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IUPUI AST 105 - Star Birth

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Lecture 11Outline of Current Lecture (2/19)I. Star Birtha. Composition of Interstellar Medium II. Interstellar ReddeningIII. 2.6 mm Radiation IV. Jean’s Instability a. Protostarsb. PMS stars c. Main sequence star V. Brown DwarfVI. Upper LimitVII. Main sequence lifetimesVIII. Red DwarfsStar Birth- Stars form due to gravitational attraction that binds partiles that make up theinterstellar medium - Composition of interstellar medium  74% hydrogen 25% helium  1% others- interstellar medium is very cold and emits almost no visible light (because it is hard to see)Interstellar Reddening- blue/purples have large scattering angles (get bent the most, easiest to scatter; purple scatters most, blue dominant) this is why our sky is blue and our sunsets/sunrises are red2.6 mm Radiation - another way to detect interstellar medium is for every carbon monoxide molecule there are about 10,000 H2 moleculesJean’s Instability - vast region of molecular hydrogen- if its sufficiently cold, gravity forces over whelm the kinetic pressure and the H2 collapses - inner layers fall in very rapidly this increases the mass in the center - protostar has formed ASTG 105 1st EditionLecture 11- Protostars do not have any nuclear fusion- Protostars glow due to increase of kinetic pressure from gravity- Protostar increases massaccretion - Pre-Main Sequence star formed when kinetic pressure is so great that the EM radiaton given off by the protostar halts mass secretion - PMS star slowly contracts Hydrogen begins fusion in the core at 10 million K The contraction stops, size is now stable At this point, PMS star becomes main-sequence star - It takes roughly 1 million years for a PMS star to become a main sequence star- The more massive a PMS star, the more quickly it becomes a main sequence star Brown Dwarf- Very small PMS stars- Here gravity is not sufficient enough to start fusion  No fusion occurring- Jupiter and Saturn are considered brown dwarfsUpper Limit - 100Msun- large mass means high fusion rate very large release of photons  blasts away outer regions  star drops below 100MsunMain Sequence Lifetimes - lifetimes on main sequence vary with massRed Dwarfs- low mass, main sequence stars masses of about 10% of our sun - slowly fuse hydrogen, surface temps about 3000K- can live up to 500 billion years - our universe is only about 14 billion years old ASTG 105 1st


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IUPUI AST 105 - Star Birth

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