Imagine a seed growing into a towering redwood tree almost instantly. That’s the kind of puzzle astronomers face when they look at the early universe with powerful telescopes like the James Webb Space Telescope (JWST). They’re seeing giant supermassive black holes, millions or billions of times heavier than our sun, existing surprisingly soon after the Big Bang. Traditional ideas about how black holes grow can’t explain how they got so big, so fast.
Contents
Now, new simulations offer a potential solution: hypothetical objects called primordial black holes could have given these cosmic giants a crucial head start.
Key Takeaways:
- Supermassive black holes are seen very early in the universe, posing a growth puzzle.
- Primordial black holes, possibly formed right after the Big Bang, could be the answer.
- Simulations show primordial black holes can grow rapidly by “eating” surrounding gas.
- This theory needs observational evidence to be confirmed.
The Giant Problem: How Did Early Black Holes Grow So Big, So Fast?
For years, scientists thought black holes grew relatively slowly, mainly through two processes: gradually pulling in surrounding gas and dust (called accretion) or merging with other black holes over millions or billions of years.
But the JWST has changed the game. It’s peering back in time further than ever before, revealing massive black holes present when the universe was less than a billion years old, some even within the first few hundred million years. The most distant one found so far, CEERS 1019, is about 9 million solar masses (9 million times the mass of the sun) and existed only 570 million years after the Big Bang.
This is like finding a fully grown redwood tree when the forest is still just saplings. “The problem here is that, when we view the early universe with more and more powerful telescopes… we keep seeing supermassive black holes,” explained John Regan, a researcher involved in the study. “This means that supermassive black holes are in place very early in the universe.”
The standard ways black holes grow simply don’t seem fast enough to create these colossal objects in such a short timeframe.
Enter Primordial Black Holes: The Early Universe Seeds?
Most black holes we know about today are called “astrophysical” black holes. These form from the dramatic death of massive stars in supernova explosions (creating stellar-mass black holes) or through repeated mergers and feeding (leading to supermassive black holes).
But scientists have long theorized about another kind of black hole: primordial black holes. Unlike their stellar cousins, these wouldn’t need stars to die. Instead, they might have formed directly from incredibly dense pockets of matter in the universe’s first second, right after the Big Bang.
An illustration depicting a tiny primordial black hole growing rapidly into a vast supermassive black hole against a cosmic background
If primordial black holes exist, they could have a significant advantage in growing quickly. For one, their initial mass isn’t limited by the size of a star. They could potentially start out much more massive than black holes born from stars.
Plus, they wouldn’t have to wait millions of years for the first stars to live and die. They’d be around almost from the very beginning. Astrophysical black holes forming from star deaths also face another problem: the energy released by the star during its life and death can blow away the nearby gas the newborn black hole needs to feed on. Primordial black holes wouldn’t have this issue.
A Race to the Center: How Primordial Black Holes Could Grow Giants
The new research, based on complex cosmological simulations, explores this idea. The team found that if primordial black holes existed, they could indeed grow extremely rapidly, primarily by accreting (gobbling up) the abundant gas — mostly hydrogen and helium — available in the early universe. Mergers with other black holes played a less significant role in these simulations.
For this feeding frenzy to be efficient enough to build a supermassive black hole quickly, these primordial seeds would need to get to where the food is most plentiful: the dense centers of early galaxies.
Diagram showing the immense size difference between supermassive black holes and hypothetical tiny primordial black holes
“For this, primordial black holes need to sink to the center of a galaxy,” Regan explained. “This can happen if there are enough primordial black holes. Only a few have to get lucky!”
The simulations suggest that if enough primordial black holes are present and make their way to galactic centers, they could potentially account for the entire population of early supermassive black holes observed by JWST. However, it’s also possible that both primordial and astrophysical black holes contributed.
Seeking the “Smoking Gun” Evidence
While promising, this theory currently relies on simulations of these hypothetical objects. To confirm it, scientists need observational evidence.
One way would be to find a very, very massive black hole in the very early universe, perhaps even earlier than the ones JWST has already found (before 500 million years after the Big Bang). Such a black hole would be incredibly difficult to explain with standard astrophysical growth models, strongly suggesting a primordial origin.
Illustration showing concentrated dark matter in the core region of a spiral galaxy, where black holes often reside
Another clue could come from finding a surprisingly small black hole in the modern universe — one less than about three times the mass of the sun. Astrophysical black holes formed from stars typically aren’t this small. Finding one could mean it grew from a primordial seed. Primordial black holes are also sometimes proposed as candidates for dark matter, adding another layer of intrigue.
“I was surprised that primordial black holes grew so rapidly and that our simulations at least matched the parameter space in which they can exist,” Regan said. “All we need now is a ‘smoking gun’ of a primordial black hole from observations.”
The research team plans to make their simulations even more realistic by including both primordial and astrophysical black holes interacting in the same cosmic environments to see if they can find distinguishing characteristics.
Until observations confirm the existence of these early universe seeds, the puzzle of giant black holes in a young cosmos remains, but primordial black holes offer a compelling path toward solving one of cosmology’s biggest mysteries.
The team’s research is available as a pre-peer review paper on arXiv.
Want to learn more about the universe’s mysterious objects? Check out our articles on supermassive black holes, the James Webb Space Telescope, and the Big Bang.
