Astronomers Confirm Betelgeuse's Companion Star Siwarha After Century-Long Mystery

In a groundbreaking revelation, astronomers have confirmed the existence of a companion star, named Siwarha, orbiting Betelgeuse, the closest red supergiant to Earth. This discovery, made using advanced Earth-based telescopes, resolves a century-old mystery that has fascinated scientists and skywatchers alike. The confirmation was announced on July 23, 2025, shedding light on the unusual brightness variations and motion patterns of Betelgeuse that have puzzled astronomers since the early 20th century.

Betelgeuse, located in the constellation Orion, has been the subject of intense study due to its unique characteristics. Despite its relatively young age of about ten million years, Betelgeuse is nearing the end of its life cycle, exhibiting a complicated surface behavior characterized by giant convective cells and periodic swelling and shrinking every 400 days. Additionally, a longer period of change, repeating every 5.78 years, led astronomers to suspect the presence of a companion star.

The historical search for this companion began as early as 1908 when irregular changes in Betelgeuse's brightness and velocity hinted at gravitational influences from an unseen object. However, these early suspicions faded as the chaotic nature of the star's surface made it challenging to obtain direct evidence. Recent advancements in observational technology have allowed scientists to revisit this hypothesis with renewed vigor.

Utilizing the NASA-NSF-funded Alopeke instrument on the Gemini North telescope, a team led by Steve Howell, a senior scientist at NASA’s Ames Research Center, successfully identified Siwarha. This high-resolution speckle imaging system enabled the team to capture thousands of ultra-short exposures, effectively overcoming atmospheric distortions that previously obscured observations. The result was a clear detection of the faint companion star, which is approximately 1.5 times the mass of our Sun and about six magnitudes fainter than Betelgeuse.

Named Siwarha, meaning 'her bracelet' in Arabic, the companion star orbits Betelgeuse at a distance roughly four times that of the Earth-Sun distance, residing within the star's outer layers. Significantly, the orbit of Siwarha is aligned with Betelgeuse's spin axis, indicating strong tidal interactions between the two stars. These interactions have likely accelerated Betelgeuse's rotation, which is unexpectedly high for a star of its size and age.

The implications of this discovery extend beyond merely confirming the existence of a companion star. The gravitational forces at play suggest that Siwarha’s orbit will gradually decay, ultimately leading to its engulfment by Betelgeuse within the next 10,000 years. This eventuality raises questions about the fate of both stars and offers insights into the final stages of massive stars before they explode as supernovae.

Historically, the notion of a binary partner for Betelgeuse was supported by early spectroscopic studies. However, the chaotic surface behavior of Betelgeuse and events such as the 2019-2020 Great Dimming, which was attributed to a dust cloud rather than a supernova, cast doubt on this idea. Advancements in observational techniques allowed researchers to analyze over a century’s worth of radial velocity and brightness measurements that revealed consistent patterns indicative of a companion star.

The confirmation of Siwarha not only answers long-standing questions about Betelgeuse but also opens new avenues for astronomical research. Martin Still, a program director at the National Science Foundation, noted that this achievement represents a significant milestone in resolving complex astronomical puzzles. Howell's team intends to continue observing Siwarha, aiming to deepen our understanding of its characteristics and interactions with Betelgeuse.

As the scientific community celebrates this monumental discovery, it serves as a reminder that some of the universe's secrets may lie hidden in plain sight, waiting for the right technological advancements and inquisitive minds to uncover them. The next opportunity to observe Siwarha in its widest orbit will occur in November 2027, promising further insights into this fascinating stellar duo.