https://www.theregister.co.uk/2017/11/13/the_most_powerful_gravitational_waves_will_be_observable_within_a_decade/

The most violent gravitational waves in the universe from supermassive black hole prangs will be detected to within ten years, according to research published on Monday.

Gravitational waves were predicted by Albert Einstein and finally discovered in 2015, a century after his theory of general relativity was formalized. Ripples through spacetime are generated when black holes collide. As they combine, a proportion of their mass is converted to energy and radiates away as a gravitational wave.