Transcript Chapter 15: The Milky Way Galaxy

Chapter 15:
The Milky
Way Galaxy
Lesson Plan
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Idea of Gallaxies
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Parson’s observations
Hubble’s observations
 Cerpheid Variables
Milky Way
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Center
 Hershel’s observations
 Interstellar gas
 Shapley’s observations (pr #7, pg 400)
Disk mapping
 21sm – radiation (pr #9, pg 405)
Nucleus
 Infrarred view
 Synchrotron radiation (pr #11, pg 409)
 X-ray radiation
 Suppermassive black hole (pr #13, pg 410)
Rotation
 Dark matter (pr #10, pg 412)
WHAT DO YOU THINK?
How many stars does the Milky Way
Galaxy contain?
 Where is our Solar System located in
the Milky Way Galaxy?
 Is the Sun moving through the Milky
Way Galaxy and, if so, about how fast?
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You will discover…
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the Milky Way Galaxy—billions of stars along with gas
and dust bound together by mutual gravitational
attraction
the properties of our Milky Way Galaxy
Earth’s location in the Milky Way
how interstellar gas and dust enable star formation to
continue in our Galaxy
that observations reveal the presence of significant mass
in the Milky Way that astronomers have yet to identify
that there is a black hole at the center of our Galaxy
Schematic Diagrams of
the Milky Way
Edge-on view showing the Milky Way’s disk
Schematic Diagrams of
the Milky Way
Two possible distributions of the spiral
arms of our Galaxy. Our Galaxy has at
least four major spiral arms and several
shorter arm segments.
Telescope of the MidNineteenth Century
Built by the Earl of Rosse in 1845, a
1.8-m-diameter telescope.
Telescope of the MidNineteenth Century
Lord Rosse’s sketch of the spiral
structure of the galaxy M51
A modern photograph of M51
(also called NGC 5194)
Messier 100 and Cepheids
Period-Luminosity Relation
Our Galaxy
Wide-angle photograph spanning half the Milky Way, as
seen from the equatorial latitudes
View Toward the Galactic Center
More than a million stars in the disk of
our Galaxy fill this view, which covers a
relatively clear window just 4º south of
the galactic nucleus in Sagittarius.
Electron Spin & the Hydrogen Atom
Mapping the Galaxy
Radio waves from various gas clouds
exhibit slightly different Doppler shifts,
permitting astronomers to sort out the gas
clouds and map the Galaxy.
Map of the Galaxy
This map (left), based on radio telescope surveys of
21-cm radiation, shows the distribution of hydrogen
gas in the Milky Way.
Two Views of Spiral Galaxy M83
Our Galaxy
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Diameter is about 100,000
ly
Sun about 26,000 ly from
the galactic center
Disk contains gas, dust
and Population I stars
Halo is composed mostly
of Population II stars.
Infrared View of the Milky Way
Taken by the COBE satellite in 1997
The Galactic Center
Two Views of the Galactic Nucleus
Radio image taken at the VLA
Two Views of the Galactic Nucleus
Infrared image showing the motion of six stars in the
vicinity of the unseen massive object at the position of
the radio source Sagittarius A* ().
Orbits of Stars in Our Galaxy
NGC 4144, very similar to the Milky Way
The Nearest Galaxy
Canis Major dwarf elliptical galaxy
Differential Rotation of the Galaxy
Stars closer to the Galaxy’s center than the Sun are overtaking
the solar system, while stars farther from the center are lagging
behind us.
The Galaxy’s Rotation Curve
Microlensing by Dark Matter
in the Galactic Halo
Gravitational fields cause
light to change direction.
Microlensing by Dark Matter
in the Galactic Halo
The light curve of the gravitational microlensing
of light from a star in the Galaxy’s nuclear bulge
by an intervening object.
WHAT DID YOU THINK?
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How many stars does the Milky Way Galaxy contain?
The Milky Way has about 200 billion stars.
Where is our solar system located in the Milky Way
Galaxy?
The solar system is between the Sagittarius and Perseus
spiral arms about 26,000 ly from the center of the
Galaxy.
Is the Sun moving through the Milky Way Galaxy and, if
so, how fast?
The Sun orbits the center of the Milky Way Galaxy at a
speed of 828,000 km per hour.
Key Terms
dark matter (missing
mass)
disk (of a galaxy)
distance modulus
galactic cannibalism
galactic nucleus
galaxy
halo (of a galaxy)
microlensing
Milky Way Galaxy
missing mass
nebula (plural nebulae)
nuclear bulge
rotation curve (of a galaxy)
Sagittarius A
Shapley–Curtis debate
spin (of an electron or
proton)
spiral arm
synchrotron radiation
21-cm radio radiation