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Galaxy cluster

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Structure of cluster of galaxies

 Updated June 01, 2013

Galaxy clusters are the biggest structures of the Universe. They are constituted by hundreds of galaxies bound together by their own gravitational attraction. Between the galaxies we find some matter constituted by warm gas there, forming a plasma, the temperature of which reaches 10 to 100 million degrees. This plasma is a strong transmitter of X-rays. The spectrum analysis of these X-rays informs about the temperature of the heap and about its dynamics. Galaxy groups form in the crossings of the strands which compose this cosmic cobweb. The Universe being constituted by matter distributed along its immense strands between which are vast bubbles empty of matter. The matter passes by along strands and converges on the knots of the cloth to form groups, then galaxy groups. Galaxy groups are not constituted that of galaxies, they are filled with extremely warm gas (10-100 million degrees) and of weak density (1 000 particles/m3). This gas is distributed in a much more diffuse and more vast way than the galaxies.


These gases fill the space between the galaxies and constitute the essential of the groups, representing a mass more important than the galaxies themselves. In these temperatures, it is totally ionized, it is about a plasma.

Image: Image of the density of a thin slice of the universe. The structure spiderweb clusters of galaxies seems to bind all these clusters by filaments of matter.

 galaxy groups

Local group


The Milky Way and the Big Nebula of Andromeda have satellite galaxies. These two huge spirals belong to an even bigger grouping of 20 galaxies among which M31, M33, Maffei I and Maffei II, the Big and the Small Cloud of Magellan, conscript Groups it local. All these galaxies move around a common center situated between our Galaxy and the Nebula of Andromeda. All the observers know the biggest and the most brilliant of all: M31, in the constellation of Andromeda. The most known heap of galaxies are Virgo, Pegasus I, Pisces, Cancer, Perseus, Coma, Ursa Major III, Hercules, Pegasus, Heap A, Centaurus, Ursa Major I, Leo, Gemini, Corona Borealis, Heap B, Bootes, Ursa Major II, Hydra II Distant from 2,5 million light years, it is the closest galaxy but especially it is the only one who is visible in the bare eye, on dark night. We can consider the Local Group, or the other groups looking like it as heap containing a number relatively restricted by objects. Galaxy groups can be more important. If we come down until the magnitude 21, there would so be 75 million galaxies among which our.


The local group is a part of an enormous complex of 10000 galaxies assembled in heap extending over some 200 million years lights, conscript local super clusters or super clusters of the Virgo. The super clusters of the Virgo and super clusters of the Hydra and the centaur fall themselves towards another big conglomeration of galaxy groups which we call the Big Attractor. Galaxy comes from Greek " galactos " which wants to say milk. Of our ground base, we participate in a fantastic cosmic ballet: the Earth propels us in 30 km/s around the Sun which splits the space in 230 km/s around the Milky Way.
This one falls in his turn towards the galaxy of Andromeda in km/s 90, each of its galaxies rush in 45 km/s towards the center of the local Group, our galaxies group. The local Group moves in 600 km/s attracted by the galaxies group of the Virgo and the super clusters of the Hydra and the Centaur, who falls in his turn towards the big Attractor.

 Local Group of galaxies, Milky Way, Andromède and Triangulum

Image: few galaxies in our Local Group of galaxies. Author Richard Powell.

Virgo cluster


The heap of the Virgo (Virgo) is a massive group of galaxies which dominates the super clusters of the Virgo. It is the closest heap of galaxies of our Galaxy, the Milky Way.
There are approximately 2000 galaxies in this heap (but 90 % of them are dwarfish galaxies).
This heap is one diameter of about 15 million years light, hardly more than our Local Group, but it contains fifty times more galaxies.


Image: The group of galaxies Virgo, dominated by M86 (at the top), M84 (to the right), NGC 4388 below and NGC 4387 in the middle.
source: Hawaiian Starlight, CFHT

 group of galaxies Virgo

Coma cluster


The heap of Coma is a galaxies group, spherical, very dense in its center.
It contains more than thousand galaxies and is situated, in 300 million light years with the heap Virgo in the constellation of the Virgo.


