Construction of the world’s largest telescope begins

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Among the number of packages sent for Christmas this year, there were 18 that make many scientists (not only) happy. They left France and traveled over 10,000 kilometers between land and sea. Destination: Cerro Amazones, Atacama Desert, Chile No bubble wrap, silica gel bags and express courier, but temperature controlled containers with air cushions, anti-shock systems and dry nitrogen cases to prevent the slightest condensation. Content? Hexagonal mirrors with a diameter of 1.4 meters. More than a special shipment, given that these are the first 18 pieces – out of 798 – that will make up the exceptional mosaic: main mirror (M1) from ben 39 meters in diameter from what will one day be built the largest optical telescope in the world. Which was called for a reason Extremely large telescope (Elt).

Estimated completion: 2028

To understand the scope of this new toy European Southern Observatory (Ace) just think that his little brother ie A very large telescope – another Polyphemus ESO, which is currently the most advanced optical telescope ever – consists of 4 primary mirrors, each “only” 8.2 meters in diameter. And that the largest telescope ever built, Gran Telescopio Canarias (in La Palma), has a primary mirror of 10.4 meters. If these numbers say little, here are some more they will be able to help you understand what we are talking abouto: The ability of an extremely large telescope to capture light will 100 million times that of the human eye and 20 times that of a very large telescope unit. This explains why the arrival of these 18 parcels in Chile is news. The eye of the new super telescope will be pointed to the sky by the end of this decade – in 2028, if all goes according to plan – to collect new information about exoplanets, distant galaxies, black holes, dark matter, among the basic projects. from Astronomy of the Future (here’s the trailer).

Pioneering optical design

The field of view will be 10 minutes of arc: the light will be collected by a flat plane 978 square metersand it will manifest itself in others as well 4 secondary mirrors before it gets to the instruments that will help scientists understand photons. As the National Institute of Astrophysics (INAF) explains, ESO’s ELT will actually have a pioneering five-mirror optical design. Specifically, “M4 will be an adaptive and flexible mirror that adjusts its shape thousands of times per second to correct distortions caused by air turbulence.” And this is just part of the technological adventure that also sees Italy at the forefront.

History

From the conception of the new European giant almost 18 years have already passed. The idea actually dates back to 2006. It took 4 years to choose a place to build it, Cerro Amazones, a barren mountain in the Chilean Andes over 3 thousand meters high, in the central part of the desert where the sky is always clear, about 23 kilometers from Cerro Paranal, home of the Very Large Telescope. Site preparation began 10 years ago, in 2014, and construction of the exterior structure in 2018, when the first hexagonal piece of the main mirror was also forged in Germany. Mirrors then they were sent to Francefor the sophisticated and long polishing phase, which began in 2023. The irregularities of the mirror surface – ESO explains – must be less than 10 nanometers (less than one-thousandth the width of a hair): the level of precision achieved by sweeping a surface with a beam of ions, atom by atom.

Facts and interesting facts about ELT

Now that I’m in Chile, segments will be covered by one very thin layer (150 nanometers) of silver, and once assembled, the relative positions of all the hexagons will be detected by more than 4,600 sensors, again to minimize errors. For anyone wondering why such a complex system was created, here it is explanation: Even with the best glass processing techniques, casting a telescope mirror larger than about 8 meters is hardly feasible, he explains Inverse.com. As INAF always reminds us, the idea of ​​a multi-segment mirror comes from Italy: it was a Jewish astronomer from Trieste Guido Horn D’Arturo (1879-1967), without whom the creation of these gigantic astronomical observatories would not have been possible. For lovers of details and curiosities, there are plenty of them on the ELT site. For example, approximately 30 million screws and bolts, 500 kilometers of cables and 1,500 kilometers of optical fiber will be needed. The building will have a height of 90 meters and a diameter of 80: a rotating structure of over 3,000 tons. And the walking time from the entrance to the top of the dome will be about half an hour.

The role of Italy and the search for extraterrestrial life

Returning to the role of Italy, the construction of the dome and the mechanical support structure of the telescope is entrusted consortium created by the Astaldi, Cimolai and EIE groups (with the largest contract ever awarded for a ground-based telescope worth €400 million). Above all, however National Institute of Astrophysics leads consortia for the construction of two essential tools: a multiconjugate adaptive optical system Morpheus (another tool for correcting atmospheric distortions) and a high-resolution spectrograph Andywhich will capture the “signature” of the first stars that appeared in the universe, will measure with greater precision the acceleration of the expansion of the universe, identify possible deviations in the basic physical constants and will look for signs of life from distant Earth-like planets.

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