Don’t tell Einstein, but black holes may have ‘hair’ on them

A confirmed couple nothing on black holes. Couples can grow from the same genetic blueprints, but they can vary in a thousand ways – from temperance to hairstyle. Black holes can have only three properties, according to Albert Einstein’s theory of gravity – mass, spinning and accretion. If these values ​​are the same for any two black holes, it is impossible to distinguish one pair from the other. Black holes have no hair, they say.

“In a classical general relationship, they would be exactly the same,” said Paul Chesler, a theoretical physicist at Harvard University. “You can’t tell the difference.”

But scientists have begun to question whether the “hairless theorem” is completely true. In 2012, a mathematician named Stefanos Aretakis – then at Cambridge University and now at the University of Toronto – suggested that some black holes may be unstable on the horizon of their event. These instability would effectively cause some regions of a black hole horizon to attract stronger than others. That would make black holes different from each other.

However, his equations only showed that this was possible for dark black holes – ones that have the greatest possible value for their mass, spinning or cost. And as far as we know, “these black holes can’t exist, at least just in nature,” Chesler said.

But what if you had a black hole that was pretty extreme, one that went close to those true values ​​but didn’t reach them properly? Such a black hole should be possible, at least in theory. Could he make visible breaks on a hairless theorem?

A paper published at the end of the month shows that it could. Additionally, this hair could be detected by wave observation centers.

“Aretakis basically suggested that some information was left on the horizon,” said Gaurav Khanna, a physicist at the University of Massachusetts and Rhode Island University and one of the coauthors. “Our paper opens up the opportunity to measure this hair.”

In particular, the scientists suggest that the remnants of either the formation of the black hole or later disturbances, such as a case falling into the black hole, could create gravity instability on or near it. on the horizon of a near-extreme black hole event. “We would expect the sign of gravity to be seen to be very different from normal black holes that are not extreme,” Khanna said.

If hair is on black holes – thus keeping some information about the past – this could affect the well-known information paradoxes of black holes sent by the late physicist Stephen Hawking, said Lia Medeiros, an expert at the Institute for Advanced Study in Princeton, New Jersey. These paradoxes dispel the fundamental conflict between general relativity and quantum mechanics, the two great pillars of 20th-century physics. “If you break one of the assumptions [of the information paradox], you may be able to solve their own paradoxes, ”said Medeiros. “One of the assumptions is a hairless theorem.”

The ramifications of that could be widespread. “If we can confirm that the actual space time of the black hole outside the black hole is different from what we expect, I think that will have a big impact on overall relevance,” he said. Medeiros, who coauthored on a paper in October addressed a geometry of black holes observed by prediction.

Perhaps the most interesting feature of this latest paper, however, is that it could provide a way to link ideas about black holes to basic physics. Finding hair on black holes – perhaps the most distant astrophysical labs in the universe – allows us to study ideas such as string theory and quantum gravity in a way that has never been possible before.

“One of the big questions with string theory and quantum gravity is that it is very difficult to confirm these predictions,” Medeiros said. “So if you have anything that’s even proven at a distance, that’s amazing.”

There are major obstacles, however. There are no guarantees that black holes are almost extreme. (The best current models usually feature black holes that are 30 percent off of extreme, Chesler said.) And even if they do, it’s not clear if wave detectors would gravity sensitive enough to see these instability from the hair.