ALMA – A visit to the ALMA project in the Atacama Desert

Finding SOUL (I)*

On May 17, 2023, moved by curiosity and passion for astronomy, I received a special authorization to visit the ALMA astronomical complex in the province of Antofagasta, municipality of Tucanao, 50 kilometers from San Pedro, in the Atacama desert, Chile. The desert is a vast region that also covers regions of Peru and reaches up to 1,000 south of Chile. We were welcomed by the complex’s visits coordinator, Danilo Vidal, who gave us an engaging and detailed tour of the facilities and an extensive and didactic explanation about the ALMA project, whose cost reached U$ 1.4 billion.

Due to adverse weather conditions – at an altitude of 5,200 meters, rapid and extreme changes require constant monitoring and precaution – we were unable to visit the plain where the 66 high-precision antennas are installed, so we had the rare opportunity to visit one of the antennas, the which, at the time, was under maintenance.

The ALMA name and human resources.

Radio telescopes are astronomical observation instruments capable of capturing a wide range of radio electromagnetic waves. Very distant galaxies, black holes and stars, not usually visible through optical telescopes, emit large amounts of radio waves. The acronym ALMA stands for Atacama Large Millimeter submillimeter Array. The work routine of scientists, researchers, technicians and support staff is complex. There are around 200 permanent employees who live in specially built accommodation in the complex, although since the beginning of the SarsCov2 pandemic, a good part of the staff has been working remotely, generally from the Chilean capital, Santiago.

ALMA is a common project that has 21 countries in collaboration with Chile (Brazil initially participated, but withdrew from the project). Effectively, there are three major representatives that coordinate the project, the ESO (European Southern Observatory) represented by 16 European countries, NAOJ ( National Astronomic Observatory of Japan ) represented by Japan and Taiwan, and the NRAO ( National Radio Astronomy Observatory ) represented by the United States. United States and Canada.

Place

What were the criteria for choosing the location in Chile, particularly in the plain of Antofagasta? And what about the choice of location for the installation of the 66 antennas in Chajnantor? How does the height and dry air (very low humidity) of the desert favorably influence radio astronomical observations in the coldest and most distant regions of the Universe?

“The worst enemy of astronomy is not light pollution, explains Danilo, but humidity.” Water vapor in the atmosphere reacts with light and obliterates it, therefore, “the higher the relative humidity of the air, the worse for astronomy”, he summarized. The Atacama is the driest desert in the world, and the higher the altitude, the greater the atmospheric pressure and the air becomes thinner, with 90% of the oxygen found below 3,000 meters of altitude. The average altitude of the Andes Mountains is 5,000 meters above sea level. Therefore, the choice of location for the ALMA project was made, mainly or especially, due to these two geographical virtues: the very low humidity associated with the Andes mountain range, the highest on Earth. The Atacama Desert met all the conditions in a unique and exceptional way.

Light

The ALMA operating system, officially inaugurated in 2013, was designed with limits in mind. What limits? Humanity could not work with large numbers and calculations of cosmological dimensions in an artisanal way, that is to say, resources became limited the more one advanced on the magnitudes detected in the cosmos. To measure distances we have several magnitudes and units of magnitude: kilometers, meters, decimeter, centimeter, millimeter, reaching the submillimeter.

Despite the fact, admitted by our current scientific knowledge, that the complex nature of light escapes our comprehension, we understand reasonably some of its properties: light is an electromagnetic wave that spreads through vacuum, it is also a particle of space that transports energy. This dual nature of light (wave-particle, electric and magnetic) has a wave amplitude that is usually measured in Hertz. What we can do is calculate the length of this wave, also known as hertzian waves. Their frequencies are lower than infrared waves, ranging between 300 GHz (3.0×10 ¹¹ Hz) and 3 kHz (3.0×10 ³ Hz).

What we capture through our vision, and we call light, is just a limited spectrum of it. Visible light comprises only a small fraction of the electromagnetic spectrum in the region of about 380 nanometers (violet) to 770 nanometers (red) in wavelength. The real light phenomenon is greater than what we can see. Our brain is what transforms the information we receive through the eyes and interprets each spectrum of light as a “color”. The lower the wave frequency, the energy will also be lower. They propagate in vacuum with the speed of light (approximately 3.0×10 ⁸ meters per second). What radio telescopes basically do is “see” and record light in the range of radio waves.

