Radio Data Reveal Betelgeuse’s Companion Distorts Its Atmosphere

Key points

• Lynn Matthews and colleagues used the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) to observe Betelgeuse between 2021 and 2026.
• The data shows Betelgeuse’s brightness temperature has returned to typical values, indicating recovery from the 2020 Great Dimming.
• The star’s atmosphere appears more elongated when the companion Siwarha is farthest from the star and rounder when it passes in front or behind, suggesting the companion is disturbing the gas.
• Siwarha is too faint to be detected directly at radio wavelengths, but its influence is visible through changes in Betelgeuse’s shape.
• The study confirms a cool atmospheric layer between the visible surface and the chromosphere, with temperatures ranging from 2,200 K to 3,500 K.

Background

Betelgeuse, a red supergiant in Orion, underwent a dramatic dimming in 2019-2020 due to a surface mass ejection. Recent studies have suggested the existence of a companion star, Siwarha, which orbits within the star’s extended atmosphere. This new study builds on earlier findings that the companion’s orbit may explain Betelgeuse’s long-term variability cycle.

How outlets are covering it

Space emphasizes the dramatic nature of the companion’s interaction with Betelgeuse’s atmosphere, using the metaphor of a 'cosmic poltergeist.' Sci.News and ALMA Observatory focus on the technical details of the radio observations and the recovery of the star’s atmosphere after the Great Dimming. Universe Today highlights the significance of the findings for understanding Betelgeuse as a binary star and the complexity of its behavior. All sources agree on the core findings but differ in their emphasis, with Space using more evocative language and the others focusing on the scientific implications.

Why it matters

This study provides the strongest evidence yet that Betelgeuse is a binary star and that its companion, Siwarha, is influencing its atmosphere. Understanding how close companions affect red supergiants is crucial for predicting the end stages of stellar evolution and the processes that lead to supernovae.

What to watch

The team plans to observe more of Siwarha’s orbit using the Next Generation Very Large Array to better understand how the companion affects the star’s atmosphere and mass loss. Further observations will help confirm the existence of Siwarha and its role in Betelgeuse’s variability.