DISTINGUISHED LECTURE SERIES 1993

Curtin University. Ian Clunies Ross Press.

Achievements and Challenges for Australian Science - Radio Astronomy

Professor Ron Ekers, Director Australia Telescope National Facility, CSIRO

Introduction

Astronomy is a fascinating subject, capturing the imagination of human beings since time immemorial. One of the most powerful of many arguments for supporting astronomy is that it encourages our sense of wonder.

In Australia the Aborigines had observed the sky and developed their cosmic mythology long before the Europeans. But soon after the Europeans arrived, Australia became established as a world centre for astronomy. Initially, this happened because Australia gave access to the Southern skies, but was later reinforced by circumstances that resulted in Australia playing a leading role in the early development of radio astronomy. Today I will speak of this more recent development of the science of astronomy in Australia, and of Australia's evolving role on the world scene.

Astronomical observations were the key reason for the voyage that led to Captain James Cook's discovery of the east coast of Australia. His commission was to observe the transit of Venus across the Sun from the island of Tahiti. This was done partly to pursue basic science which, at the time, was considered "a necessary pursuit of any civilised society". It was also done for practical reasons - astronomical navigation. Before accurate clocks were available, lunar tables were used to determine positions at sea. These tables of solar-system predictions depended on knowledge of the distance to the Sun and this could be measured by observing the transit of Venus across the Sun from several different locations. Two hundred years later the arguments for undertaking scientific ventures have not changed much and the major outcomes are often as unpredictable as the discovery of Australia.

Before continuing, let me explain my perspective. Although I am an Australian and am now director of the Australia Telescope I have spent most of my professional life overseas. As an "outsider" I can praise what I like without boasting, I can notice deficiencies, and I can provide an international perspective on the role of Australia in radio astronomy.

Achievements

Radio emission from the cosmos was discovered in the 1930s by Karl Jansky of the Bell Telephone Laboratory while investigating sources of static in transatlantic communications. This discovery was pursued by Grote Reber (an American now living in Tasmania) but there was little interest until the development of radar in the second world war provided the necessary technology.

During World War II, the CSIR (later the CSIRO) formed the Radiophysics Laboratory to conduct research in radar. After the war, David Rivett (chairman of CSIR) decided to keep the group together to continue research in peaceful uses of radio waves. At this time the main centers of activity were in the UK, the Netherlands and Australia. Although the USA had the technology they did not play a major role at this time. This occurred because their science after the end of the war was dominated by high-energy physics and, ironically, also because of the dominance of the optical astronomy community. In Australia, the group led by Joe Pawsey decided to investigate the mysterious sources of "cosmic static". This was the beginning of Australian radio astronomy, a remarkable period of excitement and discovery. The now famous names of Bernie Mills, John Bolton, Paul Wild, Taffy Bowen and Chris Christiansen dominated the world of astronomy for more than a decade.

During this period, Earth-rotation aperture synthesis was invented by Christiansen who made the first crude pictures of the Sun using radio waves. Although aperture synthesis was first demonstrated in Australia, it was independently discovered in Cambridge by Martin Ryle who was later awarded a Nobel prize. This was a key technological development, the forerunner of medical imaging techniques such as the CAT scan and NMR imaging. Papers on medical imaging still refer to the fundamental work by Australian radio astronomers. The various solar observations were highly successful and resulted in the first classification of the different types of solar bursts. Paul Wild went on to design the solar radioheliograph, a telescope that made moving pictures of the Sun's corona.

Perhaps the most spectacular discovery was made at Dover Heights where a telescope had been constructed, on a cliff overlooking the Pacific Ocean, to measure the interference between the direct radio waves and those reflected by the sea (a Loyd's mirror). John Bolton and his colleagues used it to measure positions accurately enough to identify three of the strongest of the mysterious discrete sources of radio emission. One of these was the Crab Nebula, the remnant of a star that the Chinese had seen explode 900 years ago. The other two were an even greater surprise. They were both galaxies, not stars as had been expected. They were far outside our own Milky Way but undergoing such a violent explosion that they were among the brightest objects in the radio sky! This discovery, with some help from the now very enthusiastic optical astronomers at Mt Palomar in the USA, led to the identification of the strongest radio source. It too was found to be a galaxy but now so faint and incredibly distant that it was immediately obvious that these new radio telescopes were probing the most distant reaches of the universe. A new field of astronomy was born.

