What is Gravitational Lensing effect?

**Effects of Gravity#2**

 Gravitational Lensing effect in space-time

How does gravity bent space-time to act as a 'lens' in viewing the most distant objects in outer space?

Considered as the weakest fundamental force on the atomic scale, gravity is a real game-changer when it comes to astronomy or generally, macrophysics. From planetary orbits to galaxy clusters to black hole singularities, there's no story without gravity. But that's not all, there's one more mind-blowing phenomenon that arises out of the warping of space-time and bending of light near massive stars or galaxies, called the Gravitational Lensing effect. 

Gravitational lensing effect is basically what we call it, a 'lens' made out of distortion or curvature of the space-time around a massive star or a galaxy. The more massive the object is the more the curvature will be. Our 4-dimensional universe (length, breadth, height and time),  which we call space-time, is actually like a vast elastic sheet that's filled with such curvatures or distortions, caused by objects with different energy mass distributions. Light, which was always thought to travel in straight paths, will not travel such in curved space-time. Instead, the light will follow the curved path that's been presented to it by the distorted space-time. 

Gravitational lensing (Einstein Ring)

This bending of light near a star or a galaxy will give a magnified or distorted image of distant quasars or galaxy clusters that are way behind this particular star or galaxy (lens). So, a distant object (source) would be visible to an observer as distorted and magnified. This happens if there's a star or a galaxy cluster in between the source and the observer so that the massive cluster's curvature bends the light from the source (act as a lens to the observer) and the observer can view the source object magnified. The extreme cases of gravitational lensing effects obviously occur in the black holes, around its event horizon, where photons actually form a shell by orbiting the black hole.

By G. Mikaberidze - Own work, CC BY-SA 4.0
A light source passes behind a gravitational lens (point mass placed in the centre of the image). The aqua circle is the light source as it would be seen if there were no lens, while white spots are the multiple images of the source 

In some cases, the gravitational lensing effect can cause multiple images of the same object. This is what we call an Einstein Cross (image to the right). It happens when the source, the lens and the observer is in a near-perfect alignment, and the light from the source, which is a quasar, takes multiple paths to reach the observer. In normal cases, the lens will be a massive elongated galaxy whose mass creates a space-time curvature around it.

Scientists use this technique of gravitational lensing effect to study distant galaxies, quasars and star clusters. Momentary flickering of such magnified images indicates the presence of orbiting planets in star clusters or galaxies. The most shocking fact about gravitational lensing is that most of the lensing in this universe is not done by massive stars or galaxies, but by dark matter !! Even though dark matter doesn't absorb or emit anything, it has mass, and if it possesses mass it should have some pulling effect as well. However, the lack of data about dark matter is a huge drawback to study its features.  

Anyways, the next time you look up the stars, just a reminder that it would be some distorted magnified version of a distant star or... if you're lucky, probably a quasar from a black hole !!