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N°29 I quarterly I APRIL 2013 In the News | 5 Astrophysics A New Image of the Big Bang’s Afterglow By Eddy Delcher Planck was developed by the European Space Agency (ESA) to observe the cosmic microwave background (CMB), or radiation emitted by the Big Bang roughly 14 billion years ago. To do so, the satellite spent 15 months measuring the temperature fluctuations of the CMB by measuring its intensity at nine frequencies. The nine maps thus generated were combined to remove contamination from objects obstructing the view, such as our own galaxy. Planck has delivered the most accurate map of the CMB to date, a huge step towards understanding the birth and evolution of our universe. Since its launch in 2009, Planck was able to perform over one billion measurements— the equivalent of five fullsky surveys—half of which were analyzed to provide the first batch of results. “Although most of these confirm the standard model of cosmology, there are a number of exciting surprises. For example, we find the universe’s expansion rate to be substantially lower than previously thought,” explains CNRS researcher François Bouchet from the IAP,1 who co-led the project. The proportions of matter that make up the universe were also revised. For example, dark matter, which is only observable via its gravitational influence, actually makes up 26.8% of the universe, which is about 4% more than previously surmised. “Planck’s unrivalled accuracy has also made it possible to compare large- and small-scale observations. This is similar to comparing heights in low- and high-definition images of Earth. The former identifies continents from their surrounding oceans, while the latter pinpoints less extensive structures, like Mount Everest. We found that the relative heights were not quite as expected in the standard model. As a result, new ingredients may need to be added to our description of the cosmic recipe. This is going to generate a great deal of excitement in the scientific community, opening the door to new theoretical exploration,” says Bouchet. Another important result is the confirmation of a key prediction of inflationary models. During inflation, tiny density variations, known as primordial fluctuations, occurred and were stretched to cosmological scales, seeding the growth of structures that make up our universe. Inflation then ended and gave way to ordinary matter. “We finally found in the data an imprint of the end of inflation, giving us clues on how to go beyond standard physics,” concludes Bouchet. 01. Institut d’astrophysique de Paris (CNRS / Université Pierre et Marie Curie). Contact information: IAP, Paris. François Bouchet > bouchet@iap.fr The first round of results from the Planck satellite mission are out, changing our vision of the universe. for Further information . All Planck findings are accessible on ESA’s website: > www.esa.int/ESA 01 The anisotropies of the cosmic microwave background (CM B) as observed by Planck. The map shows minute temperature fluctuations that correspond to regions of slightly different densities: the seeds of all future stars and galaxies. 02 Planck’s high-precision CM B map has allowed scientists to extract the most refined values of the universe’s ingredients to date. © photo & schema : ESA and the planck colaboration 02 01 Before Planck After Planck


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