In physical cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen.
Table of contents
- Term Record: Big Bang nucleosynthesis
- Big Bang Nucleosynthesis
- Big bang/a critique of Big-Bang Nucleosynthesis Revisited.
- Explanations (2)
- Big-Bang Nucleosynthesis
Library subscriptions will be modified accordingly. This arrangement will initially last for two years, up to the end of The Li 7 abundance is the sum of the primordial Li 7 and Be 7 abundances, as the latter decays into the former.
Big bang nucleosynthesis with stable Be 8 and the primordial lithium problem Richard T. Scherrer and Robert J. Scherrer Phys. D 96 , — Published 6 October Abstract A change in the fundamental constants of nature or plasma effects in the early universe could stabilize Be 8 against decay into two He 4 nuclei.http://bbmpay.veritrans.co.id/sant-mart-sarroca-dating-gay.php
Term Record: Big Bang nucleosynthesis
Research Areas. Big bang nucleosynthesis. Issue Vol. Authorization Required. The WMAP satellite is able to directly measure the ordinary matter density and finds a value of 4. This leads to predicted abundances shown by the circles in the graph, which are in good agreement with observed abundances.
This is an important and detailed test of nucleosynthesis and is further evidence in support of the Big Bang theory. Had the results been in conflict, it would point to 1 errors in the data, 2 an incomplete understanding of the process of Big Bang nucleosynthesis, 3 a misunderstanding of the mechanisms that produce fluctuations in the microwave background radiation , or 4 a more fundamental problem with the Big Bang theory.
Elements heavier than lithium are all synthesized in stars. During the late stages of stellar evolution , massive stars burn helium to carbon, oxygen, silicon, sulfur, and iron. Elements heavier than iron are produced in two ways: in the outer envelopes of super-giant stars and in the explosion of a supernovae. All carbon-based life on Earth is literally composed of stardust. In , Physicist George Gamow hypothesized that all of the elements might have been made in the hot and dense early universe.
Big Bang Nucleosynthesis
He suggested to his student, Ralph Alpher, that he calculate this. Alpher did so for his PhD thesis, with Robert Herman participating in much of the work. Finally, and most interesting, there is the abundance of lithium-7 nuclei with 3 protons and 4 neutrons. These nuclei are produced by nuclear fusion inside some stars, but more commonly they are destroyed.
Big bang/a critique of Big-Bang Nucleosynthesis Revisited.
Additional ways of producing lithium-7 must be taken into account: The cosmos is filled with very fast, high-energy particles, mainly protons, which are commonly called "cosmic rays". When cosmic rays collide with interstellar gas, one of the possible results are lithium-7 nuclei. Fortunately, it appears that there are some objects in the universe - even in our own galaxy! How do we know?
Stars have a layered structure - nuclear fusion reactions take place in the inner, hotter regions, but not in the outermost layers. Therefore, the composition of the outermost layers should indicate the element abundances for the matter from which a star has formed. For very old stars, that element abundance should be closer to the primordial values. For younger stars, which have formed from material contaminated with the fusion products of stars of previous generations, the abundances will be different. By systematic analysis of the light received from those outermost layers more concretely, of the different emission and absorption lines , astronomers can determine the abundances of the layer's constituent elements.
The presence of elements such as oxygen or nitrogen see above or, in this particular case, the presence of iron serve as indicators of chemical evolution: Substantial amounts of these elements suggest that a star is young, produced from the debris of other stars. Low abundances indicate that the star is rather old.
For younger stars - recognizable by their high iron content - the lithium-7 abundances can be vastly different, as seen in the following diagram, which plots iron content horizontal axis; the reference object is our sun against lithium-7 content vertical axis; plotted is the number of lithium-7 nuclei per hydrogen nucleus :. This is because the amount of lithium-7 produced in stellar fusion will vary widely depending the star's mass, temperature and initial composition.
In contrast, the lithium-7 content for most of the oldest stars stars with outer layers that contain less than a tenth as much iron as our sun is roughly constant, as the following diagram shows:. The fact that the lithium-7 abundances for these oldest stars show very little variation is strong evidence that, in the outermost layers of these stars, the lithium-7 is uncontaminated by stellar nuclear fusion. Their constant lithium content has, in fact, given these stars their name: They are called lithium-plateau stars or, alternatively, Spite plateau stars after the plateau's discoverers.
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! On average, the stars contain one lithium-7 nucleus for every 8 billion hydrogen nuclei - the ratio of lithium-7 to hydrogen nuclei is somewhere between 1. For instance, elements heavier than hydrogen are expected to migrate slowly towards deeper layers of the star, a cosmic analogue to the more familiar phenomenon of sedimentation: if you let a mixture of water and sand settle, the sand will collect at the bottom, following the earth's gravitational pull.
Armed with the results described above, we can confront the predictions of Big Bang Nucleosynthesis with astronomical observation. It is usual to plot the predictions against a parameter denoted by the greek letter eta, which is defined as the total number of protons and neutrons in our universe, divided by the number of photons in the cosmic background radiation. Here, we will concentrate on a narrow range of eta values. A more general overview, covering a much wider range of eta, can be found in the spotlight text Big Bang Nucleosynthesis: Cooking up the first light elements.
Vangioni, Institut d'Astrophysique de Paris]. In this and the following plots, the horizontal axis represents the different values of eta. The scale is logarithmic ; 10 -9 corresponds to one proton or neutron for every billion photons, 10 -8 to one for ever hundred million, and so on cf.
The vertical golden strip represents a recent determination of eta as 6. In this diagram, the vertical axis represents the helium-4 abundance - for instance, a value 0. The curve indicates the theoretical prediction for this abundance. 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.
The deuterium abundance shows impressive agreement with the eta value for the WMAP data as well as with the higher of the two possible values for helium More problematic is the lithium The following diagram shows the prediction and observational results for the numerical abundance:. As visible in the diagram, the observed abundance of lithium-7 would be consistent with the lower possible value for helium-4, but not with the combined higher helium-4 result, the deuterium value and the WMAP value.
In order to understand how this comes about, we would have to find out why, in the lithium plateau stars, lithium-7 appears to be less than half as abundant as in the early universe. Overall, Big Bang Nucleosynthesis is strongly supported by observations. But for lithium-7 and, incidentally, for the rather uncertain values for helium-3, much work will be needed to determine the primordial values from the observed data with greater accuracy.
As this work progresses, we are much more likely to learn about stellar physics than about the early universe. For the relativistic ideas behind this spotlight topic, check out Elementary Einstein , especially the chapter Cosmology. An overview of Big Bang Nucleosynthesis can be found in the spotlight text Big Bang Nucleosynthesis: Cooking up the first light elements ; information about the physics behind the predictions in Equilibrium and change. Other related spotlights on relativity can be found in the section Cosmology. The theoretical predictions in the diagrams above were kindly provided by E.
Vangioni, Institut d'Astrophysique de Paris private communication, ; for further information about these calculations, see. Coc, A.