NGC7009

Size: 82 K

Like NGC 6826, NGC 7009 has a bright central star at the center of a
dark cavity bounded by a football-shaped rim of dense, blue and red
gas. The cavity and its rim are trapped inside smoothly-distributed
greenish material in the shape of a barrel and comprised of the star's
former outer layers. At larger distances, and lying along the long
axis of the nebula, a pair of red "ansae", or "handles" appears. Each
ansa is joined to the tips of the cavity by a long greenish jet of
material, much like the hot gases that follow a bullet from the barrel
of a rifle. However, the handles are clouds of low-density gas, not
solid objects. Imagine the spectacular view from Earth if our Sun were
to produce such a nebula!

How does this system work? The recent Hubble images suggest that hot
gas escapes from the tips of the cavity. Computer simulations of this
process show that under certain conditions the winds from the star can
slide along the walls of the cavity, thence converging at the cavity's
tips. The tips act somewhat like a nozzle that form gas jets, like a
stream of water from the nozzle of a garden hose. The dense tips of
the jets might be material that the jets have plowed ahead of them as
they push forward. However, the models also predict a high degree of
gas turbulence, which is not observed. Future improvements in the
observations and refinements in the models will help us to understand
the physics of the outflows and the conditions of the jets.

Image Factoids for NGC 7009
Nickname: The Saturn Nebula
observed by HST: Apr 28 1996
distance: 0.42 kpc (1400 l.y.)
constellation: Aquarius
HST instrument: WFPC2 (2 orbits) with filters F658N (once-ionized nitrogen, shown in red), F502N (twice-ionized
oxygen, shown in green), and F469N (starlight filter, shown in blue) 

Credits for the image of NGC 7009 

   Bruce Balick, University of Washington
   Jason Alexander, University of Washington
   Arsen Hajian, U.S. Naval Observatory 
   Yervant Terzian, Cornell University 
   Mario Perinotto, University of Florence (Italy)
   Patrizio Patriarchi, Arcetri Observatory (Italy)
   NASA