Abstract
The clusters of galaxies have a diameter greater than 1 Mpc. The member galaxies have velocities of the order of 1000 km/sec and require a billion years to cross them. In some cases the galaxies require even more time to cross the cluster once, a good fraction of the age of the Universe. Even so, the velocities of galaxies inside a cluster are much greater than the velocities of stars inside a galaxy. For example, the Sun moves with a velocity of 220 km/sec about the galactic centre, while the galaxies in the Coma cluster move with velocities of 2000 km/sec. This could mean that some groups and clusters of galaxies may be unstable, having insufficient mass to hold the member galaxies together. It is more likely, however, that there is a lot more matter in a cluster than we can observe. It must be in the form of some intergalactic medium, and there must be sufficient of it to prevent the member galaxies from escaping. We have two indications that this is true: (1) The velocity curves of galaxies show that galaxies are surrounded by massive halos. (2) We frequently observe matter between the galaxies.
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© 1987 Springer-Verlag Berlin Heidelberg
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Contopoulos, G., Kotsakis, D. (1987). Distribution of Matter in the Universe. In: Cosmology. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-71464-1_4
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DOI: https://doi.org/10.1007/978-3-642-71464-1_4
Publisher Name: Springer, Berlin, Heidelberg
Print ISBN: 978-3-540-16922-2
Online ISBN: 978-3-642-71464-1
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