SKA: The latest
Ken Tapping, August 22, 2012
If you drive past our observatory, you will see, close by the road, a relatively small, innocuous dish antenna with a large package of electronics at its focus. It might be small, but contains some very innovative pieces of technology. Moreover, it is part of our contribution to the largest radio telescope in the world, which is now under construction by a consortium of nations, including Canada.
The history of radio astronomy has been driven by the dramatic developments that have happened in antenna and electronics technology, and the explosive growth in computing power. This made it a key area of astronomy. Our ability to study cosmic radio waves has shown us things about the universe we could never have seen any other way.
Technical developments have continued, enabling radio astronomers to make high-resolution images of the cosmos – what we might see if we had radio eyes. We can monitor chemical reactions taking place in the dark, cold clouds of gas and dust between the stars, and probe the universe’s youth, right back to the Big Bang itself. However, over the last few years we have been approaching some fundamental limits. Antennas above a certain size cannot keep themselves in shape under the Earth’s gravity, even using the best materials, and we are approaching Mother Nature’s limits to the sensitivity of any radio receivers we can develop.
We have reached a point where to progress further requires radio telescopes at least 100 times more sensitive that we are currently achieving. This is what we need to explore the early youth of the universe, to search for life out there on other worlds, to better understand things like Dark Matter and Dark Energy, and to understand how Einstein’s ideas are at work out there in the cosmos. If we are clever, we might be able to make receivers another two or three times more sensitive, but 100 times seems out of the question.
If we can’t make our radio receivers much more sensitive we can make our antennas larger, to collect more signal. To achieve our target we will need an antenna with a signal collecting area of one square kilometre – a million square metres. Achieving this with a single antenna would require a dish almost 1200 metres in diameter. We have no idea how one could build such a behemoth. However, we don’t wish to; it is better to build the antenna by combining thousands of small ones, like the one on our observatory campus. We get the dramatic advantage of spreading those antennas over thousands of kilometres and so achieving an incredible ability to map tiny details in the sky.
The plan is to site these antennas in remote areas of South Africa, Australia and New Zealand. One reason for choosing the Southern Hemisphere rather than a piece of sparsely populated land in Canada is that we want to be able to study the centre of our galaxy. In the Southern Hemisphere it goes overhead, whereas at our latitudes we only get a glimpse of it low in the south.
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