Life Cycles of Stars

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Life Cycles of Stars
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Stars

• Stars are a large hot balls of plasma that shine
• The Sun is the Star in our solar system
• A group of stars that form a recognizable shape
  are called constellations
• A smaller group of stars with a recognizable
  shape within a constellation are called asterisms

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Stars
Big Dipper - Asterism
Ursa Major - Constellation
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A Star is born...
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Stars are Born From NEBULAS

• NEBULA a cloud of dust and gases, that
  eventually collapse to form a star.
• The gravitational pull from a nearby star OR the
  shockwave from an exploding star can trigger the
  collapse of a nebula

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A Collapsing Nebula
Dust and gases are pulled in by gravity to form
larger masses
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A Collapsing Nebula
A mass in the middle grows larger as it spins,
pulls in more dust and gas, and heats up
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A Collapsing Nebula
A protostar has formed
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Life Cycle of Stars
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Size Matters

• Different size stars go through similar life
  cycles, however they are different
• 1) Low Mass Stars
• 2) Medium Mass Stars
• 3) High Mass Stars

All begin as nebulae that collapse to form
protostars
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Low Mass Star

• Burns slowly and lasts for 100 billion years
• Mature into a red dwarf (most stars in the
  universe are red dwarfs)
• When the fuel for nuclear fusion runs out, a red
  dwarf cools into a white dwarf

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Medium Mass Star

• Last for about 10 billion years
• When a medium mass star runs out of fuel, it
  collapses under its own gravity
• The collapse heats up and pressure increases
• Star expands and becomes a Red Giant
• Eventually, burns out to form a white dwarf

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High Mass Star

• Lasts up to 7 billion years (usually less)
• At least 10 times the size of our Sun
• When a high mass star runs out of fuel it
  collapses and expands to form a Supergiant
• Supergiants end in a massive explosion called a
  supernova
• End result 1) cosmic debris - nebula
• 2) a neutron star (or pulsar)
• 3) a black hole

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Supernova

• Supergiants that run out of fuel end in a massive
  explosion
• Many nuclear fusion reactions occur and new
  elements form and explode into space
• The debris from the explosion is the source for a
  new nebula
• What remains of the star depends on the original
  size of the star

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Neutron Star

• Remaining core of a supergiant that was less than
  40 times the size of our Sun
• Also called a pulsar
• Very dense matter made of neutrons

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Black Hole

• Remaining core of a supergiant that was more than
  40 times the size of our Sun
• The core of the supergiant, after a supernova, is
  so dense that its gravitational pull sucks in
  space, time, light and matter
• Thought to be at the centre of all galaxies

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Summary

• All stars are born from a nebula
• Nebulae collapses and pulls in dust and gases to
  form a protostar
• Depending on the size of the star that forms, a
  different fate is met
• Low and medium mass stars burn out to become
  white dwarfs
• High mass stars burn out in an amazing explosion
  called a supernova, which gives birth to a new
  nebula

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Questions

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