What if black holes were born even before the first stars and galaxies existed? Scientists believe this may have happened just moments after the Big Bang. These mysterious objects are called primordial black holes (PBHs), and they could help solve some of the biggest mysteries in the Universe, including the nature of dark matter.
Now, a new study by physicist Cristian Joana has revealed something surprising. Using powerful computer simulations based on Einstein's theory of General Relativity, he found that the early Universe may have created primordial black holes in three different ways, not just one as previously thought. The discovery could change how scientists predict the number of primordial black holes in the Universe and improve our understanding of the Universe's earliest moments.
What Are Primordial Black Holes?
Primordial black holes are different from the black holes we usually hear about.
Most black holes form when very massive stars run out of fuel and collapse under their own gravity. But primordial black holes are believed to have formed less than a second after the Big Bang, long before any stars or galaxies existed.
Scientists are interested in these ancient black holes because they may:
Make up some or even all of the mysterious dark matter.
Help explain how supermassive black holes formed so early in the Universe.
Produce gravitational waves that can be detected by future space missions.
Give scientists clues about the conditions of the Universe just after the Big Bang.
Although they have not yet been directly discovered, primordial black holes remain one of the most exciting ideas in modern cosmology.
How Can Primordial Black Holes Form?
Right after the Big Bang, the Universe was filled with tiny fluctuations in energy and matter. Most of these fluctuations were very small and eventually became galaxies and clusters of galaxies.
However, if a fluctuation became extremely dense, gravity could cause it to collapse into a black hole.
Scientists have studied this idea for many years. But predicting exactly when a fluctuation becomes dense enough to form a black hole is very difficult.
Most earlier studies focused mainly on how large the fluctuation was. They often assumed simple mathematical shapes for these fluctuations. But the real Universe is much more complicated.
This is where Cristian Joana's new research makes an important difference.
Simulating the Early Universe
Instead of using simple assumptions, Joana created detailed computer simulations that followed tiny fluctuations from their very beginning.
The simulations tracked the evolution of these fluctuations through three important stages of the early Universe.
Slow Roll
The first stage is called slow roll.
During this period, the Universe expanded incredibly fast in a process known as cosmic inflation. The field responsible for inflation changed slowly, allowing space to grow rapidly.
Ultra-Slow Roll
Next came a short period called ultra-slow roll.
During this stage, the inflaton field slowed down even more. This caused tiny quantum fluctuations to grow much larger than normal.
These amplified fluctuations later became possible seeds for primordial black holes.
Kination
Finally, the Universe entered a stage called kination, where the energy of the inflaton field was mainly in its motion rather than its potential energy.
Instead of stopping the calculations after inflation, Joana continued the simulations all the way until black holes formed. This allowed him to watch the complete process from beginning to end.
Three Different Ways Black Holes Can Form
One of the biggest discoveries of the study is that the same type of early fluctuation can produce three completely different outcomes.
1. The Trapped Inflation Method
In some regions, inflation did not end when it should have.
While the rest of the Universe moved into the next stage, these small regions continued expanding rapidly.
Eventually, they became trapped behind an event horizon and turned into primordial black holes.
This process is very different from the usual idea of matter simply collapsing under gravity.
2. The Overdense Region Method
This is the traditional way scientists expected primordial black holes to form.
A region becomes much denser than its surroundings.
When it re-enters the observable part of the Universe, gravity becomes strong enough to overcome pressure, causing the region to collapse into a black hole.
This mechanism has been studied for many years.
However, the new simulations show that the exact shape of the dense region is just as important as how dense it is.
3. The Void-and-Shell Method
The third method was the biggest surprise.
Instead of starting with a dense region, the fluctuation creates a large empty region, called a void, surrounded by a dense shell.
As the empty region expands, more matter collects in the surrounding shell.
Eventually, this shell collapses inward.
The collapsing shell squeezes the centre so strongly that it can create a primordial black hole.
This unusual mechanism had received very little attention before and shows that black holes can form in ways scientists had not fully considered.
Why the Shape of a Fluctuation Matters
One of the most important findings of the study is that size alone is not enough to predict whether a primordial black hole will form.
Earlier studies mostly measured the strength of a fluctuation at its centre.
Joana discovered that the entire shape of the fluctuation plays an important role.
For example, two fluctuations with almost the same central density may behave very differently if their outer regions have different shapes.
In the case of the void method, the surrounding shell becomes the most important part.
This means scientists cannot rely on one simple number to predict black hole formation.
Instead, they must study the complete structure of each fluctuation.
Why This Discovery Is Important
This research changes the way scientists think about primordial black holes.
Previous models often assumed that all black holes formed through one basic process.
The new study shows that there are three separate formation channels, each following different physical rules.
Because of this, future calculations must treat each channel separately.
This will help scientists make much more accurate predictions about how many primordial black holes may exist today.
Could These Black Holes Be Dark Matter?
Dark matter makes up about 85 percent of all matter in the Universe, but scientists still do not know what it is.
Primordial black holes are one possible answer.
If enough of these black holes formed in the early Universe, they could explain at least part of the missing dark matter.
The new research does not prove this idea.
However, it provides a much better way of calculating how many primordial black holes may have formed.
This will help scientists test whether they could really account for dark matter.
A New Way to Reheat the Universe
The study also suggests another exciting possibility.
After inflation ended, the Universe needed to become hot again so that particles, atoms, stars and galaxies could eventually form.
This process is called reheating.
In some theories, ordinary reheating may not work very well.
Joana's study suggests that primordial black holes could temporarily become important during this period.
As these black holes slowly evaporate through Hawking radiation, they release huge amounts of energy.
This energy could help heat the Universe again after inflation.
Future Observatories May Find Evidence
The different black hole formation methods may produce different gravitational-wave signals.
Future observatories such as LISA, Taiji, TianQin, the Einstein Telescope, and pulsar timing arrays may be able to detect these signals.
If scientists observe these patterns, they could learn not only whether primordial black holes exist but also how they formed.
Looking Ahead
Cristian Joana's research is one of the first studies to follow tiny fluctuations continuously from the earliest moments of inflation all the way to black hole formation using full General Relativity.
The study shows that primordial black holes are much more complicated than previously believed. Instead of forming through only one process, they may appear through three different pathways: trapped inflation, overdense collapse, and the newly discovered void-and-shell collapse.
These findings could improve future studies of dark matter, gravitational waves, and the evolution of the early Universe.
As scientists continue building more advanced simulations and next-generation space observatories begin searching for new signals, primordial black holes may finally move from theory to reality. If that happens, they could provide some of the strongest clues yet about what happened in the first moments after the Big Bang and help answer some of the biggest unanswered questions in modern physics.
Reference: Cristian Joana, "Primordial black holes forming during kination: the trapped, the overdense, and the void", Arxiv, 2026. https://arxiv.org/abs/2607.20423
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