DoubleBubble

Hubble 5 is a strikingly lovely "butterfly" or bipolar (two-lobed)
nebula which has received relatively little attention. Internal
motions in the nebula have been measured spectroscopically to be in
excess of 200 miles per second. The heat generated by the winds causes
the each of the lobes to expand, much like a pair of balloons with
internal heaters. The expanding lobes encounter older material ejected
previously. Supersonic shocks form where the ambient gas is compressed
and heated ahead of the rapidly expanding lobes. Atoms caught in the
shocks radiate the visible light seen in this image.

Image Factoids for Hubble 5
Nickname: Hubble's Double Bubble
observed by HST: Sep 9 1997
distance 0.7 kpc (2200 l.y.)
constellation: Sagittarius
HST instrument: WFPC2 (2 orbits) with filters F631N (neutral oxygen, shown in red), F658N (once-ionized nitrogen,
shown in green), F502N (twice-ionized hydrogen, shown in blue) 

Credits for the image of Hubble 5 

   Bruce Balick, University of Washingto
   Vincent Icke, Leiden University (The Netherlands)
   Garrelt Mellema, Stockholm University
   NASA