To stay in the forefront of this rapidly developing science, bigger and more sophisticated telescopes were needed. This resulted in a change of style as the "Big Science" era began in Australian radio astronomy. Two major projects were begun in the late 1950s. The Mills Cross and the Parkes radio telescope both obtained substantial funding from the USA. In the current climate it is hard to imagine that this was done just to promote good science. The USA took a "no strings attached" attitude; there were no arguments about who owned intellectual property and no required demonstration of economic benefit. As it turned out, these facilities have not only done good science but they have also played an important role in the USA space program and Australia has obtained great economic benefit from the research and developments.

The Mills Cross radio telescope was built by the University of Sydney to catalogue very faint radio sources. Although it produced important cosmological results its value was greatly under-rated at the time because of the intense rivalry between the Australians and the more influential group in Cambridge, England. It has been upgraded,is now called the Molongolo Observational Synthesis Telescope (MOST) and is still in operation. It still has a sensitivity as good as the best radio telescopes in the world.

The Parkes radio telescope is perhaps one of the most successful research facilities ever built. It easily exceeded the specifications of the other great radio telescopes (Jodrell Bank in the UK and Greenbank in the USA) and remained in number one position for a decade. Thirty years later it is still the workhorse of southern radio astronomy and is heavily in demand by Australian and overseas astronomers. Of the many discoveries made at Parkes in the last thirty years the quasars stand out as the most important. They caused a paradigm shift which changed the direction of extragalactic astronomy. This story started in 1963 when astronomers from the University of Sydney and CSIRO were watching a radio source (number 273 in the Third Cambridge Catalogue) as it was occulted by the Moon. The recordings showed that the radio emission came from a star-like object with a faint jet. A spectrum of the light from this star was soon obtained by Martin Schmidt using the Mt Palomar 200" telescope and he was astonished to discover that the light had been red‑shifted by an amount corresponding to a sixth of the velocity of light! The most likely interpretation was that this "star" was at great distance and red-shifted by the general expansion of the universe. This new class of objects were called quasars and many others were soon discovered at even greater distances. Apart from the relic radiation from the Big Bang itself these quasars are still the most distant objects known in the universe. They have a prodigious energy output best explained as the result of a black-hole swallowing matter in the nucleus of a galaxy that is just being formed.

During the 1970s Australia's position started to decline as other countries such as Germany, Japan, The Netherlands, France and, in particular, the USA invested more heavily in astronomy. New areas of astronomy (infrared, Xray, gamma ray) were now being opened up by the space programs in which Australia played an increasingly minor role.

A new instrument was essential to preserve the research vitality of the Australian radio astronomers. An imaging radio telescope, based on the aperture synthesis concepts invented earlier in Australia, was proposed. It was to be operated by CSIRO as a National Facility. The telescope was accepted as a Bicentennial project, acknowledging Australia's pioneering role in astronomy but looking towards the future. Completed at a cost of $50 million it was opened in 1988 and is now a prestigious and world-class observatory dedicated to the advancement of knowledge. It is a highly visible national status symbol and with 80% local content it is a showpiece for Australia's technology. It also provides Australia with membership in an exclusive global club of countries with major astronomical research facilities. By sharing this facility with overseas colleagues, Australian scientists gain access to complementary resources in other countries. Australia has been sometimes seen as a net "bludger" on the international "Big Science Facility" scene. The success of our radio and optical telescopes goes a long way to redress this imbalance.

This international exchange also gives Australia access to advanced technology developed in other countries - an access not easily obtained in other ways. To succeed, the telescope has also to remain internationally competitive, providing a harsh but realistic benchmark for Australian technology. Another example of these international connections is the partnerships with Asian countries that are being established to link the telescopes around the Pacific rim. Such partnerships can underpin successful commercial ventures.

Basic science does not normally generate short-term economic benefits and it is dangerous to justify the building of astronomical telescopes just by using technology spin‑off arguments. However, if we look at the history of radio astronomy in Australia we see that it has provided a focus and a difficult goal that has driven the technology in directions which, on the longer term, have resulted in significant dividends. An early example was the development of the aircraft landing system "Interscan" by the CSIRO radio astronomy group. This was accepted as the International Standard and is now manufactured and sold by an Australian company. More recently, the designs developed for the Australia telescope have been used to build up a communications antenna export industry that has already recovered more than the cost of the Australia telescope.

