In a wide binary, two stars orbit each other even though they're much farther apart than Pluto is from our sun, and the nearest example is easy to find: Alpha Centauri, the sun's closest stellar neighbor, consists of a bright star and a faint one separated by one-fifth of a light-year. The bright "star" is a binary itself (artist's conception shown), so Alpha Centauri actually has three separate suns. Now, computer simulations reported online today in Nature imply that wide binaries often begin life as compact triple stars, two of which join up to kick the third away. If the cast-off star remains gravitationally bound to the other two—as with Alpha Centauri—a wide binary results with the far-off star orbiting the central pair on a highly elliptical path. The key to stability is simple: The far-off star must keep its distance. Perhaps our own star was born with two others but didn't heed this advice: As the other two stars cozied up together, the sun tried to intrude, and the happy couple gave it the boot.
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