Elements beyond iron are made in large stars with slow neutron capture s-process. Elements heavier than iron may be made in neutron star mergers or supernovae after the r-process. It is thought that the primordial nucleons themselves were formed from the quark—gluon plasma during the Big Bang as it cooled below two trillion degrees.
A few minutes afterwards, starting with only protons and neutrons , nuclei up to lithium and beryllium both with mass number 7 were formed, but hardly any other elements.
Some boron may have been formed at this time, but the process stopped before significant carbon could be formed, as this element requires a far higher product of helium density and time than were present in the short nucleosynthesis period of the Big Bang. That fusion process essentially shut down at about 20 minutes, due to drops in temperature and density as the universe continued to expand. This first process, Big Bang nucleosynthesis , was the first type of nucleogenesis to occur in the universe.
The subsequent nucleosynthesis of the heavier elements requires the extreme temperatures and pressures found within stars and supernovas. These processes began as hydrogen and helium from the Big Bang collapsed into the first stars at million years. Star formation has occurred continuously in galaxies since that time. Among the elements found naturally on Earth the so-called primordial elements , those heavier than boron were created by stellar nucleosynthesis and by supernova nucleosynthesis.
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. A star gains heavier elements by combining its lighter nuclei, hydrogen , deuterium , beryllium , lithium , and boron , which were found in the initial composition of the interstellar medium and hence the star.
Interstellar gas therefore contains declining abundances of these light elements, which are present only by virtue of their nucleosynthesis during the Big Bang. Larger quantities of these lighter elements in the present universe are therefore thought to have been restored through billions of years of cosmic ray mostly high-energy proton mediated breakup of heavier elements in interstellar gas and dust. The fragments of these cosmic-ray collisions include the light elements Li, Be and B.
Later, subsequent beta decays will transform then into the heavy elements that we know. The temperature will rise even more until the new fusion reaction of nuclei begin until the production of iron iron isreached. Iron together with nickel which is next to it , are the nuclide with the greatest nuclear stability.
The ultimate fusion reactions that lead to iron can only occur within the central core of stars much larger than the sun. Beyond iron, nature uses a different known mechanism to synthesize the heaviest nuclei Gold , silver, lead, uranium. This mechanism occurs at the last stage of the life of very massive stars, which ends with an explosion. The star becomes very bright: a supernova.
The dispersion of the stellar material The Crab nebula is the remnant of a supernova explosion that occurred years ago in our galaxy and that has been observed on Earth in by Chinese astronomers and Navajo. The supernova phenomenon is due to the explosion of a big star at the end of life. During such explosions are produced by a rapid succession of neutron captures, elements heavier than iron, such as platinum, gold or uranium.
March Learn how and when to remove this template message Deuterium is in some ways the opposite of helium-4, in that while helium-4 is very stable and difficult to destroy, deuterium is only marginally stable and easy to destroy. The temperatures, time, and densities were sufficient to combine a substantial fraction of the deuterium nuclei to form helium-4 but insufficient to carry the process further using helium-4 in the next fusion step.
BBN did not convert all of the deuterium in the universe to helium-4 due to the expansion that cooled the universe and reduced the density, and so cut that conversion short before it could proceed any further. One consequence of this is that, unlike helium-4, the amount of deuterium is very sensitive to initial conditions. The denser the initial universe was, the more deuterium would be converted to helium-4 before time ran out, and the less deuterium would remain.
There are no known post-Big Bang processes which can produce significant amounts of deuterium. Hence observations about deuterium abundance suggest that the universe is not infinitely old, which is in accordance with the Big Bang theory. During the s, there were major efforts to find processes that could produce deuterium, but those revealed ways of producing isotopes other than deuterium.
The problem was that while the concentration of deuterium in the universe is consistent with the Big Bang model as a whole, it is too high to be consistent with a model that presumes that most of the universe is composed of protons and neutrons. If one assumes that all of the universe consists of protons and neutrons, the density of the universe is such that much of the currently observed deuterium would have been burned into helium Such a process would require that the temperature be hot enough to produce deuterium, but not hot enough to produce helium-4, and that this process should immediately cool to non-nuclear temperatures after no more than a few minutes.
