Stellar nucleosynthesis is the nucleosynthesis of chemical elements by nuclear fusion reactions in stars. The theory was proposed by Fred Hoyle in 1946. 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.