Out there in the Universe, there are some incredibly impressive astrophysical entities, including behemoths that dwarf anything we’re familiar with. There are stars hundreds of times more massive, and millions of times as luminous, as our own Sun is. There are galaxies and galaxy clusters thousands of times as massive as our Milky Way and Local Group. And there are black holes out there that not only dwarf our own Sun, but black holes that are so massive, they’re comparable in mass to all of the stars in the Milky Way galaxy combined. Some of them, quite puzzlingly, at first glance, even exist extremely early on in cosmic history: just a few billion years after the hot Big Bang first began.

At those extremes, the largest black holes pose a number of important cosmic questions. How did they grow so big so fast? Can physics even account for the highest-mass ones? And why do we see the biggest ones at such great distances, rather than close by? Is there something missing in our understanding?…