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Astronomers detect mysterious high-energy particle falling to Earth from space

The Amaterasu particle is one of the highest-energy cosmic rays ever detected.

Nilima Marshall
Friday 24 November 2023 16:57 GMT
An artist’s illustration of the Amaterasu particle (Osaka Metropolitan University/Kyoto University/Ryuunosuke Takeshige)
An artist’s illustration of the Amaterasu particle (Osaka Metropolitan University/Kyoto University/Ryuunosuke Takeshige)

Astronomers have detected a rare and extremely high-energy particle falling to Earth from space.

Named Amaterasu, after the sun goddess in Japanese mythology, it is one of the highest-energy cosmic rays ever detected, according to the scientists.

Its origins remain unknown but experts believe only the most powerful of celestial events – much bigger than a star explosion – can produce them.

John Matthews, a research professor at University of Utah’s department of physics and astronomy in the US, said: “Things that people think of as energetic, like supernova, are nowhere near energetic enough for this.

“You need huge amounts of energy, really high magnetic fields to confine the particle while it gets accelerated.”

The Amaterasu particle has an energy exceeding 240 exa-electron volts (EeV), which is millions of times more than what particles achieve at the Large Hadron Collider, the most powerful accelerator ever built.

It comes only second to the Oh-My-God particle, another ultra-high-energy cosmic ray which was detected in 1991, possessing 320 EeV of energy.

Toshihiro Fujii, an associate professor at Osaka Metropolitan University in Japan, said: “When I first discovered this ultra-high-energy cosmic ray, I thought there must have been a mistake, as it showed an energy level unprecedented in the last three decades.”

When ultra-high-energy cosmic rays hit Earth’s atmosphere, they initiate a cascade of secondary particles and electromagnetic radiation in what is known as an extensive air shower.

Charged particles in the air shower produce a type of electromagnetic radiation that can be detected by specialised instruments.

One such instrument is the Telescope Array observatory in Utah, US, which found the Amaterasu particle.

This mysterious event appeared to emerge from the Local Void, an empty area of space bordering the Milky Way galaxy.

The experts suggest this could indicate a much larger magnetic deflection than predicted, an unidentified source in the Local Void, or an incomplete understanding of high-energy particle physics.

Prof Matthews said: “The particles are so high energy, they shouldn’t be affected by galactic and extra-galactic magnetic fields.

“You should be able to point to where they come from in the sky.

“But in the case of the Oh-My-God particle and this new particle, you trace its trajectory to its source and there’s nothing high energy enough to have produced it.

“That’s the mystery of this – what the heck is going on?”

When I first discovered this ultra-high-energy cosmic ray, I thought there must have been a mistake, as it showed an energy level unprecedented in the last three decades

Prof Toshihiro Fujii

They hope that the Amaterasu particle will pave the way for further investigations that could help shed light on ultra high-energy cosmic rays and where the come from.

John Belz, a professor at University of Utah’s department of physics and astronomy, said: “These events seem like they’re coming from completely different places in the sky.

“It’s not like there’s one mysterious source.

“It could be defects in the structure of spacetime, colliding cosmic strings.

“I mean, I’m just spit-balling crazy ideas that people are coming up with because there’s not a conventional explanation.”

The findings are published in the journal Science.

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