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Galactic Cluster

The Virgo, Coma, Perseus, and Phoenix Clusters

Virgo Cluster M87 Figure 04-02a shows the Virgo cluster as an example of the irregular cluster. It is the closest cluster of galaxies to the Milky Way. There are about 150 large galaxies of many types in this cluster and at least a thousand known dwarf galaxies. At the core of the Virgo cluster lie the three large elliptical galaxies M84, M86 and M87 (with the jet in Figure 04-02b). These galaxies probably formed from the merger of many smaller galaxies and are much more massive than our own galaxy. The cluster contains not only galaxies filled with stars but also gas so hot it glows in X-rays. Motions of galaxies in and around clusters indicate that

Figure 04-02a The Virgo Cluster
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Figure 04-02b M87
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they contain more dark matter than any visible matter. The Virgo cluster is the dominant member within the Virgo supercluster. All the other members move around this center by its gravitational pull.
Coma Cluster Coma Cluster in X-ray

Figure 04-03 shows the Coma cluster (a member of the Coma supercluster) as an example of the regular cluster. It displays the central region with a dominant elliptical galaxy at the center. The X-ray emission from the hot and tenuous gas is illustrated in the picture on the right. The gas is thought to be produced by matter ejected from stars in the galaxies over a period of about a billion years and reaches a temperature of 107 oC.

Figure 04-03 The Coma Cluster of Galaxies

In Figure 04-04a, each of those fuzzy blob is a galaxy, together making up the Perseus Cluster. The dominant galaxy is NGC1275 -
Perseus Cluster Perseus Cluster, X-ray the large galaxy on the image left. It is a prodigious source of x-rays and radio emission as gas and galaxies falling into its center. The x-ray hot gas (not the individual galaxies) appears in the left panel of Figure 04-04b, a false color image from the Chandra Observatory. The bright central source flanked by two dark cavities is the cluster's supermassive black hole. At right, the panel shows the x-ray image data specially processed to enhance contrasts and reveals a strikingly regular pattern

Figure 04-04a Perseus Cluster

Figure 04-04b Hot Gas in Perseus Cluster [view large image]

of pressure waves rippling through the hot gas. In other words, sound waves, likely generated by bursts of activity from the black hole, are ringing through the Perseus Galaxy Cluster.

Phoenix Cluster It was found by many world-class observatories that the Phoenix cluster at a distance of 5.7 Billion lys from Earth is the most powerful X-ray source and the most massive among any known galactic clusters (Figure 04-04c). The X-ray is produced from gas cooling in the central region. Since the central black hole emits only moderate jets, gas cooling proceeds at a much faster pace (than the other clusters) causing star formation at a rate about 20 times faster than in the Perseus cluster.

Figure 04-04c Phoenix Cluster [view large image]

It is believed that this is only a short-lived phenomena. The black hole will become more active via the feeding of more material, and eventually the outflow of energy will reverse the trend.

See a "Review of Some Major Galactic Clusters".

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