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

TL;DR

This study presents evidence supporting the direct imaging detection of a stellar companion to Betelgeuse, aligning with prior predictions and observations, using optical speckle imaging during a key dimming event.

Contribution

First direct imaging evidence of Betelgeuse's stellar companion, confirming predictions about its position, brightness, and orbital phase through optical speckle observations.

Findings

Probable detection of the companion at 52 mas separation

Companion's brightness is about six magnitudes fainter than Betelgeuse

Detection aligns with dynamical predictions and orbital considerations

Abstract

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 $\sim 6$ years. 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-meter 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 three days after the predicted time of greatest elongation for the companion. A comparison of the 2020 and 2024 data reveal 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 $115^\circ$ east of north, respectively, which is in excellent agreement with predictions from dynamical considerations. The detected companion is roughly six magnitudes fainter than Betelgeuse at 466 nm.\bf{While this is only a 1.5$\sigma$ detection, the 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.