Gravitational Lensing Decoded

Gravity: What Is It?

In basic terms, gravity refers to the force of attraction between two objects having mass. It is by far the weakest force and needs objects of very high mass to produce a considerable amount of gravity.

Gravity is really important and is present in our daily lives. It is the very stuff that keeps us anchored to the ground, keeps the Earth in orbit around the Sun, the Moon around Earth, and the entire Solar System around our galaxy, the Milky Way.

What is Gravitational Lensing?

In the universe, light travels enormous distances before it reaches us. To take an example, the closest star to Earth, Proxima Cenaturi, is around 4.3 light years or about 40,208,000,000,000 km away. So, while travelling such enormous distances, some forces act upon the light and "bend" it.

Gravity is one such force. In the vast expanses light travels, gravity from enormous objects like black holes can bend its path. Gravitational lensing is defined below-

Gravitational lensing refers to the bending of light, as if by a lens, caused due to the gravity of a very large celestial body, like a galaxy cluster, black hole, etc.

Gravitational Lens

A gravitational lens is a celestial body which causes the gravitational lensing of light.

However, unlike an optical lens, the maximum deflection occurs when the light is travelling closest to the centre of the gravitational lens.

Types of Gravitational Lensing

Gravitational lensing is mainly of three types-

• Strong Lensing-
  Strong lensing is the type of lensing in which distortions are clearly visible in the form of arcs, multiple images, etc.
• Weak Lensing-
  In this type of lensing, large distortions are not visible, but when a large number of images are analysed, slight distortions are found.
• Microlensing-
  In case of microlensing, no distortions are visible, however, the light received keeps varying over time.

Some Examples of Gravity Lensing-

Let's see a few pictures in which gravitational lensing can be clearly seen-

In this image, the red galaxy has distorted the light from a blue galaxy behind it such that the blue galaxy appears as a circle of blue light.
Credit: ESA/Hubble & NASA

Here, the gravitational lensing is in such a way that the galaxies look like a smiley face.
Credit: ESA/Hubble & NASA

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Clear skies,

Aarav Iyer