Starship Asterisk*

THX1138 wrote:
As any given star is busily fusing hydrogen into helium and or helium into carbon thus keeping its outer layers from collapsing. Are there like hundreds or thousands of different nuclear explosions going on in its core, thus keeping its outer layers afloat (so to speak). Or is there just single very large nuclear detonations going off one after the other in the core creating the pressure that keeps it's outer layers from collapsing. Or is my idea of what's going on in a stars core wrong altogether in both of my descriptions

• Numerous individual miniscule nuclear explosions are going on in its core;
  each one releasing ~0.0042 nanojoules of thermal energy to keep the core hot.
  (One nanojoule is about 1/160 the kinetic energy of a flying mosquito.)

https://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain_reaction#The_pp_chain_reaction wrote:

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<<In the Sun, with a 10-million-kelvin core, hydrogen fuses to form helium in the proton-proton chain reaction. The first step involves the fusion of two ¹H nuclei (protons) into deuterium, releasing a positron and a neutrino as one proton changes into a neutron. It is a two-stage process; first, two protons fuse to form a diproton:

• ¹H + ¹H → ²He

followed by the beta-plus decay of the diproton to deuterium:

• ²He → ²H + e⁺ + ν_e

with the overall formula:

¹H + ¹H → ²H + e⁺ + ν_e + 0.42 MeV

This first step is extremely slow because the beta-plus decay of the diproton to deuterium is extremely rare (the vast majority of the time, the diproton decays back into hydrogen-1 through proton emission). The half-life of a proton in the core of the Sun before it is involved in a successful p-p fusion is estimated to be a billion years, even at the extreme pressure and temperatures found there.

The positron emitted by the beta-decay almost immediately annihilates with an electron; their mass energy plus their kinetic energy is carried off by two gamma rays (photons).

• e⁺ + e^- → 2γ (2 x 0.51 MeV)

After it is formed, the deuterium produced in the first stage can fuse with another proton to produce a light isotope of helium, ³He:

• ¹H + ²H → ³He + γ + 5.49 MeV

This process, mediated by the strong nuclear force rather than the weak force, is extremely fast by comparison to the first step. It is estimated that, under the conditions in the Sun's core, each newly created deuterium nucleus exists for only about 4 seconds before it is converted to ³He.

From here there are four possible paths to generate ⁴He. In the Sun, ⁴He is mostly synthesised via branch pp I:

• 2³He → ⁴He + 2¹H + 12.86 MeV

The complete pp I chain reaction releases a net energy of 26.732 MeV. Two percent of this energy is lost to the neutrinos that are produced.

Energy released as gamma rays will interact with electrons and protons and heat the interior of the Sun. Also kinetic energy of fusion products (e.g. of the two protons and the ⁴He) increases the temperature of plasma in the Sun. This heating supports the Sun and prevents it from collapsing under its own weight.

Neutrinos do not interact significantly with matter and therefore do not help support the Sun against gravitational collapse. Their energy is lost. The energy released by this reaction is in millions of electron volts, which is actually only a tiny amount of energy. However enormous numbers of these reactions occur constantly, producing all the energy necessary to sustain the star's radiation output. In comparison, the combustion of two hydrogen gas molecules with one oxygen gas molecule releases only 5.7 eV.>>