Runaway Galaxies and Isolated Compact Ellipticals

The result of research into compact galaxies has turned up something unexpected: isolated compact ellipticals. During their study, researchers realized that there were many compact galaxies that weren’t located near any other galaxy, making them wonder why they were out in space alone. Astronomers have already counted eleven different galaxies of this type. Most galaxies are within a cluster, but these appear to be running away from home, but they have actually been pushed.
Astronomers Dr. Igor Chilingarian of the Harvard-Smithsonian Center for Astrophysics, and co-author Dr. Ivan Zolotukhin from Moscow State University, reported that they have been studying compact ellipticals, which is a new member within the class of galaxies. Compact ellipticals are bigger than clusters, but smaller than a typical galaxy, thus creating its own group. These galaxies are typically only a few hundred light years across, while our own Milky Way is over 100,000-light years across. Their findings were recently published in Science.

It was within the study that Chilingarian and Zolotukhin figured out that of the 200 compact ellipticals they found, eleven were completely isolated from any large galaxy or galaxy cluster. Chilingarian and Zolotukhin had found runaways. Because most are found in clusters, no one was searching for the ones that were flung from home. Once Chilingarian and Zolotukhin broadened their search, they found something they weren’t entirely looking for. They noticed that the isolated compact ellipticals were moving much faster than the ones they would have recently crossed paths with.

The astronomers used information gathered by searching the archives at the GALEX satellite and the Sloan Digital Sky Survey to locate compact elliptical galaxies.

The creation of an isolated compact elliptical is believed to come about through the interaction of three galaxies moving into each other’s path. A large galaxy comes across a smaller one and pulls away most of its stars. A third, larger galaxy comes along and flings the first out and away in an elliptical direction, isolating it from the others and increasing its velocity. Runaway galaxies like these move at around six million miles per hour.