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Dish complex will study ‘cool’ cosmos

First eight ALMA dishes

The first eight ALMA dishes have already been pressed into service, 5,000 metres above mean sea level on the Chajnantor plateau in Chile. They are seen here in September 2010.

A GIANT NETWORK OF RADIO DISHES is taking shape high in the deserts of the Atacama Plateau in Chile. Known as the Atacama Large Millimetre/Submillimetre Array (ALMA), it will be used to study the ‘coolest’ parts of the cosmos.

When completed, ALMA will comprise 66, twelve-metre-diameter antennae, each weighing about 95 tonnes. The dishes will be electronically joined to form one single, huge telescope that picks up millimetre and submillimetre wavelengths from deep space.

These wavelengths are affected by water vapour in the atmosphere, which explains the choice of the high and dry site in the Atacama.

As each dish arrives from the manufacturer, it is moved on a special transporter from the Site Erection Facility (SEF) where it is assembled and tested, to the Operations Support Facility (OSF), where it is fitted with its extremely sensitive radio receivers and cooling systems.

Artist's impression of the finished ALMA

Artist's impression of the finished ALMA network of 66 dishes.

Both the SEF and OSF are at an elevation of 2,900 metres above mean sea level, which seems high enough. But the antennae’s final resting place is the observatory site on the Chajnantor plateau, which is at 5,000 metres elevation.

Cool cosmos

ALMA’s targets are the ‘coolest’ components of the universe…the tiny particles of interstellar dust and gas molecules from which everything—stars, planets and galaxies—formed and are still forming.

The array will be able to peer back in time to reveal some of the earliest galaxies, when the universe was only a few billion years old. It’ll also provide information on the formation of stars and planetary systems in the closer and more recent universe.

ALMA dish on a transporter vehicle

The ALMA antennae each weigh about 95 tonnes, and are moved around on giant transporter vehicles.

The dishes are state-of-the-art, with surface panels built and aligned to a precision of less than the thickness of a human hair. Theoretically, ALMA could spot a golf ball 15 kilometres away.

Conditions on the Chajnantor plateau are tough, with strong sunlight and fierce winds. None of the dishes have protective domes, and the air temperature can drop to –20 degrees Celsius.

ALMA is an international facility, being a partnership of Europe, North America and East Asia working collaboratively with the host country, Chile. Twenty-five antennae are being provided by Europe, 25 by North America and 16 by East Asia.

Story by Jonathan Nally, copyright Images courtesy ALMA and (ESO/NAOJ/NRAO), J. Guarda.

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