Cherenkov Telescope Array Observatory

The Cherenkov Telescope Array Observatory (CTAO) is an international scientific infrastructure project designed to study the Universe through very-high-energy gamma rays. Rather than operating as a commercial company or consumer-facing product brand, CTAO represents a shared observatory and research platform for the astroparticle-physics community. Its planned instrument will extend observations from energies of several tens of gigaelectronvolts to approximately 300 teraelectronvolts, a range that reveals some of the most energetic processes known in nature. The observatory is being developed as two geographically separated telescope arrays. CTAO-North is located at the Roque de los Muchachos Observatory on La Palma in the Canary Islands, Spain. Its scientific emphasis is on extragalactic objects and observations at the lower end of CTAO's energy range. CTAO-South is planned for the Atacama Desert in Chile, less than ten kilometres southeast of the European Southern Observatory's Paranal Observatory. The southern array is intended to provide broad energy coverage and strong access to sources in the Milky Way, including the Galactic Centre and Galactic Plane. The system is planned to contain more than 60 imaging atmospheric Cherenkov telescopes of different sizes. Large-sized telescopes are intended to capture lower-energy gamma rays, medium-sized telescopes will provide much of the core coverage, and small-sized telescopes will extend the array's sensitivity toward the highest energies. The northern site already hosts the LST-1 prototype, while additional large-sized telescopes and medium-sized telescopes are planned or under construction. The southern site is designed to accommodate medium- and small-sized telescopes. CTAO builds on the techniques developed by earlier ground-based gamma-ray facilities, including MAGIC, H.E.S.S., and VERITAS. Its planned combination of a substantially larger collecting area, a broader energy range, improved sensitivity, and wider field of view is intended to make the observatory roughly an order of magnitude more sensitive than current-generation instruments in relevant parts of the spectrum. The observatory is also designed as an open facility: qualified researchers from the wider scientific community are expected to be able to propose observations and use its data, subject to the observatory's access policies. The scientific program extends beyond the discovery and characterization of gamma-ray sources. CTAO aims to investigate cosmic particle accelerators, active galactic nuclei, supernova-related systems, star-forming regions, galaxy clusters, transient events, and possible PeVatrons capable of accelerating particles to petaelectronvolt energies. It is also intended to support studies of dark matter, cosmology, cosmic-ray propagation, and possible departures from established principles such as special relativity. By observing photons produced by the most extreme environments in the cosmos, the project seeks to connect high-energy astrophysics with fundamental physics. The headquarters is hosted by Italy's National Institute for Astrophysics, while the Science Data Management Centre is hosted by Deutsches Elektronen-Synchrotron in Zeuthen, Germany. In January 2025, the European Commission established CTAO as a European Research Infrastructure Consortium (ERIC), giving the project a formal European legal and organizational structure. The observatory is associated with the European astroparticle network ASPERA and the Astronet infrastructure-planning community. Its identity is therefore institutional and scientific rather than commercial, with its principal value lying in shared access to unique astronomical observations and data.

The Cherenkov Telescope Array Observatory emerged from the international effort to create a successor to the first generation of ground-based very-high-energy gamma-ray observatories. Facilities such as MAGIC, H.E.S.S., and VERITAS demonstrated that imaging atmospheric Cherenkov telescopes could detect brief flashes of Cherenkov light produced when gamma rays interact with Earth's atmosphere. Those instruments opened a new observational window onto cosmic particle acceleration, but their scale, energy coverage, sensitivity, and field of view remained limited. CTAO was conceived to combine the lessons of these facilities in a much larger and more capable observatory. The core design called for two arrays rather than a single site. A northern observatory on La Palma would provide access to extragalactic targets and emphasize sensitivity at comparatively lower gamma-ray energies. A southern observatory in Chile would offer comprehensive coverage of the southern sky and focus strongly on Galactic sources. Together, the sites would provide a broad view of the gamma-ray Universe, including the Galactic Centre, the Large Magellanic Cloud, the Galactic Plane, active galactic nuclei, galaxy clusters, star-forming regions, and transient phenomena. The planned array uses several telescope classes because no single telescope size can efficiently cover the entire target energy range. Large-sized telescopes are optimized for lower-energy events, while medium-sized instruments form the principal survey capability. Small-sized telescopes extend coverage toward the highest energies. More than 60 telescopes are planned across the northern and southern sites, substantially exceeding the number found in existing gamma-ray telescope arrays. Construction and site development proceeded through an international collaboration involving research institutions and infrastructure partners. The La Palma site is located within the Roque de los Muchachos Observatory at an altitude of about 2,200 metres. The LST-1 prototype was installed there, followed by preparations for additional large-sized telescopes and medium-sized telescopes. The Chilean site was selected in the Atacama Desert near ESO's Paranal Observatory, an area valued for its high altitude, dry climate, and exceptionally dark skies. Its planned instrument mix includes medium- and small-sized telescopes. The scientific ambitions of CTAO extend beyond cataloguing gamma-ray sources. The observatory is intended to examine how cosmic systems accelerate particles, how energetic particles influence galaxies and larger structures, and how extreme transient events produce radiation. Its program also includes searches for signals associated with dark matter, studies of cosmological evolution, and tests of fundamental physics, including possible energy-dependent violations of special relativity. The resulting observations are expected to complement measurements from space-based gamma-ray missions and other ground-based observatories. The project has developed an institutional structure around shared international access. Its headquarters is hosted by Italy's National Institute for Astrophysics, and its Science Data Management Centre is hosted by Deutsches Elektronen-Synchrotron in Zeuthen, Germany. CTAO is linked with the ASPERA European astroparticle network and Astronet. In January 2025, the European Commission established the observatory as a European Research Infrastructure Consortium. This designation formalized CTAO's status as a European research infrastructure and created a durable framework for governance, membership, construction, operations, and scientific access.

