Gravitational waves - a vibration in the universe's spacetime

 

Image: Flickr

Gravitational waves are ripples in the spacetime fabric of the universe caused by events that emit excess energy. In 1916, a physicist named "Albert Einstein" predicted the existence of gravitational waves in the universe in his general theory of relativity. 

Just as when an iron ball is placed on a bed, the surface of the bed is bent inward, so the mass of material bends the space time fabric inward. This will change the time of the object as well. 

Image: DeviantArt

If objects that bend this spacetime are accelerated, instead of moving at a uniform velocity, some waves will form in their spacetime fabric. These waves are called gravitational waves .

These waves decrease in intensity as they move away from the source. These waves can also cause some change in the shape of objects in the universe. That is, when they pass through the Earth, one side of the Earth is stretched and the other side is contracted. Once they are gone, the earth will return to its original state. (as shown below)

GIF: Wikimedia commons 

These waves travel at the speed of light in all directions from the source. Excessive gravitational waves are produced by events such as the collision of black holes, supernova, and the collision of neutron stars. Even small-scale gravitational waves can be generated by the rotation of neutron stars that are not in a perfect, spherical configuration. 

These gravitational waves remained a prediction until 1974 after Einstein. In the same year 1974,  Joseph Taylor and Russel Hulse, two  astronomers, discovered the existence of binary pulsars 21,000 light years away. 

When they studied them further, they noticed that there was a change in their orbital period. This rate of change was consistent with the rate predicted for the generation of gravitational waves in Einstein's general theory of relativity. Joseph Taylor and Russel Hulse were awarded the Nobel Prize in 1993 for the discovery of these binary pulsars. 

After them, many astronomers mathematically demonstrated gravitational waves with pulsars and other astronomical phenomena. However, there is no solid evidence for their existence in this universe. All were just mathematical speculations.

Then on September 14, 2015, NSF LIGO , an American research observatory, found the first evidence of gravitational waves. Scientists there detected a gravitational wave caused by the collision of two black holes 130 million light years away. These gravitational waves were detected by an L-shaped  interferometer .

laser interferometer gravitational-wave observatory (LIGO) 
Image: Flickr

An L-shaped interferometer here spans about 4 kilometers in two perpendicular directions. As mentioned earlier, when a gravitational wave passes through our earth, our earth contracts and expands. At that time, any arm of this L-shaped system will be compressed or stretched. Therefore, there will be a change in the light received from them. With this change the gravitational waves were confirmed. 

As these gravitational waves come from billions of kilometers away, their impact is attenuated billions of times. A gravitational wave detected by LIGO in 2015 was ten thousand times smaller than the nucleus of an atom. So the contraction of earth would have been very small. 

Albert Einstein who was the first to predict these tiny waves, believed that they won't be detected by humans.

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