Home News Science The Earth is hit by particles of antimatter of unknown origin

The Earth is hit by particles of antimatter of unknown origin

An international team of researchers concludes that it is impossible for pulsars to be solely responsible for the positrons that hit the Earth.

This artist’s impression shows the magnetar in the very rich and young star cluster Westerlund 1. This remarkable cluster contains hundreds of very massive stars, some shining with a brilliance of almost one million suns. European astronomers have for the first time demonstrated that this magnetar — an unusual type of neutron star with an extremely strong magnetic field — was formed from a star with at least 40 times as much mass as the Sun. The result presents great challenges to current theories of how stars evolve, as a star as massive as this was expected to become a black hole, not a magnetar.

Astrophysicists are aware that the Earth is often “hit” by cosmic rays from the depths of the universe. Among 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 nobody is completely sure where or how they are made.

The most widespread hypothesis among astronomers is that the Earth is plagued by 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 they should.

One study concludes that the amount of positrons that reach 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 rotate, they act as a giant particle accelerator, breaking particles and producing new matter from energy.

In this process, particles arise, such as electrons, and their “twins” of antimatter, positrons.

In 2008 a probe in the orbit of the Earth called PAMELA detected more high energy positrons reaching 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 struck by pulsars.

While the researchers discovered that pulsars were responsible for some of the extra high energy positrons, the figure was still too small to explain them all.

“The detectors at the HAWC observatory record the 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 with which pulsars interact to produce such positrons. Therefore, positrons must come from some other source, still unknown.

Dark matter, a possible explanation

“Given that 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 the researcher at the Institute of Nuclear Physics of the Polish Academy of Sciences, Sabrina Casanova.

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 constitutes 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.


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