Most black holes form when massive stars run out of fuel and collapse under their own gravity.

When stars much bigger than our Sun use up all their hydrogen fuel, they can no longer hold up against gravity. This causes their cores to collapse in a violent process. Sometimes this collapse triggers a huge explosion called a supernova, blowing away outer layers but leaving behind a very dense core. If this core is heavy enough, it keeps collapsing until it becomes a black hole, a point with gravity so strong that not even light can escape.