Lesson Objectives
The students will be able to. . .
Identify
the conditions necessary for fusion to occur inside
a star.
Relate the color of a star to its temperature.
Discuss the importance of the H-R diagram to
astronomers.
Describe the phases in the life cycle of a sun like star
Discus how the deaths of super massive stars are
responsible for the creation of the heavier elements.
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Index







What is a star?
Nuclear Fusion
Types of stars
Classifying stars
Stars are like people
A star is born
Stars get old too






Silent death
Out with a bang
Remains
Deaths of super massive
stars
Exceptional deaths
Black holes
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Introduction
Today’s topic
What stars really are
How stars are classified
Star life cycles
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What is a star?
A
giant ball of gas
They
emit light and
heat through nuclear
reactions
They
are powered by
fusing Hydrogen into
Helium
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Nuclear Fusion
Certain conditions must be met for fusion to occur
Extremely
high values for density, temperature, and
mass.
For
example, the density at the sun’s core is 158.0g/cm. That
is 18 times the density of copper
The
sun’s core reaches a temperature of 15 million degrees
The
sun has a mass of 330,000 Earths
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Fusion occurs in a star’s core
Hydrogen
is fused
into Helium
Some
mass is lost and
converted to energy
The
energy is given
off as heat and light
E=MC2
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Types of Stars
Main
sequence stars
Sun
sized stars
Giants
Have
Super
a diameter of 250 times the size of the sun
Giants
Have
a diameter of 1000 times that of the sun. The largest known is
2700 times the sun’ size.
White
Dwarfs
Are
the size of small planets ex. Sirius the largest white dwarf has a
diameter of 10,400km.
Neutron
Have
stars
a diameter of only 20 – 30km
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Types of Stars
Stars are classified by their characteristics
Size
Temperature
Brightness
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Classifying Stars
Stars are also classified based on
temperature and brightness using the H-R
diagram
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Stars are like people
They have life cycles of their own.
They
are born
They live a life
They grow old
They die and have remains
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A Star is born
All stars begin their lives as a cloud of gas
The
cloud is mainly hydrogen
Gravity causes the denser portion to collapse
This
forms a proto star
The
gasses continue to collapse pressure and temperature
increase.
Nuclear fusion begins
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A star isn’t born
Sometimes
there is not enough mass
Fusion
never starts
Gravity holds gases around a core
These are the brown dwarfs
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Stars live on the main sequence
While
on the main sequence stars consume
their hydrogen fuel source.
Most stars spend 10 billion years here
Larger
stars die faster because they use up thier
fuel
Smaller stars can last up to 50 billion years
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Stars get old too
The
stars run out of Hydrogen fuel
Gravity contracts the core
The
temperature gets hot enough to ignite the
Helium
The
star expands and the outer layers cool
The star becomes a red giant
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Silent death
The
nuclear reactions stop
Gravity crushes the matter together as close as
possible
The
core glows brightly becoming a white dwarf
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Out with a bang
Sometimes
the outer layers are blown away in
an enormous explosion called a super nova
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Remains
When
a white dwarf stops glowing it becomes
a black dwarf.
The black dwarf is usually surrounded by a
planetary nebula.
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Deaths of super massive stars
Some
stars are so massive that they create
neutron stars
Their
explosions are so violent that all that is left
behind are the neutrons of the atoms
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Star Power
It
is in the incredible power of neutron stars
and white dwarfs that the heavier elements are
formed
Temperature
exceeds 7 million degrees
The density is so great that a thimble of matter
weighs more than an elephant.
All of the elements are born from hydrogen
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Exceptional deaths
Some
super novas create a phenomena called
a black hole.
The
gravity is so strong that light is pulled in
Black holes occur at the center of galaxies
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Black Hole at Galactic Center
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Black Hole Flash
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The End?
Some
scientists believe that black holes will
devour the entire universe.
They
Some
could recreate the big bang
believe the universe will expand forever.
There
is not enough mass to pull it back together
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Credits
Slide show by
Nick Delciappo
Cleveland public schools
Reference
Hsu, Tom. Foundations of Physical Science with Earth and Space
Science, Delta Education LLC, New Hampshire, Second
edition, 2007 pp.639-646.
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