- #1
- 1,271
- 7
Is there a rigorous definition for what constitutes a galaxy cluster or a super cluster, or are they just identified in an ad-hoc manner?
Chronos said:Galactic clusters are gravitationally bound groups of galaxies. Gravitationally bound means their mutual gravitational attraction surpasses the repulsive effects of cosmological expansion [at least for the forseeable future]. Superclusters are gravitationally bound groups of galactic clusters. Again, their gravitational attraction appears to at least slow the effects of cosmological expansion. This is, however, an interesting question. See, for example:
"The Influence of the Cosmological Expansion on Local Systems"
http://www.iop.org/EJ/article/0004-637X/503/1/61/36143.text.html
sylas said:Cosmic expansion is not a replusive effect. You can call "dark energy" a repulsive effect; but it is far too small to be of much significance on the scale of a cluster.
bombadil said:Hi Sylus, what's wrong with saying cosmological expansion has "repulsive effects"? Expansion (with Dark Energy or without) is important and inhibits the growth of structure like galaxy clusters. As long as one doesn't associate "repulsion" with "force" it seems as good a word as any to describe what's going on.
-bombadil
sylas said:It's true that expansion can inhibit the growth of clusters... but NOT because of a repulsive effect. It is rather because of expansion itself.
In other words, it's ad-hoc.Chronos said:Galactic clusters are gravitationally bound groups of galaxies. ... Superclusters are gravitationally bound groups of galactic clusters.
jimmysnyder said:In other words, it's ad-hoc.
A galaxy cluster is a large group of galaxies held together by gravity. It can contain hundreds to thousands of galaxies, as well as hot gas and dark matter.
Galaxy clusters and superclusters are formed through the process of gravitational attraction. As matter in the universe clumps together, it creates these large structures.
A galaxy cluster is a group of galaxies, while a supercluster is a group of galaxy clusters. Superclusters are much larger in scale and can contain thousands of galaxy clusters.
No, galaxy clusters and superclusters are not evenly distributed in the universe. They tend to cluster together in certain regions and are separated by vast empty spaces known as voids.
Studying galaxy clusters and superclusters can provide insights into the structure and evolution of the universe. They also help us understand the role of dark matter and dark energy in shaping the universe.