Event Horizons: The Point of No Return

An event horizon is the invisible boundary around a black hole.
Once something crosses it—even light—it can never escape.
The size of the event horizon depends on the black hole’s mass.
For a stellar black hole, it may be only a few kilometers wide.
For a supermassive black hole, it can span billions of kilometers.
Time appears to slow down near the event horizon, as seen by distant observers.
To an outside viewer, objects seem to freeze at the edge, fading from view.
Inside, all paths lead inevitably toward the black hole’s singularity.
Event horizons can also create “shadows,” the dark silhouettes imaged in M87 and Sagittarius A*.
They mark the ultimate boundary of physics—where our current understanding breaks down.