Caltech has the BICEP telescope (Background Imaging of Cosmic Extragalactic Polarization). BICEP2 is an experiment designed to measure the polarization of the cosmic microwave background (CMB) to unprecedented precision, and in turn answer crucial questions about the beginnings of the Universe. BICEP operates at 100 GHz and 150 GHz at angular resolutions of 1.0° and 0.7°, respectively, with an array of 98 polarization-sensitive detectors, mapping a large region of the sky around the South Celestial Pole. The telescope successfully deployed to the Amundsen-Scott South Pole Station in November 2005 and will take data until the end of 2008.
UPDATE – Wired – The team at the Harvard-Smithsonian Center for Astrophysics has announced they’ve found “The First Direct Evidence of Cosmic Inflation.” The scientists say that after three years of research and staring at a patch of sky, they have found and observed waves (signals of light) that are the “smoking gun” of cosmic inflation and echoes of the Big Bang theory.
The scientists have data that represents the first images of gravitational waves, or ripples in space-time. In the plainest English possible: these waves have been described as the “first tremors of the Big Bang” and were created fractions of a second after our universe came to be. They were part of Albert Einstein’s General Theory of relativity, but have never been seen.
Since the cosmic microwave background is a form of light, it exhibits all the properties of light, including polarization. On Earth, sunlight is scattered by the atmosphere and becomes polarized, which is why polarized sunglasses help reduce glare. In space, the cosmic microwave background was scattered by atoms and electrons and became polarized too.
“Our team hunted for a special type of polarization called ‘B-modes,’ which represents a twisting or ‘curl’ pattern in the polarized orientations of the ancient light,” said co-leader Jamie Bock (Caltech/JPL).
Gravitational waves squeeze space as they travel, and this squeezing produces a distinct pattern in the cosmic microwave background. Gravitational waves have a “handedness,” much like light waves, and can have left- and right-handed polarizations.
“The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness. This is the first direct image of gravitational waves across the primordial sky,” said co-leader Chao-Lin Kuo (Stanford/SLAC).
The team examined spatial scales on the sky spanning about one to five degrees (two to ten times the width of the full Moon). To do this, they traveled to the South Pole to take advantage of its cold, dry, stable air.
“The South Pole is the closest you can get to space and still be on the ground,” said Kovac. “It’s one of the driest and clearest locations on Earth, perfect for observing the faint microwaves from the Big Bang.”
They were surprised to detect a B-mode polarization signal considerably stronger than many cosmologists expected. The team analyzed their data for more than three years in an effort to rule out any errors. They also considered whether dust in our galaxy could produce the observed pattern, but the data suggest this is highly unlikely.
“This has been like looking for a needle in a haystack, but instead we found a crowbar,” said co-leader Clem Pryke (University of Minnesota).
Gravitational waves from inflation generate a faint but distinctive twisting pattern in the polarization of the CMB, known as a “curl” or B-mode pattern. For the density fluctuations that generate most of the polarization of the CMB, this part of the primordial pattern is exactly zero. Shown here is the actual B-mode pattern observed with the BICEP2 telescope, with the line segments showing the polarization from different spots on the sky. The red and blue shading shows the degree of clockwise and anti-clockwise twisting of this B-mode pattern.
The Guardian UK reported intense speculation last week among cosmologists that the US BICEP2 team is on the verge of confirming they have detected “primordial gravitational waves” – an echo of the big bang in which the universe came into existence 14 billion years ago.
Rumors have been rife in the physics community about an announcement due on Monday from the Harvard-Smithsonian Center for Astrophysics. If there is evidence for gravitational waves, it would be a landmark discovery that would change the face of cosmology and particle physics.
Gravitational waves are the last untested prediction of Albert Einstein’s General Theory of Relativity. They are minuscule ripples in the fabric of the universe that carry energy across space, somewhat similar to waves crossing an ocean. Convincing evidence of their discovery would almost certainly lead to a Nobel prize.
“If they do announce primordial gravitational waves on Monday, I will take a huge amount of convincing,” said Hiranya Peiris, a cosmologist from University College London. “But if they do have a robust detection … Jesus, wow! I’ll be taking next week off.”
Martin Hendry at the University of Glasgow works on several projects designed to directly detect gravitational waves. “If Bicep have made a detection,” he says, “it’s clear that this new window on the universe is really opening up.”
According to theory, the primordial gravitational waves will tell us about the first, infinitessimal moment of the universe’s history. Cosmologists believe that 10-34 seconds after the big bang (a decimal point followed by 33 zeros and a one) the universe was driven to expand hugely.
