Scientists tell of 'runaway' planets

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CAMBRIDGE, Mass., March 22 (UPI) -- U.S. scientists studying "runaway" stars tossed out of our galaxy at great velocities say they've confirmed the same thing can happen to planets.

The first runaway star was discovered seven years ago, heading out of the Milky Way at 1.5 million mph, and new research says planets must be doing the same thing -- at speeds up to 30 million mph, the Harvard-Smithsonian Center for Astrophysics reported Thursday.

"These warp-speed planets would be some of the fastest objects in our galaxy," astrophysicist Avi Loeb said. "If you lived on one of them, you'd be in for a wild ride from the center of the galaxy to the universe at large."

So-called hypervelocity planets are produced in the same way as hypervelocity stars, researchers said.

A double-star system wanders too close to the supermassive black hole at the galactic center, where strong gravitational forces rip the stars from each other, sending one away at high speed while the other is captured into orbit around the black hole.

The researchers modeled what would happen if each star had an orbiting planet or two and found the star ejected outward could carry its planets along for the ride, while a star captured by the black hole could have its planets torn away and flung into interstellar space at tremendous speeds.

"Other than subatomic particles, I don't know of anything leaving our galaxy as fast as these runaway planets," study lead author Idan Ginsburg of Dartmouth College said.