Primordial black hole

A hypothetical black hole formed in the early universe when unusually dense regions collapsed under gravity. Unlike stellar black holes, it could have formed before stars existed.

Cosmic density perturbation: A small variation in matter or energy density across space in the early universe. A sufficiently large perturbation could make a region collapse into a primordial black hole.
Dark matter: Matter inferred from its gravitational effects that emits, absorbs, or reflects little or no light. Primordial black holes have been proposed as a component of dark matter.
Stellar black hole: A black hole formed by the gravitational collapse of a massive star or stellar remnant. Its stellar origin differs from formation out of early-universe density fluctuations.
Primordial black hole mass function: The distribution of primordial black-hole abundance across black-hole masses. Formation models predict different mass distributions, and observations constrain each range differently.
Gravitational collapse: The contraction of matter under its own gravity, potentially forming a compact object or black hole. Primordial black holes form when early-universe overdensities collapse beyond their pressure support.
Gravitational microlensing: The temporary brightening of a background object when a foreground mass bends its light. Microlensing surveys constrain compact primordial black holes across some mass ranges.
Supermassive black hole: A black hole with a mass millions to billions of times that of the Sun, usually found in a galaxy's center. Its known galactic setting and growth history differ from the proposed primordial origin.
Primordial black hole constraints: Observational limits on the abundance of primordial black holes as a function of mass. Multiple independent measurements leave only restricted ranges for a substantial dark-matter contribution.
Cosmological horizon: A boundary set by the finite distance light can travel in an expanding universe. The horizon mass at formation helps set the characteristic mass of a primordial black hole.
Gravitational waves: Ripples in spacetime produced by accelerating masses, including merging compact objects. A primordial origin has been considered for some black-hole merger signals.

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