Telescopes and radio telescopes

Generally, the lay public in astronomy does not understand why the most distant astronomical bodies cannot be reached through mere eye inspection, but only through the radiation emanating from these bodies. Evidently, for the non-specialized public, everything that defies common sense is more difficult to understand. For example, in the case of radio telescopes, why were lenses and mirrors replaced by very sophisticated light wave detectors? It is worth mentioning that it would be very important to expand communication strategies to popularize and disseminate discoveries in radio astronomy.

Common telescopes, even the most modern ones, basically use reflection and refraction. The larger the size of a telescope’s mirror, the more photons are captured, and therefore accumulate more information. The larger the diameter of the telescope, the more light it captures. However, there are clear limits, since even if we managed to produce much larger mirrors, there would still not be enough technology to build, for example, a telescope with a mirror 2 kilometers in diameter.

Radiotelescope and radio interferometer

I expose more details of what a radio telescope means and the methodology of a radiointerferometer, and what are the main differences from common telescopes, even the most sophisticated ones, and how the idea of the “Array” arises.

This means clarifying for the public how the methodology was made possible due to the limitations of building telescopes with sufficient diameters to capture the incidence of light waves/radiation within the spectrum that ALMA proposes to capture.

What each ALMA radioteleoscope unit can detect is this spectrum of millimeter and submillimetre light. The expression ” Array ” refers to an ” ordered set of information ” that allows a greater angular resolution and that works analogously to a wide angle lens creating the effect of zoom. In ALMA, this set was elaborated through the installation of 66 antennas, 54 of them with 12 meters in diameter, distributed in a vast region of 16 kilometers. The “radar network” is interconnected to, forming a “functional unit”, apprehend information coming from the most distant and coldest regions of the Universe. This ordering, also known as interferometry in the case of ALMA, simulates a “mirror” or a “field” with a diameter of 16 kilometers, which makes ALMA the largest radio telescope system in the world.

Pioneering spirit and scientific protagonism

The ALMA project was a world pioneer when it assumed the coordination to manage to process the first image of a black hole. Needless to explain what was its importance for the world scientific community, and for the expansion of knowledge in astrophysics and cosmology. Especially in scientific research into the origins of the Universe.

ALMA’s findings hold an impressive average of one scientific paper per day, usually published in the main peer reviewer scientific journals in the world and according to Vidal, for its leadership and capacity for agglutination and cooperation between researchers in relation to astronomical phenomena linked to the beginnings of the Universe , ALMA has also been known as “The United Nations of World Astronomy”

One can list, by way of example, some of his main discoveries and revolutionary breakthroughs at ALMA: formation of planetary disks, nebulae, star nurseries, discovery of the oldest spiral Galaxy ever detected (https://almaobservatory.org/ en/press-releases/alma-discover-most-ancient-galaxy-with-spiral-morphology/2021), the discovery of the presence of oxygen in galaxies 13.2 billion years old ( https://alma-telescope.jp/en /alma10th/galaxy-formation ). In August 2014, the laboratory managed to detect an important molecule (acrylonitrile) in the atmosphere of Saturn’s moon, Titan, ( https://alma-telescope.jp/en/alma10th/molecule ) and also revealed the main chemical components derived from hydrogen, in the tail of a comet. And the investigation, mentioned above, which resulted in the most famous, although according to some, not the most important: it was through the ALMA project that it led the processing of the first image ever made of a black hole. The iconic photograph became a symbol of the project’s power to elucidate and consolidate its role in leading research on the origins of the Universe.

For anyone visiting the project, it will be inevitable to make some reflections and philosophical considerations on the developments of the ALMA project on other prospects and developments of research on the origin of the Universe. An apparently paradoxical aspect that emerged from this visit: verifying that the very advanced technology to detect the greatest cosmic phenomena and the probing of infinity, which researches unimaginable magnitudes and which go beyond our capacity for mathematical representation, depend on the detection of an almost invisible, of aspects of reality that escape our sense of perception.

the scientifically mysterious

On ALMA’s official website: “The ultimate question of the human species: will there be life beyond Earth?” Drawing attention to this unavoidable theme is more than a provocation, and the question is reaffirmed through the evocation of the paradox proposed by Enrico Fermi (1901-1954) : in the face of so many probabilities, why do we still not have a single unequivocal evidence of the presence of life off Earth to date?

For those who had the privilege of visiting the place, it becomes inevitable, almost mandatory, to resort to a new question: “Could it be that the more you try to elucidate the Universe, the more scientifically mysterious it becomes?”

Those interested in astronomy can access the official ALMA website for more information.

Special thanks to Silvia and Iael Rosenbaum, Hotel Explora, Projeto ALMA and Danilo Vidal

*Photos taken on site by the author.