spaceSpace and Physics

Betelgeuse May Be Spinning Faster Than Expected Because It Ate A Sun-Like Star


Jonathan O'Callaghan

Senior Staff Writer

Orion's left shoulder is the red supergiant, Betelgeuse. Marc Ward/Shutterstock

Betelgeuse is one of the most famous stars in the night sky, being the left shoulder of the equally well-known Orion constellation. But it looks like this red supergiant star may be hiding a few secrets.

According to a new study published in the Monthly Notices of the Royal Astronomical Society, Betelgeuse is spinning much faster than we expect, and the reason might be that it ate a Sun-like star earlier in its life.


“It’s spinning 150 times faster than any plausible single star just rotating and doing its thing,” lead author J. Craig Wheeler from the University of Texas at Austin said in a statement.

Betelgeuse is about 15 to 25 times the mass of our Sun, but it is an astonishing 1,000 times the size. It is just 10 million years old, compared to our Sun at 4.6 billion years, and as a red supergiant it will live a relatively short life before it explodes as a supernova any time in the next 10,000 years. At just 640 light-years away, the explosion will be easily visible to the naked eye on Earth.

As objects get bigger, they are expected to spin slower. The classic analogy is how an ice skater brings their arms in to spin faster, and vice versa. But that’s not the case here. Our Sun spins at about 6,900 kilometers per hour (4,300 miles per hour), but the much larger Betelgeuse spins faster, at 54,000 km/h (34,000 mph).

Wheeler and his team’s proposal to account for this is that 100,000 years ago, when it first expanded into a red giant, Betelgeuse may have swallowed a rotating companion roughly the same mass as the Sun.


There is no direct evidence for this theory as yet. But Wheeler said that there was a shell of matter sitting near Betelgeuse that was consistent with the idea. If Betelgeuse did eat a star, it would have fired off matter at about 36,000 km/h (22,400 mph), which would be roughly in the position this shell is in today.

This theory would account both for Betelgeuse’s rapid rotation and this shell nearby. Wheeler’s team is planning to use asteroseismology, looking at sound waves impacting the surface of the star, to see what’s happening inside it and perhaps find more evidence for this idea.


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