The mysterious dark matter has not yet been directly detected. It is therefore not clear whether it actually exists in the assumed form. However, measurements at the nuclear research center CERN show a way to indirectly track down dark matter.
The flow of antimatter particles from the depths of the galaxy to Earth can provide information about the previously mysterious dark matter. In order to be able to better interpret this stream of particles, a research team at the nuclear research center CERN near Geneva carried out measurements on antimatter. With the help of these experiments, the physicists then simulated the permeability of the galaxy for antihelium-3 nuclei. The team writes in the journal “Nature Physics” that indirect conclusions about dark matter can be drawn from the number and energy of such nuclei.
The research results should help in the interpretation of specific measurements: The second alpha magnetic spectrometer (AMS-02) on the International Space Station (ISS) measures the composition of cosmic rays. In addition, the GAPS balloon experiment over the Arctic will examine cosmic rays for antihelium-3 nuclei from 2025.
So far, dark matter is only a suspected form of matter, it has not yet been directly proven. Physics can use dark matter to explain the movement of galaxies and stars within galaxies. The researchers want to use antimatter to track down this previously mysterious form of matter.
Antimatter has very similar properties to matter, except that the particles have a different electrical charge. While a proton, which is part of the atomic nucleus, carries a positive charge, the antiproton has a negative charge. When matter and antimatter particles collide, they usually annihilate into gamma rays – i.e. high-energy electromagnetic radiation – and disappear.
It is generally assumed that antimatter – such as antihelium-3 nuclei – is formed either when two particles of dark matter collide with each other or when cosmic rays hit matter with high energy. The researchers in the Alice Collaboration at CERN have now produced antihelium-3 nuclei by allowing protons – the main component of cosmic rays – and lead atoms to collide at very high speeds in the particle accelerator LHC (Large Hadron Collider). In doing so, they determined the probability of the resulting antihelium-3 nuclei interacting with matter or radiation.
On the basis of this data, the scientists then simulated the flight of antihelium-3 nuclei through the galaxy. For antihelium-3 nuclei, which result from the collision of dark matter particles, they came to a permeability of about 50 percent: From the areas of origin tens of thousands of light years away, around half of these antihelium-3 nuclei flying towards Earth come close to Earth on.
For the higher-energy antihelium-3 nuclei, which are formed from the interaction between cosmic rays and matter, the research team found a permeability of 25 to 90 percent, depending on the energy content of the nuclei. From these calculations, it would be possible to distinguish between the two sources of antihelium-3 nuclei in terrestrial measurements – dark matter or cosmic rays hitting known matter – and trace them back to possible regions of origin.
“Our results show for the first time, based on a direct absorption measurement, that antihelium-3 nuclei coming from the center of our galaxy can reach near-Earth locations,” Alice physics coordinator Andrea Dainese is quoted as saying in a CERN release. It should be remembered that the interstellar space, i.e. the universe between the star systems, has only a very low matter density, namely about one atom per cubic centimeter. For comparison: a diamond has a density of 180,000 billion billion (1.8 times 10 to the power of 23) atoms per cubic centimeter.
