“white dwarf”的概念、定义、翻译、参考文献-科学参考

white dwarf

Physics

A compact stellar object that is supported against collapse under self-gravity by the degeneracy pressure of electrons. White dwarfs are formed as the end products of the evolution of stars of relatively low mass (about that of the sun); high-mass stars may end up as neutron stars or black holes (see stellar evolution). White dwarfs consist of helium nuclei (and carbon and oxygen nuclei in the more massive cases) and a degenerate gas of electrons. A typical white-dwarf density is 10⁹ kg m⁻³; white dwarf masses and radii are in the region of 0.7 solar masses and 10³ km respectively. There is a maximum mass for white dwarfs, above which they are unstable to gravitational collapse—this is known as the Chandrasekhar limit and is about 1.4 solar masses.

Astronomy

A small, dense star that is the end-result of the evolution of all but the most massive stars. White dwarfs are thought to form from the collapse of stellar cores once nuclear burning has ceased there. The core is exposed to view when the outer parts of the star are driven off to form a planetary nebula. Such a core contracts under its own gravity until, having reached a size similar to that of the Earth, it has become so dense (5 × 10⁸ kg/m³) that it is supported against further collapse by the pressure of electron degeneracy. White dwarfs are formed with high surface temperatures (above 10 000 K) because of the heat trapped within them, released both by previous nuclear burning and through gravitational contraction. They gradually cool, becoming fainter and redder. White dwarfs may constitute 30% of the stars in the solar neighbourhood, but because of their low luminosity (typically 10⁻³ to 10⁻⁴ of the Sun’s) they are very inconspicuous. The maximum possible mass for a white dwarf is 1.44 solar masses, the Chandrasekhar limit. An object of greater mass would contract further and become either a neutron star or a black hole. See also D star.

Space Exploration

A small, hot star, the last stage in the life of a star such as the Sun. White dwarfs make up 10% of the stars in the Galaxy; most have a mass 60% of that of the Sun, but only 1% of the Sun's diameter, similar in size to the Earth. Most have surface temperatures of 8 000° C or more, hotter than the Sun. However, being so small, their overall luminosities may be less than 1% of that of the Sun. The Milky Way contains an estimated 50 billion white dwarfs.
White dwarfs consist of degenerate matter in which gravity has packed the protons and electrons together as tightly as is physically possible, so that a spoonful of it weighs several tonnes. White dwarfs are thought to be the shrunken remains of stars that have exhausted their internal energy supplies. They cool slowly, and fade over billions of years.

单词	white dwarf
释义	white dwarf Physics A compact stellar object that is supported against collapse under self-gravity by the degeneracy pressure of electrons. White dwarfs are formed as the end products of the evolution of stars of relatively low mass (about that of the sun); high-mass stars may end up as neutron stars or black holes (see stellar evolution). White dwarfs consist of helium nuclei (and carbon and oxygen nuclei in the more massive cases) and a degenerate gas of electrons. A typical white-dwarf density is 10⁹ kg m⁻³; white dwarf masses and radii are in the region of 0.7 solar masses and 10³ km respectively. There is a maximum mass for white dwarfs, above which they are unstable to gravitational collapse—this is known as the Chandrasekhar limit and is about 1.4 solar masses. Astronomy A small, dense star that is the end-result of the evolution of all but the most massive stars. White dwarfs are thought to form from the collapse of stellar cores once nuclear burning has ceased there. The core is exposed to view when the outer parts of the star are driven off to form a planetary nebula. Such a core contracts under its own gravity until, having reached a size similar to that of the Earth, it has become so dense (5 × 10⁸ kg/m³) that it is supported against further collapse by the pressure of electron degeneracy. White dwarfs are formed with high surface temperatures (above 10 000 K) because of the heat trapped within them, released both by previous nuclear burning and through gravitational contraction. They gradually cool, becoming fainter and redder. White dwarfs may constitute 30% of the stars in the solar neighbourhood, but because of their low luminosity (typically 10⁻³ to 10⁻⁴ of the Sun’s) they are very inconspicuous. The maximum possible mass for a white dwarf is 1.44 solar masses, the Chandrasekhar limit. An object of greater mass would contract further and become either a neutron star or a black hole. See also D star. Space Exploration A small, hot star, the last stage in the life of a star such as the Sun. White dwarfs make up 10% of the stars in the Galaxy; most have a mass 60% of that of the Sun, but only 1% of the Sun's diameter, similar in size to the Earth. Most have surface temperatures of 8 000° C or more, hotter than the Sun. However, being so small, their overall luminosities may be less than 1% of that of the Sun. The Milky Way contains an estimated 50 billion white dwarfs. White dwarfs consist of degenerate matter in which gravity has packed the protons and electrons together as tightly as is physically possible, so that a spoonful of it weighs several tonnes. White dwarfs are thought to be the shrunken remains of stars that have exhausted their internal energy supplies. They cool slowly, and fade over billions of years.
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