Cosmic particle accelerators
Nikhef’s Cosmic Radiation research programme focuses on the Netherlands’ contribution to the Pierre Auger Observatory for cosmic rays in Argentina. The researchers analyse measurements and help develop further extensions. Auger investigates the sources and nature of high-energy cosmic particles.
What are cosmic rays?
In the universe, many violent astrophysical processes release particles that often reach Earth with enormous energy. Their impact on the atmosphere causes avalanches of charged particles known as cosmic rays. When these cosmic rays reach the Earth’s surface, they can be detected using detectors. From the signals, it is possible to deduce the energy of the incoming particles and the direction of the source in the night sky.
There are still many scientific questions surrounding cosmic rays. The nature of the incoming particles is not well understood. At the same time, their energy is often demonstrably much greater than that which terrestrial accelerators can produce. But exactly what cosmic processes emit these particles is the subject of much international research.
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What does the Pierre Auger Observatory investigate?
Through the Radboud University in Nijmegen, Nikhef is closely involved with the Pierre Auger Observatory for cosmic rays in the remote Pampas of Argentina. There, spread over an area of 3,000 square kilometres, are approximately 1,700 water-filled tanks equipped with sensors that record incoming particles. Radio antennas on these tanks detect the electromagnetic signals from the particle showers in the atmosphere. Along the edges of the site, 25 ultraviolet telescopes observe the light from the particle showers against the dark night sky.
The energy of cosmic rays ranges from approximately 1 GeV to 100 EeV. Above 1 EeV (10^18 eV), we refer to ultra-high-energy particles.
Low-energy particles are known to drift through our Milky Way like a gas, and their origin often lies in burnt-out stars following a supernova explosion. Moreover, they are very numerous. The ultra-high-energy particles that the AUGER research focuses on are much rarer. They have an energy more than 100 million times greater than the highest energy we can generate in particle accelerators on Earth, and thus may offer insights into new physics beyond the Standard Model.
By measuring the properties of the particle avalanche with great precision, the researchers determine where the cosmic rays come from and what energy they possess. They are also trying to ascertain the mass of the original cosmic rays: is it as light as hydrogen, as heavy as iron, or something in between?
The properties of the particle showers depend on the particles’ interactions with the atmosphere. Here, scientists are looking for clues to new physics at energies that existing particle accelerators cannot reach.
By comparing the directions of arrival of the high-energy radiation with the positions of known objects in the sky (black holes, galaxies, supernovae), researchers are trying to determine where this cosmic radiation actually comes from.
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Nikhef and Auger
The Cosmic Radiation research programme is led by Nikhef partner Radboud University in Nijmegen. This group comprises around 15 researchers. Together with international colleagues, Nikhef scientists have developed detection stations for the observatory to study radio signals generated by the interaction of a particle shower with the Earth’s magnetic field and the atmosphere.
Nikhef also plays a leading role in installing radio antennas for the observatory, as well as in interpreting the data generated by them.
In addition, Nikhef in Nijmegen has made a major contribution to both the design and production of the new thin scintillator detection layer for the observatory.
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More information
The Cosmic Rays – Auger research program is led by the Nikhef group at Radboud University Nijmegen.
Learn more about the international Pierre Auger Observatory: https://auger.org
Programme leadership Cosmic Rays
Charles Timmermans
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