2. Gas and dust inhibit the jet of particles!
Spiral versus Elliptical
galaxies

4. Jet
Narrow line region clouds
10 – ly
Broad Line Region
(Light months)
Dusty Molecular torus
10 – 1000 ly
Black Hole
100 million solar masses
Accretion Disk (light days)

5. Blazar (BL Lac type)
CD Quasar
LD Quasar
BLRG
NLRG
Elliptical Galaxy

7. Narrow line region clouds
10 – ly
Broad Line Region
(Light months)
Dusty Molecular torus
10 – 1000 ly
Black Hole
100 million solar masses
Accretion Disk (light days)

8. BAL QSO
QSO (SEYFERT I)
FIR GALAXY (SEYFERT II)
Spiral Galaxy

9. Hubble Deep Field

10. Hubble Ultra Deep Field

11. Hubble Ultra Deep Field

12. Hubble Ultra Deep Field
Elliptical Galaxy
Spiral Galaxy
Spiral Galaxy

13. Hubble Ultra Deep Field
Spiral Galaxy
Spiral Galaxy

14. Hubble Ultra Deep Field
Elliptical Galaxy
Elliptical Galaxy
Spiral Galaxy
Spiral Galaxy

15. Hubble Ultra Deep Field
Elliptical Galaxy
Elliptical Galaxy
Spiral Galaxy
Spiral Galaxy

16. Hubble Ultra Deep Field
Elliptical Galaxy
Elliptical Galaxy
Irregular Galaxies
Spiral Galaxy
Spiral Galaxy

17. Are galaxies doing anything strange?
Cosmology questions
Are galaxies doing anything strange?

18. The spectral features of virtually all galaxies are redshifted  They’re all moving away from us

19. Edwin Hubble, using Cepheids as standard candles, was one of the first to measure distances to other galaxies
By measuring distances to galaxies, Hubble found that redshift and distance are related in a special way

21. The Hubble Law y = mx +b velocity = (H0)i(distance) + 0
H0 is the ‘Hubble constant’

24. The Hubble Law:
velocity = (H0)i(distance)

25. Redshift of a galaxy tells us its distance through Hubble’s Law:
velocity H0
redshift (z) is defined:

26. Remember?:
We can re-write it:

27. And with a little bit of algebra we can get to this:
The so-called Doppler factor.
So the redshift can be written:
And in the non-relativistic limit (v<<c)

28. Homework #11
Hubble originally got 250 km/s/Mpc for the Hubble constant. How old is the universe with that value of H0?
If a galaxy has a redshift of 0.02, how fast is it traveling away from us?
How far away is the galaxy?

29. Distances of farthest galaxies are measured from redshifts

30. How do distance measurements tell us the age of the universe?
Cosmology questions
How do distance measurements tell us the age of the universe?

31. Thought Question
Your friend leaves your house. She later calls you on her cell phone, saying that she’s been driving at 60 miles an hour directly away from you the whole time and is now 60 miles away. How long has she been gone?
A. 1 minute
B. 30 minutes
C. 60 minutes
D minutes

32. Thought Question
Your friend leaves your house. She later calls you on her cell phone, saying that she’s been driving at 60 miles an hour directly away from you the whole time and is now 60 miles away. How long has she been gone?
A. 1 minute
B. 30 minutes
C. 60 minutes
D minutes

33. Thought Question
Your observe a galaxy moving away from you at 0.1 light-years per year, and it is now 1.4 billion light-years away from you. How long has it taken to get there?
A. 1 million years
B. 14 million years
C. 10 billion years
D. 14 billion years

34. Thought Question
Your observe a galaxy moving away from you at 0.1 light-years per year, and it is now 1.4 billion light-years away from you. How long has it taken to get there?
A. 1 million years
B. 14 million years
C. 10 billion years
D. 14 billion years

35. Hubble’s constant tells us the age of the universe because it relates velocities and distances of all galaxies
Age =
~ 1 / H0
Distance
Velocity

36. Distances between faraway galaxies change while light travels

37. Distances between faraway galaxies change while light travels
Astronomers think in terms of lookback time rather than distance
lookback time
distance?

38. Expansion stretches photon wavelengths causing a cosmological redshift directly related to lookback time

39. Cosmological Horizon
Maximum lookback time of 14 billion years limits how far we can see

40. Surface of a balloon expands but has no center or edge

41. Cosmological Principle
The universe looks about the same no matter where you are within it
Matter is evenly distributed on very large scales in the universe
No center & no edges
Not proven but consistent with all observations to date

42. How are galaxies grouped together?
Cosmology questions
How are galaxies grouped together?

43. Spiral galaxies are often found in groups of galaxies
(up to a few dozen galaxies)

44. Elliptical galaxies are much more common in huge clusters of galaxies
(hundreds to thousands of galaxies)