![Betelgeuse Is Not Alone](https://cdn.slatesource.com/4/f/c/4fc72f1d-de8c-48be-9ea5-28039a88e120.webp) # Betelgeuse Is Not Alone - [Made in Slatesource](https://slatesource.com/@steph/betelgeuse-is-not-alone) - By [Steph](https://slatesource.com/@steph) - Created on Aug 28, 2026 ## A Century Ends: Betelgeuse Has a Companion Star Betelgeuse is one of the most studied stars in the sky. It is the red supergiant on Orion's right shoulder, 650 light-years away, 15 to 20 times the mass of the Sun and so large that 400 million Suns could fit inside. Astronomers have pointed every major instrument at it for decades. And for a century they suspected it was not alone, held back by one thing: the star is tens of thousands of times brighter than whatever might be orbiting it. That changed on July 28, 2026, when a team led by Miguel Montarges (Observatoire de Paris) published direct images of a stellar companion orbiting Betelgeuse, taken with the SPHERE instrument on ESO's Very Large Telescope (VLT) in Chile's Atacama Desert. The paper appeared in Astronomy and Astrophysics. "This is the conclusion of a century-long quest," Montarges said. "We have shown that Betelgeuse is not single, it is accompanied by a very discreet companion." The companion has been formally named Siwarha by the International Astronomical Union. [Astronomy and Astrophysics: VLT/SPHERE images the candidate companion of Betelgeuse (Montarges et al., 2026)](https://www.aanda.org/articles/aa/full_html/2026/07/aa61023-26/aa61023-26.html?utm_source=slatesource) ![](https://cdn.slatesource.com/4/f/c/4fc72f1d-de8c-48be-9ea5-28039a88e120.webp) ## Credit: ESO/M. Montarges et al. The VLT SPHERE image taken in December 2024, when Siwarha was at its farthest point from Betelgeuse as seen from Earth. Betelgeuse itself has been removed by the processing software. The companion appears to the left, marked with a crosshair. The circle shows the original size of Betelgeuse for scale. The detection significance is 6.1 sigma, meaning the probability of a random false positive is essentially zero. ## Bigger Than Expected, and That Is Why We Missed It The companion was predicted to have roughly 1 solar mass. When Hubble searched for it in ultraviolet light and Chandra looked in X-rays, they found nothing. The Gemini North telescope attempted a direct image in late 2024 and got a 1.5-sigma hint, too faint to claim. What the VLT revealed is that Siwarha has approximately 2 to 3 times the mass of the Sun, significantly heavier than any prior model suggested. Co-author Anthony Boccaletti (Observatoire de Paris) explained the irony: "It is remarkable to see how SPHERE and advanced post-processing techniques, originally developed to find exoplanets, also excel at detecting a companion around a massive, evolved star like Betelgeuse." The companion was harder to find partly because previous instruments were calibrated to look for something dimmer. Montarges himself admitted: "Honestly, I thought we did not have the sensitivity to detect Betelgeuse B as it was predicted. Because it is more massive than predicted, we see it." Betelgeuse mass (times the Sun) 15 to 20 Siwarha mass (times the Sun) 2 to 3 Orbital period 2,100 days (6 years) Orbital separation roughly 4 AU Detection significance 6.1 sigma Image taken December 2024 Paper published July 28, 2026 Years of the quest 100 ## The Six-Year Rhythm That Astronomers Could Not Explain Betelgeuse has two well-known brightness cycles. The shorter one, about 420 days, is driven by the star's own pulsation. The longer one, roughly 2,000 days, has puzzled astronomers since the 1970s. It is called the Long Secondary Period (LSP) and no internal mechanism could fully account for it. Six years is 2,190 days. The orbital period of Siwarha is 2,100 days. The match is close enough that the LSP now has an explanation: the companion moves through Betelgeuse's outer atmosphere on each orbit, pulling material, casting shadows, and modulating the star's light as seen from Earth. A mystery that ran for half a century closes at the same moment as the century-long search for the companion itself. ## The Wake That Gave the Game Away In January 2026, a team at the Center for Astrophysics (Harvard and Smithsonian), led by Andrea Dupree, announced they had detected a dense gas wake trailing behind Siwarha using Hubble data. "It's a bit like a boat moving through water," Dupree said. "The companion star creates a ripple effect in Betelgeuse's atmosphere that we can actually see in the data." That paper used Hubble observations. The July 2026 VLT result provided the direct image. The two studies, one detecting the wake and one photographing the star itself, confirm each other from different angles and different instruments. [CfA / Harvard and Smithsonian: Scientists Detect Wake of Betelgeuse's Companion Star (Dupree et al., January 2026)](https://www.cfa.harvard.edu/news/cfa-scientists-detect-wake-betelgeuses-elusive-companion-star?utm_source=slatesource) ![](https://cdn.slatesource.com/f/0/3/f03b8476-69e2-47a8-9c3e-3f223179d36c.webp) ## Credit: ESO/M. Montarges et al. The 2024 VLT image of the Betelgeuse system, showing the companion Siwarha at the point of maximum elongation. The processing algorithm, PACO ASDI (originally built for exoplanet searches), suppressed Betelgeuse's overwhelming glare to reveal the faint companion star. ## What Happens When Betelgeuse Goes Supernova Betelgeuse is in the final stages of stellar life. Astronomers expect it to explode as a supernova sometime in the next 100,000 years, a window that sounds vast but is essentially immediate on cosmic timescales. When it does, it will briefly outshine the Moon and be visible in daylight from Earth. Siwarha is at roughly 4 AU from Betelgeuse, closer than Jupiter is to our Sun. When the supernova comes, Siwarha will be in the blast. Astronomers do not yet know whether it will be consumed, ejected at high velocity, or survive in some altered form. That is now a research question with real numbers attached, because for the first time the companion's mass and orbit are measured rather than guessed. ## What Comes Next The next opportunity to observe Siwarha will come in late 2027, when it re-emerges on the far side of Betelgeuse. ESO's Extremely Large Telescope, under construction at Cerro Armazones in Chile, will eventually provide still sharper views. Montarges noted: "We still need to observe it in one year on the other side of the star, but there is very little space left for doubt." Betelgeuse has been watched by humanity for thousands of years. It dimmed dramatically in 2019 and 2020, an event now likely explained at least in part by Siwarha's orbit. The star that would not give up its secrets has finally given one up. And it is bigger than anyone predicted. [ESO Press Release eso2611: Astronomers Find Strongest Evidence Yet That Betelgeuse Has a Companion](https://www.eso.org/public/news/eso2611/?utm_source=slatesource)