A team of Russian astronomers has announced the discovery of eleven galaxies that are on the run, after being pushed away from their original clusters, and are now floating adrift in what scientists describe as intercluster space.
"These galaxies are facing a lonely future, exiled from the galaxy clusters they used to live in," said Igor Chilingarian, an astronomer at the Harvard-Smithsonian Center for Astrophysics and Moscow State University.
Runaway stars can be ejected from their galaxies if they are travelling at a greater speed than the galaxies "escape velocity." When a rocket blasts off from Earth, escape velocity can only be achieved if the rocket is supplied with enough energy to exceed 11.2 kilometers per second or 25,000 miles per hour. In the case of a star, it would need to be traveling at a speed of 537 kilometers per second or over 1.2 million miles per hour.
For a galaxy to escape the extreme gravitational forces of its cluster, it would have to achieve a velocity of up to 3,000 kilometers per second or 6 million miles per hour, depending on the mass of the cluster.
The 11 galaxies on the run were found by accident while Chilingarian and co-investigator Ivan Zolotukhin, of the L'Institut de Recherche en Astrophysique et Planetologie and Moscow State University, were scouring publicly available data from the Sloan Digital Sky Survey and the GALEX satellite for compact elliptical galaxies.
These types of galaxies are rare, but researchers were able to find 200 previously unknown compact ellipticals, 11 of which were found to be alone, separated and moving really fast.
"The first compact ellipticals were all found in clusters because that's where people were looking. We broadened our search, and found the unexpected," said Zolotukhin.
Compact elliptical galaxies are thought to originate from larger galaxies that go through gravitational interactions with other galaxies in their neighborhood. This means that small elliptical galaxies such as these that are 1,000 times smaller than our Milky Way Galaxy are often expected to be found close to a larger "parent" galaxy.
So what caused these galaxies to travel so far away from home? Researchers believe that a similar gravitational mechanism to the one that produces runaway stars is also responsible for sending these galaxies off on their own.
"We asked ourselves, what else could explain them? The answer was a classic three-body interaction," said Chilingarian. When gravitational fields of three cosmic objects meet each other, normally the lightest of them gets thrown off its trajectory.
"This is the same phenomenon, but working on a different scale," Zolotukhin detailed on the matter.
