Both theory and observation lead astronomers to believe this to be the case. In higher-mass stars, the dominant energy production process is the CNO cyclewhich is a catalytic cycle that uses nuclei of carbon, nitrogen and oxygen as intermediaries and in the end produces a helium nucleus as with the proton-proton chain.
Gradually it became clear that hydrogen and helium are much more abundant than any of the other elements. This creates a helium-4 nucleus through a sequence of chain reactions that begin with the fusion of two protons to form a deuterium nucleus one proton plus one neutron along with an ejected positron and neutrino.
A star gains heavier elements by combining its lighter nuclei, hydrogendeuteriumberylliumlithiumand boronwhich were found in the initial composition of the interstellar medium and hence the star.
Processes[ edit ] There are a number of astrophysical processes which are believed to be responsible for nucleosynthesis.
Elements formed during this time were in the plasma state, and did not cool to the state of neutral atoms until much later. It is now known that the elements observed in the Universe were created in either of two ways. Synthesis of these elements occurred either by nuclear fusion including both rapid and slow multiple neutron capture or to a lesser degree by nuclear fission followed by beta decay.
Triple-alpha process and Alpha process Main sequence stars accumulate helium in their cores as a result of hydrogen fusion, but the core does not become hot enough to initiate helium fusion.
They fuse helium until the Nucleosynthesis in stars is largely carbon and oxygen. Hoyle proposed that hydrogen is continuously created in the universe from vacuum and energy, without need for universal beginning.
The difference in energy production of this cycle, compared to the proton—proton chain reaction, is accounted for by the energy lost through neutrino emission. In stars around the mass of the sun, this begins at the tip of the red giant branch with a helium flash from a degenerate helium core and the star moves to the horizontal branch where it burns helium in its core.
This can then form oxygen, neon, and heavier elements via the alpha process. Some of those others include the r-processwhich involves rapid neutron captures, the rp-processand the p-process sometimes known as the gamma processwhich results in the photodisintegration of existing nuclei.
In the years immediately before World War II, Hans Bethe first elucidated those nuclear mechanisms by which hydrogen is fused into helium. Further support comes from the consistency of the other light element abundances for one particular baryon density and an independent measurement of the baryon density from the anisotropies in the cosmic microwave background radiation.
Most of the deuterium then collided with other protons and neutrons to produce helium and a small amount of tritium one proton and two neutrons. The primary stimulus to the development of this theory was the shape of a plot of the abundances versus the atomic number of the elements.Big Bang Nucleosynthesis The Universe's light-element abundance is another important criterion by which the Big Bang hypothesis is verified.
It is now known that the elements observed in the Universe were created in either of two ways. The development of new observational, experimental, and computational technologies is changing our understanding of the origins of the elements by thermonuclear burning in stars. Gamma-ray lines from newly made radioactive nuclei have been identified using instruments onboard low-Earth orbiting satellites.
Grains in meteorites have isotopic anomalies which suggest that the grains were put. Nov 12, · Explanation of element formation through Big Bang Nucleosynthesis, Stellar Nucleosynthesis, and Supernovae Nucleosynthesis. The elements that are formed in each type of Nucleosynthesis and the characteristics required for each type.
Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the heavier elements. The processes involved began to be understood early in. The subsequent nucleosynthesis of the elements (including all carbon, all oxygen, etc.) occurs primarily in stars either by nuclear fusion or nuclear fission.
Note: The above text is excerpted from the Wikipedia article " Nucleosynthesis ", which has been released under the GNU Free Documentation License. A star's energy comes from the combining of light elements into heavier elements in a process known as fusion, or "nuclear burning".
It is generally believed that most of the elements in the universe heavier than helium are created, or synthesized, in stars when lighter nuclei fuse to make heavier nuclei.
The process is called nucleosynthesis.Download