Galaksijoukko

Galaksijoukko, also known as a galaxy cluster, is a large-scale structure in the universe consisting of hundreds to thousands of galaxies bound together by gravity. These clusters are the largest known gravitationally bound structures in the universe, and they are often found at the intersections of filaments in the cosmic web, the large-scale structure of the universe.

Galaxy clusters are primarily composed of dark matter, with ordinary matter (baryonic matter) making up a smaller fraction. The baryonic matter is predominantly in the form of hot gas, which emits X-rays due to its high temperature. This hot gas is often visible in X-ray images of galaxy clusters.

The dynamics of galaxy clusters are influenced by the presence of dark matter and dark energy. The gravitational pull of dark matter holds the cluster together, while dark energy is thought to be responsible for the accelerated expansion of the universe, which affects the evolution of galaxy clusters over cosmic time.

Galaxy clusters are important for studying the large-scale structure of the universe and the properties of dark matter and dark energy. They also provide insights into the formation and evolution of galaxies and the intergalactic medium. Observations of galaxy clusters have been used to test theories of cosmology and to constrain the parameters of the standard cosmological model.