In 1915, Albert Einstein introduced general relativity, which at the time sounded like something of science fiction. His theory stated that gravity is produced by the mass of an object causing a curve in spacetime. This curvature of spacetime has an effect on objects that may pass over it. Which in the case of gravitational lensing, would be light.
As a way to confirm this theory of relativity, an astronomer by the name Arther Stanley Eddington and astronomer Andrew Claude de la Cherois Crommelin set out on 2 separate expeditions for the 1919 eclipse. Arther went to Sobrel in northern Brazil and Andrew to the Island of Príncipe off the coast of west Africa.
Through this expedition, the astronomers were able to confirm Einstein’s theory. They observed that there was a deflection of light from the stars due of the sun coming between them and the earth. This revelation completely changed the way astronomers looked at cosmic events. It channeled a world of possibilities for all the things we can discover and left us wondering just how far back we can go to find answers.(Lea, R)
WHAT IS IT?
The effect of light from a background source, making it appear as though its been passed through a lens, is called gravitational lensing. Light travels in a straight line until it comes into contact with a large object, such as a galaxy, where the fabric of spacetime seems to warp around. From a far enough distant one would notice that instead of going straight through, the light that comes into contact with said object bends around it, the same way that light bends when it is passed through a lens. This light from the background source then becomes magnified, making it appear many times brighter than it would have if it hadn’t passed through the lens. The lens being, in this case, the large object or galaxy.
Generally, the images caused by the gravitational lens is slightly distorted. When the lensing is strong, which is where light passes closest to the lens, the image is a little bit more distorted than when it is a weak lensing. A weak lensing is when the light passes slightly further from the lens.
USE
Gravitational lensing allows us to measure the mass of the lensing object and to determine the properties that it may contain. We can also use lensing to see objects from extremely far away, things from the past or objects that might’ve been too dim for our technology to pick up on before it became magnified. This could greatly aid in the research of the early universe, how things evolved at the time and what structures were even present at such a time.
With the aid of gravitational lensing we can further our study and possible understanding of dark matter. Gravitational lensing makes it easier to map out where dark matter is concentrated in our universe.
The rate at which the universe is expanding, known as the hubble constant, is also something that gravitational lensing can help astronomers measure.
SHAPES
When the background source, the lens and the observer are all perfectly aligned, the bend around the lens is equal in all directions. This causes it to look like there is a circle around the lens. The shape formed has been named the Einstein ring.
Another one of the shapes formed is called the Einstein cross. This is seen as 4 points of light around the central lens. It is formed because there is only a slight misalignment between the background source, lens and observer.
An arc shape around the lens in the most common sort of shape formed as it is very rare to have perfect alignments. This arc usually appears blue because of the many young blue stars found in the lensed galaxies.
As opposed to strong lensing, weak lensing cannot be easily identified when looking at individual spots. We need to look at much larger areas before we are able to identify that a lensing occurred in any particular area.
The smallest form of gravitational lensing known as microlensing, which causes no distortion of image, is when a star or planet passes by another star magnifying its light for just a blink of a moment. With microlensing scientists have been able to discover multiple, previously unseen, exoplanets.
DISCOVERIES
Einstein’s cross or Q2237+030, discovered 1985. A galaxy about 400 million light years away lensed a quaser which is 8 billion light years away. This lensing formed 4 images arranged in a cross like pattern surrounding the lensing galaxy.
Abell 370, which is a massive cluster of galaxies acts as a lens for multiple other galaxies. It forms stunning images around the lensing galaxies including one known as the dragon, which is a bright curved streak of light.
MACS J1149.5+2223, discovered 2014. This is a supernova that was lensed from the MACS J1149.5+2223 galaxy cluster. The supernova was able to be observed multiple times because its light came at multiple intervals.
CONCLUSION
We have only scratched the surface of the things we can do with the knowledge of gravitational lensing. Even with only this scratch we have discovered a magnificent amount of data. With more time we will uncover mysteries about the universe that we never thought possible.
BIBLIOGRAPHY
Gianopoulos, A., & Gianopoulos, A. (2026, August 6). Hubble Gravitational Lenses – NASA Science.
Tuhin, M., & Tuhin, M. (2026, May 17). Gravitational Lensing: Nature’s cosmic magnifying glass.
Pearson, E. (2026, June 15). Beginner’s guide to gravitational lensing.
Lea, R. (2023, May 31). A cosmic magnifying glass: What is gravitational lensing?
