Chapter 33 Winter 2011

Chapter 33 Winter 2011 - Life history of a star Chapter 33...

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Chapter 33 History of a Star Did you read chap. 33? a) Yes b) No Life history of a star Humanity has not been around long enough to watch a star go through all these processes, but as we look out into the universe we can see various stars in all these stages of their life cycles, and can infer what happens. Fundamental principles that govern the life cycle of a star: 1. The law of gravitational interaction 2. The law of electromagnetic interaction 3. The strong interaction 4. The conservation of mass-energy Key to understanding square4 Gravitational force pulls material in amount of mass is important square4 Electromagnetic, nuclear forces push material out (“gas pressure”) type of reaction/energy determines how much push square4 Balance determines condition of star
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Beginnings square4 Space is mostly empty About 1 atom/ m 3 square4 Matter denser in galaxies 10 6 atoms per m 3 in the interstellar regions (much better vacuum than we can achieve on earth, however) The Eagle Nebula
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Incubation period square4 Cold dense pockets of gas are called dark nebula. square4 Pockets where matter is more dense give rise to a group or cluster of protostars . ( red arrows ) square4 Light from protostars creates emission nebula A Stellar Nursery: Horsehead Nebula Protostar Cycling: balance between gravity and gas pressure square4 Rising temperature inside protostar causes gas to push back against gravity. square4 The collapse slows. square4 Radiation escapes, pressure decreases, collapse begins again. square4 Slow cycles continue for ~10 M years. square4 The protostar shines by: Gravitational potential energy Thermal, kinetic energy Light energy A plasma (ionized gas) is created when protostar gets hot enough Energy is given off when A. Elements lighter than iron fuse. B. Elements lighter than iron fission. C. Elements heavier than iron fuse. D. Elements heavier than iron fission.
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Stellar Birth square4 All stars are a condensation of gas that is balancing gravitational collapse against thermal explosion. The life history of a star is determined by which force is dominating.
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