Black Holes with Hair: Dirty Instead of Clean

Black holes may not be as smooth as scientists once believed. One theory seems to indicate that these black holes may have "hair." The findings could lead to a new understanding of black holes, which could impact future models.

In 1963, Roy Kerr proposed a "clean" black hole model, which is the current theoretical paradigm. According to this model, black holes are defined by only two quantities. There's the mass of the black hole and the angular momentum, which is a black hole rotation velocity. When a high mass star collapses at the end of its life, its memory is lost forever. All that's left is a black hole with all distinctive features; almost all black holes, mass and angular momentum aside, look almost the same.

Yet apparently that may not be the case. There could be distinctive features that a black hole possesses that could make them look differently.

"Black holes, according to our calculations, may have hair," said Thomas Sotiriou, one of the researchers, in a news release. "Although Kerr's 'bald' model is consistent with General Relativity, it might not be consistent with some well-known extensions of Einstein's theory, called tensor-scalar theories. This is why we have carried out a series of new calculations that enabled us to focus on the matter that normally surrounds realistic black holes, those observed by astrophysicists. This matter forces the pure and simple black hole hypothesized by Kerr to develop a new 'charge' (the hair, as we call it) which anchors it to the surrounding matter, and probably to the entire Universe."

That said, this theory needs to actually be tested. Currently, researchers suggest that it could be confirmed through observations carried out with interferometers, which are instruments capable recording gravitational waves.

"According to our calculations, the growth of the black hole's hair is accompanied by the emission of distinctive gravitational waves," said Sotiriou in a news release. "In the future, the recordings by the instrument may challenge Kerr's model and broaden our knowledge of the origins of gravity."

So do black holes have hair? That's a good question. Scientists will have to continue their research in order to confirm or deny the hypothesis. For now, though, the research reveals a possibility that should be investigated further.