How Does a Black Hole Evaporate?

In 1974, Stephen Hawking showed that quantum mechanics near a black hole event horizon leads to the creation of particle-antiparticle pairs from vacuum energy fluctuations. Normally, these virtual pairs annihilate instantly. But at the event horizon, one particle can fall into the black hole while the other escapes as real radiation. To conserve energy, the infalling particle must have negative energy (from the black hole perspective), reducing the black hole mass slightly. Over time, this process — Hawking radiation — causes the black hole to lose mass and shrink. The radiation temperature is inversely proportional to the black hole mass: stellar-mass black holes radiate at only ~10^-8 Kelvin (colder than the cosmic microwave background, so they actually gain mass from their surroundings), while a hypothetical microscopic black hole would radiate intensely and evaporate in a burst of particles. A stellar-mass black hole would take roughly 10^67 years to evaporate — far longer than the current age of the universe (13.8 billion years). Hawking radiation has never been directly detected but is supported by analogous experiments with sonic black holes.