From ESOblog (EU): “Ten years exploring the cold dark universe”

From ESOblog (EU)


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European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte] (EU) (CL)

Antennae Galaxies

On the Ground

8 October 2021

Ten years ago this week, the Atacama Large Millimetre/submillimetre Array, also known as ALMA, officially opened to astronomers for “early science”. The occasion was marked with the publication of its first images, revealing the swirling gas in the colliding Antennae Galaxies. Since then, ALMA has detected complex molecules, discovered discs where planets are forming, and has even helped give us the first glimpse of a black hole. To find out more about how this ambitious project came to be, we spoke to Richard Hills, ALMA Project Scientist; Itziar de Gregorio-Monsalvo, ESO Staff Astronomer when ALMA started operating and now Head of the Office for Science in Chile; and Paola Andreani, Head of the European ALMA Regional Centre at that time and now Head of the Office for Science in Garching.

At 5000 metres above sea level, high in the Chilean Andes, the Chajnantor plateau is one of the loneliest places on Earth. It is, however, home to ALMA, a giant array of 66 antennas spread over 16km, turning their great white heads in graceful unison to look deep into the distant Universe.

“What we can see with ALMA is the cold Universe, regions dark to our eyes but that shine bright at millimetre/submillimetre wavelengths,” explains de Gregorio-Monsalvo. “With ALMA we can mainly see cold dust and gas coming from different regions of the Universe, from very distant galaxies to nearby objects, revealing with unprecedented detail how galaxies, stars and planets form and evolve, and the building blocks of life.”

This panoramic view of the Chajnantor Plateau shows the site of the Atacama Large Millimeter/submillimeter Array (ALMA), taken from near the peak of Cerro Chico. Babak Tafreshi, an ESO Photo Ambassador, has succeeded in capturing the feeling of solitude experienced at the ALMA site, 5000 metres above sea level in the Chilean Andes. Light and shadow paint the landscape, enhancing the otherworldly appearance of the terrain. In the foreground of the image, clustered ALMA antennas look like a crowd of strange, robotic visitors to the plateau. When the telescope is completed in 2013, there will be a total of 66 such antennas in the array, operating together.

ALMA is already revolutionising how astronomers study the Universe at millimetre and submillimetre wavelengths. Even with a partial array of antennas, ALMA is more powerful than any previous telescope at these wavelengths, giving astronomers an unprecedented capability to study the cool Universe — molecular gas and dust as well as the relic radiation of the Big Bang. ALMA studies the building blocks of stars, planetary systems, galaxies, and life itself. By providing scientists with detailed images of stars and planets being born in gas clouds near the Solar System, and detecting distant galaxies forming at the edge of the observable Universe, which we see as they were roughly ten billion years ago, it will let astronomers address some of the deepest questions of our cosmic origins.

ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte](EU)(CL), on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

As a project, ALMA is unprecedented both in scale and in its pioneering example of international collaboration in astronomy. Despite the isolation of its surroundings, it was the coming together of different cultures and organisations that made its conception possible. But it wasn’t always going to be that way…

“The ALMA project was a dream that various astronomers across the world began to form back in the 1990s”, explains Hills. “A lot of people working in the field [of millimetre-wavelength astronomy] realised that they needed a much bigger telescope and, in particular, a telescope that used lots of relatively large antennas spread over a really large region.”

Such a telescope is called an interferometer, which works by combining the light from each of its antennas to discern much finer details than would be possible with an individual antenna. The technique is notoriously challenging — “Interferometry is a very tricky beast!” confirms Andreani.

Initially, three separate groups in Europe, Japan and the USA developed plans for such a telescope. But it soon became apparent that the best way to realise this dream would be to merge these projects, creating one large facility instead of three separate ones. The three major astronomical institutes that agreed to undertake this ambitious project were ESO in Europe, the National Radio Astronomy Observatory (NRAO) in the USA, and the National Astronomical Observatory of Japan (NAOJ) in East Asia. The three partners also shared the construction of the antennas, with slightly different designs but ultimately the same specifications. ESO and NRAO would provide 25 12-m antennas each, and NAOJ would contribute 4 12-m antennas and 12 7-m ones.

Once the partners had come together and the plans for the three projects were developed into a single telescope design, ALMA started to come to life in 2001, with plans for a 10-year construction period. Working as a Project Scientist, Hills was able to experience first hand some of the challenges and triumphs of this process. “I think the original plan back in 2000 was that we would be ready for this so-called early science period, in 2007, and by 2007 we hadn’t even got the first antenna!” he says.

Fortunately after a slow start, ALMA’s construction quickly picked up pace. “There was no time to be bored!” says de Gregorio-Monsalvo. “There were so many things to develop and test to make ALMA possible that the first light seemed really far-off. But thanks to the effort of a great team the goal was achieved.”

