Nebulae are observed to flow. The final expulsion of gas by a star as it forms a planetary nebula – the ionised shell of gas often observed surrounding a young white dwarf – is one of the most poorly understood stages of stellar evolution. Such nebulae form extremely rapidly ( about 100 years for the ionisation). The formation process is inherently difficult to observe. Here are reported optical observations of the stingray nebula,… collimated outflows are already evident, the nebular structure that focuses the outflows is identified. – Images from the Hubble space telescope.

Nature volume 392/ 2^nd April 1998, p.469