October 22, 2014

11.05.10: Ancient Galaxy Mergers.

Hickson Compact Group 31. (Credit: NASA/HST/ESA/S. Gallagher/J. English).

Hickson Compact Group 31. (Credit: NASA/HST/ESA/S. Gallagher/J. English).

 

   Astronomers may have found a cosmological missing link in the realm of galactic evolution. The early universe was a crowded place; galaxy mergers must have been much more common in the primeval universe than they are today. But studying those early collisions has been problematic; the immense distances involved over time and space mean that resolving clusters and individual stars are out of the question. Now, a team from the University of Western Ontario led by Sara Gallagher has published a study of an object which may serve as a “living fossil” of those early times; Hickson Compact Group 31. A cluster of irregular galaxies “only” 166 million light years away in the constellation Eridanus, this merger has somehow escaped coalescence over 10 billion years of cosmic history to just begin merging. “Because HCG 31 is so nearby,” Gallagher notes, “we can indentify individual star clusters.” In fact, two main components of HCG 31 approach visual magnitude +13 and have been snared by amateur instruments. HCG 31 is approximately 75,000 light years in diameter, and will probably one day form one huge elliptical galaxy. To conduct this study, Gallagher utilized time and instruments that spanned the spectrum, from Hubble in visible light to Spitzer in infrared to Galex and Swift in the ultraviolet. It is amazing that astronomers now have such capabilities in their bag of tricks at their ready disposal!