White dwarf
Dwarf star
One of the forms that white dwarf [1] (はくしょくわいせい, white dwarf[1]) can take a fixed star for the end period of the evolution. The mass is big with around one of several minutes from the sun and the degree, but a mosquito net as for the diameter at the same level as the earth reduce so as to be big, and is the very high-density heavenly bodies.
Several hundred including the subordinate star (Sirius B) and station wagon マーネン star of Sirius are known. Among the heavenly bodies which mass has a bigger than a brown dwarf of the sun neighborhood, it is thought that a quarter is occupied in the white dwarf [2].
Table of contents
I it in a formation process
In the fixed star within 3 times of the sun, a central nucleus becomes helium by a fusion reaction of hydrogen mass, and when temperature goes up it, it is a red giant-star and the outer stratum region made of hydrogen takes the form of the planetary nebula and is released in the outer space, and it is the central nucleus which remained in a white dwarf. I utter light and heat for residual heat when it was the central nucleus of the fixed star and pressure by the gravity, and a high temperature white dwarf for 100,000 degrees is seen in the center of the planetary nebula including the spiral nebula of ring nebula and Aquarius of Lyra, dumbbell form nebula of Vulpecula from 50,000 degrees the surface temperature that outer stratum region is stripped off, and it was just possible for. Because there is not an energy source to raise a fusion reaction anymore, surface temperature gradually falls down, and, in these stars, the color changes into O B A F G K M and the spectral class in a cooling process, too, and it is in a black dwarf star finally; and with the electromagnetic wave is said that cannot observe it. It is predicted that the sun becomes more the white dwarf about in 5000000000 years.
Willem Jacob Louis ten devised the word "white dwarf" [3].
After the existence of the thing that a theory was proposed in the neutron star and the black hole not being proved until the 1960s, and a fixed star of the large mass becoming the supernova, and having exploded, it was thought that the central nucleus became the white dwarf.
Physical property
As for the best-known Sirius subordinate star (Sirius B), as for the diameter, as for 0.016 times, mass of the sun, 1.06 times, the mean density are considered to be 400,000 times of the water as a white dwarf (from "a science chronological table for 2,000 years for"). From there, the surface gravity is calculated with approximately 116,000 times in comparison with solar approximately 4,100 times, earth. A pressure incline of the degeneration pressure by this which the electron in the atom degenerates a fermi for the high density, and cannot form a further degeneration state from exclusion principle of Pauli and gravity of the star match, and the white dwarf can keep the form.
The white dwarfs more than approximately 1.4 times of the sun mass do not exist (they refer to チャンドラセカール limit). It is a neutron star without being able to finish supporting the shrinkage of the star by the gravity by the electronic degeneration pressure when it is more than 1.4 times, or it is either which lets you cause gravitational collapse and free gravity energy at a stretch, and explodes. The latter is said to be a type II supernova explosion.
A white dwarf is the heavenly body which does not evolve anymore, and only gets cold, but may be active as a nova and Ia type supernova only when I constitute normal fixed star and proximity binary. I am piled up, and hydrogen which is stripped off from the star of the partner by the gravity of the white dwarf, and performed accretion is heated by the potential energy at the time of the fall and strong gravity by the surface and wakes up nuclear fusion when I exceed a limit. Mechanism to expand when nuclear fusion becomes active in a center at the normal fixed star, and temperature and pressure go up it, and to lower the speed works and it is stable and continues releasing energy, but there is not such an action in a degenerate gas, and the nuclear fusion drives recklessly and blows off hydrogen which laid thick on the surface. This is a nova.
When there is much quantity of descent of hydrogen, heat piles up, and nuclear fusion may be carried out at the surface. In that case, the mass of the white dwarf increases, and the nuclear fusion takes charge in a center when I exceed チャンドラセカール limit and leads to an Ia type supernova explosion.
A material constituting a white dwarf is helium, carbon, oxygen which occurred because of a fusion reaction (elsewhere with neon or magnesium). In 2004, an American study group points out the possibility that there is a huge diamond in the white dwarf. This depends on carbon which is the component of the white dwarf crystallizing under high pressure, but there is the indication that the aspect except the diamond is more stable at the high pressure [4], and [5] is not sure at all what kind of crystal structure is really stable under the high pressure such as the white dwarf. This is because it is thought that the white dwarf consists of gas and plasma like a normal fixed star.
Source
- ^ a b "Oxford astronomy dictionary" Asakura Bookstore, first edition first impression, page 313. ISBN 4-254-15017-2。
- ^ Ledrew, Glenn (2001). "The Real Starry Sky". It is .
- ^ Holberg, J. B. (2005). "How Degenerate Stars Came to be Known as White Dwarfs." American Astronomical Society Meeting 207 207:1,503. Bibcode 2005AAS...20720501H.
- ^ M. T. Yin and M. L. Cohen, Phys. Rev. Lett., Vol. 50, No. 25 (1983) 2006.
- ^ S. Scandolo, G. L. Chiarotti and E. Tosatti, Phys. Rev. B53 (1996) 5051.
Allied item
This article is taken from the Japanese Wikipedia White dwarf
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