Lesley Cowling talks to a UCT professor who is introducing the world to new galaxies
TONY FAIRALL greets questions on his subject with a wry smile and the deceptive simplicity of a Zen master. When your daily work combines the task of mapping the unimaginable – our universe – and a job as director of Cape Town’s planetarium, where you need to teach children and other neophytes about the cosmos, you have to have a special touch.
Exposure to the realities of the universe can crack the ordinary notions of our world and make it all seem a little beside the point.
Try this for a Zen concept: Fairall, associate professor at the University of Cape Town (UCT), was part of a team of astronomers who recently located a rich cluster of galaxies in a region of the universe dubbed “the Great Attractor”. Our galaxy and our neighbouring galaxies are all streaming towards it at the speed of 600km/ second, but with no danger of collision – it is moving away from us at the even faster rate of 5 000km/second.
Where is it going? Why are we chasing it? And why so fast?
Fairall smiles gently. “Actually, by cosmological standards, 600 kilometres a second is quite sedate.”
Our galaxy is moving towards the attractor because of gravity – such a large clump of cosmic matter exerts a pull on its neighbours, drawing galaxies after it as it moves through space.
Fairall compares the movements of the universe to a currant cake baking in an oven. As the cake gets bigger, the currants move away from each other.
The baking cake phenomenon is a result of how the universe began. Fairall says that, scientifically, the accepted way as to how the universe began is the “Big Bang” theory.
“In the beginning, everything was very dense – and all that we know of in the universe was confined into a very small volume,” he says. “The volume grew explosively larger – much like a bomb going off.”
It is still doing that today, though more slowly. Some of the material in the volume – originally very hot gas – cooled into galaxies, while the space between the galaxies is still expanding.
Over and above this cosmological expansion, astronomers have long been aware of the streaming of galaxies towards a particular region, but until earlier this year there had always been a blank spot on the map that the “Great Attractor” now occupies.
This was partly because the region is somewhat obscured by the Milky Way. Galaxies, Fairall explains, are like towns or villages – a vast number of suns and their satellites bunched together and surrounded by dark matter. They are separated from each other by empty space.
The shape of a galaxy is usually disc-like – a spiral or coil of material – and our galaxy is typical in this respect. Our solar system is not at the centre of the galaxy, but off to one side, and the Milky Way, seen only from the Southern Sky, is the bulk of our galaxy.
Trying to look beyond and through it is like trying to see through the high-rises and suburban ridges of a city to the area beyond. Fairall and UCT student Patrick Woudt worked with four international astronomers to map what was behind the Milky Way, using a whole-sky photographic survey.
The photographs were magnified 50 times and then carefully scrutinised to separate the stars of the Milky Way from what lay further out in space. This is a painstaking process.
As Fairall points out, the photographs are two-dimensional and don’t have depth, so they show galaxies next to each that might be quite far apart. To find out how far from us each galaxy or star was, Fairall and Woudt used the telescope at the South African observatory at Sutherland. He would look at each galaxy, and from the spread of colours it produced work out the distance of the galaxy from us.
This process was also used by Fairall’s colleagues at European observatories based in South America, and it unearthed more than 10 000 previously obscured galaxies. The observations enabled the astronomers to calculate the size and mass of the “Great Attractor”.
The leader of the research is Dr Rene Kraan-Korteweg, of the observatory of Paris- Meudon, who began collaborating with Fairall in 1991. He has visited the Sutherland observatory several times.
The “Great Attractor” is 300-million light years away. This makes the discovery historic in another sense – not only a modern event, but a phenomenon of the past. Light takes time to travel across distance. This time is negligible when the light is coming to us from the moon, but as the distance increases, time becomes history.
What Fairall and his team have mapped and seen is 300-million years old. The “Great Attractor” may look somewhat different from what the telescopes have made visible to us, but we will only know what those differences are 300-million years from now.
This makes mapping the universe increasingly a process of mapping the past as astronomers reach further and further out into the universe.
The technology of the Hubble telescope has made the furthest areas of the universe visually accessible and, in covering this immense distance, has crossed the divide of history to show the origins of the universe.
The lifetime of the universe is around 15- billion years, so when astronomers start to look at a distance of 15-billion light years away – whatever direction they point the telescope – they no longer see stars and galaxies, but clouds of opaque gases. Those are the materials from which a universe grows, and what astronomers are seeing is the beginning of its life.
“It’s as if we are an egg, surrounded by shell,” says Fairall. The map of the universe, seen from above in a God’s eye- view, is therefore a circle, with our galaxy right at its centre.
“Beyond this line are licorice allsorts,” Fairall quips, pointing to the circular boundary. “And no one can prove any different.”
Astronomy sites: http://da.saao.ac.za http://fits.cv.nrao.edu/www/astronomy.html