Home Page | Overview | Site Map | Index | Appendix | Illustration | About | Contact | Update | FAQ |
objects are in the vicinity of the Virgo Cluster. By the 1960s enough data have been collected to classify the clustering of the galaxies. It can be grouped into two categories - the regular and the irregular. Their properties are shown in Table 04-01 below. Figure 04-01a shows a typical cluster of galaxies at z = 1.10 with contours for X-ray emission. Figure 04-01b shows another cluster about 1 billion light year further away. The X-ray emission shown in purple reveal the hot intracluster gas. It is estimated that the composition of a cluster is 10% galaxies, 20% intracluster medium (gas), and 70% dark matter. | ||
Figure 04-01a Cluster of Galaxies 1 [large image] |
Figure 04-01b Cluster of Galaxies 2 [large image] |
Property | Regular Clusters | Irregular Clusters |
---|---|---|
Symmetry | Marked spherical symmetry | Little or no symmetry |
Concentration | High concentration of members toward cluster center | No marked concentration to a unique cluster center; often two or more nuclei of concentration are present |
Collisions | Numerous collisions and close encounters | Collisions and close encounters are relatively rare |
Types of galaxies | All or nearly all galaxies in the first 3 or 4 magnitude intervals are elliptical and/or S0 galaxies | All types of galaxies are usually present except in the poor groups, which may not contain giant ellipticals. Late-type spirals and/or irregular galaxies present |
Number of galaxies | Order of 103 or more | Order of 10 to 103 |
Diameter (Mpc) | Order of 1 - 10 | Order of 1 - 10 |
Subclustering | Probably absent or unimportant | Often present. Double and multiple systems of galaxies common |
Radial velocities dispersion | Order of 103 km/sec | Order of 102 - 103 km/sec |
Mass (from Virial Theorem) | Order of 1015 Msun | Order of 1012 - 1014 Msun |
Other characteristics | Cluster often centered about one or two giant elliptical galaxies | |
Examples | Coma cluster (A1656); Corona Borealis cluster (A2065) | Virgo cluster, Hercules cluster (A2151) |
1. Starting from a system of high temperature gas and a quiet supermassive black hole, the gas cools down and flows inward (called cooling flow) as it emits X-rays, which carry off a lot of energy. 2. Some of the gas in the cool flow condenses into stars that become part of the central galaxy, and some sinks all the way down to feed the supermassive black hole. In so doing, it creates an accretion disk and activates high-power jets. 3. The supermassive black hole in the center of | ||
Figure 04-01c Cluster Structure [view large image] |
Figure 04-01d Cluster Evolution [view large image] |
galaxy is expected to spin up over time as they accrete gas. By the time the black hole has swallowed enough gas to double its mass, its outer |