This is a star that
has gone beyond the point of hydrogen fusion, but is still performing
fusion as its energy source. Helium is the main fuel of
post-main-sequence stars, although all of the elements lighter than
iron can fuse, sometimes. These stars tend to be quite variable
over the long term, but during their Red Giant [[linkey]] stage, they
are quite low density and moderate temperature, making them an ideal
environment to work on how to live in environments hotter than the
inside of a
Gas Giant planet
[[linkey]], although at some stages quite a bit less dense.