http://hubblesite.org/newscenter/archive/releases/2015/45/image/a/
December 3, 2015: Hunting for faraway galaxies that existed long, long ago is like a fishing trip for astronomers. So far only the "big fish" have been found, bright galaxies that existed just a few hundred million years after the big bang. Now, using the Hubble and Spitzer space telescopes, astronomers have caught a "smaller fish," a very compact and faint early galaxy that was forming 400 million years after the big bang, which happened 13.8 billion years ago.
As there are many smaller fish than big fish in the sea, the new finding is evidence for an underlying population of dim galaxies that must have been common in the early universe. Hubble's upcoming successor, the James Webb Space Telescope, should be able to survey this population. But for now, Hubble can do some pioneering work by exploiting a "zoom lens" in space that captures a galaxy that would otherwise not be detectible. The phenomenon is called gravitational lensing, where the intense gravity of a cluster of galaxies magnifies the light of fainter background sources.
Astronomers needed the infrared sensitivity of both the Hubble and Spitzer telescopes to measure the galaxy's great distance through its color, which is affected by the expanding universe.
