Ever wonder what happens to a black hole at the end of its life, if such a thing can be said for a black hole? Does it sit there unchanging, or perhaps have a different end state? Physicist Steven Hawking put forth the idea that the fate of a black hole is essentially the same as that of a drop of water on a countertop: in both cases over time they just evaporate away.
Water evaporates because the molecules near to the surface are warmer than the other molecules on average. These warmer molecules also have higher energy and thus are able to leave the drop and escape into the air. Similarly, a black hole would also need to have matter (or equivalently light) escape.
The conundrum facing physicists is that black holes are famous for not allowing any matter or light that enters its surface to be freed back into space. This is why they are called “black,” afterall. Does this mean the story is over, and black holes cannot evaporate?
A team of researchers recently started investigating this problem using a bathtub of swirling water (to simulate the spinning black hole), and little pieces of paper confetti thrown into the water. They are finding that a ray of light bouncing off of the swirling tide pool of water (or equivalently off of the swirling tide pool of matter) can gain additional energy along the way. This process of shoplifting energy from the black hole is called “superradiance.”
In this situation it is the swirling nature of the black hole that assists with the superradiance process. Over a very very long period of time, these little bits of light stolen in miniscule amounts from the black hole add up to equal the total mass of the black hole.
Superradiance processes such as this one eventually empty the black hole entirely of its contents, until the black hole just disappears from the universe.
In this way, what appears to be a grammar school science fair project is turning into some of the best evidence yet that it is possible for energy and matter to leave a black hole. And it is all made possible by the properties of matter “going down the drain.”