The Life-Cycle of a Star

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The Life-Cycle of a Star
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The Nebular Model

• A nebula is just a cloud of interstellar dust and
  gas.
• Nebulae are sometimes referred to as baby
  factories for stars.
• Stars are formed from the dust and gas from a
  nebula.
• The nebula is important because it is dense
  enough to form stars most other locations in
  the universe are not that dense.
• are believed to be formed by exploding stars or
  left over from the beginning of the universe.

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The Bubble Nebula
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The Ghosthead NebulaDo you see the ghost?
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The Eagle Nebula
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The Beginning

• Our Solar System began as a Nebula.

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The Beginning

• Our Solar System began as a Nebula.
• Something, a large star passing by maybe, started
  the nebula spinning in a counterclockwise
  direction.

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The Beginning

• As this loose mass of gas and dust spun, it began
  to flatten out, kind of like pizza dough.

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The Beginning

• As this loose mass of gas and dust spun, it began
  to flatten out, kind of like pizza dough.

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The Beginning

• As this loose mass of gas and dust spun, it began
  to flatten out, kind of like pizza dough.
• But as it flattens it begins to form a bulge in
  the center.(I wonder what will form here?)

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The Beginning

• The Sun will form in the bulge and the planets
  will form in the accretion disk.
• 99 of all the mass of the Nebula ends up in the
  bulge.

Sun
Accretion Disk
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The Formation of the Sun

• Our Sun forms in the bulge of the nebula.
• As the gasses and dust became more compact, they
  began to attract each other towards the center.
  This is called gravitational contraction.

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The Formation of the Sun

• As the particles got closer together they sped up
  - this increased their kinetic energy (energy of
  motion).
• Since this increase in kinetic energy also means
  a increase in temperature, the bulge is getting
  hotter.
• It is also getting denser.
• At this point what will become our local star,
  the Sun, is just a protostar.

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The Formation of the Sun

• Ultimately the temperature and density reach
  critical values for nuclear fusion to occur.
• At this point our protostar has become a star. We
  are so proud!!!

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The Formation of the Sun

• In nuclear fusion, two hydrogen atoms are given
  enough energy to come together and form a helium
  atom.
• This releases more energy.
• The energy released in this process is what
  powers the sun. Some of it causes more hydrogen
  to fuse into helium, and the rest works its way
  into space.
• Lets watch.

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Fusion of Hydrogen in the Sun
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Fusion of Hydrogen in the Sun
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Fusion of Hydrogen in the Sun
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Fusion of Hydrogen in the Sun
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Fusion of Hydrogen in the Sun
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Fusion of Hydrogen in the Sun
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Fusion of Hydrogen in the Sun
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Fusion of Hydrogen in the Sun
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Fusion of Hydrogen in the Sun
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Fusion of Hydrogen in the Sun
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The fusion reaction in the core of a star doesnt
stop at Helium.
Helium (Atomic 2) can fuse with Hydrogen
(Atomic 1) to form Lithium (Atomic 3).
Two Helium (Atomic 2) atoms can fuse to form
Beryllium (Atomic 4).
In stars the size of the Sun (medium to small)
this process continues up to Carbon (Atomic
6). Larger stars can provide more energy so this
process continues up to Iron (Atomic 26).
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This is another view of the Eagle Nebula. At the
top of each pillar you can see stars being born.
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This is a view of another Nebula, Abaurigae. At
the center you can see a star being born.
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This is a view of another Nebula. In the upper
right you can see a star being born.
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This is a view of the Orion Nebula. The bright
spot is a star which has formed. The dark ring is
an accretion disk where planets may form.
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Fusion Gravity
Fusion exerts an external Pressure outward on the
star and gravity pulls inward. The two opposing
forces balance each other out. This determines
the size of the star
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Fusion Gravity
Fusion exerts an external Pressure outward on the
star and gravity pulls inward. The two opposing
forces balance each other out. This determines
the size of the star
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Fusion Gravity
Fusion exerts an external Pressure outward on the
star and gravity pulls inward. The two opposing
forces balance each other out. This determines
the size of the star
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Fusion Gravity
Fusion exerts an external Pressure outward on the
star and gravity pulls inward. The two opposing
forces balance each other out. This determines
the size of the star
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Fusion Gravity
Fusion exerts an external Pressure outward on the
star and gravity pulls inward. The two opposing
forces balance each other out. This determines
the size of the star
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Fusion Gravity
Fusion exerts an external Pressure outward on the
star and gravity pulls inward. The two opposing
forces balance each other out. This determines
the size of the star
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Fusion Gravity
Fusion exerts an external Pressure outward on the
star and gravity pulls inward. The two opposing
forces balance each other out. This determines
the size of the star
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Gravity Fusion

