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In the center of most stars, hydrogen fuses together to form helium. Fusion in stars releases so much heat that the process alone keeps their mass from collapsing in on itself due to [[gravity]]. It is the reason that stars are so stable as well. If the core of a star starts to collapse, more fusion reactions occur and it expands again from the heat. If the core expands too far, less fusion reactions occur and it collapses back down.

In the center of most stars, hydrogen fuses together to form helium. Fusion in stars releases so much heat that the process alone keeps their mass from collapsing in on itself due to [[gravity]]. It is the reason that stars are so stable as well. If the core of a star starts to collapse, more fusion reactions occur and it expands again from the heat. If the core expands too far, less fusion reactions occur and it collapses back down.

Scientists here on earth are trying to make nuclear fusion in the laboratory a useful energy source. Uncontrolled fusion causes thermonuclear explosions, which are used in the [[hydrogen bomb]].  

Scientists here on earth are trying to make nuclear fusion in the laboratory a useful energy source. One example is the European Toroidal Reactor near Cambridge in England. Uncontrolled fusion causes thermonuclear explosions, which are used in the [[hydrogen bomb]].  

== Sources ==

== Sources ==