The mysterious cosmic particles that baffle astronomers

On May 27, 2021, a large detector system in the US state of Utah recorded an unusual phenomenon: an extremely high-energy particle from the distant universe penetrated Earth’s atmosphere and unleashed a massive shower of secondary particles. With an energy of 240 billion billion electron volts (240 exaelectronvolts), it is just behind the previous record holder, the “Oh My God” particle, recorded in 1991.

The origin of these extremely high-energy particles is still not completely known. No celestial body can be traced as the origin of the particle recorded in 2021 and Amaterasu was named after a Japanese god, the discovery team now reports in the journal.Sciences“.

“There is simply nothing that can produce such high energies.”

On the contrary: In the direction from which the Amaterasu particle came, there is a region that astronomers call the Void, a huge void in which there are hardly any galaxies. “High-energy particles should only be slightly deflected by magnetic fields in the universe,” explains John Matthews, spokesman for the Telescope Array Detector System in Utah. “But when we trace the paths of the ‘oh my’ particle and this new particle, there is simply nothing that can produce such high energies.”

Earth’s atmosphere is constantly exposed to particles – mostly protons – from space. Most come from our Sun, while the most energetic particles originate from distant neutron stars and black holes. However, particles with energies of more than 50 billion billion electron volts (50 eV) are considered puzzling. This is ten million times more energy than the largest particle accelerator on Earth can produce, and roughly equivalent to the energy of a powerful baseball concentrated into a small elementary particle. So far, sky researchers have no explanation for these extremely high-energy particles.

Large detection systems are needed to track down “oh my” molecules.

But such molecules are rare. Experts estimate that the atmosphere is hit by such a massive particle only per square kilometer every hundred years. Therefore, large detection systems are necessary to track down mysterious particles. The telescope array in Utah consists of 507 three-cubic-meter particle detectors spread over a total area of ​​700 square kilometers.

If a high-energy particle penetrates Earth’s atmosphere, it collides with atoms and molecules there, setting off a massive chain reaction that eventually creates a shower of billions of elementary particles. Detectors in the telescope array do not record the original particle, but rather these secondary particles. In the Amatrasu event, 23 detectors responded over an area of ​​48 square kilometers.

From the energy and time sequence of the recorded secondary particles, researchers can then reconstruct the energy and direction from which the original cosmic particle entered Earth’s atmosphere.

Do previously unknown physical phenomena produce extreme particles?

Since it is unclear where the Amaterasu particle comes from, speculation is rife: perhaps previously unknown physical phenomena are producing the extreme particles. “It could be imperfections in the structure of spacetime,” says John Bales of the University of Utah, for example. “There are a whole lot of absolutely crazy proposals.” But perhaps there is no “new physics” necessary to explain particles. “It is also possible that it is a strong scattering caused by a magnetic field in the vicinity,” the researchers wrote in the journal Science, as such scattering would mislead researchers when tracking the particle’s path.

The team hopes to solve such mysteries using the detector system within a few years. Because the telescope array is expanding rapidly. With an additional 500 detectors, an area of ​​2,900 square kilometers will eventually be covered. This means that scientists will then have access to a much larger number of extremely high-energy particles.

Rnd/dpa