Shave and a Haircut

Ariadna Uxue Palomino Ylla, Nagoya University Illustration of a stylized black hole and the rindown pattern emitted when black holes merge. In theory, the structure of a black hole is amazingly simple. It depends on only three things: mass, rotation, and electric charge. All you’ve got to do is compress objects down tightly enough for the black hole to form. Radioactive waste, old tax returns, a massive cloud of helium, you name it. Compress it into a black hole, and all the information and atomic structure become irrelevant. A black hole is just that simple. At least according to the no-hair theorem. Now a new study finds that if real black holes violate the no-hair theorem, it will be seen in the gravitational waves of their mergers.1 The no-hair theorem gets its name from John Wheeler, who contrasted it to the mathematical hairy ball theorem about how to cover a sphere with particular features. Since a black hole’s event horizon has no unique features, Wheeler argued, then “black…