On 14 September 2015, a team of scientists from MIT has detected gravitational waves for the first time with the help of two identical LIGOs(Laser Interferometer Gravitational wave Observatory), situated at Livingston (Louisiana) and Hanford (Washington).
Three scientists of the team, Rainer Weiss, Berry C. Barrish and Kip S. Thorne won novel prize of physics in 2017, for this achievement.
What are Gravitational Waves ?
In the early decades of 19th century, when Albert Einstein was working on his General Theory of Relativity, his basic assumption was- "no object in the universe can have speed greater than the speed of light". But there was a conflict with the theory of gravity, proposed by Newton 200 years ago. According to Newton, the effect of gravity is instantaneous on interstellar bodies, and if so, then gravity is faster than light. So, to support his stand on the assumption, Einstein came up with a new idea in 1916. He stated, "every mass in the space, distorts four dimentional space time". Greater the mass will be, greater will be the distortion. To comprehend this theory he suggested to assume the universe like a stretched fabric. When a heavy mass is placed over it, the fabric gets distorted and creates a slope upto a definite circumference. If an another mass or object comes across this circumference, it's likely to fall over the heavier one rotating in a definite orbit.
When a heavy mass like neutron star or black hole moves in space, ripples are created and which travel all the way through the space distorting space time. These ripples are called Gravitational Waves.
These waves vanish, travelling through the space because of small amplitude. But when any voilent event such as, explosion of a Neutron star or merging of two Black holes or Big Bang takes place, a huge amount of energy is released and amplitude of gravitational waves created, are high enough to travel billions of light years. But it was a theory based prediction untill 1974 as there wasn't any proof of their physical existence. In 1974 two astronomers found a binary pulsar(two extremely heavy and dense stars) orbiting each other. After 40 years of continuous observation they found these stars are getting closer which was a kind of similar system described by Einstein one century back ....Hence confirmed the existence of gravitational waves, but still confirmations were either indirectly or mathematically untill they were physically detected by the LIGO on 14 September 2015, created by merging of two black holes 1.3 billion light years away from us.
Why these waves were too difficult to detect ?
Though effects of gravitational waves are extereme around origin but travelling through billions of light years in the universe their amplitude diminish to thousands of the size of subatomic particles like protons or neutrons. Therefore a highly precise and sensitive instrument was required to detect those small effects and MIT group made it possible.
How LIGO works ?
LIGO consists of L shaped vacuum tunnel whose arm extends 4 kms each. At the end of each arm(tunnel) there is a high precision mirror and a base at the junction which splits a laser beam orthogonally.
The central building fires a laser beam which splits up and travels inside the perpendicular tunnels. Reflecting back from the mirrors, they meet at the base and cancel out each other due to interference. Gravitational Waves when pass through the earth it's been squeezed and outstreched due to the space time distortion, resulting one of the arm to shorten or extend and vice versa. Consequently, there is a difference in phases of the beams and detected by the photo detector as shown in the picture. But this is also sensitive to external source of vibrations such as storm, lightning, movements of vehicles etc. To avoid such detections, two identical LIGOs are installed at two corners of USA, Livingston and hanford, separated by 3000 kms and should have same results to confirm a gravitational wave.
Readings, recorded on 14 September 2015
How Useful these waves are ?
Since LIGO's first detection we have gained unexpected insight into the cosmos.That's because gravitational waves are new way of "seeing" what happens in space : we can now detect events that would otherwise leave little or no observable light, like black hole collisions. And with this latest detection, astronomers were able to combine gravitational waves with more traditional ways of seeing the Universe, helping to untangale mysteries about the dense, dead objects known as neutron stars. "Most of us fully expect that we are going to learn things we didn't know about black holes in other ways, and we knew about neuton stars. but we hope there are all sorts of other phenomena that we can see mostly because of the gravitational waves they emit. That will open a new science."
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