A nearby galaxy that looks like a smiley face harbors a dark secret: It has twin supermassive black holes, not just one. This rare find could shed light on what happens when ginormous galaxies collide.
Supermassive black holes churn at the heart of most galaxies, including our own, weighing millions of times the sun’s mass and radiating billions of times more energy. These black holes sometimes radiate so much that they’re considered active galactic nuclei, but that type is very rare, comprising only about one percent of galaxies. It’s even more unusual, then, to find a galaxy with twin AGN. This is only the second one ever found.
Astronomers think stupendously disruptive events like galaxy collisions could spur AGNs to switch on, by sending huge amounts of gas spiraling toward the pre-existing black holes. The gas gets superheated as it falls toward the event horizon, radiating X-ray energy. It stands to reason, then, that some galaxies would have two AGNs — two products of a merger that occurred some time in the past. But astronomers weren't finding any.