What is the min mass, size of that mass,and min event horizon circumference for a black hole?

Question

In other words; how massive does a group of atoms have to be before they collapse in on themselves, can we make that happen in a lab? Then what is the smallest size of that group. What kind of event horizon would that generate?

Answer 1

The Schwarzschild radius 1/(2M - r) where M is the mass of the object and r is it's radius, assuming spherical symmetry. It is not so much a matter of a mass as it is of density. As far as I am aware there is no minimum anything for black holes, and general relativity breaks down at the quantum level so answering your question is not possible at this time.

To branch more into theory, the minimum size for a stable black hole is a size where it gains more matter than it loses via Hawking evaporation.