The primordial black holes would be the thing that revolutionize science if we can find them.

The theory of black holes says that the mass of the black hole determines the distance of the event horizon from the black hole's singularity. The lower mass a black hole has the closer the event horizon is to its singularity or if a black hole has no singularity. We can talk about the event horizon distance to the center of the black hole. Maybe stellar mass black holes have a singularity. 

And supermassive black holes don't have that thing. But then we can start to think about extremely low-mass black holes. The low-mass black holes can exist anywhere. Theoretically, those things can hide on planets, in asteroids, or even in some sand bites. And if somebody can find those things they can give an answer to quantum computing and give endless energy sources. 

When we think about extremely low-mass black holes that pull particles and gas around them. Those things can turn the black hole into a grey hole. The extremely dense object that involves a black hole. The escaping velocity from the grey hole's shell can be very close to the speed of light. 

The distance of the low-mass black hole's event horizon is closer to the singularity than a high-mass black hole. There is a theoretical possibility that the event horizon can be inside the object's shell. The fast rotating structures like neutron stars are things. 

That can make it possible. That the hypothetical black hole inside them cannot pull that shell inside them. That requires that the shell's speed must be so high, that it crosses escaping velocity on the distance where that structure is from the event horizon. 

 So it's possible. That somewhere in the universe is the neutron star that surface or shell orbits the black hole. That would be an interesting variation of the quasi-stars. Quasi stars are hypothetical black-hole-powered stars. 

The sub-stellar mass black holes are possible if the star or some other energy source sends energy that presses the planet or even some asteroid into a black hole. There is a theory that very small-mass black holes are the thing behind Dark matter. There is no minimum mass for black holes. The only requirement is that energy can push particles or some other object into extremely dense form. 

The energy must smash all particles and quantum fields in the atom into entirety called a singularity. Those extremely low-mass black holes can be far different than we think. When we think about low-mass black holes they can form things called quasi-stars around them. 

Theoretically, those things formed in the Early universe.  But theoretically, those things can form in very special situations. The black hole can impact some supergiant stars. They pull the internal structures of that star into them. And if the star's shell rotates fast enough it doesn't fall to the black hole. That model caused one interesting model. 

Can that kind of quasi-star-type phenomenon form on some planets or even in asteroids? That requires an extremely low-mass black hole that travels into the planet's core. Then that black hole forms a shell around it using the planet's liquid structures. Sometimes is introduced a model that the small-size black holes can turn neutron stars into quasi-neutron stars. That means inside those extremely dense neutron objects can hide small- about Earth-mass black holes. That model is very interesting. 

https://scitechdaily.com/dark-matters-secret-hideouts-are-primordial-black-holes-lurking-nearby/

https://en.wikipedia.org/wiki/Quasi-star