by the presence of a low-mass companion orbiting deep within Betelgeuse’s atmosphere. Another team of scientists also reported a possible detection. And now, for the first time, they have firm evidence that a companion is disrupting the atmosphere of this supergiant star.

Dupree said:

The idea that Betelgeuse had an undetected companion has been gaining in popularity for the past several years, but without direct evidence, it was an unproven theory. With this new direct evidence, Betelgeuse gives us a front-row seat to watch how a giant star changes over time. Finding the wake from its companion means we can now understand how stars like this evolve, shed material and eventually explode as supernovae.

Now, with Betelgeuse eclipsing its companion from our point of view, astronomers are planning new observations for its next emergence in 2027. In addition, this breakthrough might also help explain similar mysteries in other giant and supergiant stars.

Bottom line: Astronomers have detected the influence of Betelgeuse’s companion star, Siwarha, on the gas around the red supergiant star. It could explain Betelgeuse’s mysterious dimming.

Via NASA

Read more: New details about Betelbuddy, Betelgeuse’s companion star

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