Who needs particle accelerators when you can just use black holes?

As any particle physicist will tell you, if you want to find new particles, you're going to need a lot of energy. This is why huge accelerators are used to propel particles to nearly the speed of light.

But scientists are now suggesting that there may be another way — if we can detect some previously undiscovered particles, called axions, as they accumulate around black holes. An axion is a hypothetical elementary particle with a very low mass. It was postulated by the Peccei-Quinn theory in 1977 to resolve a nasty problem in quantum physics.

Because Einstein said that mass is directly related to energy, it is assumed that very little energy is required to produce these axions. The trick now is for scientists to find them.


And to perform that trick, Daniel Grumiller and Gabriela Mocanu of the Vienna University of Technology have turned their attention to quantum physics, which suggests that every particle can be described as a wave. Because the wavelength corresponds to a particle's energy, heavy particles have small wavelengths, but the low-energy axions would have wavelengths that extend many kilometers.

Research by Grumiller and Mocanu, in conjunction with work done by Asmina Arvanitaki and Sergei Dubovsky, show that axions can circle a black hole, similar to electrons circling the nucleus of an atom. But instead of the electromagnetic force, it is the gravitational force which acts between the axions and the black hole.

There's another very important difference that distinguishes electrons and atoms from axions and black holes: Electrons are fermions and axions are bosons. Fermions can never be in the same state, whereas many bosons can occupy the same quantum state at the same time. This results in the so-called "boson-cloud" which surrounds a black hole. It is supposed that the boson-cloud continuously draws energy from the black hole, causing the number of axions in the cloud to increase.

But the researchers suggest that this cloud is not necessarily stable — which is good news. In a press release, Daniel Grumiller explained: "Just like a loose pile of sand, which can suddenly slide, triggered by one single additional grain of sand, this boson cloud can suddenly collapse." When this collapse happens, a "bose-nova" (no, not Brazilian dance music) could be measured, an event that would make space and time vibrate and emit gravity waves.

So, are Grumiller and Mocanu right? We won't know until at least 2016 – the year a new gravity wave detector will be constructed with enough sensitivity to detect the ones emitted by the bose-novas. In the meantime, we'll just have to stick with particle accelerators.

Image provided by the Vienna University of Technology.