The primary goal of BICEP2 is to measure the very faint polarization of the cosmic microwave background (CMB). The CMB is a nearly perfect, uniform black body at 2.7 K, with degree-scale temperature anisotropy of about 0.1 mK and polarization on the order of microkelvin. This radiation was emitted 380,000 years after the Big Bang, at the time of recombination, when the Universe first became transparent to light. The temperature anisotropy and polarization of the CMB are some of the most powerful ways of understanding the early Universe. Cosmologists believe the Universe experienced a rapid period of cosmic inflation during its first fraction of a second, exponentially expanding from a dense, hot subatomic volume. Many models of inflation predict that this rapid acceleration would have generated gravitational waves that would remain energetic enough 380,000 years later to leave an imprint on the CMB. BICEP2 is searching for this imprint by measuring the pure-curl component of the CMB polarization on degree angular scales, which is largely free of contamination from sources other than primordial gravitational waves.
The original BICEP telescope observed from 2006-2008, and recently published the most sensitive maps of CMB polarization at the angular scales most sensitive to inflation. The results include clear detection of the curl-free E mode polarization and an upper limit of r<0.72 (95% confidence level) on primordial gravitational waves. They also demonstrate a successful approach to making sensitive measurements of CMB polarization. BICEP2 builds on the success of BICEP1, replacing horn-coupled bolometers with antenna-coupled TES arrays fabricated at JPL. This change allows an increase in the number of pixels, and preliminary tests show an an improvement in mapping speed of a factor of 8. BICEP2 was deployed in November, 2009, and is continuing to take data through the Southern Hemisphere winter from its observing site at the Amundsen-Scott South Pole Station, which offers excellent environmental conditions for microwave astronomy.
KIPAC is a participant in BICEP and BICEP2 through the group of Chao-Lin Kuo. The group also actively worked in the deployment of a larger telescope, the Keck Array, in the 2010/11 season. Our collaborators on BICEP2 are Caltech, JPL, Harvard, Chicago, Berkeley, San Diego, British Columbia, and Toronto.
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"First light" map of temperature and polarization of the Milky Way Galaxy from BICEP2, February 2010. Microwave radiation emitted by spinning dust grains, aligned in the magnetic field of the galaxy, is about 1-3% polarized (polarization magnitude and direction shown by white line segments).