Stellar Evolution

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Stellar Evolution
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Stellar Evolution NGC 3603
circumstellar disks around young stars
blue super-giant with its ring and bipolar
outflow marks the end of the life cycle.
progressing to aging, massive stars in a young
starburst cluster
Bok globules and giant gaseous pillars (evidence
of embryonic stars),
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STAGE ONE

• Stars begin as a NEBULA - a dark cloud of gas and
  dust
• Made mostly of hydrogen and helium with small
  amounts of heavier elements

Eagle Nebula M16
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Horse Head Nebula
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Veil Nebula
Trifid Nebula
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Thackeray's Globules in IC 2944
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Omega or Swan Nebula
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Ghost Head Nebula
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• The nebula begins to contract and gravitational
  attraction increases
• It continues shrinking and starts to spin.
• Eventually it forms a flat disk with a PROTOSTAR
  in the middle

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Planetary Disks Forming
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STAGE TWO - Main Sequence

• Longest part
• Energy is produced as fusion take place in the
  core of the star
• The energy from fusion balances the force of
  gravity and makes it a very stable stage

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Stage Three

• Happens when almost all of the hydrogen atoms
  have fused into helium atoms
• The core contracts due to the force of gravity

• This increases the temp and causes the helium to
  fuse into carbon
• This gives off a lot of energy and the star
  swells up to a giant or supergiant star

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Stage Four

• Helium fusion ends
• The star loses its outer gases and reveals a core
• An expanding shell of gases shed by this dying
  star forms a PLANETARY NEBULA

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Ant Nebula
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Helix Nebula
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Stingray nebula (Hen-1357), the youngest known
planetary nebula.
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The "Spirograph" Nebula
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Cats Eye Nebula
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• The star collapses inward and forms a hot dense
  core of matter called a WHITE DWARF

• Some white dwarfs may explode into a NOVA while
  they are cooling

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What about really BIG stars??

• Stars with masses 10 -100 times greater than the
  sun can produce a huge explosion called a
  SUPERNOVA

SN1987A
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What happens after the explosion?

• The core may contract into a very small, dense
  ball of neutrons called a NEUTRON STAR

• If it rotates it is called a PULSAR

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• Really large stars contract with greater force
  and become a BLACK HOLE

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Centaurus A (Hidden Black Hole)
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Classifying Stars

• Hertzsprung-Russell (HR) Diagram
• Plots temp. v. luminosity
• Most stars are main sequence

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