Galaxy cluster

A galaxy cluster is the association of more than one hundred of Galaxie S dependant between them by the Gravitation. In on this side 100, one speaks rather about Groupe of galaxies, even if the border between group and cluster is not clearly defined.

These clusters are characterized by their form (specific, spherical, symmetrical or unspecified) like by the distribution and their numbers of galaxies (to several thousands). They were formed there is 10 billion years, which is relatively early compared to the age of the universe (approximately 15 billion years). These clusters can themselves join in group larger to form Superamas.

The galaxy clusters are the stable structures, i.e. its components cannot escape from the well of gravitational potential of the cluster, largest and most massive of the current Universe.

Our Galaxy belongs to a Groupe of galaxies, including/understanding about thirty galaxies, called local Groupe , itself included in the Superamas of the Virgin.

Some examples:

Antlia-Sextans group: located at only 5,5 million light-years of the Local group;
Virgo Cluster: located at approximately 60 million light-years, it could contain more than 1.500 galaxies in a ray of only 7 million light-years;
cluster of Hercules (A2151): The richest cluster of the supercluster of Hercules. Located at 365 million light-years, it would contain a hundred galaxies;
Coma cluster (A1656): Spherical cluster of at least ten million light-years in diameter and container of the thousands of galaxies.

Distribution

The distribution of the clusters does not seem homogeneous in the Universe: Empty areas côtoient dense areas like " the Finger of God " in the constellation of Bérénice or the " Large Wall ".

The majority of the galaxies, approximately 90%, belong to a cluster or a supercluster, and 20% of the galaxies belong to a cluster containing of the hundreds even thousands of other galaxies.

Composition

In addition to galaxies, a galactic cluster contains very hot between 10⁷K and 10⁸K and very thin gas (weak density generally ranging between 10^-3 and 10^-2 particles per cm ³), which emits X-rays via the process of continuous Rayonnement of braking. It seems that this gas is of paramount origin but the presence of iron shows that there was later contamination. This contamination comes mainly from the explosion in supernovas of stars present in the galaxies hosts of the cluster. The old stars, rich in heavy elements, disseminate while exploding, these elements in the interstellar environment then intra-cluster.

When the galaxy cluster did not undergo collisions with other clusters for a certain time, the gas intra-cluster is spread out in the field of gravity of the cluster: it is in hydrostatic balance.

The total mass of the gases is much larger (of a factor 2 or 3) that mass of the galaxies which it contains. In spite of that, the mass of the cluster is not enough high to correspond with the observations of the movement of the galaxies. Thanks to the concept of the black Matter, its mass would be divided into 5% from galaxies, hot gas 15% and black matter 80%.

Generally, the clusters have these properties:

They contain between 50 and 1.000 galaxies.
Their mass total lies between 10¹⁴ and 10¹⁵ solar masses.
They have a diameter from 2 to 10 Mpc.
the dispersion speeds for each galaxy is from approximately 800 to 1.000 km/s.

See too

List of galaxy cluster
elliptic Spiral galaxy
Galaxy

External bonds

Description of the clusters and superclusters close

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