When a star significantly larger than our Sun exhausts its nuclear fuel, it can no longer sustain the outward pressure needed to counterbalance the force of gravity pulling its mass inward. This imbalance ultimately triggers a dramatic gravitational collapse, which can cause the star’s entire mass to collapse into a point of infinite density and zero volume. A black hole is born.
Although I’m overly simplifying things, this is essentially how black holes form. It follows that stars preceded black holes in the early universe. However, a new study that leveraged the unprecedented ability of the James Webb Space Telescope (JWST) to peer back into the early cosmos farther than ever before found something extraordinary.
This research challenges the traditional view that black holes form after galaxies. Instead, it suggests that black holes could have played a significant role in the formation of stars and galaxies during the universe’s early years.
“We know these monster black holes exist at the center of galaxies near our Milky Way, but the big surprise now is that they were present at the beginning of the universe as well and were almost like building blocks or seeds for early galaxies,” said lead author Joseph Silk, a professor in the Department of Physics and Astronomy at Johns Hopkins University and at the Institute of Astrophysics, Paris, Sorbonne University.
“They really boosted everything, like gigantic amplifiers of star formation, which is a whole turnaround of what we thought possible before — so much so that this could completely shake up our understanding of how galaxies form.”
Galactic co-evolution with the first black holes
Shortly after JWST entered operation in mid-2022, the world was stunned by the fantastic images it beamed back of the cosmos. Unlike its predecessor, the Hubble Space Telescope, which primarily observes in the visible and ultraviolet light, JWST specializes in infrared astronomy. This capability is crucial for observing the distant universe: as the universe expands, light from the earliest stars and galaxies is stretched into the infrared part of the spectrum, a phenomenon known as redshift. JWST’s sophisticated instruments and large mirror, which is about 6.5 meters in diameter (compared to Hubble’s 2.4 meters), enable it to collect faint infrared signals with extraordinary detail.
This explains how the JWST, the most powerful telescope ever, was able to find the earliest known galaxies, some dating to just 330 million years after the Big Bang. But during such observations, astronomers also noticed something that they didn’t really expect: these distant (or early) galaxies appear much brighter than they should. This can only mean that these ancient galaxies harbored very high numbers of young stars and supermassive black holes — logically these should have appeared much later. So, what’s going on?
This new analysis from Silk and colleagues suggests that black holes might have actually appeared at the dawn of time. These early black holes didn’t need old dying stars to appear. In fact, they helped birth new stars, effectively supercharging galaxy formation.
The study explored the feedback mechanisms of active galactic nuclei (AGN), regions surrounding supermassive black holes that are luminous due to the accretion of matter. The model built by the researchers revealed a dynamic evolution of AGN feedback across cosmic time.
Black holes: the seeds of early galaxies
Although black holes are often portrayed as terrifying cosmic bodies with gargantuan appetites for mass and energy, there’s much more to it. Due to their immense gravity, black holes generate massive magnetic fields that trigger violent storms and eject turbulent plasma in their vicinity, sort of like cosmic-sized particle accelerators. As a result, gas clouds encountering these charged particles would have collapsed under their gravity, triggering star formation.
“We can’t quite see these violent winds or jets far, far away, but we know they must be present because we see many black holes early on in the universe,” Silk explained. “These enormous winds coming from the black holes crush nearby gas clouds and turn them into stars. That’s the missing link that explains why these first galaxies are so much brighter than we expected.”
Initially, in the early universe, this feedback positively influenced star formation. It did so through mechanisms such as radiatively cooled turbulence and momentum-conserving outflows, which contributed to the condensation and collapse of gas into stars. Later, these outflows slowed, reducing the gas available for new stars. This would explain why some early galaxies are brighter than those that appear much later.
This evolution in feedback mechanisms is key to explaining how galaxies and their central black holes coevolved, and it provides insight into the observed diversity in galaxy properties across the universe.
“We thought that in the beginning, galaxies formed when a giant gas cloud collapsed,” Silk explained. “The big surprise is that there was a seed in the middle of that cloud — a big black hole — and that helped rapidly turn the inner part of that cloud into stars at a rate much greater than we ever expected. And so the first galaxies are incredibly bright.”
But if this was truly the case, how did these black holes appear if not from collapsed stars? The researchers propose an intriguing mechanism by which black holes formed through the direct collapse of massive gas clouds, circumventing the need for prior star formation or the growth from smaller black holes.
However, that’s not to say this is the last word on the matter — far from it. This is why the researchers rely on upcoming observations by the mighty James Webb telescope, which is expected to provide new, more precise counts of stars and supermassive black holes in the known universe.
“The big question is, what were our beginnings? The sun is one star in 100 billion in the Milky Way galaxy, and there’s a massive black hole sitting in the middle, too. What’s the connection between the two?” he said. “Within a year we’ll have so much better data, and a lot of our questions will begin to get answers.”
The findings appeared in the Astrophysical Journal Letters.
