Planets Reported to Shape Planetary Nebulae

Author:  Jessica Kloss

Institution:  Princeton University
Date:  April 2008

For more than a century, the term "planetary nebula" has been a confusing one for students of astronomy. Widely regarded as among the most beautiful objects of the night sky, planetary nebulae,illuminated clouds of gas and dust cast off from a dying star,were previously thought to have nothing to do with planets. Now, however, Rich Blackman and his team of astronomers at the University of Rochester contend that the name "planetary" nebula, once deemed a misnomer, may take on new meaning.

We've learned much about planetary nebulae since astronomers 300 years ago mistakenly named them for their resemblance to the outer planets in our solar system. Since the mid-19th century, astronomers have known that these nebulae form when a medium sized star, such as our Sun, reaches the end of its life cycle and runs out of fuel to burn. Its core then contracts while it throws its outer layers millions of miles into space. Astronomers call this ejected material the star's "envelope," which can contort into fantastic shapes.

Blackman, a professor of physics and astronomy, has discovered that if a dying star has a low mass companion, such as a large, Jupiter-sized planet or a small star, then the companion has an influence on the shape of the nebula. Blackman's team found that companions with very wide orbits nearer to the outer edges of the envelopes are likely to have a restraining effect on the expanding envelope much as a belt would on an expanding balloon. Companions with orbits very close to the star, on the other hand, can cause the envelope to evolve into a disk, or form twin jets at the poles of the dying star, spouting envelope material into space.

This discovery affects our understanding of planetary nebulae, which are known and often named for the diverse shapes they form in the sky , like the Cat's Eye Nebula, or the Ant Nebula. As Blackman said, "few researchers have explored how something as small as a very low-mass star, a brown dwarf, or even a massive planet can produce several flavors of nebulae and even change the chemical composition of the dust around these evolved stars."

The Rochester team is now applying their discoveries to the observed chemical compositions of planetary nebulae.

Written by Jess Kloss

Reviewed by Amy Liu

Published by Pooja Ghatalia