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The stars in context: the Milky Way Galaxy Lecture 12, 07.22.2010 CAPSTONE 07.22.2010 CAPSTONE.07.22.2010.Galaxy The Nebulae • Kant figured it out (1754) • Herschel (William) and his son John, both lords, tried to prove Kant right (1785, 1850) • 1850, Sir John admitted that his father’s great quest had failed. • By 1900, virtually all astronomers agreed that the extent of the Universe was the edge of the Milky Way (~100 kpc). • By 1918, Harlow Shapley had shown that the Galaxy had a center and that the Sun was not near the center. 07.22.2010 CAPSTONE.07.22.2010.Galaxy Great Debate • Great debate, Heber Curtis and Harlow Shapley. 1921. • Analogy of dust lanes to Cygnus rift, Curtis. Shapley won ( all the points were on his side) • Curtis was right, but formally lost • Lamb/Pacynski and GRB, 2nd debate. 07.22.2010 CAPSTONE.07.22.2010.Galaxy Cygnus Rift (Encyclopedia of Astronomy) Regions with no stars are dust clouds 07.22.2010 CAPSTONE.07.22.2010.Galaxy Curtis’ argument 07.22.2010 CAPSTONE.07.22.2010.Galaxy Hubble and expansion • Cepheid variables proved that some galaxies were far way (recognized by variability and VERY luminous). • By 1929, the expansion of the Universe was known, clearly separating galaxies from Galactic nebulae. • Note: it was known that Galactic nebulae had emisson spectra and galaxies had continous (stellar) spectra, but no one figured it out. 07.22.2010 CAPSTONE.07.22.2010.Galaxy Overview of the Galaxy • Scale—15kpc, 8kpc from Sun to Center. • Spiral structure—Morgan (1952), by mapping stars, others later in 21cm emission of H I. • Arms 1kpc across, 50 kpc long, we are at an inner edge. • Zone of obscuration. • Arms have : young stars, dust, forming stars, dying stars. • Rotation speed is 10’s of km/sec of pattern of spiral. Actual star motion is 250 km/sec. • This must be removed from measures of galaxies to get a true redshift, just as Earth’s motion around the Sun and the peculiar motion of the Sun must be removed to get the true motion of stars. CAPSTONE.07.22.2010.Galaxy 07.22.2010 Details • • • • • • • • • Globular clusters: halo RR Lyr stars: halo T Tau stars : near densest clouds. White dwarfs: everywhere (but only seen locally because too faint) Planetary nebulae: everywhere, but not many seen. Red giants: everywhere, easiest halo stars to see. AGB: everywhere O stars: dust lanes B stars: plane of galaxy, away from dust (which has moved out of the way) • A stars and cooler: everywhere, but of dramatically different ages. 07.22.2010 CAPSTONE.07.22.2010.Galaxy Details II • • • • • • • • Thick disk Thin disk Halo Galactic center Star formation rate: 1 per year Star death rate 1/hundred years (SNe) Neighbors SMC, LMC, Andromeda, local group, then nothing for 5Mpc. • Accretion of dwarf galaxies 07.22.2010 CAPSTONE.07.22.2010.Galaxy Map of the Universe • http://www.astro.princeton.edu/~mjuric/ universe/ 07.22.2010 CAPSTONE.07.22.2010.Galaxy