StarDate: December 22, 2009

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Family ties are always complicated. But two giant stars that make up the system known as Capella will take it to extremes. As each star dies, it will change the other one -- perhaps in drastic ways.

Capella is high in the northeast at nightfall, and almost directly overhead around midnight. It's one of the brightest stars in the northern sky, so it's easy to see.

To the eye alone, Capella looks like a single star. But that pinpoint of light is actually two stars. They were born from the same cloud of gas and dust about 400 million years ago, so they're stellar siblings. They're a close-knit family, too -- they're separated by less than the distance from Earth to the Sun.

Each star is bigger, brighter, and more massive than the Sun. And each one is nearing the end of its life. The stars are going through a series of dramatic changes that are causing their outer layers to puff up like balloons.

Fairly soon, the heavier of the two stars, which is aging a little faster, should get so big that its companion will begin to steal some of its gas. And that will start a complex series of interactions that no one can predict.

The companion star may be rejuvenated for a while. Later, it may send gas back to the heavier star -- which by this time may consist of no more than a dense corpse. As the gas piles on, it could trigger a series of big explosions -- or one titanic explosion that would rip the star to bits -- tearing apart a close stellar family.

Script by Damond Benningfield, Copyright 2009

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