A Halo ring going off isn't the same as a fusion reactor. You do notice that we see not a single ounce of debris from The battle of the Bias or the 300 year flood war? Even for the vastness of space since all of these actions happened within 60 light years of earth somebody would have seen something. A [b]tactical[/b] fire is going to destroy everything. ONI isn't going to be able to travel to a random point outside of the galaxy.