The Chajnantor plateau, 5,000 metres above sea level in the Chilean Andes, is one of the most inhospitable places on Earth. The thin air makes breathing difficult, there is no water in sight and fierce winds often force the temperature down to 20C (68F) below freezing.
On this desolate, Mars-like terrain, however, the world's most expensive and sophisticated observatory has just stirred into life.
The Atacama Large Millimetre/Sub-millimetre Array (Alma) will open astronomers' eyes to the half of the universe that has, until now, been hidden to modern telescopes. It can already peer through the distant clouds of dust and debris in which the earliest stars, galaxies and planets were made and, when it is fully operational in 2013, the observatory will find a previously unseen galaxy every three minutes.
"When a star forms, it forms in these cold, dusty gas clouds," said John Richer of the University of Cambridge and a project scientist for Alma. "The moment it's formed it's shrouded in this dusty material, out of which only half of the light from a typical star escapes. Many other stars are formed in very dense clouds and their light is completely absorbed by the dust in these clouds."
These soot-like clouds of dust, which are also the birthplace of planets like the Earth, obscure stars from modern optical and infrared equipment, such as the Hubble Space Telescope. While the dust hides the stars, however, it also gets heated by the starlight to a few degrees above absolute zero (-273C). The dust then emits radiation of its own at sub-millimetre wavelengths, which can be detected on Earth by Alma.
Sub-millimetre light waves are similar to the radiation used by microwave ovens and 1,000 times longer than the light we see with our eyes. Detecting these means that astronomers will be been able to build a more complete picture of the universe. "If you combine the optical images with the [Alma] images you reveal all the star-forming activity, you're not missing half of the picture," says Richer.
Astronomers picked the inhospitable Andean site for their new observatory because it has year-round clear skies and is one of the driest places in the world. Sub-millimetre radiation is absorbed by water and there has been no rain in parts of the Atacama desert for many hundreds of years. An advantage of being so high up is that Alma will be able to capture images as sharp as anything of which Hubble is capable. Shifts of astronomers control the dishes from a more hospitable base at more than a thousand metres below the Chajnantor plateau.
After more than two decades of design and construction, Alma opened for the use of astronomers around the world this week. Sitting in the desert plateau are 20 identical radio antennas, each one 12 metres in diameter. When the €1bn (£860m) observatory is complete in two years, it will have 66 of the carbon-fibre antennas, which can be arranged in countless configurations, up to 10 miles apart across the mountains, depending on the measurements astronomers want to make.
"Alma has got such a fantastic increase in sensitivity compared to previous sub-millimetre wave telescopes, we're expecting that, every three minutes that Alma is observing the sky, it will discover one brand new galaxy somewhere in the universe," said Richer.
Despite being incomplete, the observatory has already started doing science. The first scientific image, taken by measurements from 16 of the dishes installed on the Chajnantor site, shows the violent swirls of the Antennae galaxies, a pair of distorted spiral galaxies that are in the process of colliding about 70m light years from Earth. The blue colours represent the best quality optical image taken of this region of space so far, by the Hubble Space Telescope. The red, pink and yellow show previously unseen wavelengths of light emanating from the vast carbon monoxide clouds that float in and between the galaxies, imaged by Alma for the first time. These clouds contain gases with a total mass several billion times that of our sun and, as such, are a reservoir for the formation of future stars.
Among the other experiments chosen for the first year of Alma operations is studying the supermassive black hole at the centre of the Milky Way, Sagittarius A*, which is 26,000 light years from Earth.
Dense gas and dust clouds normally obscure the black hole but Alma will be able to see through them.
Heino Falcke, an astronomer at Radboud University Nijmegen in the Netherlands, said: "Alma will let us watch flares of light coming from around this supermassive black hole, and make images of the gas clouds caught by its immense pull. This will let us study this monster's messy feeding habits. We think that some of the gas may be escaping its grip, at close to the speed of light."
Alma is a collaboration between the 15 member countries of the European Southern Observatory with the US, Japan, Chile, Taiwan and Canada. The UK contribution, funded by the Science and Technology Facilities Council, includes detectors and design input from Cambridge, Kent and Manchester Universities, and construction of the cooling systems in the radio antennae at the Rutherford Appleton Laboratory in Oxfordshire.
"Projects like Alma require an enormous amount of patience – many of us have been working on this for more than a decade," said Gary Fuller, of the University of Manchester. "There have been many obstacles to be overcome, but I've no doubt that it will all be worth it – it's great to see the first scientific observations beginning for astronomers from the UK and around the world."
Alma in numbers
Height of observatory above sea-level: 5,000 metres
Number of radio antennae when Alma is complete: 66
Total collecting area: up to 7,240 metres squared
Computing power: 17 quadrillion operations per second (1.7x10^16)
Project cost: €1bn
Countries involved: 20
• This article was amended on 4 October 2011. The original stated that sub-millimetre light waves are 1,000 times shorter than those of visible light. This has been corrected.
