If even light can’t escape them, how do we know black holes exist?

Interesting fact:

Black holes were a prediction of Albert Einstein’s theory of relativity. Because of their, well, blackness, they can’t be directly seen. But we can observe the effect their gravity has on the movement of surrounding stars. Then there’s gravitational lensing: massive black holes bend light around them, revealing a distorted view of what’s beyond. In addition, the gas and particles orbiting a black hole at breakneck speed before falling in are superheated, which means they shine incredibly bright. Some of these particles on our side of the event horizon escape and are visible as light, which leads us to our final bullet point.