Extreme black holes have hair that can be combed

Black holes are considered to be among the most mysterious objects in the universe. Part of their intrigue stems from the fact that they are, in fact, among the simplest solutions to Einstein’s field equations of general relativity. In fact, black holes can be entirely characterized by only three physical quantities: their mass, their spin, and their charge. Since they do not have additional “hairy” attributes to distinguish them, black holes are said to be “hairless” – black holes of the same mass, rotation and charge are exactly the same as each other.

Dr Lior Burko of Theiss Research in collaboration with Professor Gaurav Khanna of the University of Massachusetts at Dartmouth and the University of Rhode Island alongside his former student, Dr Subir Sabharwal, discovered that a special type of black hole violates the uniqueness of the black hole, the so-called “no hair” theorem. Specifically, the team studied extreme black holes – holes that are “saturated” with the maximum load or spin they can carry. They discovered that there is a quantity that can be constructed from the curvature of space-time on the horizon of the black hole that is conserved and measurable by a distant observer. Since this amount depends on how the black hole was formed, and not just the three classic attributes, it violates the uniqueness of the black hole.

This quantity constitutes “gravitational hair” and potentially measurable by recent and future gravitational wave observatories such as LIGO and LISA. The structure of this new hair follows the development of a similar quantity found by Angelopoulos, Aretakis and Gajic in the context of a simpler “toy” model using a scalar field and spherical black holes, and extends it to perturbations gravitational rotating ones.

“This new result is surprising,” said Burko, “because black hole uniqueness theorems are well established, and in particular their extension to extreme black holes. There must be an assumption of the theorems that is not satisfied, to explain how the theorems do not apply in this case. “Indeed, the team followed previous work by Aretakis, which found that even though the external disturbances of extreme black holes decay as they do. also do for regular black holes, along the event horizon, some disturbance fields evolve over time indefinitely. “Uniqueness theorems assume the independence of time. But the Aretakis phenomenon explicitly violates the independence of time along the event horizon. It is the loophole through which hair can come out and be combed large. distance by a gravitational wave observatory, ”Burko said. Unlike other work that has found hair in the scalarization of black holes, Burko noted that “in this work we were working with Einstein’s theory under vacuum, with no additional dynamic fields which modify the theory and which may violate the principle of strong equivalence. “

The team used very intensive numerical simulations to generate their results. The simulations involved using dozens of high-end Nvidia graphics processing units (GPUs) with more than 5,000 cores each, in parallel. “Each of these GPUs can perform up to 7 trillion calculations per second; however, even with such a computing capacity, the simulations seem to end for several weeks,” Khanna said.

Provided by Theiss Research