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August 24, 2013

One of the prominent star patterns of late summer and autumn, the Great Square of Pegasus, is low in the east as the sky gets good and dark. It represents the body of the mythological flying horse.

Another horse is to the upper right of the Great Square — Equuleus, the little horse. In mythology, it represented Pegasus’s little brother. It’s not that much to look at — four faint stars form a shape that resembles a sail.

The brightest of those four is known as Alpha Equulei, at the lower right corner of the sail. It’s almost 200 light-years away. Yet it’s visible to the unaided eye in part because it actually consists of two stars, which have an interesting future.

Both stars are roughly twice as massive as the Sun, and several times larger. Yet they’re separated by less than the distance between the Sun and Earth.

One of the stars is nearing the end of its life, so it’s puffing up to giant proportions. Before long, it’ll get so big that its companion will start to pull gas from its outer layers. The giant will continue to expand, though, perhaps eventually engulfing the companion. By then, the companion may be starting its own end game, also puffing up to become a giant.

No one is certain how the scenario will play out. The two stars could merge to form a single star. Or they may stay separated, passing material back and forth until the outer layers dissipate — leaving behind a pair of small but hot stellar corpses known as white dwarfs.


Script by Damond Benningfield, Copyright 2013

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