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Double Double

September 30, 2017

Most of the stars in the Milky Way galaxy are members of binaries — two stars that are bound to one another by their mutual gravitational pull. But a system in Lyra, the harp, is a rarity: two binaries that are held together by their gravity, creating a family of four stars.

Epsilon Lyrae stands quite close above Vega, one of the brightest stars in summer and autumn skies, which is high in the west at nightfall.

Through binoculars, it’s easy to see the system as two pinpoints of light, known as Epsilon 1 and Epsilon 2. And a small telescope reveals the binary nature of each of those points. Since all four stars can be seen on their own, Epsilon Lyrae is also known as the Double Double.

One of the most remarkable things about the system is that all four of its stars are quite similar. All of them are bigger, hotter, and heavier than the Sun. It’s rare to find a double binary in which all of the stars are so much alike.

Current estimates say the system is about 800 million years old — roughly one-sixth the age of the Sun. That’s a long time for two binaries to remain stuck together. But they may not cling to each other forever. As Epsilon Lyrae orbits the center of the galaxy, it’s tugged by the gravity of passing stars and gas clouds, as well as “tides” created by the galaxy as a whole. Someday, that may pull the binaries apart, sending them on their separate ways — turning the Double Double into two single doubles.


Script by Damond Benningfield


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