A central mystery surrounds the supermassive black holes that haunt the cores of galaxies: How did they get so big so fast? Now, a new, computer simulation–based study suggests that these giants were formed and fed by massive clouds of gas sloshing around in the aftermath of the big bang.
“This really is a new pathway,” says Volker Bromm, an astrophysicist at the University of Texas in Austin who was not part of the research team. “But it’s not … the one and only pathway.”
Astronomers know that, when the universe was just a billion years old, some supermassive black holes were already a billion times heavier than the sun. That’s much too big for them to have been built up through the slow mergers of small black holes formed in the conventional way, from collapsed stars a few dozen times the mass of the sun. Instead, the prevailing idea is that these behemoths had a head start. They could have condensed directly out of seed clouds of hydrogen gas weighing tens of thousands of solar masses, and grown from there by gravitationally swallowing up more gas. But the list of plausible ways for these “direct-collapse” scenarios to happen is short, and each option requires a perfect storm of circumstances.
For theorists tinkering with computer models, the trouble lies in getting a massive amount of gas to pile up long enough to collapse all at once, into a vortex that feeds a nascent black hole like water down a sink drain. If any parts of the gas cloud cool down or clump up early, they will fragment and coalesce into stars instead. Once formed, radiation from the stars would blow away the rest of the gas cloud.