I believe bgodina91 had a different question from orbital mechanics.
To maintain the KISS system (Keep It Simple, Stupid) let's look at the sun as a huge ball of plasma. Note that plasma is not just the fourth state of matter: it is the state where elements fuse, and under enough pressure, the strong/weak force interaction is less powerful than gravity. Note that the POSTULATED fifth state is compact mass, that amounts to a purely energetic state, but let's not go there for the moment.
Basically, we're talking a plasmatic/nuclear interaction that goes thus:
/H + P (uud) + P (uud) = (convert U-D)= N+(pion) = PN (UUD) (UDD). Therefore, PN+PN+N . . . = (^2^He^3,4,5^).
Two forces are constantly at work: gravity and nuclear fusion. Heat (derived frompressure/nuclear fusion) constantly drives the Sun to expand, and gravity keeps it together. It will do so for the next 5x10^9 years at least.
Then what happens, theoreticians have no clue.
I am the first to concur with Einstein and Teller: the protons (hydrogen stripped of electrons) will overload, and fuse rapidly into He^4 and He^5 plasma, held loosely with pions. But as far as the rest of the conversion goes, your guess is as good as mine.
My best guess is that the sun will begin to glow more red than now, not because it is going to cool off, but because the internal structure of the sun will change: more ^10 Ne ^22, 23 will form in the chromosphere than we see presently, and will glow with the expected spectra.
As stars react, they develop more and more heavy elements: from Li-Fe of various isotopes. When the sun reaches > 12.25% Fe, creating the rest of the periodic table up to ^92^U^238^, the heavier elements will start dragging in electrons. In a surprisingly short time, the sun will decrease its radiation, causing gravitational collapse.
From there, all bets are off.
Hawking says the sun will become a nova.
Susskind says it will go supernova.
Guth says it will become a black hole.
I say that we won't be around long enough to find out.