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A lecture I'd given on spiral galaxies, barred spirals, mass of galaxies, Sgr A, Elliptical galaxies, standard candles, dark matter, composition of the universe, back in my university days.

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  • Astronomy Avoidance Zone
    Where does the galaxy located in the universe?
  • Type Ia
    Globular Clusters and galaxy halo
    Population II, low amount of metals
  • Mercury,
    Lunar, Solar/Lunar eclipses
  • Both speeds are clockwise in this example
    Inner region faster (hit wave)
    Outer slower (hit by wave)
  • Lost angular momentum, from the matter that falls into the central black hole
  • Because the peak wavelength for these stars is at 5.1x106/T=5.1x106 nmºK/30000ºK= 170nm, a much shorter wavelength than even J at 1.25µm=1250nm. Blackbodies at wavelengths much longer than their peaks all asymptote to the same form so the infrared won't identify these stars easily.
  • Luminosity is related to observable apparent brightness and distance.
  • Luminosity is related to observable apparent brightness and distance.
  • Luminosity is related to observable apparent brightness and distance.
  • Luminosity is related to observable apparent brightness and distance.
  • Luminosity is related to observable apparent brightness and distance.
  • Luminosity is related to observable apparent brightness and distance.
  • Galaxies

    1. 1. GALAXIES
    2. 2. Review  The distance of Andromeda  Island Universes  Galactic Coordinate System  The location of the sun in MilkyWay (Shapely)  Oort’s method and mapping the Milky Way  Proper motion
    3. 3.  The rotation curve of MilkyWay  Metallicity  Stellar populations  The distribution of stars in MilkyWay  The Formation of a galaxy  Classification of galaxies
    4. 4. Test Where are these objects located in sky/Milky Way?
    5. 5. NGC 6946 and NGC 6939 Face on spiral galaxy Open Cluster In Cepheous Messier Marathon
    6. 6. Supernova in NGC 6946
    7. 7. Test What type this supernova is? What population the originating star was?
    8. 8. Normal Galaxies Spirals Ellipticals Morphology Disk + bulge, Spiral arms All bulge Stellar population Young and old stars Old stars only Interstellar material Present Virtually none Star Formation Present None Kinematics Disk rotating, Bulge and halo have random 3-D orbits Little rotation, mostly random 3-D orbits
    9. 9. Spiral ArmsWinding Problem
    10. 10. Spiral Pattern  1960 Lin-Shu theory of density waves  Spiral arms are waves of excess density  Stars are crowded together temporarily  Cosmic traffic jam  Stars enter and exit the wave just as cars enter and exit a jam
    11. 11. Precession of orbits
    12. 12. No Wave Fixed frame Rotating frame
    13. 13. Aligned Orbits Bar Wave Spiral Wave
    14. 14. Resonances  Spiral arms are instance representation of waves  Corotation circle  ωorbital* = ωwave  Lindblad resonances  Particular point in orbit
    15. 15. Bars  Computer simulations predicts:  Bars are formed besides spiral arms  Resonance  Bars transfer the lost angular momentum  Bars destroy themselves
    16. 16. Question  We know bars are formed necessarily  Bars destroy themselves  And 75% of spiral galaxies are barred spirals. How?
    17. 17. Summary  Galaxies are not born with a given shape (barred or unbarred)  A typical spiral galaxy spend ¾ of its life time barred
    18. 18. Galactic Center  Evidences of stellar formation in the last 50 million years  ISM orbits the center in a orbit with inner radius of 2pc  Strong magnetic field (milli-Gauss)  Compact radio source (Sgr A)  High radial velocities and proper motion  Existence of a large unseen, compact object
    19. 19. Problem  We can observe the center of the MilkyWay in infrared light  We predict there are hot, massive stars there  We cannot distinguish the exact spectral type of the stars in the center of the MilkyWay  Why?
    20. 20. Problem  Find the mass of Sgr A  A star identified rotating SgrA, with orbital velocity = 1000 km/sec that lies 0.01 pc from SgrA.
    21. 21. Problem  Is galaxy a Keplerian system?  VLBA measurements of SgrA set limits of ~3AU for the size of SgrA:What is SgrA?
    22. 22. VLBA Vary Long Baseline Array
    23. 23. Rotation in Elliptical Galaxies and Bulges of Spirals  Stars have random velocities in 3D
    24. 24.  Δλ = Observed size of a spectral line  σ =Velocity dispersion
    25. 25.  Faber-Jackson Relation Gravitational binding energy (potential of a mass distribution of radius R and mass M) Kinetic energy Virial theorem
    26. 26.  Faber-Jackson Relation Assumption Luminosity and the velocity dispersion in a elliptical galaxy are related.
    27. 27.  Faber-Jackson Relation Assumption Luminosity and the velocity dispersion in a elliptical galaxy are related.
    28. 28. Tully-Fisher Relation  Luminosity of spiral galaxies are related to their velocity width.  Standard candle
    29. 29. Tully- Fisher Relation as Standard Candles
    30. 30. Luminosity  Elliptical galaxies:  Ie : surface brightness at re  re : radius enclosing 50% of flux
    31. 31. Luminosity  Spiral galaxies:  I0 : central surface brightness  r0 : disk scale length
    32. 32. Problem  A star is orbiting around a galaxy. Orbital velocity = v Distance from the center of the galaxy = R Find the mass within R.
    33. 33. Evidences  1933: Fritz Zwicky studied the motions of 7 galaxies in a group in Coma Cluster  Dynamic Mass: mass calculated using gravitation laws and the velocity dispersions  Dynamic Mass / Luminosity Mass > 400  Clusters: temporal structures
    34. 34. Evidences  1970:Vera Rubin noted rotation curve of spiral galaxies (dynamic vs. luminous mass)  Dynamic mass is measured using gravitational influences  Gravitation laws are false! Or luminous mass is not accurate  There are large amount of hidden mass
    35. 35. Dark Matter  Dark matter is not significant in Solar System  Dark matter surrounds spirals and ellipticals’  Dark matter is significant in galaxy clusters
    36. 36. Dark matter was not required if  Large structures (eg. Galaxies) weren’t bound systems (galaxies are bound systems at least in a time equals to the age of the universe)  Gravity laws were wrong in large scales
    37. 37. Candidates for Dark Matter  Neutrinos or other exotic sub-atomic particles  Byronic matter
    38. 38. Sub-atomic particles  Widely distributed  No interaction with regular (baryonic) matter  Absent in solar neighborhood
    39. 39.  Axions: required to explain some aspects of the strong nuclear force  Neutrinos  Supersymmetric particles  WIMPS (Weakly Interacting Massive Particles), CHAMPS, etc.
    40. 40.  Baryonic Matter: not luminous. ancient white dwarfs, brown dwarfs, chunks of cold matter significantly larger than the wavelength of visible light, small black holes
    41. 41. What have been found  No axions orWIMP was found.  Neutrinos may have non-zero mass.  But the large amount of massive neutrinos arise other problems.  MACHO: Massive Compact Halo Objects  brown dwarfs or dim white dwarfs or other low mass stars  MilkyWay halo has 50% MACHOs.With masses around 0.1 to 0.5% of the mass of the sun.