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Chapter 16

Chapter 16. Hubble ’ s Law. Outline. Review Hubble ’ s Law. Probable Job Opportunity. The Academic Success Program regularly funds Astronomy Tutors/ Study Group leaders. If you might be interested in this for next semester, please let me know via email.

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Chapter 16

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  1. 1

  2. 2

  3. Chapter 16 Hubble’s Law 3

  4. Outline • Review • Hubble’s Law 4

  5. Probable Job Opportunity • The Academic Success Program regularly funds Astronomy Tutors/ Study Group leaders. If you might be interested in this for next semester, please let me know via email. 5

  6. Possible explanations for Dark matter include everything except A) WIMPs B) Brown dwarfs C) Black holes D) Dark dust clouds E) MACHOs 6

  7. Possible explanations for Dark matter include everything except A) WIMPs B) Brown dwarfs C) Black holes D) Dark dust clouds E) MACHOs 7

  8. Count every “F” in the following text: FINISHED FILES ARE THE RES ULT OF YEARS OF SCIENTI FIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS... A=2 B=3 C=4 D=5 E=6 8

  9. Count every “F” in the following text: FINISHED FILES ARE THE RES ULT OF YEARS OF SCIENTI FIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS... 9

  10. Extending the Distance Scale • Variable Stars • Tully-Fisher Relationship • Supernovae • Cosmological Redshift 10

  11. Figure 14.7Variable Stars on Distance Ladder • Greater distances can be determined than typically available through spectroscopic parallax, because these variables are so bright. 11

  12. Figure 15.12Local Group 12

  13. Tully-Fisher Relationship 13

  14. Figure 15.9Galactic “Tuning Fork” • Galaxies are classified according to their shape (Hubble classification) • Elliptical • Spiral • Irregular 14

  15. Figure 15.10Galaxy Rotation • Rotation rates can be determined using Doppler shift measurements • Blue shift indicates moving towards you • Red shift indicates moving away from you 15

  16. Tully-Fisher Relationship • Rotation speed can be used to determine a galaxy’s total mass. • A close correlation between rotation speed and total luminosity has been observed. • Comparing (true) luminosity to (observed) apparent brightness allows us to determine distance • Distance scale can be extended to ~200 Mpc. 16

  17. Figure 15.11Extragalactic Distance Ladder 17

  18. Which of these does not exist? A) a .06 solar mass brown dwarf B) a 1.6 solar mass white dwarf C) a six solar mass black hole D) a million solar mass black hole E) a 2.7 solar mass neutron star 18

  19. Which of these does not exist? A) a .06 solar mass brown dwarf B) a 1.6 solar mass white dwarf C) a six solar mass black hole D) a million solar mass black hole E) a 2.7 solar mass neutron star 19

  20. Supernovae • Type II Supernovae • Are a result of a very massive star’s core collapse • Can vary in brightness, since the cores can vary in size. • Therefore, they are not a good distance indicator. 20

  21. Supernovae • Type I Supernovae • White dwarf, carbon detonation • Are a result of a white dwarf exceeding its Chandrasekhar limit (1.4 Msolar). • They are all about the same size. • They are very good distance indicators (Standard Candles). 21

  22. Standard Candles • Standard Candles are easily recognizable astronomical objects whose luminosities are confidently known. • Term usually only refers to very luminous objects • Type I supernovae • Other objects might include • Rotating spiral galaxies • Cepheid variables • Main sequence stars 22

  23. Figure 15.11Extragalactic Distance Ladder 23

  24. Chapter 16 Hubble’s Law 24

  25. Thought Experiment • You observe (with a telescope) several cars driving on US 160. They are all moving away from you. What pattern can you detect? Car distance speed Car 1 15 miles 5 mph Car 2 105 miles 35 mph Car 3 54 miles 18 mph Car 4 240 miles 80 mph Car 5 81 miles 27 mph Car 6 165 miles 55 mph 25

  26. Cosmological Redshift 26

  27. Figure 16.1Galaxy Spectra • Early 20th Century astronomers observed that most galaxies were moving away from us. 27

  28. Figure 16.2Hubble’s Law • Hubble plotted the recession velocity against the distance of the galaxies, and found a direct relationship. 28

