But why study these high-energy cosmic rays?
For one thing, scientists like a good mystery and the origins of cosmic rays is one of the biggest unknowns in physics.
But understanding them better could lead to improved insights on fundamental physics, such as how our universe was created, and why objects have mass. Snow told Seeker high-energy cosmic rays are clues to the very structure of the universe.
“High-energy cosmic ray particles are one of several messengers from outer space that we use to learn about the structure of the universe, for example, the distribution of where the billions of other galaxies apart from the Milky Way are located,” he said. “We now know that galaxies are not uniformly distributed in outer space. Rather they group themselves in clusters and super-clusters.”
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Also, scientists don’t know the exact source of high-energy cosmic rays. There have been theories, but the intense conditions needed to generate such energetic particles can be mind-boggling.
“We know that shock waves coming from stars dying in the form of a supernova could accelerate cosmic ray particles up to energies reaching about 10 to the 15th electron volts,” Snow explained. “But our paper is about cosmic ray particles of much higher energies, greater than 8 times 10 to the 18th electron volts. We can only speculate what the sources of these particles may be.”
Snow said physicists can learn the most about specific sources by studying the arrival directions of the very highest energy particles, since their measured arrival directions essentially point straight back to their sources.
Snow said the source must come from some faraway “extragalactic astrophysical catastrophes, something like two galaxies colliding or a galaxy with a super-massive black hole at its center which is exploding and shooting streams of ultra-high energy particles into intergalactic space.”
“We know there are galaxies which have an active galactic nucleus at their center — a very violent and hot center — which could be explained by one of these super-massive, exploding black holes,” he said.
“But,” Snow continued, “these highest energy, undeflected cosmic ray particles come to us very rarely which is one reason why the Pierre Auger Observatory plans to collect data for at least 10 more years, with planned upgrades to the current detectors, to observe more of the very highest energy particles whose arrival directions should point straight back to the objects that accelerated them to such energies.”
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