Long before the first stars, rare overdense regions in the hot early universe may have collapsed directly into black holes. If some were massive enough to survive Hawking evaporation, they could still move silently through galactic halos, bend starlight, disturb orbits, merge in darkness, or contribute to the invisible mass known as dark matter.

This episode follows the evidence trail from early theoretical work by Yakov Zel’dovich, Igor Novikov, Stephen Hawking, and later researchers, through microlensing surveys, gamma-ray limits, cosmic microwave background constraints, and gravitational-wave searches by LIGO, Virgo, and KAGRA. The strongest conventional view is that many observations have sharply limited primordial black holes across much of the possible mass range, and that most detected black holes can be explained by ordinary stellar or galactic processes. The strongest alternative scientific possibility is that a hidden population still survives in difficult-to-test windows, especially at asteroid mass, or as rare seeds for early supermassive black holes.

No primordial black hole has been confirmed. The question remains whether the invisible mass around galaxies is made only of unknown particles, or whether part of it is a fossil population of black holes from the universe’s first moments.

This podcast uses artificial intelligence in its research, writing, production, and narration. Episodes are editorially reviewed before publication.

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YES OR NO: Could primordial black holes make up a major share of dark matter??????