Hi all,
I'm consolidating my notes for Physics P1 (Edexcel) and I've realised I'm not too clued up about one aspect of the life cycle of stars :/
As I understand it in my notes, when a main sequence star becomes a red (super)giant, it
stops the nuclear fusion of hydrogen because the hydrogen supply has been exhausted, and it instead begins fusing helium protons together. Base knowledge - tick
My notes explain that the core of the star becomes denser but that the star expands. My confusion comes from this:
is this true and if so, why does the core of the star become denser and why does the star expand?I suppose my guess is that when the hydrogen supply is exhausted, the star releases less gas because of less nuclear fusion (and so it exerts a lowered force of gas pressure), so the resultant force between the gas pressure and the gravitational force of the star is changed from zero (which is what defined it as a main sequence star) and so the star has a higher gravitational force - which leads the core of the star to collapse. Yet surely if the core of the star collapses because it has a higher gravitational force, the star should not expand as well?
This probably goes well beyond the syllabus, but I'm cautious because statement 3.12 asks us to "describe the role of gravity in the life cycle of stars". I see from some research that there's such thing as variable stars between MSSs and red (super)giants, with stars finding hydrogen from pockets outside of the core before the supply completely burns out (and that carries a sort of understandable way to answer my questions, albeit a very long answer), so I have a feeling the question is even unanswerable thanks to P1 oversimplification :P
All help would be very much appreciated. Thank you ever so much in advance. And all the very best of luck in your exams