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Mutant star's behavior baffles astronomers

A giant star in the Canis Majoris constellation isn't acting like itself, and scientists are doing their best to figure out why.

Because of its massive size, Xi1 can be seen with the naked eye in Canis Majoris. But observation with an X-ray-sensing telescope revealed its strange and secret life. ESA/XMM-Newton/L. Oskinova (University of Potsdam)

When the European Space Agency turned its X-ray-sensing XMM-Newton telescope on a star known as Xi1 Canis Majoris, scientists there got quite a surprise. Even though the star is 15 times bigger than our own sun, it was sending out regular X-ray pulses five hours apart.

While such pulsations are typical in what are known as "degenerate stars" like white dwarves or neutrons, they've never before been seen from normal stars, according to the researchers. Plus, even though Xi1 Canis Majoris burns at almost 50,000 degrees Fahrenheit, that's not considered hot enough to produce the amount of X-rays the star is throwing off.

So what's going on with the tricky star, which is located about 1,400 light years away in the constellation Canis Major? Astronomers simply don't know.

The only clue they have at the moment is that the star is also emitting visible light waves through its stellar wind that sync up with the X-ray pulses. Stellar, or solar, winds are the stream of particles -- like light-creating photons -- that come off a star due to its intense heat. In this case, the light pulses are driven by what's known as the kappa mechanism, changes in the way radiation is absorbed and re-emitted inside a star.

"For me personally, this work has shown that stellar winds and the high-energy radiation that comes from them must be linked by some physical mechanism to what is happening inside the star," says the study's lead researcher, Lidia Oskinova from the University of Potsdam. In other words, the fact that these photons and the X-ray pulses inside the star are acting in unison indicates a link between the two that could help explain the star's unique activity.

"This is breakthrough science because it shows that X-ray pulsations can take place not only in exotic objects but in normal stars too," said Norbert Schartel, ESA XMM-Newton Project Scientist in a statement. "New physical processes governing stellar winds can now be studied."

The researchers' findings were published in Nature Communciations on Tuesday. They plan to continue investigating the strange behavior of Xi1 Canis Majoris through computer modeling.