Re: How does the principle of conservation of energy apply to a supernova?

Supernovas do not violate the conservation of energy.  While it may seem 
that they generate energy out of nothing, they actually release the energy
that is stored in the nuclei of atoms.

Atoms are made of a very dense and small center, called the nucleus.
The nucleus contains most of the mass of each atom.  Surrounding the
nucleus are electrons.

Nuclei are composed of two types of particles:  protons and neutrons.
These are nearly the same, except that the proton has a positive 
electrical charge, while the neutron has no charge.  Electrons have a
negative charge.

Under conditions of very high temperature and density, the nuclei of
atoms can collide at very high speeds.  This can result in nuclei
sticking together (called fusion) or breaking apart (called fission).

In many cases, nuclear fusion releases energy.  The Sun, for example,
gets its energy by fusing several hydrogen nuclei into helium.  The 
energy keeps the Sun hot for many billions of years.

In supernova explosions, the material gets extremely hot and dense -
there are a couple of ways that this can happen.  Under these conditions,
all sorts of nuclear reactions can take place (both fission and fusion),
and the result is that a tremendous amount of energy can be released.
In a few seconds, a big supernova can release the same amount of energy
as the Sun does during its entire 10 billion year lifetime.