原文:
Explanation: How can a round star make a square nebula? This conundrum comes to light when studying planetary nebulae like IC 4406. Evidence indicates that IC 4406 is
likely a hollow cylinder, with its square appearance the result of our vantage point
in viewing the cylinder from the side. Were IC 4406 viewed from the top, it would
likely look similar to the Ring Nebula. This representative-color picture is a
composite made by combining images taken by the Hubble Space Telescope in 2001 and
2002. Hot gas flows out the ends of the cylinder, while filaments of dark dust and
molecular gas lace the bounding walls. The star primarily responsible for this
interstellar sculpture can be found in the planetary nebula's center. In a few million
years, the only thing left visible in IC 4406 will be a fading white dwarf star.