Astronomers have observed 11 runaway galaxies wandering aimlessly around in spaaace.
The discovery was revealed by star-gazing boffin Igor Chillingarian of Harvard-Smithsonian Center for Astrophysics (HSCA) and Moscow State University, who was the lead author of a study published in the Science journal on Friday.
Scientists dub objects runaways when they move quicker than escape velocity.
In the words of the HSCA such an object "will depart its home never to return. In the case of a runaway star, that speed is more than a million miles per hour (500 km/s). A runaway galaxy has to race even faster, travelling at up to 6 million miles per hour (3,000 km/s)."
Chillingarian worked with his co-author Ivan Zolotukhin to initially attempt to track down compact ellipticals – which are members of a class of galaxies containing "tiny blobs of stars" and span only a few hundred light-years.
Our Milky Way, in contrast, is 100,000 light-years across.
However, the boffins – who pored over public stashes of datasets from the Sloan Digital Sky Survey and NASA's GALEX satellite – discovered 11 runaway galaxies during their painstaking search when they identified 200 previously unknown compact ellipticals.
Before now, scientists were only aware of roughly 30 compact elliptical galaxies in space.
"The first compact ellipticals were all found in clusters because that's where people were looking. We broadened our search, and found the unexpected," Zolotukhin explained.
It had been previously theorised that lonely compact galaxies had come from larger galaxies stripped of most of their stars by an even bigger galaxy.
Based on that logic, compact galaxies should all be found hanging around near big mothership galaxies.
Instead, the newly uncovered compact ellipticals were not only isolated but also moving at a faster speed.
The HSCA explained the latest theory:
A hypervelocity star can be created if a binary star system wanders close to the black hole at the center of our galaxy. One star gets captured while the other is thrown away at tremendous speed.
Similarly, a compact elliptical could be paired with the big galaxy that stripped it of its stars. Then a third galaxy blunders into the dance and flings the compact elliptical away. As punishment, the intruder gets accreted by the remaining big galaxy.
"We asked ourselves, what else could explain them? The answer was a classic three-body interaction," Chilingarian concluded, before adding: "We recognised we could use the power of the archives to potentially unearth something interesting, and we did." ®