AST-L19-ch12__3

AST-L19-ch12__3 - 1 Stellar Midlife/Aging 1 Stellar...

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Unformatted text preview: 1 Stellar Midlife/Aging 1) Stellar Stability/ Main Sequence life 2) Stellar lifetimes 3) Red Giant 4) White Dwarf 5) Supernova 6) More massive stars Today’s Lecture: purpose & goals AST 1002 Planets, Stars and Galaxies Review y) (luminosit burning hydrogen of rate mass) (solar hydrogen of amount x (years) 1x10 10 = MS t t MS = 1/M 2.5 x 10 10 years Gases and Dust Molecular clouds Mostly cold and very low density But enough mass in 50-150 l.y.-wide cloud to form 20,000 solar-mass stars Parts hotter ( Emission nebulae , HII ) – heated by nearby Blue giant stars Protostars/Birth of a Star Same process as formed our solar system Original source of energy is gravity (infall of matter) heat if over 10 million K at core, nuclear fusion turns on (if fails <0.08M brown dwarf ) Stellar Lifetime Review: Main Sequence Lifetime Main Sequence Lifetime t = 10 10 x (M/L) years = 10 10 x (M/M 3.5 ) years (more general form) t ms = 1/M 2.5 x 10 10 years Remember: Mass-Luminosity Relation L ~ M 3.5 0.2M 2 trillion years 1M 10 billion years 10M 32 million years 80M 175 thousand years Example: Choose a star that is ten solar masses. How l ong w ill i t surv i ve as a ma i n sequen c e star ? M = 10 so l ar masses L ~ 3x 10 3 so l ar l um i nos i t i es t ~ 10 10 (10/3x1000) ~33 million years or more precisely: t = 10 10 x(1/10 2.5 ) yr = 10 10 (1/10 2 )x(1/10 0.5 ) yr = 31.7 million years We estimate that a star 10 times the Sun’s mass will remain stable for only about 30 million years ! (Much shorter than the Sun!!) Example2: Choose a star that is 80 solar masses (among the most massive stars). How l ong w ill i t surv i ve as a ma i n sequen c e star ? M = 80 so l ar masses L ~ 4.5x 10 6 so l ar l um i nos i t i es solving: t = 10 10 x(1/ M 2.5 ) yr t = 10 10 x(1/ 80 2.5 ) yr = 10 10 (1/80 2 )x(1/80 0.5 ) yr = 10 10 /(6400)x(8.94) yr = 175 thousand years Example3: Choose a star that is 0.12 solar masses (among the least massive stars, but not right 0.08M ). How l ong w ill i t surv i ve as a ma i n sequen c e star ? M = 0.12 so l ar masses L ~ 3.6x 10-3 so l ar l um i nos i t i es solving: t = 10 10 x(1/ M 2.5 ) yr t = 10 10 x(1/ 0.12 2.5 ) yr = 10 10 (1/0.12 2 )x(1/0.12 0.5 ) yr = 10 10 /(0.0144)x(0.3464) yr = 2.004 trillion years 2 How Luminous, How Long?...
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This note was uploaded on 10/13/2011 for the course AST 1002 taught by Professor Gerstein during the Spring '08 term at FSU.

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AST-L19-ch12__3 - 1 Stellar Midlife/Aging 1 Stellar...

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