I'm new to the forum, and I am just gonna jump straight into a few questions regarding fusion in main sequence stars that I hope you guys may elucidate for me:
1) In the first step of proton-proton process involves taking two protons and make a deuteron, while releasing a positron and neutrino in the process. As far as I understand, both the positron and neutrino are matter and not pure energy (like photon in the gamma radiation). But since the positron will most likely annihilate with a free flying electron very soon after it's released, does this energy get counted towards "energy created" in the overall proton-proton fusion process?
2) The mass of a neutron is heavier than that of a proton - so how do two proton come together to form a deuteron yet still have enough excess energy to release a positron and neutrino in the process? Does this have anything to do with the kinetic energy of the fast-moving protons before them combine into a deuteron?
3) The CNO cycle can happen in main sequence stars when the core reaches a certain temperature. However, the proton-proton fusion only generates helium as its by product; carbon, nitrogens, and oxygens are not created until later in the life of a star where it's hot enough in the core to conduct helium fusion. How do stars early in the main sequence have access to C, N and O - are they already present in the interstellar medium before the protostar is even formed? If that's the case, is it correct in thinking that main sequence stars that can perform CNO cycle can only born out of the remnants of a previously dead/failed/exploded star?