We can thank a team of over 1,000 scientists from 86 institutions around the world.
Picture this for a minute: More than a billion light-years away, a pair of black holes collided. They had been circling each other for longer than you could imagine, but ever so slowly they were coming closer and closer together, and by the time they were a mere few hundred miles apart, they were whipping around in space at nearly the speed of light, distorting spacetime along the way.
Once theses black holes, each approximately 150 kilometers wide with masses 29 and 36 times that of our sun, collided and formed a singular black hole, an enormous amount of energy was released — more than all the stars in the universe combined — in the form of gravitational waves.
This merger, which resulted in the first recording of gravitational waves on September 14, 2015 at 09:50:45 UTC (05:50:45 EDT) by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Hanford, WA, and Livingston, LA, observatories, actually happened 1.3 billion years ago! Isn’t that mind-boggling?
So, how were the researchers able to finally detect these elusive waves that were predicted to exist by Albert Einstein just over 100 years ago?
First, you have to understand that gravitational waves carry information about how they were created. Even though the events that release gravitational waves are violent and astronomical, the effects on spacetime here on Earth is very subtle, because we are so far away.
Although physicists agreed that gravitational waves exist, they had no hard evidence… until now of course! The sole purpose for building LIGO, an extremely sensitive optical instrument that uses laser interferometers, was to search for gravitational waves.
This discovery was made possible by the enhanced capabilities of Advanced LIGO (upgraded recently), which detected gravitational waves during its first observation run, and also thanks to a team of over 1,000 scientists from 86 institutions around the world.
This is what you need to build a gravitational-wave interferometer, according to The Conservation: two light beams traveling between pairs of mirrors down pipes running in perpendicular directions, for example, north and west. Sounds simple, right? It isn’t.
The interferometer pipes or arms are each 4 kilometers long, and were constructed with a correction for the curvature of the Earth in a place isolated from the vibrations of the ground. Not only that, the tubes have to be vacuums so that contaminants and gas don’t affect the laser light between the mirrors.
The mirrors also have to be adjusted daily by computer operators — mirror positions and angles drift slowly due to temperature changes, mechanical relaxations, and even the position of the moon. It is no easy task!
How it works is that, if a gravitational wave were to pass through, it should stretch space in one direction and shrink it in the other. Now on Earth, that would cause the mirrors to swing by teeny, tiny amounts, so that the distance between one pair of mirrors gets smaller, while the other gets larger. This swinging is the mirrors responding to the stretching and compressing of spacetime.
These changes are then recorded by a detector, and to make sure that the signals are not flukes or caused by environmental factors, there are two of these L-shaped machines positions at opposite ends of the US (Louisiana and Washington). If both of them do the same thing at the same time… well, then it is time to get excited.
And luckily, the dedication of the scientists and engineers involved in the development and maintenance of LIGO has led to one of the biggest breakthroughs in the field of astrophysics — the detection of gravitational waves.
They all deserve a round of applause.
You can watch this short video explaining the scientific masterpiece that is LIGO.