Astrophysicists find no 'hair' on black holes

Summary

In 2012, physicists showed that this paradox is tightly linked to the nature of the event horizon. They’d known since the 1970s that black holes emit radiation, and that this radiation probably somehow carries the scrambled information about the stuff that fell into the hole. Now they imagined what would happen if an astronaut who was about to cross the horizon of an ancient black hole communicated with someone far away — an observer who had gathered the radiation emitted by the black hole over its lifetime. The result of the thought experiment was puzzling: The astronaut and the faraway observer would end up with two copies of the same information, one recovered over the black hole’s long lifetime and the other from close by. The extra copy is a problem, again spoiling the careful accounting of probabilities that quantum mechanics relies on. Some physicists concluded that something strange must happen just outside the horizon to disrupt the astronaut’s information gathering. Short Hair, Long Hair Attempts to address the information paradox usually add extra detail outside the event horizon, referred to as quantum hair. The researchers who came up with the thought experiment about the astronauts in 2012 suggested that a shell of extremely high-energy particles called a firewall might lie just outside the horizon, breaking the connection between the two observers. Alternatively, the physicist Samir Mathur argues that black holes don’t have a horizon at all. Instead, he says that they are “fuzzballs” — each one a quantum combination, or superposition, of many different configurations of space-time, making the black hole’s edges fuzzy. Other ideas include “gravastars” that resemble black holes but are surrounded by shells of exotic matter, and so-called regular black holes — reimagined versions of the objects that lack the infinitely dense points in their centers known as singularities. This zoo of proposals all introduce new effects outside the horizon that should cha...