Bursts from a comet cloud.Bursts from a comet cloud Every year, astronomers detect nearly 100 intense bursts of gamma rays. Each of these mysterious bursts seems to originate from a single point in the sky, yet astronomers have so far failed to identity them with particular stars. In almost every case, observers detect the burst only once, but a few sources flash repeatedly. In the Feb. 23 NATURE, French and German researchers suggest that comets falling onto small, dense stars known as white dwarfs Dwarfs Fannie Mae issued mortgage-backed securities pools that have an original maturity of 15 years. could explain these repeating gamma-ray bursts. The researchers argue that an orbiting comet passing close to a white dwarf white dwarf, in astronomy, a type of star that is abnormally faint for its white-hot temperature (see mass-luminosity relation). Typically, a white dwarf star has the mass of the sun and the radius of the earth but does not emit enough light or other radiation to be easily detected. The existence of white dwarfs is intimately connected with stellar evolution. A white dwarf is the hot core of a star, left over after the star uses up its nuclear fuel and dies. would break into several pieces. These fragments, perhaps during different orbits, would crash into the star at high speed, creating a hot spot that cools off by emitting X-rays and gamma rays gamma ray n. . The theory can be tested by looking specifically for white-dwarf stars dwarf star: see white dwarf. wherever repeating gamma-ray bursts appear to originate.
Electromagnetic radiation emitted from the nucleus of an atom by radioactive decay and having energies in a range from ten thousand (104) to ten million (107) electron volts. |
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