Astrophysicists are aware that the Earth is frequently “hit” by cosmic rays from the depths of the universe. Out of all that matter, there is a group of particles, called positrons , which are, so to speak, the opposite version of electrons.
Positrons make up a small percentage of the cosmic rays that reach Earth, and no one is completely sure where or how they are made.
The most widespread hypothesis among astronomers is that the Earth is plagued with these “antielectrons” due to a type of massive star, the pulsar. But there is one fact that intrigues scientists: There are more of these particles than there should be.
A study concludes that the amount of positrons reaching Earth is much higher than it should be, and its origin cannot be due to pulsars.
Pulsars are neutron stars that channel charged particles into a beam with their super strong magnetic fields. When they spin, they act like a giant particle accelerator, breaking up particles and producing new matter from energy.
In this process, particles emerge, such as electrons, and their antimatter “twins”, positrons.
In 2008 a probe in Earth orbit called PAMELA detected more high-energy positrons arriving in our cosmic neighborhood of the cosmos than we expected.
Now, a large team of international researchers has analyzed recent measurements from the High-Altitude Water Cherenkov Observatory (HAWC) in Mexico to test the hypothesis that excess antimatter could have been hit by pulsars.
While the researchers found that pulsars were responsible for some of the extra-high-energy positrons, the number was still too small to explain all of them.
“Detectors at the HAWC observatory record gamma radiation emitted by a certain population of electrons produced by pulsars and accelerated by them to enormous energies,” according to physicist Francisco Salesa Greus of the Polish Academy of Sciences in Krakow.
However, there are not enough electrons that pulsars interact with to produce that many positrons. Therefore, the positrons must have come from some other source, still unknown.
Dark matter, a possible explanation
“Since the participation of nearby pulsars in the generation of high-energy positrons that reach us is so modest, other explanations are increasingly likely,” according to Sabrina Casanova, a researcher at the Institute of Nuclear Physics of the Polish Academy of Sciences.
One of these explanations may be that these positrons come from dark matter. A tempting idea, given that it would provide us with a way to begin to understand dark matter, which makes up a quarter of the mass of the Universe .
Dark matter and the origin of ultrafast positrons remains a mystery.
For now, we can only wait and keep watching.
Reference: Extended gamma-ray sources around pulsars constrain the origin of the positron flux at Earth
AU Abeysekara, A. Albert. Science 17 Nov 2017: Vol. 358, Issue 6365, pp. 911-914. DOI: 10.1126 / science.aan4880
