26.3 Life Cycle of Stars

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26.3 Life Cycle of Stars
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26.3 How Stars Form

• Take lots of acting classes and read books How
  to avoid the paparazzi

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Baby
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Nebula

• Large cloud of gas and dust

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The birth of a Protostar

• Stars are created by gravity.

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The birth of a Protostar

• Gravity pulls a nebula's dust and gas into a
  denser cloud.
• As the nebula contracts, it heats up

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The birth of a Protostar

• When the contracting cloud of gas and dust has
  enough mass it forms a star called a protostar. 

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The birth of a Protostar

• As a protostar contracts, its internal pressure
  and temperature continue to rise.  

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Quite simply said.

• A star is formed when a contracting cloud of gas
  and dust becomes so dense and hot that nuclear
  fusion begins.

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26.3 Adult Stars

• The grown up ones

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Adult
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How long till you grow up?

• Spend 90  of their lives on the M-S.  
• A star's mass determines the star's place on the
  main sequence and how long it will stay there.

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Quick and Hot

• Massive stars have large cores
• Produce the most energy.
• Bluest and brightest M-S stars.
• 300,000 times brighter than the sun.
• Use up their fuel relatively quickly
• Last only a few million years.

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Sunnys the middle child

• Stars similar to the sun occupy the middle of the
  main sequence.
• A yellow star like the sun has a surface
  temperature of about 6000 K
• Remains stable on the M-S for about 10 billion
  years.

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Small is the way to go!

• Small, cool stars are long-lived.
• Mass about 1/10 of the suns
• Gravitational force is just strong enough to
  create a small core where nuclear fusion takes
  place.
• Lower energy red stars
• The coolest least bright of all visible stars.
• May stay on the M-S for more than 100 billion
  years

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Question Why do red main-sequence stars last
longer than blue main-sequence stars?

1. They use up their hydrogen fuel at a much slower
   rate because they are smaller and cooler.
2. They use up their hydrogen fuel at a much slower
   rate because they are larger and hotter.
3. They are younger than blue main-sequence stars.
4. They have much higher mass than blue
   main-sequence stars.

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Question Why do red main-sequence stars last
longer than blue main-sequence stars?

1. They use up their hydrogen fuel at a much slower
   rate because they are smaller and cooler.
2. They use up their hydrogen fuel at a much slower
   rate because they are larger and hotter.
3. They are younger than blue main-sequence stars.
4. They have much higher mass than blue
   main-sequence stars.

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26.3 The Death of a Star

• Please pay your respect with a moment of silence

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Old Age Death by Obesity
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Stars don't last forever.

• Core begins to run out of H.
• Gravity becomes greater than pressure.
• Core starts to shrink.
• Core temp rises and H fuses.
• Energy flowing outward increases expanding the
  star.

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Stars don't last forever.

• Atmosphere expands and cools to red. The star
  becomes a red giant.
• Core collapses, gets hot so helium fuses.
• This produces carbon, oxygen, and heavier
  elements.
• Star stabilizes and its outer layers shrink and
  warm up.
• In this period, the star remains in the upper
  right part of the H-R Diagram.  

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The fate of a dying star

• Fuel runs out in a star's core. The star's death
  cause it to become a
• white dwarf
• neutron star
• black hole
• We will complete project life cycle of a star
  to help master this concept.

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Review 26.3Key Concepts

• A star is formed when nuclear fusion begins.
• A star's mass determines the star's place on the
  main sequence and how long it will stay there.
• A star ends up as a white dwarf, neutron star, or
  black hole once it exhausts its fuel supply.

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