Betelgeuse is something of a "superstar" in the night sky, but new research suggests that the red supergiant that marks the shoulder of the constellation Orion might have an interesting past.

The star is closely watched not only because it's so bright, but because it's also quite ancient and ready to go supernova any day now (or thousands of years from now, which still qualifies as "soon" on the cosmic timescale). As it has approached the end of its lifespan, Betelgeuse has swollen up to many times its original size.


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Astronomer J. Craig Wheeler of The University of Texas at Austin says new evidence leads him to believe that the luminous red star may have once had a companion star that it eventually swallowed as it grew.

The clue to the star's mysterious past came when a team of undergraduates working with Wheeler used a computer modeling program called MESA to model its rotation for the first time.

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

One possibility is that the star once had a companion about the size of our own sun orbiting it that was swallowed by Betelgeuse when it expanded into the red supergiant we see today. Wheeler believes that once the smaller star was absorbed, it would transfer the angular momentum of its own orbit to the outer layers of Betelgeuse itself, speeding up the remaining star's rotation.

Wheeler needed some evidence to bolster his theory, and he found it in the form of matter that would have been shot out into space following this star-swallowing event like a massive cosmic burp.

"I went to the literature, in my naiveté, and read about Betelgeuse, and it turns out there's a shell of matter sitting beyond Betelgeuse only a little closer than what I had guessed," Wheeler said.

There is some debate over the origin of this shell of matter, but Wheeler says it as evidence that something happened at Betelgeuse around the time the star expanded into a supergiant. Next up, he and his team hope to study the star's surface for further evidence Betelgeuse may have once eaten its neighbor.

The research is published online this week in the journal Monthly Notices of the Royal Astronomical Society.

Source: University of Texas-Austin

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