See also Counterexamples to Relativity.
Not to be confused with "gravity waves". Learn the difference.
Gravitational waves were accurately predicted by the Theory of Relativity, which claims that distortions in space travel at the speed of light away from a mass that accelerates or decelerates.
Gravitational waves have never been directly observed; naturally, because gravity is invisible. However, they have recently been detected.
They have also been the subject of a prank:
|“||In 2010 researchers from the Laser Interferometer Gravitational-Wave Observatory detected the first direct evidence of gravitational waves — crucial proof of relativity. After thousands of hours of verification, they learned that the signal was a “blind injection,” an authorized prank by colleagues to check their work.||”|
-  Gravitational waves from black holes detected, BBC