Scientists have found evidence of antimatter in cosmic rays that might suggest the existence of a class of never-before-observed particles. These particles could make up dark matter – the strange substance that accounts for 85 per cent of the Universe's mass but has never been observed directly.
A new study suggests that particles of antihelium (the antimatter version of helium) detected by equipment on the International Space Station may have been created by a new class of Weakly Interacting Massive Particles, or WIMPs. It's believed that dark matter could be made up of WIMPs.
"WIMPs are particles that have been theorised but never observed, and they could be the ideal candidate for dark matter," said lead author Pedro De la Torre Luque, one the physicists behind the study at the Institute of Theoretical Physics in Madrid. "Of the numerous best-proposed models, most have been ruled out today and only a few of them survive."
Nuclei of antihelium observed in cosmic ray surveys carried out by the space station's Alpha Magnetic Spectrometer (AMS-02) could have been created when two WIMPs collide and annihilate. This could produce matter, antimatter and energy, the researchers say.
Antimatter can be thought of as a ‘mirror image’ of normal matter. It has the same mass but its qualities, such as electric charge, are opposite.
Researchers believe that some antimatter was formed during the Big Bang, but more is constantly created by certain cosmic events, even though it is very difficult to observe.
"If you see the production of antiparticles in the interstellar medium, where you expect very little, it means something unusual is happening. That's why the observation of antihelium was so exciting," said De la Torre Luque.
"Theoretical predictions suggested that, even though cosmic rays can produce antiparticles through interactions with gas in the interstellar medium, the amount of antinuclei, especially antihelium, should be extremely low,"
"We expected to detect one antihelium event every few tens of years, but the around ten antihelium events observed by AMS-02 are many orders of magnitude higher than the predictions based on standard cosmic-ray interactions. That's why these antinuclei are a plausible clue to WIMP annihilation."
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