They form near the end of a red giant's life, as the outermost layers of gas puff off gently, leaving a remnant white dwarf core.
They form near the end of a red giant's life, as the outermost layers of gas puff off gently, leaving a remnant white dwarf core. They generally assume a spherical or barrel shape as they continue to expand from the surface of the generating red giant. The Helix one in Aquarius and the Ring one in Lyra are classic examples of these structures.  FTP, name these bright clouds of gas once mistakenly associated with forming solar systems and now known to be a specific type of nebula.
They form near the end of a red giant's life, as the outermost layers of gas puff off gently, leaving a remnant white dwarf core.
planetary nebula (prompt on just "nebula")