Image: Galaxies group Coma

The super clusters of Coma (Bernice's Hair) is one of galaxies group the most known.

 super clusters of Coma

Fornax cluster


The group of galaxies Fornax is in about 65 million light years of the Earth. The galaxies of the heart of the heap Fornax seem to move in the direction of a common point, attracted by the dominant gravity of invisible structures of dark matter of this region.
There is in the direction where is situated the System of the Furnace a dwarfish galaxy, distant from 600 000 light years.
It belongs to the Local Group, that is to the small heap of galaxies in which is also the Milky Way, our galaxy.


Image: The group of galaxies Fornax of the look-out observatory Chandra reveals emissions with high energy of several huge galaxies close to the center of the heap Fornax and an immense diffuse cloud of warm gas emitting X-rays.

 galaxies Fornax

Shapley cluster


On the photo above, the blue objects are galaxies and the yellow objects are stars in the foreground.
In the center of the group, we find a gigantic elliptic galaxy (ESO444-46) of a diameter of more than 340 000 light years.


Image: clusters Shapley A3558

 clusters Shapley A3558

Hydra cluster


The group of galaxies of the Hydra, nicknamed so because of the constellation which accommodates it, covers approximately 10 million light years and contains more than 100 brilliant galaxies.
The study of the radiation X emitted by the gas which it contains in quantity between its galaxies revealed an abnormally important proportion of dark matter.
Abell 1060 (A1060) is the other name given to this group hydra.
With the group of the Virgo and that of the Centaur (A3526), the group of the Hydra is one three bigger group of galaxies unless 200 million light years of the Milky Way.
It is current to refer to this region of the sky under the name of 'super clusters Virgo -Hydra - Centaurus'.


Image: Galaxies group Hydra

 Galaxies group Hydre

Clusters of galaxies Hydra or Abell 1060


This group of galaxies is probably in the process of fusion. This amazing set of three galaxies is known group NGC 7771 lies about 200 million light-years away in the constellation Pegasus.
The largest barred spiral galaxy NGC 7771 (right), is about 75,000 light-years. It will absorb over time other galaxies to form one, even greater. Throughout their repeated passages close to one of the other, these galaxies will eventually merge into effect in a single large galaxy. Taking place over hundreds of millions of years, this process is part of the normal evolution of galaxies, that also will know our own galaxy, the Milky Way.


Among the billions of stars that merge into a single galaxy, probably few stars collide with each other due to the vast "empty" space. Red regions of galaxies are regions of star formation. The blue areas are hot young stars that have already formed. One can also observe regions of dust around galaxies that show the incredible amount of matter that exists around.

Image: The cluster of galaxies NGC 7771, includes NGC 7769 galaxy bottom left image, the large galaxy NGC 7771 on the right and the small galaxy NGC 7770 above NGC 7771. credit & copyright: Kent Biggs

 group of galaxies NGC 7771

Quintet cluster


Stephan's Quintet is a group of galaxies, that is a group of very close galaxies some of the others. It contains normally 5 main galaxies but only 4 are visible on this image. The galaxies incur because of their strong mass and it is likely that they will merge one day. The galaxies are strongly perturbed by the effect of their gravitational interaction.
We notice it on this image by the distended forms of the strands which extend very far from the center of the galaxy. The members of this group are NGC 7317, NGC 7318a, NGC 7318b, NGC 7319 and NGC 7320. If the first 4 galaxies form a relatively compact group, the fifth, NGC 7320 is away from the group but situated in the same region.


