L1820GH09Stars_Star_formation

L1820GH09Stars_Star_formation - Star formation Lecture...

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star formation Star formation •Lecture topics: stages in star formation •Text reading: Chapter 3 – 3.4; Chapter 4 – 4.1-2
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star formation The physics of stars - review A star begins simply as a roughly spherical ball of (mostly) hydrogen gas, responding only to gravity and it’s own pressure. To understand how this simple system behaves, however, requires an understanding of: 1. Fluid mechanics 2. Electromagnetism 3. Thermodynamics 4. Special relativity 5. Chemistry 6. Nuclear physics 7. Quantum mechanics X-ray ultraviolet infrared radio
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star formation The sun as a star The sun is a “middling” star – • not the biggest or smallest • not the brightest or faintest • not the hottest or coolest • not the most massive or least massive Range of properties for normal stars: 9 radius: ~10 -2 –10 3 R sun 9 luminosity: ~10 -4 –10 6 L sun 9 temperature: ~3000-30000K (sun is ~6000K) 9 mass: ~0.1-50 M sun Now – a brief look at stars other than the Sun
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star formation The H-R Diagram Temperature (K) L u m i n o s t y ( / )
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star formation The Hertzsprung-Russell diagram stars do not randomly populate the L,T plane •colours and luminosities of stars are strongly correlated •the±Hertzsprung-Russe l (1914) diagram proved to be the key that unlocked the secrets of stellar evolution • principal feature is the main sequence (dwarfs) •the±br ighter±stars±are± known as giants BLUE
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star formation Types of Stars Assuming stars are approximately blackbodies: K m 00290 . 0 max = T λ 4 2 4 T R L σπ = Means bluer stars are hotter Means brighter stars are larger Betelgeuse is cool and very, very large White Dwarfs are hot and tiny
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star formation Star Sizes: one method measure: temperature from spectrum measure: distance using parallax measure: apparent magnitude This gives the luminosity L=4 π R 2 T 4 measure star’s temperature measure star’s luminosity calculate star’s radius
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star formation Types of stars Intrinsically faint stars are more common than luminous stars
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star formation Stellar (main sequence) lifetimes For low mass stars: Sun Sun L L K T M M 4 3 10 05 . 5 10 74 . 2 085 . 0 × = × = = What is the lifetime of such a star? BLUE Colour RED Luminosity For high mass stars: Sun e Sun L L K T M M 6 4 10 1 . 1 10 27 . 5 90 × = × = = Remember: for MS stars, energy is primarily from H->He fusion
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star formation Stellar lifetimes • From observations of the cosmic microwave background, we know the Big Bang occurred about 13.7 billion years ago • Galaxies have been observed at a time when the Universe was less than 1 billion years old. • Thus stars have been forming
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This note was uploaded on 04/15/2009 for the course PHYS 275 taught by Professor Harris during the Winter '09 term at Waterloo.

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L1820GH09Stars_Star_formation - Star formation Lecture...

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