Black Holes Existed at the Dawn of Time, Birthing Stars and Encouraging Galaxy Formation
By Carolyn Collins Petersen
The Universe is full of galaxies, many containing supermassive black holes. That sparked a question: which came first—the galaxies or their black holes? The answer is becoming very clear, thanks to the first year of observations made by the James Webb Space Telescope (JWST). Black holes were in the Universe from the earliest times, along with the very first galaxies. And, they helped shape the cosmos we observe today.
Astronomers once had a hierarchical view of how things formed in the early Universe. They thought the earliest stars formed first followed by the earliest galaxies. Then the black holes came along and it appears they grew very quickly. However, JWST observations hint at a different timeline: supermassive black holes were likely there already in the first “epochs” of cosmic history. They accelerated the formation of new stars in the early Universe even as they grew with their galaxies. That’s according to Joseph Silk and a team of astronomers who just published an analysis of JWST images and data from the telescope’s first year. They suggest that black holes and galaxies co-existed and influenced each other’s development during the first 100 million years of cosmic existence.
“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 Silk, a professor of physics and astronomy at Johns Hopkins University and at Institut 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.”
Conventional Wisdom about Black Holes and Galaxies
For decades, astronomers argued that the very first stellar black holes formed when the earliest supermassive stars came to the end of their lives. Those stars have often been characterized as monsters and loners in the infant Universe. They lived very short lives and exploded in hugely catastrophic supernova events, blasting most of their outer layers out to space. The remaining cores collapsed and created some of the earliest stellar black holes. Black holes likely combined and accumulated more matter—forming the seeds of the first supermassive ones at the hearts of galaxies.
At the same time, the conventional wisdom about galaxies said that they formed when giant gas clouds collapsed. Waves of star formation followed, and presumably, more stellar black holes.
Does JWST Upend Current Theories? Maybe, Sort of
That conventional wisdom isn’t completely wrong. However, it doesn’t explain the supermassive black holes that existed so early in cosmic time—long before they should have. That’s something astronomers are still working to understand. And, it doesn’t explain why some very early galaxies look so very darned bright. But, this is where the early supermassive black holes play their role. Silk says something else was going on in the early gas clouds—something unusual. “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.”
JWST observations bear out this brightness discovery. The telescope has spotted distant early galaxies that appear to be a lot brighter than astronomers expected. Observations also show an unusually high number of really bright stars “way back then”, along with supermassive black holes. They’re much more massive for their age than expected. So, thanks to them, our views of the Universe using JWST are changing astronomy.
What Do Astronomers Think Now about Early Black Holes?
Since black holes are the key to understanding these early findings, let’s look at what their early presence means. It appears that maybe early galaxies and their supermassive black holes grew up together in the infant universe. Although these monsters wield tremendously strong gravitational fields that nothing can escape, the supermassive black holes announce their presence in other ways. They have hugely strong magnetic fields that act like giant particle accelerators. We often see jets of material speeding away from black holes, largely accelerated by the action of those magnetic fields. The jets are bright in various wavelengths of light, and all the activity brightens the cores of the galaxies where the black holes live. There’s also a definite uptick in star formation in them.
“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.”
JWST spots everything but the black holes and based on its observations, Silk and his team suggest that the infant Universe went through two phases. Both were influenced by black holes in different ways. At first, high-speed outflows (jets and winds) impacted surrounding gas clouds and boosted the rate of star formation. Then, the black hole activities slowed down and that affected the rate of star formation. Silk pointed out that the outcome was a reduction in the amount of gas available to form stars in the first galaxies. So, the bright galaxies that JWST is seeing formed with the help of their black holes.
Next Steps
JWST observations remain the key to figuring out if this new two-phase idea of cosmic evolution pans out. The telescope should provide precise counts of stars and supermassive black holes in the infant Universe and should confirm what Silk and his team predict.
More than that, however, the story doesn’t end with the infant Universe. We have 13.5 billion years of cosmic evolution to explain. And, now that the link between early black holes and galaxies is firming up, it raises questions about the supermassive ones in the galaxies we see today.
“The big question is, what were our beginnings?,” said Silk. “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.”
For More Information
Which Came First: Supermassive Black Holes or Galaxies? Insights from JWST
Which Came First: Black Holes or Galaxies? (press release)
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February 14, 2024 at 01:15AM
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