Since nothing can escape from the gravitational force of a black hole, it was long thought that black holes are impossible to destroy. But we now know that black holes actually evaporate, slowly returning their energy to the Universe. The well-known physicist and author Stephen Hawking proved this in 1974 by using the laws of quantum mechanics to study the region close to a black hole horizon.

The quantum theory describes the behavior of matter on the smallest scales. It predicts that tiny particles and light are continuously created and destroyed on sub-atomic scales. Some of the light thus created actually has a very small chance of escaping before it is destroyed. To an outsider, it is as though the event horizon glows. The energy carried away by the glow decreases the black hole's mass until it is completely gone.

This surprising new insight showed that there is still much to learn about black holes. However, Hawking's glow is completely irrelevant for any of the black holes known to exist in the Universe. For them, the temperature of the glow is almost zero and the energy loss is negligible. The time needed for the black holes to lose much of their mass is unimaginably long. However, if much smaller black holes ever existed in the Universe, then Hawking's findings would have been catastrophic. A black hole as massive as a cruise ship would disappear in a bright flash in less than a second.