Astronomy Notes - Chapter 9: The Lives of Stars From Birth...

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Chapter 9: The Lives of Stars From Birth Through Middle Age instellar medium – material between stars; contains at least 10% of all the observed mass in our Galaxy reflection nebula – a bluish haze starlight scattered by the instellar gas and dust molecular clouds – made up of nebulae embedded in much larger bodies of gas and dust - largest molecular clouds = giant molecular clouds dark nebulae – sufficiently dense regions of interstellar gas and dust; prevent most of the visible light from behind them getting to us emission nebulae – regions of interstellar gas and dust that glow from energy they receive from nearby stars, from exploding stars, and from collisions between nebulae interstellar extinction – darkening of light by intervening gas and dust in space interstellar extinction – star or object at visible wavelengths through the interstellar medium that appear redder than normal - short-wavelength starlight is scattered by dust grains more than is the long-wavelenght light - violet = scattered most - red = scattered least supernova remnants – ashes (gas and dust) of many such dead stars across the sky - have a distinctly arched appearance - As it passes through the surrounding interstellar medium, the supernova remnant slams into preexisting matter, exciting the electrons in the atoms and molecules there, causing the gases to glow H-R Diagram evolutionary track – graph of changes in temperature and luminosity of a star over time - a high mass star collapses faster than a low mass star, and stars fusion more quickly birth line – protostar changes into pre-main-sequence star T Tauri star – pre-main-sequence stars of spectral type G, K, or M that are ejecting lots of gas - brightness changes a lot over time because of activity - can lose up to 0.4 Msun during this phase
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upper limit for star formation: somewhere around120 Msun (solar masses) - Protostars above this mass will have such high surface temperatures they will expel their outer ayers lower limit for star formation: 0.08 Msun (75 Mjup) - Protostars below this mass are too small, won’t collapse enough - to reach 10^7K in core, won’t start fusion = brown dwarf H II regions – ionized hydrogen emission nebulae - lots of red light from HII regions because of red H spectral line (n=3 to n=2) O-B association – collection of hot, bright O and B stars producing ionizing radiation in a molecular cloud - creates H II region and shock waves and causes additional star formation to occur Stars in a cluster begin forming at approximately the same time. -
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This note was uploaded on 03/29/2011 for the course ASTR 1101 taught by Professor Mcgimsey during the Spring '11 term at Georgia State University, Atlanta.

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Astronomy Notes - Chapter 9: The Lives of Stars From Birth...

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