What is the defining boundary feature of a black hole from which escape is impossible, even for light?
Answer
The event horizon.
A black hole is characterized by an extreme gravitational field where spacetime is warped so profoundly that a boundary exists beyond which nothing can return. This boundary is known as the event horizon. Once any particle, including photons of light, crosses this threshold traveling inward, the escape velocity required exceeds the speed of light, making escape physically impossible. The singularity resides at the very center, but the event horizon is the critical surface defining the region of no return.
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