That depends on who you ask. I subscribe to the hypothesis that the Sun is a quark-gluon plasma, and that its movement in the sky is governed by the strong nuclear force. Its energy source is the mutual annihilation of quarks and antiquarks, which explains how something so small has such longevity; it is both exceedingly dense and exceedingly efficient.
However, the corona is made up of the same materials as in RET, as evidenced by its absorption spectrum.