"If there are lots of black holes out there, some of them must surely pass through our backyard every now and then."

We now know that black holes occur frequently throughout the universe. One Sagittarius A* sits at the center of our galaxy, the Milky Way. In fact, according to NASA most galaxies of a similar size have monster black holes at their center. Sagittarius A* has approximately 4 million times more mass than the Sun.

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?

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.

"Primordial black holes do not live in the solar system. Rather, they're streaming through the universe, doing their own thing," said researcher Sarah Geller.