On May 27, 2021, a large detector system in the US state of Utah registered an unusual phenomenon: an extremely high-energy particle from the distant cosmos had penetrated the Earth’s atmosphere and triggered a huge shower of secondary particles. With an energy of 240 trillion electron volts (240 billion billion or exa-electron volts), it is just behind the previous record holder, the Oh My God particle, registered in 1991.
The origin of such extremely high-energy particles is still completely unknown. The discovery team now reports in the journal Science that no celestial object could be traced as the origin of the particle registered in 2021 and named Amaterasu after a Japanese deity.
On the contrary: in the direction from which the Amaterasu particle came, there is a region that astronomers call a “void”, a huge void in which there are hardly any galaxies. “Particles with such high energy should only be slightly deflected by magnetic fields in the cosmos,” explains John Matthews, spokesman for the Telescope Array detector system in Utah. “But when we trace the trajectories of the Oh My God particle and this new particle, there is simply nothing there that could produce such high energies.”
Earth’s atmosphere is constantly hit by particles – mostly protons – from space. Most of them come from our sun, while more energetic particles originate from distant neutron stars and black holes. However, particles with an energy of more than 50 billion billion electron volts (50 exa-electron volts) are puzzling. That’s around ten million times more energy than the largest particle accelerator on Earth can produce, and is roughly equivalent to the energy of a flying baseball concentrated into a tiny elementary particle. Celestial researchers still have no explanation for these extremely high-energy particles.
But such particles are rare. Experts estimate that the atmosphere is only hit by such a monster particle per square kilometer every hundred years. Large detector systems are therefore necessary to track down the mysterious particles. The Telescope Array in Utah consists of 507 three-cubic-meter particle detectors spread over an area totaling 700 square kilometers.
If a high-energy particle penetrates the Earth’s atmosphere, it collides with atoms and molecules there, triggering a huge chain reaction that ultimately creates a shower of billions of elementary particles. The detectors of the Telescope Array register not the original particle, but these secondary particles. In the Amaterasu event, 23 detectors responded over an area of 48 square kilometers.
From the energy and time sequence of the recorded secondary particles, the researchers can then reconstruct with what energy and from which direction the original cosmic particle entered the Earth’s atmosphere.
Since it is unclear where the Amaterasu particle comes from, speculation is rampant: perhaps previously unknown physical phenomena produce the extreme particles. “It could be defects in the structure of space-time,” says John Belz of the University of Utah. “There are a large number of completely crazy proposals.” But perhaps no “new physics” is necessary to explain the particles. “It could also be a strong deflection caused by a magnetic field in the nearby area,” the researchers write in Science – because such a deflection would mislead the researchers when tracing the particle’s trajectory.
The team hopes to solve such puzzles with the detector system in a few years. Because the Telescope Array is being expanded rapidly. With 500 additional detectors, an area of 2,900 square kilometers will ultimately be covered. And this means that the scientists are likely to come across a significantly larger number of extremely high-energy particles.
2023-11-24 11:57:24
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