A black hole is a region of spacetime where the gravitational pull is so strong that not even light can escape. It is created by the collapse of a massive star, which has exhausted its nuclear fuel and can no longer support its own weight. When the core of the star collapses inward, its mass is compressed into a small region of space, creating a singularity with infinite density. Beyond the singularity lies the event horizon, the point of no return. Anything that crosses the event horizon is trapped inside the black hole, unable to escape its immense gravitational pull. Black holes can vary in size, from a few times the mass of our sun to billions of times its mass. They have important effects on the surrounding environment, including the way they shape the orbits of nearby stars and influence the growth of galaxies.