
Hypothetical black holes formed in the early universe, influencing galaxy formation.Primordial black holes are hypothetical black holes that would have formed in the extremely dense, hot conditions of the early universe, shortly after the Big Bang. Unlike stellar black holes, which are the collapsed cores of massive stars, primordial black holes could have formed from the direct gravitational collapse of overdense regions in the primordial plasma. Their masses are not constrained by stellar evolution and could range from as little as a fraction of a gram to many thousands of solar masses, depending on when and how they formed.
The concept was first proposed in 1966 by Yakov Zel'dovich and Igor Novikov, and independently by Stephen Hawking in 1971, who also linked them to dark matter.
In the early universe, quantum fluctuations in density could have created regions dense enough to collapse into black holes. The process would be analogous to the formation of stars, but without the need for cooling or nuclear fusion. Once formed, these black holes would behave like ordinary black holes, but their small size (if low-mass) would make them radiate via Hawking radiation, potentially evaporating over cosmic timescales. Heavier ones could persist to the present day and act as a component of dark matter, influencing structure formation through their gravitational pull.
Primordial black holes are a leading candidate for dark matter, and their detection is a major goal in astrophysics, using gravitational wave observatories, microlensing surveys, and gamma-ray telescopes.
A primordial black hole with the mass of a mountain would be only about the size of a proton.
| M_{\rm PBH} | variable | mass of the primordial black hole — mass kilogram |
| M_{\rm eq} | variable | horizon mass at matter-radiation equality — mass kilogram |
| T_{\rm eq} | variable | temperature at matter-radiation equality — temperature kelvin |
| T_\star | variable | temperature at formation time — temperature kelvin |





















