The large scale structures like galaxies, clusters of galaxies and super-clusters of clusters in the universe form by clustering of smaller structures in a hierarchical manner. The dwarf structures cluster to form galaxies, the galaxies in turn cluster to form galaxy clusters, and the galaxy clusters in their turn build superclusters of galaxy clusters. The process of clustering seem to follow very similar process: Streams of smaller structures encounter each other, like streams falling in a reservoir and creating turbulent eddies. The eddies, which form, make the next level of larger structures. These larger structures in turn move as a greater stream and fall into a greater reservoir and create even greater eddies and thus it carries on in the next higher scale. Thus the universe follows a fractal pattern while building the structures.
The dwarf structures, from where the galaxies form, seem to be created in a “dark realm”. They rise from the darkness as “smoke” from dark gases and move as filaments blown by some pressure. On the way the “smoky” balls form and these “balls” start their journey in the cosmos. The merging of these “smoky balls” create the dwarf structures which become the building blocks of galaxies.
The origin of the dark “smoke” appears to be the so-called “void” like the famous “Bootes Void”. One can observe many clustering of galaxies around this void. The most interesting of these clusters is the Coma cluster of galaxies, which shows very rich structure with interesting dynamical activities, which churn the “dark galaxies” into luminous ones and form a zone to study how clustering may occur in the universe.
Like filaments of “smoke” galaxy clusters also follow streaming motions : For exapmle Virgo, Hydra, centaur and Perseus. Pisce clusters. They seem to move towards a great “reservoir” beyond Shapley supercluster. In Horologium-Reticulum one observes an enormously large clustering in the form of a three armed luminous world.
How far the universe may follow this hierarchical clustering is difficult to conceive. The understanding of the distances of the objects, based on the belief in the big-bang model and redshift measurements, may not be correct. We do not have any reliable way to guess the distances beyond the study of luminosities of objects in different wavelengths and holding on to the view that the objects in the cosmos behave in similar way in whatever distances they may exist. Self similarity of a fractal in higher scale may also aid one to explore the distances of objects.
I shall give some examples of the hierarchical clustering starting with dwarf “smoky balls” to the super-cluster and show how they may have taken shapes by following similar mechanism where, besides gravity, turbulence and magnetic fields possibly play central roles. shall particularly emphasize the dynamics of cooling flow and ejection which give most structures their appearances of spiral forms where ejected material cool and flow back towards the centre again.
The structure formation scenario presented here is based on my own understanding which may differ substantially from many others working in this field. However I have tried to follow the studies made by others to get a better understanding of the cosmic phenomena. As I have mentioned earlier I have taken a distance from big-bang model and the redshift measurements as the criteria for speeds and distances of cosmic objects.
Next: Galaxy groups
