PHOTO NO.: STScI-PRC96-13a 


HUBBLE CAPTURES COLLISION OF GASES NEAR DYING STAR

This colorful image from the Hubble Space Telescope shows the 
collision of two gases near a dying star.  Astronomers have dubbed 
the tadpole-like objects in the upper right-hand corner "cometary 
knots" because their glowing heads and gossamer tails resemble 
comets.  Although astronomers have seen gaseous knots through 
ground-based telescopes, they have never seen so many in a single 
nebula.

Hubble captured thousands of these knots from a doomed star in the 
Helix nebula, the closest planetary nebula to Earth at 450 light-years 
away in the constellation Aquarius.  Each gaseous head is at least 
twice the size of our solar system; each tail stretches 100 billion 
miles, about 1,000 times the Earth's distance to the Sun.  The most 
visible gaseous fragments lie along the inner edge of the star's ring, 
trillions of miles from the star at its center.  The comet-like tails
form a radial pattern around the star like the spokes on a wagon 
wheel. Astronomers have seen the spoke pattern using ground-based 
telescopes, but Hubble reveals for the first time the sources of
these objects.
 
Astronomers theorize that the gaseous knots are the results of a 
collision between gases. The doomed star spews the hot gas from 
its surface, which collides with the cooler gas that it had ejected 
10,000 years before. The crash fragments the smooth cloud 
surrounding the star into smaller, denser finger-like droplets, like 
dripping paint.  Astronomers expect the gaseous knots, each several 
billion miles across, to eventually dissipate into the cold blackness 
of interstellar space.
 
This image was taken in August, 1994 with Hubble's Wide Field 
Planetary Camera 2.  The red light depicts nitrogen emission 
([NII] 6584A); green, hydrogen (H-alpha, 6563A); and blue,
oxygen (5007A).

Credit:  Robert O'Dell, Kerry P. Handron (Rice University, 
Houston, Texas) and NASA