1. Galaxies and the Universe

2. Galaxies  ______________ galaxy Structure Determined by using ______ telescopes Large spiral galaxy About 100,000 light-years wide Thickness at the galactic nucleus is about 10,000 light-years _____ spiral arms of stars Sun is 30,000 light-years from the center

3. The Milky Way galaxy appears in our sky as a faint band of light.

4. Dusty gas clouds obscure our view because they absorb visible light. This is the ____________ ________ that makes new star systems.

5. All-Sky View

6. Face-on view of the Milk Way Galaxy

7. We see our galaxy edge-on. Primary features: disk, bulge, halo, globular clusters

8. Galaxies  Milky Way galaxy Rotation Around the galactic nucleus Outermost stars move the slowest Sun rotates around the galactic nucleus once about every 200 million years Halo surrounds the galactic disk Spherical Very tenuous gas Numerous globular clusters

9. If we could view the Milky Way from above the disk, we would see its spiral arms.

10. Sun’s orbital motion (radius and velocity) tells us mass within Sun’s orbit: 1.0  10 11 M Sun

11. ____________________ are found around short- lived high-mass stars, signifying active star formation.

12. ___________ nebulae scatter the light from stars. Why do reflection nebulae look bluer than the nearby stars? For the same reason that our sky is blue!

13. Disk: ___________ nebulae, blue stars  star formation Halo: No ___________ nebulae, no blue stars  no star formation

14. Much of star formation in disk happens in ________________ Whirlpool Galaxy

15. Our galaxy probably formed from a giant gas cloud.

16. Halo stars formed first as gravity caused the cloud to contract.

17. The remaining gas settled into a spinning disk.

18. Stars continuously form in the disk as the galaxy grows older.

19. Warning: This model is oversimplified.

20. Infrared light from center Radio emission from center

21. Swirling gas near center

22. Orbiting star near center

23. Stars appear to be ________ something massive but invisible … a black hole? Orbits of stars indicate a mass of about 4 million M sun.

24. X-ray flares from galactic center suggest that tidal forces of suspected black hole occasionally tear apart chunks of matter about to fall in.

25. Hubble Deep Field Our deepest images of the universe show a great variety of galaxies, some of them billions of light-years away.

26. Galaxies and Cosmology A galaxy’s age, its distance, and the age of the universe are all closely related. The study of galaxies is thus intimately connected with _________ —the study of the structure and evolution of the universe.

27. Galaxies  Other galaxies Existence was first proposed in mid-1700s by Immanuel Kant Four basic types of galaxies ______ galaxy _____ extending from nucleus About 30% of all galaxies Large diameter of 20,000 to 125,000 light years Contains both _______ and ___ stars e.g., Milky Way

28. Spiral Galaxy disk bulge halo

29. Great Galaxy, a spiral galaxy, in the constellation Andromeda

30. Galaxies  Other galaxies Four basic types of galaxies _____________ galaxy Stars arranged in the shape of a bar Generally quite large About 10% of all galaxies ___________ galaxy Ellipsoidal shape About 60% of all galaxies Most are smaller than spiral galaxies; however, they are also the largest known galaxies

31. Barred Spiral Galaxy: Has a bar of stars across the bulge

32. Lenticular Galaxy: Has a disk like a spiral galaxy but much less dusty gas (intermediate between spiral and elliptical)

33. Elliptical Galaxy: All spheroidal component, virtually __________ component

34. Galaxies  Other galaxies Four basic types of galaxies ________ galaxy Lacks symmetry About 10% of all galaxies Contains mostly _______ stars e.g., Magellanic Clouds

35. Irregular Galaxy: Neither spiral nor elliptical

36. Galaxies  Galactic cluster Group of galaxies Some contain thousands of galaxies ____________ Our own group of galaxies Contains at least 28 galaxies Supercluster Huge swarm of galaxies May be the largest entity in the universe

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

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

39. If the center of a galaxy is unusually bright, we call it an active galactic nucleus. _________ are the most luminous examples. Active Nucleus in M87

40. Quasars powerfully radiate energy over a very wide range of wavelengths, indicating that they contain matter with a wide range of temperatures.

