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Astronomers may not have observed the fabled "Stairway to Heaven," but they have photographed something almost as intriguing: ladder-like structures surrounding a dying star. A new image, taken with NASA's Hubble Space Telescope, reveals startling new details of one of the most unusual nebulae known in our Milky Way. Cataloged as HD 44179, this nebula is more commonly called the "Red Rectangle" because of its unique shape and color as seen with ground-based telescopes.

Q & A: Understanding the Discovery

1. 1. Why does the nebula look red?




The nebula is made up of gas and dust. Mixed in with the dust are molecules, which emit light in the red portion of the spectrum. Astronomers are not yet certain which types of molecules are producing the red color that is so striking in the Red Rectangle. They suspect that the red color is produced by hydrocarbons — an organic compound containing only carbon and hydrogen - which form in the cool outflow from the star in the center of the nebula. This central star began its life as a star similar to our Sun. It is now nearing the end of its lifetime, and is in the process of ejecting its outer layers to produce the visible nebula.

2. 2. What processes produced the nebula's shape?




Hubble's sharp pictures show that the Red Rectangle is not really rectangular, but has an overall X-shaped structure, which the astronomers involved in the study interpret as arising from outflows of gas and dust from the star in the center. The outflows are ejected from the star in two opposing directions, producing a shape like two ice-cream cones touching at their tips.

3. 3. What are the ladder-like features?




These straight features, which appear like rungs on a ladder, make the Red Rectangle look similar to a spider web, a shape unlike that of any other known nebula in the sky. The rungs may have arisen in episodes of mass ejection from the star occurring every few hundred years. They could represent a series of nested, expanding structures similar in shape to wine glasses, seen exactly edge-on so that their rims appear as straight lines from our vantage point.