If you're a science enthusiast, follow science blogs, and you get excited when our scientists make new discoveries then I'm happy for you, and you will be happy too for having come here to read this article.
If you're the opposite of the kind of people I mentioned above and you just roll your eyes when our scientists make new discoveries, then I'm happy that you cared to read so far and I must tell you that you will not be disappointed if you kept reading on.
Heard the name before? Where?
One of the reasons why you're at this article is that this name seems too familiar. You may or may not know much about it but you've definitely heard this name do the rounds in newspapers, on TV, and on the Internet! Let's take another round here, another shot, because it's about time to get high (not literally; just talking about the sky guuyyss)! I won't call it false memory if you think you've come across this term before. Gravitational Waves really did make it to the headlines; and not for no reason. We'll dig into the details in a while, but first, let me tell you where and when might you have read or heard of this term before?
Feb 11, 2016 - The LIGO and VIRGO Science Collaborations made the announcement of the first ever detection of the gravitational waves!
Scientists in the Ligo Scientific Collaboration have directly observed the ripples of gravitational waves for a third time. Pictured is an artist's impressions of the waves
Feb 12, 2016 - That's the day when you most probably came across the fascinating name - Gravitational Waves. Unsurprisingly. Because it was everywhere. Literally everywhere. Everyone was talking about it. In fact, some people were way too excited to know it. And no, I am not even talking about the people who actually put in years of their lives in the detection of these waves and made significant, Nobel Prize worthy contributions to the field of gravitational-wave astronomy. I am talking about people like you and me who fancy black holes and all the other things in the outer space!
Now! What ARE these waves?
If you've read my article on the Black Hole Information Paradox, you know about the spacetime fabric, which is the name given collectively to space and time. Gravitational waves are ripples in that very space-time fabric. Massive accelerating objects like neutron stars and black holes orbiting each other are capable of disrupting the space-time fabric so that the ripples (waves) radiate from the source at the speed of light. The existence of these waves was predicted by Albert Einstein in the year 1916 based on his general theory of relativity. The incredible fact is that while the mathematical evidences and proofs of the existence of gravitational waves have been with us for several years, starting from 1974, the first physical detection was made possible only after a hundred years, in 2015, after Einstein's predictions.
If you're still having trouble imagining what gravitational waves are like, you would want to consider an analogy. Visualize throwing a stone in a pond and then seeing the ripples that its impact makes on the surface of water. Similar is the case of the gravitational waves. The waves in the space-time fabric are analogous to the ripples in water; only at a super massive scale. When these waves pass by space-time, they stretch or contract it.
Strongest gravitational waves are formed by catastrophic events such as:
colliding black holes
collapse of stellar (galactic) cores
coalescing neutron stars or white dwarfs
wobbly rotation of neutron stars that are not perfect spheres, and
the remnants of gravitational radiation created by the birth of the Universe itself!
An animated illustration of two neutron stars orbiting each other and then coalescing to form gravitational waves.
(Credits: NASA/Goddard Space Flight Center)
These waves carry information about their cataclysmic origins and also valuable information about the nature of gravity itself. Talking of their magnitude, gravitational waves can be extremely violent and disastrous. It was just lucky for us that by the time the first waves reached us, they were generating variations in space-time smaller than the size of an atomic nucleus.
An interesting excerpt from the description given on the website of LIGO CALTECH goes as follows and is a clear indication of the remarkable nature of Einstein's prediction:
"Though gravitational waves were predicted to exist in 1916, actual proof of their existence wouldn't arrive until 1974, 20 years after Einstein's death. In that year, two astronomers working at the Arecibo Radio Observatory in Puerto Rico discovered a binary pulsar--two extremely dense and heavy stars in orbit around each other. This was exactly the type of system that, according to general relativity, should radiate gravitational waves. Knowing that this discovery could be used to test Einstein's audacious prediction, astronomers began measuring how the period of the stars' orbits changed over time. After eight years of observations, it was determined that the stars were getting closer to each other at precisely the rate predicted by general relativity. This system has now been monitored for over 40 years and the observed changes in the orbit agree so well with general relativity, there is no doubt that it is emitting gravitational waves."
The great detection!!
The existence of gravitational waves was further confirmed by many astronomers who started to study the radio emissions from pulsars and found similar effects. But these confirmations were never made through actual physical contact. They were always either indirect or mathematically proven.
But that was the case only up till Sep 14, 2015, when LIGO (Laser Interferometer Gravitational-wave Observatory) physically detected deformations in the space-time itself caused by the passing gravitational waves. These waves were generated by two colliding black holes nearly 1.3 billion light years away! Which means that the collision occurred at a place from where light took 1.3 billion years to reach us. This also means that this collision took place these many billion years ago! (Yes, long before even our Earth was formed!)
In an article dated Sep 27, 2017, The Guardian very elegantly explains the working of the LIGO interferometer and the process of detecting gravitational waves as shown in the following images:
After the detection, the parameters relating to these waves are plotted. One of the most important troubles is that since the wavelengths recorded are extremely small, they may get lost in the noise surrounding the detectors. But the good news is that scientists use very precise methods and filter noises to make sure that they do not confuse some random signals coming from the outer space with gravitational waves. In fact, the frequency signals obtained at both the stations - Hanford at Livingston - had to be consistent with each other in the permitted time limits. Given below is the Frequency vs Time graph recorded at LIGO Hanford and LIGO Livingston respectively from the Black Hole merger of Sep 2015, named GW150914.
That would be enough description about THE waves. But I had compiled some incredible facts I came across about gravitational waves while doing my bit of the research on the topic. Keep scrolling to read them.
These waves are so minuscule that Albert Einstein himself doubted that they could ever be detected.
The waves given off by the cataclysmic merger of GW150914 reached Earth as a ripple in spacetime that changed the length of a 4-km LIGO arm by a thousandth of the width of a proton which is proportionally equivalent to changing the distance to the nearest star outside the Solar System by one hair's width!!
The energy released by the binary as it spiralled together and merged was immense. The peak emission rate reached was greater than the combined power of all light radiated by all the stars in the observable universe!
The observation confirms the last remaining unproven prediction of general relativity and validates its predictions of space-time distortion in the context of large scale cosmic events (known as strong field tests).
The second observation of gravitational waves was made on Dec 26, 2015 and announced on Jun 15, 2016. Three more observations were made in 2017, including GW170817, the first observed merger of binary neutron stars, which was also observed in electromagnetic radiation.
The Indian initiative IndIGO - Indian Initiative in Gravitational-wave Observations - has been formed with the major purpose of setting up the LIGO-India detector, which would help enhance the network of gravitational wave detectors worldwide.
LIGO has archived and released the collected data to the public and you can use it too! Here is where to find it - LIGO Data.