Flamingo - Nature - Shedding light on the origin of the universe
Light from sources beyond our earth can stream down – in good weather! – bringing information about the cosmos to those who were prepared to look up and wonder. So commenced the science of astronomy, helped by the invention of the telescope exactly four hundred years ago, which is why we are celebrating the Year of Astronomy in 2009.
Animals have been able to see (or in scientific terms, have had some organ to detect a narrow wave band of electromagnetic radiation) for perhaps upwards of a billion years. This wave band was ‘selected’ because it travels though air easily and is good at forming images of objects of everyday size. Of course, it’s what we call visible light. Advanced animals, especially humans, by developing an eye and brain, learned to form accurate pictures of the world around them, being able to detect danger and possible sources of food at considerable distances, which gave them an enormous advantage over other animals who depended on short-range senses of smell or touch.
Electromagnetic radiation covers literally the whole spectrum, from wavelengths a millionth of a millimetre long to hundreds of metres. Most of this can’t travel through the atmosphere – thankfully, because gamma and x-rays fry organic compounds and life on earth could never have developed. Molecules like ozone in the upper atmosphere trap them, which is why the holes in the ozone layer are a matter of great concern.
However, there is also a wavelength 'window' in the range of a few millimetres up to a metre or so, to which the atmosphere is transparent. It is irre-levant to human senses, it fact we did not even know about it until the 1930s. But just as with visible light, rays in this range – very short radio waves – come streaming down to earth from the cosmos, and the study of these forms the subject of radio astronomy. In fact, there are many exotic objects and systems in the universe which are radio sources, but which don't emit significant light, and we would not have suspected their existence, let alone assessed their importance, without radio astronomy. There is no suggestion that aliens are out there signaling to us. At least, not yet!
Among radio’s mesmerising discoveries, are the famous ‘3-cm’ background, which is literally the residual rumble from the big bang still echoing around the universe, and which you can hear, in theory, by tuning your radio off the station and turning the volume up full blast; and the 21-cm hydrogen line. Just as you can see the characteristic yellow light of sodium street lights far into the distance, so we can observe the remote doings of galactic and inter-galactic hydrogen, the fundamental element in the universe. Radio can also cut through the clouds of interstellar dust, which are as optically opaque as an Arabian sandstorm.
Radio astronomy is quite different from optical astronomy. Of course it has its own telescopes – we are familiar with the parabolic dishes used for satellite communication – radio telescopes are similar but larger. But not all are dish shaped – there can be arrangements that look like traditional TV aerials, or even Heath Robinson-like arrays of metal plates or wires.
One upside of radio astronomy is that you can do it in the daytime because the radio waves are not affected by sunlight. No need to observe in the middle of a freezing night. But the big downside is resolution. With optical light and just a pair of bi-noculars, you can see objects, whether terrestrial or celestial, in very fine detail. But the vision of radio telescopes, because of the much longer wavelengths, is extremely blurred, like a person with terrible cataracts. It's like being in a room and detecting some light, but having only a vague idea of where the window is, or like trying to observe the moon, seeing only a splodge of light in the northern sky! A bigger telescope or dish improves matters, but to achieve anything like visual acuity we need a trick. This uses the principle of the range finder – two separate images from different viewpoints which you adjust until they coincide. That gives you a fix on precisely where your target is. We can do the same with radio telescopes – if we observe the same radio source with two receivers say 100 kilometres apart, we can pin down the position of the source, in the sky, much more precisely. Of course, there are some technical issues in communicating and combining the signals, but it can be done. It's called interferometry, and we can achieve a resolution equivalent to having one telescope 100 kilometres in diameter, which would be an impossibility. By the way, these sources emit radio waves by natural if exotic means.
But why stop at two telescopes? Why stop at 100 kilometres? If we could have hundreds of radio telescopes, all pointing at the same object, spread out over thousands of kilometres, what might be achieved?
This brings us to the SKA – not a type of dance but the Square Kilometre Array project. Oh, before that, one more thing. Astronomers, both optical and radio, have to get away from other people. Other people spew radiation around. They install extravagant garden lighting which looks pretty but which pours most of its wattage uselessly into the sky. They like to use cars and appliances and cellphones, which spray radio interference everywhere. Where there are people, there's light or radio pollution, against which the faint signals from unimaginable distances have no chance. So in choosing a site for either an optical or radio telescope, the first requirement is to look for somewhere deserted, like a desert, in fact. Paradoxically, somewhere where you can also get access to reliable power and high-quality communications. (And preferably not somewhere where temperatures drop to minus 30 degrees or receive 10 metres of snow per year – delicate equipment doesn't like it).
But we were talking about hundreds of instruments over thousands of kilometres. Where do we find deserted, or at least thinly inhabited, stretches of thousands of kilometres, with the other attributes mentioned above? There seem to be only two answers: the arid regions of central Australia, or, as we hope, Southern Africa in the Northern Cape region of South Africa, southern Namibia, Botswana, northern Mozambique, and even territories beyond.
Both of these regions are short-listed for the SKA project, which will comprise hundreds of radio tele-scopes of different designs, depending on the radio wavelengths being received. It doesn’t mean that everything will be contained within one square kilometre – it means that the combined receiving area of all the instruments will be about that. Actually the precise arrangement would be rather like a sunflower, with a dense central region, a less dense ring surrounding that, and then lengthy 'petals' of telescopes stretching out into the distance. Or, as you might poetically and appropriately imagine, like the structure of a spiral galaxy, with its core, halo, and delicately drifting outer arms.
Of course, in this part of the world, we fervently hope that the project will come to Africa, as it will provide an enormous boost to science on the continent, almost as important, dare we say, as 2010 in South Africa will be to football. It is a much longer-term exercise – decision on location will only be made around 2011, first construction about 2015 and first light, or rather first radio, in the early 2020s. If the African bid is successful, the centre of operations will be near Carnavon in the Northern Cape, but at least four centres composed of dozens of telescopes will be based in Namibia, and it is crucially important that Namibia has the trained scientists, engineers and technicians to support a very sophisticated facility.
A report back and presentation meeting of all country partners in the African SKA bid was held in Windhoek in August.
Once up and running, the scientific potential of the SKA, and its ability to throw light (or radio?) on the origin and fate of the universe and of the matter within it, is staggering. An astronomer at the Windhoek meeting told me that it’s expected that at least three Nobel prizes will come out of the instrument (because the SKA is functionally one giant telescope), such as: the three-dimensional mapping of galaxies in hydrogen ‘light’ out to the visible edge of the universe, and pinning down the nature of the infamous dark matter and dark energy; filling in the ‘missing links’ in the cosmological record, such as the as yet mysterious gap between a half billion year from the Big Bang, when the universe cooled down enough to become transparent, and a billion years later, when the first galaxies formed; and extreme tests of Einstein’s general relativity.
Yet these are just the expected topics. What more discoveries will emerge which are unexpected? Let’s build the SKA (in Africa!) and see. Bill Torbitt is a lecturer in mathematics at the Polytechnic of Namibia.
