Primordial Black Holes Can Have Low Masses

The mass restriction you are referring to only applies to black holes that form in Type-II supernova. These are called core-collapse black holes and their masses are typically several to many times the mass of the Sun.

Primordial black holes have different mass restrictions because they form in different ways. The possible mass range for PBHs is very roughly 10^-20 grams to 1,000 solar mass. They are thought to form in the “early” high density/temp/pressure phase of the global expansion of the observable universe.

However, PBHs with masses below that of the planetary-mass range are thought to radiate and disintegrate with time. PBHs with masses over 100 solar masses are ruled out as dark matter because the existence of so many very massive black holes would have been detected long ago.

In the mass range for the dark matter ultracompacts predicted by Discrete Scale Relativity, no black hole mass restrictions are violated in the case of primordial black holes.

Thanks for your questions!