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Tuesday, March 4, 2008

Universe Loaded With Natural Magnifying Glasses

One of the best tools astronomers have to glimpse the distant universe is a technology that nature invented. Cosmic magnifying glasses called gravitational lenses help scientists zoom in on far-away scenes they could never spot otherwise.

In a recent survey of a section of the universe, researchers counted 67 new gravitational lenses, leading them to believe there are nearly half a million similar lenses in the rest of the universe.

"Gravitational lenses amplify the signal," said Peter Capak, an astronomer at California Institute of Technology who worked on the study. "It's like a second telescope in front of your telescope. We can see things that are much fainter than we can normally see."

These natural telescopes are created when massive objects distort the space-time around them through the strength of their gravitational pull, causing light to bend as it travels through the warped space.
If a gravitational lens lies between us and a distant object, then the image of the object we see can be distorted and magnified.

In the rare case that a gravitational lens is perfectly aligned between Earth and a distant object, "typically you can get at least a factor of 10 � 50 magnification," said Jean-Paul Knieb, an astronomer at Laboratoire d'Astrophysique de Marseille, France, leader of the study.

The effect was predicted in the 1930s by Einstein's general theory of relativity, and was first observed in 1979.

The 67 newly discovered lenses are caused by large galaxies, although clusters of galaxies often produce strong gravitational lenses too.

A team of astronomers used the NASA/ESA Hubble Space Telescope, along with follow-up observations from the ground, to image a 1.6 square degree field of sky (about nine times the area of the full Moon) in great detail. The researchers then pored over the images by eye to spot the tell-tale circular warping signatures of gravitational lenses.

In addition to giving scientists a better idea of how many gravitational lenses are out there, the discovery will help researchers study the spread of dark matter around the galaxies causing the lenses.

"The main thing the gravitational lenses do for us is they allow us to study the mass distribution in individual galaxies," Capak told "A lot of the mass is contained in dark matter. We want to understand how the dark matter is distributed."

By analyzing patterns in the warping of space-time caused by the gravitational lenses, the scientists hope to gain a better understanding of the structure of galaxies.

"You can think of the lenses as glass beads," Capak said. "If you hold up a glass bead and look thorough it, it distorts the picture behind it. The shape of the glass bead is what's causing the different distortions. The shape of the mass distribution in galaxies is distorting the background in different ways."

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