On 19 December 2018, the Cherenkov Telescope Array Observatory (CTAO) and the European Southern Observatory (ESO) signed the final agreements needed for CTA’s southern hemisphere array to be hosted near ESO’s Paranal Observatory in Chile.

A total of three agreements were signed over the course of the week: between the Chilean government and ESO; between ESO and CTAO (press release available 20 December); and between the Chilean National Commission for Science and Technology (CONICYT) and CTAO (read press release in English or Spanish). With these three agreements in place, the CTAO will be able to begin construction on the southern site. The hosting agreement with the Instituto de Astrofísica de Canarias (IAC) is already in place to host CTA’s northern hemisphere array at the Observatorio del Roque de los Muchachos in La Palma, Spain. Construction on both the northern and southern arrays is expected to begin in 2020.

CTA will be the next generation ground-based instrument in the detection of gamma rays, which are very high-energy electromagnetic radiation emitted by the hottest and most powerful objects in the Universe — such as supermassive black holes, supernovae and possibly remnants of the Big Bang. To provide access to the whole sky, the CTA Observatory will have two sites, with 19 telescopes in the northern hemisphere and 99 in the southern hemisphere.

The southern site of CTA is 11 kilometres southeast of the location of the Very Large Telescope at ESO’s Paranal Observatory in the Atacama Desert and only 16 kilometres from the construction site of the upcoming Extremely Large Telescope. This is one of the driest and most isolated regions on Earth — an astronomical paradise. In addition to the ideal conditions for year-round observation, installing CTA at the Paranal Observatory brings the advantages of ESO’s infrastructure. The existing infrastructures and facilities, and ESO’s long-lasting experience spearheading international astronomical projects in Chile, will all support the construction and operation of the new telescope array.

Current gamma-ray telescope arrays only consist of a handful of individual telescopes, but CTA — with its larger collecting area and wider sky coverage — will be the largest and most sensitive array of gamma-ray telescopes in the world, with unprecedented accuracy and 10 times more sensitive than existing instruments.

Although the Earth’s atmosphere prevents gamma rays from reaching the surface, CTA’s mirrors and high-speed cameras will capture the short-lived flashes of eerie blue Cherenkov radiation produced when gamma rays interact with the atmosphere. By detecting this Cherenkov light, scientists will be able to trace the gamma ray back to its cosmic source.

On 17 December 2018, CTAO’s Managing Director, Federico Ferrini, met CONICYT’s Executive Director, Christian Nicolai Orellana on 17 December to sign a scientific collaboration agreement, which aims to foster astronomical research in Chile, capitalising on the opening of a new observational window as enabled by CTA-South.

“The installation of this new observatory will bring the study of the most extreme phenomena in the Universe to Chile,” explained Nicolai. “The project will be complemented with the installation of another array of telescopes in the northern hemisphere, which will foster scientific collaboration between both sides of the globe. In this way, Chile will be hosting the greatest concentration of technology observing phenomena from Earth. Thus, reaffirming Chile and its spectacular sky, the natural astronomical laboratory par excellence, as a world leader in astronomy.”

“The scientific collaboration agreement with CONICYT was an important first step in strengthening the confidence of the Chilean Government in scientific collaboration and to achieve the installation of CTA telescopes in Chile, with ESO’s involvement,” commented Ferrini. “We are looking forward to collaborating with CONICYT to develop a brilliant community of Chilean scientists and engineers that will become an important part of both Chile’s future and the future activities of CTA.”

On 19 December 2018, Federico Ferrini, Managing Director of the Cherenkov Telescope Array Observatory (CTAO), met with ESO’s Director General, Xavier Barcons, at the ESO offices in Santiago, Chile. In the presence of ESO’s Director for Operations, Andreas Kaufer, and other ESO personnel, they signed the agreement for the construction and operation of CTA’s southern array within ESO’s Paranal site in northern Chile.

Deputy Minister of Foreign Relations of Chile Carolina Valdivia Torres and ESO’s Director General also signed the agreement that enables ESO to host CTA-South at the Paranal Observatory site, as an ESO Programme.

“Operating CTA at Paranal will open a new window on the Universe for astronomers in the ESO Member States, Chile, and worldwide,” commented Xavier Barcons. “ESO’s rich experience of maintaining and operating fleets of telescopes in remote areas will be invaluable for the CTA project.”

“Thanks to the agreements signed today, CTAO will not only benefit from Chile’s spectacular night sky but also from ESO’s facilities and deep experience, which will be an invaluable contribution to the realisation of this ambitious system of telescopes” said CTAO Managing Director, Federico Ferrini. “Furthermore, the synergies between ESO and CTAO will mark this new, fast-growing era of multi-messenger astrophysics for decades to come as we explore potential collaborations with other large infrastructures such as ALMA, SKA and gravitational wave interferometers.”

The scientific scope of CTA is extremely broad: from understanding the role of relativistic cosmic particles to the search for dark matter. CTA will explore the extreme Universe, probing environments from the immediate neighbourhood of black holes to cosmic voids on the largest scales. It may even lead to brand new physics as it studies the nature of matter and forces beyond the Standard Model.

More than 1400 scientists and engineers from 31 countries across five continents are engaged in the scientific and technical development of CTA. The shareholders of the current legal entity — CTAO gGmbH — are the representatives of ministries and funding agencies from Australia, Austria, the Czech Republic, France, Germany, Italy, the Netherlands, Japan, Slovenia, South Africa, Spain, Switzerland and the United Kingdom [1]. They are currently preparing for the establishment of a European Research Infrastructure Consortium — the CTAO ERIC — which will then construct the immense observatory. The ERIC will be composed of CTAO’s Member States and associated countries.

Notes [1] The Netherlands and South Africa attend as observers. This project is receiving funding from the European Union’s Horizon 2020 research and innovation programs under agreement No 676134.