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.
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
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
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
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?
17.
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?
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.
34.
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
37.
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.
Editor's Notes
Astronomy Avoidance Zone
Shapley
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
Climate
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.