Extensive, multi-year observations conducted by instruments aboard the NASA/ESA Hubble Space Telescope, alongside ground-based observatories at the Fred Lawrence Whipple Observatory and Roque de Los Muchachos Observatory, have illuminated how a diminutive stellar entity, designated Siwarha, navigates through the expansive outer layers of Betelgeuse. This revelation not only demystifies long-standing cosmic enigmas but also significantly bolsters our comprehension of the evolutionary trajectories of massive celestial bodies.
This artist’s concept shows the red supergiant star Betelgeuse and an orbiting companion star. Image credit: NASA / ESA / Elizabeth Wheatley, STScI / Andrea Dupree, CfA.
Betelgeuse, a red supergiant star located approximately 724 light-years distant in the constellation Orion’s shoulder, is estimated to be 8 million years old.
With a radius roughly 1,400 times that of our Sun, it ranks among the most colossal stars currently cataloged.
Also designated Alpha Orionis or Alpha Ori, Betelgeuse stands as one of the most luminous stars, radiating more light than 100,000 Suns combined.
This stellar behemoth is approaching the twilight of its existence; its eventual explosive demise, a supernova, is predicted to be so brilliant that it will be observable in daylight for several weeks.
For many decades, astronomers have diligently monitored fluctuations in Betelgeuse’s luminosity and surface characteristics, seeking to unravel the underlying causes of its peculiar behavior.
Scientific intrigue was notably piqued when the giant star seemingly underwent an outburst, or ‘sneeze,’ resulting in an unanticipated dimming in 2020.
Two prominent periods of variability in the star’s output have particularly puzzled researchers: a shorter, approximately 400-day cycle, which has recently been linked to internal stellar pulsations, and a more extended, secondary cycle spanning approximately 2,100 days.
Previously, scientific speculation encompassed a range of hypotheses, including the influence of large convection cells, accumulations of dust, magnetic phenomena, and the potential presence of an undetected companion star.
Recent investigations have posited that the prolonged secondary cycle is most plausibly explained by the orbital presence of a lower-mass companion star deeply embedded within Betelgeuse’s extensive atmosphere. While another research group reported a potential detection, definitive observational proof remained elusive until this recent breakthrough.
Now, for the first time, compelling evidence has been obtained confirming that a companion star is indeed perturbing the atmosphere of this supergiant.
This evidence includes observable alterations in the star’s spectral signature—the specific wavelengths of light emitted by various elements—and shifts in the velocity and orientation of gases within its outermost atmospheric layers, attributed to a wake of denser material.
This distinctive trail materializes shortly after the companion star transits across the face of Betelgeuse, an event that recurs approximately every six years, or roughly every 2,100 days, thereby validating theoretical predictions.
“The scenario is analogous to a vessel navigating through water; the companion star generates a pattern of disturbances within Betelgeuse’s atmosphere that is detectable in our observational data,” stated Dr. Andrea Dupree, an astronomer affiliated with the Harvard & Smithsonian’s Center for Astrophysics.
“This marks the inaugural instance where we are witnessing direct indications of this wake, or gaseous trail, substantiating the conclusion that Betelgeuse indeed harbors a concealed companion that significantly influences its visual appearance and operational dynamics.”
The research team’s findings are slated for publication in the Astrophysical Journal.
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Andrea K. Dupree et al. 2026. Betelgeuse: Detection of the Expanding Wake of the Companion Star. ApJ, in press; arXiv: 2601.00470
