NASA's Hubble Space Telescope Observations Track Influence Of Betelgeuse's Companion Star, Siwarha
The impending collapse of Betelgeuse, a red supergiant star, promises a celestial spectacle. When it finally happens, the star will shine as brightly as the Moon in the sky for about two weeks and remain visible during the daytime for 6-12 months after that. This event, however, is shrouded in uncertainty, with scientists grappling to predict its exact timing.
Betelgeuse's dimming and brightening patterns have sparked speculation about an imminent supernova. Recent observations suggest that the star might explode in a very short time, measured in human decades, rather than the vast astronomical timescales we're used to. But the complexity doesn't end there. Betelgeuse's constant expulsion of dust and gas obscures our observations, making it appear as though the star is dimming or getting brighter.
Adding another layer of intrigue, in 2024 and 2025, two independent teams concluded that a periodic dimming of the star, occurring approximately every 2100 days, was likely caused by a companion star orbiting within Betelgeuse's atmosphere, named Siwarha. This discovery raises the possibility that Betelgeuse might be part of a binary system, which could explain the 'great dimming' event of 2019/2020.
The name Betelgeuse, meaning 'Hand of al-Jawzā’', is linked to an old Arabian female figure whose stars align with Greek Orion. The companion star, orbiting the hand of al-Jawzā’, was named Siwarha, or 'Her Bracelet', by the discovery team.
Red giants like Betelgeuse exhibit 'long secondary periods', variations in brightness over long periods. These periods are often attributed to companion stars. Based on Betelgeuse observations, the teams proposed that it might be part of a binary system, explaining the 2019/2020 dimming event.
A new study, using NASA's Hubble Space Telescope and ground-based telescopes, tracked Betelgeuse's light changes over eight years. The team believes they've detected Siwarha's wake as it moves through Betelgeuse's atmosphere, akin to a boat's wake in water. This direct evidence confirms Betelgeuse's companion star, shaping its appearance and behavior.
Until now, scientists suspected a companion star, but these observations provide stronger evidence. The study resolves a significant mystery about the giant star, explaining its dimming behavior every 2100 Earth days. The discovery offers a unique opportunity to observe a giant star's evolution, material shedding, and eventual supernova explosion.
By tracking Betelgeuse's gas and dust, and their direction and speed, the team concluded that the 2100-day variation was due to the companion star's transit across Betelgeuse's disk. The companion's gravitational pull focuses surrounding wind, creating a trailing wake, with denser gas accumulating behind the shockwave. This wake is expected to be variable due to multi-temperature turbulent gas and high velocities.
The wake expands laterally at a speed of approximately 6 km/s, becoming smaller during the companion's transit but widening as the orbit progresses, covering a larger fraction of the disk.
Currently, the companion star is obscured by Betelgeuse's disk, but astronomers plan further observations when Siwarha emerges in August 2027. The study, posted on the preprint server arXiv, has been accepted for publication in The Astrophysical Journal.
