An enduring mystery of astrophysics is how supermassive black holes formed so quickly after the Big Bang. Now, a new simulation suggests a novel explanation for how the seeds of these huge black holes might have come to be.
Reporting in Nature, an international team finds that massive black holes are the product of supermassive stars, maybe 10,000 times the mass of the Sun. Hypotheses about these stars make them rare and dependent on intense radiation from other stars, but that doesn’t appear to be the case in this new simulation.
According to the new research, supermassive stars formed in dense starless regions and the radiation from other, more distant, stars was only a minor contributor. The stars quickly collapsed into massive black holes that grew by feeding on the abundant gas present in the dense region.
"Astronomers observe supermassive black holes that have grown to a billion solar masses in 800 million years," lead author Professor John Wise, from the Georgia Institute of Technology, said in a statement. "Doing that required an intense convergence of mass in that region. You would expect that in regions where galaxies were forming at very early times."
The work is based on the Renaissance Simulation suite, which was used to help researchers work out how the universe evolved during its early years. They discovered 10 dark matter halos that should have formed stars given their masses but only a dense gas cloud appeared to exist. The team used the Stampede2 supercomputer to re-simulate these halos at a higher resolution. And that’s where they saw the black holes forming.
These overdense regions have a large amount of dark matter creating a deep gravitational well. Gas falls into it and collapses into massive stars or directly into a black hole.
"In this study, we have uncovered a totally new mechanism that sparks the formation of massive black holes in particular dark matter halos," Wise said. "Instead of just considering radiation, we need to look at how quickly the halos grow. We don't need that much physics to understand it – just how the dark matter is distributed and how gravity will affect that. Forming a massive black hole requires being in a rare region with an intense convergence of matter."
While the regions that can birth these black holes are rare, they appear to be more common than previously thought. The researchers hope to use the simulation to study the life cycle of these massive black holes from their formation until now.