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. You probably need to download the file for the animations to work.

1. GALAXIES

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.  The rotation curve of MilkyWay
 Metallicity
 Stellar populations
 The distribution of stars in MilkyWay
 The Formation of a galaxy
 Classification of galaxies

4. Test
Where are these objects located in sky/Milky Way?

5. NGC 6946 and NGC
6939
Face on spiral galaxy
Open Cluster
In Cepheous
Messier Marathon

6. Supernova in NGC 6946

7. Test
What type this supernova is?
What population the originating star was?

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. Spiral ArmsWinding Problem

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. Precession of orbits

12. No Wave
Fixed frame Rotating frame

13. Aligned Orbits
Bar Wave Spiral Wave

14. Resonances
 Spiral arms are
instance
representation of
waves
 Corotation circle
 ωorbital* = ωwave
 Lindblad resonances
 Particular point in
orbit

15. Bars
 Computer simulations predicts:
 Bars are formed besides spiral arms
 Resonance
 Bars transfer the lost angular momentum
 Bars destroy themselves

16. Question
 We know bars are formed necessarily
 Bars destroy themselves
 And 75% of spiral galaxies are barred spirals.
How?

18. Summary
 Galaxies are not born with a given shape
(barred or unbarred)
 A typical spiral galaxy spend ¾ of its life time
barred

19. 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

20. 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?

21. 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.

22. Problem
 Is galaxy a Keplerian system?
 VLBA measurements of SgrA set limits of
~3AU for the size of SgrA:What is SgrA?

23. VLBA
Vary Long Baseline Array

24. Rotation
in
Elliptical
Galaxies
and Bulges
of Spirals
 Stars have random
velocities in 3D

25.  Δλ = Observed size of a spectral line
 σ =Velocity dispersion

26.  Faber-Jackson Relation
Gravitational binding energy
(potential of a mass distribution of
radius R and mass M)
Kinetic energy
Virial theorem

27.  Faber-Jackson Relation
Assumption
Luminosity and the velocity dispersion in a elliptical
galaxy are related.

28.  Faber-Jackson Relation
Assumption
Luminosity and the velocity dispersion in a elliptical
galaxy are related.

29. Tully-Fisher Relation
 Luminosity of spiral galaxies are related to
their velocity width.
 Standard candle

30. Tully-
Fisher
Relation
as
Standard
Candles

31. Luminosity
 Elliptical galaxies:
 Ie : surface brightness at re
 re : radius enclosing 50% of flux

32. Luminosity
 Spiral galaxies:
 I0 : central surface brightness
 r0 : disk scale length

33. Problem
 A star is orbiting around a galaxy.
Orbital velocity = v
Distance from the center of the galaxy = R
Find the mass within R.

35. 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

36. 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

38. Dark Matter
 Dark matter is not significant in Solar System
 Dark matter surrounds spirals and ellipticals’
 Dark matter is significant in galaxy clusters

39. 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

40. Candidates for Dark Matter
 Neutrinos or other exotic sub-atomic
particles
 Byronic matter

41. Sub-atomic particles
 Widely distributed
 No interaction with regular (baryonic) matter
 Absent in solar neighborhood

42.  Axions: required to explain some aspects of
the strong nuclear force
 Neutrinos
 Supersymmetric particles
 WIMPS (Weakly Interacting Massive
Particles), CHAMPS, etc.

43.  Baryonic Matter: not luminous.
ancient white dwarfs, brown dwarfs, chunks
of cold matter significantly larger than the
wavelength of visible light, small black holes

44. 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.