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MSU AST 308 - nov12

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1The actual agenda:•Inflation--------------• Present-day structure• The case for dark matter• Gravitational lenses• The nature of dark matter• The growth of structure• Galactic evolutionThe Syllabus:Homework for next Wed. Nov. 14:CO 30.4, 27.10, 27.12(= 28.10, 25.10, 25.12 1sted.)In 30.4, use Tend of GUT epoch= 1028K989695959492898784848381767573737271706560Midterm 2scoresDue Friday Nov. 16The Structure of the Universe• The Local Group• 2 main mass concentrations• MW + satellites–LMC–SMC• M31 + satellites–M32–M332The Brightest Members of the Local Group (an old list)Galaxy Clusters1000’s of galaxiesHercules Cluster3The Local Supercluster• Biggest component: Virgo Cluster (1014M).• Local Supercluster (1015M)Virgo Cluster(2000 galaxies)Blue = 0oKRed = 4oKBlue = 2.724oKRed = 2.732oKDipole Anistropy4Structure upon structure• Local Group• Virgo Cluster (1014M).• All part of Local Supercluster (1015M)• Local Supercluster is part of streaming motion towards “Great Attractor”•1016-17M• located 45 Mpc away.• Detected by extra motions superimposed on “Hubble Flow”.Virgo Cluster(2000 galaxies)LocalSuperclusterBubbles and VoidsIncluding SDSS (Sloan Digital Sky Survey)cz(km s-1) Î211 MpcHarvard Center for Astrophysics (CfA) survey (1985)5Bubbles and VoidsIncluding SDSS (Sloan Digital Sky Survey)Projected on skyDark Matter• About 85% of gravitationally interacting matter is invisible.• Detected solely by its gravitational effects.• Line of evidence reaching back to Zwicky (1933)• Baryonic matter constrained by BBN (Big Bang Nucleosynthesis), WMAP• ΩB= .04• This includes large component of invisible Baryons• But ΩMatter= 0.27 Mass/Luminosity• Local stellar luminosity function: M/L = 0.67• Our Galaxy, at larger scales:• Oort limit: M/L ~ 2.7• Slice through disk (Bahcall & Soniera) ~ 5• Rotation curve > 30• Escape speed > 30• Pop II dynamics (glob. clusters, etc.) ~ 27• Magellanic stream > 806Dark matter in nearby galaxies• Rotation curves of spiral galaxies• expect Keplerian r -1/2curve once outside of mass distribution• but rotation curves are flat as far out as they can be traced • ==> dark halos• typically M/L > 28h• Central regions of Elliptical Galaxies• Virial theorem:• or… compare surface brightness, velocity dispersions to isothermal sphere model• M/L ~ 12hRGMr52=σE galaxy X-ray halos • Hot x-ray emitting gas in E galaxies is in hydrostatic equilibrium•ρ(r), T(r) measured from X-ray bremsstrahlung emission:• M87 is best case for study• Giant E1 at center of Virgo cluster• Linear increase in M out to r = 300 kpc• M(<300 kpc) ~ 1013M☼– 99% dark matter• ==> M/L ~ 750[CO 27.18, pg. 1066]Volume emissivity:[CO 27.17]7Galaxy Groups & Clusters[CO 27.16]• Local Group Dynamics –The Impending MW – M31 Collision• Approaching each other at 119 km/s• Current separation: r = 770 kpc Î collision in r/v ~ 6x109yrs.• Rough mass estimate from Kepler’s laws• P = age of Universe with r = 0 at t = 0 • Binney & Tremaine: • more exact analysis, same answer (M = 3-5x1012M☼)• M/L ~ 100 (V-band)(kinetic energy) = -(potential energy) + (total


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