Cosmic Rays
Cosmic Ray Research: Probing Ever Higher Energies
The history of cosmic ray research is a story of scientific adventure. For nearly a century,
cosmic ray researchers have climbed mountains, ridden hot air balloons, and traveled to the far corners of the
earth in the quest to understand these fast-moving particles from space. They have solved some scientific
mysteries -- and revealed many more. With each passing decade, scientists have discovered higher-energy, and
increasingly more rare,
cosmic rays. The Pierre Auger Project is the largest scientific enterprise ever conducted
in the search for
the unknown sources of the highest-energy cosmic rays ever observed.
The Mystery of High-Energy Cosmic Rays
Scientists love a mystery, because solving a mystery in nature means the opportunity to learn something new
about the universe. High-energy cosmic rays are just such a mystery.
Something out there -- no one knows what -- is hurling incredibly energetic particles around the universe.
Do these particles come from some unknown superpowerful cosmic explosion? From a huge black hole sucking stars to
their violent deaths? From colliding galaxies? We don't yet know the answers, but we do know that solving
this mystery will take scientists
another step forward in understanding the universe.
The Big Events
It was as if they went out to catch butterflies, and caught an F-111 aircraft.
It wasn't supposed to happen. Cosmic ray researchers were dumbfounded when their "Fly's Eye" detector
in the high Utah desert in the western USA turned up an incoming particle from space with an energy
six times higher than their theory allowed. Two years later, on the other side of the world,
a Japanese detector recorded another of these "impossible" events. These two carefully
documented cosmic rays, whose energy is so high it defies explanation,
have spurred the effort to build a new detector big enough to capture and study many more
of these high-energy particles, and to try to discover where they came from.
A Detector 30 Times the Size of Paris
Each second, about 200 cosmic ray particles with energies of a few million electron volts strike
every square meter of the earth. While these low-energy cosmic rays are plentiful, cosmic rays at
higher energies are far rarer. Above the energy of 1018 eV, only one particle each week
falls on an area of one square kilometer. Above the energy of 1020 eV, only one particle
falls on a square kilometer in a century! To find and measure these rare events, a high-energy cosmic
ray study needs a truly giant detector.
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