A star dies when it runs out of fuel to burn, how quickly this happens depends on. The mass is related to the amount of fuel available. The luminosity is related to the rate at which the fuel is used up (rate of nuclear. We can build models of stars that show how they will evolve for a given mass and luminosity. The sun ~ 4. 5 billion years old. When the barrier is overcome by quantum tunneling the two nuclei get close enough to be fused together by the strong force this is nuclear fusion. Without tunnelling chance of nuclear fusion is miniscule, with it hydrogen collisions will result in fusion, but there are so many atoms that this happens a lot. 1 kg of hydrogen in 0,933 kg of helium out. Results in same amount of energy released from burning 20,000 tons of coal. Star formation: competition between gravity and pressure.