The true nature of dark matter is still very much unclear, so physicists are trying different approaches to work out what the mysterious substance is.
A German-Hungarian team has used the supercomputer JUQUEEN at the German Electron Synchotron (DESY) to establish the allowed range of masses that dark matter can have to explain its effects on the universe. The particle they believe is a good candidate is called the axion, and according to their calculations, published in Nature, it can be up to 10 billion times lighter than the electron.
There is very strong evidence for the existence of dark matter from cosmological studies. The shape, size, and distribution of galaxies all hint towards something we cannot see. In the last estimate, from the European satellite Planck, 85 percent of the matter in the universe is believed to be dark matter.
“Dark matter is an invisible form of matter which until now has only revealed itself through its gravitational effects. What it consists of remains a complete mystery,” explains co-author Dr Andreas Ringwald, from DESY, in a statement. “The adjective ‘dark’ does not simply mean that it does not emit visible light. It does not appear to give off any other wavelengths either – its interaction with photons must be very weak indeed.”
While understanding it on cosmic scales has been hard, the search for actual particles of dark matter has been even more difficult. Dark matter is not predicted by the most accurate theory of particle physics, known as the Standard Model, and researchers like Ringwald are picking at its limitations to find new physics.
He recently suggested an extension of the Standard Model, with the axion as the candidate for dark matter. The axion is needed to fix something in our description of the strong nuclear force, which keeps protons and neutrons stuck to each other in atoms. The strong nuclear force doesn’t appear to have a preference when it comes to matter and antimatter, but since the universe is made of matter, there should be one.
Axions could solve this, but before they can fix our physics, we need to find them, and so far there’s no proof of their existence. Yet, there are some current and planned experiments that are designed to look for them that might find some evidence.
“However, to find this kind of evidence it would be extremely helpful to know what kind of mass we are looking for,” continued Ringwald. “Otherwise the search could take decades, because one would have to scan far too large a range.”
A new supersensitive detector has been recently approved in the US, and it is expected to start hunting dark matter in 2020.