Capella

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As the Sun ages, it'll so do without interference from any partner stars. But for most stars, that's not the case. They have one or more companions. And if the companions are close enough, they can have a profound effect on how the other changes as it gets older.

An example is the star system Capella, in Auriga, the charioteer. The bright yellow-white star is in the northeast at sunset, and stands directly overhead around midnight.

Capella is actually a binary -- two stars locked in a tight orbit around each other. They're separated by less than the distance between Earth and the Sun.

That closeness could play a role in how the stars end their lives.

Both stars are late in life, so they've both puffed up to many times their original size. In fact, they're so big that their surfaces are only about 50 million miles apart -- a mere hop on the stellar distance scale.

One of the stars is a little more massive than the other, so it's aging faster than its companion. Fairly soon, its outer layers will blow off into space, leaving only its hot, dense core, known as a white dwarf.

Some of the gas from this star will fall onto the surface of its companion. And the white dwarf will pump out a lot of radiation, heating the side of the companion that faces it. These factors will effect how the second star evolves. They may speed up its evolution, causing it to "die" an early death -- one of the costs of living with another star.

Script by Damond Benningfield, Copyright 2008

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