Runaway planets are universe's fastest objects

Washington, March 23 (IANS) Runaway planets zipping through space at mind-numbing speeds of 30 million miles per hour are now the fastest objects in the universe, says a study.

Seven years ago, the discovery of the first runaway star, shooting out of our Galaxy at a staggering speed of 1.5 million mph, set astronomers on a course of exploration.

If a star can get tossed outward at such an extreme velocity, could the same thing happen to planets, they asked themselves, the journal Monthly Notices of the Royal Astronomical Society reported.

"Other than subatomic particles, I don't know of anything leaving our galaxy as fast as these runaway planets," said Idan Ginsburg of Dartmouth College, US, who led the study, according to a Harvard-Smithsonian statement.

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

A typical hypervelocity planet would slingshot outward at seven to 10 million mph. However, a small fraction of them could gain much higher speeds under ideal conditions, even as high as 30 million mph.

Such speedy worlds, called hypervelocity planets, are produced in the same way as hypervelocity stars. A double-star system wanders too close to the supermassive black hole at the galactic centre.

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. For this study, the researchers simulated what would happen if each star had a planet or two orbiting nearby.

They found that the star ejected outward could carry its planets along for the ride. The second star, as it's captured by the black hole, could have its planets torn away and flung into the icy blackness of interstellar space at tremendous speeds.