The first apparent example of an Einstein ring, a celestial illusion predicted by physicist Albert Einstein more than 50 years ago, has been discovered by astronomers.

They found an elliptical ring they believe occurs because radio waves are bent by the gravity of a distant cosmic object. The discovery, reported in the British journal Nature, was made by Jacqueline N. Hewitt of Massachusetts Institute of Technology and other radio astronomers.The scientists say the sighting is another example of a gravitational lens.

During the past decade, several celestial mirages have been spotted. A galaxy relatively close to Earth acts as a lens, bending the light emitted by a more distant object. In most of the other examples, the result has been the appearance of two objects where only one actually exists.

However, the latest probable gravitational lens is bending radio waves, rather than light, into a ring.