Wandering supermassive black holes — those that don’t lie at their galaxies’ centers — may be tricky to find, but not all black holes that wander are lost! A new study demonstrates how we can hope to discover these missing nomads in the future.
When two galaxies collide, the resulting galaxy will contain multiple supermassive black holes. [NASA/Hubble Heritage Team (STScI)]
When Galaxies Collide
We know that the center of every massive galaxy hosts a supermassive black hole weighing millions to billions of solar masses. But galactic centers aren’t the only place that supermassive black holes can lurk! In fact, we expect that the majority of galaxies host many more of these monsters beyond just the central supermassive black holes. Why? Because galaxies merge.
Structure in our universe is largely built hierarchically: over time, galaxies have frequently collided with each other, growing progressively larger with each merger. But with each of these mergers, at least two supermassive black holes — one from each of the merging galaxies — are introduced into the resulting turmoil.
While gas and stars reorder themselves neatly into a new galaxy, eventually erasing all evidence of the merger, the black holes aren’t as well-behaved. Indeed, simulations ...