Date: January 16, 2011
Title: Planck Releases its First Data
Podcaster: Chris North and Stuart Lowe
Links: http://planck.cf.ac.uk/, http://www.esa.int/planck
Description: In May 2009, the European Space Agency launched the Planck satellite to observe the echoes of the big bang. For over 500 days Planck has been continuously observing the sky, with two instruments, over a broad range of frequencies. The first scientific data were released on 11th January 2011. In this episode we talk to some of the scientists involved with the mission to find out what these first results tell us.
Bio:
Chris North is a researcher at Cardiff University where he works on Planck’s High Frequency Instrument (HFI). He is also coordinates UK-wide outreach activities for the Herschel Space Observatory.
Stuart Lowe helped with the construction and testing of Planck’s Low Frequency Instrument (LFI). He works for Las Cumbras Observatory Global Telescope (LCOGT).
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Donovan Willette. Let us look to the skies and remember the words of Carl Sagan: “Imagination will often carry us to worlds that never were. But without it we go nowhere.
Transcript:
Chris North: Hello. I’m Chris North from Cardiff University in the UK and I’m here at a meeting in Paris that’s talking about some new results from the Planck satellite. It was launched in 2009 by the European Space Agency and since August of 2009 has been in the routine phase of its mission; scanning the sky continuously. The data released in January 2011 comprises data taken from the start of that routine mission until about June 2010 – about 10 months of data – by which time it had scanned the sky 1.5 times. Now Planck’s primary mission is to observe the Cosmic Microwave Background. The Cosmic Microwave Background is the relic radiation from the big bang and studying it in detail can tell us an awful lot more about the structure of the Universe, its history, and possibly even how it began in the first, tiniest fraction of a second. Now although it’s looking back at the Cosmic Microwave Background that gets very brief mention at this conference. What’s being discussed here are foregrounds. These are objects that Planck has to look at and look through to see the Cosmic Microwave Background. One of the things it is seeing are what are called compact sources. Although these objects may be compact as seen by Planck, they’re not necessarily compact at all; some of them are distant galaxies – incredibly large – and some of them are indeed entire clusters of galaxies. These are being released in a catalogue called the Early Release Compact Source Catalogue. There are over 15,000 objects and they cover a huge range of physical characteristics. I spoke to Bruce Partridge, from Haverford College, about what we are learning from the catalogue.
Bruce Partridge: Well there are a large variety of objects but I’d start by making the following point. Planck has opened up a new chunck of frequency space – a new window that we haven’t explored before, that roughly runs from between ground-based radio astronomy and satellite-based infrared astronomy. So it’s not surprising that we’re seeing a variety of new sources. Opening up a new frequency window is roughly the equivalent of finding a new continent and the kind of objects we are finding are, in principle, could be radically different. Think for a moment about the discovery of Australia. Who would’ve expected kangaroos?
Chris North: It’s like finding marsupials.
Bruce Partridge: Exactly. But is Planck finding marsupials? Even as we extend to this new frequency regime, at higher frequencies than you can do from the ground, we’re still finding that the sources that Planck sees are essentially radio galaxies where the radio emission is associated with a central black hole. So that in itself is an interesting discovery and somewhat unexpected. The dusty galaxies that we might have been seeing are not strongly present in the Planck sample. So lots of bright radio galaxies and relatively few dusty galaxies. When you look at sources in our own galaxy, then the zoo of animals becomes considerably more interesting. One of the things Planck has really done, and done magnificently well, is to find the little cold cores in our own galaxy where stars are forming.
Chris North: So these are the very initial stages of stars.
Bruce Partridge: The very initial stages. We ordinarily think of stars as being very hot but in fact they start out in clumps of matter that are quite low in temperature. Planck, because it is able to work at longer wavelengths in the infrared, is seeing this very cold matter. There are literally thousands of these stellar nurseries visible in Planck [data]; one of the most interesting discoveries, I think, of the early-release catalogue.
