Ask Ethan: How are black holes active if nothing escapes from them? (opens in new tab)

When it comes to the Universe, there’s one class of object that achieves more extreme conditions than any other: black holes. While other objects may be dense — the centers of an iron-rich planet, a white dwarf star, a uranium nucleus, or a neutron star — only a black hole packs so much mass into such a small volume that it actually creates an event horizon. An event horizon represents a boundary between our observable Universe, where we reside, and a black hole’s interior, where all infallin...