One of the things a red giant does is change size.
I was taught about Red Giants by astronomy teachers and books. What really causes them can get pretty complex.. But it can, generally, be summarized
in the following way.
When a star is born, it is bluish and extremely hot because of how stars always first burn off heavier metals and other elements first. Later on in
life they primarily burn hydrogen and helium (like our sun, which produces the sun's very distinct yellowish/orange color) along with smaller amounts
of other elements.
How a star maintains it's semi-circular shape is a delicate balance of outward nuclear energy being produced within the star and the constant, inward
crush of gravity. Elements required to initiate the nuclear reactions don't last forever. What results is a complex battle between the star's
gravity and the star's internally created nuclear reactions.
How this was explained to me is pretty simple to understand.
The star's gravity starts to compress the star, making it smaller. This continues until the ingredients are once again correct for nuclear reactions
to take place within, since they can't take place when the star is it's normal size anymore due to the star running out of nuclear fuel. The
compression of the star also compresses the leftover nuclear fuel deep within, which then ignites under gravitational pressures and all kinds of other
exotic "ingredients". This forces the star and all of its components outward as the energy released overcomes the star's gravity.
This forces the star outward and makes it many times larger than it would ordinarily be. What will usually happen is the gravity will eventually
begin to overcome the outward momentum. The star begins to fall/collapse again under its own gravity. Suddenly, the nuclear fuel, again, ignites
under immense forces and temperatures which releases untold amounts of energy, which AGAIN forces the star outward further and further. Every time
the outward momentum is overcome by gravity, the star has more inward gravitational momentum, which has the potential to create much more violent
nuclear chain reactions each time, which then pushes it out further, etc..etc..
For stars like our sun, I think you end up with a planetary nebula where one of these outward "breaths" of the star just continued outward into
space forever.. Which make for some pretty amazing astrophotography, apparently.
For some stars, what probably happens is that they're so large and massive that instead of expanding out forever, one of the violent, inward crushing
cycles actually continues towards the core of the star and under the immense gravitational collapse it forms a singularity (black hole) by piercing
the fabric that makes up the universe as we know it. The size of the black hole will always be dependant on the size and mass of the star that
created it. Thus, the largest stars are most likely to produce the largest black holes.
This light curve from Wikipedia shows the star's apparent magnitude between 1988-2002:
You can easily look at this chart and visualize the inevitable tug of war between gravity and nuclear chain reactions that is taking place (or WAS
taking place since what we're seeing now was the star as it looked 600 years ago.)
I guess the star continues to be shrinking from what UC Berkley has to say. But if you look at this particular chart you can see that this really
isn't anything new for this particular star. The patterns of the star's changes in apparent magnitude don't seem to foretell any kind of imminent
runaway collapse that would create a supernova. At least not right now.. Of coarse, we don't understand the process well enough to predict these
types of events based on past scientific data. We just don't know what will happen and when. All we can tell is that the star is currently
shrinking.. That doesn't tell us a whole lot. We won't know when the star goes supernova until it actually happens. That's what I gather.
A supernova being created by a star of this size and mass.. Pretty likely from what everyone has been saying. So it is probably inevitable that the
star WILL go supernova at some point. any guess is just a guess. Noone knows if the current collapse will continue to produce a supernova.