Galaxy cluster

Galaxy clusters have a size of up to several thousand galaxies that move at different speeds in the common gravitational field. According to prior research, they are the largest structures in the universe that are gravitationally bound. Their 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.

Classification of galaxy clusters

Similarly, how to classify galaxies according to the Hubble sequence schema even clusters of galaxies can be classified according to their morphological type. The classification is, however, less clear and the physical explanation of the morphology usually difficult. Thus far no classification scheme has prevailed, however, enjoys the scheme of Rood and Sastry (RS ) scheme some popularity, probably because of its similarity to the Hubble diagram. After the RS scheme, a distinction based on the distribution of the ten brightest members of clusters following types:

• CD clusters are dominated by a single giant cD galaxy in the center. Example, the cluster Abell 2634 in the constellation of Pegasus, which is about 400 MLJ removed and is dominated by NGC 7720 and Abell 2199, which lies in about 430 MLJ away in the constellation Hercules and the Hercules Supercluster.
• B- heap (from binary) are dominated by a pair of cD galaxies. The prime example is the famous Coma cluster of galaxies ( Abell 1656), another example of the MLJ 260 distant cluster of galaxies Abell 569 in the constellation Lynx.
• L- clusters are characterized by an approximately linear arrangement of the largest galaxies in the center. One example is the Perseus cluster of galaxies ( Abell 426 ), which is about 230 MLJ away in the Perseus - Pisces supercluster.
• C- heap (of English core) are distinguished by a single dense core with a number of large galaxies. Examples are the Hydra cluster of galaxies ( Abell 1060 ), which is located about 150 MLJ and belongs to the Hydra- Centaurus Supercluster, and the 210- MLJ distant cluster of galaxies Abell 262 in the constellation Andromeda, which is part of the Perseus - Pisces supercluster. Even the one pictured above clusters of galaxies Abell 1689 is from the RS- type C.
• F- heaps are flat, that is, much flattened in one direction, but without strong concentration in the center. Examples are the approximately 290 remote MLJ Leo cluster of galaxies ( Abell 1367 ) in the Coma supercluster and the nearly six GLj IRAS 09104 4109 distant clusters.
• I have a bunch of irregular structure, with no clearly defined center or multiple centers. Examples are the Virgo cluster of galaxies and the Hercules cluster of galaxies ( Abell 2151 ), a spiral- rich clusters in the same supercluster at a distance of about 485 MLJ.

Methods for the detection of galaxy clusters

• The next cluster of galaxies can be seen as brighter galaxies concentration in sky shots. This method was refined by George Abell and his staff, totaling over 4000 galaxy clusters identified since the 1950s at the Palomar Observatory Sky Survey by corresponding observations in the southern sky up to redshifts of 0.2. Distant galaxy clusters stand out only weakly from the foreground and background from other galaxies and are thus difficult to detect.
• Since clusters of galaxies contain many bright elliptical galaxies with similar red colors, they give themselves away in a large-scale study of the color and brightness of galaxies by a occurring in a small area red sequence.
• With space telescopes, X-ray astronomy galaxy clusters can be found on her hot gas.
• Small changes in the cosmic background radiation as it passes through the hot gas of a galaxy cluster ( Sunyaev - Zeldovich effect) can be identified with certain radio telescopes.

Dark matter in galaxy clusters

A detailed analysis of the proper motions of the galaxies in galaxy clusters with the virial theorem shows that all visible matter is insufficient to ensure the cohesion of the clusters by gravity. This observation was first made ​​in 1933 by Fritz Zwicky in the Coma cluster of galaxies. Also the later discovered in X-rays hot gas does not have enough mass. These observations gave the first indication of a previously declared phenomenon, which is summarized below dark matter today.

Gravitational lens effect

Galaxy clusters can the light far standing behind them astronomical objects focused with their gravity and amplify ( gravitational lensing ). This reinforcement is an important tool to investigate extremely faint background galaxies at redshifts up to z> 6 still can.

Notes

• Galaxy clusters