What causes a black hole to form in space?

A black hole forms when a massive amount of matter is compressed into an extremely small space, causing gravity to become so strong that nothing, not even light, can escape. The most common cause is the death of a massive star, typically one at least 20 times the mass of our Sun. When such a star exhausts its nuclear fuel, it can no longer support itself against gravity and collapses inward. This triggers a supernova explosion, and if the remaining core is massive enough, it collapses into a singularity, forming a black hole. Black holes can also form through the merger of neutron stars or, in the case of supermassive black holes, through processes not yet fully understood in the early universe.