41. The accretion of gas onto a supermassive black hole appears to be the only way to explain all the properties of quasars.

42. Radio galaxies don’t appear as quasars because dusty gas clouds block our view of the accretion disk.

43. The gravitational potential energy of matter falling into a black hole turns into kinetic energy. Friction in the accretion disk turns kinetic energy into thermal energy (heat). Heat produces thermal radiation (photons). This process can convert 10–40% of E = mc 2 into radiation. Energy from a Black Hole

44. Jets are thought to come from the twisting of a magnetic field in the inner part of the accretion disk.

45. Do supermassive black holes really exist?

46. ____________ _____ at center of Milky Way stars indicate a black hole with mass of 4 million M sun.

47. Orbital speed and distance of gas orbiting center of M87 indicate a black hole with mass of 3 billion M sun.

48. Many nearby galaxies—perhaps all of them— have supermassive black holes at their centers. These black holes seem to be ________ active galactic nuclei. All galaxies may have passed through a quasar- like stage earlier in time. Black Holes in Galaxies

49. Hubble also knew that the spectral features of virtually all galaxies are __________  they’re all moving away from us.

50. Red shifts  Doppler effect Change in the wavelength of light emitted by an object due to its motion Movement away stretches the wavelength Longer wavelength Light appears redder Movement toward “squeezes” the wavelength Shorter wavelength Light shifted toward the blue

51. Red shifts  Doppler effect Amount of the Doppler shift indicates the rate of movement Large Doppler shift indicates a high velocity Small Doppler shift indicates a lower velocity  Expanding universe Most galaxies exhibit a red Doppler shift Moving _____

52. Raisin bread analogy of an expanding universe

53. Red shifts  Expanding universe Most galaxies exhibit a red Doppler shift Far galaxies Exhibit the greatest shift Greater velocity Discovered in 1929 by Edwin Hubble _________ Law – the recessional speed of galaxies is proportional to their distance Accounts for red shifts

54. Hubble’s law: velocity = H 0  distance By measuring distances to galaxies, Hubble found that redshift and distance are related in a special way.

55. Redshift of a galaxy tells us its _________ through Hubble’s law: distance = velocity H 0

56. We measure galaxy distances using a chain of interdependent techniques.

57. Cosmological Principle The universe looks about the same no matter where you are within it. Matter is ______ distributed on very large scales in the universe No _______ and no _____ Not proved but consistent with all observations to date

58. The expansion rate appears to be the same everywhere in space. The universe has no center and no edge (as far as we can tell).

59. One example of something that expands but has no center or edge is the surface of a balloon.

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

62. We still can’t directly observe the earliest galaxies.

63. ______________ theory  Accounts for galaxies moving away from us  Universe was once confined to a "ball" that was Supermassive Dense Hot

64. Big Bang theory  Big Bang marks the inception of the universe Occurred about 15 billion years ago All matter and space was created  Matter is moving ________  Fate of the universe Two possibilities Universe will ____________ Outward expansion will stop and gravitational ____________ will follow

65. The main question Does the universe have enough kinetic energy to escape its own gravitational pull? –What is the escape velocity of the Universe?

66. Big Bang theory  Fate of the universe Final fate depends on the average _______ of the universe If the density is _____ than the critical density, then the universe would ________ Current estimates point to _____ then the critical density and predict an _______________, or open, universe

67. Fate of universe depends on the amount of _______ _______ Critical density of matter Not enough dark matter Lots of dark matter

68. Amount of matter is ~25% of the critical density, suggesting fate is eternal expansion Not enough dark matter

69. But expansion appears to be speeding up! Not enough dark matter ____________?

70. Estimated age depends on both dark matter and dark energy. old older oldest

71. Is the expansion of the universe accelerating?

72. The brightness of distant white-dwarf supernovae tells us how much the universe has expanded since they exploded.

73. An accelerating universe is the best fit to supernova data.

74. http://www.vene.ws/tesina/wormhole.jpg