# Another use for black holes

As particle detectors, according to scientists from the Vienna University of Technology.

The basic idea is that it uses hypothetical particles known as axions; by hypothetical, I mean “not proven to exist yet”. They have a very low mass, currently predicted to be about 10^-6 to 1 eV/c^2, which in kg translates as 1.78*10^-42 to 1.78*10^-36 kg – still not low enough to be considered “negligible” in physics! By Einstein’s famous equation E = mc^2, this means it would take a relatively low (pun not intended) amount of energy to produce one, between 10^-6 and 1 eV – between 1.6*10^-25 and 1.6*10^-19 joules.

One of the fundamentals of quantum mechanics is that particles also have wave-like properties; the relationship between a particle’s energy and its wavelength is E = hc/λ, where h is Planck’s constant, c is the speed of light in a vacumn, and λ is the wavelength. from this, you can see that the wavelength is inversely proportional to the energy required, and since this is quite low for an axion, they would have very long wavelengths – if my calculations for those energy ranges are correct, they could range between 1 metre and 800 km.

Because axions are hypothesised to be electrically neutral, they would interact with a black hole through a gravitational attraction; and since they are bosons, they can be in the same state at the same time. The idea is that this creates a cloud of bosons, which can in turn create a nova that generates gravitational waves.

So, using hypothetical particles to detect and potentially prove the existence of hypothetical waves. If it works out, I suspect a Nobel Prize will be going their way!