When most of us hear the words “black hole,” we think of a giant, dead star. We picture an enormous star, much bigger than our own sun, reaching the end of its life. It runs out of fuel, collapses under its own massive weight, and explodes in a supernova. What’s left behind is a point of gravity so strong that nothing, not even light, can escape. This is a “stellar” black hole, and it’s the most common type we talk about.
But there is another kind of black hole, a much more mysterious and ancient type. These are not the children of dead stars. They are thought to be relics from the very birth of the universe itself. Scientists call them “primordial black holes,” and they are one of the most exciting and puzzling ideas in all of science. They are completely theoretical, meaning we have not proven one exists for certain. But if they are real, they could solve some of the biggest mysteries we have, including the puzzle of dark matter.
These objects would have been born in the fiery chaos of the Big Bang, in the very first second of time. This makes them completely different from the black holes we see forming today. They have a different origin story, they can come in very different sizes, and they might be all around us, hiding in plain sight. So, if they did not come from stars, where did these ancient objects actually come from?
What Makes a Primordial Black Hole Different from a Normal Black Hole?
The biggest difference between a normal black hole and a primordial black hole is their “birth story.” It’s a bit like the difference between a tree that grows over decades and a diamond that is formed in an instant under extreme pressure. A normal, stellar black hole is the end of a life cycle. You need a massive star, one at least three times the mass of our sun, to live a long life and then die in a specific way. Its own gravity must be strong enough to crush its core down to an infinitely small point. Because you need a giant star to make one, stellar black holes have a minimum size. They are always at least a few times heavier than our sun.
Primordial black holes, or PBHs, are the complete opposite. They are not the end of anything; they are from the very beginning of everything. They formed in the first tiny fractions of a second after the Big Bang, long before the first stars or galaxies ever existed. In those first moments, the universe was not a calm, empty space. It was an incredibly hot, dense soup of energy and particles, expanding at an unbelievable rate. This “soup” was not perfectly smooth. Some spots were, just by chance, slightly denser than the spots next to them. In the extreme conditions of the baby universe, gravity was so powerful that it could take one of these extra dense “lumps” and crush it directly into a black hole.
This different origin is what makes PBHs so special. Because they were not made from stars, they are not limited by a star’s size. A PBH could, in theory, be almost any size. Some models predict PBHs could have formed with the mass of a large asteroid or a mountain, but be physically smaller than a single atom. Others could be as heavy as a planet, or even thousands of times heavier than our sun. This huge range of possible sizes is a key feature that sets them apart. A stellar black hole has a “minimum weight” to be born, but a primordial black hole does not.
How Could a Black Hole Form Just After the Big Bang?
To understand how a primordial black hole could form, we have to try to picture the universe at less than one second old. It is a picture our minds can barely handle. There were no atoms, no light, no stars. There was only a “primordial soup” of pure energy and tiny particles, unbelievably hot and dense, and expanding faster than the speed of light. This period is often called “inflation.” Think of this soup as a pot of boiling, lumpy oatmeal. While most of it is smooth, there are some lumps and bumps where the oatmeal is thicker. The very early universe was just like this, but with density instead of oatmeal.
In some of these tiny, random regions, the density of energy and matter might have been huge—perhaps 50% or more denser than the area around it. In our universe today, a dense lump like that would just spread out. But in the first second of the Big Bang, the pressure and gravity were at their most extreme. When one of these extra dense “lumps” got squeezed by the expansion of the universe around it, its own internal gravity became so strong that it overwhelmed every other force. The lump could no longer hold itself up. It collapsed in on itself instantly, creating an event horizon and becoming a black hole.
No star was needed. No supernova explosion happened. It was a direct collapse of pure density. This is the key idea. The universe itself acted as the “factory” for these black holes. The conditions for this to happen were perfect only in that first tiny, tiny fraction of a second. As the universe continued to expand and cool down, it quickly became too thin and not-so-dense for this process to ever happen again. This is why primordial black holes are “primordial”—they are ancient artifacts, frozen in time from the very first moment of creation. If they exist, they are nearly 13.8 billion years old, the true “senior citizens” of the cosmos.
Can Primordial Black Holes Be Very Big or Very Small?
Yes, and this is perhaps the most fascinating part of the theory. The size of a primordial black hole would depend entirely on the size of the “lump” of dense soup that it formed from. Because these lumps could have been random sizes, the resulting PBHs could have a huge range of masses. This is completely different from stellar black holes, which are all “heavyweights.”
