What happens when star fuel tritium and deuterium extinguishes?

Answer 1

A star goes through the following primary fusion processes in its life:

1. proton-proton burning, H + H --> D + e+ + νe + 0.42 MeV; followed by deuterium-proton burning, D + H --> He3 + γ + 5.49 MeV; followed by helium-3 burning, He3 + He3 --> He + H + H + 12.86 MeV; this reaction chain is followed 86% of the time in a typical main line star, the other 3 proton-proton burning reaction chains are rarer but all yield ordinary helium-4. (at no point does the star conduct DT burning, it just eventually runs out of ordinary hydrogen-1)
2. when the star runs out of hydrogen to burn it must switch to a process called triple alpha burning, He + He + He --> C12 + e+ + e− + 7.275 MeV; to do this its core contracts until the pressure and temperature are high enough to ignite triple alpha burning, the extra energy release causes the outer layers of the star to expand and cool, it has left the main line and become a red giant
3. when the red giant runs out of helium to burn its core collapses further, igniting additional reactions (see links for details)

Answer 2

When tritium and deuterium combine and burn as fuel in a star, they undergo nuclear fusion to produce helium and release a huge amount of energy in the form of light and heat. Once the fuel is depleted, the star's core will contract under its own gravity, causing a change in its structure and potentially leading to the star's eventual evolution into a white dwarf, neutron star, or black hole depending on its mass.