Hubble Spies Most Distant, Early Galaxies Yet

This story was updated at 5:56 p.m. ET.

WASHINGTON ? The Hubble Space Telescope has taken the deepest look into the universe yet, revealing some of the most distant, earliest galaxies to form after the Big Bang.

The images peer back about as far as Hubble can look, to about 600 million to 800 million years after the theoretical Big Bang, team scientists said. The universe is about 13.7 billion years old.

"Essentially we are looking back 13 billion years" and looking at very faint objects, said Garth Illingworth of the University of California, Santa Cruz. "We're pushing Hubble to the limits to find these objects."

This deeply penetrating view of the universe, snapped by Hubble over four days in August, was first revealed last month. Some of the insights into the early universe gleaned from these images, as well as close-ups of some of the most distant known galaxies, were revealed here today at the 215th meeting of the American Astronomical Society.

The galaxies spied in these images are invisible in the visible part of the light spectrum, but stood out clearly in the infrared images. They are some of the earliest galaxies yet seen.

"The galaxies have primordial-like characteristics," Illingworth said, though he cautioned that "we're not finding primordial galaxies." The very first galaxies will take a telescope like the upcoming James Webb Space Telescope to find.

Hubble scientists also assembled a full-color panoramic view of thousands of galaxies in various stages of assembly. The image, which covers the range of wavelengths from ultraviolet to near-infrared, was pieced together from observations by the WFC3 in September and October 2009, as well as 2004 images from Hubble's Advanced Camera for Surveys.

The 7,500 galaxies in the image show astronomers various stages of galactic evolution over the history of the universe. The image covers galaxies that existed from just 650 million years after the Big Bang to just 1 billion years ago.

The distant, young galaxies in the Hubble images still give astronomers a picture of what the environment of the early universe. By judging the galaxies ages, scientists can guess at when galaxies actually first formed in the universe.

"These are extremely vigorously star-forming galaxies," Illingworth said.

And by combining the Hubble images with data from the Spitzer Space Telescope, astronomers can tell that some of the stars in these early galaxies are several hundred million years old, which suggests that the galaxies themselves began forming just a few hundred million years after the Big Bang.

"The faintest galaxies are now showing signs of linkage to the origin of the first stars," said team member Rychard Bouwens, also of the University of California, Santa Cruz. "They are so blue that they must be extremely deficient in heavy elements, thus representing a population that has nearly primordial characteristics."

The galaxies are very faint and very small, only about 5 percent of the size of the Milky Way and 1 percent of its mass.

"These are the seeds of the great galaxies today," Illingworth said.

The new Hubble images also shed light on the universe's so-called reionization era, the farthest back that astronomers can see. For the first few hundred thousand years after the Big Bang, the universe was a hot, murky mess, with no light radiating out.

But about 400,000 years after the Big Bang, temperatures in the universe cooled, electrons and protons joined to form neutral hydrogen (meaning it had no charge), and the murk cleared. Some time before 1 billion years after the Big Bang, neutral hydrogen began to form stars in the first galaxies, which radiated energy and changed the hydrogen back to being ionized, or charged. This was what astronomers call the reionization period.

One big questions is what exactly in the early universe triggered the ioniziation period. Early galaxies are one likely culprit, but astronomers don't yet know whether or not these galaxies could put out enough energy to set off the reionization.

The infrared images were taken with Hubble's new Wide Field Camera 3, which was installed during Hubble's most recent (and last) servicing mission over the summer.

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