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ALMA - an observatory that's on top of the world

Paul Sutherland, Feature writer
Dec 20, 2011, 8:00 UTC

Sen—I have been to a fair few astronomical observatories around the world. But this is the first time that I've needed a medical to visit one. I'm at ALMA, the planet's most advanced telescope, constructed at the driest, most inhospitable place on Earth.    

It has taken three days of driving to get here, through an alien landscape of reddish brown hills, strewn with rocks, that looks more like Mars. ALMA is the Atacama Large Millimetre Array and it seems almost impossible that it could be here in a place where simply breathing can become a struggle.   

There are no trees here, high in Chile's Atacama Desert in South America. No plants or greenery of any kind and no birds sing. But at an air-deprived altitude of more than 5,000 metres (16,000 ft) - half the height that airliners cruise - man has built an astonishing experiment to explore the universe.  

A vast spread of telescopes, looking like giant versions of satellite TV dishes, have begun work on the desolate Chajnantor Plain as the world's largest, highest and most technologically amazing observatory. They are working together to probe the furthest reaches of space, looking billions of years back in time for clues to how life began.  

For my visit for Sen, courtesy of the European Southern Observatory (ESO), I first needed a letter from my doctor back in the UK to say I was medically fit for high altitude. But on arriving at ALMA's Operational Support Facility "only" 3,000 metres high, those of us wanting to head on up were obliged to undergo a further check on our blood pressure before we were allowed to make the journey.  

We didn't need to make any physical effort to reach the dizzy heights of ALMA. Our minibus slipped and slid on a smooth dirt road wide enough for the giant dishes to be ferried up to their observing site from the base where they are assembled. Gradually the landscape changed including a zone of giant cactus plants, some hundreds of years old and growing at the rate of just one centimetre a year.  

Our first stop at Chajnantor was at a telescope called APEX - the Atacama Pathfinder Experiment telescope - built as a pathfinder for ALMA to test the techniques, but which carries out valuable scientific research of its own. This 12-metre wide dish, operating at millimetre and submillimetre wavelengths, is the largest of its type in the southern hemisphere. Like ALMA, it observes in a region of the electromagnetic spectrum between infrared and radio wavelengths to study the cold, dusty ancient Universe. Unlike visible light, these signals from space get soaked up by humidity in the atmosphere and so cannot be observed from low altitudes, hence the need to operate at such an extreme height.  

Moving on, the awe-inspiring sight of the first 22 dishes in the ALMA array came into view, standing against a magnificent backdrop including the Licancabur volcano on the border with Bolivia. Soon there will be 66 dishes here, with more to follow after that at varying distances from the main array, covering an area of 23,000 square metres. But impressively, they will all work together as a single telescope 10km wide as their individual observations are woven together by computers, a technique that requires precise synchronisation of the instruments by performing up to 17million billion computations a second. For our visit, the dishes were constantly and rapidly turning together in all directions in an impressive demonstration of how they will operate that was like a technological ballet.  

ALMA project scientist Professor Richard Hills, originally from the University of Cambridge, explained that thousands of kilometres of fibre-optic cabling, much buried underground, had to be precisely measured with allowances made for changes due to temperature and movement of the telescopes. He told Sen: "Waves arrive from space and we have to make sure that we get relative times of arrival of the signals at the different antennas to exquisite precision in order to synchronize the signals."  

The benefit of using such an array is that, with each dish super-cooled to a temperature of -272.85 C to guard against interference and loss of data, the telescope will be able to zoom in on the Universe with unprecedented sensitivity. In fact it will observe in ten times greater detail than can be achieved by the Hubble space telescope when it watches the visible sky. The rate of discoveries is expected to be such that a new galaxy will be found every three minutes.

Professor Hills said work with APEX had already successfully mapped clouds of gas and dust to show regions where new stars were being born. ALMA will take such observations much further. He said: "APEX can find a dense cluster in the region but is not able to see what's going on inside. With ALMA we’d be able to make a high-resolution image and see the individual objects within that clump, the disks of gas around the young stars."  

The quality of the observing site was clear from the deep blueness of the sky above, reminding us how thin the air was. Blotting out the Sun with a little finger, there was none of the glare that you see surround it at home. The sky seemed blue to its edge. We had to be careful to move gently as the lack of oxygen is tiring and disorienting. As I kept "forgetting" to breathe properly, I was glad to have the aid of an aerosol of oxygen, resembling a spray-can of furniture polish, to help keep me topped up!  

The hostile conditions on this plateau mean that no one in their right minds would want to work up here for long. For this reason the individual antennas, each weighing 120 tonnes, are assembled at a yard at the lower support facility from parts made by companies across the world. Each dish's reflector is formed from 264 aluminium panels that are positioned to a surface accuracy of one thousandth of a millimetre. The antennas are designed for low maintenance to avoid exhausting repairs at the site or having to bring dishes back down the hill. The ingenuity that achieves this includes, for example, building the structures out of carbon fibre and using powerful magnetic repulsion rather than lubrication to allow metal surfaces to glide over each other.  

Then the antennas are individually transported from the yard's sheds to the observing site by massive 28-wheel transporters that crawl with the power of 1,400 brake horsepower. Each trip uses 2,000 litres of diesel fuel to travel the few kilometres to the plateau.  

Back at ALMA operations centre, we visited the control room where it was a relief to be able to breathe again relatively normally. Looking just like any open-plan office you might find around the world, it is the nerve centre from which astronomers operate the telescopes and gather the data.  

When I visited, the team had just taken their first test image with ALMA, using just 12 individual telescopes in the array. Their target was the Antennae - two colliding galaxies like our own Milky Way where merging clouds of gas had become new cosmic nurseries. ALMA's special vision was able to show the spots where new stars were being born.  


The first image taken by ALMA, of the Antennae Galaxies, is combined with a photo in visible light by the Hubble Space Telescope. Credit: ESO/NAOJ/NRAO/NASA/ESA.

Professor Hills said: "This image will tell us the speeds at which the clouds are coming together, their size and how much gas they contain. It is part of the science-verification procedure. But it is already showing us that we can get similar results as other telescopes - but better!"