Galaxy clusters targeted by Hubble's Frontier Fields

These are NASA/ESA Hubble Space Telescope natural-colour images of four target galaxy clusters that are part of an ambitious new observing program called The Frontier Fields. This program will look deeper into the Universe than ever before. With a boost from natural "zoom lenses" found in space, they should be able to uncover galaxies that are as much as 100 times fainter than what the Hubble, Spitzer, and Chandra space telescopes can typically see. The gravitational fields of the clusters brighten and magnify far-more-distant background galaxies that are so faint they would otherwise be unobservable. The foreground clusters range in distance from 3 billion to 5 billion light-years from Earth.

For information on the exposures and colours in this image, visit http://hubblesite.org/newscenter/archive/releases/2013/44/fastfacts/.