In 1979, three British-American astronomers, Walsh, Carswell and Weymann discovered by chance in the sky the first example of a gravitational lens mirage, an illusion at the cosmic scale, which consists of two images of a bright background quasar (an active galactic nucleus), formed by a gravitational lens in the foreground.
The formation of such cosmic mirages had been predicted within the general relativity developed in 1917. According to this theory, Einstein predicts that light rays emitted by a distant background source are deflected near a heavy and compact foreground massive object (the lens) located along the line of sight, like a star, a galaxy or even a cluster of galaxies. Therefore, a large concentration of mass may act as a kind of lens, called a gravitational lens.
A simple educational experience makes it possible to simulate such effects (see below).
Gravitational lens simulator: A didactical experiment designed by J. Surdej (Department of Astrophysics, Geophysics and Oceanography, Liege University) for RéjouiSciences (Faculty of Sciences, ULg)
To buy a lens - click here!
You can find more informations on the DIDACTICAL EXPERIMENT ON GRAVITATIONAL LENSING page
Introduction to the theory of gravitational lensing
Lectures No 1 - 3 (pdf files + videos:mov, avi) given by Jean Surdej (in french):
Number of papers related to gravitational lensing published per year, during the past 50 years.
The most recent papers by the Liège AEOS group dedicated to gravitational lens studies are listed hereafter: