Dark matter is one of the deepest mysteries of the universe: no one can see it but scientists are sure it exists.
It is the glue that holds the universe together. And now physicists are on the brink of explaining it.
Nasa scientists report that hints of dark matter may have been detected in the Alpha magnetic spectrometer of the ISS. But they cannot conclusively say whether this is the proof they are looking for.
Maybe the answer will be revealed by the Darkside 50 experiment being carried out in a laboratory built under the Gran Sasso mountain in Italy. The lab is covered by 1,400 metres of rock which protects it from cosmic rays.
Cristiano Galbiati, a physicist and the main investigator for the Darkside 50 Experiment, told euronews: “Without dark matter, the universe would not look like it does today. The amount of matter, which is heavy and slow, would have been insufficient without dark matter, to accrete the clusters of galaxies and galaxies, and ultimately to form the universe we know today. So it’s a fundamental, intellectual question to be addressed in order to understand the origins of our system and the evolution of our universe.”
At the Gran Sasso National Laboratory, engineers are preparing a metal sphere, four metres in diameter, with 110 expensive light detecting devices, called photomultiplier tubes. The devices are called scintillators and are able to capture the slightest light emission and turn it into an electronic signal that can be computer analyzed.
Paolo Lombardi, the lead engineer for the Darkside 50 Experiment, said: “This is a very crucial phase. During this period we are installing the photomultiplier tubes, which are optical sensors that will detect the light produced here in the liquid scintillator and convert the light into electrical signals that can be processed by our electronics, and also later on also processed by our data analysis.”
The sphere is assembled inside a cylinder 11 metres wide and 10 metres high, which contains 1,000 tons of water, in order to isolate it even more from cosmic radiation. This sphere will also contain a small capsule filled with 50 kilos of liquid argon, a rare naturally depleted gas that is found deep underground. In its liquid form at -180 Celsius, it can emit light and release electrons when hit by other particles.
Cristiano Galbiati explained: “Argon is the most important part of the project because it’s the target material, what it means: it offers two different means of detecting ionizing radiations, whether it’s from radioactivity, natural radioactivity, or it’s from dark matter.”
Because dark matter is made of “weakly interacting massive particles” and because liquid argon is extremely reactive to particle impacts, if dark matter particles hit one or two argon particles then (because argon can emit light and release electrons when hit by other particles) scientists should be able to record the phenomenon and therefore prove that dark matter exists.
The project is funded by a panel of European, US and Chinese institutions and is expected to run for three years.