Galaxy groups and clusters

Galaxy groups and clusters of galaxies are collections of galaxies in the universe.

Galaxies are not uniformly distributed in space, but occur more frequently in structures that have formed since the beginning of the expansion of the universe under the influence of gravity and are held together by this. Galaxy groups and clusters of galaxies still form larger objects, the galaxy superclusters. Galaxies that are obviously not part of a group or cluster, called field galaxies. After today's presentation, all these structures parts of a large-scale foam-like distribution of clusters and interconnecting filaments to cavities (English voids) are grouped with low galaxy density. The development of this large-scale structure of small random density fluctuations after the Big Bang, and under the influence of gravity is an important issue in cosmology.

Groups of Galaxies

Smaller clusters of galaxies with less than 50 members in a volume with a diameter of up to 10 million light-years ( MLJ ) are called groups. Their mass is about 1013 solar masses; the velocities of its members vary by about 150 km / s The demarcation of clusters of galaxies is not sharply defined.

Even our Milky Way system is in a group, the Local Group. Besides the Milky Way This includes the spiral galaxy M 31 in the constellation of Andromeda, M 33 in the constellation triangle as well as several companion galaxies such as the Magellanic Clouds.

Galaxy clusters

Galaxy clusters have a size of up to several thousand individual galaxies, all moving at different speeds in the common gravitational field of the cluster. According to prior research, they are the largest structures in the universe that are gravitationally bound. The mass is about 1014 to 1015 solar masses in an area typically 10 to 20 MLJ, at speeds that are scattered around about 500-1000 km / s ( so-called peculiar velocities ). The main part of the mass of galaxy clusters is made ​​out of dark matter (about 80 %).

Clusters of galaxies are of a thin, 10 to 100 million K penetrated hot gas, which can be observed through its X-ray radiation. This gas makes up about 15 % of the mass of a galaxy cluster. The rest of the mass (5 %) is present in the stars and planets of the galaxy. In the center of galaxy clusters there is often a huge elliptical galaxy like M87 in the center of our next cluster of galaxies, the Virgo cluster of galaxies in the constellation Virgo ( the Virgin ). In the constellation Chemical furnace is located in the center of the Fornax cluster of galaxies, which is only slightly further away than the Virgo cluster, the giant elliptical galaxy NGC 1399. It has a broad diffuse halo and is therefore the closest to us so-called cD galaxy. Another near heap, whose galaxies are still visible with slightly larger amateur telescopes, the Coma cluster of galaxies in the constellation Coma Berenices. This cluster is a typical example of a large cluster of galaxies whose center is dominated by two giant elliptical galaxies from the cD type. This bunch is about 300 MLJ away.

In the dense central regions of galaxy clusters are found mostly elliptical galaxies, while galaxies in the outskirts of clusters, galaxies in groups and field galaxies are mostly spiral galaxies.