Stellar evolution Carbon-burning process

during helium fusion, stars build inert core rich in carbon , oxygen. inert core reaches sufficient mass collapse due gravitation, whilst helium burning moves gradually outward. decrease in inert core volume raises temperature carbon ignition temperature. raise temperature around core , allow helium burn in shell around core. outside shell burning hydrogen. resulting carbon burning provides energy core restore star s mechanical equilibrium. however, balance short-lived; in star of 25 solar masses, process use of carbon in core in 600 years. duration of process varies depending on mass of star.

stars below 8–9 solar masses never reach high enough core temperature burn carbon, instead ending lives carbon-oxygen white dwarfs after shell helium flashes gently expel outer envelope in planetary nebula.

in stars masses between 8 , 11 solar masses, carbon-oxygen core under degenerate conditions , carbon ignition takes place in carbon flash, lasts milliseconds , disrupts stellar core. in late stages of nuclear burning develop massive stellar wind, ejects outer envelope in planetary nebula leaving behind o-ne-na-mg white dwarf core of 1.1 solar masses. core never reaches high enough temperature further fusion burning of heavier elements carbon.

stars more 11 solar masses start carbon burning in non-degenerate core, , after carbon exhaustion proceed neon-burning process once contraction of inert (o, ne, na, mg) core raises temperature sufficiently.