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Lecture 28

PHYS 183 Lecture 28: PHYS 183 - Lecture 28

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PHYS 183
Gilbert Holder

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Lecture 28 March 29, 2017 How can we figure out what the milky way looks like? - Light and dark stuff? Molecular cloud spectrum - Lots oh helium and hydrogen in the universe in general - Different for clouds - For every type of molecule there are certain vibrational, rotational modes that are excited by certain wavelengths of light Molecular absorption - In stars (esp. hot stars) there are no molecules as temperatures are to high - In cold gas, can have molecules - Molecules absorb specific wavelengths of light too o Due to motion of molecules Doppler broadening - Moving gas particles, at high temp, absorb wider range of wavelengths, due to Doppler shifting of particles some moving away from observer, some moving towards - Dust blocks out light Hydrogen spin-flip transition: 21-cam line - Atomic hydrogen can absorb and emit light at wavelength = 21 c, frequency =1420 MHz - Hydrogen can flip, and emit light when it does does not happen often - Predicted to be observable in 1944 by van der Hulst - Observed in 1951 by Ewen and Purcell GET NOTES FROM LECTURE RECORDING Cannot take picture of milky way - Stars are formed from H, He from the big bang along with from material in molecular clouds - Those stars spend their lives producing the elements heavier than H, He (up to Fe) - The massive stars the spray their elements into their environments via supernovae - The resulting supernova remnants expand into the interstellar medium, enriching it - The process of star formation continues, becoming enriched with heavier elements as time progresses How did milky way form? - Clump of gas - The particles hit each other, eventually start going around in circle o They cancel each other out in 2/3 directions why solar system is flat - Spiral density waves form The centre of the galaxy - Traditionally hard to study - Dust extinction at visual wavelengths enormous total obscuration in visible light - Studied mainl
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