The net effect is shown at right. These reactions can be photoreactions as shown here. At the same time it was clear that oxygen and carbon were the next two most common elements, and also that there was a general trend toward high abundance of the light elements, especially those Nucleosynthesis hydrogen helium of whole numbers of helium-4 nuclei.
It is now known that the elements observed in the Universe were created in either of two ways. But BBFH could not produce enough helium. Hydrogen fusion nuclear fusion of four protons to form a helium-4 nucleus  is the dominant process that generates energy in the cores of main-sequence stars.
The BBFH theory, as it came to be known, postulated that all the elements were produced either in stellar interiors or during supernova explosions.
This high percentage of helium argues strongly for the big bang model, since other Nucleosynthesis hydrogen helium gave very small percentages of helium.
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.
Data from Boesgaard, A. This would bring all the mass of the Universe to a single point, a "primeval atom", to a state before which time and space did not exist.
Because of the very short period in which nucleosynthesis occurred before it was stopped by expansion and cooling about 20 minutesno elements heavier than beryllium or possibly boron could be formed. FowlerAlastair G. The half-life of the neutron is seconds.
After 1 second, the only reaction that appreciably changes the number of neutrons is neutron decay, shown at right. This can then form oxygen, neon, and heavier elements via the alpha process. Claytonfollowed by many others. Thanks to the pioneering efforts of George Gamow and his collaborators, there now exists a satisfactory theory as to the production of light elements in the early Universe.
Eventually the temperature gets so low that the electrostatic repulsion of the deuterons causes the reaction to stop. If it had been slower, more of the free neutrons would have decayed before the deuterium stability point and there would be less helium.
The ratio of the number of baryons per photon was one of the contributions of the discovery of the 3K background radiation. In this way, the alpha process preferentially produces elements with even numbers of protons by the capture of helium nuclei. Star formation has occurred continuously in galaxies since that time.
After helium is exhausted in the core of a star, it will continue in a shell around the carbon-oxygen core. Helium fusion first begins when a star leaves the red giant branch after accumulating sufficient helium in its core to ignite it. These processes began as hydrogen and helium from the Big Bang collapsed into the first stars at million years.
The nuclei of these elements, along with some 7Li and 7Be are considered to have been formed between and seconds after the Big Bang when the primordial quark—gluon plasma froze out to form protons and neutrons. In the years immediately before World War II, Hans Bethe first elucidated those nuclear mechanisms by which hydrogen is fused into helium.
The subsequent nucleosynthesis of the heavier elements requires the extreme temperatures and pressures found within stars and supernovas. This graph is a corrected version of one from this LBL page.Which shows the correct order of events during the process of nucleosynthesis billsimas.comen nucleus formed,isotope of hydrogen tritum formed,helium nucleus formed/5(9).
After the hydrogen in the star's core is exhausted, the star can burn helium to form progressively heavier elements, carbon and oxygen and so on, until iron and nickel are formed. Up to this point the process releases energy.
The Big Bang Nucleosynthesis theory predicts that roughly 25% the mass of the Universe consists of Helium. It also predicts about % deuterium, and even smaller quantities of lithium.
The important point is that the prediction depends critically on the density of baryons (ie neutrons and protons) at the time of nucleosynthesis. Stellar nucleosynthesis is the process by which elements are created within stars by combining the protons and neutrons together from the nuclei of lighter elements.
All of the atoms in the universe began as hydrogen. Fusion inside stars transforms hydrogen into helium, heat, and radiation. Big Bang Nucleosynthesis Gamow, Alpher and Herman proposed the hot Big Bang as a means to produce all of the elements. However, the lack of stable nuclei with atomic weights of 5 or 8 limited the Big Bang to producing hydrogen and helium.
In the years immediately before World War II, Hans Bethe first elucidated those nuclear mechanisms by which hydrogen is fused into helium. Fred Hoyle's original work on nucleosynthesis of heavier elements in stars, occurred just after World War II.
His work explained the production of all heavier elements, starting from hydrogen.Download