Amaterasu: the new mysterious high-energy particle and its yet unknown origin 

By Mayank Chhaya –

A single, anonymous particle travels extragalactic distances to somehow end up on Earth, gets named out of human sentimentalism and becomes an important discovery that might yet rewrite at least part of particle physics, if not physics itself.

That is the story of Amaterasu, a rare and extremely high-energy particle that fell to Earth on May 27, 2021, and is only not getting peer respectability via the publication of a paper about it in the journal Science. Particle physicists are mystified by Amaterasu. What is causing them to scratch their heads is that the particle, named the sun goddess in Japanese mythology, is coming from an apparently empty region of space.

It is one of the highest-energy cosmic rays ever detected.

“What the heck is going on?” has been the reaction of Professor John Matthews of the University of Utah, one of the co-authors of the paper and a co-spokesperson of Telescope Array.

“What we are talking about here is an extremely energetic particle. It has about as much energy as a fast-pitch baseball or if you held a lead brick, not a ceramic brick, and dropped it down on your toe, you will feel that. That’s a huge amount of energy,” Professor Matthews told Indica News.

The energy he is talking about is 224 exa-electron volts (EeV) that Amaterasu had. One EeV is 10 raised to the 18 electron volts. Compared that with the “Oh My God!” particle, detected in October 1991 by the Fly’s Eye camera in Dugway Proving Ground, Utah with 320 EeV. Matthews said the difference between the two is not huge but significant.

Perhaps the most mystifying aspect of Amaterasu is that physicists do not know where it came from.

“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?” Matthews said.

Not being an astrophysical object or even a product of any immediately recognizable cosmic event, the singular particle has caused a lot of buzz within the scientific community with some saying it has the potential to significantly alter particle physics and hence physics itself.

Asked whether he thought Amaterasu had the potential to alter physics, he said, “We have 30 of these particles above 10 the 20th. If we expand by a factor of four and we collect four or five times this much data if we find those sources, in which case we can study those sources and that will be interesting. Or if we don’t find sources and they are still coming from random places in the sky then now you have got a big mystery. We’ve got to solve that mystery.”

He said, “Is it the decay of dark matter or other remnants out there that we don’t understand or are we somehow sneaking around the microwave background or what? So, I think there is high potential here for something new and exciting to come out once we get a little more data.”

The hunt for cosmic rays has been by telescope Array has been going on since 2008 and the discovery of Amaterasu is expected to heighten interest in this particular realm of particle physics.

Incidentally, the grand shrine of Ise in Honshu, Japan, which is home to Amaterasu, was likely first constructed about 2400 years ago.  The shrine is at the heart of Japanese culture.

[Photo credit: http://www.telescopearray.org]