Runaway Planets Travel at Speeds up to 30 Million Miles Per Hour

Posted on March 22, 2012

Runaway Planet

Astronomers found a runaway star leaving our galaxy at a speed of 1.5 million miles per hour seven years ago. The runaway stars travel so fast they leave a bow shock. Researchers at the Harvard-Smithsonian Center for Astrophysics say planets could also reach an extreme velocity - up to 30 million miles per hour - if sent hurling out of our galaxy by a supermassive black hole.

In the artist's conception above, a runaway planet zooms through interstellar space. New research suggests that the supermassive black hole at our galaxy's center can fling planets outward at amazing speeds. Eventually, these worlds will escape the Milky Way and travel through the intergalactic void. The illustration also shows a glowing volcano on the planet's surface.

These 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 center. 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.

Astrophysicist Avi Loeb of the Harvard-Smithsonian Center for Astrophysics, says, "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."

Loeb also said, "Travel agencies advertising journeys on hypervelocity planets might appeal to particularly adventurous individuals."

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 interstellar space at tremendous speeds. The astronomers say a typical hypervelocity planet would slingshot outward at 7 to 10 million miles per hour. However, a small fraction of them could gain even much higher speeds under the most ideal conditions.

Image: David A. Aguilar/Harvard-Smithsonian Center for Astrophysics