The Betelgeuse Enigma: The Betelbuddy Hypothesis

TL;DR

This paper addresses the Betelgeuse enigma by synthesizing photometric history, variability analyses, and direct-imaging results to evaluate the Betelbuddy binary hypothesis. It argues that the Great Dimming arose from surface mass ejection and dust obscuration rather than impending core collapse, while also presenting accumulating evidence for a close, low-mass companion within Betelgeuse's extended atmosphere. A key contribution is the December 2024 direct-imaging result from the Alopeke instrument, which tentatively detected a companion (Betelbuddy/Siwarha) at ~52 mas with ~1.5 solar masses, signaling a crucial testable prediction for 2027. The findings have significant implications for understanding variability and mass transfer in red supergiants and demonstrate the potential of high-angular-resolution speckle imaging to uncover close companions in luminous evolved stars.

Abstract

In the past six years, Betelgeuse has been in the news and drawn significant public interest. Starting in October 2019, Betelgeuse underwent a striking dimming event, fading from magnitude 0.5 to 1.7 by mid February 2020 a threefold decrease in brightness This gave rise to a number of speculative debates that the star was on the verge of a supernova, a moment of eerie quiet before the cosmic outburst. In a previous article, the author discussed the most accepted explanation to the dimming caused by episodic mass loss that released large dust grains, which obscured Betelgeuse's light and made it appear fainter. This interpretation suggested that the dimming was not a precursor to a supernova, as Betelgeuse is likely still far from reaching that stage. On 21 July 2025, the existence of the companion star was confirmed with direct imaging, for the first time, by the alopeke instrument on the 8.1 m Gemini North telescope. The companion is 6 magnitudes fainter than Betelgeuse and orbits close to Betelgeuse itself, within the supergiant star's extended outer atmosphere. The stellar companion was detected at an angular separation of 52 mas and a position angle of 115 deg east of north. These measurements, along with its brightness, being roughly 6 magnitudes fainter than Betelgeuse at 466 nm, are in excellent agreement with dynamical predictions. Although this was only a 1.5 sigma detection, the agreement in the companion's appearance, separation, position angle, magnitude difference, and estimated mass is reasonable, making the result tentatively acceptable. The next optimum period for observations is November 2027, when we hope to get better observations. This article describes the interesting twists and turns of this study and what lies in the future for Betelgeuse and its companion, Betelbuddy or Siwarha.

Figures (7)

• Figure 1: A schematic of the Orion constellation, with a small pink arrow indicating the location of Betelgeuse in Orion’s left shoulder. Image credit: Wikimedia Commons
• Figure 2: The four-panel graphic explains the Great Dimming with a dust cloud. A hot blob of plasma was likely ejected from a large convection cell on the star. As the gas rapidly expanded away from the star, it cooled and turned into a giant dust cloud. This dust cloud blocked the light from a quarter of the star's surface when seen from Earth. Credit: NASA/ESA/Elizabeth Wheatley (STScI).
• Figure 3: Betelgeuse imaged by Atacama Large Millimeter/submillimeter Array (ALMA), in the millimeter continuum. The star is $\approx$ 1400 times larger than our Sun. The orbital paths of the Solar System planets are shown for comparison. Crédit: ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella
• Figure 4: AAVSO photometric data in the V and B bands traces Betelgeuse's brightness over the last eight years, capturing the profound Great Dimming event of late 2019 to early 2020. The timeline also marks the dates of two speckle observations. (Image Credit: AAVSO)
• Figure 5: Infographic explaining Betelbuddy and its affect on the brightness of Betelgeuse. Credit: Lucy Reading-Ikkanda/Simons Foundation