Everything about The Cosmic Background Imager totally explained
The
Cosmic Background Imager (or
CBI) is a 13-element
interferometer perched at an elevation of 5,080
metres (16,700 feet) at
Llano de Chajnantor Observatory in the
Chilean
Andes. It started operation in 1999, and is used to study the
cosmic microwave background radiation.
CBI conducts measurements at frequencies between 26 and 36
GHz in ten bands of 1Ghz
bandwidth. It has a resolution of better than 1/10 of a degree. (In comparison, the pioneering
COBE satellite, which produced the first detection of fluctuations in the microwave background in
1992, had a resolution of about 7 degrees.) Among the key findings of the CBI is the fact that fluctuations which have a small size on the sky are weaker than fluctuations which have a large size on the sky, which confirmed earlier theoretical predictions. More technically, CBI was the first experiment to detect intrinsic anisotropy in the
microwave background on mass scales of galaxy clusters; it provided the first detection of the
Silk damping tail; it has found a hint of excess power at high-l multipoles (CBI-excess) than expected from the
ΛCDM model; and it has detected fluctuations in the
polarization of the microwave background obtaining the first detailed E-mode polarization spectrum providing evidence that it's out of phase with the total intensity mode spectrum.
The CBI was built at the
California Institute of Technology, and employed sensitive radio amplifiers from the
National Radio Astronomy Observatory; two similar experiments are the
Very Small Array, operated on the island of
Tenerife, and the
Degree Angular Scale Interferometer, operated in
Antarctica. Both of these experiments used radio interferometry to measure CMB fluctuations at lower resolution over larger areas of the sky. Another experiment operated from Antarctica, the
Arcminute Cosmology Bolometer Array Receiver, used total power (bolometric) detection and a single antenna at higher frequency and similar angular resolution to obtain results comparable results to the CBI. The confluence of these and other CMB experiments employing different measurement techniques in recent years is a great triumph of observational cosmology.
CBI is a collaboration among a number of institutions in the US and Europe. It also closely collaborates with Chilean institutions
Universidad de Chile and
Universidad de Concepcion.
In 2006, new 1.4 m antennas replaced the old 0.9 m dishes for more high-resolution studies in total intensity mode. In this stage, CBI is being called CBI-2. In June 2008, CBI-2 will stop observations and the 13-antenna instrument will be dismounted to install the new
QUIET telescope.
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