Dec 16, 2012

The intricate structure of the Helix Nebula – seen in January 2012

A new infrared picture reveals the intricate structure of the Helix Nebula, the rust-colored remains of a star like our sun that puffed up as it died and shed its shells of gas and dust into space. These thin clouds of molecular gas are difficult to see in visible light, but infrared detectors can pick them out, and they show up in the new image as a dark red haze. The Helix Nebula is a complex object composed of dust, ionized material and molecular gas, arrayed in an intricate, flower-like pattern.
The dying star at the heart of the Helix Nebula is evolving to become a white dwarf, a shrunken, super-dense object that can pack a sun's worth of material into a sphere the size of Earth. The star is visible as a tiny blue dot at the center of the picture.

The main ring of the Helix is about 2 light-years across, roughly equivalent to half the distance between our sun and its closest star. However, wispy material from the nebula spreads out at least 4 light-years into space from the central star.

In visible light, fine details in the Helix are largely obscured by dust. But the infrared view—snapped by the European Southern Observatory's VISTA telescope—can pierce this veil to see radiating filaments of cooler gas in the rings as well as a faint halo of thinly spread gas that extends to at least four light-years from the dead star's core.

Nebula, in astronomy, refers to a localized conglomerate of the gaseous and finely divided dust particles that are spread throughout interstellar space. Before the invention of the telescope, the term nebula (Latin, “cloud”) was applied to all celestial objects of a diffuse appearance. As a result, many objects now known to be star clusters or galaxies were called nebulas.

Nebulas exist within other galaxies as well as in our own Milky Way galaxy. They are classified as planetary nebulas, supernova remnants, and diffuse nebulas, including reflecting, emission, and dark nebulas. Small, very bright nebulas known as Herbig-Haro objects are found in dense interstellar clouds, and are probably the products of gas jets expelled by new stars in the process of formation.

Helix Nebula was discovered by Karl Ludwig Harding, probably before 1824. It is one of the closest to the Earth of all the bright planetary nebulae. The estimated distance is about 215 parsecs or 700 light-years.

Helix is a planetary nebula, a strange object that forms when a star like our sun exhausts its hydrogen fuel. The star's outer layers expand and cool, creating a huge envelope of dust and gas. Radiation flowing from the dying star ionizes this envelope, causing it to glow. Despite their name, planetary nebulas have nothing to do with planets. Rather, the term refers to their superficial resemblance to giant planets, when observed through early telescopes. (Adapted from National Geographic, Wikipedia, Encarta encyclopedia, and Internet sources)