Ripples in the Cosmic Microwave Background Radiation

Abstract

The Cosmic Microwave Background Explorer satellite (COBE) of NASA, launched in 1989, measured with unprecedented precision the intensity of the cosmic microwave background radiation (CMB) at many wavelengths and in all directions over the sky. The spatial resolution (sharpness) of the microwave optics in the satellite was 7°—14 times the diameter of the full moon. This means that the temperature of the background radiation was measured in separate areas of the sky with this size. The result is a sky map on which one can see that (small) temperature differences between such areas on the sky exist. These are depicted in Fig. 14.1. Before this map could be obtained, the observations first had to be corrected for the Doppler effect produced by the motion of the sun with respect to the background radiation, with a speed of about 390 km/s (see Fig. 9.14). This Doppler effect causes the temperature on one half of the sky to be slightly higher than average and on the other half to be slightly lower than average. The motion of the sun relative to the background radiation is a combination of the motion in its orbit around the Galactic centre and the motion of our Galaxy relative to the average background of distant galaxies. The last-mentioned motion, with a velocity of a few hundred km/s, is probably caused by the attraction of the other galaxies in the Local Group and of the Virgo Cluster (see Chap. 6), or of the local super cluster of which the Local Group and the Virgo Cluster are members.

If you are religious, it is like seeing the face of God

George Smoot, American astrophysicist,

2006 Physics Nobel laureate