1. ASTR 1020 – April 13 . Final Problem Set Due Today
Next Observatory Night April 17
Next Exam April 20
Review Session Wednesday 19th
Website

2. Galaxies are Close Together
Unlike stars, they run into each other.
30,000pc wide, but only 500,000pc apart
Stars million miles wide but trillions apart

4. Cluster of Galaxies

5. Gravitational Lenses Einstein predicted light bends
as it goes around massive objects.
Just like an orbiting body.

8. The Distance Scale
All the things astronomers have done to gain a handle on distance

9. Solar System Distances to 3AU
Radar
Measure time of flight of signal bouncing off planets
Transit of Venus
Captain Cook in Hawaii
Time that Venus hits limb of Sun

10. Parallax to 100pc
I year cycle

11. Main Sequence Fitting to 55,000pc
Plot enough stars and the
Main Sequence becomes
clear.
This works out to Magellanic
Clouds.
Beyond that, MS stars too
faint

12. Cepheid Variables to 100Mpc

13. Period-Luminosity Relationship
Cepheids are bright and can be seen at very large distances.

14. Type I Supernovae
All Type Ia supernovae are the same brightness. That white dwarf that implodes
and then explodes is always about the same. And they’re bright. You can see them
at billions of parsecs!
Apparent magnitude can be converted to distance.

15. Tully-Fisher Relation
The brighter the galaxy is,
the faster it rotates.
Use radio spectrum to measure
Doppler width.
Not super accurate, but it
works.

16. The Distance Scale

17. Redshift of Galaxies Hubble found that galaxies are redshifted.
The absorption lines are
those of the stars that
make up the galaxy.

18. Hubble’s Law The more distant the galaxy, the greater the redshift.
The more distant is the galaxy,
the faster it is flying away from
us.
H0=70 km/s/Mps

19. Example Galaxy in Virgo Cluster is at 15Mpc
will recede at v = 70 km/s/Mpc x 15Mpc = 1050km/s
dl = l x v/c = 4000Å x 1050/300,000 = 14Å
a 4000Å line will appear at 4014Å

20. Example 2
l0 = 1216Å but is observed at l = 1228Å
dl = 12

21. A Modern Hubble Diagram

22. Galaxies are Flying Apart
Galaxies remain same size. They just get farther apart.
Effect is the same no matter which position you occupy

23. Expanding Universe Current Universe The volume of the universe is
increasing.
Early Universe

24. The Age of the Universe Notice: At time zero, d = 0
All galaxies are at zero distance!
The universe has zero volume!
when t=1/H

25. The Beginning Before 13 billion years ago, there was no before.
Time and space started with the Big Bang
We will return to this in a few more lectures

26. Galaxies are Moving
Gravity attracts them to mass centers.

27. Redshift Survey Galaxies across the sky. Distance from redshift.
“The Great Wall”

28. More Galaxies

29. The Texture of the Universe

31. Theory of Structure Structure grew out of minor fluctuations.
Gravity causes density regions
to enhance.
The very origin of structure.

32. The Cosmic Web

33. Active Galactic Nuclei
Seyfert Galaxies 1948
Radio Galaxies 1954
Quasars
BL Lac’s
Blazars
They’re all manifestations of the same thing.

34. Seyfert Galaxies

35. Quasar QUAsi Stellar Radio source  Quasar (Sometimes QSO)
Completely enigmatic

37. Huge Redshifts
The Brightest Objects in the Universe

39. Quasar Spectrum Originally found from radio But not all have radio.
Broad spectral output from radio to gamma-ray

40. In a Galaxy Far, Far Away Long, Long Ago

41. The Most Distant Quasar z=5

42. Host Galaxies Quasars are in host galaxies
Mostly just outshine the entire galaxy

43. The AGN Model The Nucleus of the Galaxy is the Clot of Stars
around the giant black hole that’s fallen to the bottom
of the galaxy gravitational well.
As more material falls in, the black hole grows and the
nucleus can get very bright.
I think all major galaxies have a BBH (big black hole) in the center.
This is yet to be proven. Certainly a substantial fraction do.

44. Feeding a Quasar Accretion disk is formed of stars
and clouds that wander too near the
big black hole.
Tidal forces rip them apart.
They settle into an accretion disk.
When there’s no material falling in,
the quasar goes quiet.

45. Spectrum Width of line implies velocities of 30,000km/s !
High Orbital Speed implies deep gravitational well.

47. AGN Accretion Disk Simulations @ 0.1as
Courtesy of Phil Armitage, U. Colorado and C. Reynolds, U. Maryland

48. Jets

50. Jets

51. Fields Twist to Make Narrow Jet

52. Radio Galaxies
Very Large Array
Very Large Baseline Array

54. Cygnus A

55. Radio Lobes Lobes contain 1053 Joules of energy
in relativistic electrons.
Mass energy equivalent
of a million stars!

56. Wind Blows Jets

57. Full Model

58. Superluminal Expansion
Radio interferometers
see blobs emitted by
AGN’s from base of jet.
Watch them expand.
Know distance, so can
measure speed.
v = 900,000km/s
v = 3c
Superluminal ! ?
Is Einstein’s ghost worried?

59. Phase Velocity Point of impact can move v > c
Nothing traveling that fast.

60. Better Explanation Blob moves close to speed of light toward us.
Its closer later.
Makes sideways motion appear speeded up.