Today in Astronomy 142: the Milky Way - Astro Pas Rochester

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Mass per unit area of the Galaxy’s disk, in theSun’s neighborhoodRecall formula for pressure in terms of particle numberdensity, speed and momentum (lecture, 9 February):Number of particles that hitwallTypical momentum per particleTime interval in which they hitConsider a certain class of stars to be gas particles, andconsider the component of their motion perpendicular to theGalactic plane.Suppose the distribution of these stars extends above andbelow the plane by some scale height H/2. Consider starslying on the ends of a cylinder of Galactic matter that extendsabove and below the plane.Astronomy 142 12
Mass per unit area of the Galaxy’s disk, in theSun’s neighborhood (continued)Weight of the cylinder, approximately:dAIf stellar “gas pressure” balances gravity,thendWH/2Compare to force on test mass m frominfinite plane with mass per unit area µ(presumably done in PHY 121 or 122):Force from gravity:dW(All on RHS observable.)Astronomy 142 13
Page 1 and 2: Today in Astronomy 142: the Milky W
Page 3 and 4: The Milky Way’scentral regions, i
Page 5 and 6: HI observations of the LMCKim et al
Page 7 and 8: More edge-on galaxiesNGC 4217 (HST
Page 9 and 10: Schematic structure of the Milky Wa
Page 11: Motions of stars in the Galaxy, and
Page 15 and 16: An easier way to estimate the force
Page 17 and 18: Dark matter I: the Galactic disk in
Page 19 and 20: Dark matter IIAstronomy 142 19
Page 21 and 22: Spiral structureAstronomy 142 21
Page 23 and 24: Density wave theory for spiral stru
Page 25 and 26: Spiral structureAstronomy 142 25
Page 27 and 28: X-shaped bulgeAstronomy 142 27

Today in Astronomy 142: the Milky Way - Astro Pas Rochester

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