1. ASTR 1040 – November 28 Planetarium, December 5
Last Observatory December 5
Third Mid-Term Exam December 7
Last Lecture December 14
Final Exam December 16
Website

2. Want to explore teaching as a career? Interested in STEM Outreach?
This Spring 2018 Take…
Step 1: EDUC 2020 (1 credit)
Real experience teaching real kids, in Elementary school
Registration priority for math, science, engineering & open option majors
Scholarships, fellowships and internships available

3. Hubble Sequence
(not an evolutionary sequence!)

6. Elliptical Galaxy

7. Elliptical

8. Sombrero Galaxy

23. M87 in Virgo Cluster

27. Mass of Galaxies From Orbital Considerations Orbital velocity of stars
binary galaxy orbital velocities
clusters of galaxies
They All Show Dark Matter

28. Rotation Curves Without Dark Matter
Hydrogen emits a radio emission line at l = 21cm
Doppler shift allows us to measure orbital velocity of gas clouds vs radius

29. Dark Matter Mass to Light Ratio:
Mass in Solar Masses divided by Luminosity in Solar Luminosities
Sun has M/L of 1 (by definition)
Rigel M=20 L=  M/L = .01
Pros Cen M=.1 L =  M/L = 100
Galaxies typically have M/L of 7 to 10
Something like 85% of the mass is dark matter

30. Dark Matter
Dark matter is in Ball  We can measure its distribution even though we don’t know what it is.
Dark Matter
Regular Matter

31. What is Dark Matter? WHAT IS DARK MATTER????? Some possibilities:
Ionized Gas
Small Stars
Planets
Baseballs
Black Holes
Neutrinos
Neutralinos
A flaw in Newton’s Laws
MAssive Compact Halo Objects (Machos)
Weakly Interacting Massive Particles (Wimps)
Astronomers don’t know what most of the matter in the universe is!

32. 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

33. Bullseye!

34. N-body Simulations

36. Cluster of Galaxies

37. X-ray Clusters Over last 10 Billion years there have been many
galaxy collisions in these crowded clusters.
When two galaxies pass through each other stars
will continue on their original path – more or less.
Interstellar gas clouds collide and cannot pass through
each other. They get stripped and pass into the
gravitational well of the cluster. This fills with very
hot shocked gas over time.
So hot it emits x-rays.
Shows matter distribution. (Mostly dark matter again.)

38. Coalescence
After galaxies collide, on average, the friction causes them to drop
down toward the center. Eventually they settle to the bottom.

39. CD Galaxy
A Galactic Cannibal
M87 has eaten 100 of its own.

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

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

44. 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

45. Parallax to 100pc
I year cycle

46. 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

47. Cepheid Variables to 100Mpc

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

49. 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.

50. 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.

51. The Distance Scale

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

53. 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