quinta-feira, novembro 13, 2003
Fantástico sítio, o deste senhor Jan Curtis.
Halo of the Cat's Eye
"Explanation: The Cat's Eye Nebula (NGC 6543) is one of the best known planetary nebulae in the sky. Its haunting symmetries are seen in the very central region of this stunning false-color picture, processed to reveal the enormous but extremely faint halo of gaseous material, over three light-years across, which surrounds the brighter, familiar planetary nebula. Made with data from the Nordic Optical Telescope in the Canary Islands, the composite picture shows emission from nitrogen atoms as red and oxygen atoms as green and blue shades. Planetary nebulae have long been appreciated as a final phase in the life of a sun-like star. Only much more recently however, have some planetaries been found to have halos like this one, likely formed of material shrugged off during earlier active episodes in the star's evolution. While the planetary nebula phase is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years."
An Intermediate Polar Binary System
"Explanation: How can two stars create such a strange and intricate structure? Most stars are members of multiple-star systems. Some stars are members of close binary systems where material from one star swirls around the other in an accretion disk. Only a handful of stars, however, are members of an intermediate polar, a system featuring a white dwarf star with a magnetic field that significantly pushes out the inner accretion disk, only allowing material to fall down its magnetic poles. Shown above is an artist's depiction of an intermediate polar system, also known as a DQ Hercules system. The foreground white dwarf is so close to the normal star that it strips away its outer atmosphere. As the white dwarf spins, the columns of infalling gas rotate with it. The name intermediate polar derives from observations of emitted light polarized at a level intermediate to non-disk binary systems known as polars. Intermediate polars are a type of cataclysmic variable star system."
posted by Luís Miguel Dias quinta-feira, novembro 13, 2003