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March 18, 2011 > NASA's Space Place: Thank Goodness the Sun is Single

NASA's Space Place: Thank Goodness the Sun is Single

It's a good thing the Sun is single. It could easily be otherwise. About two-thirds of nearby sun-like stars are not. They and a companion star orbit each other like dancers doing a waltz.

Sun-like stars in close double-star systems-called binary systems-can be okay for a few billion years. But then they go bad... very bad.

How bad? According to data from NASA's Spitzer Space Telescope, close binary stars can destroy their planets along with any life.

Some sun-like binary stars orbit each other only a few million miles apart. That is close-so close that the strong pull of the gravity of each star distorts the shape of the other. Normally, stars spin independently of one another (our sun rotates once every 26 days), but the change in shape of close binary stars changes their spin. The two stars stop rotating independently, and they just keep one face locked toward the other, as the Moon does toward Earth.

Such a close binary is a built-in time bomb. The two stars spiral inward, orbiting each other closer and closer, faster and faster. When they get close enough, the two stars rotate as a single star in just 3 or 4 days.

Then, watch out! Such fast spinning makes each star's magnetic field get much stronger. The stars' violent magnetic interactions can shoot out monster flares. These flares can bathe a planet in massive amounts of ultraviolet light (like a very, very bad sunburn) and destroy any life on the surface.

Worst of all, as the two stars grow closer, the gravitational forces throughout the star system begin to change, disturbing the orbits of any planets. Sometimes the planets are nudged right into on-coming traffic! As the planets slam into each other, they shatter into red-hot asteroid-sized bodies. Such violence is certainly not good for any life trying to take root on the planet.

Finally, the planets are broken up into nothing but a ring of warm dust. It is this dust that Spitzer is so good at detecting.

See other fascinating images from the Spitzer Space Telescope by playing Spitzer Concentration at

This article was written by Trudy E. Bell and Diane K. Fisher. It was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

Planetary collisions such as shown in this artist's rendering could be quite common in binary star systems where the stars are very close.

Editor: You can download a hi-res version of this image at

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