Lecture 16Significance of the Hertzsprung Russell Diagram - PowerPoint PPT Presentation
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Lecture 16Significance of the Hertzsprung Russell Diagram
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Physical argument 2: what powers the stars (where do they get their energy ... Stars spend a much longer time here than in other parts of the HR diagram ... – PowerPoint PPT presentation
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Title: Lecture 16Significance of the Hertzsprung Russell Diagram
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Lecture 16Significance of the Hertzsprung
Russell Diagram
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Understanding the Main Sequence (stars like the
Sun)
- A statistical argument (no physics)
- Physical argument 1 what holds stars up?
- Physical argument 2 what powers the stars (where
do they get their energy supply?)
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The nature of the Main Sequence 1 the MS as a
Cambus Stop
- Many more people seen on the sidewalk near a
Cambus stop than a random point
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The Main Sequence is a long-lived phase of
stellar evolution. Stars spend a much longer time
here than in other parts of the HR diagram
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Argument 2 What holds stars up?
Demo
Gravity tends to squeeze a star into ever-smaller
object. What resists this tendency?
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Argument 3 The problem of 19th century
astrophysics
- What keeps the interior of the Sun and stars hot?
- What provides the power source of the Sun over
billions of years?
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The problem of the solar luminosity
- Luminosity 3.8E26 Watts 3.8E26 Joules/sec
- Chemical reactions (gasoline, explosives) yield
of order 1E06 Joules/kilogram - The mass of the Sun is 2E30 kilogram, so total
store of energy is 2E36 Joules - This would keep the Sun burning for about 170
years!!!! Historical rather than geological
times!!!!
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Some vastly more powerful energy source (than
chemical reactions) must be occurring in the Sun
and stars
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A microscopic view of chemical reactions
interactions of the electron cloud
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Nuclear reactions interactions among the nuclei
(Figure 17.2)
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