On the small side, some PBHs could be microscopic. Scientists talk about PBHs that might have the mass of a large mountain, or even just a car. An object with the mass of a mountain would be crushed into a black hole smaller than the nucleus of an atom. These “micro” black holes are impossible to create in today’s universe. Nothing we know of can crush a mountain with that much force. But the Big Bang could have done it easily. Even smaller PBHs could have formed, perhaps with the mass of a paperclip, but these tiny ones would not have survived to the present day.
On the large side, some of the “lumps” in the early universe could have been enormous, creating PBHs that were hundreds or even thousands of times the mass of our sun. These are called “intermediate-mass” black holes. Scientists have a big puzzle right now: when we look at the centers of galaxies, we see “supermassive” black holes that are millions or billions of times the mass of our sun. The problem is, we see them in the very early universe, in galaxies that are very young. They seem to have grown too big, too fast. A normal stellar black hole would not have had enough time to eat enough gas and stars to get that big.
This is where primordial black holes could be the answer. What if these early galaxies were “born” with a large PBH already in them? A PBH with the mass of 100,000 suns, formed in the Big Bang, would act as a “seed.” This seed would sit in the middle of a forming galaxy, and its powerful gravity would pull in gas and dust, allowing it to grow quickly into the supermassive black hole we see today. This idea helps solve the “too big, too fast” problem and is a major reason why astronomers are so interested in PBHs.
What Is Hawking Radiation and Does It Affect These Black Holes?
In the 1970s, the famous physicist Stephen Hawking came up with a revolutionary idea. He proposed that black holes are not perfectly “black” forever. He showed that, due to the strange rules of quantum physics, black holes must slowly “leak” energy back out into space. This process is called “Hawking radiation.” It is a very, very slow process for the giant black holes we know about. A black hole the mass of our sun would take trillions upon trillions of years to “evaporate” completely, far longer than the current age of the universe.
However, Hawking’s theory also said that the smaller the black hole, the faster it evaporates. A black hole’s temperature is inversely related to its mass. This means a giant black hole is very, very cold and leaks extremely slowly, like a giant water tank with a single, microscopic pinprick. But a tiny black hole would be incredibly hot and would leak energy at a furious rate, like a small bucket riddled with holes.
This has a huge consequence for primordial black holes. According to the theory, any PBH that was created with a mass less than that of a large asteroid (about 100 million tons) would have had a short life. Even though they are 13.8 billion years old, they would have already “leaked” away all their mass and evaporated by now. The ones with the mass of a car or a paperclip would have vanished almost instantly.
But here is the exciting part: as a black hole loses mass, it gets hotter and evaporates even faster. This creates a runaway effect. In the very last second of its life, a tiny primordial black hole would release all its remaining energy in a final, brilliant “pop.” This “pop” would be a powerful burst of high-energy light called gamma rays. Scientists are actively searching the sky for these specific gamma-ray bursts. If we ever detect one, it would be a “smoking gun”—proof that tiny black holes existed and that Hawking’s theory of evaporation is correct. So far, we have not found such a signal, but the search continues.
Are Primordial Black Holes the Answer to Dark Matter?
This is the billion-dollar question and the main reason PBHs are such a hot topic in 2025. For decades, scientists have been facing a huge mystery. When we look at galaxies, including our own Milky Way, we see that they are spinning. But they are spinning so fast that the gravity from all the stars, gas, and dust we can see is not nearly strong enough to hold them together. They should fly apart, like children flying off a merry-go-round that is spinning too quickly.
To solve this, scientists proposed that there must be some other “stuff” out there that we cannot see. This invisible substance must have gravity, and there must be a lot of it—about five times more than all the normal matter in the universe combined. We call this “dark matter.” We know it is there because we can see its gravity bending light and holding galaxies together, but we have no idea what it is. For a long time, the leading theory was that dark matter is made of a new, undiscovered microscopic particle. But after decades of searching with sensitive detectors, we have found nothing.
This has led scientists to reconsider an old idea: what if dark matter is not a new particle at all? What if dark matter is just… primordial black holes? This is a very elegant solution. PBHs would be “dark” because their gravity is so strong that light cannot escape. They would have gravity, which is what we need to hold galaxies together. And they would have been formed in the Big Bang, so they would be spread throughout the universe, forming the “scaffolding” for galaxies to form around. They tick all the boxes.
For this theory to work, the PBHs would have to be of a very specific size. They cannot be too small (like mountain-mass), because those would have evaporated by now due to Hawking radiation. They also cannot be too large (like sun-mass), because we would have seen them. A large black hole passing in front of a distant star would bend its light in a way we could detect, an effect called “gravitational lensing.” We have looked for this and have not found enough of them to account for all dark matter. This leaves a “sweet spot” or “window” of possibility: dark matter could be made of a huge number of PBHs that are all roughly the mass of an asteroid. These are too small to see with lensing easily, but just large enough to have survived for 13.8 billion years without evaporating.
