Why do stars with masses greater than 1.2M(sun) have convective cores?

[vertices]

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?

 

[vertices]

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]

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).

yes, i see it now. thanks:)

 

[Oberst Villa]

"..stars with masses greater than 1.2M(sun) have convective cores...

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 ?