In 2015 two powerful telescopes detected something physicists had been seeking for more than one hundred years—gravitational waves from the collision of two black holes. This announcement thrilled the scientific community. Since the eighteenth century, astronomers have predicted the existence of massive, invisible stars whose gravity would not let anything—even light—escape. In the twenty-first century, sophisticated technologies are bringing us closer to seeing black holes in action. Meet the scientists who first thought of black holes hundreds of years ago, and learn about contemporary astrophysicists whose work is radically shaping how we understand black holes, our universe, and how it originated.