How Are Scientists Looking for Primordial Black Holes Today?
Because PBHs are so mysterious and could solve so many problems, scientists are using several different methods to hunt for them right now. The search is active and uses some of our most advanced technology.
First, there is the search using gravitational lensing. As mentioned, any object with gravity will bend the path of light that passes near it. If a PBH, even one with the mass of a planet, were to pass directly between Earth and a distant star, the PBH’s gravity would act like a magnifying glass. For a brief moment, it would focus the star’s light, causing the star to look temporarily and suddenly brighter, then fade back to normal. This specific “flicker” is called “microlensing.” Telescopes on Earth and in space, like NASA’s Nancy Grace Roman Space Telescope (set to launch soon), are designed to stare at millions of stars at once, just waiting to catch one of these telltale flickers.
Second, we are searching with gravitational waves. Since 2015, detectors like LIGO, Virgo, and KAGRA have been “listening” to the universe. They do not listen for sound, but for “ripples” in the fabric of space-time itself, called gravitational waves. These waves are created by massive cosmic events, most famously when two black holes spiral into each other and merge. When we detect a merger, we can calculate the mass of the two black holes that collided. So far, most mergers have been between stellar black holes. But what if LIGO detected a merger between two objects that were each only one time the mass of our sun? A star cannot make a black hole that small. Such a discovery would be earth-shattering proof that a different kind of black hole—a primordial black hole—must exist.
Third, as we discussed, there is the search for Hawking radiation. Scientists use gamma-ray telescopes, like NASA’s Fermi Telescope, to scan the sky for the final “pop” of an evaporating micro black hole. This signal would be very distinct. Finding one would not only prove PBHs exist, but also prove that Stephen Hawking’s famous theory was correct. This three-pronged attack—lensing, gravitational waves, and evaporation—gives scientists their best chance of finally finding one of these ancient objects.
Has the James Webb Telescope Found Evidence for Them?
This is one of the newest and most exciting developments in the search. The James Webb Space Telescope (JWST) was designed to look back in time to see the first galaxies that ever formed. And in 2024 and 2025, it has been finding things that are deeply puzzling and that might point directly to primordial black holes.
JWST is finding “supermassive” black holes that are already huge in the “cosmic dawn,” less than a billion years after the Big Bang. As we covered, these black holes seem to be too big to have grown from a star so quickly. They must have started from a “heavy seed.” This is where it gets interesting. JWST has spotted objects that astronomers are calling “Little Red Dots” or “LRDs.” These are objects in the very distant, early universe. When scientists studied one of them, named QSO1, they got a shock. It appears to be a black hole with a mass of about 50 million suns. But the galaxy of stars around it is tiny, much, much smaller than expected for such a giant black hole.
This object does not look like it grew by eating a galaxy; it looks like the black hole came first. This is a huge clue. The scientists who made the discovery stated that this “naked” massive black hole is almost impossible to explain with normal star and galaxy formation. The only theories that can explain it are those that involve a “heavy seed.” This seed could be from the direct collapse of a giant gas cloud, or it could be a primordial black hole that formed in the Big Bang and was just “waiting” for a small galaxy to form around it. While this is not yet a direct discovery of a PBH, it is some of the strongest indirect evidence we have ever found. It suggests that massive objects did exist before stars, and primordial black holes are the most well-known theory to explain that.
Could a Primordial Black Hole Be Dangerous to Earth?
Whenever we talk about black holes, it is natural to wonder if they are dangerous. What would happen if one of these “asteroid-mass” primordial black holes, which might be dark matter, came flying through our solar system? Would it be a disaster?
Theoretically, yes, it would be very bad. Even a black hole with the mass of a mountain would be tiny—smaller than an atom—but its gravity would be just as strong as a mountain’s. If it passed near Earth, it would not “suck us in” from far away, but its intense, focused gravity could trigger massive earthquakes or volcanoes as it passed by. If it were to hit Earth directly, it would pass straight through the planet from one side to the other in seconds, creating a tunnel of unimaginable destruction and releasing as much energy as a massive nuclear bomb.
However, the key thing to remember is that space is unbelievably empty. The chances of a wandering primordial black hole, if they even exist, ever coming close enough to our solar system to cause a problem are practically zero. The distance between stars is vast, and the solar system is a tiny target in a cosmic ocean. Scientists are not worried about this scenario at all. The danger is not zero, but it is so low that it is not something anyone needs to lose sleep over. The scientific value of finding one would be far, far greater than any tiny risk they pose. They are objects of pure curiosity, not of fear.
