Astronomy is one of the oldest sciences, with pre-historic civilisations examining the sky and the motion of stars and planets. Since then the technology has improved constantly, but now an ambitious project will truly push the boundaries of our understanding of the universe by building the world’s largest telescope. This telescope won’t be a single telescope – instead over 3000 individual radio telescopes will together form a telescope on a scale never seen before – the Square Kilometre Array. The SKA project is an international collaboration which is currently made up of 10 members (but is expected to grow), with a select committee from the International Council of the SKA currently deciding where to host it. The two options are southern Africa and Australia and New Zealand, with a decision expected by the end of 2011.
There are 3 types of telescope used in astronomy, optical, radio and infrared, with each type of telescope needs to be located in specific areas which provide the perfect conditions. Optical telescopes, for example, need to be located in a region which has no outside light sources such as the glow from cities. They are also obviously best suited in regions which have clear skies with few clouds to obscure the images. A further complication is that the atmosphere of Earth actually distorts the optical image, so ideally optical telescopes are placed as high in the atmosphere as possible to reduce the amount of distortion, such as on top of mountain ranges. The Hubble Telescope takes this concept to the extreme by being placed outside of the atmosphere, allowing it to take incredibly detailed images.
The main requirement for the location of a radio telescope is for very little background radiation, such as telecommunications or radio and television transmissions. This means they must be placed far from civilisation, and the deserts of southern Africa or Western Australia are ideal for these reasons. During preliminary assessment of the locations for the SKA testing revealed that the background radio transmissions in the WA deserts were extremely low, significantly less than those in Africa in fact. According to Peter Quinn, one of the senior members of the Australian SKA bid, this should put the Australian site at a distinct advantage.
What radio astronomy measures
Stars release radiation over the entire spectrum of wavelengths, meaning they need to be detected by all three types of telescope to form a whole picture of the universe. Radio astronomy measures the high frequency wavelength radiation released by stars.
There are several basic measurements radio telescopes can achieve. If radiowaves being released from a star are being measured constantly, dip sharply, then return to their previous levels, it is highly likely that there is a planet orbiting that star. This dip in radiation is the point when the planet moves in front of the star, temporarily shielding the telescope from the radiowaves emitted from the star. Using this basic principle, astronomers are able to measure the size of planets, the speed they are travelling, and how long it takes for them to complete an orbit of the star.
Galaxies can affect each other similar to tides in the ocean. When they approach each other, move away, or merge, they can change the shape of other galaxies through massive magnetic forces. These changes in shape result in differences in their radiowave emissions, allowing astronomers to understand the structure and shape of galaxies, as well as how they interact, and understand more about these magnetic forces which shape the universe.
Using radiowaves and the Doppler Effect, astronomers can also examine the movement of objects in the universe. The Doppler Effect says that the frequency of waves, whether they are radiowaves, soundwaves, or visible light waves, changes as objects move. As an object approaches, the waves are closer together, however once the object passes the waves become spread out. This is why a siren on emergency vehicles is high pitched as it approaches (short wavelengths), and then the sound changes to a lower pitch as it passes (long wavelengths). The speed at which an object is travelling changes the distance between the waves, with a faster object causing longer wavelengths. Astronomers apply this principle to measure the speed of objects in the universe. If an object is moving away, by measuring the wavelength of the radiowaves coming off it they can calculate the speed of the object. From the speed it is moving, they can then measure the distance from the telescope, allowing precise measurements of the size of solar systems, galaxies, and the universe as a whole.
The SKA will also be able to search for intelligent life throughout the universe. This can be accomplished by detecting and examining the formation of Earth-like planets. Additionally, the sensitivity of the SKA may allow the detection of extremely faint radio transmissions being released by other civilisations. Our Earth gives off radiowaves from human activities, and it may be possible that other intelligent civilisations also release similar radiowaves.
Possibly one of the most interesting applications of radio astronomy is understanding the formation of the universe during the big bang. This concept of essentially looking back in time seems confusing to many people, but is based on quite a simple principle.
Imagine you are looking at a person standing right in front of you. The time it takes for the light (which is what you see) to go from them to you is extremely short. If you then take a step back, it takes slightly longer for light from them to reach you. The further back you stand, again, the longer the light takes to travel from them to you. Now if you were to stand an incredibly long way away, the light would take a long time to reach you, however the image you see would be how they looked when that light left them on its way to you. In the time it has taken to travel that extremely long distance however, the person will have aged, but you will still be seeing them as they were when the light first began its journey. So, you are effectively looking back in time – you are looking at an image when they were younger than they actually are due to the length of time taken for the light to travel across the distance.
The same principle applies in astronomy. An object an extremely long distance away will have released radiowaves an extremely long time ago, but because of the time it takes for those radiowaves to travel across the distance, we are only receiving them now. So what is being detected now was released from a star many millennia ago. If you can detect radiowaves which were released from further away, the older those radiowaves are, and essentially the further back in time you are seeing. It is possible that radiowaves which were released during the big bang, or as astronomers refer to the time just after the big bang, “First light”, are only being received on Earth now from objects extremely far away.
By measuring these extremely old radiowaves we will be able to form a picture of the events which shaped the universe. The further back astronomers can detect will provide more and more information, however they are hopeful that a project on the scale of SKA will be able to detect radiowaves from “First light”, and resolve just what occurred during and just after the big bang to form the universe.
To measure objects further away, the telescope needs to have a larger collection area. However, the distance away you can measure and size of the collection area aren’t a direct relationship; rather they exist as an exponential relationship. This means that to measure something 10 times further away, the collection area of the telescope needs to be 100 times bigger. This is where the SKA comes in to play. With 3000 telescopes each of 15 metres diameter the SKA has a collection area, as the name suggests, of one square kilometre. In short, this is substantially bigger than any telescope project ever built before, and will give astronomers unprecedented sensitivity.
By spacing the telescopes further apart astronomers can also increase the resolution of the images they produce. Having telescopes placed far apart, but still linked, will give incredibly sensitive and high-quality images. The proposal siting SKA in the WA outback will have outstations positioned as far away as New Zealand. The proposal siting SKA in Africa cannot match this spacing, and therefore would not be able to produce images of as high quality.
The SKA is one of the most ambitious science projects ever attempted. Next article will talk about some of the technical requirements for such a project, but we’ll leave the final words of this article to Peter Quinn, who when discussing what effect SKA will have on our understanding of the universe said “I think we’ll be surprised and find something we never expected.”
Thanks to my friends at the RiAus and Peter Quinn from the Australia and New Zealand SKA project. More information is at www.ska.gov.au
Dr Ben Lewis 