Chris North: So it’s seeing some of these tiny sources in our own galaxy, it’s seeing these radio galaxies and these dusty infrared galaxies but it’s also seeing these massive clusters of galaxies at a range of distances from us and it picks them up through something called the Sunyaev-Zel’dovich effect.
Bruce Partridge: That’s right. In American-English the Sunyaev-Zel’dovich effect is the scattering of radiation coming to us from early in the Universe and as it passes through the gas in these hot, dense clusters of galaxies that introduces a change in the intensity you see; at low Planck frequencies it is a dimunition or a cool spot and at high Planck frequencies it’s the opposite. The great advantage of this signal is that it’s independent of the distance of the cluster. It’s a little bit anomalous but that’s how it works out. We’re learning a great deal about the conditions of the gas in these clusters of galaxies which in turn tells us something about how they’re formed. In addition, the number of clusters as a function of distance out in the Universe will eventually, not yet but eventually, tell us something about the entire history and structure of the Universe. That’s to come. We’re still hoping that bright people either involved in Planck or not will be able to find surprises in the ERCSC that we don’t yet know about. There are 15,000 sources in this catalogue so surely there are some surprises – the wallabys if you will of the astronomical world. So go look for ’em.
Chris North: So many astronomers are going to be pouring over this catalogue over the next year or decades perhaps looking for some bizarre objects that might reveal new physics and a new understanding of our Universe. As well as looking at these compact sources Planck also measures what we call diffuse radiation. This is material that’s spread over the sky such as dust or gas in our galaxy. In the 1990s some emission from something else in our galaxy – another diffuse medium – was found that couldn’t be explained initially. It was called the anomalous microwave emission and Planck has helped us understand what it really is. I spoke to Clive Dickinson from the University of Manchester about our current thinking about what causes this anomalous microwave emission.
Clive Dickinson: Planck is extremely good at measuring gas and dust which is the material in between the stars in our own galaxy. In particular, the dust grains which are formed in the interstellar medium – Planck measures those very accurately. We’re measuring the different components of the interstellar medium with Planck and what we’ve found is that some of these dust grains – the extremely small ones – are actually emitting at radio wavelengths. Up until recently we never thought [the dust grains] emitted in the radio.
Chris North: A lot of this dust, this interstellar dust, is warmed by stars and emits at normally far infrared and submillimetre wavelengths. Planck sees a lot of that very cold material. The grains of dust we’re talking about are almost like grains of sand but much smaller, say, a tenth the size and they’re normally made of silicates or carbonate a bit like sand or graphite or something. These other grains are much, much smaller.
Clive Dickinson: That’s right. So these large grains, as you say, they emit thermal emission – we often call it thermal dust – and we see that very clearly with the Planck High Frequency Instrument which is at hundreds of GHz or submillimetre – we see that very clearly. The very interesting thing, the new thing, is the emission at longer wavelengths or lower frequencies. So this is the Low Frequency Instrument. This is not from thermal dust but from spinning dust and these are much smaller grains. Rather than them being, like you say, the size of sand or a bit smaller it’s actually more like nanometre sizes. So only 50 – 100 atoms and they’re very, very small and because they’re very, very small they can be spun up to very high frequencies and that’s what allows them to emit in the radio and we see that at low frequencies with Planck.
Chris North: Planck is actually the third generation satellite to observe the Cosmic Microwave Background. Its predecessors were NASA satellites called COBE and WMAP. COBE was launched in 1990 and WMAP in 2001 and [WMAP] was only recently switched off. Planck is going to do even better than both of these satellites. It’s looking with higher resolution and higher sensitivity. One of the scientists who worked on WMAP was Joanna Dunkley from the University of Oxford. At the press conference to release these new results from Planck I spoke to her about how it compared to the WMAP results.
