What details about stellar evolution were revealed by the observation of planetary nebulae?

They revealed complex, symmetrical shapes that challenge simple models of how a star sheds its outer layers.

Planetary nebulae represent the final stages of a star's life, characterized by the shedding of outer gas layers. Before detailed observations, models of how stars end their lives were relatively simple. The high-resolution imagery provided a view of intricate, complex, and symmetrical patterns that indicated a much more dynamic process. By capturing stars in various stages of life, astronomers developed a comprehensive understanding of stellar evolution, tracing the process from cold, dark gas clouds to the final, brilliant gaseous remnants left behind by dying stars.