What is "gravitational lens"

n. (context astronomy English) A massive body that produces distorted, magnified or multiple images of more distant objects when its gravitational field bends the path of light rays.

A gravitational lens refers to a distribution of matter (such as a cluster of galaxies) between a distant source and an observer, that is capable of bending the light from the source as the light travels towards the observer. This effect is known as gravitational lensing, and the amount of bending is one of the predictions of Albert Einstein's general theory of relativity. (Classical physics also predicts the bending of light, but only half that predicted by general relativity.)

Although either Orest Khvolson (1924) or Frantisek Link (1936) is sometimes credited as being the first to discuss the effect in print, the effect is more commonly associated with Einstein, who published a more famous article on the subject in 1936.

Fritz Zwicky posited in 1937 that the effect could allow galaxy clusters to act as gravitational lenses. It was not until 1979 that this effect was confirmed by observation of the so-called " Twin QSO" SBS 0957+561.