Underestimation of dust threatens BICEP results
22 Sep 2014 by qmjwtjwqdb.d qmjwtjwqdb.d
Spinning dust grains have put a dampener on the celebrations that cosmologists have found faint signals of cosmic background radiation released a fraction of a second after the Big Bang.
In March, scientists working on the BICEP2 project announced that their highly sensitive telescope in the South Pole had detected cosmic ripples left in the sky by the super-rapid expansion of space that must have occurred with the Big Bang.
The team believed they had found B-mode polarisation, a characteristic twist in the directional properties of Cosmic Microwave Background (CMB), waves of gravitational energy that ripple in the fabric of space time leaving an indelible mark on the sky.
However, swirls of foreground dust can create identical polarisation patterns, meaning this needs to be removed from the data to obtain an unambiguous view of the primordial background signal. By the time the scientists published their paper in Physical Review Letters in June, they had downgraded their level of confidence.
Although they had used all available information from other sources to eliminate this foreground dust, the scientists acknowledged that they had not used any data from the ESA’s Planck satellite, and it is this which is threatening one of the biggest scientific claims of the year.
In a paper published on arXiv, Planck scientists found that the area of the sky observed by BICEP contains significantly more dust than was assumed.
“We show that even in the faintest dust-emitting regions there are no ‘clean’ windows in the sky where primordial CMB B-mode polarisation measurements could be made without subtraction of foreground emission," they wrote.
"Unfortunately, according to our analysis, the effect of contaminants and in particular of gases present in our Galaxy cannot be ruled out", said Carlo Baccigalupi, SISSA cosmologist and one of the authors of the study.
BICEP2 and Planck scientists have come to an agreement to share data before publishing a paper later this year.
"We have started a collaboration with BICEP2. We are directly comparing their data with the Planck data, in the same frequency, 150 GHz, and trying to exploit the image of the contaminants we reach with Planck at other frequencies", said Baccigalupi. "This way, we hope to be able to give a definitive answer. In fact, we might find that it was indeed a contamination, but, given that we're optimists, we might even be able to exclude it with confidence. This way, Planck could give a crucial contribution to the discovery of evidence of gravitational waves from the Big Bang in cosmic background radiation. Such a discovery would open a completely new window onto unknown scenarios in the study of the primordial Universe and very-high-energy physics".
