British and American astronomers have discovered a new kind of galaxy, a member of the group of "peculiar" galaxies, using the Hubble Space Telescope.
These galaxies, over three billion light years away from the earth, appeared as no more than tiny splodges of light through ground-based telescopes. But the precision of the HST has enabled the astronomers to identify the blue- coloured patches as a previously unknown class of peculiarly-shaped galaxy.
They are so far away that the light the telescopes receive set out when the Earth was newly formed.
The discovery - a result of the Anglo-American "Medium Deep Survey" - was announced by Richard Ellis, Karl Glazebrook, and Basilio Santiago of the Institute of Astronomy at Cambridge University and Richard Griffiths of Johns Hopkins University in Baltimore.
"The aim of the program is to use the HST as a time machine to look about eight billion years back in time in a universe which is about 16 billion years old," explained Richard Ellis.
Professor Ellis and his colleagues studied a sample of 301 galaxies, down to a visual magnitude of about 23 or 24, about one million times fainter than the dimmest star visible to the naked eye. They found an expected number of examples of the orderly spiral and elliptical galaxies which astronomers are familiar with in our local part of the universe.
But they were able to spot about as many again which looked very unusual. "The fraction that is irregular is much higher than we see today." The peculiar galaxies which appeared in definition through the HST resemble those which were common in the universe billions of years ago. "Galaxies at these remote distances in the past are much more irregular and assymmetric."
The astronomers are now hoping to find out why the galaxies are so faint and diffuse. They suggested that they may have merged into larger galaxies but said the most probable explanation is that their star formation has been extinguished and that they are now a lot dimmer than they used to be. They also intend to measure the distance of the irregular galaxies from earth using ground-based telescopes, and plan longer exposure imagings with the HST, with exposure ten or 12 times greater than the three or four hours used in the previous experiments.