Copyright © 1979 by Annual Reviews. All rights reserved
|
| Annu. Rev. Astron. Astrophys. 1979. 17:
135-87 Copyright © 1979 by Annual Reviews. All rights reserved |
With the recognition of galaxy clusters as dynamical entities, it was
realized that the internal kinematics could be used to measure average
masses of galaxies.
Zwicky (1933) and
Smith (1936)
applied the virial
theorem to the Virgo cluster using the small sample of radial velocities
then available and found that the virial mass exceeded by a factor of
several hundred that expected from the sum of the masses of individual
galaxies. In a classic paper
Zwicky (1937)
derived an M / LB of 500 for the Coma cluster which he compared with the M /
LB
3 for the solar
neighborhood. Thus the ``missing mass,'' or more properly ``invisible
mass,'' problem was born. Since then, our understanding of the structure
and properties of clusters of galaxies has grown enormously (see reviews
by Abell 1975,
van den Bergh 1977,
Bahcall 1977).
However, the problem
of invisible mass in the great regular clusters has not abated.