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November 25, 2017

A pair of bright stars with an even brighter future is one of the highlights of the northern sky on late-autumn nights.

Capella, the brightest star of Auriga, the chariot driver, is in the northeast as night falls. The yellow star arcs high overhead after midnight, and is in the northwest at first light.

What looks like a single point of light is really two stars that are gravitationally bound to each other. They’re closer together than Earth is to the Sun, so even with giant telescopes it’s almost impossible to see them as individual stars.

Each star is at least two-and-a-half times as massive as the Sun, and a good bit bigger and brighter. And in the years ahead, they’ll get bigger and brighter still. That’s because both stars are nearing the ends of their lives. Now, they’re undergoing changes that are causing their outer layers to puff up.

Over time, each star should swell to dozens of times the size of the Sun, and shine hundreds of times brighter. Then the stars will blow off their outer layers, leaving behind their exposed cores, known as white dwarfs. But how that will play out is uncertain. As the first one puffs up, it will transfer some of its gas to the other, altering the evolution of both stars.

The clouds of gas around them will drag the two stars closer together. In the far distant future, they could slam together, creating a supernova — blasting both stars to cosmic dust.

We’ll have more about Capella tomorrow.

Script by Damond Benningfield

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