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Space scientists trying to understand the enigmatic origin of powerful cosmic rays have detected a very high-energy particle they believe traveled to Earth outside the Milky Way galaxy.
The energy of these subatomic particles, which are invisible to the naked eye, is equivalent to dropping a brick on your toe from waist height, according to the authors of new research published Thursday in the journal Science. It rivals the single most energetic cosmic ray ever observed, the “Oh-My-God” particle discovered in 1991, the study found.
Cosmic rays are charged particles that travel through space and rain down on Earth constantly. Low-energy cosmic rays can emanate from the sun, but very high-energy ones are exceptional. They are thought to travel to Earth from other galaxies and from extragalactic sources.
“If you hold your hand out, one (cosmic ray) goes through the palm of your hand every second, but those are really low-energy objects,” said study co-author John Matthews, a research professor at the University of Utah.
“When you go out to these really high-energy rays, it’s more like a square kilometer per hundred. It’s never going through your hands.”
Despite years of research, the exact origin of these high-energy particles remains unclear. They are thought to be associated with the most energetic phenomena in the universe, such as those associated with black holes, gamma-ray bursts and active galactic nuclei, but most discovered so far appear to come from a vacuum or empty space — when there are no violent heavens. events are taking place.
Tracking high-energy cosmic rays
The recently discovered particle, called the Amaterasu particle after the sun goddess in Japanese mythology, was spotted by a cosmic ray observatory in Utah’s West Desert called the Array Telescope.
The Telescope Array, which began operating in 2008, consists of 507 ping-pong table surface detectors covering 700 square kilometers (270 square miles).
He observed more than 30 ultra-high-energy cosmic rays but none bigger than the Amaterasu particle, which hit the atmosphere above Utah on May 27, 2021, raining secondary particles to the ground where it picked up they are the detectors, according to. the study.
“You can look at … (at) how many particles hit each detector and that tells you what the energy of the primary cosmic ray is,” Matthews said.
The event triggered 23 surface detectors, with a calculated energy of about 244 ex-electron volts. The “Oh My God” particle detected more than 30 years ago was a 320 volt exa-electron.
For reference, 1 exa-electron volt equals 1 billion gigaelectron-volts, and 1 gigaelectron volt equals 1 billion electron volts. That would make the Amaterasu particle 244,000,000,000,000,000,000 electron volts. By comparison, the typical electron energy in the polar aurora is 40,000 electron volts, according to NASA.
An ultra-high-energy cosmic ray carries thousands of times more energy than any man-made particle accelerator such as the Large Hadron Collider, the most powerful accelerator ever built, explained Glennys Farrar, professor of physics at New York University.
“What is needed is a region of very high magnetic fields — like a super-sized LHC, but natural. And the conditions required are really exceptional, so the sources are very rare, and the particles are dispersed into the vast universe, so the chance of one hitting Earth is very small,” said Farrar, who was not involved. with the study, via email.
The atmosphere largely protects people from any harmful effects from the particles, although cosmic rays sometimes cause computer glitches. The particles, and space radiation more broadly, pose a greater risk to astronauts, and can cause structural damage to DNA and alter many cellular processes, according to NASA.
A mysterious source
The source of these ultra-high-energy particles baffles scientists.
Matthews, co-spokesman for the Telescope Array Collaboration, said the two largest recorded cosmic rays appeared to be “random” – when their trajectories are traced back, there appears to be nothing high-energy to cause particles of the such production. The Amaterasu particle, specifically, appeared to come from what is known as the Local Void, an empty area of space at the edge of the Milky Way galaxy.
“If you take the two highest energy events – the one we just found, the ‘Oh-My-God’ particle – those don’t even seem to point to anything. It should be something quite close. Astronomers with visible telescopes can’t see anything that big and violent,” Matthews said.
“It comes from a region that is like a local empty space. It is void. So what the heck is going on?”
Expanding the Telescope Array may provide some answers. When complete, 500 new detectors will enable the Array Telescope to shower showers of radiation-induced particles across 2,900 square kilometers (about 1,120 square miles) — an area nearly the size of Rhode Island, according to a University of Utah statement.
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