Einstein's General Theory of Relativity predicted more than 80 years ago that light from a distant object would travel a curving path if it passed close to a massive object along the line of sight from Earth. The gravitational warping of space around a massive object, Einstein theorized, would have somewhat the same effect as a glass lens on a beam of light, although the image produced by a gravitational lens would be distorted, out of focus and often broken up into multiple images.
In 1979, astronomers verified this prediction when they discovered the first gravitational lens -- direct evidence that a massive object (like a galaxy) between Earth and a more distant object was warping space, and thereby curving and focusing light from the background object.
A typical gravitationally lensed image, astronomers say, resembles the distorted image of an object seen through the base and stem of a wine glass with its bowl cut off.
Since 1979, more than 20 of these relativistic oddities have been identified. All of them greatly distort the magnified images of distant objects behind them, but they sometimes allow scientists to study galaxies and quasars near the edge of the universe that would be otherwise undetectable. The degree and type of distortion of the image of a distant object also reveal information about the sometimes invisible gravitational lens in the foreground.
Monday, astronomers at the University of Manchester, England, and the Hubble Space Telescope team disclosed the discovery of a new gravitationally lensed system in which the distant object, the gravitational lens and Earth are in nearly perfect alignment. The infrared image of this combination made by the space telescope is a complete circle, not the usual collection of disconnected arcs. Both the lensed image of the distant object and the massive galaxy acting as the lens are visible, and together, they have been designated B1938(plus)666.
"At first sight," said Dr. Ian Browne of the University of Manchester, "it looks artificial and we thought it was some sort of defect in the image, but then we realized we were actually looking at a perfect Einstein ring."
The object was discovered by six radiotelescopes operated in concert by Manchester University's Jodrell Bank Observatory as the equivalent of an instrument 135 miles wide. The radio image they captured shows only a fragmented group of bright arcs, because the radio-emitting part of the distant object is slightly out of alignment with Earth. But when the Hubble Space Telescope was subsequently aimed at the object, the galaxy's infrared emission region proved to be perfectly in line with the gravitational lens and Earth, and the Einstein ring appeared.