Joanna Dunkley: For a start it’s extrememly exciting to see the first results from Planck having seen maps of the microwave sky from WMAP and now we’ve gone ahead and now we’re seeing them from Planck. What Planck is doing beyond WMAP is looking at the sky at much higher resolution and in different colours than WMAP could. We see the microwave sky in a way that WMAP couldn’t show us. One of the things is we zoom in at much higher resolution. We can see patterns on the sky that we couldn’t see before. One of the reasons for doing that is to try and pick out features from the beginning of the Universe that can tell us more about, for example, the very earliest moments in the Universe and hopefully the properties of it as a whole. By doing that Planck also allows us to see small objects billions of light years from us, for example clusters of galaxies, that weren’t resolvable before, that can tell us about things like dark energy; how fast the Universe is expanding and why. By seeing those objects in between us and that first light from the beginning of the Universe, that tells us more about science.
Chris North: So there’s lots of results here about the interstellar medium, about galaxies and about clusters of galaxies. What a lot of people are really waiting for is the cosmology. Unfortunately that will take about 2 years before the results can be released and that is due to the huge amount of work that needs to be put in to fully understand the data from Planck. One of the people working on the High Frequency Instrument – one of two instruments on Planck – is Ken Ganga from the astro-particle and cosmology lab in Paris. I spoke to him about why it was going to take two years to get this data out and what some of the challenges we’ve got ahead are.
Ken Ganga: We knew that this would be hard. The more sensitive your instrument is, the longer it takes to figure out all the little peculiarities.
Chris North: Because you pick up more peculiarities.
Ken Ganga: The more sensitive your instrument is the more delicate features on the sky you can see but also the more delicate problems you can see. It’s like looking at a beautiful person. From afar you can see they’re beautiful but the closer you look they’re still beautiful but you can see blemishes on their faces as well. It’s the same thing with the sky here. I can give you a few examples as well. There are both things that we knew would be difficult like dealing with sensitivity and known problems with the instrument and there are also always surprises in an experiment like this. So, for example, when we launched we started to see that there were more cosmic rays hitting our detectors than we’d actually expected. We see these because we are more sensitive than any other instrument that’s ever been up there. So it was something of a surprise but it was also because we have more sensitivity we seen more of these kinds of blemishes. It simply takes time to digest the problem, understand the problem, diagnose the problem, and then remove the problem so that we can dig down to the science we really want to see.
Chris North: So it’s not just the stuff in our galaxy and beyond that we have to try and see through to get rid of to get some of the cosmology. It’s actually the effects due to the instruments themselves. It’s a very hard task. Are you confident that we’ll get the data out in two years?
Ken Ganga: Oh we will certainly have results out in two years. I’ve worked in this field since 1994 I believe and this is some of the best data that I’ve ever seen. I think we will get our first results out in the next two years. I also think that it’s going to take decades to really completely mine all of the science that’s buried within the Planck data set.
Chris North: Planck is a huge mission – much larger than any of its predecessors – and coordinating such a mission with so many hundreds of people takes an awful lot of work. Jan Tauber is the ESA project scientist for Planck. I spoke to him about what it was like to work on a project which was so large.
Jan Tauber: I think Planck certainly has broken sociological ground, I’d say, in astronomy simply because of its size. Clearly the experiment is a very unusual one for astronomy. Astronomers are used to working in small groups or even individually in many cases and we’ve had to learn how to work in a very big group.
Chris North: Planck is continuing to scan the sky and will do so until its helium runs out. The helium is used to cool these instruments to very low temperatures to make them sensitive enough to pick up the faint emission from the Cosmic Microwave Background and all these faint sources between us and it. Over the next two years Planck scientists will be working incredibly hard on getting at the cosmological data. In the mean time there are many more results to come out on the interstellar medium, star formation, galaxies both near and far. Perhaps in a year’s time we’ll be able to look again at some results from Planck. If you’d like more information about Planck you can look at some of the websites. The ESA website is www.esa.int/planck and in the UK we have one at plancksatellite.org.uk and there are many more websites about Planck from many other organisations involved with the mission around the world. So, for now, goodbye.
End of podcast:
365 Days of Astronomy
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