Astronomers have pieced together the deepest-ever view of the universe, peering back more than thirteen billion years.
Called the eXtreme Deep Field, or XDF, the photo covers one small patch of sky at the center of the original Hubble Ultra Deep Field – less than the angular diameter of the full moon – and combines 10 years worth of Hubble images.
Even in this tiny area, the XDF contains about 5,500 galaxies, including many that are much fainter than those revealed bythe Hubble Ultra Deep Field. It includes very deep exposures in red light from Hubble’s new infrared camera, enabling new studies of the earliest galaxies in the universe.
Hubble pointed at a tiny patch of southern sky for a total of 50 days over a ten-year period, with a total exposure time of two million seconds. More than 2,000 images of the same field were taken with the Advanced Camera for Surveys and the Wide Field Camera 3, and combined to make the XDF.
“The XDF is the deepest image of the sky ever obtained and reveals the faintest and most distant galaxies ever seen. XDF allows us to explore further back in time than ever before,” says Garth Illingworth of the University of California at Santa Cruz.
The XDF reveals galaxies that span back 13.2 billion years in time – just half a billion years after the Big Bang. For this reason, most of the galaxies in the XDF are seen when they were young, small, and growing – often violently, through mergers and collisions.
The James Webb Space Telescope, now under construction, will also be aimed at the XDF, and should be able to find even fainter galaxies that existed when the universe was just a few hundred million years old. Its infrared vision is ideally suited to push the XDF even deeper, into a time when the first stars and galaxies formed, says the team.
