To find darkness, scientists search the universe for light.
Spotting black holes is tricky. Because they don’t give off light, astronomers have a difficult time pinpointing their location. But when a black hole gets close enough to an object, like a star, for example, and begins consuming the object's mass, the matter that pours into its gravitational clutches can get so hot that it glows and releases energy in the form of X-ray light. The most powerful X-rays are emitted from the hottest material swirling just outside the edge of the black hole. By observing this light with space telescopes, scientists can determine where black holes are hiding in the cosmos. Watch the video to see a black hole in action.