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Charles Hakes
Fort Lewis College
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Charles Hakes
Fort Lewis College
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Chapter 16
Hubble’s Law
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Fort Lewis College
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Outline
• Review
• Hubble’s Law
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Fort Lewis College
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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.
Charles Hakes
Fort Lewis College
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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
Charles Hakes
Fort Lewis College
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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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Fort Lewis College
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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...
A=2
Charles Hakes
Fort Lewis College
B=3
C=4
D=5
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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
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Extending the Distance Scale
•
•
•
•
Variable Stars
Tully-Fisher Relationship
Supernovae
Cosmological Redshift
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Fort Lewis College
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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.
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Fort Lewis College
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Figure 15.12
Local Group
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Fort Lewis College
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Tully-Fisher Relationship
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Fort Lewis College
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Figure 15.9
Galactic “Tuning Fork”
• Galaxies are classified according to their
shape (Hubble classification)
• Elliptical
• Spiral
• Irregular
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Fort Lewis College
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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
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Fort Lewis College
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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.
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Fort Lewis College
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Figure 15.11
Extragalactic Distance Ladder
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Fort Lewis College
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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
Charles Hakes
Fort Lewis College
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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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Fort Lewis College
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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.
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Fort Lewis College
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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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Fort Lewis College
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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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Fort Lewis College
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Figure 15.11
Extragalactic Distance Ladder
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Fort Lewis College
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Chapter 16
Hubble’s Law
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Fort Lewis College
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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
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
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Fort Lewis College
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Figure 16.1
Galaxy Spectra
• Early 20th
Century
astronomers
observed that
most galaxies
were moving
away from us.
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Fort Lewis College
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Figure 16.2
Hubble’s Law
• Hubble plotted the
recession velocity
against the distance of
the galaxies, and
found a direct
relationship.
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Fort Lewis College
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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
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Fort Lewis College
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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?
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Fort Lewis College
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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?
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Fort Lewis College
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Hubble’s Law
recessional velocity = Ho x distance
• How long ago was that galaxy at your
location?
• time = distance / velocity
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Fort Lewis College
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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
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Fort Lewis College
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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!
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Fort Lewis College
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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)
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Fort Lewis College
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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.
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Fort Lewis College
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Figure 16.3
Cosmic Distance Ladder
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Fort Lewis College
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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
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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
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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) Hubble’s law
D) Radar ranging
Charles Hakes
Fort Lewis College
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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) Hubble’s law
D) Radar ranging
Charles Hakes
Fort Lewis College
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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) Hubble’s law
D) Type I Supernovae
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Fort Lewis College
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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) Hubble’s law
D) Type I Supernovae
Charles Hakes
Fort Lewis College
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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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Fort Lewis College
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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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Fort Lewis College
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Large-Scale Structure
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Fort Lewis College
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Large-Scale Structure
• Use the scale of 1m = 1 A.U.
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Fort Lewis College
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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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Fort Lewis College
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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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Fort Lewis College
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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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Fort Lewis College
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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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Fort Lewis College
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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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Fort Lewis College
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Figure 16.9
First Galaxy Survey from the mid-1980’s
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Fort Lewis College
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Figure 16.10
The Local
Universe
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Fort Lewis College
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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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Fort Lewis College
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Figure 17.1
Galaxy Survey
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Fort Lewis College
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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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Fort Lewis College
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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 today’s topics?
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Fort Lewis College
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