How can we assert $\mathrm{ matter } / \mathrm{ antimatter } \gg 1$ further than $locally$?

Question

I read many hypothesis to explain the asymmetry between the quantity of matter and antimatter in the universe, most notably through an asymmetry in initial baryogenesis. This assymetry would explain that now matter is in much higher quantity than matter. Asymmetry that I tried to express as { matter } / { antimatter } $\gg$ 1 or $ {N_B} / {N_\bar{B}} \gg 1$.

What permit to assert, to measure this asymmetry if the spectrum of antimatter stellar objects would be indistinguishable from the spectrum of matter ones?

Is the spectrum of matter and antimatter different?

What permit to assert a galaxy is made of matter and not of antimatter?

If there is no evidence, why so many physicists (Sakharov…) work on an explanation of "scarcity" of antimatter?

My personnal fast analysis point of vue is that we didn't take enough into account the fact that as an observer we aren't in a free position to make a correct measure of matter / antimatter received. We are here in the center of a solar system, a galaxy made essentially of matter. This local huge amount of matter is a natural absorbing filter which will stop most of the antimatter cosmic rays reaching us (the observer).

I would say we are like an observer who would look at the sun through a yellow filter and would conclude that the sun has a spectrum with a black ray on yellow.

Answer 1

Is the spectrum of matter and antimatter different?

It is in interactions that one can know whether some celestial object is made of matter as the earth or of antimatter. When matter meets antimatter there is release of specific gamma energies , as in electron positron annihilation to two gamma rays.

All the observational data from astrophysics lead to the conclusion that in the observable universe matter dominates by orders of magnitude.

1) a probe landed on a comet , no explosion,

2) cosmic rays from sun and the galaxy are predominantly matter

3)there is no dominant signal in cosmic gamma rays of electron positron annihilation that would happen in the boundary of galaxies and clusters of galaxies if they were composed of different matter content.

So it is an observational fact that the observable universe is dominated by matter, and the explanation is a matter of research still.

What permit to assert a galaxy is made of matter and not of antimatter?

The interface at the edges between galaxies, (space is never completely empty of matter) would radiate with the specific annihilation signals in the gamma ray spectra.

If there is no evidence, why so many physicists (Sakharov…) work on an explanation of "scarcity" of antimatter?

The evidence was listed above.

See also my answer here.