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Gravity helps astronomers see the unseen

Dense galaxy-size 'lenses' and the fact that light is bent by dark matter let researchers peer deeper into the universe.

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Einstein predicted that the gravity of a massive object such as a galaxy will bend light like a lens. In some cases, the lensing can image distant objects that lie behind the galaxy. Astronomers have studied such gravitational lenses for decades. Now they are ready to turn them into a powerful tool to test the latest theories of the structure and evolution of the universe.

Far from being a cosmic oddity, gravitational lensing appears to be ubiquitous. New research suggests that there may be half a million strongly lensing galaxies scattered across the sky. Other research has traced strands of unseen dark matter by the way their gravity distorts light. These strands wrap the universe in an invisible web.

Some of this research is from the COSMOS Project that aims to survey thoroughly a small patch of sky about nine times the area of the full moon. Jean-Paul Kneib with the Lab­­or­­atoire d'Astronomique de Marseille, France, and Cécile Faure at the University of Heidelberg, Germany, led a team that sifted through 2 million galaxy images taken by the Hubble Space Telescope. They found 67 strong gravitational lenses in that small space of sky.

Such lensing usually occurs when light from a distant galaxy is magnified and distorted by a cluster of galaxies that lie between the distant galaxy and us. But, in the project's announcement last month, Dr. Kneib says that, "what we are observing here is a similar effect but on a much smaller scale – happening around a single but very massive galaxy."

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