Gravitational Waves Discovered!

After a century of searching, scientists have directly observed the first Gravitational Waves!

Scientists part of the LIGO (Laser Interferometer Gravitational-Wave Observatory) collaboration, announced today the first direct detection of Gravitational Waves. In a special press conference, scientists described the detection which occurred back in September 2015. The source of the gravitational waves was from two merging black holes, with 26 and 31 times the mass of our own Sun, in a distant galaxy, located in the Southern hemisphere.

LIGO consist of the worlds two most sensitive gravitational wave detectors (and in fact, the most sensitive measuring devices ever built), both located in the USA. The detectors have been searching for evidence of this elusive physics effect for several decades, yet their existence was first predicted Albert Einstein in 1915 in his Theory of General Relativity.

Gravitational waves are invisible, similar to sound waves. They will travel through any space and object that crosses their path. As they pass through an object, they physically squash and stretch it as well as the space around it. It is this effect that allows us to detect them. The two LIGO detectors are able to detect very small changes in the length of two long tunnels at each detector, using lasers fired at right angles to each other. If one laser travels down one of the perpendicular tunnel faster or longer that the other, then a gravitational wave must have passed through it. And this change in time is how gravitational waves are detected.

One arm of the LIGO site on Hanford reservation (By Umptanum - wikipédia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2591541)

But these gravitational waves are very small. A vast number of them are passing through you this second, yet you probably haven't noticed yourself changing size. This is because they stretch and squash you by less than the size of an atom! This is why it has taken over 100 years for us to build detectors good enough to detect them.

But what creates these ripples in space? Well, any object that accelerates. Black holes spinning around each other, stars exploding or even just you driving your car down the road. The bigger the objects, the stronger the gravitational waves. In the case of the detections today, the gravitational waves were created by two black holes, each around 30 times larger than the sun, which span around each other very closely before merging together. It was this close in-spiralling of the black holes that created the strong signals that LIGO detected.

This discovery is just the beginning of gravitational wave astronomy. Most objects in the Universe can be seen with traditional telescopes. However some objects and events, such as black holes, faint objects and dusty objects, are invisible to normal telescopes. Gravitational wave detectors will allow us future to study these objects and events in the future, making the invisible part of the Universe very easy to see.