Galaksiryväksistä

Galaksiryväksistä, often translated as galactic clusters or simply clusters, refers to the largest known gravitationally bound structures in the universe. These are not to be confused with globular clusters, which are collections of stars within a single galaxy. Galactic clusters are vast congregations of galaxies, typically numbering in the hundreds or thousands, all bound together by their mutual gravitational attraction. They are separated by immense distances from other clusters, with tenuous intergalactic medium filling the space between them.

The formation of galactic clusters is a complex process that unfolds over billions of years. They are thought to originate from initial density fluctuations in the early universe. Regions with slightly higher densities attracted more matter, including dark matter and galaxies, eventually leading to the formation of these colossal structures. Clusters continue to grow by accreting smaller groups of galaxies and individual galaxies from their surroundings.

Galactic clusters are crucial laboratories for understanding cosmology. Studying their composition, distribution, and evolution provides insights into the distribution of dark matter, the expansion rate of the universe, and the large-scale structure of the cosmos. The hot gas that fills the space between galaxies within a cluster, known as the intracluster medium, emits X-rays and can be analyzed to determine the cluster's mass and temperature. Examples of nearby galactic clusters include the Virgo Cluster and the Coma Cluster.