THE LIFE CYCLE OF STARS

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THE LIFE CYCLE OF STARS
This star has entered the last stage of its
life cycle
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• The first stage of star formation is NUCLEAR
  FUSION
• Gravity pulls clouds ofgas and dust (nebulae)
  together into a sphere as it becomes denser, it
  gets hotter and the hydrogen changes to helium.

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• Stars are classified by
• Size
• Brightness
• Mass
• Color
• Temperature
• Spectrum
• Age

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TYPES OF STARS

• MAIN SEQUENCE STARS this is the second phase
  and the longest phase
• Energy is generated in the core as hydrogen atoms
  fuse into helium atoms
• Stars are about 98 Hydrogen and Helium
• The sun in this stage (10 million yrs. to become
  this stage has been shining for 5 billion years
  ) Earth is 4.6 billion years old

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GIANTS AND SUPERGIANTS

• Third stage RED GIANT
• RED GIANT A large reddish star late in its life
  cycle - a star that expands and cools once it
  uses all of its hydrogen
• Eventually will shrink
• When shrinks atmosphere grows large and cools
  to a red giant or red supergiant
• In 5 billion years the sun will become a red
  giant

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• Red giants 10 or more times bigger than the
  sun.
• Red Supergiants at least 100 times bigger than
  the sun.

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WHITE DWARFS AND RED DWARFS

• WHITE DWARF a small, hot, dim star that is the
  leftover center of an old star
• No hydrogen left
• Can shine for billions of years before they cool
  completely
• RED DWARF low-mass stars
• Oldest stars in the universe

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BLUE STARS

• BLUE STARS very massive blue stars are not in
  the main sequence very long.
• They quickly use up the hydrogen in their cores
• Expand and turn into giants or supergiants

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SUPERNOVAS

• A main sequence star with a mass of more than
  about 10 Suns experiences a spectacular end.
• It swells into a red supergiant with cooling,
  expanding outer layers.
• Eventually its core collapses, causing a huge
  explosion known as a supernova

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• A gigantic explosion in which a massive star
  collapses and throws its outer layers into space

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NEUTRON STARS and PULSARS

• NEUTRON STAR a star that has collapsed under
  gravity to the point that the electrons and
  protons have smashed together to form neutrons
• If the core of a supernova has relatively low
  mass, the core will be crushed into a tiny, super
  dense neutron star
• PULSAR a spinning neutron star

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BLACK HOLE

• A volume of space in which gravity is SO GREAT
  that nothing can escape, not even light, although
  objects can fall in
• If the core of a supernova has a mass of more
  than about two Suns, its own gravity will squash
  it further, into a black hole.

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HR Diagram (page 592 593)Shows the
relationship between a stars surface temperature
and absolute magnitude.
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Hertzsprung-Russell Diagram

• The temperature is given along the bottom of the
  diagram.

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Hertzsprung-Russell Diagram

• The absolute magnitude (brightness) is given
  along the left side.

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Hertzsprung-Russell Diagram

• The Hot (blue) stars are located on the LEFT
• The Cool (red) stars are located on the RIGHT.

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Hertzsprung-Russell Diagram

• The BRIGHT stars are at the TOP.
• The DIM stars are at the BOTTOM.

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• The DIAGONAL pattern where most stars lie is the
  MAIN SEQUENCE.
• The SUN is located in the middle of the diagram.
• Average stars like the sun become giants or
  supergiants (Right) and then down to the left to
  become white dwarfs.