Stars have a layered structure - nuclear fusion reactions take place in the inner, hotter regions, but not in the outermost layers. When the first stars formed millions of years later, a new type of nucleosynthesis began that builds up heavier elements by fusing lighter elements together in the cores of the stars. Specifically, the theory yields precise quantitative predictions for the mixture of these elements, that is, the primordial abundances at the end of the big-bang. As the diagram indicates, the conservative estimate derived from the observations covers a very large range of possible values for eta, which is consistent both with the prediction and with the WMAP determination of eta. Therefore, the composition of the outermost layers should indicate the element abundances for the matter from which a star has formed.
Fortunately for astronomers, there are indicators of how much chemical evolution particular objects have undergone, most importantly the presence of elements such as oxygen and nitrogen. There are no known post-Big Bang processes which can produce significant amounts of deuterium. The earliest nucleosynthesis took place for only a few minutes following the big bang that began the universe, creating nuclei of hydrogen each hydrogen nucleus has 1 proton and of helium 2 protons and a tiny amount of lithium 3 protons. In order to test these predictions, it is necessary to reconstruct the primordial abundances as faithfully as possible, for instance by observing astronomical objects in which very little stellar nucleosynthesis has taken place such as certain dwarf galaxies or by observing objects that are very far away, and thus can be seen in a very early stage of their evolution such as distant quasars. It is thought that the primordial nucleons themselves were formed from the quark—gluon plasma during the Big Bang as it cooled below two trillion degrees.
Nucleosynthesis Mechanisms of atomic nuclei formation Most of the nuclei of atoms that make up our daily life were formed in the furnace of stars, and for others during violent stellar cataclysms.
Fortunately for astronomers, there are indicators of how much chemical evolution particular objects have undergone, most importantly the presence of elements such as oxygen and nitrogen. Nucleosynthesis Mechanisms of atomic nuclei formation Most of the nuclei of atoms that make up our daily life were formed in the furnace of stars, and for others during violent stellar cataclysms.
The second reason for researching non-standard BBN, and largely the focus of non-standard BBN in the early 21st century, is to use BBN to place limits on unknown or speculative physics.
If such a cloud is sufficiently hot, certain atomic reactions involving helium atoms more precisely, helium atoms regaining an electron they had previously lost lead to characteristic emissions of electromagnetic radiation at precisely defined frequencies.
Star formation has occurred continuously in galaxies since that time. While the helium-3 content can only be determined with substantial uncertainty, the results appear to be the same for all regions, whatever their distance to the galactic center. Fortunately, it appears that there are some objects in the universe - even in our own galaxy! Then, other light nuclei are formed among them carbon and oxygen. One can insert a hypothetical particle such as a massive neutrino and see what has to happen before BBN predicts abundances that are very different from observations. Any light that reaches us from those quasars shows us the universe as it was about ten billion years ago.
Consequently, these fusion processes can only destroy, but never produce deuterium. In order to infer the primordial helium-4 abundance, astronomers turn to certain dwarf galaxies. The minimum temperature required for the fusion of hydrogen is 5 million degrees. Timeline[ edit ] Periodic table showing the origin of each element.
The pressure of this radiation prevents the star from contracting further. Only some combinations of protons and neutrons are stable. These fusion reactions release energy, which radiates some form of light and heat. Burbidge , Fowler and Hoyle  is a well-known summary of the state of the field in
Overall, Big Bang Nucleosynthesis is strongly supported by observations. Given current models of stellar evolution, this is a surprising result - they predict an overall increase of helium-3 due to stellar nuclear fusion.
It is believed that during supernovae explosion an extraordinarily intense neutron flux is produced. Bombarded by such a flux, the iron nuclei grow very rapidly through successive neutron captures. From stellar physics, one can estimate that they are between 10 and 13 billion years old - the most ancient such stars have been around for around 95 per cent of the age of the universe! Here, we will concentrate on a narrow range of eta values. The pressure of this radiation prevents the star from contracting further.
The vertical golden strip represents a recent determination of eta as 6. Any light that reaches us from those quasars shows us the universe as it was about ten billion years ago. IN2P3 Stars are formed from a cloud of material composed primarily of hydrogen. Nucleons are protons and neutrons.