Image: The group of galaxies of Stefan's Quintet or ESO 3598. Well known by the amateurs, the group of the Quintet is situated in the constellation of Pegasus, about a distance about 340 million light years of the Milky Way and was discovered in 1877 by the French astronomer Edouard Stephan, since the look-out observatory of Marseille.
Credit NASA / ESA

 Stefan's Quintet

Perseus galaxy cluster or Abell 426


The Perseus cluster (Abell 426) is part of the Perseus-Pisces Supercluster (Pisces-Perseus) in the constellation of Perseus, 250 million light years. It contains about 190 galaxies and the Perseus-Pisces Supercluster contains about 1000 galaxies. This is one of the biggest visible sky objects. Almost all visible spots on the image are galaxies. The Perseus cluster is one of the closest galaxy clusters. The first star map belongs to our own Galaxy, the Milky Way, they are distinguished by their diffraction spikes. At the center of the cluster, the main galaxy of the cluster NGC 1275 can be seen, this is the largest galaxy visible on the left of the image. The galaxy NGC 1275 is a prodigious source of X-radiation and radio.


Image: The Perseus cluster of galaxies, or Abell 426. The Perseus cluster is part of the Perseus-Pisces Supercluster in the constellation of Perseus, located about 250 million light years.

 Perseus galaxy cluster or Abell 426

Seyfert Sextet cluster


Seyfert Sextet is a group of galaxies located about 200 million light-years, in the head of the constellation Serpens. The constellation Serpens is the only constellation divided into two parts, the head and the tail, separated by the constellation Ophiuchus. The cluster galaxies Seyfert Sextet actually contains only 4 galaxies in gravitational interaction.
They are located in a small region of about 100 000 light-years, the size of our Galaxy. On the picture we see against the top center in the horizontal position, the galaxy NGC 6027 the brightest group galaxy, NGC 6027b upper right in oblique position, the spiral galaxy NGC 6027c horizontally and striped by a belt of dust clearly visible, it is located under NGC 6027b, NGC 6027e in the upper left has no bulb, it is not a galaxy of stars but simply a tail of stars hung by tidal effect to the nearby galaxy NGC 6027.


The galaxy NGC 6027a bottom of the image is a spiral galaxy in vertical position. The beautiful spiral galaxy NGC 6027d, the only galaxy seen from above, a small galaxy is more distant than others and is not part of the cluster of Sextet Syfert, it is likely that this group of galaxies, except NGC 6027d, bound by gravity in a confined space, merged into one large galaxy in the next billion years. Each of interacting galaxies has a width of about 35 000 light-years.

Image: This image from the Hubble Space Telescope, shows us the Seyfert Sextet is a group of galaxies in the constellation Serpens about 200 million light years.
Credit image: Hubble Legacy Archive, NASA, ESA;

 Seyfert Sextet

Cluster of galaxies Abell 2744


The Hubble Space Telescope still amazes us with this cluster of galaxies Abell 2744 is the most massive and deepest ever photographed all clusters of galaxies. This photograph shows some of the youngest galaxies ever detected in the deep cosmos. The immense gravity of the cluster Abell 2744 distorts space so that the image we see is distorted by the curvature, as through a lens we see the magnified galaxies that are much farther behind Abell 2744.
The most distant galaxies are about 12 billion years, they were born shortly after the Big Bang. In this exhibition Hubble reveals nearly 3000 background galaxies interspersed with images of hundreds of galaxies leading belonging to the cluster. Far Away Galaxies appear not only brilliant, but also stained, stretched and duplicated through the gravitational field of Abell 2744. The gravitational lensing amplifies the background galaxies, as much as 10 to 20 times they are brighter and larger than they really are. Moreover most of these galaxies would be invisible without the gravitational lensing.


Long exposure Hubble images will be combined with Spitzer and Chandra X-ray Observatory NASA to provide new insights into the origin and evolution of galaxies and their black holes companions.

Image: This long exposure of the galaxy cluster Abell 2744 is performed by the Hubble Space Telescope. The image of the cluster massive galaxies (foreground) is the deepest ever made. The farthest galaxies around 12 billion years, they were born shortly after the Big Bang.

 Cluster of galaxies Abell 2744

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