The precise positions of more than a million galaxies are to be mapped by a new telescope which, astronomers hope, will finally resolve the mystery surrounding the formation of galaxies such as our own Milky Way in the early days of the universe.
The telescope - part of the Sloan Digital Sky Survey and under construction in New Mexico in the United States - may also shed light on the ultimate fate of the universe: whether it will go on expanding for ever or will eventually contract.
At the focus of the telescope's three-metre mirror will be optical fibre cables so the light from each galaxy is piped to an individual spectrometer for analysis. In this way, it should be able to analyse the light from 300 galaxies simultaneously.
Between 50 billion and 200 billion galaxies are now thought to exist, so the telescope will identify fewer than one in 50,000 of them. Each of these "star cities" is itself immense, containing billions of stars and so vast that it would take light more than 100,000 years to travel from one side to the other.
The presence of the galaxies and the way they cluster is a major puzzle for cosmologists, Dr Mario Livio of the Space Telescope Science Institute told the annual meeting of the American Association for the Advancement of Science in Baltimore.
The fundamental cosmological principle was that the universe ought to be uniform. But ground-based telescopes had revealed a large-scale structure which is spongy or bubble-like, he said. There were huge dark voids while clear filaments and clumps were formed of anything from a dozen to a thousand or so luminous galaxies.
To reconcile the cosmological principle with the observed map of the universe, Dr Livio said, astronomers have turned to "dark matter" which they believe makes up more than 90 per cent of the stuff of the cosmos but which remains invisible, evident only by the pull of its gravitational attraction.
There are two theories of this: some astronomers favour exotic, as yet undiscovered, subnuclear particles known as "cold dark matter"; others favour "hot dark matter" composed of subnuclear particles which have been fleetingly glimpsed in particle physics experiments.
Neither model works too well, Dr Livio conceded. "The basic assumptions of the Big Bang theory are extremely good," he said. But the details, especially of the hot and cold dark matter scenarios "look vulnerable". That is why, he said, it was vital to "compare observations with theory".
Observations from the Sloan Digital Sky Survey and more pictures from the Hubble Space Telescope will give detailed measurements on the distribution of distant galaxies and provide a stringent test for any theory as to how the smoothness of the early universe could have so quickly yielded clusters of galaxies, according to Dr Livio.
Indirectly, they should also measure the amount of dark matter and thus show whether there is so much material in the universe that it will eventually collapse in on itself under the force of its own gravitation, coast to a gentle halt, or go on expanding for ever.Reuse content