C.17 The Milky Way

1. C.17 The Milky Way When we try to pick out anything by itself, we find that it is tied to everything else in the universe. John Muir (1838-1914)

2. For comparison of the following slides, the distance from the Sun to Neptune is 8.44 light hours or .000963 light years.

3. For comparison the Milky way is 100,000 light years in diameter.

4. Nebulas • A glowing cloud of gas and dust is called a nebula • There are 3 different kinds. Emmission, Dark and Reflection. • Emission nebula - a cloud of glowing gas • The Great Nebula in Orion is an Emission nebula. • It is 1,344 light years away and 24 light years across.

5. The Trapezium. A group of 4 stars in the middle of the Orion Nebula. These are young, hot, blue stars.

7. Dark Nebulas • In a dark nebula dust and gas that is not glowing is outlined by glowing gases and stars behind it. • The Horsehead Nebula, which is close to the Great Nebula in Orion, is an example of a dark Nebula • It is 13 light years across and 1500 light years away

9. The Snake Nebula in the constellation Ophiuchus

10. Barnard Dark Nebula in Ophiuchus

13. N44 superbubble - Larg Magellanic cloud

14. Reflection Nebula • Reflecting Nebulas occur when clouds of gas and dust reflect the light of stars that are within. • The Pleiades, Seven sisters, or Subaru is an example of a Reflection Nebula. • It is about 12 light years in diameter and 440 light years away.

17. North American and Pelican Nebulas

19. The Heart and Soul nebulae stretch out nearly 580 light-years across, they are 7500 light years away in the constellation Cassiopeia

20. Cone Nebula

21. The Cone Nebula and the Christmas Tree cluster. The cone nebula is 7 light years long and 2,700 l.y. away.

22. Lagoon Nebula

23. Center of Lagoon NebulaThe light from M8 we see today left about 5000 years ago. Light takes about 50 light years to cross this section of M8.

24. Carina Nebula 2 light years in diameter and 8,000 l.y. away.

27. Hubble Space Telescope image showing Eta Carinae and the bipolar Homunculus Nebula which surrounds the star. The Homunculus was created in an eruption of Eta Carinae, the light from which reached Earth in 1843. Eta Carinae itself appears as the white patch near the center of the image, where the two lobes of the Homunculus touch

30. Rosette Nebula

32. Coal Sack

33. Milky Way Structure • Harlow Shapley deduced the structure of the Milky Way in 1920. • He noticed that globular clusters were all in the same general area of the sky. • In plotting their distances from the earth he noted that they form a spherical halo above and below the galactic plane. • This halo was centered around a point thousands of light years away. • Shapley realized that this point must be the galactic center.

34. Hypothetical Structure • Based on observations people first felt that the Milky Way was a spiral galaxy and that we are located on the Orion spur. • Our galaxy is about 100,000 light years across. We are about 33,000 light years from the nuclear bulge. • Our sun and spiral arm rotates around the nuclear bulge in a clockwise direction.

35. Milky Way Structure cont. • The use of different types of telescopes has helped us get a better idea of the shape of our galaxy. • This is an infrared photo of our galactic disk and bulge taken by the COBE satellite.

39. Globular clusters - a halo of these exist around the Galactic core

40. Modern Galaxy maps • The first good map of the Milky Way was made by Oort, Kerr and Westerhout (1958) • They mapped neutral hydrogen in the plane of the galaxy. • 1976 Yvonne and Yvon Georgelin mapped all of the bright nebula and showed they existed in the spiral arms.

41. Milky Way Map cont. • In the 1990’s researchers first found evidence that our galaxy is a barred spiral galaxy. • The early maps based on these observations looked like this one.

42. Studying the center • Observations of radio waves and infrared radiation help us penetrate the thick dust and light that hides the center. • A very bright radio wave source is indicated in the center of our galaxy ( as bright as 80 million suns) • In the center there is evidence of an extremely narrow radio source 10 A.U. across. This could be a massive black hole. • It is called Sagittarius A • This slide is a radio image of the central disk taken from the Very Large Array, near Soccoro, New Mexico.

45. Chandra X-ray picture of bulge

46. The Chandra X-ray Observatory is a satellite launched by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.

47. Chandra is sensitive to X-ray sources 100 times fainter than any previous X-ray telescope. The Earth's atmosphere absorbs the majority of X-rays. This requires a space-based telescope to make these observations.

48. Chandra Observatory is the 3rd of NASA's 4 great Observatories. The first was Hubble Space Telescope; second the Compton Gamma Ray Observatory, launched in 1991; and last is the Spitzer Space Telescope. Compton Gamma Ray Observatory Spitzer Space Telescope

49. The Spitzer Space Telescope is an infrared space observatory launched in 2003.The planned mission period was to be 2.5 years with an expectation that the mission could extend to five more years until the onboard liquid helium supply was exhausted. This occurred on 15 May 2009.

50. In keeping with NASA tradition, the telescope was renamed after successful demonstration of operation, on December 18, 2003. Unlike most telescopes which are named after famous deceased astronomers by a board of scientists, the name for SIRTF was obtained from a contest open to the general public.The contest led to the scope being named in honor of Lyman Spitzer, one of the 20th century's great scientists. Spitzer wrote a 1946 report for RAND describing the advantages of an extra-terrestrial observatory and how it could be realized with available (or upcoming) technology.