Black Holes Have 'Hair' That Can be Combed, Study Says

A group of researchers found a kink in the black hole "no hair" theorem.
Chris Young

The "no hair" theorem states that black holes only have three defining properties: mass, angular momentum, and electrical charge — the "hair" is a metaphor that relates to any other properties aside from these three.

A new study from researchers from Theiss Research, the University of Massachusetts Dartmouth, and the University of Rhode Island shows that one special type of black hole does, in fact, violate the principles of the "no hair" theorem.


A kink in the "no hair" theorem

The team focused on extremal black holes: a type of black hole "saturated" with the maximum charge or spin it's possible for them to carry.

They discovered that there is a quantity, or property, that can be constructed from the spacetime curvature at the black hole horizon that is conserved, and measurable from Earth. 

As this quantity depends on the manner in which the black hole is formed, and not on the three classical properties, it violates black hole uniqueness characterized by the "no hair" theorem.

Gravitational hair

The quantity discovered by the research team constitutes "gravitational hair" the research team says. They claim it is potentially measurable by recent and upcoming gravitational wave observatories like LIGO and LISA.

"This new result is surprising because the black hole uniqueness theorems are well established, and in particular their extension to extreme black holes," Dr. Lior Burko of Theiss Research explains in a press release"There has to be an assumption of the theorems that is not satisfied, to explain how the theorems do not apply in this case."

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"The uniqueness theorems assume time independence. But the Aretakis phenomenon explicitly violates time independence along the event horizon. This is the loophole through which the hair can pop out and be combed at a great distance by a gravitational wave observatory," he continues.

Combing for the mysteries of the cosmos

The team made their discovery using intensive numerical simulations. They used dozens of the highest-end Nvidia graphics-processing-units (GPUs) with more than 5,000 cores each, in parallel. 

"Each of these GPUs can perform as many as 7 trillion calculations per second; however, even with such computational capacity the simulations look many weeks to complete," says Gaurav Khanna of the University of Massachusetts Dartmouth.

The new study points towards new ways by which we can measure black holes and, by proxy, learn more about the mysteries of the cosmos.

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