AST- 105 1st EditionLecture 14Outline of Last LectureI. Stellar Temperature, Color, and Spectra Outline of Current Lecture I. Star FormationII. Cloud CollapseIII. ProtostarsIV. Stellar EvolutionCurrent Lecture I. Star Formationa. Stars form in cold, dense interstellar clouds.b. Dark Nebula- a dense cloud of gas and dusti. Darkness absorbs visible light and obscures starts behind it.II. Cloud Collapsea. Cloud Collapse- Clouds in outer space can go in and out of hydrostatic equilibrium.i. Gravity will cause the cloud to collapse if it is compressed by a shock wave.b. A cloud collapse can be triggered by:i. Near supernovaii. Cloud passing through spiral arm of galaxyiii. Cloud coalitionIII. Protostarsa. Protostars- protostars are surrounded by dense gas and dust clouds from which they form.i. Protostars are best observed in infared.ii. IR is less absorbed by dust than visible light is.b. When the central temperature of a protostar reaches 10^7 K, Hydrogen Fusion begins in core. i. Contraction stops.ii. Star sits on the main sequence for the duration of its life. IV. Stellar Evolutiona. Evolutionary Track- path of star in the H-R diagram as L and T changei. Track of protostar approaches main sequence from above, right (higher luminosity, lower temperature) ii. Protostars have high luminosity and low temperature.b. Reflection Nebulae- bluish haze seen around hot, young starsi. Due to interstellar dust:1. Dust reflects blue light more effectively than red light.2. Blue haze in reflected in star light.3. Stars behind dust appear redder than their true
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