Gravitational collapse

The fomiation of molecules was the first step toward local gravitational collapses which led to, among other things, the production of this encyclopedia. 

Our planet Earth contains significant amounts of elements all the way up to Z = 92. This indicates that our solar system resulted from the gravitational collapse of a cloud of matter that included debris from second-generation stellar supemovae. Thus, our sun most likely is a third-generation star. The composition of a third-generation star includes high-Z nuclides, but the nuclear reactions are the same as those in a second-generation star. 

Protostar A star early in the evolutionary process, shortly after the initial gravitational collapse. 

Harrison, B. K., Thome, K. S., Wakano, M., Wheeler,J.A. (1965). Gravitational Theory and Gravitational Collapse Chicago, University of Chicago Press. 

B.K. Harrison, K.S. Thorne, M. Wakano, and J.A. Wheeler. Gravitation theory and gravitational collapse , University of Chicago Press, 1965. 

At the other extreme, the neutrinos and gamma rays emitted by a supernova in 1987 brought brilliant confirmation of the most elaborate theoretical speculations concerning the mechanisms of stellar explosion and the gravitational collapse which immediately precedes it. 

A scenario imagined by Zwicky in 1938 was for a long time the only explanation of the phenomenon. According to this view, a supernova marks the transformation of a normal star into a neutron star, drawing its energy from gravitational collapse. This led astronomers to think that the death of a star was the transition from luminous perfection to a kind of dark perfection. 

Thus, when an iron core develops, reactions capable of generating energy come to an end and the star loses its only means of resisting against gravitational collapse. Disaster is indeed imminent. 

Apart from this phenomenon, gravitational collapse has another important effect. The tremendously hot neutron star in the making emits a copious supply of thermal neutrinos and antineutrinos. These transfer some 10 erg, that is, almost all the gravitational energy liberated by compaction of part of the original star into a neutron star with mass around 1.5 Mq and radius 10 km. 

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. 

However, the entombment of iron is only perpetrated by gravitational-collapse supernovas. Their thermonuclear counterparts are more liberal and, one might say, more final, for they leave behind no corpse, no bones, and no scrap iron. They owe this propensity for total destraction to the rigidity and fragility of the exploding body, the white dwarf, a porcelain ornament that is sure to break when it falls. But thermonuclear supernovas, though lavish providers of iron, are rare. Very special conditions must be fulfilled for these explosions to occur. 

Stars form when dense regions of cold molecular clouds undergo gravitational collapse. In dense molecular cloud cores, the temperature is in the order of 10-20 and the gas density... 

The sightings of simultaneous, bunches of neutrinos in the KII [6] and IMB [7] detectors some three or four hours before optical observations of SN1987a is surely as good a demonstration of the existence of gravitational collapse supernovae as we can desire. The very short time between neutrinos and optical visibility is a surprise, speaking to the small size and unusual nature of the progenitor. We have performed [5] one of the many parallel analyses of these neutrinos [23-28]. 

Eventually, the hydrogen fuel of the star will be exhausted and further gravitational collapse will occur. This will give rise to a temperature increase up to 1—2 x 108 K (with a density of 108 kg/m3). In this red giant, helium burning will commence. 

Eventually, the helium of the star will be exhausted, leading to further gravitational collapse with a temperature increase to 6 x 108-2 x 109 K (kT 100-200 keV). At this point the fusion reactions of the a-cluster nuclei are possible. For example,... 

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