How do black holes form and what happens at their event horizon?

Black holes form from the collapse of massive stars after they exhaust their nuclear fuel. When the core collapses under gravity, it can create a singularity, a point of infinite density surrounded by an event horizon. The event horizon is the boundary beyond which nothing, not even light, can escape the black hole’s gravitational pull. At this point, the escape velocity exceeds the speed of light. The nature of what happens at the event horizon and inside the singularity is still an area of active research, particularly in reconciling general relativity with quantum mechanics.