Assembly of the first European antenna.
Credit: S. Rossi/ESO/ALMA.

A European Atacama Large Millimeter/submillimeter Array (ALMA) antenna takes a ride on Lore, one of the ALMA Transporters, at the 2900-metre altitude Operations Support Facility in the Chilean Andes. This took place on 23 June 2010, and was the first time that European antennas have been lifted with the transporters, a procedure that was fully successful, with both moves completed in a single day.

The first two European antennas for ALMA have been moved to two new outdoor foundation pads in order to perform tests of their dish surface accuracy. In this process, known as holography, the antennas observe the signals from a special transmitter located on a nearby tower. In order to allow parallel assembly of several antennas, two new foundations have recently been built. As the newly built foundations lie between the original positions of the two antennas and the holography tower, the antennas were moved to the new locations.

In September 2011, ALMA opened for its “early science” period, with astronomers from across the globe able to use the new telescope for the first time. At this time only 16 of the eventual 66 antennas were available to use. Even then, ALMA was still bigger in scale than any previous interferometer and the excitement among the astronomical community was palpable. To observe with ALMA –– or any other telescope –– astronomers must submit proposals that are evaluated by a panel of experts; only a few will be successful. For this first observation period, ALMA received over 900 proposals, but only around 100 were selected!

Data from the first “early science” observing night arriving at the consoles in the control room.
Credit: I. de Gregorio-Monsalvo.

“The thing that was amazing was that as soon as all the equipment came together, everything worked more or less out of the box,” remembers Hills. “The first images came out and the scientific results started to flow. The results were fantastic –– well beyond our expectations in many cases.”

“It was amazing in terms of human relation and amazing in terms of scientific discovery.” agrees Adreani.

De Gregorio-Monsalvo also remembers how she felt at ALMA first light: “It was very rewarding for me and I felt very proud of myself and of my ALMA colleagues. When I saw the first light I thought that all the invested effort and all the sleepless nights had been worth it.”

During the construction of ALMA in Chile, other challenges were being tackled behind the scenes as the ALMA partners worked to define how the observatory would be operated. Three ALMA Regional Centres (ARCs) were created to interact with astronomers worldwide. “It was the first time that a big international facility built this kind of user support mode which was spread around,” says Andreani. “The main difficulty really was to communicate, and to convince people that we are always working towards the same goal — we all wanted to make this facility work and be successful. We built the entire operation. The first years were pretty intensive. We set up all the procedures, we agreed on all the policies, we wrote all the documents which are now available both for public and for internal purposes,” she says.

Ultimately the leap into the unknown regarding the organisation of ALMA paid off and Adreani felt the ARCs were especially successful. “I see that still the people supporting the users are doing a wonderful job, they are offering more and more help. I think it’s now a model which many other facilities are copying.”

Now, a decade after it opened for early science, ALMA has been at the forefront of many discoveries. “My favourite scientific discovery made by ALMA was the image of the dust disc surrounding the young star HL Tau, revealing the planetary genesis,” says de Gregorio-Monsalvo. “I still remember the awed silence of the team after we saw that image for the first time!” Hills agrees: “When that first came out it just blew our minds.”

ALMA image of the protoplanetary disc around HL Tauri.

This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system. Credit: ALMA (ESO/NAOJ/NRAO).

Messier 87*, The first image of the event horizon of a black hole. This is the supermassive black hole at the center of the galaxy Messier 87. Image via The Event Horizon Telescope Collaboration released on 10 April 2019 via National Science Foundation(US).

Another scientific highlight with ALMA is the role it played in the Event Horizon Telescope Collaboration to deliver the first image of a black hole, the supermassive black hole at the heart of the M87 galaxy. This was an impressive feat, as it required combining data gathered by several radio telescopes all over the world, functioning as a single planet-sized facility. “When we built the telescope we knew the science specifications that needed to be reached, but we were not prepared to see transformational science in just one single image,” says de Gregorio-Monsalvo.

“Indeed it is delivering very astonishing results in all astronomical fields,” adds Andreani.

In addition to its scientific achievements, all the scientists agree that ALMA has been a triumph of cooperation on a global scale. “It holds up as an example of international collaboration paying off. It certainly couldn’t have been done in its successful form by a single one of the partners,” says Hills.

See the full article here .


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European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte] (EU) is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte] (EU) is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design,

ESO Very Large Telescope 4 lasers on Yepun (CL)

European Southern Observatory(EU)/MPG Institute for Radio Astronomy [MPG Institut für Radioastronomie](DE) ESO’s Atacama Pathfinder Experiment(CL) high on the Chajnantor plateau in Chile’s Atacama region, at an altitude of over 4,800 m (15,700 ft).

European Southern Observatory(EU) ExTrA telescopes at erro LaSilla at an altitude of 2400 metres.