photos at "more photos" link on the right). This building hosts two
telescopes, SPT on the left, and BICEP2 on the right. They are both
looking at different aspects of CMB, cosmic microwave background, an
imprint of what the Universe might have been like way at the
beginning. They are both impressive in their own right.
The South Pole Telescope measures the intensity and polarization
anisotropy of the CMB. They have a higher angular resolution than
BICEP, and they can detect galaxy clusters through the spectral
distortion imprinted on the CMB, and can set constraints on dark
energy that cause the expansion of the universe to accelerate. They
have 960 channels of bolometers and TES (transition edge sensors) as
their detectors, and use squid readout. Roughly 750 channels are
operational, and are looking at CMB at 90, 150, and 220 GHz.
BICEP is measuring the polarization at 100 GHz dn 150 GHz at angular
resolutions of 1.0 and 0.7 degrees respectively with an array of 98
polarization-sensitive bolometers (PSBs). They map a large region of
the sky near the South Celestial Pole. Its design is optimized to
provide exquisite sensitivity to CMB polarization on medium to large
angular scales, allowing it to directly probe for the gravitational
wave signature of inflation.
SPT uses pulse tubes to cool their detector so there is no need to
keep a stock of liquid helium. The detector is kept around 250 milli-
Kelvin - now that's really cold! I have never seen so much and such a
long liquid-helium transfer line in my life. Dana and Daniel, the two
winter-overs opened the roof of the building and showed the telescope
move: very smooth and surprisingly fast.
Because they are looking at radio frequencies, these telescopes are
operational even when the sun is up.
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