A black hole is a region in space where the gravitational pull is so strong that nothing, not even light, can escape from it. They are formed when massive stars collapse under their own gravity at the end of their life cycle. The boundary around a black hole, called the event horizon, marks the point of no return for anything that gets too close. Black holes can vary in size, with some being only a few times the mass of our Sun, while others, known as supermassive black holes, can be millions or billions of times more massive. They are often found at the centers of galaxies, including our own Milky Way.