Cosmology

Much of the effort of the Observatory is directed towards imaging the cosmic microwave background radiation. This radiation is a very faint relic of the stage when the Universe was a small hot fireball with an age of only some 300,000 years. In the time since it was emitted the expansion of the Universe has caused the radiation to cool to a temperature of only 2.7 degrees above absolute zero, and it is now detectable only at radio wavelengths. By mapping differences in radiation intensity from point to point across the sky, one can find out about the growth of material structures in the Universe as the fireball phase was ending. This tells us about the formation of the galaxies and galaxy clusters that populate the Universe now, and allows us to infer the physical conditions in the Universe when it was only a fraction of a second old.

The difficulty with microwave background imaging, however, is that the point-to-point intensity variations are only about one part in one hundred thousand, requiring extremely sensitive purpose-built telescopes. One telescope designed to map the microwave background is the Cosmic Anisotropy Telescope - CAT - shown on the right. This has 3 receiving horn aerials working at 2 cm wavelength and maps the fluctuations on a scale of about half a degree.

The Ryle telescope is also used for microwave background mapping. It is sensitive to scales from 1 second of arc to several minutes. It has recently provided the image below of a faint dip (shown black) in the intensity of the background (shown in red) as the radiation travels towards us through a galaxy cluster. The size of the dip and the cluster's recession speed have enabled us to estimate the age of the Universe as nearly 20 billion years.

The MRAO
An Introduction to Radio Telescopes
Stars - Birth and Death
Aperture Synthesis with Light
Galaxies and Quasars

Last Modified 13 October 1998
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