The universe seems to be full of dark matter, yet no one knows what it’s made of. The best guess is that invisible particles called weakly interacting massive particles, or WIMPs, contribute all this missing mass. And that idea matches the latest data generated by the Alpha Magnetic Spectrometer, or AMS, experiment. This instrument lives on the International Space Station, and it may be seeing direct signs of dark matter. The study is in the journal Physical Review Letters. [M. Aguilar et al, (AMS Collaboration), Electron and Positron Fluxes in Primary Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the International Space Station]
The AMS catches charged particles flying through space. Its new results show more positrons than expected. Positrons are the antimatter counterparts to electrons. Normal astrophysical processes create some positrons, but not as many as AMS registered. One possible explanation is that these excess positrons are a by-product of dark-matter interactions. That is, they’re being created by the elusive WIMPs.
When two WIMPs collide, they can annihilate each other, giving rise to other particles—such as positrons. The data from AMS so far match these predictions.
The positrons might also have a more mundane source, such as the spinning stars called pulsars. Time will tell if the space-based AMS has indeed seen the first sign of what makes up dark matter—or if we’re still stuck in the dark.