Worlds largest Thermometer Camera to shed light on evolution after Big Bang

The worlds largest bolometer camera for sub-millimetre astronomy has been put into service at the 12-m APEX telescope, located on the 5100m high Chajnantor plateau in the Chilean Andes.

Munich, Aug 6 : The world's largest bolometer camera for sub-millimetre astronomy has been put into service at the 12-m APEX telescope, located on the 5100m high Chajnantor plateau in the Chilean Andes.

LArge BOlometer Camera (LABOCA) was specifically designed for the study of extremely cold astronomical objects and, with its large field of view and very high sensitivity, it promises to open new vistas in the knowledge of how stars form and how the first galaxies emerged from the Big Bang.

"A large fraction of all the gas in the Universe has extremely cold temperatures of around minus 250 degrees Celsius, a mere 20 degrees above absolute zero. Studying these cold clouds requires looking at the light they radiate in the sub-millimetre range, with very sophisticated detectors," said Karl Menten, director at the Max Planck Institute for Radioastronomy (MPIfR) in Bonn, Germany, that built LABOCA.

Menten said the bolometer, which is in essence a thermometer, would be used to detect incoming radiation by registering the resulting rise in temperature.

Essentially, a bolometer detector combines many tiny bolometer units into a matrix, much like the pixels are combined in a digital camera. Its extremely thin foil absorbs the incoming light, and any change of the radiation's intensity results in a slight change in temperature of the foil, which is then registered by sensitive electronic thermometers.

LABOCA observes at the sub-millimetric wavelength of 0.87 mm, and consists of 295 channels, which are arranged in nine concentric hexagons around a central channel. The angular resolution is 18.6 arcsec, and the total field of view is 11.4 arcmin, a remarkable size for instruments of this kind.

According to Menten, to be able to measure such minute temperature fluctuations, the bolometers need to be cooled down to less than 0.3 degrees above absolute zero, minus 272.85 degrees Celsius.

"Cooling to such low temperatures requires using liquid helium, which is no simple feat for an observatory located at 5100m altitude," said Carlos De Breuck, the APEX instrument scientist at the European Southern Observatory.

But it is not very simple to measure the weak temperature radiation of astronomical objects. The signals from space are heavily absorbed by water vapour in the Earth's atmosphere.

Though for this very reason, telescopes for this kind of astronomy are built on high, dry sites, and that is why the 5100m high plateau at Chajnantor in the extremely dry Atacama Desert was chosen; but even under such optimal conditions the heat from Earth's atmosphere is still a hundred thousand times more intense than the tiny astronomical signals from distant galaxies.

Very special software is required to filter such weak signals from the overwhelming disturbances, De Breuck said.

"It is a bit as if you were trying to see stars during the day," added Axel Weiss of the MPIfR and leader of the team that installed LABOCA on APEX.

ANI