Fermi, NASA’s gamma-ray telescope, has detected antimatter particle beams produced by thunderstorms. This is the first time such a phenomenon has been observed.

Antimatter is the mirror image of matter: particles of antimatter and matter have the same mass but opposite electric charge. For example, a positron is the mirror image of an electron, having a positive electric charge. Antimatter and ‘normal’ matter were created in equal amounts when the Universe was born (though there are more and more doubts considering this equivalence), but for reasons that are still unclear, antimatter completely disappeared, leaving matter we now observe in our Universe. When matter and antimatter come in contact, they annihilate each other giving rise to high-energy photons (gamma-rays).

Scientists already knew about terrestrial gamma ray flashes (TGFs) being produced during thunderstorms, but they found only now that some of the high-energy photons are converted into pairs of electrons and positrons. Fermi, designed to monitor gamma-rays, has detected some of them with energies of 511,000 electron volts, a signal indicating an electron has met a positron. Since its launch in 2008, Fermi has identified 130 TGFs: most of the time, the spacecraft was located above a storm, but in four cases, Fermi was pretty far from storms. However, scientists think the spacecraft could have been magnetically connected to a storm occurring somewhere else, thus explaining the observation.

What is happening inside a thunderstorm and the role of lightning in the production of antimatter are far from being understood, but this new discovery might help physicists better understand the formation and nature of TGFs.