The Hubble Space Telescope has revisited the region of space made famous in its Ultra Deep Field image to reveal even more distant galaxies with its new Wide Field Camera 3.

The Hubble Ultra Deep Field (HUDF) was created in 2004, and now, five years later and with more sophisticated instrumentation than ever before, including the Wide Field Camera 3, Hubble has taken another look, but this time in longer, near-infrared wavelengths.

"We can now look even further back in time, identifying galaxies when the Universe was only five percent of its current age – within one billion years of the big bang," says Daniel Stark from the Institute of Astronomy in Cambridge, part of a UK team studying the new image.

The image was created over four days of pointing for 173,000 seconds of exposure time. The faintest and reddest objects are likely the oldest galaxies ever identified, formed just 600-900 million years after the big bang. Hubble can see these early inhabitants because their light is stretched out of the ultraviolet and visible regions of the spectrum into near-infrared wavelengths by the expansion of the Universe.

"The expansion of the Universe causes the light from very distant galaxies to appear redder, so having a new camera on Hubble which is very sensitive in the infrared means we can identify galaxies at much greater distances than was previously possible," says Stephen Wilkins of Oxford University.

The new image provides insights into how galaxies grew during the Universe's early years, but also presents an intriguing puzzle. "We know the gas between galaxies in the Universe was ionised (where electrons are removed from their host atomic nuclei) early in the history of the cosmos, but the total light from these new galaxies may not be sufficient to achieve this," says Andrew Bunker of Oxford University.

While these new observations are likely to be the most sensitive images Hubble will ever take, the most distant galaxies will provide ideal targets for Hubble's successor, the James Webb Space Telescope, scheduled to launch in 2014.

To learn more about Hubble's discoveries, including spectacular images from the new instruments, check out our new publication Hubble Reborn.