VLT/SPHERE images of the candidate companion of Betelgeuse

Abstract

Context. Although the binary fraction of massive main-sequence stars is well established, this is much less so the case for red supergiant (RSG) stars due to the primary’s brightness as well as its complex and strong surface activity. Aims. Betelgeuse is the most studied RSG. In 2024, through a reinterpretation of its long secondary period (LSP), a close orbiting stellar companion was suggested to exist, with a maximum elongation in December 2024. Our goal with this work was to search for this secondary component. Methods. We used extreme adaptive optics direct imaging with the Very Large Telescope SPHERE-ZIMPOL instrument by leveraging the pupil tracking mode of the telescope in angular plus spectral differential imaging (ASDI). Image processing was performed through ASDI PAtch Covariances (PACO ASDI) and principal component analysis (PCA). Results. The candidate Betelgeuse B was detected at 6.1σ with PACO ASDI and at 5.1σ with PCA in the CntHa filter on December 6, 2024. The separation is 52.32 ± 0.18 mas, and the position angle is 117.12 ± 0.60°. Assuming the two stars are coeval, the companion is a 2.6 to 3.1 M⊙ young main-sequence star. Conclusions. Our observations provide strong evidence that Betelgeuse has a close companion, though formal confirmation that Betelgeuse B is indeed gravitationally bound awaits a second observing epoch. The predicted existence of a companion based on LSP variability and the evidence of the presence of the secondary source reported here identifies LSPs as a potential new avenue for RSG-companion studies, and assessments of their impact on RSG surface and wind structure.