Gravitational waves
Ripples in spacetime from violent cosmic events — predicted 1916, first measured 2015.
Gravitational waves are ripples in the fabric of spacetime, produced when massive objects — such as merging black holes — accelerate violently. Einstein predicted them in 1916 from general relativity.
They are extraordinarily faint; only on 14 September 2015 did the LIGO observatories make the first direct detection. It was announced in February 2016, earned the 2017 Nobel Prize in Physics and opened a new way of observing the universe.
Source: Wikipedia: Gravitational waves — Read the full article on Wikipedia.