Event Horizon

black holes · space · physics

The ultimate point of no return. An event horizon is an invisible boundary surrounding a black hole. Once anything crosses this boundary, it cannot escape, no matter how fast it tries to go. Even light itself gets trapped inside.

Faster than escape speed. To escape from Earth, a rocket needs to travel at about 25,000 miles per hour. At an event horizon, the escape speed would need to be faster than the speed of light, which is impossible for anything with mass.

Light cannot break free. Because light is the fastest thing in the universe and even light cannot escape an event horizon, we can never see what is inside. An event horizon is like nature's ultimate curtain that hides what lies beyond.

Size depends on mass. Smaller black holes have tiny event horizons, while massive black holes have enormous ones. A black hole from a dead star might have an event horizon the size of a city, but a supermassive black hole could have one bigger than our entire solar system.