In the middle of the driest desert in the world, 3,000 meters above sea level, the skeleton of a steel dome, as wide as the sand of the Roman Colosseum and almost as tall as Big Ben, interrupts the reddish Atacama wasteland ( in northern Chile). The structure erected on Mount Armazones will be the dome of the ELT (Extremely Large Telescope), and as its name indicates, it will be the largest telescope on the planet capable of detecting visible and infrared light. It is the star project of European Southern Observatory (ESO) —an organization that brings together 16 countries of the old continent, Australia as a strategic partner and Chile, as host—, and plans to see its first light in 2028.
“When the ELT begins to operate, anything we find beyond will prove that everything we know is wrong,” predicts German astronomer Elyar Sedaghati from Paranal Hill, a remote Chilean location with a landscape more similar to Mars than Earth. . ESO has located there the giant telescopes that make up the VLT (Very Large Telescope), which is currently the largest optical-infrared observatory in the Southern Hemisphere and the second in the world, after Mauna Kea in Hawaii (USA). .
There is a tradition among astronomers at the Paranal Observatory of gathering to watch the sunset next to the VLT. The murmur of their conversations and the strong breeze hitting their windbreaks is the only thing that can be heard at the top of the mountain, more than 2,600 meters high and two hours by car from the nearest town. The sun sets over a blanket of thick, compact clouds that, tinted orange by the last rays, blend in with the sea. When the Pacific Ocean does appear clearly on that horizon, it means that the clouds are too high and will make it difficult to observe the universe at night.
The future plan of the European Southern Observatory is to complement the work of the VLT, operational since 1999, and the ELT, which is halfway through its construction process. The strength of the former is provided by its four 8.2 meter diameter optical telescopes. The second will largely come from its main mirror, 39.3 meters in diameter, made up of 798 segments that are being manufactured in different European countries. “The observation capacity of this telescope must be thought of as when you are on the road and you see a car on the other side. From a distance, the two headlights look like a single point, but if you get close enough you can make out that there are two. How far away can you identify them? It depends on the size of the eye diameter. The diameter of the telescope is the same, they are eyes looking at the sky,” explains Italian astronomer Eleonora Sani, who was part of the team that made observations of the first kilonova, the most important discovery of 2017, according to the scientific magazine Science.
To put into perspective what the ELT will be able to do, Spanish astrophysicist Juan Carlos Muñoz compares it to the very powerful James Webb Space Telescope (JWST): “The ELT is going to have a diameter about six times larger than large and a light-collecting capacity almost 30 times greater, which will allow even the first galaxies at the dawn of the universe to be seen in greater detail.” He also anticipates that it will open the door to knowing if the Milky Way’s black hole rotates and if so, at what speed. “For that we need to see very faint stars that pass very close to the black hole. By combining the VLT tools with those that the ELT will have, we will be able to map the orbits of those stars in three dimensions to find out,” he points out. “It’s going to be a revolution. Not just one step [para la humanidad]it will be a leap,” adds an enthusiastic Sani.
What do you hope to find? Elyar Sedaghati, whose field of research is the atmosphere of exoplanets, points out that current data is too limited to develop theories about them. “I have the feeling that when we start observing them with the ELT we are going to realize that our theories, which basically work with one-dimensional models, are completely inadequate and that we have to start developing three-dimensional models, incorporating climate theory,” he maintains, in the hope that the future most powerful telescope on Earth will help explain how the atmospheres of other worlds can exist, and how they circulate. Taking it to a more general level, Sedaghati adds: “We are actually very ignorant about how galaxies evolve over billions of years.”
The construction of the ELT began in 2017 and by mid-2023, 50% of the tasks of that macroproject were completed. The construction managers explain that the first half took a long time because it involves many prototypes and tests, in addition to the stoppage due to the pandemic, but that the second phase “should be much, much shorter.” The 798 segments that will make up the main of the telescope’s five mirrors, as well as other parts of the optical instrument, are being manufactured in different countries in Europe and will begin to arrive in Chile in the first half of 2024. The German Tobias Müller, director of ELT assembly, integration and verification projects, estimates that they will take one day for each of the hundreds of mirror segments that arrive, which must be cleaned and installed mechanical components, such as sensors and cables: “This has not been done never. It is a process that can be the beginning of an industry.”
The dry environment and high altitude of the Atacama Desert, together with the lack of light pollution and a sky that is clear 300 days a year, are the perfect cocktail for observing the cold universe, invisible to conventional telescopes. And it also offers a clear spectacle to the naked eye, to the eyes of anyone curious to observe the sky.
Once the sun sets and the Andes and the Pacific disappear into darkness, you don’t have to look up to find several million stars. Just look in front, to the side or behind to see them. Against this backdrop, shooting stars, for example, are not looked for: they appear, and continually. The small and large Magellanic clouds can be seen in detail, two dwarf galaxies that orbit like satellites around the Milky Way, taking at least 1,000 million years to complete their orbit. The constellation of Orion also stands out, and in it the red supergiant Betelgeuse, a star much larger than the Sun and which is almost at the end of its life.
The Milky Way, invisible from many locations due to light pollution, shines over the Paranal observatory. Only the lasers ejected by one of the VLT’s telescopes interrupt the starry panorama. With these instruments, it was confirmed that there is a supermassive black hole in the center of our galaxy, in research that received the Nobel Prize in Physics in 2020. From that same esplanade it is impossible to see the gigantic skeleton of the 6,000-ton dome of the ELT, located just 20 kilometers away. However, astronomers, accustomed to the illusion produced by what is imperceptible to the eye, say they wait with hope because they know it is there.
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