The Probable Direct-imaging Detection of the Stellar Companion to Betelgeuse

Betelgeuse—the closest M-supergiant to the Sun—has recently been predicted to host a lower-mass stellar companion that orbits the primary with a period of ∼6 yr. The putative stellar companion is thought to cause the long photometric modulation observed in Betelgeuse, which cannot be explained by stellar pulsations. Additionally, radial velocity and astrometric data also point to a stellar companion. Here we present diffraction-limited optical speckle imaging observations obtained on the 8.1 m Gemini North telescope in 2020 and 2024. The 2020 observations were taken during the Great Dimming event and at a time when the stellar companion was predicted to be unobservable because it was directly in line with Betelgeuse itself. The 2024 observations were taken 3 days after the predicted time of greatest elongation for the companion. A comparison of the 2020 and 2024 data reveals no companion in 2020 (as expected) and the probable detection of a companion in 2024. The presumed stellar companion has an angular separation and position angle of 52 mas and 115° east of north, respectively, which is in excellent agreement with predictions from dynamical considerations. The detected companion is roughly 6 magnitudes fainter than Betelgeuse at 466 nm. While this is only a 1.5σ detection, five results are in reasonable agreement with the predictions: the appearance of the companion at quadrature; the angular separation from Betelgeuse; the position angle with respect to Betelgeuse; the magnitude difference; and the estimated mass of the companion.