“brown dwarf”的概念、定义、翻译、参考文献-科学参考

brown dwarf

Physics

An astronomical object with a mass intermediate between the mass of a planet and that of a small star. The mass of a brown dwarf is large enough to generate energy by gravitational pressure, but not large enough to sustain nuclear fusion. The energy is radiated as electromagnetic radiation. Brown dwarfs are faint objects, which are expected to shine for about 100 million years before cooling. Their masses lie between a few times the mass of Jupiter and 80 times the mass of Jupiter. It has been suggested that brown dwarfs may contribute to the missing mass of the universe.

Astronomy

An object that, because of its low mass (less than 0.08 solar masses), never becomes hot enough to begin hydrogen fusion in its core although it can produce some nuclear energy for a few million years from the fusion of deuterium, a heavy isotope of hydrogen, which requires lower temperatures than normal hydrogen fusion; hence it is considered to be not a star, but a substellar object. Brown dwarfs have surface temperatures of about 2000 K and cooler. They thus have a very low luminosity and are difficult to detect. Brown dwarfs may be at least as numerous as visible stars but because of their low masses are not thought to be a significant component of the galactic dark matter. The first brown dwarf to be identified with certainty was a companion to the nearby red dwarf Gliese 229, photographed by the Hubble Space Telescope in 1995. Brown dwarfs are now assigned the spectral types L, T, and Y (see L Dwarf; T Dwarf; Y Dwarf). An object below about 0.01 solar masses (about 10 Jupiter masses) is regarded as a planet.

Space Exploration

An object less massive than a star but denser than a planet. Brown dwarfs do not have enough mass to ignite nuclear reactions at their centres, but shine by heat released during their contraction from a gas cloud. Groups of brown dwarfs have been discovered, and some astronomers believe that vast numbers of them exist throughout the Galaxy.
The first brown dwarf to be positively identified was Gliese 229B (GI229B), in the constellation Lepus, by US astronomers using images from the Hubble Space Telescope. It is about 50 times as massive as Jupiter but emits only 1% of the radiation of the smallest known star and has a surface temperature of 650° C.

单词	brown dwarf
释义	brown dwarf Physics An astronomical object with a mass intermediate between the mass of a planet and that of a small star. The mass of a brown dwarf is large enough to generate energy by gravitational pressure, but not large enough to sustain nuclear fusion. The energy is radiated as electromagnetic radiation. Brown dwarfs are faint objects, which are expected to shine for about 100 million years before cooling. Their masses lie between a few times the mass of Jupiter and 80 times the mass of Jupiter. It has been suggested that brown dwarfs may contribute to the missing mass of the universe. Astronomy An object that, because of its low mass (less than 0.08 solar masses), never becomes hot enough to begin hydrogen fusion in its core although it can produce some nuclear energy for a few million years from the fusion of deuterium, a heavy isotope of hydrogen, which requires lower temperatures than normal hydrogen fusion; hence it is considered to be not a star, but a substellar object. Brown dwarfs have surface temperatures of about 2000 K and cooler. They thus have a very low luminosity and are difficult to detect. Brown dwarfs may be at least as numerous as visible stars but because of their low masses are not thought to be a significant component of the galactic dark matter. The first brown dwarf to be identified with certainty was a companion to the nearby red dwarf Gliese 229, photographed by the Hubble Space Telescope in 1995. Brown dwarfs are now assigned the spectral types L, T, and Y (see L Dwarf; T Dwarf; Y Dwarf). An object below about 0.01 solar masses (about 10 Jupiter masses) is regarded as a planet. Space Exploration An object less massive than a star but denser than a planet. Brown dwarfs do not have enough mass to ignite nuclear reactions at their centres, but shine by heat released during their contraction from a gas cloud. Groups of brown dwarfs have been discovered, and some astronomers believe that vast numbers of them exist throughout the Galaxy. The first brown dwarf to be positively identified was Gliese 229B (GI229B), in the constellation Lepus, by US astronomers using images from the Hubble Space Telescope. It is about 50 times as massive as Jupiter but emits only 1% of the radiation of the smallest known star and has a surface temperature of 650° C.
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