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U07a1 Life of the Stars Review Assignment - Coursework Example


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U07a1 Life of the Stars Review Assignment

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. It isn't a star yet because the center isn't hot enough for fusion. 2. What is degeneracy pressure, and how does it differ from thermal pressure? Explain why degeneracy pressure can support a stellar core against gravity even when

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the core becomes cold. The pressure maintained by a body of degenerate matter is called the degeneracy pressure. Thermal pressure is "the ordinary pressure of a gas arising from motions of particles that can be attributed to the object's temperature" Thermal pressure increases when temperature or thermal energy increases. Stars can maintain internal thermal pressure with help from nuclear fusion and gravitational contraction. Internal thermal pressure can only be maintained if the energy a star radiates into space is replaced. The Pauli Exclusion Principle in quantum mechanics forbids electrons (and all fermions with half integer spin including neutron) occupying the same state. Basically, each electron must have different energy when they are packed together, as they are in a white dwarf. The number of available low energy states is too small and many electrons are forced into high energy states. When this happens the electrons are said to be degenerate. These high energy electrons make a significant contribution to the pressure. Because this pressure arises from a quantum mechanical effect, it is insensitive to temperature, i.e., the pressure doesn't go down as the star cools. This pressure is known as electron degeneracy pressure and it is the force that supports white dwarf stars against their own gravity. 3. Why does helium fusion require much higher temperatures than hydrogen fusion? Briefly explain why helium fusion in the Sun will begin with a helium flash. Helium fusion requires much higher temperatures than hydrogen fusion because the nuclei carry a much greater positive charge. This means higher speeds are necessary in order to overcome the nuclei repelling each other. The basic reaction of helium fusion is that it converts 3 helium nuclei into one carbon nucleus. It requires a much higher tempe


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)…
Author : kundekeely
U07a1 Life of the Stars Review Assignment essay example
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