Astronomers discover two peanut-shaped star systems

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Washington, April 1 : Astronomers have spotted two new star systems, which are the first of its kind, sharing stellar material to form the shape of a peanut.

Discovered by Ohio State University astronomers and their colleagues, the first star system is 13 million light years away, tucked inside Holmberg IX, a small galaxy that is orbiting the larger galaxy M81.

After studying it between January and October 2007 with the Large Binocular Telescope (LBT) on Mt. Graham in Arizona, the astronomers regard this system as unusual because it's what they have called a "yellow supergiant eclipsing binary".

It contains two very bright, massive yellow stars that are very closely orbiting each other. In fact, the stars are so close together that a large amount of stellar material is shared between them, so that the shape of the system resembles a peanut.

In a repeating cycle, one star moves to the front and blocks our view of the other. From Earth, the star system brightens and dims, as we see light from two stars, then only one star.

The two stars in this system appear to be nearly identical, each 15 to 20 times the mass of our sun.

Jose Prieto, Ohio State University graduate student, who analyzed the new star system, uncovered another one a little less than 230,000 light years away in the Small Magellanic Cloud, a small galaxy that orbits our own Milky Way. he star system had been discovered in the 1980s, but was misidentified. When Prieto re-examined the data that astronomers had recorded at the time, he saw that the pattern of light was very similar to the one they had detected outside of M81.

The stars were even the same size - 15 to 20 times the mass of the sun - and melded together in the same kind of peanut shape. The system was clearly a yellow supergiant eclipsing binary.

"We didn't expect to find one of these things, much less two," said Kris Stanek, associate professor of astronomy at Ohio State.

The find may help solve another mystery. Of all the supernovae that have been studied over the years, only the two newly discovered have been linked to yellow supergiants - and that's two more than astronomers would expect.

According to Prieto, Stanek, and their colleagues, yellow binary systems like the ones they found could be the progenitors of these odd supernovae.

"When two stars orbit each other very closely, they share material, and the evolution of one affects the other," said Prieto.

"It's possible two supergiants in such a system would evolve more slowly, and spend more time in the yellow phase - long enough that one of them could explode as a yellow supergiant."

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