Above the map of the microwave background, the first light emitted 380,000 years after the Big Bang, revealed by the Planck satellite. Two characteristics of light are represented. On one hand, the temperature of the light – orange color areas correspond to a slightly warmer temperature than the average (270 ° C), and blue areas correspond to a slightly colder than average. On the other hand, the polarization of light, that is to say, the direction in which the light “vibrates”, represented by small shaped patterns of “waves”. Credits: ESA / Planck / CNRS

The Planck mission has revealed the crucial early childhood secrets of our Universe. Two important information is delivered including: the birth of the first stars, which occurred later than expected, and the age of the Universe, revised (slightly) down.
European collaboration Planck delivered February 5th 2015 major results as regards infancy of our universe ( it will be remembered, the Planck satellite has mapped from 2009 to 2013 the CMB or the first light emitted in the Universe , 380,000 years after the Big Bang) . These results fell by some 100 million years the timing of the first stars began to shine, revise the age of the universe down, and finally fournnissent valuable information about the “content” of the universe. We proposoons you a short summary of these results:

The age of the first stars

The results delivered by the Planck Collaboration reveal that the first stars began to shine 550 million years after the Big Bang, not 450 million years as was believed. This may seem trivial, but in reality, this offset is very important. Indeed, it illuminates an old mystery: that of reionization . Reionization? To understand, we need to recount here the “film” of the birth of the universe.
There are 13.8 billion years, the Big Bang occurs. The early universe is then filled with a hot plasma in particular consisting of protons, electrons and photons. At that time, the Universe is too hot for that electrons can be captured by protons: hence the atoms can not form. As for the light, it can not spread a kind of fog making the Universe completely opaque.

At that time, the protons (which, remember, are positively charged) being separated electrons (negatively charged), astrophysicists say that the universe was “ionized”. Indeed, recall that the ionization involves removing or adding electrical loads to an atom, to give it an electric charge is positive or negative (whatever the final electrical charge, the atom is in any case electrically neutral after an ionization). But this is the situation at that time in the Universe: electrically charged particles (negatively for some positively for others) were traveling in the Universe, never combine together .

Then, the Universe is expanding and cooling, electrons and protons eventually combine and then form electrically neutral atoms (sometimes referred this period of “recombination”). The Universe ceases to be opaque to become transparent. At that time, that is to say, about 380,000 years after the Big Bang, a very important event occurs: the first light radiation is emitted in the Universe. This is the famous cosmic microwave background , often called “background radiation.”

Paradoxically, the Universe then enters what astrophysciens call “dark ages”, a period that will last for several hundred million years. Indeed, during this period, no light source is still active: the universe is then in total darkness.

Then, a few hundred million years after the Big Bang, things are starting to change: the universe is gradually entering the famous so-called period of “reionization”, during which the first stars and the first galaxies, if then put to shine. The ultraviolet radiation emitted by the stars starts to split electrically neutral hydrogen atoms (one remembers they were combined 380,000 years after the Big Bang), which again generates electrons and protons (hence the re-ionization). This period of reionization, in which the universe is illuminated gradually closes a billion years after the Big Bang about (note that these days, the universe is still considered ionized ).

But so far, astrophysicists thought that reionization started 450 million years after the Big Bang. In other words, this means that the stars were supposed to have started to shine from that moment. Problem: at that time, the density of atoms flowing in the universe was very strong, and the stars could not have been alone successfully ionize the surrounding atoms. This is why astrophysicists had been reduced to imagine the existence of unknown forms of energy, which would somehow “helped” the young star reionize the Universe.

But this new age of the first stars revealed by Planck just one stroke solve old problems. Indeed, if the first stars began to shine 100 million years later than was hitherto supposed, that is to say, 550 million years after the Big Bang instead of 450 million years, so no need to invoke unknown forms of energy to understand why the stars were alone reionize the Universe. In fact, 550 million years after the Big Bang, the density of matter in the universe was a little lower (the Universe is being extended in the meantime), which largely left open the possibility for the sole star of begin this process of reionization …

The age of the Universe

With the results from Planck, the new age of the Universe is now 13,770,000,000 years, not 13,819,000,000 years as had been previously calculated.

The content of the Universe

Again, Planck provides valuable results. They reveal that the Universe’s material content is as follows:

• 4.9% of its current energy is composed of ordinary matter (that we know)
• 25.9% of this content is made ​​up of dark matter , the hypothetical form of matter not yet detected, and whose nature is unknown
• 69.2% of another form of energy, distinct from dark matter and the precise nature’s most mysterious (it is often called dark energy or dark energy )