Philosophy Now Forum

QuantumT wrote: ↑Wed May 23, 2018 8:23 pm Well, I don't mean that the deuterium atoms still are intact inside the star, but they are the building blocks of it. They were atoms before they became a star.

Any particular building block was in the form of deuterium for only a short time. It turns out that neutron stars are made of (wait for it...) neutrons! Most of them did not exist back when the star was still a normal burning star, so it is a stretch to say that they are the building blocks of it. A young star is built from mostly protons and electrons, very few of which remain in a neutron star.

Noax wrote: ↑Wed May 23, 2018 10:40 pm Any particular building block was in the form of deuterium for only a short time. It turns out that neutron stars are made of (wait for it...) neutrons! Most of them did not exist back when the star was still a normal burning star, so it is a stretch to say that they are the building blocks of it. A young star is built from mostly protons and electrons, very few of which remain in a neutron star.

Let's remember it's all theories. We never examined a neutron star. We just imagine how they came to be, and what they're made of, based on the light emitting from them.
Neutron stars is a "modern" phenomena in the universe. Modern meaning atleast half a dozen billion years older than TBB. Neutrons does not exist on their own, so they must have come from atoms containing them, right? Thus deuterium. The simplest and richest source of neutrons in the universe.

I might be wrong. Astro physics is not my stronghold. Quantum mechanics is. But to me it seems like an elegant explanation.

QuantumT wrote: ↑Wed May 23, 2018 11:35 pm Neutrons does not exist on their own, so they must have come from atoms containing them, right? Thus deuterium. The simplest and richest source of neutrons in the universe.

Since you asked, I looked it up. The early universe consisted of almost all hydrogen and a bit of helium. Stars burn that hydrogen, not deuterium, since there is hardly any of it. A rich source it is not. The vast majority of neutrons are manufactured in stars, not acquired by them.

There are two main reactions that stars use to consume hydrogen: Proton-proton chain reactions and CNO cycles. The former dominates in smaller stars, and the latter in larger ones. but both process occur in all hot stars. Both reactions manufacture two neutrons that did not exist before.

The proton-proton reaction is more dominant in a smaller star like our own. The threshold is apparently 1.3 solar masses.
Picture is here: https://en.wikipedia.org/w/index.php?ti ... he_Sun.svg
6 protons (regular hydrogen) come in, two go out, plus a Helium which has the two manufactured neutrons. Also two each of positrons, neutrinos, and gamma rays result from the reaction. The two positrons annihilate two electrons, preserving the charge change when two protons were changed into neutrons. I see a deuterium nucleus that exists very briefly in this reaction, which almost immediately changes into Helium-3.

CNO cycle is illustrated in this picture: https://en.wikipedia.org/wiki/File:CNO_Cycle.svg
This one is a catalytic loop. Four protons (hydrogen nuclei) enter the cycle, and one Helium exits (two protons, two manufactured neutrons). The neutrons are manufactured one at a time, on the right when the unstable N13 decays into C13, and again on the left when the unstable O15 decays into N15. The same additional particles result, except I see three gamma rays this time, not two. There is no deuterium anywhere in this cycle.
Large stars that eventually become neutron stars initially manufacture a lot of neutrons this way. The vast majority of neutrons are manufactured in the supernova event when the star actually transitions to a neutron star, and it is done by just compressing the electrons into the protons to directly form a liquid neutron soup that is not matter consisting of ordinary atoms at all.