The understanding of the nature of the periodic table elements is one of the most studied topics of nuclear astrophysics. There are several nuclear reactions leading to the formation of the periodic table elements. The most common formation process by which different elements are produced in the universe is the fusion of two nuclei to form a heavier one. This process is able to release energy for elements before 56Fe that is the nucleus with the greatest binding energy per nucleon. Beyond this limit, fusion processes require energy from the system to occur. In order to explain the existence of nuclei with A > 60, we need to have a global view of the existence of the various nuclei known to us.
The process by which new atomic nuclei are created from preexisting nucleons is called nucleosynthesis. The initial composition of the universe was established by primordial nucleosynthesis occurred moments after the Big Bang [1]. It was then that H and He, which today are by far the most abundant species in the universe, formed to become the content of the first stars. The nuclear primordial gas was made for 76% of H and D in part much smaller, 24% of 3He and 4He with a prevalence of 4He and traces of 10 parts per million of 7Li and 6Li [2]. With the formation of stars, heavier nuclei (C, O, Na, Mg, Si) were synthesized through fusion reactions, a process that continues today. Some light elements, such as Li, Be and B are formed during the spallation process, which is the interaction between the cosmic rays and C, N, O atoms present in the Interstellar Medium (ISM).
It is currently accepted that stellar nucleosynthesis leads to the formation of heavier elements that astronomers call metals. Metals can be ejected into the ISM in the later stages of stellar evolution, through mass loss episodes. Star formation produces stars which, after a time delay, eject heavy elements into the ISM, including newly synthesised ones in the stellar interiors. Star formation from this enriched material, in turn, results in stars with enhanced abundances of metals. This process occurs repeatedly over time, with the continual recycling of gas, leading to a gradual increase in the metallicity of the ISM with time. Supernovae and compact object mergers are also important to chemical enrichment. They can eject large quantities of enriched material into interstellar space and can themselves generate heavy elements in nucleosynthesis.
The present paper does not concern itself with a general discussion of nucleosynthesis, apart from a few introductory comments, but rather it attempts to survey the recent developments, both experimental and theoretical, which have been attained in nucleosynthesis and nuclear astrophysics. For a complementary analysis, the more interested reader is referred to some recent reviews on this subject [3, 4, 5]. This review is organized as follows: in section 2 Big Bang nucleosynthesis is briefly discussed, with focus on the problem of the primordial Li. This is followed by an overview of the physics of elements production in stars (section 3), paying particular attention to the solar neutrino problem. In the following section 4 we discuss the synthesis of neutron and proton-rich nuclei showing the state of art of the s-, r- and p-process models. The last studies and observations of different astrophysical scenarios (gamma-ray bursts, kilonova) which promise to clarify the origin of the heaviest elements are reviewed in section 4.3.3. Finally, we present the conclusion with some future prospects. A recent review of some of the material covered in this paper is in [6].