Pierre Auger << pyair oh zhay >> Observatory is the world’s largest facility for detecting high-energy particles from space, known as cosmic rays. The observatory consists of 1,600 detectors. They are spread over about 1,200 square miles (3,000 square kilometers) of a plain by Malargüe (south of Mendoza), Argentina. The observatory takes its name from the French physicist Pierre V. Auger, who researched cosmic rays during the 1930’s. Hundreds of scientists from more than a dozen countries have worked on the project.
Cosmic rays are electrically charged particles, such as protons or heavier nuclei (cores) of atoms. Such particles continuously rain down on Earth from space. The Pierre Auger Observatory was designed to determine the source of those cosmic rays with the greatest energies, called ultra-high-energy cosmic rays.
When a cosmic ray enters Earth’s atmosphere, it collides with the nucleus of one of the atoms that make up the air. The impact produces additional particles, which then hit other nuclei to create even more particles. The particles rain down in an event called an air shower or extensive air shower. An ultra-high-energy cosmic ray can generate an extensive air shower consisting of billions of particles.
Each of the observatory’s detectors includes a tank that holds about 3,000 gallons (11,400 liters) of pure water. When a particle from an extensive air shower enters the water, it produces a flash of light that the detector can measure. Using information from multiple detectors, scientists can calculate the energy of the original cosmic ray and the direction from which it arrived.
The observatory also gathers data using four clusters of telescopes placed along the edges of the arrangement of detectors. On clear, dark nights, the telescopes detect ultraviolet light emitted when the particles of a shower interact with nitrogen in the atmosphere.
The Pierre Auger Observatory began collecting data in 2004. In 2007, analysis of the data produced the first evidence that ultra-high-energy cosmic rays come from active galactic nuclei, the extremely bright cores of some galaxies (see Galaxy (Other types of galaxies)). Scientists think that such cores are powered by black holes millions to billions of times as massive as the sun.
See also Cosmic rays.
