Betelgeuse, the well-known red supergiant star located in the constellation Orion, has been confirmed to have a previously unseen stellar companion, according to recent observations by an international team of astronomers. Using the Very Large Telescope (VLT) in Chile, researchers captured the clearest images to date of the smaller star, dubbed “Betelgeuse B,” which orbits close to the red giant.
The discovery, led by Miguel Montargès of the Observatoire de Paris, marks the culmination of a century-long search for a companion star thought to influence Betelgeuse’s longstanding and complex variability in brightness. Betelgeuse is known for fluctuations in luminosity across multiple time scales, including a roughly six-year cycle. The newly identified companion may help provide an explanation for these rhythmic changes.
Historical records attest to Betelgeuse’s prominence in the night sky for millennia. Ancient Chinese astronomers documented its color more than 2,000 years ago, while the Greek astronomer Ptolemy noted its distinctive reddish-yellow hue in the second century. Over time, observations indicate Betelgeuse has grown redder, consistent with its classification as a red supergiant nearing the end stages of stellar evolution.
Although the presence of a companion star had been hypothesized for decades, earlier attempts to detect it were unsuccessful. Recent orbital calculations published in 2024 predicted the companion would reach its greatest apparent separation from Betelgeuse in December of that year, prompting Montargès’s team to focus their observations on the anticipated location. The researchers were able to identify Betelgeuse B with greater clarity than expected.
The companion star is believed to be a relatively young main-sequence star with a mass estimated between 2.6 and 3.1 times that of the Sun, making it more massive and luminous than initially predicted. Montargès described the finding as a remarkable scientific milestone, highlighting the rarity of discovering a significant companion near such a well-studied star.
Data suggest the companion completes an orbit around Betelgeuse approximately every six years, aligning with the star’s established brightness cycles. However, the exact mechanism by which Betelgeuse B affects its larger partner remains uncertain. One hypothesis proposes that the companion might periodically clear away some of the circumstellar dust surrounding Betelgeuse, temporarily increasing the star’s brightness as seen from Earth. Yet, calculations indicate this alone would account for only a fraction of the observed luminosity variations.
The team now favors the idea that gravitational interactions between the two stars may stir up gas and dust in Betelgeuse’s extended atmosphere, contributing more substantially to the changes in brightness. To definitively confirm the companion’s orbit and role, further observations are planned for when Betelgeuse B moves to the opposite side of the primary star.
Montargès emphasized that while additional data are needed, the evidence leaving little doubt about the companion’s presence represents a significant advancement in understanding one of the night sky’s most iconic stars.