To resolve such uncertainties, Dressler said astronomers will need more time to study other galaxy clusters with the degree of sharpness promised by the computer-enhanced space telescope images. Galaxy clusters are attractive targets for in-depth study, he added, because they have samples of all types of stellar formations in one place at one time.
Divining how galaxies were created and why they take different shapes--from delicate spirals with their many newborn stars to regular ellipticals with older stars to the curious irregular galaxies full of wisps of hydrogen--is one of the most avidly pursued goals in astronomy today.
One intriguing prospect for further study, Dressler said, is the 10-billion-year-old galaxy cluster found while making images of the much closer 4 billion-year-old galaxy cluster. The older cluster, which is so far from Earth that it took 10 billion years for light to reach here, appears as faint and fuzzy dots in the background of those photographs.
Astronomers who had seen this ancient cluster found it particularly tantalizing because not all of the objects within it seem large enough to count as full galaxies. They said this could mean that these small objects are some wholly new kind of galaxy, or even that they are a much sought-after galactic building block known as a "protogalaxy."
Dressler said the ancient cluster, which is seen as it appeared only 1 billion or 2 billion years after the Big Bang theoretically created the known universe, is particularly interesting because, it seems to be relatively unremarkable. As such, he said, it is much more like our own Milky Way, and thus more likely to help explain how the Milky Way came to exist.
Ironically, news about the discovery of this "ordinary" galaxy cluster came a month after another group of scientists using the Hubble said that they had recorded images of "luminous knots" at the core of another 10-billion-year-old galaxy cluster. This other ancient cluster, which emits strong electromagnetic signals, already had been discovered by radio astronomers.
George Miley of Leiden University in the Netherlands said the knots could be giant clusters of as many as 10 billion stars in the process of formation, or they could be clouds of dust or gas caught in a "searchlight" beam of energy being radiated from a massive black hole at the galaxy's core.
Because of its optical problems, the space telescope is unable to send back detailed images of either ancient cluster, even with computerized image enhancement. Scientists hope the newer wide-field camera to be installed next year will improve their view of these targets.
Galactic Mug Shots
\o7 Distant, 4\f7 -\o7 billion-year-old galaxies that appeared as little more than shapeless smudges to ground-based telescope operators have been rendered much sharper with computer-enhanced images from the Hubble Space Telescope.
Astronomers have organized these galactic mug shots in a "Hubble atlas" ranging from some nearly spherical elliptical galaxies, on the left, to wispy spiral galaxies and lumpy irregulars, on the right. All these galaxies were found in one cluster.
About 30% of these galaxies are spiral-shaped. That is about six times the percentage among more modern galaxies, indicating a significant and relatively rapid evolution in the structure of the universe.\f7