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'Astrophysical brass in the microwave muck'

Jonathan Amos | 10:30 UK time, Wednesday, 12 January 2011

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.

Planck telescope


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 all its frequencies

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."

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The collection of nine all-sky maps on this page is what Planck sees in the nine frequencies across its two instruments.

AME as seen by Planck

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."

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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

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


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  • 1. At 3:34pm on 12 Jan 2011, aborky wrote:

    Jonathan Amos: CMB, (Cosmic Microwave Background)...comprises those photons, or particles, of light...first allowed to sweep out across the cosmos...Until that time, the photons bashed into free electrons at every turn; the Universe was opaque.'

    'In the beginning...darkness was over the abyss...then there was light...light which could be seen...light that separated out from the darkness.'

    Note please this is merely pointing out the curious coincidence when you make appropriate adjustments to the technical language of another era then their way of looking at the world may turn out to seem not so very different from our own.

    ...much as when similar adjustments are made for many rabble rousing denunciatory declamations made in the present era, they suddenly start sounding identical to the "Burn the witch!", "Burn the heretic!" brayings of the ideology obsessives of yesteryear.

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  • 2. At 4:26pm on 12 Jan 2011, Resigningeye wrote:

    Johnathan, I was interested to note a vaguely overlapping circular artifact in the data, particularly visable in the 70 and 100GHz bands. I was wondering if the source of this ever came up in discussion with the project scientists? Given the angular size of this structure it must be fairly close to the spacecraft. Solar contamination? Supernova remanent? Speck of dust on the detector? Thanks.

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  • 3. At 9:52pm on 12 Jan 2011, Bob wrote:

    The circular artifacts commented on by Resigningeye are due to uneven sky coverage, so that the seemingly darker patches at the top and bottom are in fact noisier. It appears at these frequencies because the galactic signals are so weak but the map contrast has been turned up so they look similar to the others. Cosmic Microwave Background signal which would be strong here has been removed so you start to see the intrinsic noise of the receivers. In the final maps with more data and full sky coverage together with the all important CMB signal, those circles won't exist any more.

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  • 4. At 1:37pm on 13 Jan 2011, outsider wrote:

    Thats a fine tool.

    But, its usefullness lies in your hands. I watched the interview in your video about revealing space from above. First I wan not made clear about the capacity of the camera (in the teleccope), does it brings the colors in where the dencity is different? I would presume so but in my eyes, eyes of a layperson, there is no colors in space. The real color is yellow - flash, like we see on the sum and the moon from here. Is there any blue in space? Like in our sky? I would expect so. But I am not sure. Can you eleborate what are the real colors and the colors that the camera brings in to point out different dencities (like the egg shape of the universe). Because all I understand from the egg picture is the shape - eggy like.
    Other videos show brights spots around the solar system and explanation about the black holes taking in energies and taking out electricwaves. Even close to Earth. But what does it mean relating to our solar system? I mean it is part of the living (or dieing) solar system. So is our sum loosing power and leaving some of it to black holes? are the black holes friendly to our solar system? Are they like a hoover cleaning the mess left out?
    I would like your interviewers to ask those questions, after hearing about the technical details of the amount of the energy coming out of the black holes. And make more note, verbally, as to the colors applied by the camera apposed to the real colors of space and what does it meam (dencity?).

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  • 5. At 5:13pm on 17 Jan 2011, waofy wrote:

    "One scientist's noise is another scientist's data"

    I simply can't emphasise enough how true that opening statement is. I'd also like to point out that it's a major problem, since many people (including scientists) dismiss such sources as unimportant and containing no real information.

    I'm currently doing a PhD in nonlinear dynamics and a huge part of the work is getting information out of the "noise" that other people are very quick to remove with filters. In reality though there is no such thing as noise, only the complexity of the real world.

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  • 6. At 7:41pm on 19 Jan 2011, chockybiccy wrote:

    With telescopic observation, the area of view at any distance is proportional to the distance squared. With a uniform distribution of galaxies, the observed mass at any distance will also be proportional to distance squared. Radiation is reddened in proportion to the mass of the emitting system.
    It follows that all observed distant radiation is reddened in proportion to the distance squared. There will be a limiting distance where the frequency of radiation is reduced to zero.
    The velocity of light is slowed when passing through a transparent medium, in proportion to the density. The universe is a transparent medium. We are effectively living in a block of glass or a large crystal sphere.
    Conclusions from above: Hubble shift and the CMB are observational artefacts. Dark energy is also not required.

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