Exploding black holes could expose hidden dimensions

Ker Than
05 February 2008



Cosmic flares shot from exploding black holes could provide long-sought proof of extra spatial dimensions, new calculations suggest.

Theoretical physicist Stephen Hawking predicted that black holes evaporate through a quantum process known as "Hawking evaporation" and can explode in brief bursts of energy before vanishing completely.

Only mini-black holes roughly as massive as an asteroid or smaller would be able to evaporate completely within the lifetime of the universe. And such tiny black holes may have been created in large numbers within 1 second of the big bang, as elementary particles clumped together at extreme energies.

Now, researchers led by Michael Kavic of Virginia Tech in Blacksburg, US, say the evaporation of such "primordial" black holes could emit detectable radiation – if the universe contains additional dimensions beyond the familiar three of space and one of time. Such extra dimensions are predicted in some theories that try to unify gravity and quantum mechanics, such as string theory.

In the presence of extra dimensions, black holes would wrap around these extra dimensions to form "black strings." "You can envision this as a rubber band wrapped around a fire hose," Kavic told New Scientist. "As the black hole evaporates, it eventually becomes too small to wrap the extra dimension."

Unique pulse

He and colleagues predict that when a black string snaps, it will expose the extra dimension by creating a pulse of radiation with a unique electromagnetic signature. "We would know them if we saw them," Kavic told New Scientist.

By analysing the frequency of the pulse, scientists could calculate the size of the extra dimension, which could lend insight into which cosmological model best describes the universe. "The size of the black string is directly related to the size of the extra dimension at the time of the explosion," Kavic says.

The team says the light pulses could be detected by radio telescopes capable of scanning the entire sky in one sweep, such as Virginia Tech's Eight-meter-wavelength Transient Array.

"Traditional radio telescopes only focus on a very small part of the sky at any one time," Kavic said. "This means that they could easily have missed these kinds of pulses."

Good timing

The new test comes at an opportune time, says Charles Keeton, an astronomer at Rutgers University in New Jersey, US: "Our ability to observe exploding black holes is limited only by the sensitivity of our radio telescopes, and that is getting better."

But while much theoretical work has been done on primordial black holes and extra dimensions, their existence remains unproven.

"The big question is whether such black holes are produced in the first place," says Avi Loeb of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, US. "In principle, it's possible to make such black holes, but in the standard model of cosmology, it is not natural."

"There are a lot of layers here of nonstandard assumptions," Loeb told New Scientist. "If nothing could be observed in this context, then it would not surprise me."

While definitely a gamble, the payoffs from such a search would be enormous, Kavic argues. The successful detection of the kind of black hole explosion the team predicts would confirm not only the existence of extra dimensions, but also of primordial black holes and Hawking evaporation.

"All three of these are quantum gravitational phenomena [and] would drastically alter our view of space-time and the fundamental nature of our universe," Kavic says.

The team has submitted the study to Physical Review Letters.

Source: http://space.newscientist.com