Question: What is a black hole and how are they formed?

Emma Dean answered on 9 Mar 2016:

A black hole is usually formed when a star supernovas (explodes) and then gravity causes it to collapse back down. Gravity compresses all the matter down into a highly dense compact object. The gravitational pull of these objects is so strong that if light falls in, it cannot come back out. Light can’t escape a black hole because it can’t travel fast enough to overcome the gravitational pull. Because black holes absorb light, we can’t see them. This is why we say they are black.