This image released by NASA in Washington on September 9, 2009 shows Gravitational Lensing in Galaxy Cluster Abell 370 through The Hubble Space Telescope’s newly repaired Advanced Camera for Surveys (ACS). Abell 370 is one of the very first galaxy clusters where astronomers observed the phenomenon of gravitational lensing, where the warping of space by the clusterÕs gravitational field distorts the light from galaxies lying far behind it. This is manifested as arcs and streaks in the picture, which are the stretched images of background galaxies.
A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is “bent” around a massive object (such as a cluster of galaxies) between the source object and the observer. The process is known as gravitational lensing, and is one of the predictions of Albert Einstein’s general theory of relativity.
Although Orest Chwolson is credited as being the first to discuss the effect in print (in 1924), the effect is more usually 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.
