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Charles Hakes Fort Lewis College 1 Charles Hakes Fort Lewis College 2 Chapter 16 Hubble’s Law Charles Hakes Fort Lewis College 3 Outline • Review • Hubble’s Law Charles Hakes Fort Lewis College 4 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. Charles Hakes Fort Lewis College 5 Possible explanations for Dark matter include everything except A) WIMPs B) Brown dwarfs C) Black holes D) Dark dust clouds E) MACHOs Charles Hakes Fort Lewis College 6 Possible explanations for Dark matter include everything except A) WIMPs B) Brown dwarfs C) Black holes D) Dark dust clouds E) MACHOs Charles Hakes Fort Lewis College 7 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 Charles Hakes Fort Lewis College B=3 C=4 D=5 8 E=6 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... Charles Hakes Fort Lewis College 9 Extending the Distance Scale • • • • Variable Stars Tully-Fisher Relationship Supernovae Cosmological Redshift Charles Hakes Fort Lewis College 10 Figure 14.7 Variable Stars on Distance Ladder • Greater distances can be determined than typically available through spectroscopic parallax, because these variables are so bright. Charles Hakes Fort Lewis College 11 Figure 15.12 Local Group Charles Hakes Fort Lewis College 12 Tully-Fisher Relationship Charles Hakes Fort Lewis College 13 Figure 15.9 Galactic “Tuning Fork” • Galaxies are classified according to their shape (Hubble classification) • Elliptical • Spiral • Irregular Charles Hakes Fort Lewis College 14 Figure 15.10 Galaxy Rotation • Rotation rates can be determined using Doppler shift measurements • Blue shift indicates moving towards you • Red shift indicates moving away from you Charles Hakes Fort Lewis College 15 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. Charles Hakes Fort Lewis College 16 Figure 15.11 Extragalactic Distance Ladder Charles Hakes Fort Lewis College 17 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 Charles Hakes Fort Lewis College 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 Charles Hakes Fort Lewis College 19 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. Charles Hakes Fort Lewis College 20 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). Charles Hakes Fort Lewis College 21 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 Charles Hakes Fort Lewis College 22 Figure 15.11 Extragalactic Distance Ladder Charles Hakes Fort Lewis College 23 Chapter 16 Hubble’s Law Charles Hakes Fort Lewis College 24 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 Car 2 Car 3 Car 4 Car 5 Car 6 Charles Hakes Fort Lewis College 15 miles 105 miles 54 miles 240 miles 81 miles 165 miles 25 5 mph 35 mph 18 mph 80 mph 27 mph 55 mph Cosmological Redshift Charles Hakes Fort Lewis College 26 Figure 16.1 Galaxy Spectra • Early 20th Century astronomers observed that most galaxies were moving away from us. Charles Hakes Fort Lewis College 27 Figure 16.2 Hubble’s Law • Hubble plotted the recession velocity against the distance of the galaxies, and found a direct relationship. Charles Hakes Fort Lewis College 28 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 Charles Hakes Fort Lewis College 29 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? Charles Hakes Fort Lewis College 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? • How long ago was that galaxy at your location? Charles Hakes Fort Lewis College 31 Hubble’s Law recessional velocity = Ho x distance • How long ago was that galaxy at your location? • time = distance / velocity Charles Hakes Fort Lewis College 32 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 Charles Hakes Fort Lewis College 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 • 1/Ho has the units of time! Charles Hakes Fort Lewis College 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! 1/Ho gives the age of the universe. (approximately) Charles Hakes Fort Lewis College 35 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. Charles Hakes Fort Lewis College 36 Figure 16.3 Cosmic Distance Ladder Charles Hakes Fort Lewis College 37 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. Charles Hakes Fort Lewis College 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. Charles Hakes Fort Lewis College 39 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 Charles Hakes Fort Lewis College 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 Charles Hakes Fort Lewis College 41 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 Charles Hakes Fort Lewis College 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 Charles Hakes Fort Lewis College 43 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 Charles Hakes Fort Lewis College 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 Charles Hakes Fort Lewis College 45 Large-Scale Structure Charles Hakes Fort Lewis College 46 Large-Scale Structure • Use the scale of 1m = 1 A.U. Charles Hakes Fort Lewis College 47 Large-Scale Structure • Use the scale of 1m = 1 A.U. • The Earth is 1 m from the Sun Charles Hakes Fort Lewis College 48 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 Charles Hakes Fort Lewis College 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 The center of the Milky Way galaxy would be 4 times as far as the moon. Charles Hakes Fort Lewis College 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. • The Andromeda galaxy would be near Mars Charles Hakes Fort Lewis College 51 Large-Scale Structure • Redshift surveys of galaxies are used to determine the large-scale structure of the universe. Charles Hakes Fort Lewis College 52 Figure 16.9 First Galaxy Survey from the mid-1980’s Charles Hakes Fort Lewis College 53 Figure 16.10 The Local Universe Charles Hakes Fort Lewis College 54 Large-Scale Structure • Redshift surveys of galaxies are used to determine the large-scale structure of the universe. • Observed structure includes: • Strings • Filaments • Voids • The most likely explanation is a slice through “Bubbles.” • Only a few of these “slices” have been completed. Charles Hakes Fort Lewis College 55 Figure 17.1 Galaxy Survey Charles Hakes Fort Lewis College 56 Galaxy Survey • The universe is homogeneous - it looks the same everywhere • The universe is isotropic - it looks the same in all directions • Cosmological principle - the universe is isotropic and homogeneous. Charles Hakes Fort Lewis College 57 Three Minute Paper • Write 1-3 sentences. • What was the most important thing you learned today? • What questions do you still have about today’s topics? Charles Hakes Fort Lewis College 58