For the first time we've been able to simulate what gravitational waves (actually ripples in spacetime) look like as two black holes merge. This isn't easy because time and space around the black holes is modified, so when you take relativity into account you run into effects like infinite density and time coming to a stop. Programs generally don't like this and crash. So, to keep it "simple", they assumed two equal-sized and non-spinning black holes. They're now working to incorporate mergers of different sizes, and I assume they'll eventually add the effects of spin.
The visualization is quite beautiful.
There are experiments attempting to actually detect these fluctuations in spacetime, but it's incredibly difficult. They are looking for a change in distance of one-hundred-millionth of the diameter of a hydrogen atom. Dude, that's some pretty precise measurment.