Molecular clouds b. Dust lanes 4. Hydrogen clouds heat up enough from outside light that nuclear fusion can begin b. Large interstellar clouds collapse under their own gravity and break up c. A protostar which is warm enough to emit infrared light, but not yet hot enough for hydrogen burning 8.
Excess helium builds up from nuclear fusion in the core and pushes outward d.
Hydrogen burning in a shell around the core creates extra pressure, which overcomes gravity 9. Expelled outer envelope of a star, ejected when helium fusion stops 10. Red giant 11. A binary system consists of a main sequence star and a white dwarf. After accreting hydrogen and burning it off many times, the white dwarf accumulates enough matter to burn carbon.