To more fully explain the Stargate thing, it was essentially the increasingly-common sci-fi trope of the Nova Bomb: drop a device into the star that eliminates enough of its mass, or changes its quantum properties enough, that one of the forces that keeps a "healthy" star in balance and burning weakens or disappears. Stars depend on a balance between the gravity of all that hot gas collapsing under its own collective weight, and the incredible force of the ultrahot gas in the stellar core undergoing nuclear fusion and trying to blow up like an absurdly huge nuke.
If you halt the nuclear reactions somehow, then the star will collapse under its own gravity and compress into something like a neutron star or black hole; the shock of the changes the matter goes through during the change will actually cause the outer layers of the star to blow off in a final cataclysmic explosion. This is one type of supernova. If you merely stop the exploding nuclei from producing any pressure, the star actually expands to become a red giant for a few million years, swallowing and vaporizing any planets that happen to be orbiting close enough (like Earth for example), and then eventually blowing off the outer layers in a less-intense explosion that can be expected to burn off the atmospheres and seas of any planets that didn't get swallowed by the giant directly. The core is left as a white dwarf in this case, and this is what is referred to as a nova. It's what our own sun is expected to do in about 5 billion years.
If, OTOH, you weaken the gravity somehow, or cancel it out completely, the pressure from the exploding stellar core will basically turn the star into the expanding explosion of plasma one would normally expect from a nuke the size of a hundred planets. Sometimes this could leave a stellar remnant behind, sometimes not- it depends on how you explain the cancel-out-gravity problem, since we don't know any way to do that today.
On Stargate SG-1, they sent the stargate dialed open to the "black hole planet"- encased in a force field so as to prevent premature detonation- into the local star. The force-field would wink out when its machinery was overloaded by conditions deep within the star, and by that point the gate would be close enough to the stellar core to start siphoning off mass from it. This, in turn, would weaken the gravity of the star sufficiently to cause it to explode as described above.
In Star Trek: Generations (sorry to raise the specter of this movie, but it is relevant), it was explained that the Trilithium nova bomb worked along the first principle: it disrupts the nuclear reactions going on in the stellar core and thus causes the star to prematurely implode/explode as a supernova.
The Supernova Bomb introduced in the Hitchhiker's Guide to the Galaxy series of books used the gravity principle in reverse. Rather than weaken the gravity, it greatly increased the explosion pressure within each stellar core so that the balance was undone that way; it did this by being a "junction box in hyperspace" which would apparently link the stellar cores of "every major sun" together all at once, which would mean that every such star would have not only its own pressure to contend with, but also the pressure of every other star thus linked- and obviously that would destabilize the stars affected. The Supernova Bomb was specifically designed as an "ultimate weapon" capable of destroying the universe.
I'm simply saying that sometimes it seems the laws of physics from our world can't always really be applied to a place like say, The Forgotten Realms... I mean if God's attacking the world directly tend not to change things all that much... An exploding sun? "Elmonster cleanup on aisle three please..."
