Very Massive Star

Abstract. We have studied the effects of an hypothetical initial generation made only of very massive stars (M > 100M , pair-creation SNe) on the chemical and photometric evolution of spheroidal systems. We found that the effects of Population III stars on the chemical enrichment is negligible if only one or two generations of such stars occurred, whereas they produce quite different results from the standard models if they continuously formed for a period not shorter than 0.1 Gyr. In this case, the results produced are at variance with the main observational constraints of ellipticals such as the average [< a/Fe > ] ratio in stars and the color-magnitude diagram. 

Only one or two first stellar generations containing normal stars plus very massive stars included in the best model of PM04, produce negligible effects on the subsequent photo-chemical evolution, when either the yields of HW02 or those of UN are adopted. Therefore, these models are acceptable and we cannot assess Pop III existence nor disproved it. 

The second conclusion is based on the fact, that as soon as a star enters the Wolf-Rayet phase, its remaining life-time 1s extremely short (a few 10 years), simply because of the high mass-loss rate. Hence, Its total life-time is mainly determined by its age at the onset of the high mass-loss rate. If a star enters the Wolf-Rayet phase very early, or even at zero age, it cannot exist longer than the very massive stars, regardless of its initial mass. 

The present equations will be useful when the acceleration occurs deep interior or when the gravitational energy release is important in the energy conservation equation. In such cases we will have different structures from that of the usual solutions. Further investigation will be desired in many cases such as red giants or very massive stars. 

Figure 7.6 Ancient stars have a carbon core surrounded by a helium-fusing shell which is itself encased by a helium and a hydrogen-fusing shell. Small stars, less than 1.4 times the Sun s mass, die quietly. Very massive stars exploded, belching their carbon-heavy elements into space. These heavy elements, like carbon, eventually found their way into primitive life-forms on Earth.

Bob smiles. Brunhilde, you are a wonderful repository of facts. Thank you. Bob strokes the piezoelectric undersurface of the flexscreen, and Brunhilde makes a soft purring sound. But let s return our discussion to the death of stars. The exact final state of a star depends on its mass. A star less than 1.4 times the Sun s mass dies calmly. Very massive stars explode before their death. Stars about the mass or our Sun become fat red giants when all the helium fuel is consumed. ... 

Multiple lines of evidence exist for a population of live radionuclides, such as 26Al or 60Fe, which were injected into the proto-solar cloud or disk prior to the formation of CAIs (e.g. Tachibana et al. 2006). Isotopic abundances suggest that the isotopes have originated in a supernova, possibly with a very massive star progenitor that also underwent a Wolf-Rayet phase (Bizzarro et al. 2007). If this interpretation is correct, the Sun must have formed in a very rich and dense stellar cluster, such as the Carina Nebula, very much unlike the Taurus or other low-mass star-forming regions. Luminous massive stars in such clusters may truncate or fully evaporate protoplanetary disks around other cluster members. Two key questions remain open. How close in time and space did the supernova explode... 

Very massive stars (stars whose masses are more than 100 times the mass of our sun) are the source of heavier elements. When such a star has converted almost all of its core hydrogen and helium into the heavier elements up to iron, the star collapses and then blows apart in an explosion called a supernova. All of the elements heavier than iron on the periodic table are formed in this explosion. The star s contents shoot out into space, where they can become part of newly forming star systems. 

There is one well-established anomaly in the isotopic composition of galactic cosmic rays, the excess of 22Ne. The ratio 22Ne/20Ne is enhanced by a factor of 4 compared with the solar reference value [23], It can be explained only by the special conditions of nucleosynthesis. The enhancement of neutron rich isotopes would be expected in the highly evolved very massive stars in... 

Very Massive Stars (M > 1OOM0), if they exist, explode by means of pair creation and are called pair-creation SNe. In fact, at T 2 109 K a large portion of the... 

It is now recognized that only very massive stars (typically 5 to 10 times the solar mass) have the opportunity to form the larger amounts of carbon, nitrogen, and oxygen that are dispersed in violent stellar winds at the end of their... 

Astrophysical sodium is produced in various ways that depend on the mass and life stage of a given star. In very massive stars that experience carbon-burning, sodium 23 results from the following reaction and is then distributed into the interstellar medium (ISM) in the supernova explosion of the star. 

Further nuclear reactions take place in very massive stars. There, carbon atoms and oxygen atoms combine together to form heavier elements. Silicon (Si) forms from two oxygen atoms. Two carbon atoms combine to form neon (Ne) and... 

One kind of evidence about where cosmic rays come from and what kind of stars and stellar explosions really dominate among their sources is the isotopic ratios of various isotopes of neon, iron, and other heavy elements these isotope ratios suggest that at least one population is indeed the very massive stars with strong stellar winds however, whether these stars provide most of the heavier elements, as one theory proposes, is still quite an open question. 

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