ANNUAL MEETING CANBERRA 2 – 5 May 2000
Dr Chris Tinney received his PhD from the California Institute of Technology for studies of the faintest stars ever observed. Awarded both NASA Hubble and European Southern Observatory (ESO) Fellowships, he then spent 2 years as an ESO Fellow studying brown dwarfs, while shuttling between Germany and Chile. He returned to his native Australia in 1994 to join the Anglo-Australian Observatory (AAO). As well as heading up several important new instrumentation efforts at the AAO, he is the Australian leader of a search for planets around most of the brightest stars in the southern sky.
The universe: Looking out – looking forward
The birthplace of worlds
by Chris Tinney
cgt@aaoepp.aao.gov.au
Abstract
Of the challenges facing astronomers, what could be more exciting than the quest to understand where we come from: How do stars form? How do planets form? How is the evolution of life triggered? And most challenging of all, are there planets out there with other life forms on them? Dr Tinney will discuss the ways in which Australia is ideally placed to make major contributions to research on these fundamental questions in the very near future.
My colleagues have discussed the areas of astronomy which look to the very edge of the universe. I would like to take a more local perspective, where we seek to understand the very birthplaces of worlds.
With the discovery of the first giant planets around nearby stars in the last 5 years, this area of research has exploded in interest. So even finding Earth-like planets around other stars is still 20 or 30 years away. In the next 10 years we expect to make significant progress in understanding how solar systems like our own have formed.
Questions
How do stars form? What determines their mass? What environments do they form in? What makes a star have planets? What determines the nature of planets? How does life get started? How does it survive?
Australian astronomers have played a key role in these questions. They found the first free-floating brown dwarfs an 'intermediate' class of objects between stars and planets. They have then used these brown dwarfs as proxies for extra-solar planets. And last year they detected circular polarisation in nearby star-forming regions in the constellation of Orion, providing the first real evidence that biological processes (like chirality) on planets might be driven by their stellar environments.
Making stars
Our galaxy is a rotating, churning mixture of gas, dust and stars with our sun lying far out on one edge – in which regions of dense gas frequently become gravitationally unstable. As a result they collapse to form new clusters of stars.
Stars come in a range of sizes, from 100 times the size of our sun down to one-twelfth of its mass. Anything smaller won’t burn nuclear fuel. Unfortunately, we don’t have a detailed understanding of how the mass of a given star is determined. We do know, however, that mass of the host star has a dramatic impact on the planetary environment.
Making planets
Planets form in accreting discs of gas and dust around stars. Dust particles agglomerate to form larger and larger particles, eventually building up to the rocky cores of planets. Planets distant from a star can also attract large quantities of ice onto their rocky cores, building up large masses and eventually accreting gas as well, to form 'gas giants' like Jupiter. Planets closer to a star can’t do this, and remain as rocky cores.
Until recently we have had only one example of planets to study, our own solar system. In 1584 Giordano Bruno suggested that other stars may have planets. Four hundred years later, in 1995, the first planet outside our solar system was detected. We are now finding lots of objects around other stars via the 'wobble' these planets produce in their parent star. This 'wobble' is measured as a tiny change in the star’s velocity, though great precision is required to detect it. We do not see any radiation from the planets because anything they radiate is overwhelmed by the radiation of their much brighter parent star. So we only observe the 'indirect' effect of these planets.
Perhaps the most important result of this work has been that, so far (though the search progresses), we haven’t seen any extra-solar planetary systems that look like ours. The paradigm we have built on our solar system may not in fact always apply.
Understanding planets via brown dwarfs
Brown dwarfs are a bit like stars and a bit like planets. Astronomers have used them as proxies for planets because they are single and their light is not swamped by a parent star. In one particular nearby brown dwarf they have observed changes in brightness, which suggest the existence of weather patterns, as seen in solar system planets.
The Gemini twins are two 8-metre telescopes, one in Hawaii and the other in Chile. They will offer Australian astronomers (via a 5 per cent share) the chance to peer inside the star formation process with unprecedented sensitivity and resolution.
With the Gemini telescopes becoming Australia’s front-line facility, new operating models will have to be found for our current largest facility – the Anglo-Australian Telescope at Siding Spring. One suggestion being strongly pursued is that it be used for a greatly expanded survey for planets in the southern sky. The largest, in fact, in existence.
Other relevant projects in the near future are the Space Interferometry Mission (SIM) in 2006, followed by the Terrestrial Planet Finder (TPF) in about 2010. TPF has the ambitious aim of detecting Earth-like planets around other stars, and seeking the signatures of life processes on those planets. All offer opportunities for Australian astronomers to be involved and they will increase our knowledge in understanding the birthplaces of worlds.
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.