Australian perspective

Australia is an isolated country located in the Southern Hemisphere. Many key factors that have influenced Australia's success in astronomy are related to its geographic location, and our isolation has a strong effect on our scientific culture.

First, I will talk about the importance of our niche in the Southern Hemisphere. A small country can still play a leading role in big science but it has to be very selective. Australia has enormous natural advantages for conducting astronomical research and clearly we have been able to exploit our special niche. The part of the sky visible from the Southern Hemisphere is particularly interesting; the centre of the Milky Way passes overhead and our nearest neighbours, the Magellanic Clouds, are only visible from the south. We are the only technologically developed country in the Southern Hemisphere but are still relatively free from radio interference (and light pollution).

As an example, let us go back to February 1987 when we witnessed one of the most exciting events in modern astronomy - the appearance of a bright supernova (an exploding star) in the Large Magellanic Cloud. No supernova visible to the naked eye had been seen for over 400 years so this was indeed a very rare event and it provided all astronomers in the Southern Hemisphere with an unprecedented opportunity to follow the development of an exploding star from the beginning. Although the initial burst of light has now faded away, the next phase of the explosion is only just beginning as the debris from the exploding star, travelling at tens of thousands of kilometres per second, ploughs into the surrounding medium. Radio astronomers in Australia are currently taking a sequence of images of the developing supernova remnant, and astronomers from all round the world wait in eager anticipation to see what will happen next.

Our location has the obvious advantage of making many unique observations possible, but it also has a more subtle advantage of gaining entry for Australia into multinational programs. Take space astronomy. This is one of the most rapidly developing and exciting new areas of science, but Australia no longer has a significant space program of its own and has insufficient funding to buy its way into the space programs of other countries. We can, however, use our Southern Hemisphere observatories as a lever to become involved in these developments.

I will now turn to Australia's isolation. If we recognise the effects of this isolation on our scientific culture we may be better placed to exploit the advantages while we live with the disadvantages. One of the disadvantages is our lack of appreciation for our real position in the world; we tend to overrate the impact of our successes and there is much overselling of the local product by the media. Another disadvantage is that we also miss some of the synergy coming from the international excitement generated by new discoveries and advances. Reading the scientific journals does not fully recreate the required ambience, but "e‑mail", the new electronic medium for scientific collaboration, is starting to overcome this. Also, the normal checks to or encouragement of developing ideas that come from interactions with colleagues does not occur because there are unlikely to be enough people working in the same area. This has both good and bad effects. Because of our isolation, the worst effects of the scientific "bandwagons" are avoided, and this allows more independent development and fresh ideas. But the limited feedback during the process of evaluating good and bad ideas may result in someone pushing a bad idea, while being spurred on as an "Aussie battler" fighting the outside world.

The result of our history of isolation and the need to be independent has made Australians more innovative and less specialised than their European or North American counterparts. It is often not possible to go out and buy whatever we want and so we have to improvise. The high level of innovation that occurred in the early development of radio telescopes in Australia is an obvious example.

Challenges

We are already linking radio telescopes spread across Australia to obtain the equivalent resolving power of a telescope as large as the entire country. A global network of telescopes, including Australia, has now been formed to create the largest possible telescope on the surface of the earth. But such a telescope needs to be even larger to resolve the elusive black holes thought to power exploding galaxies and quasars. This future challenge can be met by linking up with radio telescopes in space. Both Russia and Japan are preparing such telescopes for launch in the mid 1990s and they will need to link them to the Southern Hemisphere telescopes in Australia. We will therefore be able to participate in these ambitious experiments.

Let me conclude with a most exciting discovery that has just been made using these linked telescopes. We have observed the minute distortion of a quasar caused when space is warped by the gravity of a massive galaxy along the line of sight. We can see the quasar along two different paths and this provides a direct measure of the separation between the two paths, and therefore the scale of the universe. So, we have come full circle - the expedition to measure the scale of the solar system from the transit of Venus resulted in the discovery of a continent large enough and far enough south to measure the gravitational distortion of a quasar that can determine the scale of the universe!

Version 2, 22/06/92

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