ALMA

High on the Chajnantor plateau in Chile’s Atacama desert, ESO is building state-of-the-art telescopes 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. This is why telescopes for this kind of astronomy must be built on high, dry sites, and why ESO has chosen the 5100 m high plateau at Chajnantor.

Here, together with its international partners, ESO is building ALMA, the Atacama Large Millimeter/submillimeter Array. The ALMA site is some 50 km east of San Pedro de Atacama in northern Chile, in the Atacama desert – 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 2300 m higher than the VLT on Cerro Paranal.

ALMA will be a single instrument, composed initially of 66 high-precision antennas, and operating at wavelengths of 0.3 to 10 mm. The main array will have fifty 12-m diameter antennas, acting together as a single telescope – an interferometer. An additional, compact array of 7m and 12m diameter antennas is also foreseen. The antennas can be moved across the desert plateau over distances from 150 metres to 15 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 VLTI.

Construction of ALMA started in 2003 and will be completed in 2012; it will become incrementally operational from 2010 on.

ALMA will provide scientists with detailed images of stars and planets being born in gas clouds near our Solar System. It will also detect distant galaxies forming at the edge of the observable Universe, which we see as they were roughly ten billion years ago. ALMA will provide a window on celestial origins that encompasses both space and time, providing astronomers with a wealth of new scientific opportunities.

A Global Endeavour

The ALMA project is a partnership between Europe, Japan and North America in cooperation with the Republic of Chile. ALMA is funded in Europe by ESO, in Japan by the National Institutes of Natural Sciences in cooperation with the Academia Sinica in Taiwan and in North America by the U.S. National Science Foundation in cooperation with the National Research Council of Canada. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of Japan by the National Astronomical Observatory of Japan and on behalf of North America by the National Radio Astronomy Observatory, which is managed by Associated Universities, Inc.

More Information

For more information please visit the ALMA Project Web site.