The baryon and lepton asymmetry is a subject of great embarrassment for official physics and particularly for the cosmology of the “Big Bang” genesis of the universe, which supposedly followed that singular event. In fact any discussion in official astrophysics about antimatter is a taboo! The “Big Bang” was supposed to produce equal amount of matter and antimatter.
But as is always the case with “perfect” symmetry of mathematics and the ugly reality of material existence and also for the convenience of our official theoretical physicists; the spontaneous symmetry breaking that gave rise to the reality of world, is never perfect, because in that case nothing could exist, least of all us! There is always a “Big Bug”; the breaking is never “totally symmetric” but there is always some tinny asymmetry for some reason (will of God perhaps). So the story goes that there was a little excess of matter over antimatter produced in the Bang; and that accounts for the existence of matter in the universe and the stuff we are made of.
But aside from this story of genesis, antimatter was discovered in the Milky Way galaxy in early 60s or 70s, but was never taken seriously and even now there is a tendency not to discuss this taboo subject. So far at least three large patches of antimatter clouds in the Milky Way are known. These are identified by the 511 keV emission glow as these clouds of antimatter undergo annihilation processes at the periphery with the surrounding dust matter particles of the Milky Way. One, long known as “the mouse” is close to the galactic centre, Sagittarius A*. Recent NASA INTEGRAL satellite 511 keV map also found many so-called double stars emitting 511 keV emitting rays probably related to the presence of antimatter: https://www.nasa.gov/topics/universe/features/antimatter_binary.htm
There are also two giant gamma ray emitting bubbles symmetrically positioned across the galactic plane and extending 50, 000 light years into space as shown in the NASA image: https://www.nasa.gov/images/content/498884main_DF3_Fermi_bubble_art_labels.jpg
In addition there is a diffuse gamma ray halo that bathes the whole Milky Way galaxy (Probably all other galaxies as well), that forms the basis of more than a decade old article: Article The Cosmic Gamma-Ray Halo - New Imperative for a Dialectical...
But most of all, gamma-ray bursts (GRBs) points to the enormous scale presence of antimatter in the universe. The GRBs are extremely energetic explosions that have been observed in distant galaxies. Bursts can last from ten milliseconds to several hours. Although processes leading to such enormous energy events are not yet clear, only matter-antimatter annihilation processes seem to be the most obvious explanation, but carefully avoided by main stream physics. http://astronomy.swin.edu.au/cosmos/G/Gamma+Ray+Burst
The REAL fact of the matter is that chance accumulated both matter and antimatter cosmic objects in the form of nebulae, stars, star-clusters, even whole galaxies are imperatives and an iron necessity of a materialist dialectics/quantum electrodynamics based cosmology. Such annihillation processes are necessary for the manifestation and the dynamics of an infinite, eternal and ever-changing universe! https://www.amazon.com/Dialectical-Universe-Some-Reflections-Cosmology/dp/9840414445
Article Ambartsumian, Arp and the Breeding Galaxies*
https://www.amazon.com/Philosophy-Space-Time-Whence-Cometh-Matter/dp/984041884X