---------------------------------- NGC 6537 ----------------------------------
Like Hubble 5, NGC 6537 is another 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.

As the outward flowing winds slide past the walls of the lobes, they can generate waves, much as do winds passing over a lake. This takes time. Apparently the process has been underway long enough to make the edges of the lobe walls look as if they've started to fracture into wave crests.

Nickname: The Red Spider Nebula
observed by HST: Sep 12 1997
distance 0.58 kpc (1900 l.y.)
constellation: Sagittarius
HST instrument: WFPC2 (2 orbits) with filters F658N (once-ionized nitrogen, shown in red), F656N (once-ionized hydrogen, shown in green), and F502N (twice-ionized oxygen, shown in blue)

Credits for the image of NGC 6537

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