How does a black hole form in outer space?

A black hole forms when a massive star, typically more than 20 times the mass of our Sun, reaches the end of its life. As the star exhausts its nuclear fuel, the outward pressure from fusion reactions can no longer counteract gravity. The core collapses suddenly and violently, triggering a supernova explosion. If the remaining core mass is sufficient, gravity overwhelms all other forces and crushes the matter into an infinitely dense point called a singularity, surrounded by an event horizon from which nothing, not even light, can escape. Black holes can also form through other means, such as the merger of two neutron stars or the direct collapse of extremely massive stars without a supernova. Supermassive black holes at galaxy centers likely formed through mergers and accretion over billions of years.