Gravitational lensing is a phenomenon that has often occured in Space. It is the bending of light from a light source over long distances. The observer usually sees a hollow circle of light rather than the entire light source. This phenomenon itself is intriguing but it could indicate the presence of a black hole.
A black hole has been known to be so strong that it has the capability of bending light. The problem with just determening the presence of a black hole from this phenomenon may not be able to tell us the location of this black hole. Since the light is reaching the observer from a very long distance, the black hole could be anywhere in between.
Lensing might also occur due to scattering of light. There could be millions of celestial objects between the observer and the light source. Anything that could cause refraction or reflection can cause this phenomenon. It would all depend on the angle at which the light source is observed. The name is gravitational lensing becuse light is known to bend only in the presence of a lens or gravity.
Finally its just light bending because of the effect of gravity and the distance the light has to travel. Lensing only occurs with far off light sources so you could only imagine the intensity of brightness at the source.
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