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Gravitational Lensing

The curvature of spacetime plays tricks in  our eyes. Much of the deep universe is shifted and magnified by the warping effect of gravitational lensing. For our eye, light travels in straight lines. We catch the photons in our eyes and trace their path backwards. This is true for short distances which are applicable to human beings. But let us say that there was a pool of water or glass in between the object and our eyes. In that case our eye would not be able to detect the path of the photons. We perceive distorted images as our eye tries to enforce over-simplistic physics on a complex reality. It turns out that the universe is just like a giant rippling pond and many things do not exist where they seem. In the real universe, both space and time can be curved and the path travelled by light follows the curve. Einstein’s general theory of relativity describes the real universe as a flexible, dynamic, dimensional grid that only resembles our mind’s eye Euclidean lattice in the absence of mass and energy. The curvature produced by mass gives gravity. Light follows this curvature, and so gravity bends the path of light. The prediction of general relativity , that gravity deflects the path of light rays ,was one of the first to be directly verified. IN 1919, British astrophysicist, Sir Arthur Eddington loaded a ship full of astronomers and set sail for the island of Principe off the West coast of Africa and sent a second ship to Brazil. The mission was to catch an eclipse of the sun and to measure the tiny change in the position of nearby stars due to the deflection of their light by the sun’s gravitational field. It was seen  in the images captured that the stars had shifted. Their light paths were slightly deflected, making them appear a bit farther from the sun. The deflection angle seems to be exactly what Einstein had predicted.

The gravitational field of any massive object converges passing light rays, like a badly designed lens. For stars, this effect is typically small. However, when we look out there at the universe, we see gravitational lensing everywhere. It has  become a very powerful tool for studying the universe. It is most spectacular when we see extreme warping of the shapes if there are distant galaxies. As their light travels through the deep gravitational wells of intervening galaxies and galaxy clusters, they are greatly magnified in brightness and stretched into arcs and rings. These are noy only beautiful, but they are also useful. The illusion results from our mind’s eye projecting straight lines onto a curved spacetime.

Earlier this year, astronomers led by Kailash Sahu of the Space Telescope Science Institute in Baltimore, Maryland, announced the discovery of the first known isolated stellar-mass black hole.

The black hole is 5,000 light-years away.   Thanks to the power of its gravity to act as a gravitational lens, magnifying the light of a background star 19,000 light-years away. It was initially spotted by two ground-based surveys, the Polish-led Optical Gravitational Lensing Experiment which mostly uses the Las Campanas Observatory in Chile, and the Microlensing Observations in Astrophysics project at the Mount John University Observatory in New Zealand. This black hole wandering in the space lanes of our Milky Way galaxy alone could be the smallest black hole yet found, according to one estimate of its mass.

Discuss Gravitational Lensing and other topics at the Technology College at Amrapali Institute, Haldwani. Amrapali Educational Institute is a top ranked institute in Uttarakhand.

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