Editing Stellar evolution (section)

===Main sequence stellar mass objects===
{{Main|Main sequence}}
{{Annotated image|image-width=325|width=325
|caption=The evolutionary tracks of [[stars]] with different initial masses on the [[Hertzsprung–Russell diagram]]. The tracks start once the star has evolved to the [[main sequence]] and stop when [[Nuclear fusion|fusion]] stops (for massive stars) and at the end of the [[red-giant branch]] (for stars {{solar mass|1}} and less).<ref>{{harvtxt|Prialnik|2000|loc=Fig. 8.19, p. 174}}</ref><br/>A yellow track is shown for the [[Sun]], which will become a [[red giant]] after its main-sequence phase ends before expanding further along the [[asymptotic giant branch]], which will be the last phase in which the Sun undergoes fusion.
|imagemap=
<imagemap>
Image:Zams and tracks.png|325px
poly 380 230 780 530 750 560 350 260 [[Main Sequence]]
desc none
</imagemap>
|annotations=
{{Annotation|65|45|[[Wolf-Rayet star|WR]]}}
{{Annotation|170|35|[[Luminous blue variable|LBV]]}}
{{Annotation|230|35|[[Yellow hypergiant|YHG]]}}
{{Annotation|130|45|[[Blue supergiant|BSG]]}}
{{Annotation|270|65|[[Red supergiant|RSG]]}}
{{Annotation|290|100|[[Asymptotic giant branch|AGB]]}}
{{Annotation|270|130|[[Red giant|RG]]}}
}}
For a more-massive protostar, the core temperature will eventually reach 10 million [[kelvin]], initiating the [[proton–proton chain reaction]] and allowing [[hydrogen]] to fuse, first to [[deuterium]] and then to [[helium]]. In stars of slightly over {{convert|1|solar mass|kg|abbr=on}}, the carbon–nitrogen–oxygen fusion reaction ([[CNO cycle]]) contributes a large portion of the energy generation. The onset of nuclear fusion leads relatively quickly to a [[hydrostatic equilibrium]] in which energy released by the core maintains a high gas pressure, balancing the weight of the star's matter and preventing further gravitational collapse. The star thus evolves rapidly to a stable state, beginning the [[main sequence|main-sequence]] phase of its evolution.

A new star will sit at a specific point on the main sequence of the [[Hertzsprung–Russell diagram]], with the main-sequence [[spectral type]] depending upon the mass of the star. Small, relatively cold, low-mass [[red dwarf]]s fuse hydrogen slowly and will remain on the main sequence for hundreds of billions of years or longer, whereas massive, hot [[O-type main-sequence star|O-type stars]] will leave the main sequence after just a few million years. A mid-sized [[G-type main-sequence star|yellow dwarf]] star, like the Sun, will remain on the main sequence for about 10 billion years. The Sun is thought to be in the middle of its main sequence lifespan.