The Mass Contained in Clusters (2) ...
In order to produce X-rays of the energies observed, the gases must have temperatures
of 10-100 million degrees.
The animation below right
illustrates how X-rays are produced in hot plasmas when the fast
electrons are accelerated by the slower moving ions. The X-ray emission depends on the
temperature of the gas because this influences the frequency and the violence of the
interactions between the electrons and the ions.
Mass of the X-Ray Gas
Careful study of this hot but confined X-ray gas in clusters indicates that the mass of the gas is at least
comparable to the mass of the visible matter, and can be as much as 5 times larger. However, this does not solve
the missing mass problem, since we need factors of 10-100, not factors of
1-5 to account for the dark matter.
In fact, the observation of the hot X-ray gas confined in clusters makes the missing mass problem worse.
The presence of this confined gas
indicates that the gravity
exerted in groups and clusters of galaxies must be even larger than thought before its discovery,
for otherwise the hot gas would have been expected to
disperse long ago.
