Dark matter, the most mysterious "stuff" in the universe, may be a sort of cosmic matchmaker, allowing supermassive black holes to overcome a final hurdle before colliding and merging into one.
Astronomers have understood for some time that when galaxies clash to create larger, misshapen galaxies, the supermassive black holes that sit at their centers draw together as well. Eventually, these black holes also merge, creating an even more monstrous supermassive black hole and a high-pitched "scream" of ripples in the very fabric of space and time called gravitational waves.
