Press Release
Physicists at Cambridge University have taken the first sharp picture of ripples in the relic radiation from the Big Bang. This was done using a new radio telescope of radical design situated near Cambridge. The picture shows detail fine enough to see the features in the early universe that turn into groups of galaxies --- galaxies like our own Milky Way.
Radiation from the Big Bang fireball has been travelling across the universe, cooling as space expands. Today, we see the faint relic radiation in all directions on the sky at a temperature of just 3 degrees centigrade above absolute zero, giving a picture of the universe when it was less than one 50,000th of its present age. Because galaxies must have formed out of the primeval fireball, astrophysicists have predicted that they will have left imprints in the radiation. Across the sky, there should be tiny variations in the temperature of the relic radiation. However, these ripples are very weak---only one 100,000th of a degree C.
In 1992, the NASA satellite COBE managed to detect faint ripples in the relic radiation, but the pictures were very blurred. COBE could only see temperature variations on angular scales bigger than 10 degrees on the sky---equivalent to a map of the world that doesn't show any detail smaller than 1000 km across. However, the most interesting information about the early universe is expected to be revealed on much smaller scales, of only about 1/4 degree---equivalent to features 25km across on a map of the world.
The new telescope, CAT (Cosmic Anisotropy Telescope), has been designed specifically to make detailed pictures of the relic radiation on these small scales. CAT receives the relic radiation at radio wavelengths of about 2 cm and combines the signals from three separate antennas spaced about 2 metres apart. In this way, CAT is able to filter out the atmospheric effects which otherwise cause severe problems when trying to view the cosmic ripples. Other projects attempt to overcome atmospheric contamination by either flying above it in a balloon, going into space, or operating in a `thin' atmosphere such as at the South Pole. CAT's ingenious design also makes it relatively cheap---only 250,000 pounds, compared with 300 million dollars for COBE.
From the properties of the image, scientists can obtain vital information on just what happened in the early universe and distinguish between competing cosmological theories. The CAT has already provided valuable new information but we need to obtain more details about the `ripples' in order to see how they turn into galaxies and groups of galaxies.
The CAT --- a prototype instrument --- shows that this fundamental research can be done cheaply from the ground. Following this success, the Particle Physics and Astronomy Research Council, which funded the CAT, has now agreed to fund a full-scale instrument which will be at least 10 times more sensitive than the CAT and allow a much wider range of features of the background radiation to be mapped. This instrument will be sited in Tenerife and is expected to be operational by 2000.
The new results will be published in the April 10 issue of the Astrophysical Journal Letters.