Well Mike, My first thought as to the stability of the galactic antimatter cloud is that it is probably fairly stable. While it will be losing particles to collisions with normal matter, it will also be gaining particles from the various sources that produced it in the first place. The sources of course would be black holes, and super novae and other high energy activities. Of course I expect that it will vary from time to time, but on the average I would expect it to stay about the same. Of course I am no expert on this, so don't expect that this is the last word.

Bill Gill

C is not the speed of light in a vacuum.
C is the universal speed limit.