what is the smallest possible size of a black hole?
A black hole the mass of the sun is about 3 km in radius (Schwarzschild radius or radius of the event horizon), and the radius is directly proportional to the mass. If you can compress matter to a high enough density you can theoretically make a black hole arbitrarily small, but practically there is no known way to create black holes except in the collapse of massive stars. The smallest black hole that we know of is about 5 solar masses, so about 15 km in radius. There is a hypothesis that smaller black holes could have been created during the very early phase of the big bang, but these have never been seen.
One question. Is it true that the larger stars with more mass will become smaller black holes as they will collapse further under their own pressure? Or does it not work like that? I don't know much about physics so excuse any questions that might be stupid haha