Charles Hakes

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Chapter 16

• Hubbles Law

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Outline

• Review
• Hubbles Law

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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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Possible explanations for Dark matter include
everything except

• A) WIMPs
• B) Brown dwarfs
• C) Black holes
• D) Dark dust clouds
• E) MACHOs

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Possible explanations for Dark matter include
everything except

• A) WIMPs
• B) Brown dwarfs
• C) Black holes
• D) Dark dust clouds
• E) MACHOs

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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...
• A2 B3 C4 D5
  E6

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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...

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Extending the Distance Scale

• Variable Stars
• Tully-Fisher Relationship
• Supernovae
• Cosmological Redshift

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Figure 14.7Variable Stars on Distance Ladder

• Greater distances can be determined than
  typically available through spectroscopic
  parallax, because these variables are so bright.

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Figure 15.12Local Group
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Tully-Fisher Relationship
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Figure 15.9Galactic Tuning Fork

• Galaxies are classified according to their shape
  (Hubble classification)
• Elliptical
• Spiral
• Irregular

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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

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Tully-Fisher Relationship

• Rotation speed can be used to determine a
  galaxys 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.

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Figure 15.11Extragalactic Distance Ladder
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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

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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

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Supernovae

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

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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).

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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

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Figure 15.11Extragalactic Distance Ladder
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Chapter 16

• Hubbles Law

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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

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Cosmological Redshift
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Figure 16.1Galaxy Spectra

• Early 20th Century astronomers observed that most
  galaxies were moving away from us.

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Figure 16.2Hubbles Law

• Hubble plotted the recession velocity against the
  distance of the galaxies, and found a direct
  relationship.

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Hubbles Law

• recessional velocity Ho x distance
• Ho is Hubbles 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

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Hubbles 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?

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Hubbles 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?

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Hubbles Law

• recessional velocity Ho x distance
• How long ago was that galaxy at your location?
• time distance / velocity

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Hubbles Law

• recessional velocity Ho x distance
• How long ago was that galaxy at your location?
• time distance / velocity
• 1 Mpc 3.09x1019 km

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Hubbles 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!

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Hubbles 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)

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Hubbles 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.

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Figure 16.3Cosmic Distance Ladder
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Which of the following is inferred by Hubbles
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.

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Which of the following is inferred by Hubbles
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.

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What method would be most appropriate to
determine the distance to a nearby galaxy?

• A) Spectroscopic parallax
• B) Cepheid variables
• C) Hubbles law
• D) Radar ranging

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What method would be most appropriate to
determine the distance to a nearby galaxy?

• A) Spectroscopic parallax
• B) Cepheid variables
• C) Hubbles law
• D) Radar ranging

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What method would not be appropriate to determine
the distance to a nearby galaxy?

• A) Tully-Fisher relationship
• B) Cepheid variables
• C) Hubbles law
• D) Type I Supernovae

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What method would not be appropriate to determine
the distance to a nearby galaxy?

• A) Tully-Fisher relationship
• B) Cepheid variables
• C) Hubbles law
• D) Type I Supernovae

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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

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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

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Large-Scale Structure
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Large-Scale Structure

• Use the scale of 1m 1 A.U.

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Large-Scale Structure

• Use the scale of 1m 1 A.U.
• The Earth is 1 m from the Sun

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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

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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.

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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

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Large-Scale Structure

• Redshift surveys of galaxies are used to
  determine the large-scale structure of the
  universe.

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Figure 16.9First Galaxy Survey from the
mid-1980s
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Figure 16.10The Local Universe
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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.

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Figure 17.1Galaxy Survey
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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.

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Three Minute Paper

• Write 1-3 sentences.
• What was the most important thing you learned
  today?
• What questions do you still have about todays
  topics?