  29. Hubble’s Law recessional velocity = Ho x distance • Ho is Hubble’s constant, the slope of the line on the previous plot • Precise value is somewhere between 50-80 km/s/Mpc • Tully Fisher and Cepheid variable measurements suggest higher values (70-80 km/s/Mpc) • Type I supernovae suggest lower values (50-65 km/s/Mpc) • Modern accepted value ~70 km/s/Mps 29

  30. Hubble’s Law recessional velocity = Ho x distance • Exercise: if Ho = 50 km/s/Mpc, what is the recessional velocity of a galaxy that is 500 Mpc away? 30

  31. Hubble’s Law recessional velocity = Ho x distance • Exercise: if Ho = 50 km/s/Mpc, what is the recessional velocity of a galaxy that is 500 Mpc away? • How long ago was that galaxy at your location? 31

  32. Hubble’s Law recessional velocity = Ho x distance • How long ago was that galaxy at your location? • time = distance / velocity 32

  33. Hubble’s Law recessional velocity = Ho x distance • How long ago was that galaxy at your location? • time = distance / velocity • 1 Mpc = 3.09x1019 km 33

  34. Hubble’s Law recessional velocity = Ho x distance • How long ago was that galaxy at your location? • time = distance / velocity • 1 Mpc = 3.09x1019 km • 1/Ho has the units of time! 34

  35. Hubble’s Law recessional velocity = Ho x distance • How long ago was that galaxy at your location? • time = distance / velocity • 1 Mpc = 3.09x1019 km • 1/Ho has the units of time! • 1/Ho gives the age of the universe. (approximately) 35

  36. Hubble’s Law • Distances can be determined simply by measuring the redshift. • The most distant objects show redshifts greater than 1. • Relativity must be used to determine velocities approaching c. • This is the “top” of the distance ladder. 36

  37. Figure 16.3Cosmic Distance Ladder 37

  38. Which of the following is inferred by Hubble’s Law? A) The greater the distance, the more luminous the galaxy B) The more distant a galaxy, the more evolved its members are C) The larger the redshift, the more distant the galaxy D) The larger the gravity lens, the more massive the galaxy cluster. 38

  39. Which of the following is inferred by Hubble’s Law? A) The greater the distance, the more luminous the galaxy B) The more distant a galaxy, the more evolved its members are C) The larger the redshift, the more distant the galaxy D) The larger the gravity lens, the more massive the galaxy cluster. 39

  40. What method would be most appropriate to determine the distance to a nearby galaxy? A) Spectroscopic parallax B) Cepheid variables C) Hubble’s law D) Radar ranging 40

  41. What method would be most appropriate to determine the distance to a nearby galaxy? A) Spectroscopic parallax B) Cepheid variables C) Hubble’s law D) Radar ranging 41

  42. What method would not be appropriate to determine the distance to a nearby galaxy? A) Tully-Fisher relationship B) Cepheid variables C) Hubble’s law D) Type I Supernovae 42

  43. What method would not be appropriate to determine the distance to a nearby galaxy? A) Tully-Fisher relationship B) Cepheid variables C) Hubble’s law D) Type I Supernovae 43

  44. What does the Hubble constant measure? A) The density of galaxies in the universe B) The luminosity of distant galaxies C) The rate of expansion of the universe D) the speed of a galaxy of known redshift E) the reddening of light by intergalactic dust clouds 44

  45. What does the Hubble constant measure? A) The density of galaxies in the universe B) The luminosity of distant galaxies C) The rate of expansion of the universe D) the speed of a galaxy of known redshift E) the reddening of light by intergalactic dust clouds 45

  46. Large-Scale Structure 46

  47. Large-Scale Structure • Use the scale of 1m = 1 A.U. 47

  48. Large-Scale Structure • Use the scale of 1m = 1 A.U. • The Earth is 1 m from the Sun 48

  49. Large-Scale Structure • Use the scale of 1m = 1 A.U. • The Earth is 1 m from the Sun • The Nearest star is near Albuquerque 49

  50. Large-Scale Structure • Use the scale of 1m = 1 A.U. • The Earth is 1 m from the Sun • The Nearest star is near Albuquerque • The center of the Milky Way galaxy would be 4 times as far as the moon. 50

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