Primordial black holes are a type of black hole that may have formed not from the collapse of stars, but in the very early stages of the universe. It is suggested that they could have appeared shortly after the Big Bang, when the universe was still extremely hot and dense. For this reason, their formation mechanisms are completely different from those of stellar-mass or supermassive black holes.
In the early universe, the density of matter and energy was extremely high. Small density fluctuations could have made some regions denser than others. If a density contrast exceeded a critical threshold, that region could have collapsed directly into itself and formed a black hole. In this process, star formation is not required; the collapse happens directly on a cosmic scale.
The possible mass range of primordial black holes could be very wide. They may have formed at scales ranging from microscopic black holes with masses near that of atoms, to objects comparable in mass to stellar black holes. This diversity depends on how density was distributed in the early universe.
The existence of primordial black holes has not yet been confirmed. However, some cosmological observations—especially gravitational microlensing events—are used to search for possible signatures. Sudden and temporary increases in a star’s brightness can indicate the presence of an unseen mass passing in front of it.
The cosmic microwave background radiation also plays an important role in primordial black hole research. Black holes formed in the early universe may have influenced surrounding matter in ways that left subtle imprints in the cosmic background. For this reason, highly sensitive cosmological maps are used in the search for indirect evidence.
Primordial black holes have also been linked to dark matter. Some theories propose that a fraction of the universe’s dark matter could be made of primordial black holes. Although this hypothesis has not been confirmed, it remains actively explored in modern cosmology.
If primordial black holes truly exist, they would be unique relics capable of providing direct information about the universe’s earliest seconds. This would make them extremely important not only for black hole physics, but also for cosmology.
In conclusion, primordial black holes form the most speculative yet most exciting group in black hole classification. If their existence is established, it could lead to profound changes in our understanding of the universe’s initial conditions and the dark matter problem.