Nikhef scientists, together with colleagues from around the world, perform research at the Pierre Auger Cosmic Ray Observatory, an international observatory for the detection of ultra-high-energy cosmic radiation, located on the plains of western Argentina. They do so to learn more about the nature and origins of this mysterious cosmic radiation.
Each and every second, millions of cosmic rays pound the atmosphere, causing showers of subatomic particles. Low-energy particles wander about our Galaxy, often originating from the remnants of burnt-out stars after a supernova explosion. Ultra-high-energy particles are more rare and have energies of more than 100 million times the highest energy that can be generated on Earth using particle accelerators.
How does Nature accelerate particles to reach such extremely high energies? What particles does cosmic radiation consist of? Where do they come from? What happens during their ultra-high-energy collisions with Earth’s atmosphere? At the Pierre Auger Observatory in Argentina, an international collaboration of scientists looks for answers to these questions.
The Pierre Auger Observatory comprises several detectors:
- The particle detector consists of more than 1600 water tanks scattered over an area of 3000 square kilometres, where showers of secondary particles, caused by the impact of ultra-high-energy particles onto the atmosphere, are being detected.
- Whenever a shower of particles travels through the atmosphere, it also causes fluorescence. The light emitted in this way is detected by 27 highly sensitive telescopes that are located along the perimeter of the observatory and look at the sky above the area. This detector only works when it is completely dark, with no moon or clouds.
- New techniques are also being developed at the observatory, for example to detect the radio signals that result from the interaction of a shower of particles with the Earth’s magnetic field and the atmosphere.
Nikhef researchers and their colleagues at the Pierre Auger Observatory study particles with energies between 100 thousand TeV and 1 billion TeV, the highest energy investigated thus far.
By very carefully measuring the properties of a particle shower, the researchers determine where the cosmic radiation originated and which energy it has. They also work to reveal what the mass of the original cosmic ray is: is it as light as hydrogen, as heavy as iron, or somewhere in between?
By comparing the angles of incidence of the highest-energy radiation with the positions of known cosmic objects (black holes, galaxies, supernovae), they try to discover the origins of the cosmic radiation.
Together with international colleagues, Nikhef scientists develop detection stations for studying radio signals caused by the interaction of a particle shower with the Earth’s magnetic field and the atmosphere.
Research on a test set-up of almost 7 km2 has already proven to be successful: it was shown that the technique to determine the angle of incidence, energy, and nature of the incoming cosmic radiation by means of radio signals is comparable or even better than conventional techniques. Focus is currently being shifted to applying this knowledge towards measurements at a larger scale.