convective cores - why?

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from Carol and Ostie (textbook):

"stars with masses greater than 1.2M(sun) have convective cores due to the the highly temperature dependent CNO cycle."

QUESTION:

why does the fact the CNO cycle is sensitive to temperature mean that the core is convective?

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bump:)

Ignition

Tere is just one answer, no. The core is thermodynamic system with spherical interfasis. The core takes part in the star cicle.

astrorob

Hydrogen burning processes in large stars, as you've pointed out, is dominated by the CNO cycle. This is confined to the central regions of the star and so there's a large energy flux which naturally favours a convective central region.

The resulting steep radiative gradient towards the centre makes the core unstable against convection (http://en.wikipedia.org/wiki/Schwarzschild_Criterion).

vertices

yes, i see it now. thanks:)

Oberst Villa

A factor of 1.2 is pretty close.... Suppose our sun would be just above that limit, and the increased luminosity would be compensated by a more distant earth orbit - would we notice that we have a star with a convective core ? As I understand it, there would be a turbulent flow, would these turbulences cause (high) fluctuations of the luminosity of the sun ?