Journey to gravitational wave

  • July, 2021

Today we are going to look at 2 major topics first one is gravitational waves & the second one is GW170817. Now if you don't know what this GW170817 don't worry you will know at end of this blog but first let's understand what is a gravitational wave.

Gravitational wave

If mass bends space-time, then mass under acceleration must create ripples, or waves, in space-time which we called Gravitational wave. Such a simple & short definition right, well the concept isn't . But to understand gravitational. wave we need to understand core of this waves, reason behind it - Gravity.

What is Gravity according to Einstein ?


Albert Einstein published his theory in 1916, and in it, he showed that time and space are inextricably linked. Together they form the fabric on which the Universe is built – space-time. One way of thinking about space-time is to imagine it as a two-dimensional sheet (i know, in reality, there are four dimensions of space-time, but a sheet is much easier to imagine !). According to Einstein, gravity is the result of the warping of space-time.

Any object with mass warps the space-time in its vicinity, effectively making a dent in the space-time into which objects with less mass will ‘fall’. This is the object’s gravitational field. Imagine a bowling ball making a dent in our imaginary sheet – if you roll a marble close to the bowling ball, it will fall towards it and accelerate. Although it might look like the marble is attracted to the bowling ball, really it is just following the only path that the sheet will allow it to.

Weakest of them all

Now I am sure you have a clear idea about the type of gravity that causes the gravitational wave. Now let me tell you the definition once again - If mass bends space-time, then mass under acceleration must create ripples, or waves, in space-time which we called Gravitational-wave. And if we call in layman's term It is a bit like moving the tips of two fingers together then apart in a bowl of water and creating waves that ripple out across the water’s surface.

Gravity is the weakest force of all 4 fundamental forces so to create a gravitational wave that can detect and travel long distances we need an extremely massive object. So generally a massive object moving through space-time will create waves that ripple out across the Universe. Even though any object with mass under acceleration will generate gravitational waves – the Earth does as it is accelerated by the Sun’s gravity and so do you as you run down the street, but these are far too small to be detected.

Finding source

Now let's talk about the first detection of a gravitational wave - as we talk the strength of gravitational wave increases the more accelerating the object is the first detection of gravitational wave came from two rapidly accelerating black holes locked in a death spiral.
The two black holes were detected by the Laser Interferometer Gravitational-wave Observatory (LIGO); two identical facilities in Louisiana and Washington State. The black holes were 29 times and 36 times the mass of the Sun and were locked together by their mutual gravitational attraction, orbiting very quickly around a shared center of mass.

First Detection of Gravitational Wave

As they orbited, they plowed through space-time, throwing out gravitational waves. But gravitational waves can’t be made for free – it takes energy to churn up the fabric of the Universe – and, with each orbit, the black holes lost energy, which was carried away by the gravitational waves, and their orbit shrank, drawing the two black holes closer and closer together.As their orbit shrank, the black holes accelerated, which created more powerful gravitational waves, which caused their orbit to shrink more, which caused the black holes to accelerate even more.

This vicious circle could only end one way: the black holes collided. With this collision, the black holes merged and formed a single, even more, massive black hole. This newly formed black hole was 62 times the mass of the Sun, which means that three whole Sun’s worth of mass was lost in the collision. All of this missing mass had been converted into gravitational energy.

Now all of these is mathematically and theoretically define process but the detection is not exactly our traditional image of the even! You can’t see the effects of gravitational waves, but you can measure how they affect an object they pass through.

How LIGO works ..

As a gravitational wave travels through space-time, it causes it to stretch in one direction and compress in the other (think of a wave ripple through a caterpillar as it moves).

This, in turn, causes an object that occupies that region of space-time to also stretch and compress as the wave passes over them. So, when a gravitational wave passes the Earth, it will cause the planet to be ever so slightly squashed and stretched, and this is what LIGO is designed to detect. LIGO’s two four-kilometer-long arms are arranged in an L-shape, so, as a wave passes through, one arm is lengthened and the other shortened. Lasers traveling up and down the arms can measure the smallest change in length that would indicate that a gravitational wave has passed through. This is exactly what happened.

Why so late .?

These Gravitational waves are one of the last unconfirmed predictions of Einstein's theory which publish 100 years ago, and the reason behind its late detection was our equipment and technology, gravitational waves have traveled the tens of millions of light-years to Earth, they are so weak that it takes extremely sensitive equipment to detect them. To put this into context, the amount of distortion created by the two black holes and measured by LIGO’s detectors was less than the width of a proton (the tiny particle that, along with the neutron, makes up the nucleus of an atom!).

Now I am pretty sure you get a better idea about what is a gravitational wave, now let's talk about one of the most amazing examples of gravitational waves so far ...

Detection of GW170817 Multimessenger Signal