A region of space where matter is packed so densely that nothing, not even light, can escape its gravity; the boundary of that trap is the event horizon. Predicted by Einstein’s general relativity in 1916 and long doubted, black holes were confirmed by orbiting stars, X-ray sources, gravitational waves (2015), and a direct image (2019). Supermassive ones anchor most galaxies, and at each center theory predicts a singularity where known physics breaks down.
Picture a place where the universe stops making sense. Pack enough mass into a small enough space and gravity grows so strong that to escape you would have to travel faster than light, which nothing can do. So nothing leaves. Light itself falls in and never comes back out. The edge of that trap is called the event horizon, a boundary you can cross only one way. A century ago black holes were just a strange answer hiding in Einstein's equations, a result most physicists assumed nature would never actually build. Then the evidence arrived: stars whipping around invisible giants, gravitational waves from two of them colliding, and in 2019 an actual photograph of one's dark shadow. They turned out to be everywhere. And at the center of each, theory says, sits a point where our laws of physics simply give out.