Gravitational waves are a prediction of the Theory of General Relativity.

This is the lowdown:

• The existence of gravitational waves was inferred by Einstein’s Theory of General Relativity, but they were only very recently directly detected by Advanced LIGO
• It took decades for scientists to develop the technology that was able to detect them
• Adanced LIGO fires lasers into long L-shaped underground tunnels and gravity waves, if they are present, disturb the light within the apparatus

• Accelerating masses produce waves that propagate at the speed of light
• Gravitational waves are ripples in the fabric of space and time – the so-called construct of spacetime
• They are produced by violent cosmic events, like black holes merger and colliding galaxies
• Potential detectable sources include merging black holes and neutron stars in theory
• The detection of gravitational waves opens up the Universe to completely new investigations.