Monday, October 10, 2011

Giant eye to glimpse a new galaxy every three minutes

The Chajnantor plateau, 5000 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 below freezing.

But it's on this desolate, Mars-like terrain that 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 fully operational in 2013, it 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 Earth, obscure stars from modern optical and infrared equipment, such as the Hubble Space Telescope. While the dust hides the stars, 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 1000 times shorter than the light we see with our eyes. Detecting these means astronomers will be 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 Andean site because it has year-round clear skies and is one of the driest places on Earth. Sub-millimetre radiation is absorbed by water and there has been no rain in parts of the Atacama desert for 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 1000 metres below the Chajnantor plateau.



No comments: