The Hubble eXtreme Deep Field (XDF) is an image of a small part of space within the constellation Fornax showing the deepest-ever image of the sky –maybe the most zoomed-in photograph ever–. Released on September 25, 2012, the XDF is a follow-up to the famous Hubble Ultra-Deep Field photo created in 2004(*).
The XDF was assembled by combining 10 years of NASA Hubble Space Telescope photographs taken of a tiny patch of sky at the centre of the original Hubble Ultra Deep Field, with a total cumulative exposure time of two million seconds, or approximately 23 days, which resulted in 2,000 individual photos showing the same little section of the sky. The XDF contains about 5,500 galaxies even within its smaller field of view. The faintest galaxies are one ten-billionth the brightness of what the human eye can see.
Looking deeper into the universe also means peering farther back in time. The universe is now 13.7 billion years old. On December 12, astronomers announced they have seen the further back in time than ever before and have uncovered a previously unseen population of seven primitive galaxies that formed more than 13 billion years ago, when the universe was less than 3 percent of its present age. The newly discovered galaxies are seen as they looked 350 million to 600 million years after the big bang. Their light is just arriving at Earth now.
(*) You can enjoy this “fly-thru” view of the Hubble Ultra-Deep photo which scientists created using red-shift calculations of the galaxies: