Big bang nucleosynthesis
Big bang nucleosynthesis timeline
Although this zero point itself is outside the domain of the physical model, arbitrarily small times near but not equal to zero are within the scope of the model. The strongly interacting particles are composed of two or three quarks and are known as hadrons. All of the other naturally occurring elements were created in stars. However, this conversion involves a weak interaction and is too slow to occur during the Big Bang. This has proved to be of limited usefulness in that the inconsistencies were resolved by better observations, and in most cases trying to change BBN resulted in abundances that were more inconsistent with observations rather than less. But BBFH could not produce enough helium. This relatively low value means that not all of the dark matter can be baryonic, ie we are forced to consider more exotic particle candidates. Eventually the temperature gets so low that the electrostatic repulsion of the deuterons causes the reaction to stop. What nuclei are produced, and in what amounts, is the result of a race between the various nuclear reactions on the one hand and the inevitable cooling that accompanies the expansion of the universe on the other. There has been a dispute about the actual primordial helium abundance in the Universe: either The fit is good but not perfect. Except in the leftmost part, the pale blue strip indicating the observed value for helium-4 can hardly be distinguished from the theoretical curve. 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. 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. This interpretation is subject to systematic uncertainty, for which an estimate is included in the plotted abundance range.
When the temperature changes more rapidly than the forward and backward reaction rates can follow, the abundances become fixed near values appropriate to this last equilibrium temperature. Compared to the models and shown as the cross-hatched bands are recent estimates of the abundances and their uncertainties reported by K.
Quite Possibly! The temperature drops during the universe expansion until the neutrons and protons have frozen out. The graph above shows the time evolution of the abundances of the light elements for a slightly higher baryon density. Because of this effect, if the energy content in one model of the universe is larger than that of a second model of the universe at a moment of time, its rate of expansion will also be larger. The following stages occur during the first few minutes of the Universe: Less than 1 second after the Big Bang, the reactions shown at right maintain the neutron:proton ratio in thermal equilibrium. The graph above shows the predicted abundance vs. A very few helium nuclei combine into heavier nuclei giving a small abundance of Li7 coming from the Big Bang. Please help improve this section by adding citations to reliable sources. The fit is good but not perfect. A similar enigma exists for the deuterium. Nuclear physics in an expanding universe As the universe cools, the matter content changes - new particles are formed out of the preexisting ones, such as protons and neutrons forming out of quarks. By the same token, the element abundances we see around us are not the "primordial abundances" right after Big Bang Nucleosynthesis, but have been altered by later stellar processing. Burles, S.
The deuteron:proton ratio when the reactions stop is quite small, and essentially inversely proportional to the total density in protons and neutrons. At present just the excess of matter particles over antimatter particles remains in existence.
Big bang nucleosynthesis ppt
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. Eventually the temperature gets so low that the electrostatic repulsion of the deuterons causes the reaction to stop. The words "arbitrarily near zero" mean that there can be as many zeros between the decimal point and the first nonzero number as one may sensibly describe. Data from Boesgaard, A. One consequence of this is that, unlike helium-4, the amount of deuterium is very sensitive to initial conditions. The vertical grey band indicates the density range where there is good agreement between the model and the observations of 2D. After 1 second, the only reaction that appreciably changes the number of neutrons is neutron decay, shown at right. Both theory and observation lead astronomers to believe this to be the case. If it had been faster, there would be more neutrons and more helium. All in all, this match between theory and observation constitutes one of the big successes of the standard models of cosmology. The shaded areas represent measurements from regions which have a very small abundance of heavy elements, so that they seem to be good samples of primordial abundances. 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. The first point is true because the universe is in the reverse of a free-fall collapse—a free expansion. The green deuterium curve meets the pale green strip indicating the observed value almost exactly at the value indicated by the WMAP observations vertical golden strip , and similarly the WMAP observations, the magenta helium-3 curve and the observed upper limit for helium-3 coincide very well.
In the time prior to element building, neutrinos are formed in equilibrium with their associated electrons, muons, and tau particles. The graph above shows the predicted abundance vs. The fit is good but not perfect. Hence observations about deuterium abundance suggest that the universe is not infinitely old, which is in accordance with the Big Bang theory.
What elements/isotopes are formed via big bang nucleosynthesis
And a new measurement of the free neutron lifetime is 6 sigma smaller that the previous world average, giving a new prediction of the helium abundance of The green deuterium curve meets the pale green strip indicating the observed value almost exactly at the value indicated by the WMAP observations vertical golden strip , and similarly the WMAP observations, the magenta helium-3 curve and the observed upper limit for helium-3 coincide very well. Roger K. These observed abundances simultaneously fit the big bang model within a narrow range. A normal corkscrew goes down into the cork when it is turned clockwise as viewed from above. Neither free fall nor free expansion involve frictional processes, and so these two processes are time-reversed versions of each other. The fit is good but not perfect. Retrieved September 05, from Encyclopedia. Because of this effect, if the energy content in one model of the universe is larger than that of a second model of the universe at a moment of time, its rate of expansion will also be larger. The abundance ratio was about seven protons for every neutron. The baryons can only account for about 8 percent of the mass needed to achieve a closed universe. Nollett, and M. 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. The reactions at right also produce helium and usually go faster since they do not involve the relatively slow process of photon emission.
In the absence of the neutrons, the first step would have to combine two protons to form a product described as 2He. The process of forming the hydrogen and helium and other trace constituents is often called " big bang nucleosynthesis ".
At the earliest stages that can be modelled using current physical theories, the universe was filled with radiation and elementary particles - a hot plasma in which energy was distributed evenly.
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