Press Release

Construction begins on the first and largest gamma-ray observatory in Chile

18 December 2025

CTAO-South time-capsule monument unveiling (Credit: ESO/CHEPOX)

Yesterday, a groundbreaking ceremony for the CTAO’s southern array facility took place at the European Southern Observatory’s (ESO’s) Paranal site in Chile, marking the beginning of construction of the telescope foundations. The CTAO, or Cherenkov Telescope Array Observatory, will be the world’s largest and most powerful gamma-ray observatory, providing new insights into the high-energy Universe. Its southern array will be the first gamma-ray observatory to be built in Chile.

“We are happy to welcome this innovative facility to ESO’s family. It’s our pleasure to see the start of construction of the southern site of this powerful observatory here at Paranal in Chile’s Atacama Desert — a place with the most pristine skies on Earth. This groundbreaking is a huge milestone for both the CTAO and ESO, but also for Chile as this new facility will strengthen the country’s position as a global hub for astronomy,” said ESO Director General Xavier Barcons in his welcoming speech during the groundbreaking ceremony.

The CTAO is an international project, in which ESO is a founding partner and host to its southern array; several ESO Member States are also involved in the project and scientific teams around the world, including in Chile, are preparing to observe with this facility in the coming years. The start of the construction of the foundations, work being led by a consortium of Chilean companies, paves the way for the first telescopes to be deployed at Paranal by the end of 2026.

For the celebration, representatives of CTAO, ESO, the Chilean government and local authorities gathered at ESO’s Paranal Observatory. In addition to ESO’s Director General, participants at the ceremony included Andreas Kaufer, ESO Director of Operations; Thomas Klein, ESO Director of La Silla Paranal Observatory; Volker Heinz, CTAO Construction Programme Manager; Stuart McMuldroch, CTAO Director General; Francisco Colomer, Chair of the CTAO ERIC Council; Ricardo Díaz, Governor of the Antofagasta Region; Valeska Molina, Regional Secretary of the Ministry of Science, Technology and Innovation for Antofagasta Region; and Alejandra Pizarro, Director of the Chilean National Agency for Research and Development (ANID). Following a welcome and speeches, a time capsule was buried next to the future array area. It was filled with elements from Chile and CTAO partners, as well as scientific items, representing good wishes and goals for the telescopes now under construction.

“Thanks to the commitment of our partners from around the world and the support of ESO as our hosts here in Chile, we are now turning a vision into reality as construction begins on what will be the most advanced gamma-ray observatory on Earth,” said McMuldroch.

“We are proud to host the CTAO’s southern array and operate it right here at ESO’s Paranal Observatory, together with ESO’s Very Large Telescope and ESO’s Extremely Large Telescope,” said Klein. “This revolutionary facility will transform our understanding of the Universe, opening a new window onto the most energetic phenomena in the cosmos”.

The CTAO is designed to detect very high-energy gamma-rays emitted by the most violent and powerful events in the Universe. It will comprise over 60 telescopes at two sites: CTAO-South and CTAO-North [1] — one in each hemisphere — with a total collection area of over 1 million square metres. The southern site alone will have more than 50 telescopes, designed to capture a broad energy range — from 20 GeV to 300 TeV, billions of times more energetic than visible light [2].

The CTAO will detect high-energy radiation with unprecedented accuracy and precision, far outstripping current gamma-ray telescopes. When an energetic gamma photon hits Earth’s atmosphere, it produces a cascade of particles that cause the emission of what is known as Cherenkov radiation — a characteristic faint blue visible-light flash. This flash lasts only a few billionths of a second so it must be imaged with super-fast and sensitive cameras, with telescopes of enormous light-gathering power operating under pristine dark skies.

By pinpointing the sources of these gamma-rays, CTAO will provide deeper insights than ever before into the most extreme events and objects in our Universe, focusing on key areas like: understanding the origin and role of relativistic cosmic particles; probing extreme environments such as black holes and neutron stars; and exploring the frontiers of physics by searching for dark matter and testing the limits of Einstein’s theory of relativity.

In 2018 the CTAO, ESO and Chilean authorities signed agreements to have the CTAO southern array hosted at ESO’s Paranal Observatory, less than ten kilometres southeast of the location of ESO’s Very Large Telescope. This region in the Chilean Atacama Desert provides the clearest and darkest skies of any astronomical observatory on Earth, thanks to Chile’s geography and the country’s commitment to the preservation of its night skies.

“By building such a powerful and important facility in this area, ESO and CTAO hold deep trust that Chilean authorities will safeguard this extraordinary site for generations to come, and secure the huge value that astronomical facilities like CTAO generate locally and globally,” says Barcons.

“Paranal is a unique place in the world to study the Universe,” highlighted Heinz. "The Atacama Desert now welcomes another world-leading facility, and, in just one year, we expect to have here CTAO telescopes providing the first-ever observations of the gamma-ray sky from Chile.”

Notes

[1] The northern hemisphere site is located at the Instituto Astrofísica de Canarias Observatorio del Roque de los Muchachos on the island of La Palma, Spain. 

[2] GeV and TeV stand for giga-electronvolts and tera-electronvolts, respectively. For comparison, visible light has an energy of just a couple of electron-volts.

More information

The CTAO ERIC (also known as CTAO Central Organisation) is in charge of the construction and operation of the CTAO. Thus, it is made up of the groups and people dedicated to the management and administration of the Observatory’s development and the overall project, science, computing and systems engineering activities. The high-level organisational structure is broken into five main groups: Director’s Office, On-Site Construction, Project Office, Project Science Office, and Administration Office. The Central Organisation is responsible for managing the CTAO’s four sites: the Headquarters hosted by the Istituto Nazionale di Astrofisica (INAF) in Bologna (Italy), the Science Data Management Centre hosted by the Deutsches Elektronen-Synchrotron DESY in Zeuthen (Germany) and the two telescope arrays, CTAO-North at the Instituto de Astrofísica de Canarias’ (IAC’s) Roque de los Muchachos Observatory on La Palma (Spain), and CTAO-South, at the ESO’s Paranal Observatory in the Atacama Desert (Chile).  

This group works in close cooperation with partners from around the world toward the development of the Observatory. Major partners include In-Kind Contribution Collaborations that are developing essential hardware and software, in addition to the CTAO Consortium, an international group of researchers who works on the scientific exploitation of the Observatory. 

The CTAO ERIC members include Austria, Croatia, the Czech Republic, the European Southern Observatory (ESO), France, Germany, Italy, Poland, Slovenia, Spain, and Switzerland. Further countries — Australia, Brazil, Japan, South Africa, and the United States — are engaged in the process of joining the CTAO ERIC as Strategic Partners or Third Parties. 

The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration for astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, Czechia, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as survey telescopes such as VISTA. Also at Paranal, ESO will host and operate the south array of the Cherenkov Telescope Array Observatory, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates ALMA on Chajnantor, a facility that observes the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society. 

Links

• CTAO website
• The CTAO on the ESO Blog: Exploring the Universe at the highest energies
• Read more about CTAO on the ESO website
• Paranal Observatory to Host World’s Largest Gamma-Ray Telescope

Contacts

Bárbara Ferreira
ESO Media Manager
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: press@eso.org

Francisco Rodríguez
ESO Head of Communication Chile
Santiago, Chile
Tel: +56 2 2463 3151
Email: francisco.rodriguez@eso.org

Alba Fernández-Barral
CTAO Chief Communications Officer
Tel: +39-051-6357-270
Email: alba.fernandezbarral@cta-observatory.org

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