ANNUAL SYMPOSIUM

Australia's science future 3-4 May 2000
Full listing of papers

Dr Bryan Gaensler received his PhD from the University of Sydney in 1998 for his work on how the debris of exploding stars (supernovae) expands into space. He then moved to the Center for Space Research at the Massachusetts Institute of Technology, where he is currently a Hubble Postdoctoral Fellow. Dr Gaensler continues to study supernovae, but also now works on neutron stars, binary systems and the interstellar medium. In 1999 Dr Gaensler won the Science and Technology category of the Young Australian of the Year Awards, and went on to be named overall 1999 Young Australian of the Year.

Symposium themes - The universe: Looking out – looking forward

Astronomy in Australia – past and future
by Bryan Gaensler
bmg@space.mit.edu
http://www.physics.usyd.edu.au/~bmg/

Abstract
Dr Gaensler will review some of the highlights of Australian astronomy in the 20th century, and will discuss some of the outstanding problems which our 21st century astronomers will tackle. In particular, he will show how Australia's distinguished history in radio astronomy leaves us well-placed to play an important role in answering some exciting questions: Where did the first stars come from? What happens when stars die? And is there anybody else out there?

Australia has some natural advantages for astronomy: a low population density, which means there is not too much pollution and the night skies are dark; a low level of radio interference; and stars that other people cannot see. The two nearest galaxies, and most of the stars in our galaxy, the Milky Way, are best seen from the southern hemisphere.

Australia's advantages have been borne out by history. Astronomy first came to Australia in the form of Captain James Cook who, in 1769, led a British scientific expedition to Tahiti to observe the transit of Venus, and then claimed the east coast of Australia for Great Britain on his way home. In 1788 William Dawes set up the first observatory at Dawes Point.

In 1821 the governor of NSW, Thomas Brisbane, set up an observatory at Parramatta to map the southern stars. Sydney Observatory was built at the Rocks in 1858. In 1864 John Tebbutt, one of the big names of 19th century astronomy, set up his observatory at Windsor, where he discovered a number of comets.

In the 20th century Australia's strengths have been in optical and radio astronomy. After the second world war, radar scientists needed something to do; they turned their antennae towards the stars. In the 1950s and 1960s astronomers at CSIRO Radiophysics, the University of Sydney and the University of Tasmania did important work. From the cliffs near Sydney they found the first sources of radio emissions. With the radiotelescope at Parkes they helped discover quasars (powerful distant galaxies) and pulsars (collapsed stars spinning very rapidly).

Today, Australian astronomers are still at the cutting edge. The Parkes telescope now has a multi-beam receiver, which lets it look at 13 adjacent parts of the sky at once. Parkes has used the multi-beam receiver to study the interaction between the Magellanic Clouds (the nearest galaxies) and our own Milky Way, and has discovered 10,000 new galaxies and 700 new pulsars (doubling the number of known pulsars).

The Australia Telescope is a set of smaller, linked dishes which together make an enormous telescope with incredibly sharp vision. It has been used to study the detailed structure of the Magellanic Clouds and looked at the twinkling of quasars. Observations of Supernova 1987A, the brightest supernova since 1604, have given a detailed picture of what happens when a star explodes.

But where do stars come from? The universe is environmentally friendly - everything is recycled. When a star explodes as a supernova, the resulting shock wave expands into space, slamming into the invisible clouds of gas scattered throughout space. These clouds then start to collapse, condensing into compact lumps which eventually become new baby stars. And the whole cycle then repeats. So stars come from other stars.

But this creates a 'chicken and egg problem'. Stars might make other stars, but where did the first stars come from? That takes us back into the dark ages, nearly 15 billion years ago, soon after the Big Bang. The gas left over from the Big Bang was spread unevenly, creating ripples in space. After 2 billion years the ripples coalesced into lumps, then formed stars and galaxies.

The sky is like a time machine. The further we see out into space, the further back in time we are seeing. When we look at something 10 light years away, the image we see is 10 years old. However when we look back about 13 billion light years in time, we don't see anything - it's dark, because the first stars have yet to form.

We can understand how these first stars were born by looking at the glow given off in radio waves by otherwise invisible gas. However this glow is extremely faint - if we want to catch the first stars forming, we need a bigger telescope, 100 times bigger than anything we have now.

Such a telescope has been proposed, and is known as the Square Kilometre Array (SKA). It will most likely be made of thousands of small dishes, which will be linked together to simulate one enormous telescope.

There are various options for the design of the SKA: the total cost would be about $1 billion (of which Australia would have to contribute about 10 per cent), and it would take about 15 years to build. The biggest decision though is where to build it. We need somewhere with a lot of flat empty space, in a country which is politically stable, not too far from the equator, and which is relatively free from radio interference. Australia meets all these criteria and also has an enthusiastic band of astronomers and engineers who want to be involved.

The SKA will not just tell us about how the first stars formed. There are countless projects which could be done with it: it could find thousands of supernovae and discover millions of new galaxies. The SKA will be so sensitive that for the first time we could actually hope to pick up interstellar TV - the signals being leaked out into space by an alien civilization. The scientific possibilities opened up by the SKA are endless - and, if we want it, it could all happen right here in Australia.

Session discussion

If the universe is flat, can we have more than one?

Brian Schmidt. It is paradoxical but if we know about another universe, then it is part of ours. If the universe is flat, then there may be an infinite number of universes like our own. So the answer is probably yes. It reaches science fantasy at this point.

What is constant in the Hubble constant?

Brian Schmidt. The Hubble constant is a measure of how fast the universe is expanding now. It is all expanding at the same rate but it may have sped up or slowed down. So it is not constant.

What new science has come from the discovery of pulsars?

Bryan Gaensler. Some pulsars are extraordinary and teach us a lot. For example, studies of one pulsar has verified the general theory of relativity, work which won Hulse and Taylor the 1993 Nobel Prize in Physics. We also learn a lot about the physics of condensed matter and magnetic fields by studying pulsars.

Is there any observation to support the idea of quark matter at high density in pulsars?

Bryan Gaensler. There's not really any evidence to support this claim at the current stage. I expect that results coming from X-ray studies of pulsars in the next few years might shed more light on this question.

If the universe is flat, does it have any energy?

Brian Schmidt. That is a philosophical question. In an infinite universe it is hard to define things.

Do theories of continuous creation have any support?

Brian Schmidt. The theories of a steady-state universe have been sidelined for the last 30 years. The cosmological constant is almost a steady-state universe. It is a similar idea, not with protons but funny stuff. The problem with a steady state is that it has no beginning. But the big bang did happen.

If the space between galaxies is expanding, what happens at the boundary between these spaces?

Brian Schmidt. It is a question of forces. If we measure the distance of Andromeda, it is coming towards us: the gravitational force exceeds expansion. It needs several million light years for the force of expansion to become stronger than gravity.

Polarised light has influenced the polarity of biological molecules. Is there any bias in the direction of polarity?

Chris Tinney. Astronomers have measured the polarisation but they are not ready to make a definitive statement on the connection. A strong flux of circularly polarised radiation in a star forming region could bias biological processes to a particular chirality on planets formed around stars in the region. Its an interesting connection, but that’s as far as we’d want to go right now.

How fast was the universe expanding a billion years ago?

Brian Schmidt. The correction within 300 million light years is almost zero. It fits within the model of general relativity, which takes account of time dilation and so on.

In A brief history of time, Stephen Hawking talked about string theory. Can you explain it?

Brian Schmidt. No. Strings are a compacted energy source in one dimension. Strings are now in disfavour. There hasn’t been any evidence for them yet.