What is the first event that happens to a star with roughly the mass of our Sun that exhausts the hydrogen in its core and stops the generation of energy by the nuclear fusion of hydrogen to helium? Order the sequence of events that the star undergoes. First 1 As it grows, its outer layers cool off and the star becomes a red giant 2 Energy from all the fusion in this growing layer (or shell) then pours outward. 3 The inert core begins to collapse due to gravity and to increase in temperature and pressure 4 The increasing temperature then heats the surrounding layers of hydrogen until nuclear fusion can start within them 5 The star than begins to swell in size 6 When all the hydrogen that's hot enough to fuse into helium has been turned into helium, the star's core no longer has a source of energy Last