Scientific American Big Bang Nucleosynthesis

Scientific American Big Bang Nucleosynthesis-15
He, which they mix into the convective envelope on the giant branch and should distribute into the Galaxy by way of envelope loss.This process is so efficient that it is difficult to reconcile the low observed cosmic abundance of He with the predictions of both stellar and Big Bang nucleosynthesis.“The conditions we create in one of these implosions are very similar in density and very similar in temperature to the interior of a star.” The first three experiments in the campaign focused on the “proton-proton 1” chain of nuclear reactions, at the beginning of the stellar nucleosynthesis cycle.

He, which they mix into the convective envelope on the giant branch and should distribute into the Galaxy by way of envelope loss.

Here we find, by modeling a red giant with a fully three-dimensional hydrodynamic code and a full nucleosynthetic network, that mixing arises in the supposedly stable and radiative zone between the hydrogen-burning shell and the base of the convective envelope.

This mixing is due to Rayleigh-Taylor instability within a zone just above the hydrogen-burning shell, where a nuclear reaction lowers the mean molecular weight slightly.

When the renowned cosmologist Carl Sagan declared that “we are made of starstuff,” he wasn’t speaking metaphorically.

As Sagan said in the TV series “Cosmos,” many of the elements in our bodies—“the nitrogen in our DNA, the calcium in our teeth, the iron in our blood”—were forged in the interiors of stars, in a process called stellar nucleosynthesis (element formation).

We show that the observed Li versus Fe trend provides a strong discriminant between alternative models for Galactic chemical evolution of the light elements at early epochs.

We critically assess current systematic uncertainties and determine the primordial Li abundance within new, much tighter limits: (Li/H) is now limited as much by uncertainties in the nuclear cross sections used in big bang nucleosynthesis (BBN) calculations as by the observed abundance itself.A new study by astronomers has found that the temperature on the nightsides of different hot Jupiters -- planets that are similar size in to Jupiter, but orbit other stars -- is surprisingly uniform, ...Researchers have modeled a method to manipulate nanoparticles as an alternative mode of propulsion for tiny spacecraft that require very small levels of thrust. Recent determinations of the abundance of the light-element Li in very metal-poor stars show that its intrinsic dispersion is essentially zero and that the random error in the estimated mean Li abundance is negligible.However, a decreasing trend in the Li abundance toward lower metallicity indicates that the primordial abundance of Li can be inferred only after allowing for nucleosynthesis processes that must have been in operation in the early history of the Galaxy.“Models of the production of nuclei in the cosmos depend on having accurate data to inform those models.And studying those reactions in conditions that are actually applicable to the interior of stars or to the universe during the Big Bang is very challenging.Big Bang nucleosynthesis begins about one minute after the Big Bang, when the universe has cooled enough to form stable protons and neutrons, after baryogenesis.From simple thermodynamical arguments, one can calculate the fraction of protons and neutrons based on the temperature at this point.By fusing elements such as tritium (a form of hydrogen) and helium in the NIF Target Chamber, a multi-institutional team of researchers hopes to gain new insights into the processes that kick-started and have sustained the universe.“All of the stellar nucleosynthesis reactions—fusion reactions that happen inside stars—produce the elements, but we can’t really see inside a star to tell how those reactions are proceeding,“ said plasma physicist Alex Zylstra of Los Alamos National Laboratory (LANL).


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