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Planetary nebula

  1. Jun 21, 2004 #1
    Hi,
    When a white dwarf is formed, why do the outer layers of gas which made it a red giant drift away to foirm a planetary nebula? Decrease gravity? Outward pressure? What exactly?
    Also, when the outer layers of a star move outwards to form a red giant, why do they cool down? (hence becoming red)
     
  2. jcsd
  3. Jun 21, 2004 #2
    Last edited: Jun 21, 2004
  4. Jun 22, 2004 #3
    So do the white dwarf and nebula kind of occur as seperate events? ie - outer layers pushed out; as the core starts to run out and emitts lots of radiation, the outer layers are pushed away? Correct? By the way, why does nuclear fusion of heavier elements (ie - helium to carbon, etc) produce more energy that hydrogen to helium fusion? (it must do to cause expansion to red giant)
     
  5. Jun 22, 2004 #4
    I reckon it is different activities governed by different states, since the body of a star has been dividing between inner and outer parts since its arrival on the main sequence. There is nuclear activity in the inner part (active energy production) and pure re-activity in the outer part (no active energy production, just energy transfer).

    I don't think that is quite correct. Red giant expansion is supposed to arise because the inner temperature gets high enough for hydrogen->helium activity to run in a shell around the helium core. That is what expands the outer part and makes the star a giant.

    Heavy element "burning" only occurs in stars 3 solar masses and up. The core pressures and temperatures get extremely high. But as long as the extensive outer part behaves like a convective processor of energy, the heated material rises, cools and emits mostly lower frequencies of light--the star becomes red. That finally comes to an end with too much nuclear energy production in shells getting stacked up below. BOOM!
     
    Last edited: Jun 22, 2004
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