Moon and Regulus

StarDate: November 9, 2009

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One way that people try to stay youthful looking is to lose weight. But one of the brightest stars in the night sky may have done it the other way around: It looks younger than it really is because it's gained weight.

Regulus is the brightest star of Leo, the lion. It's a little to the lower left of the Moon as they rise after midnight.

Until recently, astronomers thought that Regulus was no more than about 200 million years old. But that thinking changed with last year's discovery of a tiny companion quite close to Regulus: a white dwarf -- the hot, dense corpse of a once-normal star. A study earlier this year said that Regulus and the white-dwarf companion are actually around a billion years old.

When the stars were born, the one that's now the white dwarf was actually the heavier of the two. As it aged, though, it puffed up, and Regulus stole most of its outer layers of gas. As a result, Regulus is about twice as massive today as when it was born.

The extra gas altered Regulus's chemistry and its temperature -- effects that made the star appear much younger than it really is.

In the future, Regulus itself will puff up, too. Eventually, it'll engulf the white dwarf. The white dwarf and the core of Regulus might settle into an orbit around each other, inside Regulus's outer layers of gas. Or they might kick the outer layers into space, and merge to form a single white dwarf -- a dead star that can no longer hide its age.

Script by Damond Benningfield, Copyright 2009

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