What are gravitational waves? Well, for us to understand that we must first go back to the 17th century.
In 1687 Sir Isaac Newton’s work was published in a book ‘Philososphiae Naturalis Principia Mathematica’, in which he postulated that the force that makes an apple fall to the earth is also the one that keeps the moon in its orbit around the earth. Essentially, every celestial body exerts an attractive force on every other, which is known by gravitational force. He proposed that the force was propotional to the masses of the two bodies and inversely proportional to the square of the distance between them.
Discrepancies in Newtonian gravity
By the end of the 19th century, a discrepancy in Mercury’s orbit pointed out flaws in Newton’s theory. Slight perturbations were shown by Mercury’s orbit that could not be accounted for entirely under Newton’s theory. Also the issue of the instantaneous exertion of gravitational force between distant bodies contradicted Einstein’s special theory of relativity which claimed that nothing travels faster than the speed of light.
Einstein came to the rescue
In the year 1915, Albert Einstein proposed in his General Theory of Relativity that gravitational force is the result of warping of space-time fabric. This could be explained by imagining space-time fabric as a two dimensional rubber sheet where a celestial body could be assumed as a massive ball creating curvature in it. When a smaller ball is rolled on the rubber sheet, it revolves around the large ball along the curvature for a while before falling into it. Einstein said that all the bodies creates curvature around them in the space-time fabric and other bodies follows the curvature.
As pebble produces ripple in water when thrown into pond, the cataclysmic events like merging black holes in the cosmos produces ripple in the space-time fabric. These ripples are known as Gravitational Waves. These waves cascade outwards from the event at the speed of light, stretching and squeezing space-time as they go. By the time waves reaches earth, squeezing and stretching shrinks down to minute fraction of the width an atomic nucleus. According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years and then much more quickly in the final minutes. During the final fraction of a second , the two black holes collide into each other at nearly one-half the speed of light and form a single more massive black hole converting a portion of the combined black holes’ mass to energy, according to Einstein’s formula E=mc^2. This energy is emitted as a final strong burst of gravitational waves.
About the discovery
About 1.3 billion years ago two black holes swirled closer and closer together until they merged giving rise to a new black hole and created a gravitational field so strong that it distorted space-time creating gravitational waves, this collision was the first of its kind ever detected and its waves the first ever seen. The gravitational waves were detected on September 14, 2015 by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA. The LIGO Observatories are operated by Caltech and MIT. Based on the observed signals, LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the sun. About 3 times the mass of the sun was converted into gravitational waves in a fraction of a second-with a peak power output about 50 times that of the whole visible universe. Astrophysicists say the detection of gravitational waves opens up a new window on the universe, revealing faraway events that can’t be seen by optical telescopes, but whose faint tremors can be felt, even heard, across the cosmos.
How LIGO works?
Being able to detect gravitational waves opens a new window to the universe. Everything we know about the universe comes from observations made through electromagnetic waves. But unlike electromagnetic waves, gravitational waves can pass through the universe unobstructed, so they carry information that we cannot obtain otherwise. The ability to detect gravitational waves opens up the new field of gravitational-wave astronomy. Now we would be able to explore the early stages of the universe as gravitational waves can freely propagate through the hot plasma of the early universe