Compact Stars: The Quest For New States Of Dense Matter
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When this is done, the model radius still decreases with mass, but becomes zero at M limit. This is the Chandrasekhar limit. They are colored blue and green, respectively. Radius is measured in standard solar radii  or kilometers, and mass in standard solar masses.
Calculated values for the limit vary depending on the nuclear composition of the mass. A more accurate value of the limit than that given by this simple model requires adjusting for various factors, including electrostatic interactions between the electrons and nuclei and effects caused by nonzero temperature.
In , the British physicist Ralph H. Fowler observed that the relationship between the density, energy, and temperature of white dwarfs could be explained by viewing them as a gas of nonrelativistic, non-interacting electrons and nuclei that obey Fermi—Dirac statistics. A series of papers published between and had its beginning on a trip from India to England in , where the Indian physicist Subrahmanyan Chandrasekhar worked on the calculation of the statistics of a degenerate Fermi gas. Chandrasekhar's work on the limit aroused controversy, owing to the opposition of the British astrophysicist Arthur Eddington.
Eddington was aware that the existence of black holes was theoretically possible, and also realized that the existence of the limit made their formation possible. However, he was unwilling to accept that this could happen. After a talk by Chandrasekhar on the limit in , he replied:. The star has to go on radiating and radiating and contracting and contracting until, I suppose, it gets down to a few km radius, when gravity becomes strong enough to hold in the radiation, and the star can at last find peace. Miller 's biography of Chandrasekhar. Chandra's discovery might well have transformed and accelerated developments in both physics and astrophysics in the s.
Instead, Eddington's heavy-handed intervention lent weighty support to the conservative community astrophysicists, who steadfastly refused even to consider the idea that stars might collapse to nothing.
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As a result, Chandra's work was almost forgotten. The core of a star is kept from collapsing by the heat generated by the fusion of nuclei of lighter elements into heavier ones. At various stages of stellar evolution , the nuclei required for this process are exhausted, and the core collapses, causing it to become denser and hotter. A critical situation arises when iron accumulates in the core, since iron nuclei are incapable of generating further energy through fusion.
If the core becomes sufficiently dense, electron degeneracy pressure will play a significant part in stabilizing it against gravitational collapse. If a main-sequence star is not too massive less than approximately 8 solar masses , it eventually sheds enough mass to form a white dwarf having mass below the Chandrasekhar limit, which consists of the former core of the star.
For more-massive stars, electron degeneracy pressure does not keep the iron core from collapsing to very great density, leading to formation of a neutron star , black hole , or, speculatively, a quark star. For very massive, low- metallicity stars, it is also possible that instabilities destroy the star completely. Most of this energy is carried away by the emitted neutrinos. Type Ia supernovae derive their energy from runaway fusion of the nuclei in the interior of a white dwarf. This fate may befall carbon — oxygen white dwarfs that accrete matter from a companion giant star , leading to a steadily increasing mass.
As the white dwarf's mass approaches the Chandrasekhar limit, its central density increases, and, as a result of compressional heating, its temperature also increases. This eventually ignites nuclear fusion reactions, leading to an immediate carbon detonation , which disrupts the star and causes the supernova. This seems to indicate that all type Ia supernovae convert approximately the same amount of mass to energy. According to a group of astronomers at the University of Toronto and elsewhere, the observations of this supernova are best explained by assuming that it arose from a white dwarf that grew to twice the mass of the Sun before exploding.
Branch, may have been spinning so fast that a centrifugal tendency allowed it to exceed the limit. Alternatively, the supernova may have resulted from the merger of two white dwarfs, so that the limit was only violated momentarily. Nevertheless, they point out that this observation poses a challenge to the use of type Ia supernovae as standard candles. Since the observation of the Champagne Supernova in , more very bright type Ia supernovae have been observed that are thought to have originated from white dwarfs whose masses exceeded the Chandrasekhar limit. However, spectropolarimetric observations of SN dc showed it had a polarization smaller than 0.
After a supernova explosion, a neutron star may be left behind. These objects are even more compact than white dwarfs and are also supported, in part, by degeneracy pressure. A neutron star, however, is so massive and compressed that electrons and protons have combined to form neutrons, and the star is thus supported by neutron degeneracy pressure as well as short-range repulsive neutron-neutron interactions mediated by the strong force instead of electron degeneracy pressure.
The limiting value for neutron star mass, analogous to the Chandrasekhar limit, is known as the Tolman—Oppenheimer—Volkoff limit. From Wikipedia, the free encyclopedia. Maximum mass of a stable white dwarf star. Main article: Champagne Supernova. Three Hundred Years of Gravitation 1st pbk. Cambridge: Cambridge University Press. In Bethe, Hans A. Bibcode : febh. Science PDF. Bibcode : Sci Chandrasekhar limit: The maximum mass of a white dwarf star, about 1. Their policies may differ from this site.arofthesi.ga
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