Barnes and Hibbard did a computer modeling analysis of how such shapes may have evolved:
Data for my image were acquired automatically with CCDAutoPilot4 running Maxim4.62 and PinPoint Pro5 for image linking. Guiding was done with an SBIG ST-402 on an Astrodon MonsterMOAG off-axis guider. Astrodon Generation 2 LRGB filters were used, Data were calibrated and processed in CCDStack, Maxim and Photoshop CS3.
Details: Exposure Time: 16 hrs; 4 Lum, 3 hrs each R,G,B
Camera: Apogee U16M
Telescope: RC Optical 16" f/8.9 Ritchey-Chretien
Mount: Software Bisque Paramount ME