The Giant Observatory announced long-awaited results. High-energy cosmic particles can cover a vast area of several thousand square kilometers (artistic representation). Credit: A. Chantelauze / S. Staffi / L. Bret
The Hidden Shower
Most cosmic particles are protons or other charged particles, including heavy atomic nuclei such as iron. When these particles rain down on the upper atmosphere of the Earth and collide with an atomic nucleus in the air, they produce an explosion of subatomic particles. These particles collide with other nuclei and produce more particles, generating an “invisible shower” that spans a large area of the Earth by the time it reaches the surface.
The Surprising Tilt
Most researchers expected a deviation, but not to this degree, according to Piera Ghia, an astroparticle physicist at the CNRS nuclear physics institute in Orsay, France, who helped coordinate the data analysis. Astronomer Francis Halzen from the University of Wisconsin-Madison agrees. “It’s really very big. To me, it was a surprise,” says Halzen, who speaks on behalf of IceCube, the main neutrino observatory in Antarctica.
Possible Sources
The results suggest that the supermassive black holes at the center of the Milky Way galaxy are not a major source of high-energy particles. “The most likely sources are still the usual suspects,” says Mollerach: astronomical phenomena that generate intense magnetic fields, within which charged particles can move randomly and gain energy. These phenomena include active galactic nuclei – supermassive black holes that eject emissions of matter at speeds approaching the speed of light – and gamma-ray bursts from stars.
Future Upgrade
The Pierre Auger Observatory is currently in the early stages of a $12 million upgrade that should enable it to measure the relative abundance of protons and heavier nuclei in the cosmic particle flow.
References:
The Pierre Auger Collaboration. Science 357, 1266-1270 (2017).
The Pierre Auger Collaboration. Science 318, 938-943 (2007).
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