Conclusion
Primordial black holes are one of the most amazing ideas in modern science. They are not the ghosts of dead stars, but “relics” from the very first second of the universe’s birth. They were forged from the pure density of the Big Bang itself, and if they are real, they come in a huge range of sizes—from smaller than an atom to more massive than a thousand suns.
These ancient objects are more than just a curiosity. They might be the answer to one of science’s biggest problems: the mystery of dark matter. A universe filled with asteroid-mass PBHs could explain why galaxies do not fly apart. Scientists are using every tool they have, from gravitational wave detectors to powerful new telescopes like JWST, to find the first solid proof. Recent discoveries of “too-big” black holes in the early universe suggest we are on the right track.
These objects connect the smallest parts of physics (quantum mechanics) with the largest (the cosmos) and take us back to the very first moments of time. If we finally prove primordial black holes exist, how will it change our understanding of the universe’s very first second?
FAQs – People Also Ask
What is the smallest possible primordial black hole?
Theoretically, the smallest black hole that could have formed would have a mass called the “Planck mass,” which is incredibly tiny, about the mass of a dust mite or 0.02 milligrams. However, any black hole that small, or even as large as a car, would have evaporated completely by now due to Hawking radiation. The smallest ones that could still exist today would have the mass of a large asteroid or a mountain.
Have we ever found a primordial black hole?
No, as of 2025, we have not definitively proven that a single primordial black hole exists. All of the black holes we have confirmed are “stellar” (from dead stars) or “supermassive” (in the center of galaxies). However, we have found very strong indirect evidence, such as gravitational wave signals from “weird” black hole mergers and discoveries by the James Webb Space Telescope of black holes that are too big to have formed normally in the early universe.
How old is a primordial black hole?
If they exist, primordial black holes are the oldest objects in the universe, besides the background radiation itself. They would have formed in the first fractions of a second after the Big Bang, making them approximately 13.8 billion years old. This means they existed long before the first stars, planets, or galaxies.
Can a primordial black hole grow bigger?
Yes, just like any black hole, a primordial black hole can grow by pulling in and “eating” matter or energy. If a PBH is floating in empty space, it will not grow. But if it wanders into a cloud of gas or the center of a galaxy, its gravity will pull that material in, and the black hole will gain mass over time. This is why some scientists believe PBHs acted as the “seeds” for the supermassive black holes we see today.
What’s the difference between a primordial black hole and a supermassive black hole?
A primordial black hole is defined by its origin—it was born from density in the Big Bang. A supermassive black hole is defined by its mass—it is millions or billions of times heavier than our sun and is found at the center of a galaxy. The two ideas might be connected: a very large “seed” primordial black hole could have been the starting point that quickly grew into a supermassive black hole.
If dark matter is black holes, why can’t we see them?
This is because the black holes that could be dark matter would be very small, with masses similar to an asteroid. While they have strong gravity up close, they are physically tiny (smaller than an atom) and do not give off any light. They are also too small to see with “gravitational lensing” unless one passes perfectly in front of a star, which is a very rare event that we are actively searching for.
Did Stephen Hawking discover primordial black holes?
Stephen Hawking did not discover them (since they are still theoretical), but he did some of the most important work on them. The idea was first proposed by physicists Yakov Zeldovich and Igor Novikov in the 1960s. Stephen Hawking then studied them in detail in the 1970s and, most importantly, he developed the theory of “Hawking radiation,” which explains how small black holes would evaporate.
What would happen if a primordial black hole hit the sun?
A PBH would pass straight through the sun like a “cosmic bullet.” If it were a small, asteroid-mass PBH, it would barely affect the sun at all, though it might cause some vibrations or “sunquakes” as it passed through. A larger, planet-mass PBH would do more damage and release a lot of energy, but the sun would likely survive the encounter. This is an extremely unlikely event.
Why are primordial black holes so hard to detect?
They are hard to detect because they are “dark” and, if they make up dark matter, they are likely very small. They do not shine, they do not block light, and their gravity is only strong in their immediate vicinity. Our only ways to find them are indirect: seeing a star “flicker” from their lensing, hearing the “chirp” of two of them merging, or spotting the “pop” of one evaporating. All of these are very rare events.
What is the “primordial soup” from the Big Bang?
The “primordial soup” is a simple way to describe the state of the entire universe in the first moments after the Big Bang. It was not a soup of chemicals, but an incredibly hot, dense sea of energy and fundamental particles (like quarks and electrons). This “soup” was expanding and cooling rapidly, and it was out of this energetic state that all matter, and possibly primordial black holes, first formed.