Cosmic Chain Reaction: How Supermassive Black Holes Emerged From X-Rays in the Early Universe

The supermassive black holes that formed at the dawn of the universe pose a big problem for scientists—technically, they shouldn't exist.

Black holes generally form when a star collapses in on itself and explodes as a supernova. The largest of these, known as supermassive black holes, have a mass equivalent to more than one million suns. Astronomers do not know exactly how these monster black holes come to be—one theory is they swallow huge quantities of matter over billions of years, while another is that they are formed from a cluster of black holes that eventually merge into one.

Both of these, however, require time. And this is something supermassive black holes from the early universe did not have. There is evidence to suggest supermassive black holes were present just 800 million years after the Big Bang, which is just a blink of the eye cosmologically speaking.

A third way that has been proposed is a "direct collapse" black hole, which mitigates the need for a star. This says that if a gas cloud is massive enough it can collapse under its own gravity to form a black hole directly

In a study published by Nature, Kirk Barrow, from Stanford University, and colleagues from Georgia Institute of Technology and the Los Alamos National Laboratory, New Mexico, have now found that direct collapse black holes can account for supermassive black holes—and what's more, they should be able to test their theory in the very near future.

"There is a limit to how fast something like a black hole can grow," Barrow told Newsweek. "Some fraction of matter falling into a black hole is converted into light that radiates out and pushes back against the in-falling gas. One theory is that, under the right conditions, a massive black hole can form directly from a large, collapsing well of primordial gas and thus reach a higher mass more quickly."

In the study, the researchers ran a simulation of a direct collapse black hole. They looked at the black hole and its surrounding galaxy, along with the radiation from the galaxy and how it might appear through a telescope.

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File photo of a black hole. Scientists believe they now know how the first supermassive black holes emerged. iStock

They had been looking to get a better understanding of the radiation and effect that X-rays would have on the growth on supermassive black holes. "To our surprise, we discovered a chain reaction wherein the X-rays led to a burst of star formation, which later lead to a wave of supernovae," Barrow said. "This was an effect no one had predicted or even expected before, but in hindsight, it seemed to make perfect sense in the context of what we knew about star formation in the early universe."

Next, the scientists developed a way to test their simulation. They ran another simulation that showed the emission, absorption and scattering of light all the way to a telescope 13 billion light years away—allowing them to establish if, should this simulated galaxy exist, it would be visible.

"We focused on making diagnostics for the forthcoming James Webb Space Telescope," Barrow said. "We were pleased to find that JWST would be able not only detect, but also discern our simulated scenario from other galaxies in the early Universe if our diagnostics turn out to be correct. An observation by JWST would be then be followed up by other observatories to fully constrain and characterize a massive black hole-hosting galaxy. That would be a pretty big discovery."

He said one of the biggest limitations is that if the galaxy does exist, it would be smaller than a pixel on the JWST detectors—you would need quite a lot of filters to distinguish it from other objects. Furthermore, the team would ideally want to simulate the whole cosmic neighborhood and have the black hole pop up on its own accord. "[But] if our simulations turn out to be correct, this would change how astrophysicists think about the formation of black holes and the physical evolution of the galaxies around them," Barrow said.