Stars the size of the Sun or smaller gain their energy from a nuclear reaction called the proton – proton reaction.
Two protons, which are the nuclei of Hydrogen atoms, collide with each other. Very occasionally the atoms will stick together, this happens on the order of once in a billion years or so. One of the protons turns into a neutron and emits a positron, which is identical to an electron but has a positive charge, and a neutrino which is a particle with no electric charge and almost no mass. The positron eventually collides with an electron and both particles vanish in a burst of gamma rays.
The proton and neutron are soon joined to another proton forming a Helium 3 nucleus and another burst of gamma rays.
If you are not familiar with atoms, protons, electrons etc you may wish to read our tutorial “A little about atoms”.
Sun-like stars.
SUN-LIKE STARS
After another million years or so the Helium 3 nucleus is joined by another Helium 3 nucleus from another reaction forming a Helium 4 nucleus with two protons left over. These protons are then available to start another reaction.
The result of this reaction is energy in the form of gamma rays and Hydrogen nuclei (protons) being turned into Helium 4 nuclei.
Over billions of years Hydrogen is used up and Helium starts to accumulate in the core of the star. As the Hydrogen is depleted the proton-proton reaction dies out. The outward pressure caused by the energy released in the reaction decreases and the core begins to collapse. As it does it heats up and the temperature reaches 100 million degrees.
This higher temperature allows a new reaction called the triple alpha process to start.
POWERING A STAR 1