• 2026

  INNA project cancellation reported

  [1]Cherenkov Telescope Array Observatoryen.wikipedia.org

  The planned INNA development near the southern CTAO site was reported cancelled, removing a proposed source of increased artificial light near the observatory.

• 2025

  CTAO receives ERIC status

  [2]Cherenkov Telescope Array Observatory official websitectao.org

  The European Commission establishes the Cherenkov Telescope Array Observatory as a European Research Infrastructure Consortium, providing a formal legal structure for the multinational observatory.

A multinational, open-access next-generation observatory for very-high-energy gamma-ray astronomy and astroparticle physics.

• Northern gamma-ray telescope array

  CTAO-North

  The northern CTAO array is situated at the Roque de los Muchachos Observatory on La Palma in the Canary Islands. Its location and telescope configuration are intended to support observations of extragalactic objects and gamma rays at the lower end of CTAO's planned energy range. The site hosts the LST-1 prototype, with additional large-sized and medium-sized telescopes planned or under construction.

• Southern gamma-ray telescope array

  CTAO-South

  The southern array is planned for the Atacama Desert in Chile, near ESO's Paranal Observatory. It is designed to provide access to the full CTAO energy range and to concentrate on Galactic sources, including the Galactic Centre and Galactic Plane. The site is planned to contain medium-sized and small-sized telescopes and will form the southern half of the observatory's all-sky scientific capability.

• Scientific instrumentation

  Imaging atmospheric Cherenkov telescope system

  CTAO's principal instrument is a distributed system of imaging atmospheric Cherenkov telescopes. The telescopes detect the brief optical flashes produced in the atmosphere by gamma-ray showers. Multiple telescope sizes are used to balance collection area, angular resolution, field of view, and energy coverage, enabling observations from tens of gigaelectronvolts to roughly 300 teraelectronvolts.

• 2025

  Adoption of European Research Infrastructure Consortium statusStrategy

  Background

  CTAO required a formal institutional framework capable of coordinating a multinational observatory, its sites, scientific users, data systems, and long-term operations.

  Action taken

  The European Commission established CTAO as an ERIC in January 2025.

  Aftermath

  The designation formalized CTAO's legal identity as a European research infrastructure and supported the organization of its international governance and operations.

  Source

• 2026

  Planned INNA project near CTAO-South reported cancelled[1]Cherenkov Telescope Array Observatoryen.wikipedia.org

  Other

  A planned AES Andes INNA megaproject, which was reported as posing a potential light-pollution risk to the southern CTAO site, was announced as cancelled on 23 January 2026.

• 2025

  European Commission establishes CTAO as a European Research Infrastructure Consortium[2]Cherenkov Telescope Array Observatory official websitectao.org

  Other

  The Cherenkov Telescope Array Observatory received formal ERIC status from the European Commission, establishing a legal framework for its European research-infrastructure operations.

1. 1Cherenkov Telescope Array Observatoryen.wikipedia.org
2. 2Cherenkov Telescope Array Observatory official websitectao.org