Some 650 light-years away, deep in the constellation Aquarius, lies the Helix Nebula, one of the most beautiful stellar corpses ever photographed. In visible light, the nebula gases shed by a dying Sun-like star glows with a gorgeous rainbow of colors. But some of the most important clues to the Helix's structure come in the form of light that the human eye cannot see.
Enter the Spitzer Space Telescope and its infrared eyes. Yesterday, at this week's American Astronomical Society meeting in Washington, DC, Joseph Hora (Harvard-Smithsonian Center for Astrophysics) released a new view of this iconic celestial fixture. Ground- and space-based images of the Helix had revealed it contains a seemingly countless number of "cometary knots." Though superficially resembling comets, these compact blobs of gas are each about twice as large as our solar system.
Hora's image shows how the comet-like streamers are energized by ultraviolet radiation coming from the hot core of the dying star that spawned the Helix. (That hot stellar core itself is barely visible as a speck at the center of the Hubble and Spitzer images.) Hora's new view also shows that the reddish tails are relatively well shielded from the radiation, as the gases within them are less thoroughly energized than the cometary knots' inward-facing tips. In time the nebula will become redder and fainter as it expands and dissipates into the blackness of space.