Supernova hypothesis

Overall, the origin of the oxygen isotopic anomalies in the Solar System is still a matter of debate (Thiemens 2006). After the failure of the supernova hypothesis (Clayton et al. 1973), these anomalies most likely originated through chemical or physical processes within the nebula. 

Several proposals have been made about the origin of the matter from which the earth and the solar system have been formed. These proposals are mainly based on the isotopie eomposition. The supernova hypothesis explains the presence of heavy nuelei in the solar system by a supernova explosion some time before the evolution of the solar system. This hypothesis is supported by the isotopie analysis of meteorites whieh shows an anomaly in the Xe eontent. This anomaly is attributed to the decay of (ti/2 = 1.57 10 y) which must have been present during the evolution of the solar system. 

The question also arises as to where the chiral molecules came from. Were the L-amino acids or the D-sugars selected on the primeval Earth, or are exuaterresuial sources responsible for the homochirality This second possibility is dealt with by hypotheses on the effect of circularly polarised light, of extraterrestrial origin, on chiral molecules in the molecular clouds from which the solar system was formed. One such hypothesis was proposed by Rubenstein et al. (1983) and developed further by others, particularly A. W. Bonner (Bonner and Rubenstein, 1987) both scientists worked at Stanford University. The authors believe that the actual radiation source was synchrotron radiation from supernovae. The excess of one enantiomeric form generated by this irradiation process would have needed to be transported to Earth by comets and meteorites, probably during the bombardment phase around 4.2-3.8 billion years ago. 

Apart from these three facts, nuclear astrophysicists take pains to point out that the rate at which the luminosities of SNla events decline, once beyond the maximum, is commensurable with the decay of radioactive cobalt-56, son of nickel-56, atomic nucleus of noble lineage as we know. This is a common factor with gravitational collapse supernovas. SNla light curves are explained through the hypothesis that half a solar mass of nickel-56 is produced when one of these white dwarfs explodes. 

Type lb supernovae appear in or near regions of star formation in spiral galaxies (Porter and Filippenko 1987). However, Huang (1987) has found that Type II supernovae, most of which probably have main sequence masses between 8 and 15 Mq, also occur in star-formation regions. Therefore this constraint is consistent with but does not require the hypothesis that Type lb have more massive progenitors than Type II. Type lb also could have somewhat less massive progenitors than Type II. In the white-dwarf model, the initial masses are not expected to be low. If the white dwarf accretes at 10 8 M0 yr-1 at low efficiency (a few percent) from the wind of a companion, and the white dwarf needs to accumulate a few tenths of a solar mass of helium before it explodes, then the companion must be able to lose several solar masses in its wind. It would need to be initially a star of at least intermediate mass (> 5 MG). 

The most direct probe of quintessence lies in supernovae data. The reason, as we said, is that supernovae data (in the hypothesis that supernovae are... 

Wasserburg G. J., GMhnoR., and Busso M. (1998) A test of the supernova trigger hypothesis with Fe-60 and Al-26. Astrophys. J. 500, L189—L193. 

The principal sources of primary N are thought to be intermediate mass stars, with masses 4 M/Mq 7, during the asymptotic giant branch (AGB) phase. A corollary of this hypothesis is that the release of N into the ISM should lag behind that of O which, as we have seen, is widely believed to be produced by massive stars which explode as Type II supernovae soon after an episode of star formation. Henry et al. (2000) calculated this time delay to be approximately 250 Myr at low metallicities the (N/O) ratio could then perhaps be used as a clock with which to measure the past rate of star formation, as proposed by Edmunds Pagel (1978). Specifically, in metal-poor galaxies which have only recently experienced a burst of star formation one may expect to find values of (N/O) below the primary plateau at (N/O) —1.5, provided the fresh Oxygen has been mixed with the ISM (Larsen, Sommer-Larsen, Pagel 2001). 

The alternative hypothesis, that of a nucleosynthetic component carried into the early solar system by 0-rich presolar dust (see discussion in Clayton 1993) remains plausible after all, as mentioned in the Introduction, trace amounts of presolar dust is known to exist in the matrices of chondrites. However, all the high spatial (ion microprobe) measurements of the many types of primitive refractory materials discussed here have failed to find any very extreme oxygen isotopic anomalies such as might be expected if pure 0 dust (e.g. from a supernova) were incorporated into CAIs or AOAs along with local condensates. Even among the -100 true interstellar oxide grains that... 

Table 1 lists the extensive isotopic evidence for these extinct radionuclides, which demonstrates that the time between the cessation of nucleosynthesis and the formation of meteorites was so short that it supports the hypothesis that a last minute injection of nucleosynthetic products may have accompanied a supernova shock wave which triggered the collapse of the solar nebula. In this case it is likely that some of the nucleosynthetic products may not have been well mixed in the molecular cloud from which the Solar System evolved. 

---