The neighbourhood of space where the International Space Station (ISS) resides seems to be littered with unexpected quantities of antimatter 鈥� and the culprit may be mysterious dark matter particles.
鈥淲e were very surprised. This is weird, and the mechanism that is producing this amount of antimatter should be something exotic,鈥� says at the Autonomous University of Madrid in Spain. He and his colleagues found hints of this antimatter by analysing 15 years of data from the Alpha Magnetic Spectrometer (AMS-02) detector on the ISS.
It isn鈥檛 unusual to find some antimatter particles, which have the opposite electric charge to their matter counterparts, in space. That is because space is filled with energetic particles, known as cosmic rays, that create antimatter when they collide with other particles.
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However, De La Torre Luque says that AMS-02, which records cosmic ray signals, detected surprisingly large quantities of antimatter, including some unusual forms such as heavy antimatter versions of helium nuclei. This would suggest an origin beyond cosmic ray collisions.
This was so unexpected that the instrument had not been designed with the expectation of finding such a signal, although it was technically capable of doing so.
To make sense of the unusually abundant and sometimes heavy antimatter, the team turned to computer simulations of similarly unusual space-borne processes that can produce antimatter, including those involving dark matter. Dark matter is thought to make up about 27 per cent of the universe, but we know very little about its properties.
The researchers focused on hypothetical particles known as weakly interacting massive particles (WIMPs), which were conjectured in the 1980s to make up dark matter, but have never been spotted. They found that when WIMPs, should they exist, collide, they could theoretically produce antimatter particles in amounts that would match AMS-02鈥檚 observations 鈥� but even that couldn鈥檛 explain why the detector found so much antihelium.
鈥淣ormal WIMPs cannot explain the amount of antihelium detected. So, it should be something much more exotic. It could [still] be dark matter, but with some additional ingredients,鈥� says De La Torre Luque. In this way, his team鈥檚 analysis underscores the need for more work on theories of particles that could make up dark matter.
New models 鈥� of how particles like WIMPs could interact in novel ways, and of how they may be distributed across the universe and not just near the ISS 鈥� could help clarify whether AMS-02 has detected the aftermath of their collisions.
at the National Institute of Nuclear Physics in Italy says that it should be possible to detect signatures of dark matter particle collisions with devices like AMS-02, yet uncertainties in theoretical models and detector readings still lead to ambiguity when it comes to interpretation of the results. He says the researchers used a state-of-the-art model, but there is simply a lot that we don鈥檛 know about modelling and simulating dark matter.
The researchers hope to add detail to their models and pin down an origin story for all this antimatter soon. AMS-02 will continue collecting data until the ISS is decommissioned in 2030, and another team of researchers will soon launch a that will also carry a detector for antiparticles.
鈥淲e are just opening the door to understanding cosmic antinuclei and are at the beginning of a new era. More measurements in space and on the ground are crucial for pushing forward,鈥� says at the University of Hawai鈥檌 at Manoa.
Journal of Cosmology and Astroparticle Physics
