Tenerife Experiment

From Wikipedia, the free encyclopedia
Jump to: navigation, search

The Tenerife Experiment was a Cosmic Microwave Background (CMB) experiment built by Jodrell Bank of the University of Manchester and in collaboration with the Instituto de Astrofisica de Canarias (IAC). It was installed and run at the Observatorio del Teide in Tenerife in 1984 and ran with various upgrades and additional experiments until 2000. Contact was made with the Instituto de Astrofísica de Canarias (IAC) which had shown that the Teide Observatory was an ideal site for infra-red observations. An agreement was arrived at and the first radiometer (10 GHz) was installed in 1984 and so was born the Tenerife Experiment.

It measured anisotropy of the CMB on angular sizes of 5 degrees, about the size of the upper half of the constellation of Orion (from the "belt" to the "shoulders"). To reduce receiver instability, it performed fast Dicke Switching between two horns separated by 8 degrees. To remove long term drifts and atmospheric variations, it used a further switch of 8 degrees using a flat mirror in front of the horns.

There were three radiometers working at 10.45, 14.9 and 32.5 GHz (i.e. 3, 2 and 1 cm in wavelength) at the Teide Observatory, Tenerife. This allowed the identification of CMB and galactic signals since the thermal black body CMB signal has the same temperature at these frequencies, whereas galactic signals rapidally drop with frequency.

In 1994, the discovery of the "thermal footprints" in the fossil cosmic microwave radiation reinforced the "Big Bang" theory. This radiation corresponds to light emitted some 300,000 years after the "Big Bang" (almost 14,000 million years ago) and represents a "snapshot" of the state of the primordial universe, when it was much hotter and more compact.

The instruments are examples of a Dicke Radiometer, which function using a rapid switching between two horns to measure directly small temperature differences and eliminate fluctuations in the amplifiers. Tenerife radiometers used a switch frequency of 63 Hz, but even so there existed long term drifts on the scale of hours due to changes in temperature and the atmosphere. This was removed by using further switching by a mirror that moved every eight seconds in front of the horns.

Over the years, the observatory installed two more radiometers, one operating at 15 GHz and one at 33 GHz. These new instruments were scaled copies of the old 10 GHz radiometer according to their observing wavelength to obtain the same response on sky: three fields of 5 degrees across, separated by 8 degrees. In the final analysis of the data, all frequencies were necessary, so all the instruments were considered as a single experiment.

Three frequencies are required to confirm the origin of any detected signal on the sky. If the signal appears in the three instruments with the same amplitude, then it should correspond to the thermal perturbations of the Cosmic Microwave Background. This was the case in 1994, when a common signal between the three channels was detected, with a temperature of 30 microKelvins, or one part in 100,000 in the amplitude of 3 K (-270.15°C) of the background radiation. A galactic signal should have an amplitude ten times larger in the 10 GHz instrument than in the 33 GHz one.