Space & Innovation

Famous Star Betelgeuse May Have Had a Little Sister, Which It Ate

It's a star-eat-star universe and it seems that one of the most famous stars in our night sky may have cannibalistic tendencies.

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When you next wish upon a star, spare a thought for that bright dot in the constellation of Orion - it could be where an unfortunate stellar sibling got gobbled up.

As the second-brightest star on the shoulder of Orion (The Hunter), Betelgeuse is a mangled stellar mess. Coming to the end of its life, the massive red supergiant is convulsing as its superheated upper layers become stripped away by violent stellar winds. These winds are creating vast clouds of gas, a prelude to the mayhem just around the corner.

Having lived its comparatively short life of around 8 million years (to put that in perspective, our middle-aged sun has been around for 5 billion years), rapidly burning away its supply of hydrogen fuel, this massive bloated star only 700 light-years from Earth is now in the process of fusing heavier elements together. Within the next million years (some estimately put it within the next 100,000 years), Betelgeuse will become so unstable that it will explode as a supernova, a fact that has spawned all kinds of silly doomsday theories for life on Earth.

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Though Betelgeuse is so close and it is one of the most studied stars in the sky, it still holds many mysteries. And in new research published by the journal Monthly Notices of the Royal Astronomical Society, J. Craig Wheeler of The University of Texas at Austin and his team of international undergraduate students have uncovered something peculiar about the star's spin.

When a star reaches the end of its life and expands like Betelgeuse has, physics dictates that its rate of spin should slow down. A good analogy for this effect is if an ice skater spins on the spot and extends her or his arms outward, their rate of spin slows. The same physics applies to an expanding star. But that's not the case here, Betelgeuse is spinning way too fast!

"We cannot account for the rotation of Betelgeuse," said Wheeler in a statement. "It's spinning 150 times faster than any plausible single star just rotating and doing its thing."

Wheeler's team took on this puzzle and ran a series of computer simulations in an attempt to explain what's going on and one scenario emerged.

"Suppose Betelgeuse had a companion when it was first born?" he pondered. "And let's just suppose it is orbiting around Betelgeuse at an orbit about the size that Betelgeuse is now. And then Betelgeuse turns into a red supergiant and absorbs it - swallows it."

To explain the current spin of Betelgeuse, the massive star would have had to swallow a star of a similar size to our sun. Also, as the majority of stars come in in pairs (or more), it's certainly within the realms of possibility that it evolved with a smaller stellar sibling in tow.

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But just because there's circumstantial evidence of stellar cannibalism, it doesn't necessarily mean it happened; the researchers needed to find more proof. And it just so happens that, in 2012, another team of astronomers took note of two shells of interacting matter ejected from the star creating a bow shock with the interstellar medium - the tenuous gases that can be found in the space between the stars.

This ejected material has mysterious origins, but by measuring the distance the material has traveled and the speed it is traveling, the researchers were able to reveal that it was ejected around 100,000 years ago. That would be roughly the same time that Betelgeuse would have consumed its partner, according to the researchers' "star swallowing" hypothesis timeline.

Next, the researchers hope to use a technique known as asteroseismology on the star to measure waves traveling through its body. Like measuring the frequency of seismic waves during an earthquake can help geologists "see" what material is under our feet, astronomers use asteroseismology (and, for our own star, "helioseismology") to find clues as to what distant stars are made of by studying the oscillations on their surface.

If Betelgeuse really did eat its sister, the massive disturbance could be adding an extra wobble to the star's gait.

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