Bonuses from Planck

Designed to examine the sky in the realm of microwave wavelengths, this European satellite is going to show us the Universe just after the Big-Bang. It has also detected clouds of cold gas, from which new stars are formed, in our galaxy.

 

The European Planck space observatory (illustration) Credit: ESA/D. Ducros

In space since 2009, the Plank observatory belonging to the ESA, European Space Agency, has scanned the entire canopy of heaven 5 times in the microwave wavelength range. Its initial objective being that of mapping what is known as relic radiation from the Big-Bang, that is to say the first light emitted 380,000 years after the birth of the Universe and shifted into the microwave range (see this Enjoy Space article for further details).

An inconvenient but interesting “foreground”
Planck’s most sensitive instrument, the HFI (High Frequency Instrument designed with the CNES, the French Space Agency), stopped working after 30 operational months, its stock of helium 3 tasked with cooling being depleted (as planned). However, another instrument, the LFI (Low Frequency Instrument) is still going to gather data. But Planck’s harvest has already proved extremely rich. And yet, this is not a reference to the famous relic light from the early years of the Universe that will restrict the theoretical models of the Big-Bang. This data is, in fact, “mixed” with other data as the sky is abounding in microwave sources.

The sky in the microwave range by Planck after observations lasting one year. The data is to be refined when that acquired over 30 months is added. Credit: ESA/LFI & HFI Consortia

To make it easier to understand, just imagine that you are trying to record someone who is talking to you in a noisy crowd and who is not even close to the microphone. You will then have to “extract” the required words by eliminating the loud background noise caused by the other conversations. This is more or less what is happening with the microwave sky map by Planck. All the microwave radiation from our own galaxy is in the “foreground”. Therefore, to get to the state of the Universe 380,000 years after the Big-Bang, this inconvenient data has to be eliminated... Inconvenient? Well, perhaps not! This data actually contains some real “bonuses” which are of the utmost interest to astronomers.

From tomorrow’s suns to black matter
Our galaxy is actually like a flat disc with a central bulb that we see edge-on. The general architecture is therefore understood, and it is also known that new stars are formed from vast, cold clouds predominantly composed of hydrogen. The problem is that these clouds are very difficult to detect. But, said clouds also contain a small amount of carbon monoxide (CO, the same one that is very dangerous as, odourless, it can asphyxiate people without them realising it, notably via certain faulty direct-fired heating systems). Fortunately, Planck “sees” carbon monoxide in the microwave range very well!

The carbon monoxide in our galaxy (seen therefore edge-on) as observed by Planck. The carbon monoxide also indicates where the cold clouds of hydrogen, used as “fuel tanks” by the star formation areas, are to be found.Credit: ESA/Planck Collaboration

And by scanning the sky, it has thus drawn up a map of clouds of carbon monoxide in our galaxy, and consequently, the clouds of hydrogen that feed the star nurseries where tomorrow’s suns are formed. This map can be used as a base for knowing where to direct observations to be made by ground radio-telescopes which have a much narrower field of view in order to better capture the dynamics that enables our galaxy to form stars.
Planck has also detected a “microwave fog” in our galaxy. This too is part of the “foreground” which has to be eliminated in order to access the portrait of relic radiation. And, once again, this “foreground” is arousing interest amongst astronomers, quite simply because its origin remains uncertain!

Our galaxy’s “microwave fog” (the black bar is our own galaxy, excluded from the data in order to make the analysis easier). Its exact origin is still a mystery. Credit: ESA/Planck Collaboration

This radiation appears to come from the central region of our galaxy but it extends further, and resembles a synchrotron emission, that is to say the result of electrons accelerated to high speeds that pass through magnetic fields. What phenomenon is behind these accelerated electrons? Supernovae (stars that die by exploding), galactic winds or even the annihilation of black matter particles (matter that cannot be seen but whose gravitational effects can be detected)? The mystery is still to be unravelled. However, this bonus from Planck, together with the image of the cold clouds responsible for future stars, is capable of furthering our constant quest for understanding.

Published on 20 February 2012