- in one of the episodes they lure the Go'auld into an unihabited solar system then drop a spare Stargate into the sun to trigger a supernova (I think). You sort of hope that they checked that there weren't any occupied worlds within say 50 light years or so...
later - yep, a supernova - full summary here:
E.E. "Doc" Smith did this several times, most notably in the final book of the Skylark of Space series, Skylark of Valeron
where they basically blow up most of the starts in a galaxy to get rid of the evil chlorine breathers, creating a quasar, while evacuating all of the oxygen breathers to a third galaxy. This astonishing act of genocide is apparently a good thing.