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October 14, 2013

Just when you think you know a star, it turns out you don’t really know it at all.

Consider Fomalhaut, the bright, lonely star below the Moon this evening. It’s one of the 20 brightest star systems in the night sky, so astronomers have paid it a lot of attention. And it’s just 25 light-years away, so it’s fairly easy to study.

Even so, Fomalhaut is still full of surprises. Recent studies have shown that it’s about twice as old as astronomers had thought, and that it has a distant companion.

For a while, Fomalhaut’s age had been put at about 200 million years. But some recent studies have upped the age. One last year, for example, said Fomalhaut is about 440 million years old.

That result was based in part on more precise measurements of Fomalhaut’s temperature and brightness, which are key parameters in calculating a star’s age. But it was also based on observations of the nearby star TW Piscis Austrinus.

The two stars are less than a light-year apart, and they move through space at the same speed and direction. The study says that means the two stars are almost certainly a binary — two stars that were born together and remain bound to each other.

The study looked at several traits of TW Piscis Austrinus, and they all indicated an age of roughly 400 million years. So as we get to know Fomalhaut better, we’re finding that it’s older than we thought — and a good bit more complicated.

More about Fomalhaut tomorrow.


Script by Damond Benningfield, Copyright 2013

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