Gravitational lensing

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Author: Dr. Jean-Paul Kneib, OAMP, Marseille

Dr. Jean-Paul Kneib accepted the invitation on 4 October 2007 (self-imposed deadline: 1 February 2008).

Gravitational Lensing is the name given to the phenomenum of light deflection by massive bodies in the Universe. Indeed, following Einstein's General Relativity a massive object in the Universe is locally deforming the Space-Time, hence a light ray (following a geodesic) will be deflected in a similar way as b an optical lens. Although the deflection of light is also expected in the classical Newtonian theory, the deflection is twice larger in the General Relativity. For this reason, the gravitational lensing of the Sun has been one of the first test of General Relativity theory. The first measure of the Sun deflection was recorded by Sir [Arthur Eddington] during the Solar Eclipse of 1919.

Image:Lensing.jpg

Figure 1: Lens Deflection