They cannot create supernovas in their hands, if nova bombs were really that power for the planet would've been vaporized. Before you say "magic did it" let me show you this. Halo Silentium; ch. 33. As the reflective orb rotates beneath my ship, I see also the outstretched, feather-like plumes of vacuum energy pylons, drawing in the potential of an infinity of alternate realities ... aborting untold numbers of nascent universes to supply Requiem’s power. Strange that these cosmic deaths have never before struck me as cruel and futile. All of Forerunner technology has been made possible by drawing down vacuum energy. My own life, all that I know, arises out of cosmic predation. All Forerunner tech including promethean's is powered by this, if taking it it's high-end this means UNSC weapons can overpower shields with multi universal energies. So things that are obviously wrong should be ignored.