200 most important Astronomy topics - Sykalo Eugen 2023


The Pierre Auger Observatory

The universe is a vast and mysterious place that never ceases to amaze us with its wonders. One of the greatest mysteries in astrophysics is the origin and nature of cosmic rays. These high-energy particles are constantly bombarding our planet from outer space, but their source and composition remain largely unknown. To unravel this mystery, scientists built the Pierre Auger Observatory, the largest and most advanced cosmic ray detector in the world.

What are cosmic rays?

Cosmic rays are particles that come from outer space and travel at almost the speed of light. They can be protons, electrons, or atomic nuclei, and they can have energies millions or even billions of times higher than those produced in particle accelerators on Earth. Cosmic rays are everywhere in the universe, and they are constantly bombarding the Earth's atmosphere from all directions.

The discovery of cosmic rays

The existence of cosmic rays was first discovered in 1912 by the Austrian physicist Victor Hess. He made a series of balloon flights and found that the intensity of radiation increased with altitude, which suggested that the radiation was coming from outer space rather than from the Earth's surface.

Since then, many experiments have been conducted to study cosmic rays, but their origin and nature remain a mystery. Cosmic rays are difficult to study because they are very rare and highly energetic, and they interact with matter in complex ways.

The Pierre Auger Observatory

The Pierre Auger Observatory is a collaboration of more than 500 scientists from 18 countries, named after the French physicist Pierre Auger, who first proposed the idea of building a giant cosmic ray detector in the 1930s. The observatory covers an area of 3,000 square kilometers (1,160 square miles) in Argentina, near the Andes Mountains, and consists of 1,600 detectors spread over an area larger than the city of Paris.

The detectors are spread out in a triangular grid, with each detector spaced 1.5 kilometers (0.93 miles) from its neighbors. They are designed to detect the shower of particles that is produced when a high-energy cosmic ray enters the Earth's atmosphere and collides with air molecules.

How the Pierre Auger Observatory works

When a cosmic ray enters the Earth's atmosphere, it collides with air molecules and produces a shower of secondary particles, including protons, neutrons, electrons, and gamma rays. These particles continue to collide with other air molecules, creating a cascade of particles that spreads out over a large area.

The detectors of the Pierre Auger Observatory are designed to detect the secondary particles in the shower as they pass through the atmosphere and reach the ground. Each detector consists of a large plastic tank filled with 12,000 liters (3,170 gallons) of purified water, with three photomultiplier tubes mounted on top to detect the faint flashes of light produced by the particles as they pass through the tank.

The signals from the detectors are sent to a central data acquisition system, where they are analyzed to reconstruct the direction, energy, and nature of the primary cosmic ray that produced the shower.

What have we learned from the Pierre Auger Observatory?

Since its completion in 2008, the Pierre Auger Observatory has collected data on millions of cosmic ray events, providing insights into the origin and nature of these mysterious particles.

One of the most significant discoveries made by the observatory is that cosmic rays with energies above 10^19 electronvolts (eV) are extragalactic in origin. This means that they come from sources outside our Milky Way galaxy, such as distant quasars, active galactic nuclei, or gamma-ray bursts.

The observatory has also found that the cosmic ray flux is not uniform in all directions, but has a preferred direction, which suggests that there are large-scale structures in the universe that affect the propagation of cosmic rays.