Full Idea
I think it is part of the essence of a star that the radiation pressures that oppose the star's tendency to gravitational collapse has its source in the release of no-longer-needed nuclear binding energy when colliding nuclei fuse in the star's hot core.
Gist of Idea
The essence of a star includes the released binding energy which keeps it from collapse
Source
Peter van Inwagen (Material Beings [1990], 07)
Book Reference
Inwagen,Peter van: 'Material Beings' [Cornell 1995], p.68
A Reaction
A perfect example of giving the essence of something as the bottom level of its explanation. This even comes from someone who doesn't really believe in stars!