Well, I think we are talking about 2 different antimatter clouds here.
The ones in the Physorg.com article are ones that exist for a long period of time and inhabit the voids that have been found in the universe. For reference when the large scale structure of the universe was first studied it was found that all the galaxies tended to lie in long streams connected kind of like a 3D fish net. In between these streams there are voids where there is little or no matter. I expect you could Google and find something about this, after all everything else is on the net. These voids, as I mentioned are where the antimatter that is causing the expansion of the universe would be located. But as I said I kind of doubt that because I would expect that antimatter to clump up and form antimatter stars and galaxies.
The antimatter in the Space.com article are particles that are created and exist within the galaxy. At first thought you would think that they would be destroyed immediately upon creation, when they met a normal matter particle. But the density of matter in the galaxy is only about 1 particle per cm^3 (
Nasa's CosmoCopia]. At that density there is plenty of room for some sharing. Presumably the gamma rays they have been detecting are from the occasional times when they don't share nicely. At the scales we are talking about within the galaxy the individual particles would be gravitationally repulsive, but electrons and protons would be electrically attractive, and at the distances involved the attraction would overcome the repulsion.
Bill Gill
