Primordial universe mapped by Planck

Able to see in the realm of microwave wavelengths, the European space observatory Planck has spent 30 months scanning the entire sky. The data gathered will show astronomers what the Cosmos looked like just 380,000 years after the Big Bang.

 

An artist’s impression of the Planck satellite. Credit: ESA/C. Carreau

In astronomy, to look into the distance, is also to go back in time. For instance, when we observe a galaxy like NGC 224 (also called the Andromeda galaxy) located about 3 million light years away from us, we see it as it was 3 million years ago, the time it took for the light to reach us.

Aux premiers temps du Cosmos
If we now imagine looking even further, a lot further. We will then be confronted with a shift towards red wavelengths. The Universe is expanding and this “stretching” causes a shift in visible light towards red, then infrared wavelengths and even beyond. Consequently, in order to see the Cosmos as it was just 380,000 years after the Big Bang, we have to examine a light which is more than 13 billion light years away from us. And there, the shift is right in the microwave wavelength range. A “faded” light which, although it bears witness to a temperature of 3,000°C (just before it was a billion degrees!), requires instruments able to perceive a temperature very close to absolute zero (-270°C).

Diagram of the HFI instrument, the result of collaboration between the CNRS, the French National Centre for Scientific Research, and the CNES, the French Space Agency). Credit: ESA/AEOS Medialab

Launched in 2009 by an Ariane 5, the European Space Agency’s Planck satellite is fitted with an instrument known as HFI (High Frequency Instrument) which is able to detect temperatures of barely 0.1°C above absolute zero. Although it worked for much longer than was originally calculated, the instrument has now exhausted the helium that cooled it. But in 30 months it accomplished its mission: to scan the entire sky 5 times in order to draw up a map of the minute differences in temperature that existed in the primordial Universe. These are, as it were, the “lumps” in the “original soup” from which began the grouping of matter which led to the main structures such as stars and galaxies that exist in today’s Cosmos.

The entire sky by Planck in the microwave wavelength range (after one year of observation). The blue data essentially comes from very cold sources in our galaxy (seen by segment). All the data now has to be very carefully sorted so that only the signal from the Universe as it was 380,000 years after the Big-Bang is extracted. Credit : ESA/LFI & HFI Consortia

The data will take time to be analysed, but the results will greatly restrict the cosmological models and, therefore, the scenario surrounding the birth of our Universe!?
Planck’s mission is not quite finished however since its second instrument (LFI - Low Frequency Instrument) should remain active for a large part of 2012 and complete the data already acquired.

Published on 18 January 2012