A Hundred Year Search Just Ended: Betelgeuse Has A Companion, And We Have Seen It

Astronomers digitally removed Betelgeuse from an image of Betelgeuse, and a second star was sitting exactly where the models said it should be. One of them described jumping out of their chair.

The European Southern Observatory has released the clearest Betelgeuse companion star image yet, captured with the Very Large Telescope. The companion, Betelgeuse B, has been suspected for roughly a hundred years. Nobody had managed to see it.

Why nobody could find it before

Betelgeuse is enormous and extremely bright, and the companion orbits close enough to be lost in that glare. The observation was taken in December 2024, timed deliberately for the moment the companion was predicted to sit at its widest apparent separation from the primary as seen from Earth. Even then it only appeared once Betelgeuse itself had been subtracted from the frame.

That is a fairly brutal test of a model. You predict where a thing should be, point one of the largest telescopes on the planet at the exact spot at the exact time, remove the object that has been hiding it, and check.

The mass is the surprising part

The data point to a companion of between two and three solar masses. That is heavier than anyone had predicted, and it changes what the object explains.

Betelgeuse's brightness has two rhythms. There is the famous shorter pulsation that people have watched for generations, and underneath it a slow six year wobble known as the long secondary period. Astronomers have argued about the cause of that wobble since before radio astronomy existed. A companion of this mass fits it, and it also feeds into the harder question of how and when Betelgeuse eventually goes supernova.

How to look at it yourself

You cannot see Betelgeuse B. Nobody could until now, and it took the VLT. But Betelgeuse itself is a naked eye star, the orange shoulder of Orion, and it is worth knowing which point of light this argument has been about.

Honest advice: you do not need a telescope for it. A modest pair of binoculars like the Celestron Cometron 7x50 pulls the colour out far better than magnification does, and the orange is the whole point. Orion returns to evening skies through autumn in the northern hemisphere.

If you want more to look at in the meantime, this morning brought a 96 percent partial lunar eclipse, the Roman Space Telescope launches on 30 August, and for a different kind of extreme star, physicists recently confirmed vacuum birefringence around a magnetar.

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