Supernovae environment

Guided by early compilations of the cosmic abundances as reflected in solar system material (e.g., Suess and Urey, 1956), Burbidge cr a/. (1957) and Cameron (1957) identified the nuclear processes by which element formation occurs in stellar and supernova environments (i) hydrogen burning, which powers stars for —90% of their lifetimes (ii) helium burning, which is responsible for the production of and the two most abundant elements heavier than helium (iii) the a-process, which we now understand as a combination of... 

The environment must be free from life-threatening supernovae. 

The strengths of the model are its natural connection to supemovae and star formation and that the supernova remnant would have enough time to form iron via the decay of nickel and cobalt to possibly produce the claimed iron lines. Moreover, it is expected to be a baryon-clean environment. The model is, however, very sensitive to the fine tuning of parameters. Moreover, GRB030329 places a rather strict limit of a few hours on the delay between the SN and the GRB and thus rules out the supranova model for at least this particular burst. 

If the time scale of neutron capture reactions is very much less than 3 -decay lifetimes, then rapid neutron capture or the r process occurs. For r-process nucleosynthesis, one needs large neutron densities, 1028/m3, which lead to capture times of the order of fractions of a second. The astrophysical environment where such processes can occur is now thought to be in supernovas. In the r process, a large number of sequential captures will occur until the process is terminated by neutron emission or, in the case of the heavy elements, fission or (3-delayed fission. The lighter seed nuclei capture neutrons until they reach the point where (3 -decay lifetimes have... 

Stars actually do not provide enough time at any temperature for this state to be reached. But it is so nearly reached that thermal equilibrium may be a very accurate approximation. Reactions among nuclei are so slow at normal stellar temperatures that this state is not even approximately approached. The best approximation is found within supernovae, despite the fact that the explosive environment changes in mere seconds. But nuclear reactions are so fast at T = 5 billion degrees that a fair approximation may be achieved in much less than one second. Even then, the state achieved is quasiequilibrium, rather than equilibrium. 

Pressure within stars can increase to the point where sub-atomic particles fuse to form 2H, 3He, 4He, and 5He. The a-particle is the most stable of these units and becomes formed in sufficient excess to add progressively to each of four starting units to produce nuclides in four series of mass number An, 4n 1, An — 2, as observed [21]. Under these conditions the protonmeutron ratio for each series approaches unity with increasing mass number. At a certain age, a star of such magnitude explodes as a supernova to release the synthesized material into low-pressure environments in which a phase transition ensues. This transition consists of an inversion of energy levels... 

It is generally accepted that the r-process synthesis of the heavy neutron capture elements in the mass regime A S 130-140 occurs in an environment associated with massive stars. This results from two factors (i) the two most promising mechanisms for r-process synthesis—a neutrino heated hot bubble and neutron star mergers— are both tied to environments associated with core collapse supernovae and (ii) observations of old stars (discussed in Section 1.01.6) confirm the early entry of r-process isotopes into galactic matter. 

The isotope 210Bi is not an especially good candidate for an s process reaction, because its half-life is only about five days. It is not likely to "wait around until an s-process neutron shows up. (Recall that such neutrons are available only about once every hundred years or more.) In the high-neutron-density environment of a supernova, however, the 210Bi nucleus will encounter millions of neutrons every second. Thus, the next stage in this reaction, the addition of a neutron to the 210Bi nucleus to form the next-heaviest isotope in the family, 210Bi, can occur much more readily ... 

These stars have been of central concern in a myriad of observational and theoretical works. No wonder They indeed play a key role in many chapters of astrophysics. In particular, they influence the physical and chemical states of their circumstellar environments or of the interstellar medium through their intense radiation and mass losses during their non-explosive phases of evolution, and even more so, as a result of their final supernova explosions. They may act as triggers of star formation, are essential agents of the evolution of the nuclidic content of the galaxies, accelerate particles to cosmic ray energies, and leave neutron stars or black holes at the end of their evolution. They are also the progenitors of certain 7-ray bursts. 

In associating the r-process with supernova explosions, several attempts to go beyond the canonical and MER models have been made by taking into account some evolution of the characteristics of the sites of the r-process during its development. These models are coined dynamical (DYR) in the following in order to remind of the time variations of the thermodynamic state of the r-process environment (see [24] for references). These models do not rely on any specific explosion scenario. They just assume that a material that is initially hot enough for allowing a nuclear statistical equilibrium (NSE) to be achieved expands and cools in a prescribed way on some selected timescale. This evolution is fully parameterized. 

We describe the structure of polarizing spectra in some Supemovae stars. Understanding spectropolarimetry may be critical to reveal the complicated nature of supemovae. One group of models assumes that the polarization arises from a combination of Thomson and line scattering through the aspherical supernova envelope. Another group of models assumes that the supemovae are associated with an aspherical dusty circumstellar environment. 

Alpher s preference is clearly conditioned by cosmology rather than science, but in the event it led to the total elimination of the equilibrium model from subsequent enquiry. A complicating factor in the argument is the continuously changing evidence provided by astronomical observation, in both theories, the success is measured in terms of predicted nuclear abundances and invariably these predictions depend on the nature and characteristics of known types of star, assumed as the seat of nucleogenesis. As more powerful telescopes identify new types of heavenly body, new possibilities of nuclear synthesis open up and the model has to be reworked. This process continues for the a — /d — 7 model only. The equilibrium model was abandoned before the discovery of quasars and black holes, that obviously provide more attractive environments for nuclear synthesis. The only mechanism for the dispersal of freshly synthesized material is still assumed to be supernovae and this assumption could also stand reassessment. 

The common imponderable is the topology and dimensionality of space-time, not very likely to be resolved in the foreseeable future. The smart way out is to look for the simplest solution to the problem - a closed universe with an illusionary size, suggested by an infinitude of multiple images of celestial objects. This way many exotic objects such as black holes, supernovae, quasars, radio sources and the like may be located either in the Milky Way or its immediate environs of sibling galaxies. 

Measurements with INTEGRAL of the shapes of the line profiles of radioactive heavy elements, created by explosive nucleosynthesis during supernova events, will provide information about the expansion velocity and density distribution inside the envelope, whilst the relative intensities of the lines provide direct insight into the physical environment at the time of the production. 

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