You should first define explosion and burning.
Getting a lot of light or radiation is one thing.
Getting the various parts of the ship to fly apart is another.
They are not necessarily connected. And there is also the issue of the
time scale. When stars form, before ignition of the nuclear reaction,
there is outward radiation pressure from the heat generated by the
star internal pressure. This radiation pressure dislocates the cloud
surrounding the star, which is really a very slow explosion.
Now, to get heat and radiation from the spaceship, all you need is an
energetic phenomenon. The source may be the weapon used, producing
energy by whatever means, or internal reaction in the ship (reactor
core fusion for example). The energy source of a device necessarily
contains all the energy that can be provided to that device. If all
that energy is released in a very short time, you do get a very
energetic event with dramatic consequences. Typically what you observe
when the fuel tank of a car is on fire. But a battery cell with as much energy
is as dangerous if it can release the energy quickly.
It could also be some combination. In the chemical case, oxydizing
reactions are the more common, possibly the more energetic, but they
are not the only ones. What matters is to bring something at a
high enough temperature so that it can change to a new internal
organization that has less energy, the left over energy being
dissipated, This can produce EMR and light (flame, if you wish, though
not necessarily the candle kind). The energy can also heat various
parts, turning some materials into gas, and increasing the pressure of
gas, so that it expands and makes other things fly apart. It may also
be that the gas is directly produced by the chemical reaction as in
the case of gun powder. Radiation can also push things, if there is enough of it.
Things flying apart may also be due to pressure of preexisting gas
that will push on the bulheads and hull of a vessel that has lost
structural integrity. However, given the relative masses of the ship
structure and the gas, such an explosion is likely to be slow, unless
there is another energy source in play. It is probably so weak
(without additional energy) that it does not even rip apart the
vessel, even with low structural integrity.
If you used a powerful laser to cut a ship in two, the parts would
probably drift apart slowly, even though it contained some gaseous
But if you are really good in physics, there are other ways for
destroying a ship. For example, you can used a "tider". This powerful
device left by the old race can create strong variations of the
gravity field in the vicinity of the target. The target is elongated
and then ripped to pieces by the tidal effect, without any explosion.
No survivors, unless they are tiny. It is the Sci-Fi version of
dismemberment, a popular technique some centuries ago.
Clarification added after comments below and a further question.
My answer is an attempt at a uniform presentation of energy/explosion
weapons. Then I tried to emphasize that by imagining another kind of
weapon, for which I invented the name tider.
My intention was definitely not to mislead people into believing that
it existed in some novel or movie. I would have given the reference.
I was only trying to avoid a dry presentation.
From answers to the question
Was the idea of a tidal dislocation weapon ever suggested in SciFi?, I gather that such
weapons have been considered, and Star Wars actually has gravity guns
firing gravity bombs. They do explode though, and I was trying to get
examples that do not necessarily require an explosion. But all that
is of course mostly fiction and imagination.