![]() ![]() This suggests that Types Ib and Ic are associated with short-lived massive stars, but Type Ia is significantly different. Type Ia supernovae occur in all kinds of galaxies, whereas Type Ib and Type Ic have been seen only in spiral galaxies near sites of recent star formation (H II regions). Type II supernovae are not observed to occur in elliptical galaxies, and are thought to occur in Population I type stars in the spiral arms of galaxies. There should be a lot of these gases in the extreme outer regions of the massive star involved. This model is corroborated by the observation of strong hydrogen and helium spectra for the Type II supernovae, in contrast to the Type I. This plateau is reproduced by computer models which assume that the energy comes from the expansion and cooling of the star's outer envelope as it is blown away into space. They show a characteristic plateau in their light curves a few months after initiation. Type II supernovae are modeled as implosion-explosion events of a massive star. The smooth decay of the light is also consistent with this model since most of the energy output would be from the radioactive decay of the unstable heavy elements produced in the explosion. The fact that the spectra of Type I supernovae are hydrogen poor is consistent with this model, since the white dwarf has almost no hydrogen. It is assumed that the white dwarf accretes enough mass to exceed the Chandrasekhar limit of 1.4 solar masses for a white dwarf. The model for the initiation of a Type I supernova is the detonation of a carbon white dwarf when it collapses under the pressure of electron degeneracy. Supernovae are classified as Type I if their light curves exhibit sharp maxima and then die away smoothly and gradually. These spectral features are illustrated below for specific supernovae. Type II supernovae have strong hydrogen lines. They are classified as Ib if they have strong helium lines, and Ic if they do not. ![]() The subclass type Ia refers to those which have a strong silicon line at 615 nm. They are classified as Type I if they have no hydrogen lines in their spectra. With the observation of a number of supernova in other galaxies, a more refined classification of supernovae has been developed based on the observed spectra. Type I supernovae occur typically in elliptical galaxies, so they are probably Population II stars. They die away more sharply than the Type I. Type II supernovae have less sharp peaks at maxima and peak at about 1 billion solar luminosities. The maxima may be about 10 billion solar luminosities. Supernovae are classified as Type I if their light curves exhibit sharp maxima and then die away gradually. The synthesis of the heavy elements is thought to occur in supernovae, that being the only mechanism which presents itself to explain the observed abundances of heavy elements. Supernovae are classified as Type I or Type II depending upon the shape of their light curves and the nature of their spectra. ![]() The outer layers will be opaque to neutrinos, so the neutrino shock wave will carry matter with it in a cataclysmic explosion. Electrons and protons fuse into neutrons, sending out huge numbers of neutrinos. Out of control, the process can apparently occur on the order of seconds after a star lifetime of millions of years. If the temperature increase from gravitational collapse rises high enough to fuse iron, the almost instantaneous absorption of energy will cause a rapid collapse to reheat and restart the process. In fact, either the fission or fusion of iron group elements will absorb a dramatic amount of energy - like the film of a nuclear explosion run in reverse. The " iron group" of elements around mass number A=60 are the most tightly bound nuclei, so no more energy can be gotten from nuclear fusion. ![]() The likely scenario is that fusion proceeds to build up a core of iron. It may shine with the brightness of 10 billion suns! The total energy output may be 10 44 joules, as much as the total output of the sun during its 10 billion year lifetime. A supernova is an explosion of a massive supergiant star. ![]()
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