Roger Deane and his collaborators recently found an intriguing system of not one, not two, but three supermassive black holes in orbit around one another. Two of these are extremely close to each other, and are in the process of coalescing into one.

Systems like this are interesting to astronomers not just because they're mindblowingly cool, but also because coalsecing black holes send ripples through spacetime. We don't yet have instruments sensitive enough to detect these ripples (we're working on it), but they would provide a unique insight into the Universe and would provide an exquisite test for General Relativity.

This work was just published in Nature, along with an overview piece by Greg Taylor. It's paywalled, but well worth a read if you have access.