Betelgeuse — A Giant Star with a Hidden Companion
Betelgeuse, visible to the naked eye in the constellation Orion, is well known to the general public. Immense, bright, and reddish in color, it has fascinated observers for centuries due to its variations in brightness. Now, a team of astronomers has confirmed the existence of a hidden stellar companion in close proximity to this red supergiant — a hypothesis long discussed but never proven until now.
What is Betelgeuse?
Betelgeuse is a red supergiant star, roughly 1,000 times larger than our Sun. It is also one of the brightest stars in the night sky, located about 548 light-years from Earth. Since antiquity, astronomers have noted that its brightness changes regularly. Two main cycles have been identified:
- A short cycle of about 400 days, linked to internal pulsations.
- A longer cycle of around 6 years, the cause of which had remained a mystery.
An Ancient Mystery… Finally Solved
Many scientists had long suspected that a stellar companion — a smaller star orbiting Betelgeuse — could explain the second, slower brightness cycle. However, Betelgeuse is so large, luminous, and shrouded in gas and dust that detecting such an object in its immediate vicinity has been extremely challenging.
Thanks to the ‘Alopeke instrument, installed on the Gemini North Telescope in Hawaii, a team led by Steve Howell (NASA Ames Research Center) was able to observe this companion for the first time in November 2023. This instrument uses a technique called speckle imaging, which captures thousands of very fast exposures to counteract the blurring effects of Earth’s atmospheric turbulence. This method achieves extremely high resolution, making it possible to distinguish two objects that appear very close together in the sky.
The astronomers scheduled their observation for the moment when the companion was expected to be at its greatest apparent separation from Betelgeuse’s brilliant surface, based on orbital calculations. This allowed them to detect a very faint point of light just 52 milliarcseconds away — roughly 4 astronomical units (the Earth–Sun distance) from the center of Betelgeuse.
Who is this Companion?
The companion is a young star, likely of spectral type A or B, much smaller than Betelgeuse. It is about 6,000 times less luminous in visible light, with a mass estimated at 1.5 times that of the Sun.
Remarkably, it lies within Betelgeuse’s extended atmosphere — an arrangement that is extremely rare and has never before been observed so clearly.
Why This Matters
- A Solved Mystery – This discovery explains Betelgeuse’s long-term brightness variations. The companion star disturbs Betelgeuse’s atmosphere and contributes to dust formation, which affects its apparent brightness from Earth.
- A Cosmic Laboratory – Betelgeuse is nearing the end of its life and could explode as a supernova within the next few tens of thousands of years. Studying this binary system offers a unique opportunity to better understand how massive stars evolve before their final collapse.
- A Technological Breakthrough – This detection demonstrates the power of next-generation ground-based telescopes, which can rival space telescopes for certain types of observations.
What’s Next?
Scientists plan to confirm this discovery through new observations, particularly in November 2027, when the companion will once again be well positioned for viewing. Their goals are to:
- Precisely map its orbit.
- Measure its physical characteristics.
- Model its interaction with Betelgeuse.
Source
Read the article published by NOIRLab on July 21, 2025 here.