Thousands of years mystery solved: Close companion star of Betelgeuse discovered

A research team has succeeded in discovering the suspected companion star of Betelgeuse using a special instrument at the Gemini Observatory. Its existence had only been postulated a few months ago, but it was found in December using a device called 'Alopeke. This was announced by the US research facility Noirlab, which operates the Gemini observatories. The as yet unnamed star is about one and a half times the mass of our sun. It is probably a hot, young, blue-white star (A or B class) in whose core hydrogen burning has not yet begun. It is also located about four astronomical units away from the surface of the giant star Betelgeuse and thus within the foothills of its atmosphere.

Months after hypothesis confirmed

The fact that the red giant star Betelgeuse has a companion was first postulated in the fall. At that time, a US research team explained that only this could explain the periodic fluctuations in brightness that have long been known. These are pulses that repeat every six years and which, without an external cause, would indicate that the star will soon come to an end. Using the 'Alopeke' instrument, this extremely faint companion was discovered at the predicted time using speckle interferometry. It is the first time that a companion orbiting so closely around a gigantic giant star has been found, the team explains. When the hypothesis was first presented, some had assumed that such a star could not be imaged directly.

Betelgeuse is the shoulder star of the constellation Orion and is normally one of the brightest in the night sky. It has caused quite a stir in recent years with a massive dimming followed by a brightening and similar episodes. Researchers agree that it has reached the end of its life, but the final supernova is not actually expected in our lifetime. However, there have recently been different predictions about this, and even a final supernova in a few decades has been considered possible. The discovery of the companion star should take the wind out of the sails of such speculation, because at least a periodic change in brightness is not due to processes inside Betelgeuse.

The discovery of the previously overlooked companion star in Betelgeuse now makes it clear once again that even after centuries of research into an astronomical object, there is still room for surprises. When the research group led by astrophysicist Jared Goldberg postulated the existence of the companion in the fall, they called it "Betelbuddy". Goldberg said at the time: "If Betelbuddy doesn't exist, it means that something much stranger is going on – something that we can't possibly explain with our understanding of physics." The proof, which was achieved just a few months later, is being presented this week in The Astrophysical Journal Letters.

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