Violent gas collisions that produced supersonic shock fronts in a dying
star are seen in a new, detailed image from NASA’s Hubble Space Telescope.

The picture, taken by Hubble’s Wide Field and Planetary Camera 2, is online
at . The camera was designed and built by NASA’s
Jet Propulsion Laboratory, Pasadena, Calif.

Stars like our Sun will eventually die and expel most of their material outward
into shells of gas and dust. These shells eventually form some of the most beautiful
objects in the universe, called planetary nebulae.

“This new image gives us a rare view of the early death throes of stars like our
Sun. For the first time, we can see phenomena leading to the formation of planetary
nebulae. Until now, this had only been predicted by theory, but had never been seen
directly,” said Dr. Raghvendra Sahai, research scientist and member of the science team
at JPL for the Wide Field and Planetary Camera 2.

The object is sometimes called the Rotten Egg Nebula, because it contains a lot of
sulphur, which would produce an awful odor if one could smell in space. The object is
also known as the Calabash Nebula or by the technical name OH231.8+4.2.

The densest parts of the nebula are composed of material ejected recently by the
central star and accelerated in opposite directions. This material, shown as yellow in the
image, is zooming away at speeds up to one and a half million kilometers per hour (one
million miles per hour). Most of the star’s original mass is now contained in these bipolar
gas structures.

A team of Spanish and American astronomers used NASA’s Hubble Space
Telescope to study how the gas stream rams into the surrounding material, shown in blue.
They believe that such interactions dominate the formation process in planetary nebulae.
Due to the high speed of the gas, shock-fronts are formed on impact and heat the
surrounding gas. Although computer calculations have predicted the existence and
structure of such shocks for some time, previous observations have not been able to prove
the theory.

This new Hubble image used filters that only let through light from ionized
hydrogen and nitrogen atoms. Astronomers were able to distinguish the warmest parts of
the gas heated by the violent shocks and found that they form a complex double-bubble
shape. The bright yellow-orange colors in the picture show how dense, high-speed gas is
flowing from the star, like supersonic speeding bullets ripping through a medium in
opposite directions. The central star itself is hidden in the dusty band at the center.

Much of the gas flow observed today seems to stem from a sudden acceleration
that took place only about 800 years ago. The astronomers believe that 1,000 years from
now, the Calabash Nebula will become a fully developed planetary nebula, like a
butterfly emerging from its cocoon.

The Calabash Nebula is 1.4 light years (more than 8 trillion miles) long and
located some 5,000 light years (2,900 trillion miles) from Earth in the constellation

The image was taken in December 2000 by the Wide Field and Planetary Camera
2. Additional information about the Hubble Space Telescope is online at . More information about the Wide Field and Planetary
Camera 2 is at .

Other scientists on the team include Valentin Bujarraba and Javier Alcolea of
Observatorio Astronomico Nacional, Spain, and Carmen Sanchez Contreras of JPL.

The Space Telescope Science Institute, Baltimore, Md., manages space operations
for Hubble for NASA’s Office of Space Science, Washington, D.C. The institute is
operated by the Association of Universities for Research in Astronomy, Inc., 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. JPL is a division of the California Institute of Technology in Pasadena.