This is the single most important news for mankind in the last decades if not a century so that it felt appropriate to announce it also on this forum.
Especially because this impacts scales and space geometry what is Something that interests people over here

The existence of gravitational waves was predicted by Einstein's general relativity in 1915.
Yet a century was needed to really observe them and the discovery team at LIGO is an almost sure candidate for the next Nobel.

A gravitational wave in general relativity is a stretching/compressing of the spacetime itself that travels at the speed of light (300 000 km/s).
That means that when a gravitational wave crosses the spacetime where you are trying to measure a distance, this distance will oscillate between a bigger and a smaller value during the time that the wave is traversing this piece of spacetime. The time oscillates too.

Basically all rotating bodies emit gravitational waves but their intensity is generally too small to be measured. F.ex the couple Sun-Earth is emitting with a power Worth about two 100 W light bulbs.
By emitting gravitational waves, a rotating system looses energy so that the orbits get smaller and smaller but for usual star/planet systems this process is also too slow to be measured.
The wave detected by LIGO was however emitted by the most powerful gravitational wave source in the Universe - 2 huge black holes of masses of 36 and 29 Suns orbiting each other and merging.
The resulting single black hole has a mass of 62 Suns what means that a mass of 3 Suns was transformed in energy (E=mc˛).
The merger happened 1 billion light years away what tells Something about the incredible power released by the merger - the total power released in the last moments was larger that the power emitted by all stars in the observable Universe !

In this video you see a reconstruction of what would see an observer near to the rotating black holes before being torn apart by the gravitational waves passing through his body :
https://youtu.be/Zt8Z_uzG71o