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Almost extreme black holes trying to regrow hair get cold again



  Almost extreme black holes trying to regrow hair get cold again
An artist's perception of a spinning black hole with the accretion flow and a jet. Credit: NASA / JPL-Caltech

Black holes "have no hair": no attributes that can be used to separate them. Extreme black holes (spinning at maximum allowable speed) may have an additional property, permanent hair made from a massless scale field. Almost extreme black holes (like Gargantua, the black hole in the movie "Interstellar") have hair that is a short-lived phenomenon: almost extreme black holes that try to regrow hair will lose it and get cold again.

The black holes in Einstein's theory of relativity can be fully described with only three parameters: their mass, angular momentum and electric charge. Since two black holes sharing these parameters cannot be distinguished, no matter how they were made, black holes are said to "have no hair" ̵

1; they have no additional attributes that can be used to distinguish them from each other.

In the early 1970s, the late Jacob Bekenstein provided evidence that there are no scallops with a set of assumptions about the latter properties. Researcher Lior Burko of Theiss Research said: "Since Bekenstein's evidence, several papers have found examples of scalar hair, and all these examples violate some assumption from Bekenstein. But at least the hair was made by the scalpel itself."

Recently It was shown that black holes charged with maximum possible electrical charge ("extreme black holes") may have an additional property, permanent hair made of a massless scale field, and that this newly found hair can be observed from a long distance. "A massless scalar hair doesn't break any of the assumptions behind Bekenstein's evidence. It was a big surprise to me when this new hair was found by Angelopoulos, Aretakis and Gajic, so I wanted to look at it in more detail. "It is not the scale itself, but a certain integral in a derivative of the scale field that must be calculated on the surface of the black hole, on its event horizon," Burko said.

The new hair can be observed at a great distance by calculating a different amount there. "The measurement at a great distance that Angelopoulos, Aretakis and Gajic found is strictly speaking at infinitely late times," Burko added. "These would be observers who are very distant from the black hole, and who make the measurements for an infinite future. We wanted to see what happens at late but appropriate times, to see the time dependence of the measurement and how it approaches its asymptotic En Another special thing about this new hair is that it only applies to exactly black holes, and we wanted to understand what happens when the black hole is almost extreme, but not exactly extreme. "

Burko and his colleagues Gaurav Khanna of the University of Massachusetts Dartmouth and his former student Subir Sabharwal, currently with the Eastamore Group, showed in a paper just published in Physical Review Research that measurements at a great distance approach the hair value, with the difference between them declining with the reverse time. But then they went beyond the original model used by Angelopoulos, Aretakis and Gajic, and generalized the hair to black holes that rotate at the highest possible rotational speed or just near it.

"In addition to a maximum charge value, there is also a limit to how fast a black hole can spin. Black holes that spin at the maximum allowable speed are therefore also called extreme black holes. We describe both maximum charged and spin maximum black holes with the name extreme black holes, because there are many similarities between the two, the new hair was originally found for a very useful toy model for black holes, especially black holes that are spherically symmetrical and electrically charged, but black holes in reality it is not either. we find out if this hair can also be found to spin black holes, "Burko said. "In the movie" Interstellar ", the black monster hole is almost extreme. We wanted to see if Gargantua has hair."

The team used very intensive numerical simulations to generate their results. The simulations involved the use of dozens of the most advanced Nvidia graphics processing units (GPUs) with over 5,000 cores each, in parallel. "Each of these GPUs can perform as many as 7 trillion calculations per second. But even with such computational capabilities, the simulations took many weeks to complete," Khanna said.

The team showed that for the almost extreme spinning black holes the hair is a transient behavior. At intermediate times, almost extreme black holes appear as extreme black holes, but at late times they behave like ordinary, non-extreme black holes. "Almost extreme black holes can pretend to be extreme only for so long. But eventually their non-extremity becomes obvious," Burko concluded. "Almost extreme black holes trying to regrow hair will lose it and get cold again." The team also discusses the observing functions, for example with gravitational wave observatories such as LIGO / VIRGO or LISA, for smoking gun detection of almost extreme black holes.


Simulations show how massive black holes can be formed by mergers


More information:
Lior M. Burko et al., Transient Scaling Hair for Nearly Extreme Black Holes, Physical Review Research (2019). DOI: 10.1103 / PhysRevResearch.1.033106

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Theiss Research

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Almost extreme black holes trying to regrow hair get cold again (2019, November 15)
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