Chapter 11

Chapter 11 - Note that the following lectures include...

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Note that the following lectures include animations and PowerPoint effects such as fly ins and transitions that require you to be in PowerPoint's Slide Show mode (presentation mode).
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The Formation of Stars Chapter 11
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Previous chapters have used the basic principles of physics as a way to deduce things about stars and the interstellar medium. All of the data we have amassed will now help us understand the life stories of the stars in this chapter and those that follow. In this chapter, we use the laws of physics in a new way. We develop theories and models based on physics that help us understand how stars work. For instance, what stops a contracting star and gives it stability? We can understand this phenomenon because we understand some of the basic laws of physics. Throughout this chapter and the chapters that follow, we search for evidence. What observational facts confirm or contradict our theories? That is the basis of all science, and it must be part of any critical analysis of what we know and how we know it. Guidepost
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I. Making Stars from the Interstellar Medium A. Star Birth in Giant Molecular Clouds B. Heating By Contraction C. Protostars D. Evidence of Star Formation II. The Source of Stellar Energy A. A Review of the Proton-Proton Chain B. The CNO Cycle III. Stellar Structure A. Energy Transport B. What Supports the Sun? C. Inside Stars D. The Pressure-Temperature Thermostat Outline
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IV. The Orion Nebula A. Evidence of Young Stars Outline (continued)
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The Life Cycle of Stars Dense, dark clouds, possibly forming stars in the future Young stars, still in their birth nebulae Aging supergiant
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Giant Molecular Clouds Visible Infrared Barnard 68 Star formation collapse of the cores of giant molecular clouds : Dark, cold, dense clouds obscuring the light of stars behind them. (More transparent in infrared light.)
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Parameters of Giant Molecular Clouds Size: r ~ 50 pc Mass: > 100,000 M sun Dense cores: Temp.: a few 0 K R ~ 0.1 pc M ~ 1 M sun Much too cold and too low density to ignite thermonuclear processes Clouds need to contract and heat up in order to form stars.
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Contraction of Giant Molecular Cloud Cores Thermal Energy (pressure) Magnetic Fields Rotation (angular momentum) External trigger required to initiate the collapse of clouds to form stars. Horse Head Nebula Turbulence
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Shocks Triggering Star Formation Globules = sites where stars are being born right now! Trifid Nebula
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Sources of Shock Waves Triggering Star Formation (1) Previous star formation can trigger further star formation through: a) Shocks from supernovae (explosions of massive stars): Massive stars die young => Supernovae tend to happen near sites of recent star formation
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Sources of Shock Waves Triggering Star Formation (2) Previous star formation can trigger further star formation through: b) Ionization fronts of hot, massive O or B stars which produce a lot of UV radiation: Massive stars die young => O and B stars only exist near sites of recent star formation
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Chapter 11 - Note that the following lectures include...

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