Astronomers analyzing new observations from NASA’s Hubble Space Telescope and several ground-based observatories have discovered clear signs that a recently identified companion star is shaping the environment around Betelgeuse. The study, led by researchers from the Center for Astrophysics | Harvard & Smithsonian (CfA) shows that the companion star, called Siwarha, generates a dense flow of gas as it moves through Betelgeuse’s enormous outer atmosphere. This newly observed structure helps explain the unusual, long-lasting changes seen in the giant star’s brightness and atmospheric behavior.
The results were announced at a news conference at the 247th meeting of the American Astronomical Society in Phoenix and have been accepted for publication in The Astrophysics Journal.
Eight years of observations reveal a stellar wake
Researchers identified Siwarha’s influence by carefully measuring subtle changes in Betelgeuse’s light over nearly eight years. These long-term observations revealed effects of a companion star that had 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 solves one of the most enduring puzzles about Betelgeuse. By confirming the presence of the companion, astronomers can now better explain the behavior and evolution of the star over time. This discovery also provides valuable information about the final stages of the evolution of other massive stars approaching the end of their lives.
Betelgeuse is located approximately 650 light years from Earth in the constellation Orion. It is a red supergiant of extraordinary size, large enough to hold 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 age, lose material, and eventually explode as supernovae.
Several telescopes confirm the impact of the companion
By combining Hubble data 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 models provided strong evidence for the existence 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, that is, the specific colors of light produced by different elements, as well as changes in the movement of gases in the outer atmosphere. These changes are linked to the dense wake formed by the companion star. The wake appears shortly after the companion passes Betelgeuse about every six years, or about 2,100 days, consistent with previous theoretical predictions.
“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,” said Andrea Dupree, an astronomer at CfA and lead author of the study. “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.”
Decades of strange variability explained
Astronomers have been monitoring Betelgeuse for decades, tracking changes in its brightness and surface characteristics in an effort to understand its unpredictable behavior. Interest increased in 2020 when the star unexpectedly dimmed after what was described as a stellar “sneeze.” Scientists have identified two major cycles in Betelgeuse’s variability: a shorter period of 400 days linked to pulsations inside the star, and a much longer cycle of around 2,100 days.
Before this discovery, scientists explored numerous explanations for Betelgeuse’s long-term changes. These included massive convection cells, dust clouds, magnetic activity and the potential influence of a hidden companion. Recent studies suggest that the longer cycle was best explained by a low-mass star orbiting deep in Betelgeuse’s atmosphere. Although one group reported possible detection, there was no definitive proof until now.
The newly detected wake provides the strongest evidence yet that a companion star is actively disrupting this red supergiant’s atmosphere.
“The idea that Betelgeuse has an undetected companion has gained popularity in recent years, but without direct evidence, it was an unproven theory,” Dupree said. “With this new direct evidence, Betelgeuse gives us a front-row seat to observe how a giant star evolves over time. Finding the wake of its companion means we can now understand how stars like this evolve, lose material and eventually explode as supernovae.”
In anticipation of future observations
From Earth’s perspective, Betelgeuse is currently eclipsing its companion star. Astronomers plan additional observations when the companion becomes visible again in 2027. Researchers say the discovery could also help solve similar mysteries involving other giant and supergiant stars.
Hubble’s continuing contributions
The Hubble Space Telescope has been operating for more than 30 years and continues to produce discoveries that deepen our understanding of the universe. Hubble is a collaborative project between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, oversees mission operations, with additional support from Lockheed Martin Space in Denver. The Space Telescope Science Institute in Baltimore, operated by the Association of Universities for Astronomical Research, manages Hubble science operations for NASA.
