Figure: The geometry of gravitational lenses and Einstein Rings
Gravitational lensing is a result from Albert Einstein's theory of General relativity. Instead of light from a source traveling in a straight line (in three dimensions), it is bent by the presence of a massive body, which distorts spacetime. An Einstein Ring is a special case of gravitational lensing, caused by the exact alignment of the source, lens and observer (θS = 0 in the Figure). This results in a symmetry around the lens, causing a ring-like structure.
The size of an Einstein ring is given by the Einstein radius. In radians, it is:
where
- G is the gravitational constant,
- M is the mass of the lens,
- c is the speed of light,
- dL is the distance to the lens,
- dS is the distance to the source, and
- dLS is the distance between the lens and the source.
The geometry of gravitational lenses
Credit: http://en.wikipedia.org/wiki/Einstein_ring