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Pierre Auger Observatory

The Pierre Auger Cosmic Ray Observatory is studying ultra-high energy cosmic rays, the most energetic and rarest of particles in the universe. When these particles strike the earth's atmosphere, they produce extensive air showers made of billions of secondary particles. While much progress has been made in nearly a century of research in understanding cosmic rays with low to moderate energies, those with extremely high energies remain mysterious.

The Pierre Auger Observatory is working at solving these mysteries.

References

1. The main Auger website can be found here.
2. Recent news of a possible link between the highest-energy cosmic rays and violent black holes here.
3. Information on the Northern Auger Site here.

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Cosmic Rays are charged, highly relativistic (that is, travelling with velocity that is non-negligible compared to the speed of light) particles that are constantly entering our atmosphere from outer space. When a particle reaches the Earth, it collides with a nucleus high up in the atmsosphere producing many secondary particles. Subsequently, these secondary particles collide with other nuclei in the atmosphere to produce more energetic particles. The result of this continued process is an extensive particle shower which rains down on the ground. Such a shower can cover a ground area of a few square kilometres.

Low energy cosmic rays are accelerated by magnetic fields out in space. These exist on the sun, in the solar wind, and in remnants of supernovae leftover in the Milky Way. However, these methods do not account for the high energy cosmic rays which we detect entering our atmosphere, and there is no scientific consensus of where these high energy rays actually come from. This is where the Auger Cosmic Ray Observatory comes in.

The Auger Observatory is based in Western Argentina, and is an international collaboration involving more than 250 scientists from around the world. The observatory consists of two types of detector: water tanks to detect the particles that fall to the ground, and fluroescent detectors to track the particle shower in the air. There are 1600 ground based water tanks, with a distance of 1.5km between each one, and four fluorescent detectors. The idea is that if we can document the event using these two different techniques, then we will be better able to build up a picture as to how these particle showers develop, and thus get more of an idea of the properties of the origin of the initial cosmic rays.

You can read more about the detection methods in [1] of the opening post.

There is a planned development in Colarado which will start to be constructed when the Argentinian site is completed (there are still some more water tank to be installed). This will be of the same format as its southern hemisphere counterpart, and the collaboration between the two will enable the entire sky to be covered by the observatory.

Finally, here is a picture from the Auger website showing how the two detection systems work together to build up an image of the particle shower: