Cosmic Background Imager

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Cosmic Background Imager
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The CBI Telescope
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Coordinates 23°02′S67°46′W / 23.033°S 67.767°W / -23.033; -67.767
Telescope style cosmic microwave background experiment
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CMB as measured by the CBI experiment

The Cosmic Background Imager (or CBI) was 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 operations in 1999 to study the cosmic microwave background radiation and ran until 2008.

CBI conducted measurements at frequencies between 26 and 36 GHz in ten bands of 1 GHz bandwidth. It had 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 found a hint of excess power at high-l multipoles (CBI-excess) than expected from the ΛCDM model; and it detected fluctuations in the polarization of the microwave background obtaining the first detailed E-mode polarization spectrum providing evidence that it is 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 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 was a collaboration among a number of institutions in the US and Europe. It still closely collaborates with Chilean institutions Universidad de Chile and Universidad de Concepción through the Chajnantor Observatory.

In 2006, new 1.4 m antennas replaced the old 0.9 m dishes for more high-resolution studies in total intensity mode. During this stage, CBI was called CBI-2.

In June 2008, CBI-2 stopped the observations and the 13-antenna instrument was removed from its mount. The new QUIET telescope instrument was installed in August 2008 on the CBI mount, replacing CBI-2 .

See also

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Atacama Cosmology Telescope Telescope in the Atacama Desert, northern Chile

The Atacama Cosmology Telescope (ACT) is a six-meter diameter telescope located on Cerro Toco in the Atacama Desert in the north of Chile, near the Llano de Chajnantor Observatory. ACT makes high-sensitivity, high-resolution, microwave-wavelength surveys of the sky in order to study the cosmic microwave background radiation (CMB), the relic radiation left by the Big Bang process. At an altitude of 5,190 metres (17,030 ft), it is one of the highest permanent, ground-based telescopes in the world.

Llano de Chajnantor Observatory Observatory

Llano de Chajnantor Observatory is the name for a group of astronomical observatories located at an altitude of over 4,800 m (15,700 ft) in the Atacama Desert of northern Chile. The site is in the Antofagasta Region approximately 50 kilometres (31 mi) east of the town of San Pedro de Atacama. The exceptionally arid climate of the area is inhospitable to humans, but creates an excellent location for millimeter, submillimeter, and mid-infrared astronomy. This is because water vapour absorbs and attenuates submillimetre radiation. Llano de Chajnantor is home to the largest and most expensive astronomical telescope project in the world, the Atacama Large Millimeter Array (ALMA). Llano de Chajnantor and the surrounding area has been designated as the Chajnantor Science Reserve by the government of Chile.

The Degree Angular Scale Interferometer (DASI) was a telescope installed at the U.S. National Science Foundation's Amundsen–Scott South Pole Station in Antarctica. It was a 13-element interferometer operating between 26 and 36 GHz in ten bands. The instrument is similar in design to the Cosmic Background Imager (CBI) and the Very Small Array (VSA). In 2001 The DASI team announced the most detailed measurements of the temperature, or power spectrum of the Cosmic microwave background (CMB). These results contained the first detection of the 2nd and 3rd acoustic peaks in the CMB, which were important evidence for inflation theory. This announcement was done in conjunction with the BOOMERanG and MAXIMA experiment. In 2002 the team reported the first detection of polarization anisotropies in the CMB.

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Archeops

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QUIET

QUIET was an astronomy experiment to study the polarization of the cosmic microwave background radiation. QUIET stands for Q/U Imaging ExperimenT. The Q/U in the name refers to the ability of the telescope to measure the Q and U Stokes parameters simultaneously. QUIET was located at an elevation of 5,080 metres at Llano de Chajnantor Observatory in the Chilean Andes. It began observing in late 2008 and finished observing in December 2010.

BICEP and Keck Array Series of cosmic microwave background (CMB) experiments at the South Pole

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POLARBEAR

POLARBEAR is a cosmic microwave background polarization experiment located in the Atacama Desert of northern Chile in the Antofagasta Region. The POLARBEAR experiment is mounted on the Huan Tran Telescope (HTT) at the James Ax Observatory in the Chajnantor Science Reserve. The HTT is located near the Atacama Cosmology Telescope on the slopes of Cerro Toco at an altitude of nearly 5,200 m (17,100 ft).

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Atacama B-Mode Search

The Atacama B-Mode Search (ABS) was an experiment to test the theory of cosmic inflation and distinguish between inflationary models of the very early universe by making precise measurements of the polarization of the Cosmic Microwave Background (CMB). ABS was located at a high-altitude site in the Atacama Desert of Chile as part of the Parque Astronómico de Atacama. ABS began observations in February 2012 and completed observations in October 2014.

Simons Observatory

The Simons Observatory is located in the high Atacama Desert in Northern Chile inside the Chajnator Science Preserve, at an altitude of 5,200 meters (17,000 ft). The Atacama Cosmology Telescope (ACT) and the Simons Array are located nearby and these experiments are currently making observations of the Cosmic Microwave Background (CMB). Their goals are to study how the universe began, what it is made of, and how it evolved to its current state. The Simons Observatory shares many of the same goals but aims to take advantage of advances in technology to make far more precise and diverse measurements. In addition, it is envisaged that many aspects of the Simons Observatory will be pathfinders for the future CMB-S4 array.