What is Stellar nucleosynthesis?
'''Stellar nucleosynthesis''' is the [[nucleosynthesis|creation (nucleosynthesis)]] of [[Chemical element|chemical elements]] by [[nuclear fusion]] [[Chemical reaction|reactions]] in [[Star|stars]]. This fusion reaction also creates the stars' light and heat. The theory was proposed by [[Fred Hoyle]] in 1946.<ref>{{Cite journal|last=Hoyle|first=F.|date=1946-10-01|title=The Synthesis of the Elements from Hydrogen|url=https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/106.5.343|journal=Monthly Notices of the Royal Astronomical Society|language=en|volume=106|issue=5|pages=343–383|doi=10.1093/mnras/106.5.343|issn=0035-8711}}</ref> [[Stellar evolution|Stars evolve]] because of changes in what they are made up of throughout their life. However, this does not by itself change the amount of elements in the [[universe]]. Later in its life, a low-mass star will slowly release its atmosphere through [[solar wind]], forming a [[planetary nebula]]. A high-mass star will release [[mass]] through a [[supernova]]. ==Hydrogen fusion== {{multiple image | align = right | direction = vertical | width = 300 | image1 = Fusion in the Sun.svg | caption1 = '''Proton–proton chain reaction''' | image2 = CNO Cycle.svg | caption2 = '''CNO-I cycle'''<br />The helium nucleus is released at the top-left step. }} Hydrogen fusion is the main process that makes energy in [[main sequence]] stars. Stars of all masses start on the main sequence.<ref>Seeds, M. A., ''Foundations of Astronomy'' ([[Belmont, California|Belmont, CA]]: Wadsworth Publishing Company, 1986), p. 245.</ref>{{rp|245}} Hydrogen fusion combines four [[proton]]s, which are hydrogen-1 nuclei, to make a helium-4 nucleus. In doing this, the star must convert two protons into neutrons. Less massive stars, such as the Sun, use the ''proton-proton chain reaction''. It starts with a [[collision]] of two protons. One of them becomes a [[neutron]] (after it releases a positively-charged [[positron]]). This creates a hydrogen-2 nucleus. Next, it collides with an