Two recent discoveries of black hole mergers add to the evidence that such mergers happen over and over again.
If you could zoom out from Earth far enough, our Milky Way would shrink to just one galaxy among roughly fifty neighbours clustered together by gravity. These galactic neighbourhoods vary dramatically in size, and the largest ones, containing hundreds or thousands of galaxies bound together, represent some of the most massive objects in the entire universe. Their immense scale makes them uniquely valuable laboratories for testing our understanding of fundamental physics.

