Over the years, scientists have been able to reveal the existence of quite interesting particles, pushing the entire field of physics forward with each discovery. There’s the “god particle” for example, also known as the Higgs boson, which gives all other particles their mass. There’s also the so-called “Oh my God!” A particle, a cosmic ray of unimaginable energy.
But now we have a new particle in town. It’s called the “Sun Goddess” particle, and it’s appropriately extraordinary.
This particle has an energy level a million times greater than what can be generated by even the most powerful human particle accelerators; It appears to have fallen to the ground in a shower of other, less energetic particles. Like “Oh my God!” Particles, these bits come from distant regions of space and are known as Cosmic rays. The particle was named “Amaterasu” after Amaterasu Omikami, the goddess of the sun and the universe in Japanese mythology, whose name means “bright in the sky.”
Just as its legendary name is shrouded in mystery, so too is the Amaterasu particle. Its discoverers, including Osaka Metropolitan University researcher Toshihiro Fujii, do not know where the particle came from or what it actually is. They were also still unsure of what kind of violent and powerful process could give rise to something as vital as Amaterasu.
“This is the most energetic charged particle ever detected by the Telescope Array experiment,” Fujii told Space.com.
The hope is that just as Amaterasu is credited with creating Japan in the Shinto tradition, Amaterasu’s particles could help create an entirely new branch of high-energy astrophysics.
Related: High-energy cosmic rays may originate within the Milky Way
“Oh, my God!” particle
High-energy cosmic rays are initially extremely rare, but Fujii said the Amaterasu particle has an energy level not seen in 30 years of cosmic ray discoveries.
In fact, when researchers discovered Amaterasu using the Telescope Array experiment — which involves 507 detectors spread across 270 square miles (699 square kilometers) of high desert in Millard County, Utah — they initially thought the discovery must be something wrong.
“I thought it would be my fault or a glitch, and after checking the details of the event, I was excited to find that it wasn’t a bug,” Fujii said.
The Amaterasu particle was first observed by the Telescope Array experiment on May 27, 2021, and exhibits an energy of 224 exaelectronvolts (EeV). For the competition, one EeV is equivalent to 10¹⁸ electron volts. This puts Amaterasu at an energy level comparable to the most energetic cosmic rays ever detected – yes, that’s an “Oh my!” The particle was discovered in October 1991 by the Fly’s Eye camera at Dugway Proving Ground, Utah. The latter had an energy of 320 MeV.
“The Amaterasu particle should be an important messenger from the universe about highly energetic phenomena, but we need to solve the origin of this mysterious particle,” Fujii explained.
There is no astrophysical object, or any cosmic event for that matter, in the direction from which the Sun Goddess particle appears to have come. For this reason, scientists are not entirely sure what led to its creation. However, while the origins of the Amaterasu particle may currently be unknown, Fujii has some investigative avenues to pursue. More importantly, some of these ideas could extend beyond the Standard Model of particle physics, our best blueprint for the universe’s zoo and how each of those particles interact with each other.
“One possibility is that the particle was accelerated by very energetic phenomena, such as a gamma-ray burst or a jet from a supermassive black hole feeding into the center of active galactic nuclei,” Fujii said. “Another possibility is creation in an exotic scenario such as the decay of extremely heavy dark matter – a new particle, from unknown physics outside the Standard Model.”
The team has been tracking cosmic rays using the Telescope Array Experiment in Utah since 2008, and will now continue to do so with the four-fold improved sensitivity of the newly upgraded project. They also expect other next-generation observatories to engage in cosmic ray work to help scientists embark on a more detailed investigation of the Amaterasu particle.
“Personally, I am excited to have found a new puzzle for science to solve,” Fujii concluded.
The team’s research will be published on November 24 in the journal Science.
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