The bottom part of this illustration shows the scale of the universe versus time. Specific events are shown such as the formation of neutral Hydrogen at 380 000 years after the big bang. Prior to this time, the constant interaction between matter (electrons) and light (photons) made the universe opaque. After this time, the photons we now call the CMB started streaming freely. The fluctuations (differences from place to place) in the matter distribution left their imprint on the CMB photons. The density waves appear as temperature and “E-mode” polarization. The gravitational waves leave a characteristic signature in the CMB polarization: the “B-modes”. Both density and gravitational waves come from quantum fluctuations which have been magnified by inflation to be present at the time when the CMB photons were emitted
Known as inflation, the theory was dreamed up to explain why the universe is so remarkably uniform from place to place. But it has always lacked some credibility because no one can find a convincing physical explanation for why it happened.
Now researchers may be forced to redouble their efforts. “The primordial gravitational waves have long been thought to be the smoking gun of inflation. It’s as close to a proof of that theory as you are going to get,” says Peiris. This is because cosmologists believe only inflation can amplify the primordial gravitational waves into a detectable signal.
We report results from the BICEP 2 experiment, a Cosmic Microwave Background (CMB) polarimeter specif- ically designed to search for the signal of inflationary gravitational waves in the B-mode power spectrum around `80. The telescope comprised a 26 cm aperture all-cold refracting optical system equipped with a focal plane of 512 antenna coupled transition edge sensor (TES) 150 GHz bolometers each with temperature sensitivity of 300 K CMB ps. BICEP2 observed from the South Pole for three seasons from 2010 to 2012. A low-foreground region of sky with an effective area of 380 square degrees was observed to a depth of 87 nK-degrees in Stokes Q and U. In this paper we describe the observations, data reduction, maps, simulations and results. We find an excess of B-mode power over the base lensed-CDM expectation in the range 30 to 150 ghz range. Through jackknife tests and simulations based on detailedcalibration measurements we show that systematic contamination is much smaller than the observed excess. We also estimate potential foreground signals and find that available models predict these to be considerably smaller than the observed signal. These foreground models possess no significant cross-correlation with our maps. Additionally, cross-correlating BICEP2 against 100 GHz maps from the BICEP 1 experiment, the excess signal is confirmed with 3 significance and its spectral index is found to be consistent with that of the CMB, disfavoring synchrotron or dust
This illustration displays the mechanism by which density and gravitational waves produce E- and B-mode patterns in the polarization of the CMB. For a single density wave propagating in the direction of the arrow, an electron will always see hotter and colder photons in a direction parallel or perpendicular to the plane of this single wave (a plane at right angles to the arrow). Regardless of the direction of the density wave, this can thus only produce E-mode polarization patterns (upper right). A single gravitational wave is more complex. Although it propagates in the same direction as the density wave, it stretches and squeezes space in a direction perpendicular from it. Depending on the orientation of this stretch/squeeze motion, the gravitational wave is capable of producing either E- or B-mode polarization patterns (lower right). The structure of the universe at the moment the CMB was emitted is a large combinations of these density and gravitational wave
The first BICEP instrument observed the sky at 100 and 150 GHz with an angular resolution of 1.0 and 0.7 degrees. It had an array of 98 detectors, which were sensitive to the polarisation of the CMB. The instrument was a prototype for future instruments; it started observing in January 2006 and ran until the end of 2008.
The second generation instrument was BICEP2. This instrument had a 26cm aperture with 512 pixels operating at 150GHz, and it observed from 2010 to 2012
The Keck Array consists of five polarimeters. The first three started observations in the Austral summer of 2010-11; another two started observing in 2012. All of the receivers observed at 150 GHz until 2013, when two of them were converted to observe at 100 GHz. Each polarimeter consists of a refracting telescope (to minimise systematics), which are cooled by a pulse tube cooler to 4 K, and a Focal Plane Arrays of 512 Transition edge sensors cooled to 250 mK, giving a total of 2560 detectors.
The project was funded by $2.3 million from W. M. Keck Foundation, as well as funding from the National Science Foundation, the Gordon and Betty Moore Foundation, the James and Nelly Kilroy Foundation and the Barzan Foundation.
BICEP3 will consist of 2560 detectors observing at 100 GHz. It will be deployed in the 2014-15 Austral summer season
SOURCES – BICEP2, Harvard-Smithsonian Center for Astrophysics, Wired, Guardian UK, Caltech, NY Times, wikipedia
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