If you read lots of science news you may have noticed that regular publications have announced the discovery of traces of dark matter. This time the results came from the Italian satellite PAMELA whose acronym means “Payload for Antimatter Matter Exploration and Light nuclei Astrophysics”. Launched in 2006, its task is to measure radiation and identify the regions of space where there are gluts of particles called positrons.

A positron is a particle of antimatter, the antiparticle of the electron. When these two particles meet they annihilate, releasing energy in the form of photons. We owe the theoretical prediction of antimatter to Paul Dirac in 1928, the first positron was discovered in 1932 by Carl David Anderson.

According to the theory where dark matter is destroyed, it leaves a cloud of exotic particles which are part positrons. PAMELA detected that a part of positron higher than expected would be caused by collisions of particles of dark matter.

“Many people believe that this signal comes from the dark matter, because the behavior of positrons is consistent with several theories about dark matter,” says Piergiorgio Picozza, the one who looks after the mission.

“20 years ago scientists predicted that the origin of such a signal could be the dark matter. And now the researchers could see what they had been waiting for,” says astrophysicist Gordon Kane of the University of Michigan. “Chances are that this is the most important discovery in physics in decades”

The positrons are created by interactions between cosmic rays and atoms of gas and clouds of stellar dust. But the amount detected by PAMELA cannot be explained only by these interactions. Apart from the hypothesis of dark matter, spinning pulsars could be the source of production of positrons. To determine other data from PAMELA, the Fermi Gamma-ray Space Telescope will be necessary.

Kane believes that this result could be more than just proof of the existence of dark matter, indeed many clues on the nature of this material would be within our reach. According to him the dark matter is composed of wino, a particular type of neutralino, theoretical particles that would be super-partners of Standard Model particles (electrons, quarks etc.). Within this framework the wino is the super-partner of W boson.

In particle physics, a W′ boson (or W-prime boson) refers to a hypothetical new electrically charged gauge boson that couples to Standard Model fermions via their isospin – Wiki

If dark matter consists of neutralinos, then the dark matter particles would be their own particles of antimatter, because the anti-neutralino is simply a neutralino. Thus when two particles of black matter collide, they are destroyed.

This event occurs very rarely because the dark matter particles are assumed to be infinitely small. Therefore the probability that a shock occurs in the right conditions for that destruction takes place are very low.

This explains that the dark matter could be so abundant in the universe without cancelling each other at any given time. But when these explosions occur, the positrons generated can survive for several million years, which has undoubtedly helped their detection by PAMELA.

Antimatter – harnessing the power of positrons