Uh, do you have ANY idea what it should be about? Some sort of guidance?
That said, all the best songs are about awesome shit. So it could be about a black hole forming at the edge of the universe and destroying everything until it finally swallows the sun. The chorus could be about the sun being so strong and powerful, an allegory for yourself, and then finally it is destroyed, but it's kinda triumphant also because of the Law of Conservation of Matter, and the sun not really being transformed.
From there it could be a hopeful ending where the sun/black hole combo initiate some sort of Big Bang scenario, or depressing as the sun becomes a destructive force by being one with the black hole.