Betelgeuse’s Brightness Wavers Due to a Companion Star and Its Swirling Trail of Gas
There are times when the red supergiant star Betelgeuse looks a little weird, becoming dimmer than usual. Emerging data from NASA’s Hubble Space Telescope now suggests that this mysterious change could be the work of a much smaller companion star to Betelgeuse, named Siwarha.
New observations presented in a arXiv The pre-printed paper revealed a stunning effect of Siwarha’s brush with Betelgeuse, leaving the red supergiant with an altered appearance. By carefully observing the two stars, the researchers noticed that Siwarha left a trail of dense gas as it passed through Betelgeuse’s outer atmosphere. This revelation could be a turning point in understanding why Betelgeuse’s brightness fluctuated in the past.
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Light Changes in Bételgeuse
Betelgeuse, located nearly 650 light years from Earth in the shoulder of the constellation Orion, has been studied by astronomers for centuries. It is well known as one of the brightest stars in the night sky, shining 7,500 to 14,000 times brighter than the sun. About 10 million years old, Betelgeuse is nearing the end of its life after evolving rapidly due to its immense mass; over the next 100,000 years, the aging star will burn out with a tremendous supernova explosion.
Astronomers determined that Betelgeuse goes through two significant periods of brightness variation: a 400-day cycle caused by the star’s own pulsations and a longer period of 2,100 days (nearly six years).
In 2019 and 2020, the star experienced an unusually sharp decrease in brightness, known as the Great Dimming. Astronomers discovered that this was the result of a large dust cloud ejected from Betelgeuse, but as interest in the star reached new heights, curiosity about its six-year period of variability began to grow.
The companion star of Betelgeuse
Astronomers have long suspected that Betelgeuse’s six-year period of variability could be influenced by a companion star. It was not until July 2025 that researchers announced that they had finally seen this companion star thanks to the Gemini North telescope in Hawaii. It was called “Siwarha,” an Arabic term meaning “her bracelet,” according to NASA.
Researchers are still studying Siwarha, but recent data from Hubble have now provided a better understanding of the star, which is hundreds of times smaller than Betelgeuse.
Using Hubble and ground-based telescopes at the Fred Lawrence Whipple Observatory in Arizona and the Roque de Los Muchachos Observatory in Spain, the researchers carefully tracked changes in Betelgeuse’s outer atmosphere. They observed changes in the star’s spectrum – the colors of light emitted by different elements – as well as in the speed and direction of gas shaped by a wake of denser material.
According to the researchers, this wake is clear evidence of Siwarha passing in front of Betelgeuse, which happens every six years, in accordance with the period of variability.
“It’s a bit like a boat moving on water. The companion star creates a ripple effect in Betelgeuse’s atmosphere that we can actually see in the data,” lead author of the preprint Andrea Dupree, an astronomer at the Harvard-Smithsonian Center for Astrophysics, said in a statement. “For the first time, we observe direct signs of this wake, or gas trail, confirming that Betelgeuse actually has a hidden companion that shapes its appearance and behavior.”
Waiting for Siwarha to reappear
With this latest observation of Siwarha’s wake, researchers are now more confident about their knowledge of Betelgeuse’s variations in brightness. As for Siwarha’s future, the smaller companion star will likely have a shortened lifespan; Strong tidal forces are thought to cause the star to spiral toward Betelgeuse, which could happen within the next 10,000 years.
In the future, researchers hope to study Siwarha’s wake to better understand how supergiant stars evolve over time. Although Siwarha is now obscured by Betelgeuse, it will reappear in 2027 to usher in a new wave of research into the companion star.
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