Energy transport in the Sun

In article ,
Anthony Garcia wrote:

"Sam Wormley" wrote in message
...
[snip]
It is interesting to compare internal structures with more and less
massive stars, all on the main sequence (hydrogen burning).

http://www.mhhe.com/physsci/astronom...r19/19f08.html

This is wild. In comparing the internal structure of the 0.1 solar mass
star vs the 1 solar mass star it is intuitively understandable that the
radiative region disappears. HOWEVER I find it completely odd that in
comparing the structure of the 60 solar mass star with the 1 solar mass
star that the convective region switches with the radiative region.

It makes more sense if you consider that massive stars get most of
their energy from a different cycle -- the CNO cycle -- which
has a much sharper temperature dependence than hydrogen fusion does.
It's something like fusion power proportional to T^7 for hydrogen fusion,
and more like T^13 for CNO fusion, if my 20-year-ago memories are right.
So there's a much steeper temperature gradient in the cores of
massive stars, which is what's needed to drive convection.

Stuart