It occurred to me today, that part of the reason for shrinkage of galaxies is likely due to the fusion of hydrogen into helium.
Prior to this idea, I was thinking that galaxy shrinkage occurred because of an unknown shrinkage mechanism of atoms, which is unlikely according to physics.
The helium to hydrogen shrinkage idea is simpler, and what I'll go with for now...
"Hydrogen, as deuterium and tritium atoms, fuse to
helium, here matter disappears and enormous quantities of energy
are released (E=mc2)."Also, black hole consumption of matter should account for galaxy shrinkage. It is not yet determined what amount of galaxy shrinkage is accounted for by each phenomenon.
Calculations according to data accumulated will have to be created.