What are gravitational waves?
Gravitational waves are distortions in spacetime.
Every mass in the universe which is accelerated produces these waves. Even if our techniques are advanced and very sensible, gravitational waves have to be produced by huge masses to get recognised.
We speak about masses, 30 or more times the mass of our sun wich is 1,989*10^30 kg.
To illustrate the phenomenon imagine two black holes spin around in a binary system. When they rotate around each other they speed up and get closer by time, this is a cause of the law of energy conservation,
especially on black holes there is an escape velocity equal to the speed of light.
This fast and big changes in gravitation lead to distortions in spacetime, which are observed as gravitational waves.
The more they accelerate the more spacetime is distorted and energy is transmitted into the gravitational waves they send out.
Further on these waves travel by the speed of light which causes an observer to find the spacetime distorted by the effects of strain.
You can visualize these waves like a wavefront on water surface after a stone was dropped on it's surface.
Because of the low interaction of gravitation with other masses it was hard to detect gravitational waves.
That's why we needed large events like the big bang or black holes merge with each other emitting high energy waves.
The LIGO Interferometer detected gravitational waves caused by one of these events. In this case there were two black holes rotating in a binary system and finally merging.
Right before the spinning stopped the power of 3 suns was release in less than a quarter seconds.
This is more power than every observable star emits in the Universe.
Interferometer detected the change in the length of the light rays when they're hit by this gravitational waves.
When the waves had arrived the light ray changes its length by only 1/1000 the diameter of a proton. This is exactly the distortion of spacetime we can detect.
Up to this date the exploration of the universe was reduced to electromagnetic waves
but after the LIGO event we got signals in the form of gravitational waves which adds the possibility to look for information that aren't nature of electromagnetic waves. This opens a new chapter in astronomy and astrophysics.