- Every star begins its life in a group. All the stars in the group are about the same age created in the same giant interstellar cloud of gas and dust. We call them star clusters. Our Sun was once in a star cluster. The Sun’s star cluster has long dispersed and the cloud mostly dissipated. The Orion Nebula is a famous example of another star cluster we can view today. The Pleiades Cluster is another example. It is in the constellation Taurus the Bull.
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- Star clusters can range in size from a few dozen stars to millions of stars. The cluster ages can range from a few million years old to 12 billion years of age, back to the dawn of the Universe.
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- Stars coalesce within vast clouds of mostly hydrogen molecules. Hydrogen being a single proton and a single electron forming a neutral atom. Two hydrogen atoms together make a hydrogen gas molecule. Within the gas cloud we find the dust composed of the other elements. The whole cloud is held together by gravity.
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- Within the cloud regions of denser gas and dust create more gravity. Eventually these denser regions collapse to form protostars. The cloud has many different denser regions and many protostars form until we have a cluster of stars. Clusters can come in different varieties. This review has them grouped into 5 basic types of clusters:
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- (1) Embedded clusters are the very youngest stellar group. Their clouds are so thick the visible light from the stars is completely obscured. The clusters are studied in infrared and ultraviolet light spectrums to understand the protostars that are being created.
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- (2) Globular Clusters are the oldest. They date back to the dawn of the Universe and they contain millions of stars. The parent clouds have dispersed and disappeared so all the stars are completely visible.
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- (3) T- Association Clusters contain young stars called T-Tauri Stars. Our Sun was once a T-Tauri star. These stars do not stay together for more than a few million years. In T-Clusters the mass of the cloud is much greater that the mass of the member stars. The gravity of the cloud holds the stars together. As the cloud disperses due to the solar winds of the individual stars the stars drift apart.
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- (4) O B Association Clusters contain O B type stars which are very massive. These clusters contain 10 times more stars that T-Clusters. The Orion Nebula is an O B Cluster containing 4 very massive stars and 2,000 smaller stars.
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- O B Stars create orbits of very high velocities. O B stars produce enormous solar winds. A typical “O” type star has 30 times the mass of our Sun and will exhaust all of its nuclear fuel in a few million years. (Compared to our Sun that will burn nuclear fuel for 10 billion years.) The solar winds produced ionize the surrounding gas until the parent cloud is gone and the high velocity stars are flung out of the cluster.
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- (5) Open Clusters can persist for hundreds of millions of years. They have a few O B class of stars and up to 1,000 ordinary stars. Pleiades is 125 million years old. Its parent clouds has been gone for 120 million years. The Hyades Cluster is 630 million years old. The M67 Cluster is 4 billion years old.
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- Star Clusters exist in a constant balance , or unbalance, of the attraction forces of gravity and the expansion forces of solar winds and radiation. The actor most predominate is determining which scenario the cluster follows depends on the original mass of the giant cloud. The force balance gets set in motion and the dance of interactions continues for millions of years.
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- Our Sun was once a part of a star cluster during its original formation as a protostar. It is believed to have first formed in a crowded O B Cluster. If astronomers can find stars of the same age and composition they can begin to play back the member dispersion from our parent star cluster. One such star has been located in the Alpha Centauri group of stars. It is the same age and has the same composition as our Sun.
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- Binary stars are quite common in star clusters. If the binary encounters a third star their angular momentum can speed up the orbits of the lighter star and fling it into outer space. Astronomers will have fun piecing this puzzle of star evolution back together. The Orion Nebula is a good place to study. Star formation their stopped only about 100,000 years ago. The tool of choice is computer simulations that can create a million year evolution in a matter of hours. Trial and error, new assumptions, other theories can be tried until the result matches the observations matching the real thing. An announcement will be made shortly , stay tuned.
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RSVP, please reply with a number to rate this review: #1- learned something new. #2 - Didn’t read it. #3- very interesting. #4- Send another review #___ from the index. #5- Keep em coming. #6- I forwarded copies to some friends. #7- Don‘t send me these anymore! #8- I am forwarding you some questions? Index is available with email upon request. Some reviews are at http://jdetrick.blogspot.com Please send feedback, corrections, or recommended improvements to: jamesdetrick@comcast.net. ---- “Jim Detrick” -- www.facebook.com, -- www.twitter.com, -- 707-536-3272 Sunday, March 3, 2013
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