Scientists eye a clue to the `missing' matter in the universe

Radio waves emitted in the unique shape of a halo have been discovered by an astronomer from the Massachusetts Institute of Technology and her colleagues. These researchers may have found the first ``Einstein ring.'' So-called because Albert Einstein speculated about the phenomenon in 1936, the ring is thought to be formed by radio waves emitted from a cosmic object, probably a galaxy. Researchers believe that the gravity of an unknown object between Earth and the galaxy bends the waves into an elliptical ring. This phenomenon is called gravitational lensing.

More than 90 percent of the mass in the universe is unaccounted for. It may be in the form of dark, or invisible, matter, which could be responsible for the bending radio waves.

The ring seems to correspond to a dim smudge of light when seen through an optical telescope, but takes shape when viewed with radio telescopes.

Earlier cases of gravitational lensing have appeared as arcs. If the Einstein ring turns out to be caused by gravitational lensing, it will provide unique data.

Jacqueline Hewitt of MIT, who first spotted the Einstein ring, says that the mass responsible for this lensing may be dark matter. If so, the closed, constrained shape of the newly-discovered image will tell researchers more about the distribution of that matter than could other ``open'' images, she says.

It may also give scientists data for calculating the Hubble's constant - the rate at which the universe is expanding.

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