Launched in 2009, Planck, a satellite of the European Space Agency (ESA) dedicated to the study of the cosmic microwave book today the results of its first fifteen months of observations. They provide a wealth of information on the history and composition of the Universe: the most accurate map ever obtained of the CMB, which highlights an effect predicted by the models of inflation, a downward revision of the expansion rate of the universe, a new assessment of the composition of the Universe. Many of these data were obtained from the main Planck instrument, HFI, designed and built under the direction of the Institut d’astrophysique spatiale (CNRS/Université Paris – Sud) with funding from the CNES and the CNRS.
Since its discovery in 1965, the CMB is a valuable source of knowledge for the cosmologists, a veritable “Rosetta Stone” leading to decipher the history of the universe since the Big Bang. The photon flux detectable across the sky, in the range of the radio waves, reflects the state of the universe at its early youth and contains traces of large structures that will develop later. Produced 380,000 years after the Big Bang, when the first atoms were formed, it comes to us almost unchanged and allows the scientists to access to the image of the cosmos at its birth, approximately 13.8 billion years ago. Comparing these measurements to the theoretical models can bring us a lot of information, not only regarding the evolution of the Universe since the appearance of the fossil radiation, but also relating to past events that caused them and for which astrophysicists have little observations.
A new map of the CMB
This is one of those windows on the Universe that has opened the Planck mission. Launched in 2009, this satellite of ESA has, for a year and a half, made a map of the CMB over the whole sky. Planck has two instruments, one of which, the high frequency instrument HFI, was designed and built under the direction of the Institut d’Astrophysique Spatiale (CNRS / Université Paris-Sud) with funding from the CNES and the CNRS. Thanks to them, it was able to measure with an unprecedented sensitivity the variations in light intensity of the early universe, thus refining the observations of the space missions COBE (launched in 1990) and WMAP (1998). These variations in light intensity (which are in the form of more or less bright spots) are precisely the footprints of germs of the large structures of the actual cosmos and designate where the material assembled then collapsed on itself before giving birth to stars, galaxies and clusters of galaxies.
According to some theories, the origin of these “lumps” or “fluctuations” of the CMB is to be sought in the “Inflation”, an event that occurred earlier in the history of the Universe. During this quite violent episode which would have taken place about 10 (exp-35) seconds after the “Big Bang”, the universe would have been a sudden boom and would have grown significantly, at least by a factor 10 (exp26). Planck has demonstrated the validity of one of the key predictions of the theories of inflation: the light intensity of “large-scale fluctuations” should be slightly higher than that of “small scale fluctuations.” However, for larger scales, the observed intensity is 10% lower than the predictions of inflation, a mystery that no theory can explain today. Planck also confirmed with certainty the existence of other anomalies in the past as a mysterious asymmetry of the average temperatures in opposite directions or the existence of a cold point.
Data from the Planck nominal mission gave rise to thirty simultaneous publications available on March 21, 2013 at http://sci.esa.int, and on March 22, 2013 www.arxiv.org. Amon the other results:
- Confirmation of the “flatness” of the Universe
- The downward revision of the Hubble constant, and hence of the expansion rate of the Universe
- A new evaluation, from the CMB alone, of the composition of the Universe: 69.4% dark energy (against 72.8% previously), 25.8% dark matter (against 23%) and 4.8% ordinary matter (against 4.3%).
- Unique and valuable maps to refine the scenario of the story of the universe and understand the physics that governs its evolution : they show how dark matter and ordinary matter are distributed in the sky, the “diffuse infrared background” corresponds in turn to the light emitted by the dust of all the galaxies in the past ten billion years and thus allows to identify the areas where focused the objects made of ordinary matter.
- A first analysis of the polarization of the cosmic microwave signal, which shows that the Planck data are remarkably consistent with those of the fossil radiation intensity at the scales corresponding to future galaxy clusters. A more comprehensive analysis will be provided in 2014, as well as other results of the Planck mission.
The contribution of French research in the Planck mission
France is leader in the Planck high frequency instrument – HFI essential for cosmological results: its construction costed 140 millions € and mobilized 80 researchers from ten laboratories of the CNRS, the CEA and universities, as well as many engineers and technicians. France has provided more than 50% of the funding of the construction as well as the processing of their data: half of this funding comes from the CNES, the other half from the CNRS and universities. It also participates in the financing of the mission itself through its financial contribution to the scientific program of the ESA, i.e., 15% of the cost of the mission.
A French contribution essential to the Planck project was the provision of the cooling system at 0.1 degrees above the absolute zero of the HFI instrument. This system, which gave rise to a CNES certificate, was invented by Alain Benoit (CNRS), Institut Néel (who earned the 2012 Medal for Innovation of the CNRS) and developed by the Air Liquide company. With this innovation, the HFI camera holds the cold record for a space instrument with a cryostat cooled for nearly a thousand days at -273.05 °C. (http://www2.cnrs.fr/presse/communique/2679.htm).
The exploitation of the scientific results is mainly provided by the CNRS, including Jean-Loup Puget (IAS), “Principal Investigator” of HFI, and François Bouchet (IAP), “Co-Principal Investigator” .
French laboratories involved:
- APC, AstroParticule et Cosmologie (Université Paris Diderot-Paris 7, CNRS, CEA, Observatoire de Paris), à Paris : développement de moyens de tests.
- IAP, Institut d’Astrophysique de Paris (CNRS, UPMC), à Paris : développement des objectifs scientifiques et conception du traitement des données.
- IAS, Institut d’Astrophysique Spatiale (Université Paris-Sud, CNRS), à Orsay : conception initiale et responsabilité scientifique et technique de l’instrument.
- Institut Néel (CNRS), à Grenoble : développement de la cryogénie à 0,1 K.
- IPAG, Institut de Planétologie et d’Astrophysique de l’Observatoire des Sciences de l’Univers de Grenoble (CNRS, Université Joseph Fourier Grenoble 1), à Grenoble : modélisation de l’instrument.
- IRAP, Institut de Recherche en Astrophysique et Planétologie de l’Observatoire Midi-Pyrénées (Université Paul Sabatier Toulouse III, CNRS), à Toulouse : développement de l’électronique des détecteurs.
- IRFU, Institut de Recherche sur les Lois Fondamentales de l’Univers du CEA, à Saclay : études de compatibilité électromagnétique.
- LAL, Laboratoire de l’Accélérateur Linéaire (CNRS, Université Paris-Sud,), à Orsay : développement de l’ordinateur de bord.
- LERMA, Laboratoire d’Etude du Rayonnement et de la Matière en Astrophysique (Observatoire de Paris, CNRS, ENS Paris, Université Cergy Pontoise, UPMC), à Paris : modélisation de l’instrument.
- LPSC, Laboratoire de Physique Subatomique et de Cosmologie (Université Joseph-Fourier Grenoble 1, CNRS, Grenoble INP), à Grenoble : développement de la cryogénie à 20 K.
- CC-IN2P3 du CNRS, Centre de Calcul de l’Institut national de physique nucléaire et de physique des particules (IN2P3) du CNRS : participe au stockage et au traitement des données.
- Planck website : http://www.planck.fr
- ESA Press release : http://esa.int/Our_Activities/Space_Science/Planck/Planck_reveals_an_almost_perfect_Universe
- ESA Video Release : http://spaceinvideos.esa.int/esalive