Biggest ever Gamma Ray search starts in Namibia

August 28, 2002

The world's most sensitive Gamma Ray telescopes are being inaugurated in Namibia (in Southwest Africa) on September 3rd. The High Energy Stereoscopic System (H.E.S.S.), a European/African collaboration in which the UK is a partner, will look for Gamma Rays produced by the most energetic particles in the Universe. The array initially consists of four telescopes, the first of which will become operational next week. This one telescope alone is more sensitive than any other existing ground-based array or telescope working in this particular area of the electromagnetic spectrum.

Once all four telescopes are operational in late 2003, researchers from the University of Durham will use H.E.S.S. to investigate a range of extreme cosmic environments such as the supernova remnants formed when a star dies. A major goal is to see if these are a source of cosmic rays - charged particles that constantly bombard the Earth from space. The origin of cosmic rays is difficult to determine as they are influenced by the magnetic field of our Galaxy. However, the Gamma Rays they emit travel in a straight line, so they may reveal the primary source of the cosmic rays. H.E.S.S. will also be probing the structure of pulsars (rapidly rotating stars formed when a massive star explodes at the end of its life, which emit pulses across the range of the electromagnetic spectrum) and active galactic nuclei to find the source of their energy.

Dr Paula Chadwick, of the Durham team, explains: "H.E.S.S. is set to give us unique insights into some of the most extreme environments in the universe. We have some expectations about what we will be able learn more about - supernova remnants, active galaxies and so on - but experience tells us that when you improve the sensitivity of your telescope, you see things you never expected as well. It's going to be very exciting!"

When Gamma Rays are absorbed by the Earth's atmosphere, pairs of electrons and positrons are created and emit tiny flashes of light in a process known as Cherenkov radiation. Telescopes such as H.E.S.S can detect these tiny flashes of light. By using the Earth's atmosphere as part of the detector, the telescopes have much greater sensitivity than an equivalent space based device, and can detect far fainter Gamma Ray sources than previously possible.

Gamma rays are usually produced by particles moving very rapidly. The study of Gamma Rays enables astronomers to learn more about systems that accelerate these particles, such as active galactic nuclei where supermassive black holes produce jets of particles travelling near the speed of light. These are strong and highly variable sources of gamma rays. Gamma Rays can also be produced by the annihilation of massive particles that may be the source of the 'missing mass' in the universe.

The University of Durham' s role in the design and manufacture of HESS has been in calibrating the camera that will record the Cherenkov radiation and in developing systems that will measure the atmospheric conditions. This is critically important as variations in the atmosphere, such as cloud cover, can dramatically reduce the amount of light reaching the telescopes. The Durham scientists are now working on various refinements to calibration systems, and a more efficient mirror making technique that they hope to use when the array is extended from the current 4 telescopes to the planned 12 or 16.

Namibia is an excellent site scientifically, one of the best in the world for ground-based optical astronomy and with ideal atmospheric conditions for the techniques used by H.E.S.S. However, practically it has represented a huge challenge with limited road access to the site and water, power and computing connections having to be put in place specially.
Notes for Editors

Gamma Rays are a type of electromagnetic radiation, like optical light or radio waves. Electromagnetic (em) waves have a wide range of wavelengths and they can be used to see different views of objects. Visible light only shows us what is on the surface, but other types of em waves can reveal more, like the x-rays used by doctors to see broken bones. In their quest to understand our universe, astronomers long ago branched out from visible light to examine objects that radiate in the microwave and x-ray wavelengths. However, gamma rays, the most energetic kind of EM wave have remained difficult to use until now, as there are very few strong sources for astronomers to view.

The H.E.S.S. array is named after Viktor Hess who received the 1936 Nobel Prize in Physics for his discovery of cosmic radiation.
All four telescopes should be operational by late 2003, at which point a decision will be made on whether to extend the project with additional telescopes.

More details about the H.E.S.S. project can be found at:

Picture of Paula Chadwick (Credit University of Durham)
Illustration of Cherenkov Radiation (Credit University of Durham)
Montage of H.E.S.S. telescopes (Credit H.E.S.S. collaboration)
Available at or from Julia Maddock (contact details below).

Further images are available from:
All pictures used should be credited to the H.E.S.S. collaboration.

University of Durham, United Kingdom

In Germany: Max-Planck-Institut für Kernphysik, Humboldt Universität Berlin, Ruhr-Universität Bochum, Universität Hamburg, Landessternwarte Heidelberg, Universität Kiel,

In France: Laboratoire Leprince-Ringuet (LLR), Ecole polytechnique, Palaiseau, LPC College de France, Paris, Universités Paris VI - VII, France (LPHNE),Université de Grenoble, CERS, Toulouse, CEA Saclay, Observatoire de Paris-Meudon, DAEC,

Dublin Institute for Advanced Studies, Ireland
Charles University, Prag, Czech Republic,
Yerevan Physics Institute, Yerevan, Armenia
University of Namibia, Windhoek, Namibia
University of Potchefstroom, Republic of South Africa

Contact Details

Dr Paula Chadwick will be available for comment until August 30th.
Tel 0191 374 7175

After August 30th, please contact:
Lowry McComb (
Mob: 0780 8551044
Tel: 0191 374 7175 or 01642 335323

Steve Rayner (
Tel: 0191 374 4562 or 0191 374 7175
Mob: 07941 803303

The Particle Physics and Astronomy Research Council (PPARC) is the UK's strategic science investment agency. It funds research, education and public understanding in four areas of science - particle physics, astronomy, cosmology and space science.

PPARC is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Laboratory for Particle Physics (CERN), the European Space Agency [ESA] and the European Southern Observatory [ESO]. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility, which includes the Lovell Telescope at Jodrell Bank observatory.

Science and Technology Facilities Council

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