'Astrophysical brass in the microwave muck'
One scientist's noise is another scientist's data, and this applies particularly to Europe's spectacular Planck space telescope.
Hurled to an observing position more than a million km from Earth, this observatory has been routinely scanning the sky now since August 2009. It’s on a grand quest.
Its mission is to make the definitive map of the famous Cosmic Microwave Background, or CMB. Some call it the "afterglow" of the Big Bang; I like to think of it as the "oldest" or "first" light in the Universe. It fills the sky around us.
It comprises those photons, or particles, of light that were first allowed to sweep out across the cosmos once it had cooled sufficiently to form neutral hydrogen atoms.
Until that time, the photons bashed into free electrons at every turn; the Universe was opaque. Previous studies have indicated this "uncoupling" of radiation and matter occurred about 380,000 years after the moment of creation, or about 13.7 billion years ago if you are looking through our end of a telescope.
These ancient photons' first contact is with Planck's super-cold, super-sensitive instruments. That's an extraordinary thought. All that time, all that space; and it ends with the photons striking the telescope's detectors.
Planck views the sky at nine frequencies. This allows it to pick apart - and eventually extract - the different components that obscure the CMB. In these nine views, all you see is the "reject data".
Scientists can identify tiny temperature variations in the CMB that give them insights into the early structure of the Universe and the blueprint for everything that came afterwards. All the structure we see around us today was set in motion by that initial framework.
Nasa's Cobe and WMap telescopes have already extracted a good deal of information from the CMB, and these efforts have rewarded a number of scientists with Nobel Prizes.
Esa's Planck observatory is designed to pull out every last detail, with the expectation also that it will generate "Swedish gongs".
As a consequence, Planck's data is jealously guarded. It’s one reason why announcements about the mission tend to be few and far between.
The last time the European Space Agency made a big song and dance about this flagship endeavour was back in the summer with the release of Planck's first all-sky map.
It was a stunning picture that found its way on to front pages across the globe (see bottom of posting). It contained some CMB information, carefully rendered so as not to give away any secrets, but the image was dominated by an obscuring foreground – largely light coming from our own galaxy, the Milky Way.
All of this foreground "contamination" has to be removed if scientists are to get a clear view of the CMB. And this week in Paris, the Planck Consortium (the hundreds of scientists working on the mission) published a great long list of these "rejected" sources of light in a vast catalogue.
I call it contamination, but of course this pollution is actually pure signal to the researchers who study these sources of light.
The catalogue contains thousands of items. Some are within our galaxy; others are much deeper in space.
They range from nearby ultra-cold clumps of gas and dust where future stars will form, to the diffuse light coming from galaxies shrouded in dust billions of years in the past, and which were forming stars at rates some 10 to 1,000 times faster than we see in our own Milky Way Galaxy today. Planck's project scientist Dr Jan Tauber told me:
"All this light – the CMB, the closest galaxies, distant galaxies – is mixed up, and in order to do science we have to go through a process we call component separation. We have to split apart these components. And at the end of this process, which is basically a software process, we end up with different maps. The CMB, our ultimate objective, is one of the faintest signals in the sky and therefore one of the most difficult to extract. We can’t talk about it yet because we still need to work on the data quite a bit. But some of these other signals are very strong, like the ones coming from our own galaxy and we can start to talk about them now."
The collection of nine all-sky maps on this page is what Planck sees in the nine frequencies across its two instruments.
Planck sees the spinning dust in a narrow frequency range, around 30GHz (red colour)
Studying these different frequencies allows the scientists to tease out what the different sources of contaminating light are and what they are doing.
With an eye on the British contribution to all this research, I'll pick up on one fascinating example referred to as "anomalous microwave emission" (AME).
It's a glow most strongly associated with the dense, dusty regions of our galaxy, and its origin has been a puzzle for decades. But the work by Clive Dickinson, from Manchester University, and colleagues has pretty much established now from the Planck data that this AME must be coming from dust grains that are spinning at several tens of billions of times a second. Extraordinary.
This furious behaviour is a result of collisions, either with other dust grains or with photons of ultraviolet light. Clive told me:
"This emission seems to only emit in a narrow frequency range, around 30GHz, which is exactly the frequency range that the low-frequency instrument of Planck is observing. And although it's been observed before – we’ve known about it for a number of years now – Planck data have really allowed us to map it out and create very precise spectra of these dust regions. What we’re finding is that the only real possibility for this anomalous microwave emission is electric dipole emission from spinning dust grains. It sounds horribly complicated but basically these dust grains spin extremely quickly, so quickly that they end up emitting in the microwave regime. It's one of about four components that really confuses the CMB, and we need to understand it so we are able to subtract it and therefore clearly see the CMB."
Planck continues to scan the sky. It hopes to picture everything around us five times over. This should be more than enough data to get a very clean picture of the CMB.
Planck's full-sky image released back in the summer. The gas and dust (blue/white) in our Milky Way Galaxy dominates the foreground. The CMB is seen in the magenta and yellow splodges behind