primordial black hole

The term primordial black hole refers to theoretical black holes formed in the very early universe, that did not form from the collapse of stars. There are a number of theories of how some might have formed:

• Inflation's expansion of the initial fluctuations might include sufficiently high densities to form black holes, i.e., above a Schwarzschild density, a notion consistent with observed CMB anisotropies.
• They might form from topological defects, specifically cosmic string loops.
• They might result from an early-universe QCD phase transition.
• They might result due to phenomena in a scalar-field gravity.

Theories vary regarding their resulting mass distribution. There are theories suggesting some could be large and could be seeds or contributors to the early supermassive black holes (SMBHs) known as quasars. There are also theories suggesting black holes smaller than stellar-mass black holes, with masses down to the minimum for a black hole and up into the mass range of asteroids. It is presumed that the small ones might have evaporated due to Hawking radiation, but the rest still exist. Such small ones are sometimes termed miniature black holes or micro black holes.