Study reveals how axion emission could alter black hole evaporation
The team also found that, unlike photons, electrons, or other known particles, axion emission could cause a black hole to spin faster.
Diagram showing the evaporation of a primordial black hole as its rotational speed is increased by the emission of axions.
© DR
Research conducted by the Faculty of Sciences and Technology of the University of Coimbra (FCTUC), in collaboration with the University of Oxford (UK), shows that the emission of axions through the Hawking effect could significantly alter the evaporation process of a black hole. The research findings have been published in the journal Physical Review Letters.
Axions are hypothetical ultra-light particles that are electrically neutral and weakly interactive, making them incredibly difficult to detect. String theory, first proposed in the 1970s to explain some features of the strong force, predicts that there are hundreds or even thousands of different types of axions with different masses.
The article also highlights that, unlike the emission of photons, electrons, or other known particles, the emission of axions could cause a black hole to spin faster. "We have computationally simulated the evaporation of a black hole from the beginning of the universe to the present day, taking into account the emission of known particles and a random number of axions," explains João Rosa, a lecturer at the Department of Physics of FCTUC and a researcher at the Centre for Physics of the University of Coimbra (CFisUC).
"We're very excited about the results we've obtained because we realised that we could determine whether or not there are hundreds of light axions, as predicted by string theory, simply by measuring how fast the primordial black holes spin," reveals the physicist. He adds that black holes of different masses, at different stages of evaporation, will exhibit different spinning rates, depending only on how many axion species are found in nature.
The study also shows that rotation has a measurable effect on the Hawking radiation spectrum emitted by a black hole, i.e., the variation of radiation intensity with energy. "If we find one or more of these black holes, we could use them as a real particle physics laboratory. Based on the available astrophysical data, these black holes should be relatively rare, although it is possible that one or more will pass close enough to the Solar System in the coming years for us to observe them," says the physicist.
Finally, the study concludes that the evaporation of primordial black holes could have spread the universe with axions travelling at speeds very close to the speed of light, providing another "signature" of string theory that scientists could seek to detect.
The scientific article “Evaporating primordial black holes, the string axiverse, and hot dark radiation” is available here