Forgive me if this has been ToSeek'ed and I didn't see it, but they've observed a supermassive black hole, the result of a merger, being kicked out of the host galaxy by the massive gravitational radiation recoil kick predicted by GR simulations of merger events.
We've discussed this here a few times and I knew they hadn't yet observed it, but were looking. Well, they've found one now.
This should be seen as more good, but indirect, evidence for gravitational radiation, on a par with the binary pulsar inspirals.
ETA: the recoil velocity here is *amazing*. The big boy got a kick speed of ~2700 km/s. And that is one heck of a lot of radiation blasting out in the other direction, too.
This would make for a good movie plot. We learn that one of these rogue supermassive black holes is headed right for us!
ETA2: Tony, or any other gravity simulator gurus (those who know the program well enough to quickly set it up), just for fun, run a simulation of a 100 million Sol mass ripping through the solar system at oh, say, 1000 km/s. Let it come in in the plane, and then let it come perpendicular to the ecliptic. I'd just like to see what that would do.