In the core of the Sun, hydrogen atoms are fused together in a process called nuclear fusion. This process combines the atomic nuclei of hydrogen atoms to form helium, releasing enormous amounts of energy in the form of light and heat.

More specifically, the process of hydrogen fusion in the Sun can be described as follows:

* Two protons, which are positively charged particles found in the nuclei of hydrogen atoms, overcome their natural repulsion and fuse together.

* This fusion process requires extremely high temperatures and pressures that exist in the Sun's core.

* As the protons fuse, they release energy and form a deuteron, which consists of one proton and one neutron.

* The deuteron then fuses with another proton to form a helium-3 nucleus, releasing more energy.

* Finally, two helium-3 nuclei can combine to form a helium-4 nucleus (the most common form of helium), with the release of two protons and more energy.

This sequence of reactions is known as the proton-proton chain reaction and is the dominant mechanism of energy production in stars like our Sun. The immense energy released from these fusion reactions sustains the Sun's immense luminosity and counteracts the gravitational force that would otherwise cause the Sun to collapse under its own weight.