Planck completes its first sky map

The European Space Agency has published the first all-sky image, mapped by the Planck observatory over the past year.

 

First sky map observed in the microwave range (30 to 857 GHz) by the European satellite Planck. It is possible to see the cosmic background radiation from the dawn of time in the background with, in the foreground, the disc of our Galaxy surrounded by spiralling cold gases. Credit: ESA/LFI & HFI Consortia

For the first dozen thousands of years following the “Big Bang”, the universe was filled with a hot slurry of particles subjected to pressure such that light was imprisoned in matter. Although its expansion was rapid, it took 380,000 years for the pressure to diminish sufficiently for the photons to escape.

And then there was light
Around 13.7 billion years old, this first light continues to bathe the Universe. This excessively cold, fossil radiation constitutes “background cosmic noise” which was accidentally detected in 1964. It has been studied since 1992 by the American COBE, and then WMAP, satellites in order to detect miniscule variations likely to provide us with information concerning the inner conformation of the primordial universe, before it started to become organised in the form of the structures that we know today: galaxies, clusters, superclusters, etc.

Over the past year, the European observatory Planck has been orbiting in the opposite direction to the Sun at about 1.5 million kilometres from the Earth. Its mission: to draw up a map of the sky in nine microwave bands in order to study primordial radiation with a resolution and sensitivity never before achieved. Some of its sensors are, in fact, kept at a temperature of 0.1° above absolute zero, which makes them the coldest objects in the known universe, and it is hoped that this will enable the limit of what is theoretically possible to observe from this radiation to be reached.

The date was 14 May 2009, the Planck observatory had just been launched by Ariane 5 together with the infrared telescope Herschel. Here, we can see its separation from the cryogenic stage ESC-A which had just injected it on a trajectory which was to take it to the Lagrange Point L2, 1.5 million km from the Earth. Credit: ESA - D. Ducros.

The dawn of time machine
The European Space Agency has just published the first sky map observed by Planck. In addition to natural sky radiation - in red flecked with yellow - it also shows all the objects in the foreground “blocking the view”: our Milky Way, the Magellanic Clouds and all the other galaxies, nebulae and clusters that appear in blue and light pink in this image.

Planck surveys the entire sky twice every 15 months and is to continue at this pace until 2012, with a total of 4 complete scans. It is going to take another two years to process the 500 billion raw data obtained from each scan to successfully erase the “contaminants” from the foreground of the image and to give the most accurate picture possible of the fossil radiation from the very first dawn of the Universe.

These “contaminants” have proved to be a genuine mine of information for astrophysicists who have been able to combine the observations from Planck with those from the ESA’s Herschel and NASA’s Spitzer observatories in order to study star nurseries. Planck has also made it possible to highlight the presence of astonishing cold gas clouds in the form of filaments in interstellar space. They form a gigantic web where stars are on the point of being born or have just started to form.

In this version of the map several objects worthy of note have been identified in the “foreground”: the galactic centre, the Magellanic Clouds, the Andromeda galaxy (M31), the Orion nebula, the Persei cluster, the Centaurus A galaxy (NGC 5128) and the 3C273 quasar in the constellation Virgo. Credit: ESA/LFI & HFI Consortia

In the end, Planck’s observations are not only to make it possible to compare the different cosmological models concerning the Universe in its youth, but also to determine the current expansion rate of the universe, its curvature, its density and its future. And lastly, with luck, they could lift the curtain on “dark matter” and “dark energy” which could constitute the greater part of the Universe and about the nature of which we still know virtually nothing.