Tour: Planetary Nebula: Misnamed but Not Misunderstood

Sometimes the names of objects are deeply misleading. For example, starfish are not actually fish. They are, in fact, echinoderms. And guinea pigs are not related to pigs in any way — they are rodents. Similarly, planetary nebulas have nothing to do with planets. They were misnamed when scientists looked through small telescopes in the 19th century and thought these objects looked like planets.

Today, astronomers know that a planetary nebula actually represents a phase that stars like our Sun experience when they use up much of their fuel. After the star cools and expands, it sheds its outer layers. The core of the star left behind at the center is a dense and smaller star called a white dwarf. The shells of gas linger around the white dwarf for a relatively short time in cosmic terms — tens of thousands of years — before dissipating into space. During that time, the white dwarf can illuminate and energize these jettisoned layers.

NASA's Chandra X-ray Observatory contributes to the understanding of planetary nebulas by studying the hottest and most energetic processes still at work in these beautiful objects. X-ray data from Chandra reveal winds being driven away from the white dwarf at millions of miles per hour that create shock waves during collisions with slower-moving material previously ejected by the star. Chandra's exceptional vision in X-rays contributes to the understanding of this brief, yet important, stage of stars' lives.

This gallery contains half a dozen planetary nebulas that have been observed both by Chandra and NASA's Hubble Space Telescope. While all six nebulas originated from similar physical conditions and evolved by similar processes, they currently appear somewhat different from others. The differences in the shapes and structures of these planetary nebulas may be due to the complexities of a slew of physical properties including how much of the star's winds flow from its poles, whether the star wobbles as it spins, if the star has a companion or not, and other factors.