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The short version

  • Recent observations from Chile provide strong support for the existence of a companion star to Betelgeuse, resolving a century-old mystery.
  • The companion, formally named Siwarha, appears more massive than previously theorized and orbits the supergiant roughly every six years.
  • The presence of this second star introduces uncertainty regarding the timeline for Betelgeuse’s eventual explosion as a supernova.

Astronomers have obtained what they describe as the most compelling evidence to date that Betelgeuse, one of the night sky’s brightest stars, is not solitary. Observations conducted in December 2024 using the Very Large Telescope in Chile revealed a faint object orbiting the red supergiant. These findings, published in Astronomy and Astrophysics in late July, address a hypothesis that has persisted for more than a century regarding the star’s behavior and structure.

The detection strategy relied on timing the observation when the theorized companion was at its maximum distance from Betelgeuse as viewed from Earth. This positioning minimized the glare from the primary star, allowing specialized instruments designed to block host-star light to capture the dimmer object. The team utilized technology typically employed for exoplanet hunting to isolate the faint signal against the overwhelming brightness of the supergiant.

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Analysis suggests the companion, now formally designated Siwarha, is significantly more massive than earlier models predicted. While researchers initially expected a star with mass similar to our sun, new data indicates it may be between 2.6 and 3.1 times solar mass. The object appears to complete an orbit around Betelgeuse approximately every six years, a period that aligns with recent theoretical frameworks developed by astrophysicists.

Despite the strength of the current evidence, scientists remain cautious about declaring the discovery definitive. Researchers note that confirmation will require observing the companion on the opposite side of Betelgeuse, an event expected to occur in 2027. Until then, some team members continue to refer to the object as a candidate, though many are convinced of its reality based on the latest data.

The confirmed presence of a companion star complicates predictions about Betelgeuse’s ultimate fate. Previously estimated to explode as a supernova within 10,000 to 100,000 years, the timeline is now uncertain due to potential gravitational interactions between the two stars. These interactions could either accelerate or delay the supergiant’s collapse, meaning astronomers can no longer rely on previous models that assumed Betelgeuse was a single star.

Sources behind this briefing

Go to the original reporting

  • Smithsonian Magazine↗New Images Provide the Best Evidence Yet That Supergiant Star Betelgeuse Does, Indeed, Have a Long-Theorized Stellar Companion