EMBARGOED UNTIL:  9:00 A.M. MST, January 11, 1995
PHOTO RELEASE NO.:  STScI-PRC95-01BW

HUBBLE PROBES THE COMPLEX HISTORY OF A DYING STAR 

This NASA Hubble Space Telescope image shows one of the most complex
planetary nebulae ever seen, NGC 6543, nicknamed the "Cat's Eye
Nebula." Hubble reveals surprisingly intricate structures including
concentric gas shells, jets of high-speed gas and unusual shock-induced
knots of gas.  Estimated to be 1,000 years old, the nebula is a visual
"fossil record" of the dynamics and late evolution of a dying star.

A preliminary interpretation suggests that the star might be a
double-star system. The dynamical effects of two stars orbiting one
another most easily explains the intricate structures, which are much
more complicated than features seen in most planetary nebulae.  (The
two stars are too close together to be individually resolved by Hubble,
and instead, appear as a single point of light at the center of the
nebula.)

According to this model, a fast "stellar wind" of gas blown off the
central star created the elongated shell of dense, glowing gas.  This
structure is embedded inside two larger lobes of gas blown off the star
at an earlier phase.  These lobes are "pinched" by a ring of denser
gas, presumably ejected along the orbital plane of the binary
companion.

The suspected companion star also might be responsible for a pair of
high-speed jets of gas that lie at right angles to this equatorial
ring.  If the companion were pulling in material from a neighboring
star,  jets escaping along the companion's rotation axis could be
produced.

These jets would explain several puzzling features along the periphery
of the gas lobes.  Like a stream of water hitting a sand pile, the jets
compress gas ahead of them, creating the "curlicue" features and bright
arcs near the outer edge of the lobes.  The twin jets are now pointing
in different directions than these features.  This suggests the jets
are wobbling, or precessing, and turning on and off episodically.

The image was taken with the Wide Field Planetary Camera-2 on September
18, 1994.  NGC 6543 is 3,000 light-years away in the northern
constellation Draco.

The term planetary nebula is a misnomer; dying stars create these
cocoons when they lose outer layers of gas.  The process has nothing to
do with planet formation, which is predicted to happen early in a
star's life.

This material was presented at the 185th meeting of the American
Astronomical Society in Tucson, AZ on January 11, 1995.

Credit: J.P. Harrington and K.J. Borkowski (University of Maryland),
and NASA