There is considerable speculation... whether there exist other places that are almost entirely Antimatter....asymmetry of Matter and Antimatter in the visible universe is one of the greatest unsolved problems in physics.
CP Violation is part of Standard Theory. BB Theory, beyond the "unknown first moments" begins at a point when the Universe was composed of equal ammounts of Matter and Antimatter. The Matter and Antimatter then recombine, and are anhialated, converted to pure Energy. The tiny fraction of Matter left over being our present Universe.

This can be dismissed out of hand, as the ammount of Energy created by Matter and AntiMatter anhialations is tremendous, far too much to be absorbed by the remaining Matter, and the Universe is not observed to have even the smallest fraction of that Energy.

Where is the AntiMatter?
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Standard Galactic FUSION Theory, or Supermassive Black Hole Theory, does not fit observations.

Galaxies are described as collapsing vortexes of matter. Typically collapsing material spins faster approaching the center, in conservation of Angular Momentum. In contradiction, observations show that the arms of galaxies spin at the same rate no matter the distance from the center.

Dark Matter was theorized, an unobserved substance, which creates itself and Gravitationally pulls the outer arms, to speed them up. This violates Conservation and Laws of Thermodynamics. After several rotations the ammount of Dark Matter material would grow exponentially, pulling the center of the Galaxy outward. Stars in the outer arms are too far from the theorized Supermassive Black Hole, and would not be affected by it.

How do Galaxies form?


Magnetic fields form randomly in space. Over time, they can align and grow [A]. The EM fields of planets, stars, and galaxies prevent these fields from growing very large. In deeper space, far from the influences of EM fields, these magnetic fields can become extremely large.

Magetic forces in space causes ions to move. Motion along the lines of these large magnetic fields causes high speed collisions, resulting in pair production of new particles.

This causes the Hydrogen abundance observed in Nature, as larger atoms are not created by pair production.

Particles are ejected in both polar magnetic directions, expelling Matter in one direction, and Antimatter in the other. This forms the stars in the two Galactic arms.

This Matter-AntiMatter Galaxy Theory is supported by recent satellite observations:

...Recent observations by the European Space Agency's INTEGRAL satellite may explain the origin of a giant cloud of Antimatter surrounding the galactic center. The observations show that the cloud is asymmetrical....mostly on one side of the galactic center. While the "mechanism" is not fully understood, it is likely to involve the production of electron–positron pairs...