The "Rotten Egg" Nebula: A Planetary Nebula in the Making

STScI-PRC-PR99-39 October 19, 1999
Updated August 31, 2001

There are now two 'parts' to this Rotten Egg Story - at the top of this page is the latest HST image and associated text.  The earlier part of the story follows this latest news and image.  This object is also known as the Calabash Nebula.

1. What is the object in these pictures?

This oddly shaped object is an aging Sun-like star that is near the end of its life. The Hubble Space Telescope's infrared camera, called the Near Infrared Camera and Multi-Object Spectrometer, captured a fleeting phase in the death march of this star. These images show the transformation from a red giant star into a planetary nebula, the glowing remnants of a dying star. The star is buried in dust and gas in the center of these pictures. The "wings" of material, called a nebula, are dust and gas cast off by the declining star.

2. Why do astronomers need an infrared camera to take pictures of this object?

An infrared camera "sees" through dust and gas to capture more details of the nebula's structure. Unlike most visible light, infrared light is not absorbed by dust.

3. What do the images of this dying star tell astronomers?

The star is blowing out gas and dust in two opposite directions. These blasts of gas are traveling at speeds up to 450,000 mph. The fast-moving gas and dust are forming several thin streamers (on the right of both images). A jet of material can be seen in the left lobe. On the right, wisps of material in jet-like streamers appear to strike dense blobs of gas. By studying these structural details, astronomers will gain a better understanding of the final stages in the lives of stars like our Sun.

4. Why are there two pictures of the same object?

The two pictures tell different stories about the last gasps of this dying star. The black-and-white image shows more clearly the faint detail and structure in the nebula. The color picture reveals that the composition and temperature of the material ejected from the star varies.

5. Why is this object called the "Rotten Egg" Nebula?

Astronomers have dubbed the object the "Rotten Egg" Nebula because of the large amount of sulfur compounds found in the gas surrounding the dying star. The object's "proper" name is OH231.8+4.2, and it resides in the constellation Puppis.

The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).

The object shown in these NASA/ESA Hubble Space Telescope images is a remarkable example of a star going through death throes just as it dramatically transforms itself from a normal red giant star into a planetary nebula. This process happens so quickly that such objects are quite rare, even though astronomers believe that most stars like the Sun will eventually go through such a phase.

This star, with the prosaic name of OH231.8+4.2, is seen in these infrared pictures blowing out gas and dust in two opposite directions. So much dust has been cast off and now surrounds the star that it cannot be seen directly, only its starlight that is reflected off the dust. The flow of gas is very fast, with a velocity up to 450,000 mph (700,000 km/h). With extreme clarity, these Hubble Near Infrared Camera and Multi-Object Spectrometer (NICMOS) images reveal that the fast-moving gas and dust are being collimated into several thin streamers (on the right) and a jet-like structure (on the left), which can be seen extending away from the centers of both pictures. On the right, wisps of material in jet-like streamers appear to strike some dense blobs of gas. This interaction must produce strong shock waves in the gas.

The pictures represent two views of the object. The color image is a composite of four images taken with different NICMOS infrared filters on March 28, 1998. It shows that the physical properties of the material, both composition and temperature, vary significantly throughout the outflowing material. The black-and-white image was taken with one NICMOS infrared filter. That image is able to show more clearly the faint detail and structure in the nebula than can be achieved with the color composites.

Observations by radio astronomers have found many unusual molecules in the gas around this star, including many containing sulfur, such as hydrogen sulfide and sulfur dioxide. These sulfur compounds are believed to be produced in the shock waves passing through the gas. Because of the large amount of sulfur compounds, this object has earned the nickname "The Rotten Egg" Nebula. It resides in the constellation Puppis.

These NICMOS data pose a serious challenge to astrophysical theorists: How can a star generate such tightly collimated streams of gas and dust and accelerate them to such very high velocities? William B. Latter from the California Institute of Technology and his group are using these data to obtain a better understanding of the detailed structure in the outflowing material, look for evidence for the origin of the thin streamers and jets, and learn more about the star itself. This information will give astronomers a more complete understanding of the final stages in the lives of stars like our Sun.

These results were presented at a conference called "Asymmetrical Planetary Nebulae II: From Origins to Microstructures," Aug. 3 to 6, 1999 at the Massachusetts Institute of Technology. The results also will be published in the Astrophysical Journal.

Credit: NASA, ESA, William B. Latter (SIRTF Science Center/California Institute of Technology), John H. Bieging (University of Arizona), Casey Meakin (University of Arizona), A.G.G.M. Tielens (Kapteyn Astronomical Institute), Aditya Dayal (IPAC/NASA Jet Propulsion Laboratory), Joseph L. Hora (Center for Astrophysics), and Douglas M. Kelly (University of Arizona).

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