High on the Chajnantor plateau in the Chilean Andes, the European Southern Observatory (ESO), together with its international partners, is building ALMA — a state-of-the-art telescope to study light from some of the coldest objects in the Universe. This light has wavelengths of around a millimetre, between infrared light and radio waves, and is therefore known as millimetre and submillimetre radiation.

Light at these wavelengths shines from vast cold clouds in interstellar space, at temperatures only a few tens of degrees above absolute zero, and from some of the earliest and most distant galaxies in the Universe. Astronomers can use it to study the chemical and physical conditions in molecular clouds — the dense regions of gas and dust where new stars are being born. Often these regions of the Universe are dark and obscured in visible light, but they shine brightly in the millimetre and submillimetre part of the spectrum.

Millimetre and submillimetre radiation opens a window into the enigmatic cold Universe, but the signals from space are heavily absorbed by water vapour in the Earth’s atmosphere. Telescopes for this kind of astronomy must be built on high, dry sites, such as the 5000-m high plateau at Chajnantor, site of the highest astronomical observatory on Earth.

Here, together with its international partners, ESO is building ALMA, the Atacama Large Millimeter/submillimeter Array. This is the largest astronomical project in existence. The ALMA site, some 50 km east of San Pedro de Atacama in northern Chile, is in one of the driest places on Earth. Astronomers find unsurpassed conditions for observing, but they must operate a frontier observatory under very difficult conditions. Chajnantor is more than 750 m higher than the observatories on Mauna Kea, and 2400 m higher than the VLT on Cerro Paranal.

ALMA will be a single telescope of revolutionary design, composed initially of 66 high-precision antennas, and operating at wavelengths of 0.3 to 9.6 mm. Its main 12-metre array will have fifty antennas, 12 metres in diameter, acting together as a single telescope — an interferometer. An additional compact array of four 12-metre and twelve 7-metre antennas will complement this. The antennas can be moved across the desert plateau over distances from 150 metres to 16 kilometres, which will give ALMA a powerful variable “zoom”. It will be able to probe the Universe at millimetre and submillimetre wavelengths with unprecedented sensitivity and resolution, with a vision up to ten times sharper than the Hubble Space Telescope, and complementing images made with the VLT Interferometer.

ALMA is the most powerful telescope for observing the cool Universe — molecular gas and dust as well as the relic radiation of the Big Bang. ALMA will study 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 our 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’s construction will be completed around 2012, but early scientific observations with a partial array will begin around 2011.

The information of this article was extracted from ESO’s official website.

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