In the hot, dense core of the Sun the process is specifically called the proton--proton chain takes place. The element hydrogen is converted into the element helium. Here is one animation of the process. Here is another. And here is a complete explanation. One of the elusive little sub-atomic particles involved in the proton-proton chain is the neutrino, named by the italian physicist Enrico Fermi. What progress has been made in understanding this strange ‘baby neutron’?