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u07a1 Life of the Stars Review Assignment
Finance & Accounting
Pages 3 (753 words)
Life of the Stars Review Assignment 1. What is a molecular cloud? Briefly describe the process by which a protostar forms from gas in a molecular cloud. A molecular cloud is a cloud of interstellar gas that is cold (T ~ 10 to 30K) and dense (a density of at least 300 molecules per cm3 is typical) and in which many of the atoms have bonded together to form molecules (such as H2 and CO).
It all starts with a cloud of gas. Due to gravity the cloud will start to shrink. This collapse is usually triggered by a shockwave from a nearby supernova or expanding planetary nebulae. As the cloud contracts the rotation will become faster and it will break up into individual clumps. If these masses are big enough the density and temperature in the core will become high enough so that nuclear fusion can start. Hydrogen will be converted into Helium. The "burning" of Hydrogen produce a counter pressure to gravity that will stop the gas cloud from further shrinking. The gas cloud becomes a stable star. This is the present state of our Sun. A molecular cloud is a cloud from which stars form. They're called molecular clouds because their hydrogen atoms form hydrogen molecules due to low temperatures. As a molecular cloud fragment collapses it becomes more dense. Radiation has a difficult time escaping and the central regions grow opaque. Thermal energy produced by gravitational contraction becomes trapped in the center which causes temperature and pressure to rise. At the start of collapse this thermal energy was radiated away, but now that the cloud is denser there is enough pressure to resist gravity. When this happens the cloud fragment becomes a protostar. ...
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