Dark Matter
  A review of the development of the concept of dark matter is given. I begin
the review with the description of the discovery of the mass paradox in our
Galaxy and in clusters of galaxies. In mid 1970s the amount of observational
data was sufficient to suggest the presence of a massive and invisible
population around galaxies and in clusters of galaxies. The nature of the dark
population was not clear at that time, but the hypotheses of stellar as well as
of gaseous nature of the new population had serious difficulties. These
difficulties disappeared when non-baryonic nature of dark matter was suggested
in early 1980s. In addition to the presence of Dark Matter, recent observations
suggest the presence of Dark Energy, which together with Dark Matter and
ordinary baryonic matter makes the total matter/energy density of the Universe
equal to the critical cosmological density. There are various hypothesis as for
the nature of the dark matter particles, and generally some form of weakly
interactive massive particles (WIMPs) are strongly favored. Both Dark Matter
and Dark Energy are the greatest challenges for modern physics since their
nature is unknown.
