SEATTLE - The Hubble Space Telescope has used a giant, natural magnifying glass in space to zoom in on some of the most distant and faint galaxies ever detected. However, there's a problem: Fewer galaxies are there than astronomers had expected.
The huge cosmic lens is actually a cluster of galaxies harboring a trillion stars about 2.2 billion light-years away. The combined gravity of the stars and unseen, exotic dark matter associated with the cluster exerts a strong pull on light coming from objects even farther away.
The light is bent, distorted and magnified, revealing things that could not otherwise be seen from Hubble's orbital position above Earth.
The resulting image shows a multitude of galaxies associated with the lens itself, a galaxy cluster known as Abell 1689. Many of them are yellow. More interesting are bizarre streaks, many of them blue, that represent background galaxies that have been smeared by the lens. Astronomers speculate some of them may be more than 13 billion light-years away, very near the edge of the observable universe.
The image was presented here today by Narciso Benitez and Holland Ford of Johns Hopkins University, at a meeting of the American Astronomical Society.
Benitez said only three galaxies appear to be in the range of the most distant galaxies known, what astronomers refer to as those beyond a redshift of 6.
"This is probably telling us something about galaxy evolution," he said.
More analysis is needed to pin down exactly what is in the images and how far away things are, the astronomers said. They expect to be untangling the results for months.
The gravitational lensing technique has been used before, but Hubble astronomers said this was its most detailed product. Albert Einstein was the first to predict that gravity warps space and would also distort a beam of light.
Importantly, the image should allow astronomers to map the distribution of dark matter in the galaxy. This unseen stuff is more prevalent than regular matter, such as stars and planets. Scientists don't know what dark matter is, but they know it exists because they see its effects on the speed with which stars orbit galaxies. If dark matter did not exist, galaxies would simply fly apart.
The location and concentration of normal and dark matter determine how each background galaxy is distorted. Images of the same galaxies appear on both sides of the lens.
Though the background galaxies are smeared, details in them are seen, things that otherwise would not be visible to Hubble. Astronomers found lanes of dust and clusters of stars within individual background galaxies, providing clues to how some of the universe's first galaxies were structured.
Several small red objects in the image are either nearby, cool stars or galaxies that are very far away.
The photograph is a combination of visible and near-infrared light captured in separate exposures by Hubble's new Advanced Camera for Surveys. The images were taken in June, 2002 and involved 13 hours of exposure time. Hubble is a joint project of NASA and the European Space Agency.
"We're using this fabulous instrument on Hubble in combination with the fabulous instrument that Nature has provided, these clusters of galaxies are like cosmic telescopes," Ford told SPACE.com. "What we are finding are galaxies that are less than two billion years old."
The ultimate goal, he said is to find galaxies in the first billion years after the universe formed.
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