Two categories of black holes are known to exist, and a third kind has been hypothesized but not yet detected. One kind, known loosely as a stellar black hole or low-mass black hole, is found wherever the core of a very massive star (usually twenty or more times the mass of the Sun) has collapsed. The other known kind, called a supermassive black hole, is found at the centers of galaxies and is millions or even billions of times more massive than the Sun.

The third kind of black hole, called a primordial black hole, is found at random locations in space. It is hypothesized that these black holes were created at the beginning of cosmic expansion as little “imperfections” in the fabric of spacetime. However, no such black hole has yet been confirmed to exist.