Actually how any planet would explode, as explained by sf author Wil McCarthy. [via SF Signal]
"Nor is Star Trek unique in this regard. Stars and planets are regularly destroyed in Star Wars, too, and in lots of other science fiction from the Golden Age right up to the very doorstep of the Singularity.
But here's the thing: destroying a planet takes time. They're big, dense objects, and destroying one is not like popping a balloon or even vaporizing a city with nukes."
I'll just be happy when Hollywood gets rid of that magical expanding ring of light that seems to accompany any explosion in space.