Black holes are some of the most mysterious and fascinating objects in the universe. They are regions of space where gravity is so strong that nothing—not even light—can escape from them. This happens because an enormous amount of mass is packed into an incredibly small space.
Most black holes form when massive stars reach the end of their lives. During their lifetime, these stars are powered by nuclear fusion, which generates energy and outward pressure that balances the inward pull of gravity. But when a star runs out of fuel, it can no longer support itself, and gravity causes it to collapse inward. If the collapsing core is massive enough (at least about three times the mass of the Sun), it can form a black hole.