---------------------------------- NGC 7009 ----------------------------------
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)