Gravitational Wave - Cosmic Genius

What is Gravitational Wave ?

A gravitational wave is an imperceptible (yet fantastically quick) ripple in space.

We've thought about gravitational waves for quite a while. Over 100 years prior, an incredible researcher named Albert Einstein thought of numerous thoughts regarding gravity and space.

Einstein anticipated that something exceptional happens when two bodies, for example, planets or stars—circle each other. He trusted that this sort of development could bring about ripple in space. These ripple would spread out like the ripple in a lake when a stone is hurled in. Researchers call these ripple of space gravitational waves.

Gravitational waves are imperceptible. Be that as it may, they are inconceivably quick. They go at the speed of light (186,000 miles for each second). Gravitational waves crush and extend anything in their way as they pass by.

Illustration of how mass bends space (Image credit: NASA)

What causes gravitational waves?

The most powerful gravitational waves are made when articles move at high speeds. A few cases of occasions that could bring about a gravitational wave are:

when a star detonates unevenly (called a supernova).
when two major stars circle each other.
when two black holes circle each other and merge.

In any case, these sorts of items that make gravitational waves are far away. Also, once in a while, these occasions just purpose little, feeble gravitational waves. The waves are then exceptionally powerless when they reach Earth. This makes gravitational waves hard to detect.

How do we know that gravitational field exist?

In 2015, researchers detected gravitational waves for the very first time. They utilized an exceptionally touchy instrument called Advanced LIGO (Laser Interferometer Gravitational-Wave Observatory). These first gravitational waves happened when two black holes collided with each other. The crash happened 1.3 million years back. Be that as it may, the ripples didn't make it to Earth until 2015!

Advanced LIGO is made up of two observatories: one in Louisiana and one in Washington (above). Each observatory has two long “arms” that are each more than 2 miles (4 kilometers) long.

Effect of passing

Gravitational waves are constantly passing Earth; however, even the strongest have a minuscule effect and their sources are generally at a great distance. For example, the waves given off by the cataclysmic final merger of GW150914 reached Earth after travelling over a billion lightyears, as a ripple in spacetime that changed the length of a 4-km LIGO arm by a ten thousandth of the width of a proton, proportionally equivalent to changing the distance to the nearest star outside the Solar System by one hair's width. This tiny effect from even extreme gravitational waves makes them undetectable on Earth by any means other than the most sophisticated detectors.

The effects of a passing gravitational wave, in an extremely exaggerated form, can be visualized by imagining a perfectly flat region of spacetime with a group of motionless test particles lying in a plane (e.g., the surface of a computer screen). As a gravitational wave passes through the particles along a line perpendicular to the plane of the particles (i.e. following the observer's line of vision into the screen), the particles will follow the distortion in spacetime, oscillating in a "cruciform" manner, as shown in the animations. The area enclosed by the test particles does not change and there is no motion along the direction of propagation.

The oscillations depicted in the animation are exaggerated for the purpose of discussion — in reality a gravitational wave has a very small amplitude(as formulated in linearized gravity). However, they help illustrate the kind of oscillations associated with gravitational waves as produced, for example, by a pair of masses in acircular orbit. In this case the amplitude of the gravitational wave is constant, but its plane of polarization changes or rotates at twice the orbital rate and so the time-varying gravitational wave size (or 'periodic spacetime strain') exhibits a variation as shown in the animation. If the orbit of the masses is elliptical then the gravitational wave's amplitude also varies with time according to Einstein's quadrupole formula.^[4]

As with other waves, there are a number of characteristics used to describe a gravitational wave:

Amplitude: Usually denoted h, this is the size of the wave — the fraction of stretching or squeezing in the animation. The amplitude shown here is roughly h = 0.5 (or 50%). Gravitational waves passing through the Earth are many sextillion times weaker than this — h ≈ 10⁻²⁰.
Frequency: Usually denoted f, this is the frequency with which the wave oscillates (1 divided by the amount of time between two successive maximum stretches or squeezes)
Wavelength: Usually denoted λ, this is the distance along the wave between points of maximum stretch or squeeze.
Speed: This is the speed at which a point on the wave (for example, a point of maximum stretch or squeeze) travels. For gravitational waves with small amplitudes, this wave speed is equal to the speed of light (c).

The speed, wavelength, and frequency of a gravitational wave are related by the equation c = λ f, just like the equation for a light wave. For example, the animations shown here oscillate roughly once every two seconds. This would correspond to a frequency of 0.5 Hz, and a wavelength of about 600 000 km, or 47 times the diameter of the Earth.

In the above example, it is assumed that the wave is linearly polarized with a "plus" polarization, written h₊. Polarization of a gravitational wave is just like polarization of a light wave except that the polarizations of a gravitational wave are at 45 degrees, as opposed to 90 degrees. In particular, in a "cross"-polarized gravitational wave, h_×, the effect on the test particles would be basically the same, but rotated by 45 degrees, as shown in the second animation. Just as with light polarization, the polarizations of gravitational waves may also be expressed in terms of circularly polarized waves. Gravitational waves are polarized because of the nature of their sources.