Primordial black holes (PBHs) are hypothetical black holes that are thought to have formed soon after the Big Bang. In the inflationary era and early radiation-dominated universe, extremely dense pockets of subatomic matter may have been tightly packed to the point of gravitational collapse, creating primordial black holes without the supernova compression needed to make black holes today.
Because the creation of primordial black holes would pre-date the first stars, they are not limited to the narrow mass range of stellar black holes. Yakov Borisovich Zel’dovich and Igor Dmitriyevich Novikov first proposed the existence of such black holes in 1966, while the first in-depth study was conducted by Stephen Hawking in 1971.
However, their existence has not been proven and remains hypothetical. In September 2022, primordial black holes were proposed by some researchers to explain the unexpected very large early galaxies discovered by the James Webb Space Telescope (JWST).
PBHs have long been considered possibly important if not nearly exclusive components of dark matter. Depending on the model, primordial black holes could have initial masses ranging from 10−8 kg (the so-called Planck relics) to more than thousands of solar masses. However, primordial black holes originally having mass lower than 1011 kg would not have survived to the present due to Hawking radiation, which causes complete evaporation in a time much shorter than the age of the Universe.
Primordial black holes are non-baryonic, and as such are plausible dark matter candidates. Primordial black holes are also good candidates for being the seeds of the supermassive black holes at the center of massive galaxies, as well as of intermediate-mass black holes.