Authors: Prashanth Jaikumar (Ohio U., ANL), Bradley S. Meyer (Clemson U.), Kaori Otsuki (U. Chicago), Rachid Ouyed (U. Calgary)
(Submitted on 4 Oct 2006 (v1), last revised 20 Aug 2007 (this version, v3))
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Abstract: We explore heavy-element nucleosynthesis by rapid neutron capture (r-process) in the decompressing ejecta from the surface of a neutron star. The decompression is triggered by a violent phase transition to strange quark matter (quark-nova scenario). The presence of neutron-rich large Z nuclei (40,95) < (Z,A) < (70,177), the large neutron-to-seed ratio, and the low electron fraction Ye ~ 0.03 in the decompressing ejecta present favorable conditions for the r-process. We perform network calculations that are adapted to the quark-nova conditions, and which mimic usual (n-gamma) equilibrium r-process calculations during the initially cold decompression phase. They match to dynamical r-process calculations at densities below neutron drip (4.10^11 g cm-3). We present results for the final element abundance distribution with and without heating from nuclear reactions, and compare to the solar abundance pattern of r-process elements. We highlight the distinguishing features of quark-novae by contrasting it with conventional nucleosynthetic sites such as type II supernovae and neutron star mergers, especially in the context of heavy-element compositions of extremely metal-deficient stars.
Inhomogeneous Galactic halo: a possible explanation for the spread observed in s- and r- process elements
Authors: G.Cescutti
(Submitted on 21 Feb 2007)
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Abstract: The considerable scatter of the s- and r-process elements observed in low-metallicity stars, compared to the small star to star scatter observed for the alpha elements, is an open question for the chemical evolution studies. We have developed a stochastic chemical evolution model, in which the main assumption is a random formation of new stars, subject to the condition that the cumulative mass distribution follows a given initial mass function. With our model we are able to reproduce the different features of alpha-elements and s-and r-process elements. The reason for this resides in the random birth of stellar masses coupled with the different stellar mass ranges from where alpha-elements and s-and r-process elements originate. In particular, the sites of production of the alpha elements are the whole range of the massive stars, whereas the mass range of production for the s- and r-process elements has an upper limit of 30 solar masses.
Authors: Gabriele Cescutti (Astronomy Department, Trieste University)
(Submitted on 30 Aug 2007)
Quote:
Abstract: By adopting a chemical evolution model for the Milky Way already reproducing the evolution of several chemical elements, we compare our theoretical results with accurate and new stellar data of neutron capture elements and we are able to impose strong constraints on the nucleosynthesis of the studied elements. We can suggest the stellar sites of production for each element. In particular, the r-process component of each element (if any) is produced in the mass range from 10 to 30 Msun, whereas the s-process component arises from stars in the range from 1 to 3 Msun. Using the same chemical evolution model, extended to different galactocentric distances, we obtain results on the radial gradients of the Milky Way. We compare the results of the model not only for the neutron capture elements but also for alpha-elements and iron peak elements with new data of Cepheids stars. We give a possible explanation to the considerable scatter of neutron capture elements observed in low metallicity stars in the solar vicinity, compared to the small star to star scatter observed for the alpha-elements. In fact, we have developed a stochastic chemical evolution model, in which the main assumption is a random formation of new stars, subject to the condition that the cumulative mass distribution follows a given initial mass function. With our model we are able to reproduce the different features of neutron capture elements and alpha-elements. Finally, we test the prescriptions for neutron capture elements also for the dwarf spheroidal galaxies of the Local Group. We predict that the chemical evolution of these elements in dwarf spheroidal galaxies is different from the evolution in the solar vicinity and indicates that dwarf spheroidal galaxies (we see nowadays) cannot be the building blocks of our Galaxy.
The links you give do nothing to refute Physbang's statement. If I am mistaken, then please point out specifically where you have refuted his claim.
