ESO Site Shortlisted for Cherenkov Telescope Array

15 April 2014

ESO’s Paranal–Armazones site in Chile has been shortlisted as one of two potential sites in the southern hemisphere for the international Cherenkov Telescope Array (CTA) — a large array for ground-based gamma-ray astronomy. This is an important step towards the realisation of the project and if the site is selected, this will open up a new frontier for ESO.

On 10 April 2014 Government representatives from the 12 of the countries [1] involved in the Cherenkov Telescope Array (CTA) project met in Munich and decided to start negotiations with the two sites — Aar in Namibia and ESO's Paranal–Armazones site in Chile — keeping Leoncito in Argentina as a third option.

The CTA project is an initiative to build the next generation of ground-based, very high energy gamma-ray instruments. The CTA project aims to use detection of high-energy gamma-rays to provide a deeper insight into the high-energy Universe.

The representatives received consultation from an international Site Selection Committee as well as the CTA consortium’s extensive input on the merits of the proposed sites. The Consortium expects to close the site selection by the end of 2014.

The spokesperson of the CTA Consortium, Professor Werner Hofmann said: “The site choice is on the critical path towards implementing CTA; this decision represents a major step forward and we appreciate very much the engagement and support of the funding agencies and the country delegates involved in the decision.”

Gamma-rays are emitted by the hottest and most powerful objects in our Universe — such as supermassive black holes, supernovae and possibly remnants of the Big Bang. When a high-energy gamma photon hits the Earth’s atmosphere, it may produce a cascade of secondary particles and cause emission of what is known as Cherenkov radiation — a characteristic faint blue visible-light flash. This flash may last only a few billionths of a second so must be imaged with super-fast and sensitive cameras and with telescopes of enormous light gathering power.

The Cherenkov Telescope Array is a multinational, world-wide project with which 1000 scientists and engineers from 28 countries and over 170 research institutes are involved. The CTA will provide an order-of-magnitude jump in sensitivity over current instruments [2], providing novel insights into some of the most extreme processes in the Universe. Most systems measuring Cherenkov radiation use only a handful of telescopes, but the CTA will consist of about 100 Cherenkov telescopes of 23-metre, 12-metre and 4-metre dish sizes located in the southern hemisphere, plus a smaller site in the northern hemisphere. An array of this size will increase the number of detected flashes, it will also cover the full energy range [3] and improve drastically upon the angular resolution [4], allowing for identification of the emitting objects at other wavelengths.

“Although formal discussions have not yet started, the shortlisting of Paranal-Armazones as a potential site for CTA illustrates the excellence of the site and the infrastructure for the Very Large Telescope and European Extremely Large Telescope. If chosen, CTA would take advantage of ESO’s great expertise in ground-based astronomy.” said ESO’s Director General, Tim de Zeeuw. “We look forward to the discussions with CTA.”


[1] Representatives from Argentina, Austria, Brazil, France, Germany, Italy, Namibia, Poland, Spain, South Africa, Switzerland and the United Kingdom met on behalf of the 28 countries involved in CTA.

[2] Existing similar Cherenkov instruments include: H.E.S.S., MAGIC, VERITAS and CANGAROO.

[3] The energies range from GeV (Giga-electron-volts) to TeV (Tera-electron-volts). Converting to wavelength which is more familiar to optical astronomers, this translates to 0.01 to 0.00001 pm (picometre which is 1/1000 nm).

[4] Low energy (less than 100 GeV) instruments will have a moderate field of view of about 4-5 degrees; medium energy (100 GeV to 1 TeV) will cover 6-8 degrees, and high energy instruments which will capture the most intense flashes at over 10 TeV with a much wider field of view of about 10 degrees.

More Information

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, Czechia, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.



Lars Lindberg Christensen
Head of ESO ePOD
ESO ePOD, Garching, Germany
Tel: +49 89 3200 6761
Cellular: +49 173 3872 621

About the Announcement



The Cherenkov Telescope Array
The Cherenkov Telescope Array