Two Russian astronomers have spotted 11 homeless galaxies that have been flung out of their homes to wander out in deep space, millions of light years from their nearest neighbours.
Igor Chilingarian — Harvard-Smithsonian Center for Astrophysics — and his co-author, Ivan Zolotukhin — L’Institut de Recherche en Astrophysique et Planetologie — believe that there are tens of billions of undetectable free floating planets that are straggle throughout Milky Way galaxy without being gravitationally bound to any star.
Moreover, there are about two dozen known stars that were rocketing out of our Galaxy at escape velocities of over a million miles per hour. All these objects have one thing in common, they are victims of gravitational disturbances that have left them alone to wander the void of intergalactic space.
Until 2006 astronomers knew only six compact elliptical galaxies like Messier32, home to billions of stars. Compact elliptical galaxies are bigger than star clusters but smaller than a typical galaxy — 1,000 times smaller than Milky Way galaxy — stretches only a few hundred light-years.
But in 2013, Chilingarian’ research identified almost 200 previously unknown compact ellipticals, 11 were being completely remote and far from any large galaxy or galaxy cluster.
The first compact ellipticals were all found in clusters because that’s where people were looking. We broadened our search, and found the unexpected.
The scientists think that similar to hypervelocity star, the gravitational mechanism is slingshotting these ellipticals.
We asked ourselves, what else could explain them? The answer was a classic three-body interaction.
This is the same phenomenon, but working on a different scale, a slingshot effect, when during a three-body encounter the lightest body flies away from the system.
A compact elliptical galaxy were gravitationally paired with a larger galaxy that stripped it of its stars, and that pair interacts with a third galaxy, as result, the intruder could be thrown out.
These galaxies are facing a lonely future, exiled from the galaxy clusters they used to live in.
For their resesrch, Chilingarian and Zolotukhin used data from the The Sloan Digital Survey and the GALEX satellite. Thier study could also explain why some rare isolated dwarf galaxies also appear so far from any neighbors.
Bottom line: An object is a runaway if its moving faster than escape velocity, which means it 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, traveling at up to 6 million miles per hour (3,000 km/s).