- Attachment: globular cluster, Omega Centauri
The arms do not rotate they are simply density waves that the stars are passing through as the stars rotate around the Galaxy. This is similar to traffic congestion on a commute highway. The more we discover the more spherical our galaxy becomes adding to the disk we know.
- 80% of the mass of the Galaxy lies in a spherical halo of Dark Matter that surrounds the disk. ( See index for reviews on Dark Matter). This review is about some 150 known Globular Clusters of stars that also exist in the spherical halo surrounding our galaxy disk. Looking at these clusters alone our galaxy appears as a disk inside a sphere.
- All the stars are born from giant gas clouds. Giant clouds can give birth to many stars. These groups of stars are known as Star Clusters. They are identified as a group of stars all the same distance from Earth. The stars are all about the same age, within a few million years.
- There are two general types of Star Clusters. Open Clusters that are less dense and contain 10’s of thousands of stars. These type clusters are found in the disk of the Galaxy. Globular Clusters are more dense and contain millions of stars and are found in the halo surrounding the Galaxy.
- Open Clusters contain younger stars. The several thousand stars can cover some 30 lightyears in diameter. Pleiades in the Constellation Taurus the Bull is an example of an Open Cluster.
- Globular Clusters contain millions of older stars in a spherical shape that can be up to 150 lightyears in diameter. The central region of the Globular Cluster sphere can have 10,000 stars tightly packed in just a few lightyears diameter.
- The age of the cluster is determine to be the lifetimes of stars that are at their Main-Sequence turn-off point. Above this point stars have exhausted their supply of hydrogen. Below this point stars remain in the Main Sequence still burning hydrogen. ( Refer to the H-R Diagram for more information).
- The age of an Open Cluster is about 5 billion years. The age of a Globular Cluster is about 10 billion years. Some stars are as old as 13 billion years.
- Of the 150 Globular Clusters known Omega Centauri is different from all the rest. Located in the Constellation Centaurus the Centaur., Omega is the brightest, richest, largest cluster found to date in our Galaxy. There is only one bigger that is found in the Andromeda Galaxy, Mayall II.
- Omega is 15,800 lightyears away. It contains over 5,000,000 stars, has a radius of 86 lightyears, and rotates at 18,000 miles per hour. Its spherical shape appears as large as a Full Moon. The stars in the center are so dense they are separated by just 0.1 lightyears, about 6,000 A.U. The fastest stars near the center are orbiting at 47,000 miles per hour.
- After studying some 50,000 individual stars in the Cluster astronomers have concluded that the Cluster contains multiple age groups of stars. Ages that spread over billions of years. Some are 12 billion years old.
- The conclusion is the Omega Centauri is not an ordinary Globular Cluster. It is what is left of a Dwarf Galaxy that collided with our Milky Way Galaxy. The range of metal richness of the stars means they did not form all at the same time. There are several generations of stars all mixed together. The fast moving stars near the center is evidence of a Blackhole there. An announcement will be made shortly, stay tuned.
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707-536-3272, Friday, December 23, 2011
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