Charles Hakes Fort Lewis College1

Charles Hakes Fort Lewis College2

Charles Hakes Fort Lewis College3 Chapter 16 Hubble’s Law

Charles Hakes Fort Lewis College4 Outline Review Hubble’s Law

Charles Hakes Fort Lewis College5 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 .

Charles Hakes Fort Lewis College6 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 College7 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 College8 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

Charles Hakes Fort Lewis College9 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 College10 Extending the Distance Scale Variable Stars Tully-Fisher Relationship Supernovae Cosmological Redshift

Charles Hakes Fort Lewis College11 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 College12 Figure Local Group

Charles Hakes Fort Lewis College13 Tully-Fisher Relationship

Charles Hakes Fort Lewis College14 Figure 15.9 Galactic “ Tuning Fork ” Galaxies are classified according to their shape (Hubble classification) Elliptical Spiral Irregular

Charles Hakes Fort Lewis College15 Figure 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 College16 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 College17 Figure Extragalactic Distance Ladder

Charles Hakes Fort Lewis College18 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 College19 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 College20 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 College21 Supernovae Type I Supernovae White dwarf, carbon detonation Are a result of a white dwarf exceeding its Chandrasekhar limit (1.4 M solar ). They are all about the same size. They are very good distance indicators (Standard Candles).

Charles Hakes Fort Lewis College22 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 College23 Figure Extragalactic Distance Ladder

Charles Hakes Fort Lewis College24 Chapter 16 Hubble’s Law

Charles Hakes Fort Lewis College25 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? Cardistancespeed Car 115 miles5 mph Car 2105 miles35 mph Car 354 miles18 mph Car 4240 miles80 mph Car 581 miles27 mph Car 6165 miles55 mph

Charles Hakes Fort Lewis College26 Cosmological Redshift

Charles Hakes Fort Lewis College27 Figure 16.1 Galaxy Spectra Early 20th Century astronomers observed that most galaxies were moving away from us.

Charles Hakes Fort Lewis College28 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 College29 Hubble’s Law recessional velocity = H o x distance H o is Hubble’s constant, the slope of the line on the previous plot Precise value is somewhere between 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 College30 Hubble’s Law recessional velocity = H o x distance Exercise: if H o = 50 km/s/Mpc, what is the recessional velocity of a galaxy that is 500 Mpc away?

Charles Hakes Fort Lewis College31 Hubble’s Law recessional velocity = H o x distance Exercise: if H o = 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 College32 Hubble’s Law recessional velocity = H o x distance How long ago was that galaxy at your location? time = distance / velocity

Charles Hakes Fort Lewis College33 Hubble’s Law recessional velocity = H o x distance How long ago was that galaxy at your location? time = distance / velocity 1 Mpc = 3.09x10 19 km

Charles Hakes Fort Lewis College34 Hubble’s Law recessional velocity = H o x distance How long ago was that galaxy at your location? time = distance / velocity 1 Mpc = 3.09x10 19 km 1/H o has the units of time!

Charles Hakes Fort Lewis College35 Hubble’s Law recessional velocity = H o x distance How long ago was that galaxy at your location? time = distance / velocity 1 Mpc = 3.09x10 19 km 1/H o has the units of time! 1/H o gives the age of the universe. (approximately)

Charles Hakes Fort Lewis College36 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 College37 Figure 16.3 Cosmic Distance Ladder

Charles Hakes Fort Lewis College38 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 College39 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 College40 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 College41 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 College42 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 College43 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 College44 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 College45 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 College46 Large-Scale Structure

Charles Hakes Fort Lewis College47 Large-Scale Structure Use the scale of 1m = 1 A.U.

Charles Hakes Fort Lewis College48 Large-Scale Structure Use the scale of 1m = 1 A.U. The Earth is 1 m from the Sun

Charles Hakes Fort Lewis College49 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 College50 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 College51 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 College52 Large-Scale Structure Redshift surveys of galaxies are used to determine the large-scale structure of the universe.

Charles Hakes Fort Lewis College53 Figure 16.9 First Galaxy Survey from the mid-1980 ’ s

Charles Hakes Fort Lewis College54 Figure The Local Universe

Charles Hakes Fort Lewis College55 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 College56 Figure 17.1 Galaxy Survey

Charles Hakes Fort Lewis College57 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 College58 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?