Studying images of proto-planetary nebulae is important to understanding the ‘death’ process of a star. A star begins to die when it has exhausted its thermonuclear fuel – Hydrogen and helium. The star then becomes bright and cool (red giant phase) and swells to several tens of times its normal size. It begins puffing thin shells of gas off into space. You can see these shells in this NASA/ESA Hubble Space Telescope image. See http://spacetelescope.org/images/opo9811i/
