Astr111 Photography Projects, Fall 2009

Blue Snowball Nebula, Cameron Morse

Whereas diffuse nebulae give birth to stars in the gravitational condensation of gas clouds in the interstellar space, planetary nebulae, such as the Blue Snowball Nebula, signal instead the death of stars. Rather than disperse widely across many light-years, the gases of planetary nebula are concentrated around the dying star that throws them off, with a more tightly-packed, ball-like appearance. Planetary Nebulae are the final phase in the evolution of stars, in which the dying star, having exhausted its supply of hydrogen, succumbs to gravitational forces, caving in on itself. The outer layers of its atmosphere are ejected into space. The typical radius of a planetary nebula is one light-year across, the mass of its gas only 0.3 of the solar mass, making it a far smaller object than diffuse nebulae.

At the center of the Blue Snowball Nebula is the nucleus, the opaque body of the white dwarf star, which in obeying the principles of blackbody radiation, emits a blue light. Irradiating ultraviolet light, the nucleus ionizes the gas halo that surrounds it, reflecting a white ring of light. Although the halo of ejected gases appears to be rather regular, higher-resolution images would reveal a kind of rugged terrain that comes of large-scale fluctuations. The green color is doubly ionized oxygen and is transparent. The cloud that clusters around its core is gradually expanding, and will eventually merge with diffuse nebulae that pervade the interstellar space.

References:

O'Dell, C. R. "Nebula." World Book Online Reference Center. 2005. World Book, Inc.

<http://www.worldbookonline.com/wb/Article?id=ar385540>