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La Palma completes quartet of large gamma-ray telescopes

Three new instruments join the existing telescope to study high-energy phenomena in the universe.

The quartet of large telescopes at the northern Cherenkov Telescope Array Observatory was inaugurated on La Palma on Thursday. Three new instruments join the existing LST-1. This completes a specific part of the international research project, although the full observatory is still under development.

The ceremony took place at the Observatorio del Roque de los Muchachos on the Spanish island. The Italian research institute INAF and the University of Nova Gorica report the opening on 15 October. Spanish broadcaster Cadena SER confirms the gathering in a report on the participation of the University of Jaén. It marks the completion of the group of Large-Sized Telescopes, abbreviated to LST, at CTAO's northern site.

Each of the four instruments has a mirror 23 metres in diameter. They are intended to study gamma rays: very high-energy electromagnetic radiation associated, among other things, with extreme processes around black holes and neutron stars. However, the telescopes do not capture ordinary images as a camera does. They detect extremely brief flashes of light produced when gamma rays enter the Earth's atmosphere.

This interaction produces a shower of secondary particles that causes faint flashes of light. This so-called Cherenkov radiation lasts only a few billionths of a second, the University of Nova Gorica explains. By measuring the same particle shower from different positions, researchers can reconstruct the direction and energy of the original gamma rays. The atmosphere thus forms part of the measurement method, rather than solely an obstacle between the telescope and the universe.

The progress marked by this opening lies specifically in the four telescopes working together. According to INAF, researchers can reconstruct the same phenomenon more accurately by viewing it from multiple directions than with a single instrument. Researchers therefore expect to be able both to distinguish fainter sources more clearly and to determine the origin and energy of the radiation more precisely. These are instrumental capabilities; the opening itself is not yet a new astronomical discovery.

The large mirrors are primarily intended for the lower energy range within gamma-ray astronomy. This is relevant to distant sources, because higher-energy radiation can be absorbed as it travels through the universe. The telescopes can also turn quickly to a different position. According to the institutes involved, this takes less than twenty seconds. This allows them to respond to short-lived phenomena whose timing is not known in advance.

The project is not starting entirely afresh. LST-1 was inaugurated in 2018, according to the Spanish research institute IFAE. INAF describes how this first telescope already produced scientific observations during its testing phase. The three additions build on that work. This distinction prevents the ceremony from being presented as though no research had been possible at this site until Thursday: what is new is chiefly the complete quartet working together.

CTAO encompasses more than these four instruments. The plan provides for different telescope types at a northern site on La Palma and a southern site in Chile. The newly opened group is therefore a completed part of a larger observatory under construction. The encouraging result is concrete: the research infrastructure has been expanded and construction of this quartet is complete. Future observations will have to show what discoveries follow.

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