Typically these reactions take place between hydrogen and its isotopes. The isotopes of hydrogen (
) are deuterium (D), which has a proton and a neutron in its nucleus (
), and tritium (T) which has one proton and two neutrons (
).
This type of reaction releases much more energy than chemical reactions and even more than fission nuclear reactions. The hydrogen bomb, for example, which is made by fusing a deuterium and a tritium, has a destruction power about 700 times greater than the Hiroshima bomb, which was a fission bomb nuclear.
Nuclear reactions are present in the stars like the stars, including the Sun itself.
Since these reactions take place at high temperatures, the core of stars is the ideal place for them to take place. These are chain reactions, that is, the formed products initiate new reactions and may continue to carry out fusions with other nuclei, and so on.
In the case of stars, it starts with the fusion of two protons, with the formation of a deuterium nucleus (deuteron), a neutron (responsible for releasing energy) and an electron. Later, this formed deuteron fuses with a proton, giving rise to helium-3. This helium-3 fuses with another helium-3 atom and gives rise to helium-4 and two protons. And so on, with the formation of these and other elements. The Sun transforms, at its core, several hundred million tons of helium every second. That's why it is much richer in hydrogen and helium than Earth.
Over time, stars end up dying and, when that happens, some of them eject all the known chemical elements (most of them, in fact, were formed inside the stars themselves). These elements mix with interstellar material to form new stars and other celestial bodies, including planets, like ours, with all their variety of elements; as well as to understand how these reactions are processed and what the composition of these stars made it possible for man to predict their lifetime with greater accuracy; in addition to formulating theories about the emergence of the universe and the elements that compose it, among other data of great human interest.
By Jennifer Fogaça
Graduated in Chemistry
Source: Brazil School - https://brasilescola.uol.com.br/quimica/reacoes-fusao-nas-estrelas.htm