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    MATERIAL FROM CLASS 26: Monday December 11

    Cosmic microwave background radiation

    Arno Penzias and Robert Wilson received the Nobel Prize in 1978 for their 1964 discovery of the cosmic microwave background radiation, using this horn receiver at Bell Labs:
    [Penzias and Wilson with their horn receiver at Bell Labs, 
circa 1965]


    Fluctuations in the cosmic microwave background radiation

    From the first year of the WMAP (Wilkinson Microwave Anisotropy Probe) experiment, a map showing deviations in the temperature from its average value of 2.725K. Red areas are 200 microkelvin hotter than average, dark blue areas are 200 microkelvin cooler.
    The center of the Milky Way is at the center of the image, and the disk lies horizontally along the middle. The left and right edges of the map show what is seen looking directly away from the center of the Galaxy.

    [temperature fluctuations of microwave background: WMAP1]


    To make the picture above, two effects were removed.
    1) Top: the Local Group is moving at 600km/sec (0.002c) relative to the source of the microwave background; so it appears hotter (shorter wavelengths) by about 6000 microkelvin at the top left and cooler in the lower right of the diagram. This is so large that the small fluctuations in the top map are hidden.
    2) Below: the effect of the Local Group's motion has been removed, showing the same fluctuations as in the 'green' map. But stars in the Milky Way heat dusty gas, which produces the emission shown in pink.
    Colors were produced by representing brightness at WMAP's Q-band (wavelength 0.7cm) as red, V (0.5cm) as green and W (0.3cm) as blue, adjusting the color intensities so that a blackbody spectrum at 2.735K looks grey.

    [microwave background dipole: WMAP1]