2024-02-10 15:19:44

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[EN VIDÉO] ELT: discover the European Giant Telescope The European Giant Telescope should be ready in 2025 to offer us unprecedented images…

In 2023, while the routine activities of the James Webb Space Telescope had captivated the attention of the general public in the field of astronomy, a major project was taking place on Earth, at the summit of Cerro Armazones, in the Chilean desert of Atacama, at more than 3,000 meters above sea level. It is here that the European Southern Observatory (ESO) is building the largest terrestrial telescope ever planned, theEuropean Extremely Large Telescope (ELT). Equipped with a 39-meter segmented mirror, this observatory, scheduled to enter service in 2028, promises a revolution in the field of astronomy.

Started in June 2014, the constructionconstruction of the ELT, “is progressing in accordance with forecasts”, explains Guy Perrin, astronomerastronomer at the Paris Observatory, in charge of astronomy and space research at the MESR (Ministry of Higher Education of the research) and, as such, a member of the ESO Council. To date, the observatory is more than 50% complete. The work “to finalize the remaining 50% should be much faster than that of the first half”. The ESO expects the telescope to be fully operational within four years, with “first technical light expected in spring 2028 and from fall 2028 the start of the first scientific observations with the Micado instrument.” The CNRS emphasizes that Micado will “capture high-resolution images of the UniverseUniverse in the near infraredinfrared. It will be essential for identifying exoplanetsexoplanets, revealing the detailed structure of distant galaxies, and studying individual starsstars in nearby galaxies. Micado will also represent a powerful tool for exploring environments where gravitational forces and the effects of general relativity are extremely strong, such as near the supermassive black hole at the center of our Galaxy, the Milky Way.

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Initially, a 100 meter telescope!

It was at the very beginning of the 2000s that ESO focused on the development of a giant terrestrial telescope, that is to say with a mirror measuring at least several tens of meters. The first concept studied is that ofOverWhelmingly Large Telescope (OWL), a telescope with a diameter of 100 meters! But although this project proved unfeasible due to very strong technological constraints and a significant financial risk, it did not discourage the ESO from equipping itself with a giant observatory.

The ESO therefore opted for a more realistic project. This will be the ELT with a 42 meter mirror, ultimately reduced to 39 meters for budgetary reasons, but with minimal scientific impact compared to the initial 42 meter configuration.

The observatory dome takes shape

The civil engineering works are almost complete. They involved the “leveling of the summit on which the observatory rests and the construction of its foundations.” To minimize vibrationsvibrations, “the observatory is built on huge springs which act as shock absorbers”. To date, the steel dome is “practically finished, missing only its doors and its cladding”, while the central pillar intended to “accommodate the metal structure of the telescope is already in place”.

As for the main mirror, the M1M1, which cannot be manufactured in a single piece, “it is made up of 798 hexagonal segments and made up of 6 identical sectors of 133 segments”. One hundred and thirty-three replacement segments will also be produced. In December 2023, the ELT Technical Center received the first 18 segments of the mirror where they will be prepared for their future installation on the main structure of the telescope. “Each of these segments measures 1.4 meters in diameter and approximately 5 centimeters thick, and is covered with a thin layer of silversilver which is in turn covered with a protective layer. »

Cutting-edge scientific instruments

As for scientific instruments, ESO has planned six which can be divided into two phases. There are “those of the first phase (phase 1), four in number, whose financing is essentially included in the overall ELT budget, unlike the two instruments of phase 2 which are financed by two distinct consortia. Each instrument, “the development of which spans around twenty years”, is planned to have a “lifespan of at least 10 years and represents a technological leap compared to the instruments in service today”. This development time “can be compared to that of a space mission, highlighting the avant-garde character of each instrument”.

The phase 1 instruments are Micado, a near-infrared and visible spectro-imager, Morfeo adaptive optics dedicated to Micado but which can be used for other instruments in the future, an integral field spectrograph (Harmoni) with its laser-laser tomography-tomography adaptive optics system, as well as Metis, a spectro-imager coupled to a mid-infrared coronagraphcoronograph. As for the two phase 2 instruments, they are Andes, a spectrograph allowing the study of a wide spectral band with high resolution, and Mosaic, a multi-object spectrograph operating in visible and near-infrared light.

Micado, Harmoni and Metis “will be gradually put into service from the first technical light of the ELT”. Those of phase 2 “will arrive a few years later”. As the ESO points out, it is planned that subsequently “other instruments will be installed to take into account new needs or integrate new technologies”.

The minimal impact of climate change on local weather

Despite the challenges posed by climate changeclimate change, the observatory site is “still well preserved from major climatic disturbances until now”. However, with the El Niño phenomenon, which occurs on average every four years, local meteorology can ” degrade site performance for a few months “. Regarding human activity, although astronomers have noticed an increase in the brightness of the skies at the Paranal and Amazon mountains, the ESO sites are “located in areas protected by the Chilean state that benefit from restrictions aimed at minimizing light nuisance for observations”.

Giant American telescopes shut down

Unlike the giant American observatories Giant Magellan Telescope et Thirty Meter Telescopewhose construction has been suspended for years due to financing problems and local opposition for the TMT in Mauna Kea (Hawaii), the ELT project was able to overcome various obstacles, including those related to financing, the pandemicpandemic of Covid-19Covid-19, the situation in Ukraine and the increase in costs of raw materials.

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