Amaterasu, the ultra-energetic cosmic ray of unknown origin

2023-11-23 21:00:10

And cosmic ray o extragalactic particle High-energy energy has reached the Earth’s surface from space, but it is not known where it comes from or what exactly it is. Although it may seem like science fiction, this phenomenon has occurred and has been recorded by an international team of researchers led by Professor Toshihiro Fujii from Osaka Metropolitan University (Japan).

The calls ultra high energy cosmic rays (UHECRfor its acronym in English) are exceptionally rare: they can reach more than a exaelectronvoltio (EeV)which is approximately a million times more than what the most powerful particle accelerators manufactured by humans achieve.

Ultra-high-energy cosmic rays like this one are exceptionally rare

Although the low energy ones come mainly from the Sun, it is believed that the origin of the UHECR is related to the most energetic phenomena in the universe, such as black holes, gamma ray bursts, and active galactic nuclei. However, much of the physics and acceleration mechanisms of these particles are still unknown.

Chasing these rays, Fujii and a scientific team from several countries have been carrying out the experimento Telescope Array. This system specialized in cosmic rays consists of 507 stations with scintillation detectorswhich cover an extensive area of ​​700 square kilometers in the Utah desert (USA).

Stations of the Telescope Array experiment before their distribution in the Utah desert (USA). / Institute for Cosmic Ray Research, University of Tokyo

Since the arrival of the most energetic UHECR is so infrequent – ​​it is estimated that less than one particle per century and square kilometer – their detection requires instruments with large collecting areas like this one. Your data is then automatically transferred to servers in Japan and other international collaboration countries.

Second cosmic ray with greater energy

Thus, on May 27, 2021, researchers detected a particle with an energy level of 244 EeVas reported in the magazine Science. “When I first discovered this high-energy cosmic ray, I thought it must be a mistake, since it showed an energy level unprecedented in the past three decades,” Fujii recalls.

This energy level is comparable to the most energetic cosmic ray ever observed, nicknamed the particle Oh-My-God (Oh, my God, in Spanish), which had an estimated energy of 320 EeV when it was detected in 1991. The one that has been found now, with 244 EeV, becomes the second most energetic.

The detected cosmic ray had an estimated energy of 244 EeV. / Osaka Metropolitan University/L-INSIGHT, Kyoto University/Ryuunosuke Takeshige

Given the exceptionally high energy of this particle, the authors note that it should only experience relatively small deflections by foreground magnetic fields, and therefore its entry trajectory from space would be expected to be closely correlated with its source.

However, the results show that your arrival address does not show no galaxy of obvious origin, nor any other known astronomical object that is considered a potential source of UHECR. Instead, it points to a gap in the large-scale structure of the universe, a region in which very few galaxies reside.

Amaterasu, in honor of the goddess of the Sun

The Amaterasu particle is perhaps as mysterious as the Japanese goddess herself: where does it come from? What exactly?

Among the many candidates for naming the particle, Professor Fujii and his colleagues settled on “Amaterasu“, in honor of the sun goddess who, according to Shinto beliefs, played a decisive role in the creation of Japan.

The Amaterasu particle is perhaps as mysterious as the Japanese goddess herself. Where does she come from? What exactly? These questions remain unanswered, although the authors trust that its discovery will pave the way to clarify the origins of cosmic rays and, specifically, this one.

Hypothesis about its mysterious origin

The results could indicate that there is a much larger magnetic deflection than predicted by galactic magnetic field models, that the particle comes from a unidentified source still in the local extragalactic neighborhood, or even that the comprehension Today’s understanding of the high-energy particle physics associated with these rays is incomplete.

“No promising astronomical object has been identified that matches the direction from which the cosmic ray arrived, suggesting possibilities of unknown astronomical phenomena and novel physical origins,” reflects Fujii.

No astronomical object has been identified that matches the direction from which this cosmic ray arrived, suggesting possibilities for unknown astronomical phenomena and novel physical origins.

Toshihiro Fujii (Universidad Metropolitana de Osaka)

The Japanese professor details to SINC: “It can be associated with extremely energetic phenomena, such as gamma ray bursts or active galactic nucleibut another possibility is to think of a exotic setting such as the decay of superheavy dark matter, a new particlefrom unknown physics beyond the standard model.”

In addition to continuing to operate the Telescope Array experiment, the researcher anticipates the next steps: “We need a large number of energetic particles of this type by taking more data and updating our experiment, called TAx4with quadruple sensitivities, and a new generation observatory is also needed to clarify the source” of this energetic and enigmatic cosmic ray.

Rights: Creative Commons.