Chap12LivesStars

Chap12LivesStars - Main-sequence stars are fusing hydrogen...

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Main-sequence stars are fusing hydrogen into helium in their cores, like the Sun. Luminous main- sequence stars are hot (blue). Less luminous ones are cooler (yellow or red).
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Mass measurements of main-sequence stars show that the hot, blue stars are much more massive than the cool, red ones. High-mass stars Low-mass stars
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The mass of a normal, hydrogen-burning star determines its luminosity and spectral type! High-mass stars Low-mass stars
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The core pressure and temperature of a higher-mass star need to be higher in order to balance gravity. A higher core temperature boosts the fusion rate, leading to greater luminosity. Hydrostatic Equilibrium
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Luminosity: from brightness and distance 10 −4 L Sun 10 6 L Sun Temperature: from color and spectral type 3,000 K 50,000 K Mass: from period ( p ) and average separation ( a ) of binary-star orbit 0.08 M Sun 100 M Sun (0.08 M Sun ) (100 M Sun ) (100 M Sun ) (0.08 M Sun )
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Sun’s life expectancy: 10 billion years Life expectancy of a 10 M Sun star: 10 times as much fuel, uses it 10 4 times as fast 10 million years ~ 10 billion years × 10/10 4 Life expectancy of a 0.1 M Sun star: 0.1 times as much fuel, uses it 0.01 times as fast 100 billion years ~ 10 billion years × 0.1/0.01 Until core hydrogen (10% of total) is used up
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Main-Sequence Star Summary High-mass: High luminosity Short-lived Large radius Blue Low-mass: Low luminosity Long-lived Small radius Red
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Stellar Evolution
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What are giants, supergiants, and white dwarfs?
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Off the Main Sequence Stellar properties depend on both mass and age: those that have finished fusing H to He in their cores are no longer on the main sequence. All stars become larger and redder after exhausting their core hydrogen: giants and supergiants. Most stars end up small and white after fusion has ceased: white dwarfs.
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Main-sequence stars (to scale) Giants, supergiants, white dwarfs
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Star Magnitude (type) Rigel 0.12 (B8 I) Betelgeuse 0.50 (M2 I) Bellatrix 1.64 (B2 III) Alnilam 1.70 (B0 I) Alnitak 1.77 (triple)
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Star-Forming Clouds Stars form in dark clouds of dusty gas in interstellar space. The gas between the stars is called the interstellar medium.
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Interstellar medium H (mostly), He, CO, H 2 O, NH 3 , H 2 CO Most is concentrated in giant molecular clouds Stars form out of enormous volumes of dust and gas
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Supernova explosions in cold, dark nebulae trigger the birth of stars.
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Fragmentation of a Cloud This simulation begins with a turbulent cloud containing 50 solar masses of gas. The random motions of different sections
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This note was uploaded on 03/15/2011 for the course ASTR 2003 taught by Professor Bursick,s during the Spring '08 term at Arkansas.

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Chap12LivesStars - Main-sequence stars are fusing hydrogen...

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