Black holes are regions in space where gravity is so intense that nothing, not even light, can escape. They form when massive stars collapse under their own gravity after exhausting their nuclear fuel. The core collapses into a singularity, a point of infinite density, surrounded by an event horizon, the boundary beyond which nothing can return. **General relativity** explains black holes as distortions in spacetime caused by extreme gravity. Black holes can grow by absorbing matter and merging with other black holes. They emit **Hawking radiation**, theoretical radiation that may cause them to slowly evaporate over time.