Galaxy cluster

(Last edited: Thursday, 31 August 2023, 4:12 PM)

Short Definition
Galaxy cluster is astronomical structure that consist of dark matter, hot plasma and galaxies. They are the biggest bound by gravity formations that we know of.

Detailed Definition

Galaxy clusters are the biggest structures bound by gravity. They consist in 85% of dark matter that is connecting the whole structure together. We can detect dark matter only by observing how its gravitation affects objects around it and what influence it has on light passing near it. The amount of gravity produced in clusters by dark matter is a cause for effect called “gravitational lensing”. That effect bends the light magnifying it and making the cluster into a big natural telescope. Without it, we wouldn’t be able to observe some of the smaller, further galaxies.

Most of the visible matter in galaxy clusters is in form of hot plasma called the intracluster medium (ICM). Due to the high gravitational potential energy of material the shock sends gas into really high temperatures that can raise up to 10s of millions grad Celsius. That temperature later causes the emission of X-Rays.

The smallest part of galaxy clusters are galaxies, they are around 2% of a total mass of the structure. Yet the biggest known to us galaxies are formed in clusters.


Galaxy (Noun.), originated from Ancient Greek word galaxías, that means “Milky Way”. At first used only to describe Milky Way Galaxy, later on it changed its meaning to more general.

Cluster (Noun.), derived from Proto-Germanic *klas-, *klus-, meaning “to clump, lump together”.

Sample Sentence(s)

Galaxy clusters can consist of thousands of galaxies.

Translations of Terms/Concepts into Partner Languages

French: amas de galaxies

German: Galaxienhaufen

Italian: mmasso di galassie

Polish: gromada galaktyk

Swedish: galaxhop

Links to Videos/Articles:

  1. Max Planck Institute for Extraterrestrial Physics (n.d.), Clusters and Group of Galaxies, Retrieved from
  2. Center for Astrophysics Harvard & Smithsonian (n.d.), Galaxy Clusters, Retrieved from
  3. Online Etymology Dictionary (n.d.), galaxy (n.), Retrieved from
  4. Online Etymology Dictionary (n.d.), cluster (n.), Retrieved from
  5. European Space Agency (2007, Juli), The Bullet Cluster, Retrieved from  

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