The inauguration on La Palma

On 15 October 2026, scientists and officials gathered at the Roque de los Muchachos Observatory on La Palma in the Canary Islands to inaugurate the four Large-Sized Telescopes (LST) at the northern site of the Cherenkov Telescope Array Observatory (CTAO). The Instituto de Astrofisica de Canarias (IAC) said 250 scientists and representatives of research institutions from around the world took part. Each telescope has a 23-metre primary mirror and ultrafast cameras built to catch the faint Cherenkov flashes that appear when very high-energy gamma rays strike the atmosphere. The four instruments join LST-1, a prototype that has operated since 2020. IAC director Valentin Martinez Pillet called the start of operations a significant scientific milestone and a demonstration of the observatory's capacity to host this kind of infrastructure.

Detection range and speed

The LST cover gamma-ray energies from roughly 20 gigaelectronvolts (GeV) to several teraelectronvolts (TeV), which the IAC describes as the most sensitive instruments in the world for that band. Very high-energy gamma rays are increasingly absorbed as they cross the universe, so the low-energy threshold lets researchers study sources at cosmological distances and look further back in cosmic history, to around 12 billion years ago. Each telescope stands 45 metres tall, weighs about 100 tonnes and can turn to any point in the sky in roughly twenty seconds. That agility is designed for transient events such as gamma-ray bursts and other short-lived stellar events. Operating together, the four telescopes can observe the same gamma-ray cascades from different directions, which improves sensitivity, angular resolution and energy reconstruction.

Italian and Spanish contributions

The Italian National Institute for Astrophysics (INAF) and the National Institute for Nuclear Physics (INFN) helped build the infrastructure. INAF worked on carbon-fibre structures and detection cameras for the northern site, while INFN designed components for the planned southern site in Chile. INAF also hosts the CTAO central office in Bologna. INAF's Lucio Angelo Antonelli, co-principal investigator of the LST collaboration, said Italy is contributing to most of the observatory's instruments.

“Today marks a very important step forward toward the realisation of CTAO, to which Italy contributes a wealth of scientific, design and industrial capabilities.”

Antonelli added that Italy will also build two more Large-Sized Telescopes and 37 Small-Sized Telescopes at the southern site. On the Spanish side, the Instituto de Astrofisica de Andalucia (IAA-CSIC) coordinated the development of data-analysis software for the four telescopes. Secretary of State for Science Juan Cruz Cigudosa and general secretary for research Eva Ortega visited the installations, and IAA director Olga Munoz described the milestone as the start of a new and exciting stage in studying the universe's most energetic phenomena.

Scientific goals

LST collaboration spokesperson Masahiro Teshima described the completion as the culmination of years of joint work.

“The completion of the LST subsystem is the culmination of more than 15 years of international collaboration and technological innovation.”

Teshima said the telescopes will study supermassive black holes and neutron stars, probe possible origins of cosmic rays and contribute to research on the nature of dark matter. Nobel physics laureate Takaaki Kajita, who received the 2015 prize for the discovery of neutrino oscillations, spoke at a briefing on the telescopes. He focused on multimessenger astronomy, which combines gamma rays, neutrinos and gravitational waves. He used the merger of two neutron stars as an example, since such a merger produces gravitational waves and several forms of radiation.

“Whenever we have opened a new window on the universe, we have discovered phenomena we did not expect.”

Kajita said alerts from gravitational-wave detectors such as LIGO, Virgo or KAGRA, or from neutrino observatories, could trigger an immediate search for gamma-ray counterparts. He also argued that detections by the LST could direct other observatories to the same point in the sky for study in visible light, radio and other wavelengths.

Scale of the observatory

The CTAO will eventually include more than 60 telescopes spread across two sites, the northern one on La Palma and the southern one at Paranal in Chile. The four LST completed on 15 October form the core of the northern site. The sources describe the event as a step toward the full scientific operation of the observatory, which has not yet been reached.