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 Originally Posted by OngBonga
It won't inhibit the fusion, but it surely will inhibit an explosion? An explosion will cause matter to move away from the source of the reaction, which means there is less reactant to fuel further reactions. Gravity binds a reaction together, causing it to continue in a conrolled manner.
You're assuming that only the spent fuel is carried away in the explosion. In general, the explosion will disperse the reactant(s), too, leaving some of it unsploded.
The gravity pulls back everything, the spent fuel (Helium nuclei) and unspent. The 4x as dense Helium nuclei migrate to the center, and block fusion, which migrates to a shell around the "heavy" core. The denser core has a more pronounced effect on the curvature of spacetime, which increases the pressure and fusion rate in the "burning" shell. This continued process of mass migrating to the center and increasing the fusion rate around the core is what turns a nice mid-sized star like the sun into a red giant as it ages.
For bigger stars, the helium can start its own fusion processes, which drops it's Carbon-Nitrogen-Oxygen "ash" to the core, displacing the helium fusion to a shell. The bigger the star, the more shells it will eventually sustain. Each new shell accelerates the rate of fuel consumption and heat and pressure in the core, which all compound to making each new shell's lifespan a fraction of its predecessor's.
If a star is big enough to work its way up the periodic table to iron, then it's supernova time. Iron is the lowest number element on the periodic table for which fusion is endothermic, it absorbs energy. If the fusion process in the center doesn't push back out to maintain the hydrodynamic equilibrium, then gravitational collapse is inevitable. All that in-rushing mass tries to get to the same gravitational center, further increasing the fusion rate of iron, and now the rest of the periodic table, all of it endothermic. Eventually, the pressure is so great and density so great that quantum mechanical forces dominate. The in-rushing mass has accelerated to relativistic speeds and a few crazy and fascinating things can happen at this point. The exact mechanism is not well understood as QM and GR are doing something totally sneaky.
The supernova can leave a white dwarf star formed of electron degenerate matter. An object the mass of the Sun, but the size of the Earth.
It can leave a Neutron Star, a star whose gravity is so great that (nearly) all of the protons and electrons have been forced to bond into neutrons (releasing anti-electron neutrinos in the process.) They're about twice the mass of the Sun, but 10 km in diameter.
It can leave a black hole. You know about those.
Originally Posted by OngBonga
To be fair, I have no idea when it comes to nuclear processes. I deleted a block about surface area, because I wasn't sure how it applied in this regard. Where oxygen is necessary, surface area is critical, and a big sphere has much less surface area relative to volume than a small sphere. For you bog standard explosion, I figure that's an important thing to be thinking about, but fuck know when it comes to nuclear.
Get the fully ionized nuclei moving really fast at each other. If they're moving fast enough, they will tunnel through each other's Coulomb repulsion and the strong nuclear force will bond the small nuclei to make a big nucleus. This increases the total potential energy for small nuclei (up to Iron). The fusion process radiates away this discrepant energy in the form of gamma ray photons (mostly) and neutrinos in the production of neutrons.
Stars accomplish this by being enormously massive and mostly Hydrogen, so that the heat and pressure in the confined volume conspire to make loads of potential fusing nuclei moving the right speed in all directions, so some will be heading right for each other and will tunnel into a fusion bond.
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