18 ENRO

This Hubble Space Telescope image shows us a "red and dead" elliptical galaxy -- the product of a collision between two good-sized galaxies that is slowly evolving to become a giant elliptical galaxy. Older ellipticals are nicknamed "red and dead" by astronomers because these bloated galaxies are not producing new, bluer stars, and are thus packed full of old and redder stellar populations. This type of galaxy has grown more and more common as the universe has evolved, with initially small galaxies merging and progressively building up into larger galactic structures over time.

Learn more: http://go.nasa.gov/1Zx9zCB
Image credit: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt