Astronomy in the deep freeze
Key text
This topic is sponsored by the Australian Government's National Innovation Awareness Strategy.
Astronomers are going to the coldest place on Earth to search for the heat radiated by distant objects in the universe.
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‘Great God, this is an awful place’, explorer Robert Falcon Scott recorded in his diary during his trek to the South Pole in 1912. Tragically, his words turned out to be true. Bitter cold and starvation killed him and his team before they could return from their epic journey.
Paradoxically, the extreme conditions that made life so difficult for the early explorers are now attracting astronomers to Antarctica: Australian researchers are proposing to build a permanent telescope on Antarctica's high inland plateau (Box 1: The Douglas Mawson Telescope).
Why go to Antarctica?
Most of us know that Antarctica is the coldest continent, but few know that it is also the highest and driest continent. These extremes of temperature, elevation and aridity are assets to those who study a particular branch of astronomy known as infrared astronomy (Box 2: A different window on the universe).
Antarctica’s weather offers another advantage. The presence of a high-pressure system over the continent promotes predominantly stable, clear weather. This, combined with the absence of daylight in winter, allows for extended periods of continuous infrared observation of astronomical objects.
What is infrared astronomy?
Infrared astronomy is the detection and study of infrared radiation emitted by objects in space. Over 200 years ago a British astronomer, William Herschel, discovered that the sun emitted infrared radiation. Since then, infrared astronomy has increased in importance as more sensitive instruments to detect infrared radiation have been developed.
Astronomers have found that infrared telescopes are better suited for studying certain types of objects than traditional optical telescopes or the relatively new radio telescopes.
What has infrared astronomy discovered so far?
Astronomers have discovered a great deal about the universe by using infrared telescopes. They can look at weather patterns on planets in our solar system, as well as determine the abundance and composition of their atmospheres. They have also discovered new comets and asteroids within our solar system.
Infrared astronomers are discovering planets elsewhere in the Milky Way. It is not possible to see the visible light from these planets because it is swamped by the brightness of the star it orbits. In the infrared, where planets have their maximum brightness, the brightness of a star is reduced, making it easier to detect a planet.
Most stars with a mass lower than our sun are less bright and much cooler and emit most of their energy in the infrared. These red dwarf stars are much more plentiful than stars heavier than the sun. Infrared astronomy has also played a key role in the search for very low mass stars known as brown dwarfs.
Infrared astronomers have also found that the vast reaches of interstellar space are not completely empty. Clouds of tiny dust grains between the stars absorb visible and ultraviolet light and obscure our view of distant parts of the Milky Way. However, they can be observed at infrared wavelengths. Recent observations have revealed clear evidence of objects moving around a massive, invisible source – believed to be a black hole – with a mass over a million times that of the sun.
Further afield, infrared astronomers are studying the most distant objects in the universe. Distant galaxies are much fainter and appear much redder than nearby ones. The reddening is caused by the expansion of the universe. Because it takes billions of years for light to reach us from the most distant galaxies, we see them as they were when they were young, not as they are now. During this time space itself has expanded and the wavelength of the radiation has been stretched or ‘redshifted’ by a large amount. As a result, a galaxy is more easily detected and studied in the infrared than at visible wavelengths.
Infrared down under
Infrared astronomy in Australia made its start in the early 1970s when a group at the Mt Stromlo Observatory in Canberra made the first infrared observations of the southern skies. Later a new type of infrared detector was installed at the Anglo-Australian Observatory in New South Wales and it was used in studies such as imaging the surface of Venus, observing molecular hydrogen in planetary nebulae and mapping the complex structure in the central region of our galaxy.
Although infrared astronomy continues to flourish in Australia, astronomers are hampered by the lack of world-class observing sites because Australia has no really high mountains. Observatories established by American and European astronomers on mountain tops in Hawaii and Chile provide conditions for infrared astronomy far superior to anything available in Australia. But the high Antarctic plateau now offers Australia an ideal observing site.
In 1993 a joint US-Australian team began a site-testing program at the Amundsen-Scott station at the geographic South Pole. Later a small, mobile Automated Astrophysical Site Testing Observatory began gathering data to select the best site for a permanent infrared telescope. The results from the remote-controlled observatory have confirmed that the best location on the Earth’s surface for infrared astronomy is undoubtedly Antarctica.
Australian astronomers have also been using a small infrared telescope operated by US astronomers at the South Pole – the telescope has already produced some of the sharpest infrared images ever taken. Now Australian astronomers are proposing to build a telescope three times larger than the American one, which would enable astronomers to scan much larger sections of the sky. Australia’s Antarctic telescope is to be known as the Douglas Mawson Telescope (Box 1).
Future prospects
In addition to the astronomical advantages, a facility such as the Douglas Mawson Telescope would promote international cooperation and help strengthen the Antarctic Treaty. On another level, operating a facility in such extremely harsh conditions could be a dress rehearsal for eventually establishing an outpost on the moon or on a planet such as Mars.
Perhaps the infrared astronomers are showing us that ‘this awful place’, as described by Robert Scott, is nothing less than a stepping stone to the wider universe.
Boxes
1. The Douglas Mawson Telescope
2. A different window on the universe
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Posted August 2001.