Collapsible core

Except in the dense collapsing core of a massive supernova. 

Models of hot isentropic neutron stars have been calculated by Bisnovatyi-Kogan (1968), where equilibrium between iron, protons and neutrons was calculated, and the ratio of protons and neutrons was taken in the approximation of zero chemical potential of neutrino. The stability was checked using a variational principle in full GR (Chandrasekhar, 1964) with a linear trial function. The results of calculations, showing the stability region of hot neutron stars are given in Fig. 7. Such stars may be called neutron only by convention, because they consist mainly of nucleons with almost equal number of neutrons and protons. The maximum of the mass is about 70M , but from comparison of the total energies of hot neutron stars with presupemova cores we may conclude, that only collapsing cores with masses less that 15 M have... 

The star bums its own ashes, and the ashes of its ashes, but iron will not bum and the nuclear fire goes out. Blue giants with collapsed cores open like flowers and scatter their swarms of winged atoms in the sky. The dying of their light is acknowledged with the cry of Supernova ... 

Fig. 5.4. Schematic evolution of the internal structure of a star with 25 times the mass of the Sun. The figure shows the various combustion phases (shaded) and their main products. Between two combustion phases, the stellar core contracts and the central temperature rises. Combustion phases grow ever shorter. Before the explosion, the star has assumed a shell-like structure. The centre is occupied by iron and the outer layer by hydrogen, whilst intermediate elements are located between them. CoUapse followed by rebound from the core generates a shock wave that reignites nuclear reactions in the depths and propels the layers it traverses out into space. The collapsed core cools by neutrino emission to become a neutron star or even a black hole. Most of the gravitational energy liberated by implosion of the core (some 10 erg) is released in about 10 seconds in the form of neutrinos. (Courtesy of Marcel Amould, Universite Libre, Brussels.)...

But all this cannot happen without losses along the way. Stellar corpses and collapsed cores (white dwarfs, neutron stars and black holes) are permanently removed from the great flow of nuclear evolution. It is as though their substance has been conflscated, so that it can no longer take part in the ebb and flow of matter, entering the stars in one form and re-emerging in another. Almost all elements required for life are now present. 

Hadronic equation of state at high density, p = po to 4po, Po 2.4 X 1024 g/cm3 the saturation density for the asymmetric nuclear matter found in the collapsing core. A moderate softening of nuclear matter under these conditions allows the core to collapse further into the gravitational well and thus increases the shock energy at formation. 

QUASI-STATIC AND STEADY-STATE PICTURES FOR COLLAPSING CORE OF TYPE II SUPERNOVA... 

Quasi-Static and Steady-State Pictures for Collapsing Core of Type II Supernova D. Sugimoio, A. Sasaki, and T. Ebisuzaki 420... 

Fig. 25 Schematic of transitions of chain conformation of a segmented copolymer chain with stickers in dilute solution from a random coil to an ordered coil and then from an ordered coil to a collapsed core-shell globule as the solvency of water for the PNIPAM chain backbone decreases [94]...

Intuition might tell you that the collapsing core will keep falling, squeezing itself together until it becomes so dense that it can fall no farther. This is like when you crumple a sheet of paper into a ball. You can only squeeze it to a certain point, after which it is too tightly packed to reduce its size any further. 

If the collapsing core is between 1.4 and about 2.5 times the mass of the Sun, however, the gravity will be so strong that the electron degeneracy pressure will fail. Unable to resist the weight of their own gravity, the atoms will be crushed into a ball made mainly of neutrons about 32,810 ft (10 km) across. This object is called a neutron star. 

A nova is a phenomenon that happens in a binary star system containing a white dwarf and a stable companion star. A white dwarf is the dead, collapsed core of a star that formerly was about the size of the Sun. When the Sun dies, it will become a white dwarf. Unlike the Sun, however, many stars exist in binary systems, where two stars orbit one another, hi many binaries, these stars may be separated by a distance much less than the distance from the Sun to Earth. 

Marshak, S., Tinkham, D., Alkmim, F., Brueckner, H. Bornhorst, T. j. 1997. Dome-and-keel provinces formed during Paleoproterozoic orogenic collapse - core complexes, diapirs, or neither Examples from the Quadrilatero Ferrifero and the Penokean Orogen. Geology, 25, 415-418. 

Transition from ID to multi-dimensional hydrodynamic calculations has enabled a more accurate treatment of fluid instabilities. Presently, it is recognized that even with detailed account of Boltzmann neutrino transport, additional physical properties of the collapsing core, e.g. rotation, need to be coupled with multi-dimensional calculations to produce successful neutrino-driven explosions (see e.g. [72, 105]). 

Supernovae, planetary nebulae (PNe) and, to a minor extent, stellar winds are the means to restore the nuclearly enriched material into the ISM, thus giving rise to the process of chemical evolution. There are two main Types of SNe (II, I) then divided in subclasses SNe IIL, IIP and SNe la, lb, Ic. As already mentioned before, SNe II, which are believed to be the end state of stars more massive than 1OM0 exploding after a Fe core is formed (core-collapse SNe), produce mainly a-elements (O, Ne, Mg, Si, S, Ca) plus some Fe. The amount of Fe produced by type II SNe is one of the most uncertain quantities since it depends upon the so-called mass cut (how much Fe remains in the collapsing core and how much is ejected) and on explosive nucleosynthesis. 

USM Full shot of foamable plastic is injected into a reduced-size mold cavity. Collapsible core or movable walls then expand the cavity to permit foam to expand. 

The collapsing core meanwhile becomes denser and hotter until helium is able to fuse into carbon via the triple-alpha process (helium burning). Initially two helium nuclei, or alpha particles, fuse to form an unstable and very short-lived state of beryllium. Despite the brevity of its existence (about a tenth of a femtosecond), there is a chance for some of these Be nuclei to capture alpha particles to form the basis of... 

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