Scientists detected the second highest-energy cosmic ray ever observed

Researchers have discovered one of the most powerful particles ever to strike the Earth. Cosmic rays are high-energy particles that originate in space from sources such as the sun, but this recent discovery is more powerful than anything described by known sources in our galaxy or even beyond. The particle possessed an energy of 2.4 x 1020eV, which is millions of times more than the energy of particles produced in a particle collider.

The detection was made in May 2021 using the Telescope Array, which is located near Salt Lake City in Utah. It includes 500 surface detectors dispersed across 300 square kilometers of desert to detect cosmic ray incidents. It has identified over 30 ultra-high-energy cosmic rays since 2007, but this is the most intense one yet.

It is the second most powerful cosmic ray ever observed, trailing only the Oh-My-God particle discovered in 1991. The peculiarity of these occurrences is that the researchers have no understanding where they are originating from.

“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,” said one of the researchers, John Matthews of the University of Utah, in a statement. “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?”

Even a supernova would not be powerful enough to make particles like this, and the particle appeared to come from the Local Void, an empty stretch of space on the edge of the Milky Way.

“These events seem like they’re coming from completely different places in the sky. It’s not like there’s one mysterious source,” said another of the researchers, John Belz. “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 researchers intend to employ new capabilities, such as an expansion to the Telescope Array, to identify and investigate more of these events, as well as learn more about their likely causes. "It's a real mystery," Belz said.