These elliptical and compact galaxies have been escaping their home clusters after interacting with larger galaxies.
Scientists know of about runaway stars and have discovered one runaway star cluster. Now, astronomers have found 11 runaway galaxies that have been thrown out of their homes and wonder around intergalactic space.
“These galaxies are facing a lonely future, exiled from the galaxy clusters they used to live in,” explained astronomer Igor Chilingarian from the Harvard-Smithsonian Center for Astrophysics/Moscow State University.
An object is considered runaway if it’s movement is faster than the escape velocity, which implies that it will leave its home never to return. Runaway stars reach speeds of a million mph, while a runaway galaxy has to move even faster, going at up to 6 million mph.
Chilingarian and Ivan Zolotukhin from the L’Institut de Recherche en Astrophysique et Planetologie at Moscow State University tried initially to find new members of a class of galaxies named compact ellipticals. These small blobs of stars are larger than star clusters but have lesser sizes than a normal galaxy, with a span of a few hundred light-years. In comparison, the Milky Way is more than 100,000 light-years across. Compact ellipticals are also 1,000 times lighter than a galaxy like our Milky Way.
Prior to this research, only around 30 compact elliptical galaxies were found, all of them being in galaxy clusters. To find new examples, Chilingarian and Zolotukhin went through public archives of data collected by GALEX satellite and the Sloan Digital Sky Survey.
In their quest the two astronomers identified almost 200 new compact ellipticals. Of those, 11 were extremely isolated and located far from any large galaxy or even galaxy clusters.
“The first compact ellipticals were all found in clusters because that’s where people were looking. We broadened our search and found the unexpected,” explained Zolotukhin.
These isolated and compact galaxies were not expected because scientists believed they came from larger galaxies that had lost most of their stars after interacting with an even larger galaxy. Therefore, the compact galaxies should be located near big galaxies.
Not only were the new compact ellipticals very isolated, but also they were travelling faster through space than the runaway clusters.
A hypervelocity star, which is a very fast star, can be created if a binary star system gets very close to a black hole from the center of our galaxy. One star is captured by the black hole while the other one is thrown away at incredible speeds.
Image Source: Australian Teacher