Scientists have estimated the number of "small" black holes in the universe. And no surprise: It's a lot. This number might seem impossible to calculate; after all, spotting black holes is not exactly the simplest task. Because they're are as pitch-black as the space they lurk in, the light swallowing cosmic goliaths can be detected only under the most extraordinary circumstances — like when they're bending the light around them, snacking on the unfortunate gases and stars that stray too close, or spiraling toward enormous collisions that unleash gravitational waves. But that hasn't stopped scientists from finding some ingenious ways...