Astronomers have observed three types of black holes in the universe. Stellar-mass black holes formed from the collapse of a massive star, intermediate mass black holes found in some star clusters, and supermassive black holes that lurk in the centers of galaxies.

If microscopic black holes born a fraction of a second after the Big Bang exist, then at least one may fly through the solar system per decade, generating tiny gravitational distortions that scientists can detect.

Scientists say microscopic black holes could explain the elusive "dark matter" that makes up a quarter of all matter in the universe. But can it be proven?