>That makes sense. Seeing that over time objects move further apart, would
>that argue that these two Abell clusters may have at one time been a single
>larger cluster, perhaps being pulled apart by two gravitational centers?
Although space may be expanding, objects within local environments don't
necessarily move farther apart over time. Locally, they tend to clump
together. For example, coalescence is the inevitable fate of our Milky Way,
its satellites, and the Andromeda Galaxy. Giant elliptical galaxies result
from mergers of smaller neighbor galaxies.
Likely, Abell 2197 and Abell 2199 are individual condensations in a local
supercluster of galaxies. Similarly, galaxy clusters are dispersed along the
length of the Pisces-Perseus Supercluster
(http://www.anzwers.org/free/universe/superc/perpsc.html). Most of these
Abell clusters and galaxy groups have similar radial velocities, although
they typically are farther apart than the A2197/2199 pair.
I like to think of the A2197/2199 pair as the galactic equivalent of the
double star cluster (NGC 869 and NGC 884) in Perseus. They are two close,
relatively loose, galactic clusters traveling roughly together in space. In
contrast, Abell 1656 (the Coma Cluster) is the galactic analog of Omega
Centauri.
Albert
Received on Tue Oct 4 18:32:53 2005