Introduction
Gravitational lensing is predicted by 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. 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
- is the gravitational constant,
- is the mass of the lens,
- is the speed of light,
- is the angular diameter distance to the lens,
- is the angular diameter distance to the source, and
- is the angular diameter distance between the lens and the source.
Note that, over cosmological distances in general.
Read more about this topic: Einstein Ring
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