human
I'd like to learn more about astronomy. What are the most important facts about black holes?
assistant
Black holes are regions of space-time with such strong gravitational pull that nothing, not even light, can escape from them. They are formed when stars collapse under their own gravity and become so dense that they form an infinitely small point of infinite density called a singularity. The gravity is so strong that anything that comes too close will be pulled into the black hole. Black holes have no size or shape, but they do have mass which makes them invisible to our eyes because it doesn't interact with visible light.