The team reported its results at the 247th meeting of the American Astronomical Society in Phoenix and in a study accepted for publication in The Astrophysical Journal. By tracking Betelgeuse's light over nearly eight years, they followed the influence of the companion as it moves through the giant star's outer layers, providing direct evidence for a previously suspected secondary star.
Betelgeuse lies roughly 650 light-years away from Earth in the constellation Orion and is a red supergiant so large that more than 400 million Suns could fit inside. Its proximity and size make it one of the few stars whose surface and surrounding atmosphere can be resolved directly, turning it into a nearby laboratory for studying how massive stars age, shed mass, and approach the supernova stage.
Using Hubble together with ground-based telescopes at the Fred Lawrence Whipple Observatory and Roque de los Muchachos Observatory, the team identified a repeating pattern in Betelgeuse's behavior that matches the orbital motion of the companion. They saw changes in the star's spectrum and in the speed and direction of gases in its extended atmosphere caused by a trail of denser material, or wake, that appears just after the companion crosses in front of Betelgeuse about every 2,100 days, or six years, confirming theoretical models of a low-mass companion embedded in the star's outer atmosphere.
"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," said Andrea Dupree, an astronomer at the CfA, and the lead study author. "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."
For decades, astronomers have tracked changes in Betelgeuse's brightness and surface features to understand its irregular behavior, including an unexpected dimming event in 2020 linked to a major outburst and dust formation. Two distinct variability periods stand out: a shorter 400-day cycle now attributed to pulsations inside the star itself, and a longer 2,100-day secondary period that until recently lacked a clear explanation.
Earlier studies suggested that a low-mass companion orbiting deep within Betelgeuse's extended atmosphere could drive the long secondary period, and another team reported a possible detection, but evidence remained indirect. The new Hubble and ground-based data now provide firm, repeatable signatures of a companion disturbing the star's gas, resolving a key question about Betelgeuse's internal structure and evolution.
With Betelgeuse currently eclipsing its companion from our point of view, Siwarha is difficult to isolate directly in images, so astronomers instead track its dynamical impact on the surrounding gas. The companion orbits within Betelgeuse's extended atmosphere and carves a dense wake as it moves, even though the star itself would appear as a much smaller point compared with the supergiant, which spans hundreds of times the Sun's diameter.
Astronomers are planning new observing campaigns for the next time the companion moves back out from behind Betelgeuse around 2027, which will allow further tests of models of mass loss and binary interaction in massive stars. The Betelgeuse system has become a benchmark for understanding long-period variability in other giant and supergiant stars, where hidden companions and their wakes may also shape changes in brightness and spectra.
The Hubble Space Telescope has operated for more than three decades as an international project between NASA and ESA, with NASA's Goddard Space Flight Center managing the telescope and mission operations and Lockheed Martin Space supporting operations at Goddard. The Space Telescope Science Institute in Baltimore, operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
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