Astro101103 section 5 Lec 7

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Astro101/103 section 5Lec 7

• Wen Fu

Take graded HW4 HW5, HW4 HW5 solutions Turn
in HW6 No new homework due next week
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Star birth

• Formed in molecular clouds
• Gravity overcomes thermal pressure
• Clouds collapse
• Giant, cold, dense
• Gas and dust
• anatomy of the stellar factory
• --H, He etc.
• -- CO, etc.
• --dust of silicates, ices, etc.

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Star birth

• More than one star can be formed in one giant
  cloud due to fragmentation
• A protostar is formed when the core of cloud
  starts being heated up by the gravitational
  contraction
• Central temp. keep increasing until millions of
  degrees
• Fusion begins
• When energy generation rate energy radiation
  rate,
• it becomes a real starhydrogen burning,
  main-sequence star

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Stars (stability)

• No collapse or expansion
• Stable, hydrostatic equilibrium (or,
  gravitational equilibrium)
• Force balance achieved between gravity and
  thermal pressure
• thermal pressure density, temperature
• degeneracy pressure density

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Stars (energy generation)

• Fusion makes a star shine
• 4H gtHe, requires high temp. millions of degrees
• Two fusion styles
• pp chain (10 million K)
  low-mass stars (lt1.1M_sun)
• CNO cycle (16 million K)
  intermediate, high mass stars

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PP chain
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CNO cycle
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Stars (energy transportation)

• Energy can be transported by
• -- Conduction
• -- Convection
• -- Radiative diffusion
• Stars use the latter two
• The trade between convection and radiation
  depends on the star and region within a star

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Stars (energy transportation)
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Stars (energy transportation)
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Stars (energy transportation)

• Summary
• Massive stars (gt 2 M_sun) have small
  convective cores and large radiative envelopes.
• Low mass stars (lt 1 M_sun) have small
  radiative cores and large convective envelopes.

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Protostar 30 million
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Prelim

• Make sure you have studied
• Sample prelim
• Prelim 1
• Lecture notes
• Homework