The early universe looks the same in both hemispheres according to new images from the Hubble Space Telescope. In 1995 a 10-day exposure of the Northern sky called the "Hubble deep field" gave astronomers their first detailed glimpse of the universe 12 billion years ago. Now Hubble has carried out a similar exposure for the southern hemisphere. In both case thousands of previously unseen galaxies have come to light. The results indicate that the universe formed uniformly in all directions, as predicted by current cosmological theories.
The 1995 image was taken in a small patch near the Big Dipper constellation, which astronomers previously thought was completely blank. This new image taken by the Space Telescope Science Institute and NASA’s Goddard Space Flight Center last month, was of the constellation Tucana, near the south celestial pole. “We have eagerly awaited this new set of images ever since the first deep field image, which had a dramatic impact on the entire science of astronomy, ” says Robert Williams, who was the principal investigator on the latest observation.
Astronomers are also benefiting from new instruments that have been recently fitted to the telescope, which are allowing them to make more detailed measurements. For example, they will be studying the light from a quasar in the image which travelled through numerous intervening gas clouds in galaxies and intergalactic space. These clouds of primeval hydrogen subtract specific colours from the beam. The resulting absorption spectrum, recorded by an Imaging Spectrograph on the Hubble telescope, allows astronomers to probe the hydrogen clouds to find out what they are made of and where they are. “This is going to provide an extremely important way to test our ideas of how the intergalactic medium turned into galaxies, ” says Williams. Meanwhile, a new infrared camera called NICMOS captured some of the galaxies whose light had been ‘redshifted’ because of the expansion of the universe.
