7.6. Anisotropies
Since the COBE discovery of hot and cold spots in the CMB,
anisotropy detections have been reported
by more than two dozen groups with various instruments, at various
frequencies and in various patches and swathes of the microwave sky.
Figure 10 is a compilation
of the world's measurements (including the recent WMAP results).
Measurements on the left (low
's) are at large
angular scales while most recent measurements are trying to constrain
power at small angular scales. The dominant peak at
~ 200 and the smaller
amplitude peaks at smaller angular scales are due
to acoustic oscillations in the photon-baryon fluid in cold dark matter
gravitational potential wells and hills.
The detailed features of these peaks in the power spectrum are dependent
on a large number of cosmological parameters.
![]() |
Figure 10. Measurements of the CMB power
spectrum. CMB power spectrum from the world's combined data,
including the recent WMAP satellite results
(Hinshaw et al. 2003).
The amplitudes of the hot and cold spots in the CMB depend on their angular
size. Angular size is noted in degrees on the top x axis.
The y axis is the power in the temperature fluctuations.
No CMB experiment is sensitive to this entire range of angular scale.
When the measurements at various angular scales are put together they
form the CMB power spectrum.
At large angular scales ( |
![]() |
Figure 11. The dominant acoustic peaks in
the CMB power spectra are caused by the collapse of dark matter
over-densities and the oscillation of the photon-baryon fluid into and
out of these over-densities. After matter becomes the dominant
component of the Universe, at zeq
|