Some 250 scientists and officials gathered in La Palma, Spain, to mark the completion of a giant telescope complex designed to study the most energetic light in the universe. The ceremony celebrated the finish of four 23-meter-diameter telescopes that make up the Large-Sized Telescope (LST) sub-array at the Roque de los Muchachos Observatory.
The LSTs are the most sensitive instruments in the world for observing gamma rays at energies between roughly 20 GeV and 3 TeV. They work by detecting the faint flashes of Cherenkov light produced when very high-energy gamma rays interact with Earth's atmosphere. By observing the same gamma-ray showers simultaneously from multiple directions, the four telescopes together provide improved sensitivity, angular resolution, and energy reconstruction.
The first LST, known as LST-1, was built in 2020 and has already completed observations of pulsars, studies of active galactic nuclei at cosmological distances, and rapid follow-up observations of transient phenomena such as novae and gamma-ray bursts. The three new telescopes now join LST-1 to form a fully operational sub-array.
«The completion of the LST sub-array is the culmination of more than 15 years of international collaboration and technological innovation,» said Japanese astrophysicist Masahiro Teshima, principal investigator of the LST collaboration. «These telescopes will allow us to explore some of the most extreme environments in the universe, including supermassive black holes, neutron stars and the nature of dark matter.»
The array's sensitivity to the lowest-energy gamma rays will enable astronomers to detect and study bright gamma-ray bursts at high redshift, potentially extending gamma-ray observations to sources at redshifts of around z∼4. That capability could provide new insights into the early universe, when the first stars and galaxies were forming.
The LST sub-array forms part of the larger Cherenkov Telescope Array Observatory (CTAO), which when fully operational in 2028 will cover energies from 20 GeV to 300 TeV and become the world's most powerful observatory for gamma-ray astronomy. The CTAO will consist of six LSTs, 23 Medium-Sized Telescopes operating between 80 GeV and 50 TeV, and 37 Small-Sized Telescopes working between 2 TeV and 300 TeV.
The 66 telescopes will be distributed between two sites: CTAO-North at La Palma and CTAO-South at the Paranal Observatory in the Atacama Desert in Chile. The LSTs form the low-energy core of CTAO-North, and over the coming years they will undergo commissioning and be integrated into CTAO operations.
The completion of the LST sub-array represents a critical milestone for the global astrophysics and astroparticle physics communities. It also marks a step toward full scientific operation of the CTAO, a project that has drawn contributions from research institutions worldwide.
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