Orphan planets are being flung through the galaxy at velocities that are a fraction of the speed of light, astronomers have discovered. 

An artist imagines a hypervelocity planet. Credit: David A. Aguilar (CfA)

The supercharged worlds are being fired out into space at up to 30 million miles by a supermassive black hole lying at the centre of our Milky Way. They turn into cosmic bullets when the stars they are orbiting get drawn too close to the black hole, producing a slingshot effect that ejects them from the Galaxy.

Astronomers have already found a runaway star flying out into space at 1.5 million miles an hour. That set them wondering if something similar could happen to planets. Their research showed them that the runaway planets do also exist and that some fly through the Galaxy at even more incredible speeds.

Scientist Avi Loeb, of the Harvard-Smithsonian Center for Astrophysics, said: “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 center of the galaxy to the Universe at large.”

Colleague Idan Ginsburg, of Dartmouth College, who led the research, said: “Other than subatomic particles, I don’t know of anything leaving our galaxy as fast as these runaway planets.”

The astronomers say the so-called hypervelocity planets are produced when a double-star approaches too close to the supermassive black hole. Powerful gravitational forces tear the stars apart, sending one off at high speed while the other is captured into orbit around the celestial cannibal.

When the researchers used their computers to simulate what would happen to the stars’ planets, they found that any orbiting the captured star could be ripped away and flung out into space.

Most would slingshot outwards at seven to 10 million miles per hour, but some could gain much higher speeds under perfect conditions.

That would send them flying out of the Milky Way eventually and into the great empty void between galaxies in the Universe.