Planck: final data from the mission lends support to the standard cosmological model

In 2013, ESA's Planck mission unveiled a new image of the cosmos: an all-sky survey of the microwave radiation produced at the beginning of the Universe. This first light emitted by the Universe provides a wealth of information about its content, its rate of expansion, and the primordial fluctuations in density that were the precursors of the galaxies. The Planck consortium publishes the full and final version of these data and associated articles on the ESA website on 17 July 2018. The corresponding articles have been submitted to the journal Astronomy & Astrophysics. With its increased reliability and its data on the polarisation of relic radiation, the Planck mission corroborates the standard cosmological model with unrivalled precision for these parameters, even if some anomalies still remain. For this work the Planck consortium called upon some three hundred researchers, in particular from CNRS, CNES (the French national space agency), CEA (the French Alternative Energies and Atomic Energy Commission) and several universities in France.

Planck’s view of the cosmic microwave background [Credit: ESA/Planck Collaboration]

Launched in 2009, ESA's Planck satellite mapped the cosmic microwave background, microwave radiation emitted 380,000 years after the Big Bang, when the Universe was still a hot, almost completely homogeneous gas. Tiny variations in its temperature provide information about its content, its rate of expansion and the properties of the primordial fluctuations that gave rise to the galaxies. An initial analysis of the data set was published in 2015, in the form of eight all-sky maps that included the polarisation of the cosmic microwave background, which determines how the waves that make up light vibrate on tiny scales. This key information bears the imprint of the last interaction between light and matter in the primordial Universe. However, only a preliminary analysis had been carried out on it.

Operating between 2009 and 2013, ESA’s Planck mission scanned the sky at microwave wavelengths to observe

 the cosmic microwave background, or CMB, which is the most ancient light emitted in the history of our Universe. 

Data from Planck have revealed an ‘almost perfect Universe’: the standard model description of a cosmos containing 

ordinary matter, cold dark matter and dark energy, populated by structures that had been seeded during an early 

phase of inflationary expansion, is largely correct, but a few details to puzzle over remain. 

In other words: the best of both worlds [Credit: ESA/Planck Collaboration]

The polarisation of relic radiation produces a signal 50 to 100 times weaker than that of its temperature and 10 to 20 times weaker than that emitted by the polarized emission of Galactic dust. Thanks to its HFI (High Frequency Instrument), the Planck satellite nonetheless obtained an extremely precise map of primordial polarisation across the entire sky. This was a world first and provides us with a wealth of information.

The Cosmic Microwave Background: temperature and polarisation
[Credit: ESA/Planck Collaboration]

Comprehensive, definitive and more reliable, the data published on 17 July 2018 confirms the preliminary findings, supporting a model which provides an excellent description of the content of the Universe in terms of ordinary matter, cold dark matter and dark energy (whose nature is unknown), with an inflation phase at its very beginning. This cosmological model can now be derived using temperature or polarisation data independently, with comparable accuracy. This considerably reinforces the standard model of cosmology, however surprising this may be. The results are described in a set of a dozen scientific papers, involving around three hundred researchers (see list of French laboratories involved below).

The history of the Universe [Credit: European Space Agency]

However, some anomalies and limitations remain. In particular, the rate of expansion of the Universe differs by a few percent depending on whether the data from the Hubble Space Telescope or from the Planck mission are used. This question is still an open one, and a host of telescopes will be marshalled in an attempt to resolve the issue.

Source: CNRS [July 18, 2018]