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AAO Press Releases

10 November 1997

Shortcut to understanding the Universe

Last week, a team of Australian and British astronomers used the Anglo-Australian Telescope at Siding Spring Mountain to observe and analyse almost 4000 galaxies and more than 1000 quasars in just five nights. This included two nights when over a thousand galaxies and quasars were observed.

This is the first time so many objects have been observed and analysed in such a short time, anywhere in the world. Previously it would have taken years for the same amount of data to be collected and analysed, by painstakingly observing the faint targets one at a time. Mapping the Universe in three dimensions is now possible and astronomers are now confident of completing an ambitious `redshift survey*' of a quarter of a million galaxies and 30 000 quasars in only two years.

This remarkable feat was possible due to the operation of the Two-degree Field facility (2dF) on the largest optical telescope in Australia, the 3.9-metre Anglo-Australian Telescope. The 2dF, which has been under development for the past seven years, uses optical fibres to enable 400 galaxies to be analysed simultaneously, without resetting the telescope.

Once astronomers have chosen the galaxies and quasars to be observed, a robotic fibre-positioner places each fibre very quickly, in exactly the right position to collect the light. The optical fibres then carry the light into a pair of spectrographs to be analysed. The 400 fibres currently take about 90 minutes to set-up, but there are two sets of fibres. Therefore, whilst one is being used to collect data, the robot is busy configuring the next set, thus saving valuable observing time.

Collecting the raw data is only half the battle. To cope with the enormous amount of data that is produced, staff at the Anglo-Australian Observatory have developed new computer techniques to automatically analyse the galaxy spectra and to obtain the crucial redshifts.

The observation and analysis of all these galaxies and quasars was achieved by dedicated teams of Australian and UK astronomers. Astronomers in Australia carried out the observations and sent data over the internet to their colleagues in the UK. Here British astronomers constructed increasingly detailed maps of the distant Universe, almost as fast as the observations were being carried out on the other side of the world.

Dr Matthew Colless from Mount Stromlo & Siding Spring Observatories, who leads the Australian half of the 2dF Galaxy Redshift Survey team, said "Our survey aims to map a very large and representative volume of the Universe containing 250 000 galaxies. This survey is ten times larger than any previous survey and will provide measurements which will help understand how the Universe began, and what its ultimate fate will be."

A similar increase is expected in the number of known quasarsÆ. Dr Scott Croom from the University of Durham, a member of the quasar survey team said "Although quasars are rare, their brightness means that we can observe them almost to the edge of the visible Universe, and map a region of space up to 10 billion light years distant."

The Director of the Anglo-Australian Observatory, Dr Brian Boyle praised the foresight of the Anglo-Australian Telescope Board and UK and Australian Governments for supporting the development of the 2dF instrument. He also praised the outstanding scientific and technical skills of the Anglo-Australian Observatory team, led by Dr Keith Taylor, that designed and built the 2dF system in Australia. "The 2dF is one of the most complex astronomical instruments ever to be contemplated, let alone be built and installed on a ground-based telescope. It has ensured that the Anglo-Australian Telescope will remain one of the most productive optical telescopes in the world," Dr Boyle said.
*Redshifts are measured by analysing the light emitted from galaxies. Because the Universe is expanding, distant objects are seen to be moving away from us; the farther away they are, the faster they are receding. This moving away `stretches-out' the light emitted and shifts features in the spectrum red-wards &emdash; towards longer wavelengths. The redshift is measured with a spectrograph. Since the size of the redshift depends on the speed of each galaxy, and the speed depends on the distance, by measuring redshifts astronomers can determine the distance to all the galaxies and quasars. Thus they can build up a real three-dimensional picture of the Universe, rather than the two dimensional view we see on the sky. While previous surveys have made a start by looking carefully at selected, relatively small samples of galaxies, or by looking in depth in particular directions, the 2dF on the Anglo-Australian Telescope will, for the first time, enable astronomers to build up a complete 3-D picture of a substantial part of the Universe.

ÆQuasars are galaxies with extremely bright centres. This is believed to be caused by the destruction of stars as they funnel down a massive black hole at the centre of the galaxy.

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Roger Bell
01 Jan 1998