BLACK holes do not have a reputation for giving up their secrets, but they could prove instrumental in uncovering exotic particles that are difficult to detect on Earth.
If conditions are right, a particle scattering from a spinning black hole will trigger the formation of a new particle. This also causes the black hole to lose a little angular momentum, an effect known as 鈥渟uperradiance鈥�.
Asimina Arvanitaki of the University of California, Berkeley, and colleagues say this loss of angular momentum could be exploited in the hunt for hypothetical particles called axions, which could constitute the invisible cold dark matter that appears to hold galaxies together.
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According to the team鈥檚 calculations, a single axion emitted by a spinning black hole could trigger the emission of more axions to form a cloud orbiting the black hole. The creation of each axion would draw rotational energy away from the hole. The cloud eventually gets so dense that some of it will collapse and fall into the hole while the rest is flung outwards and may escape the black hole鈥檚 gravitational field altogether.
The entire process would then start anew, with the black hole spinning more slowly than before. 鈥淚t basically continues until the black hole loses all of its spin,鈥� says co-author Sergei Dubovsky of Stanford University in California. The efficiency of the effect depends on the mass of a black hole, so the signature of the axions would therefore be a lack of fast-spinning black holes of a certain mass (). The particles could also reveal their presence in bursts of gravitational waves radiated when their clouds are torn apart around the black hole or when particles move from one axion cloud to another.
鈥淭he emission of axions basically continues until the black hole loses all of its spin鈥�
鈥淚t鈥檚 surprising you can learn about such a small, light particle by looking at a big, complicated, macroscopic object in the sky,鈥� says of Harvard University.
Axion particles will be difficult to create in the laboratory. 鈥淲e鈥檙e running into a roadblock where we can鈥檛 build accelerators much bigger than the Large Hadron Collider,鈥� says Strominger. 鈥淭his kind of observation is a very novel way of connecting the large and the small.鈥�
