Hubble captures extraordinary view of Universe

The Hubble Space Telescope (HST) has produced one of its most extraordinary views of the Universe to date.

Called the eXtreme Deep Field, the picture captures a mass of galaxies stretching back almost to the time when the first stars began to shine.

But this was no simple point and snap - some of the objects in this image are too distant and too faint for that.

Rather, this view required Hubble to stare at a tiny patch of sky for more than 500 hours to detect all the light.

"It's a really spectacular image," said Dr Michele Trenti, a science team member from the University of Cambridge, UK.

"We stared at this patch of sky for about 22 days, and have obtained a very deep view of the distant Universe, and therefore we see how galaxies were looking in its infancy."

The XDF will become a tool for astronomy. The objects embedded in it can be followed up by other telescopes. It should keep scientists busy for years, enabling them to study the full history of galaxy formation and evolution.

The new vista is actually an updating of a previous HST product - the Hubble Ultra Deep Field.

That was built from data acquired in 2003 and 2004, and saw the telescope burrow into a small area of space in the Constellation Fornax (The Furnace). Again, it necessitated many repeat observations, and revealed thousands of galaxies, both near and far, making it the deepest image of the cosmos ever taken at that time.

But XDF goes further; it dials down into an even smaller fraction of the UDF.

It incorporates more than 2,000 separate exposures over 10 years using Hubble's two main cameras - the Advanced Camera for Surveys, installed by astronauts in 2002, and the Wide Field Camera 3, which was added to the observatory during its final servicing in 2009.

Beyond the visible

To see what it does, Hubble has to reach beyond the visible into the infrared. It is only at longer wavelengths of light that some of the most distant objects become detectable.

"Modelling studies suggest that galaxies start small with fewer features and then as they grow in size they acquire the magnificent look that we can see in the closest galaxies observed in this XDF image," explained Dr Trenti.

Of the more than 5,000 galaxies in the XDF, one of them (UDFj-39546284) is a candidate for the most distant galaxy yet discovered. If this is confirmed, it means it is being seen just 460 million years after the Universe's birth in the Big Bang. Scientists time that event to be 13.7 billion years ago.

But as remarkable as the XDF is, it is a prelude for an even deeper Hubble view that is likely to be released later this year. A team led from Caltech (US) and Edinburgh University (UK) has acquired more than 100 hours of additional observations, doubling the exposure time in the all-important near infrared wavebands made possible by WFC3.

The expectation is that it will contain galaxies even closer to the Big Bang.

To see the first starlight in the Universe will most likely require Hubble's successor. The James Webb Space Telescope, which is scheduled to launch in 2018, will carry a much larger mirror and even more sensitive instruments.

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