NASA scientists have directed the Hubble Space Telescope to inspect a tiny patch of sky with an unusually long exposure time to obtain the deepest image of the sky ever obtained. The image, dubbed the Hubble Extreme Deep Field (XDF), reveals the faintest and most distant galaxies ever detected, shedding more light on the early history of the universe.
Nine years ago, NASA decided to point Hubble at a seemingly empty, randomly chosen spot in the sky – no larger than a needle's eye at arm's length – and have it gather data over one millions seconds in total exposure. The result was the iconic image dubbed the "Hubble Ultra-Deep Field" (HUDF) which, even in a space that small, revealed in excess of ten thousand galaxies.
Now, NASA has done it again, taking the experiment to new levels. With XDF, NASA took a patch of sky within the original Hubble Ultra Deep Field and doubled the exposure time to a total of two million seconds, or an impressive 23 days. Despite a much narrower field of view, the new picture shows 5500 galaxies in even greater detail, including the earliest we have ever observed.
Because the universe is expanding, light from distant galaxies is shifted into longer, infrared wavelengths. Hubble combined its two primary cameras – the Advanced Camera for Surveys and the near-infrared Wide Field Camera 3 – to take over 2000 pictures of the area in question, which were then combined to form the XDF.
The picture reveals a number of spiral galaxies similar to our Milky Way, but also many large red galaxies that have seen catastrophic collisions with other galaxies and have lost the capability of producing new stars.
Before Hubble, astronomers could only see galaxies seven billion light-years away – roughly half the age of the universe. This newly released image, however, sets a new record in that it has found galaxies existing as early as 450 million years after the Big Bang, allowing astronomers to investigate further into the past than ever before.
What's next? Armed with enhanced infrared capabilities, the James Webb Space Telescope scheduled for launch in 2018 will be equipped to discover even fainter and earlier galaxies.
The video below gives a sense for the miniscule field of view of used to take this image.