Hyperspeed Planets Are Hurtling Out of the Milky Way?

NatGeo

Runaway worlds may move at up to 30 million miles an hour, study predicts.

Artist's conception: runaway planet with an erupting volcano (bottom right). Illustration courtesy David A. Aguilar, CfA

Brian Handwerk

for National Geographic News

Published March 23, 2012

If you think life on Earth moves too fast, imagine being perched on a planet that’s hurtling through space 400 times faster than our home world.

According to a new study, astronomers predict that “hypervelocity planets” are streaking through our Milky Way galaxy at up to 30 million miles (48 million kilometers) an hour—flung from the center of our galaxy by so-called gravitational slingshots.

Only subatomic particles such as cosmic rays are known to reach higher speeds in the Milky Way. (Related: “Lightning Creates Particle Accelerators Above Earth.”)

So what would it be like on a lonely, fast-moving world? For one thing, the night sky would be a lot more dynamic, said study co-author Idan Ginsburg, an astronomy graduate student at Dartmouth College.

“If you were on the planet, from your perspective, you’d be moving so fast that in a relatively short time you’d see the galaxy just getting farther and farther away.”

Ultimately, Ginsburg said, the planet would probably get kicked out of the galaxy.

“To where? That’s a good question, but it would be a one-way ticket and a wild ride,” he said.

“The problem is that you don’t have a star or an external heat source, so your planet would get pretty cold.” (Related: “Earth-Size ‘Lone Wolf’ Planets May Host Life.”)

Planets Flung by Black Hole Slingshot

The new study was inspired by the discovery seven years ago of the first hypervelocity star, which is currently on a one-way trip out of our galaxy at a staggering 1.5 million miles (2.4 million kilometers) an hour.

Since then astronomers have spotted more than a dozen high-speed stars in the Milky Way.

Scientists believe such speedy stars originate in binary star systems, where pairs of stars orbit each other.

“When two stars orbiting each other get close enough to the massive black hole in the center of our galaxy, they feel slightly different forces, because they are at slightly different distances,” explained study co-author Avi Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA).

“Because of this difference, the gravity of the black hole is strong enough to basically rip them apart,” and one star in the pair gets launched outward at high speed.

(Related: “Black Hole in Milky Way Seen Snacking on Asteroids?”)

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