I haven't understood the mechanism by which energy from the core of a star reaches its outer layers. Primarily, heat is transfered via convection or radiation.
For stars of nearly one solar mass, radiation dominates in the inner regions because convection needs a high temperature gradient, and their cores aren't hot enough. Now, the wikipedia page says-
The outer portion of solar mass stars is cool enough that hydrogen is neutral and thus transparent to ultraviolet photons, so convection dominates.
I find this reasoning kind of counter intuitive.If the outer regions are transparent to ultraviolet photons, why does convection dominate?
A similar argument is presented in the case of high mass stars.
In the outer portion of the star, the temperature gradient is shallower but the temperature is high enough that the hydrogen is nearly fully ionized, so the star remains opaque to ultraviolet radiation. Thus, massive stars have a radiative envelope.
The above reasoning is not convincing enough. I would be grateful if someone could help me out.