Black holes formed in the early universe, called primordial black holes, are theorized to contribute to dark matter. Their existence remains unconfirmed but could explain some gravitational lensing observations.
It matters because they could solve one of physics’ biggest mysteries: the nature of dark matter.
It also affects cosmology and models of the early universe.
Primordial black holes may be hiding as part of dark matter in the universe.
[NASA, nasa.gov]