PLANCK -the key to understanding the Universe



The 3 Kelvin Cosmic Microwave Background (CMB) radiation surrounds us like a photograph of the young Universe. It's a remnant of the moment when the opaque photon-baryon plasma turned transparent and radiation (photons) decoupled from matter (baryons and dark matter particles). At that moment, when the Universe was only 300 000 years old, the photons scattered for the last time, and ever since have continued their journey unaltered towards us. The temperature of the radiation gradually decreased and is currently about 3 Kelvins -almost a perfect black body spectrum. The radiation is generated at microwave (radio) frequencies. However, the CMB is not smooth but contains tiny irregularities. These anisotropies hold the key to the yet unsolved mysteries of our Universe (such as its age, the Hubble constant, and the nature of dark matter) and can help to define the conditions of its birth, and, for example, assist in studying theories of galaxy formation.

COBE satellite was the first to measure the cosmic microwave background radiation in a proper way in 1992. The resolution was very low and the results more or less vague. The Wilkinson Microwave Anisotropy Probe (WMAP) has recently mapped the sky in more detail, however, still leaving many questions unanswered.

Cosmic microwave backgroud radiation as
                      measured by COBE, and simulated to Planck resolution Temperature map of the sky as measured by COBE (upper figure) and how the sky is predicted to look when mapped with the superior resolution of Planck satellite (lower figure).
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Planck satellite, developed by the European Space Agency ESA and scheduled for launch in February 2008, will study these tiny temperature differences more accurately than any other instrument before. To do so, the satellite must measure the whole sky. This means that it will observe all sources emitting at radio frequencies, also the ones in front of the microwave background. As a by-product we will get valuable data also of radio galaxies, interstellar gas and dust clouds, and pulsars.
However, to get accurate CMB maps, these foreground radio sources must be separated from the CMB radiation and its tiny irregularities. For this we need to know the number and brightness of the foreground sources. The Planck project is not only giving a copious number of cosmologists and astronomers a lot of work to do, but its success also requires thorough cooperation between scientists. In addition, we have also participated in the development and building of the Planck 70 GHz receivers in cooperation with Millilab.

Foreground sources must be separated from the
              microwave background

Quasar 3C 175
(Kuva: VLA/NRAO)
The researchers in Metsähovi and Tuorla study active galactic nuclei (AGNs) and quasars. They are very distant but powerful galaxies like our own Milky Way. The difference is that compared to the Milky Way, quasars radiate enormously more especially at radio frequencies. The black hole that is situated in the centre of the active galaxy, swallows up gas, dust, and stars falling from the surrounding galaxy, and burps up radio emission either continuously or as variable outbursts.

Planck satellite will measure all these sources at nine different radio frequencies. In addition we can use observations made with our own radio telescope as well other facilities around the world together with Planck observations, and so help the cosmologists to produce clear, clean maps of the cosmic microwave background.

Our Metsähovi/Tuorla team has been a part of the Planck core science programme since the beginning. It is called the Planck Baseline Core Programme and it contains both cosmological and astronomical programmes, each of which has been reviewed and accepted by the Planck Science Team. Our research is within the extragalactic point sources group, in five separate science programmes. Researchers from Tuorla are also participating in cosmological programmes.
We are also developing a software package called Quick Detection System (QDS) which will enable us to get our hands on the Planck extraglactic radio source data in about a week or two after the observation. This work is conducted in cooperation with the Planck LFI Data Processing Centre (DPC). We are also helping with several other Extragalactic Point Sources Working Group (WG 6) tasks, such as preparing the pre-launch catalogs and modelling of sources.
Planck satellite

Our research work is financed by the Academy of Finland, the Antares programme of Tekes and the Academy of Finland, Helsinki University of Technology, and University of Turku.

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