Gravitational Lensing

Abhishek Sutradhar

B. Sc 5^th Sem (Major)

Gravitational lensing, first proposed by Soldner in the year 1801 in context of Newtonian theory, when a light emitted by distant galaxies passes by massive objects in the universe, the gravitational pull from the massive objects can distort or bend the light. This is called gravitational lensing.

A gravitational lens can occur when a huge amount of matter, like a cluster of galaxies, creates a gravitational field that distorts and magnifies the light from distant galaxies that are behind it but in the same line of sight. The effect is like looking through a giant natural magnifying glass which allows to study the details of early galaxies too far away from our current telescope and technology.

Analyzing the nature of gravitational lensing pattern, researchers could compute the way dark matter is distributed within galaxies and their distance from Earth. In its initial study researchers took the simplest type of lensing which occurs when there is a single concentration of matter at the centre, such as the dense core of a galaxy. The incident rays of a distant galaxy is redirected around this core, resulting multiple images of the background galaxy. And taking the time limit, when the lensing approaches perfect symmetry, an almost complete circle of light is produced, observed and termed by Einstein as “Einstein ring”.

Taking the theory of relativity in account, is kept as an angle between line of bending of incidence.

The diverse lens images of crosses, rings, arc and more are both intrinsic and informative. It enables the distribution of matter in galaxies and observable distant universe. The probe of information on gravitational lensing gives rise unpredictable measurements and parameters, which predicts the deflection angle as

For sun, it gives 0.85”.

And,

In 1915 with General Relativity, Einstein derived the new result-

For sun, it gives 1.7”