A picture taken recently by the Hubble telescope has revealed a wealth of information about the galaxies that go to make up our universe. Scientists are now using this picture to try and piece together the history of the universe after the 'big bang' ......

The Hubble telescope is one of the successes of the modern day American space programme. Located 600 km above the earth's surface, the job of the Hubble telescope has been to try and reconstruct the history of the universe following the 'big bang'. In January of 1995, NASA was to release an extraordinary photograph taken by the Hubble telescope which showed a large number of galaxies at a resolution that had never previously been obtained. This photograph was to be appropriately named the 'Hubble Deep Field'. The photograph is currently the object of intense study, the aim being to try to find out about some of the events that make up the history of the universe.

The Questions and the Answers- studying the 'Hubble Deep Field' photograph
Before the 'Hubble Deep Field' photograph could be taken, astronomers who wanted to look beyond our galaxy, had to find a part of the sky that had the least number of stars so that the Hubble telescope could look between them and beyond. At the same time it was necessary that the selected region of the skies contained a large number of galaxies within the range of resolution of the telescope. A region of the sky was finally chosen within the constellation of Ursa Major. In this region the Hubble telescope was able to make out about 300 separate galaxies, the most distant of which were very feint (magnitude 30). The 'Deep Field' photograph revealed distant galaxies that had never before been observed so clearly. While the majority of the galaxies could have been obseved by telescopes located on the earth's surface, they would, in most cases, have come out as nothing more than blurred patches. The big advantage of the Deep Field image is that it shows the precise shapes of the galaxies. Bob Williams, one of the leading astronomers involved in the Hubble project, collected all the data and made it available on the Internet to astronomers around the world.

Following the release of the photograph, the first task facing the NASA astronomers was to count the total number of galaxies and to categorise them based on their magnitudes. From this it was possible to obtain a value called the 'Density Parameter' from which it is possible to predict the future of our universe. A 'Critical Value' was also calculated. If the Density Parameter was greater than the Critical Value then this, according to leading astronomers, was an indication that the universe would enter a period of contraction referred to as the 'Big Crunch'. If the Density Parameter were found to be lower than the Critical Value then this would be an indication that he universe would continue to expand.

The 'big bang'- did it really happen?
Both the colour and the brightness of the light emitted by a galaxy provide information on the distance that the galaxy is away from the earth and on its age. A younger galaxy is brighter than an older galaxy. These features have been studied on the Hubble Deep Field photograph. The results obtained have, to the delight of the astronomers, supported the the 'big bang' theory for the origin of the universe.

The shapes of our neighbouring galaxies- Spirals, ellipses and irregular galaxies
Another feature of the galaxies, that the Hubble telescope has allowed astronomers to view for the first time are the shapes of the galaxies. In the space neighbouring the Milky Way, 70% of the galaxies have a spiral shape, 25% are elliptic and 5% are irregular. Elliptic galaxies might have arisen from the fusion of two spiral galaxies such that the Andromeda galaxy and the Milky Way may in the future come together to form one giant elliptic galaxy. At larger distances from the Milky Way, a fourth type of galaxy is evident which cannot be classified as spiral, elliptic or irregular. This type, say some astronomers, could be young galaxies in the preliminary phases of evolution. All this would seem to suggest that galaxy formation does not occur over a limited and completed period of time but is occuring as a continous process.

A Hubble Deep Field photograph in the Southern Hemisphere
Following the Deep Field photograph taken in the constellation Ursa Major, NASA now plans to take a similar photograph in the earth's southern hemisphere. A potential region of the sky has already been chosen, located within the constellation Toucan. It is hoped that such a secondary study will not only support the results already obtained with the Deep Field photograph, but will also provide new knowledge about how our universe was formed and what changes will occur in the future within the galaxies that surround the Milky Way.