[sculptor]

Brilliant! The answer to my question, 'why does the core not expand as it heats, thereby preventing further contraction' seems to be that the mechanism of the collapse is that the electrons become degenerate, an analogy being steam condensing to water - density now constant independent of temperature. There also seems to be "a latent heat of degeneration" in which the state change releases energy. Conversely, the atmosphere is not degenerate, and so it expands when heated from within.

My next question is, why is the red giant "giant" if its surface is cool. The article didn't really address this.

Presumably a quasi-answer is that the very deep layers near to the core are intensely hot, and therefore fluffed up compared with usual. Then the next-to-deep layers are exposed to a lower gravitational field because they are futher out, and are therefore "fluffed up" compared with usual, and so on.

The surface layer doesn't "know" that there is a degenerate core. All it knows is what is happening locally, the three obvious variables being radius, local heat flux, and amount of matter contained within. It would be nice to see some digestible exposition on what sets the radius of the photosphere.

Many thanks for your pointer.