__________________ Hypography Science Forums Moderator
--- "There are no passengers on Spaceship Earth. We are all crew." - Marshall McLuhan
"We must not forget that when radium was discovered no one knew that it would prove useful in hospitals. The work was one of pure science. And this is a proof that scientific work must not be considered from the point of view of the direct usefulness of it." - Marie Curie
Heavy elements. PhysBang is pointing out that there aren't many of them which there would be if there were no big bang. To counter this you link a paper which proposes a new method of creating more heavy elements! This is not only consistent with PhysBang's argument, it supports it.
Can you explain how the theoretical ejection of heavy elements from a neutron star supports your argument? Or, is this just a random article you picked out that mentions heavy elements? Or, are you trying to support what PhysBang said? I honestly cannot figure any sensible reason you posted this. Can you please comment on this particular paper - why you posted it - what you think it claims - etc.
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Do not post links to other sites as proof of your claims without commenting what the relevant sites say and why they are important to the current discussion.
I have posted the previous posts as information to the workings of stars and the formation of the elements.
I know its not complete.
But! I thought this link hits the nail on the head
The Nuclear Cycle that Powers the Stars: Fusion, Gravitational Collapse and Dissociation
Authors: O. Manuel, Michael Mozina, Hilton Ratcliffe
(Submitted on 12 Nov 2005)
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Abstract: The finding of an unexpectedly large source of energy from repulsive interactions between neutrons in the 2,850 known nuclides has challenged the assumption that H-fusion is the main source of energy that powers the Sun and other stars. Neutron repulsion in compact objects produced by the collapse of stars and collisions between galaxies may power more energetic cosmological events (quasars, gamma ray bursts, and active galactic centers) that had been attributed to black holes before neutron repulsion was recognized. On a cosmological scale, nuclear matter cycles between fusion, gravitational collapse, and dissociation (including neutron emission) rather than evolve in one direction by fusion. The similarity Bohr noted between atomic and planetary structures may extend to a similarity nuclear and stellar structures.
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AGN, quasars, and neutron stars are highly prevalent, observable phenomena in all parts of the known universe. They have two significant properties in common: Exceptionally high specific gravity and the generation of copious amounts of “surplus” energy. In view of the repulsive forces recently identified between neutrons [3-5] and the frequency and products of galactic collisions [22], we conclude that neutron repulsion is the main energy source for the products of galactic collisions.
We know that Neutrons are produced and that these Neutrons can be changed to Protons and than to Hydrogen. Tha Via fusion to other elements.
As we speak I'm reading through compact matter such as Neutron, quark and composites and the processes involved in the production of matter from ejected degenerated matter.
Do I understand it fully? No way and it will take me a few years to do so.
The more I read, it seems that I'm learning that there is more to this than meets the eye.
As I grow I hope to add more concrete evidence to this topic.
My favorite link, THE ORIGIN OF HELIUM AND THE OTHER LIGHT ELEMENTS, provides a very nice explanation for light element production and abundances observed without the need of ad hoc model-based primordial creation.
ABSTRACT
The energy released in the synthesis of cosmic 4He from hydrogen is almost exactly equal to the energy contained in the cosmic microwave background radiation. This result strongly suggests that the 4He was produced by hydrogen burning in stars and not in the early stages of a big bang. In ddition, we show that there are good arguments for believing that the other light isotopes, D, 3He, 6Li, 7Li, 9Be, 10B, and 11B, were also synthesized in processes involving stars. By combining these results with the earlier, much more detailed work of Burbidge et al. and of Cameron, we can finally conclude that all of the chemical elements were synthesized from hydrogen in stars over a time of about 10^11 yr.
The next step of research for my learning is in the formation of subatomic particles, such as Quarks to Neutrons and protons and than to Hydrogen.
Interesting to look at the influence of the so called monopoles to Neutrons and protons.
Astronauts on board the International Space Station have recently photographed strange electric-blue clouds hovering at the edge of space. Read » | 0 comments
