Nader Khonji

It was thought black holes kick stars out of galactic centers, yet a third of giant galaxies host dense clusters snug against the hole. The clue? The hole's post-merger motion: like a cosmic tugboat, it can tow a whole swarm along.

Telescope images revealed a region in a distant galaxy where billions of stars had disappeared. The void was caused by a pair of supermassive black holes whose combined mass is an absolute record. The discovery helps understand the growth of giant galaxies.