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Hubble Telescope Reveals Farthest View Into Universe Ever

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Called the eXtreme Deep Field, or XDF, the photo was assembled by combining 10 years of NASA Hubble Space Telescope photographs taken of a patch of sky at the center of the original Hubble Ultra Deep Field. The XDF is a small fraction of the angular diameter of the full Moon. Image released September 25, 2012. (Image credit: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team)

The Hubble Space Telescope has captured the farthest-ever view into the universe, a photo that reveals thousands of galaxies billions of light-years away.

The picture, called eXtreme Deep Field, or XDF, combines 10 years of Hubble telescope views of one patch of sky. Only the accumulated light gathered over so many observation sessions can reveal such distant objects, some of which are one ten-billionth the brightness that the human eye can see.

The photo is a sequel to the original "Hubble Ultra Deep Field," a picture the Hubble Space Telescope took in 2003 and 2004 that collected light over many hours to reveal thousands of distant galaxies in what was the deepest view of the universe so far. The XDF goes even farther, peering back 13.2 billion years into the universe's past. The universe is thought to be about 13.7 billion years old.

This image compares the angular size of the XDF field to the angular size of the full moon. The XDF is a very small fraction of sky area, but it provides a "core sample" of the heavens by penetrating deep into space over a sightline of over 13 billion light-years. Several thousand galaxies are contained within this small field of view. At an angular diameter of one-half degree, the moon spans an area of sky only one-half the width of a finger held at arm's length. Image released Sept. 25, 2012. (Image credit: NASA, ESA, and Z. Levay (STScI); Image: T. Rector, I. Dell'Antonio/NOAO/AURA/NSF, Digitized Sky Survey (DSS), STScI/AURA, Palomar/Caltech, and UKSTU/AAO)

"The XDF is the deepest image of the sky ever obtained and reveals the faintest and most distant galaxies ever seen," Garth Illingworth of the University of California at Santa Cruz, principal investigator of the Hubble Ultra Deep Field 2009 program, said in a statement. "XDF allows us to explore further back in time than ever before."

The photo reveals a wide range of galaxies, from spirals that are Milky Way-lookalikes, to hazy reddish blobs that are the result of collisions between galaxies. Some of the very tiny, faint galaxies could be the seeds from which the biggest galaxies around today grew. [Most Amazing Hubble Discoveries]

The XDF is a portrait of a small area of space in the southern constellation Fornax, and spans only a small fraction of the area of the full moon. Within that region, Hubble has revealed 5,500 galaxies, many of which existed shortly after the birth of the universe.

The farthest-away galaxies are 13.2 billion light-years from Earth, meaning their light has taken 13.2 billion years to travel to Hubble's cameras. 

"The light from those past events is just arriving at Earth now, and so the XDF is a 'time tunnel into the distant past,'" according to a NASA statement. "The youngest galaxy found in the XDF existed just 450 million years after the universe's birth in the Big Bang."

Hubble was only able to image these objects by amassing light in 2,000 images of the same area, with a total exposure time of 2 million seconds, through two of its cameras: the Advanced Camera for Surveys and the Wide Field Camera 3.

Hubble was launched in April 1990, and has been visited by space shuttle crews five times since then for upgrades. The telescope, a collaboration between NASA and the European Space Agency, is still going strong, and scientists say the scope should be able to function through at least 2018.

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Clara Moskowitz
Clara Moskowitz
Clara has a bachelor's degree in astronomy and physics from Wesleyan University, and a graduate certificate in science writing from the University of California, Santa Cruz. She has written for both Space.com and Live Science.