• Gravity Fusion determine the size of a star.
• Gravity pulls the star inward.
• Fusion pushes the star outward.
• The size of the star is determined by the
  equilibrium between these two forces.

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Size and Color of a Star
The size of a star is determined by the tug-o-war
between gravitational contraction and the outward
pressure of the fusion reaction.
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Size and Color of a Star
The size of a star is determined by the tug-o-war
between gravitational contraction and the outward
pressure of the fusion reaction. But the speed of
the fusion reaction determines the color of the
star.
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Size and Color of a Star
The size of a star is determined by the tug-o-war
between gravitational contraction and the outward
pressure of the fusion reaction. But the speed of
the fusion reaction determines the color of the
star. If the fusion reaction is slow, the star is
small, cool (3200 K) and red.
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Size and Color of a Star
The size of a star is determined by the tug-o-war
between gravitational contraction and the outward
pressure of the fusion reaction. But the speed of
the fusion reaction determines the color of the
star. If the fusion reaction is a little faster,
the star is bigger, warmer (5800 K) and
yellow-orange.
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Size and Color of a Star
The size of a star is determined by the tug-o-war
between gravitational contraction and the outward
pressure of the fusion reaction. But the speed of
the fusion reaction determines the color of the
star. If the fusion reaction is even faster, the
star is bigger, hot (45,000 K) and blue.
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Size and Color of a Star
Ironically, the bigger the star, the shorter its
lifespan. This is because the fusion reaction is
running so fast in large stars that the
available fuel is used up very quickly. A blue
star lasts around 800,000 years. Our Sun (Yellow)
10 billion years. A red star about 2,000 billion
years.
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The Death of Our Sun
In about 5 billion years our sun will use up all
its Hydrogen and the fusion reaction will stop.
At this point gravity is the only force in the
sun and the sun will begin to collapse.
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The Death of Our Sun
But as the sun begins to Collapse it will get
hotter, just like when it first formed.
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The Death of Our Sun
And Hotter !!!
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The Death of Our Sun
Until fusion begins again and ....
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The Death of Our Sun
The sun expands ..
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The Death of Our Sun
Into a ..
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The Death of Our Sun
Until ..
a red giant enveloping and ultimately
incinerating the inner 3 planets. This will
include us. Ouch !!!!
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Betelgeuse
Betelgeuse is a red supergiant located in the
constellation of Orion. Betelgeuse is Orions
right shoulder. Betelgeuse will go supernova
within the next 10,000 years. When it does we
will see it for two weeks during the day and it
will cast shadows at night. If you are lucky you
may get to see this spectacular event!!!
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The Death of Our Sun
Finally the Sun will use up its remaining fuel
creating elements up through Carbon. Bigger,
hotter stars can actually create elements through
Iron. The Fusion Reaction Stops at Carbon (Iron)
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The Death of Our Sun
At this point the outer layer of the sun will be
blown into space along with the elements formed
in its core and the heavier elements formed
during the explosion. These elements will be
used to form other stars and planets. The atoms
that formed you probably came from the death of
an earlier star!!!!! What remains of the Sun will
collapse into a white dwarf- a cooler but denser
burnt out ember of the sun
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White Dwarf H1504
Eventually this white dwarf will cool and no
longer emit light. At this point it will no
longer be visible. This is the fate of our Sun.
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If the sun were slightly larger it would become a
neutron star. A neutron star is much denser
than a white dwarf. 1 teaspoon of matter from a
neutron star would weigh as much as a
mountain. If the sun were 3 times as large it
would never stop collapsing on itself and become
a black hole.