February 8, 2006

Planetary Building Blocks Seen around Huge Stars

By Gina Keating

LOS ANGELES (Reuters) - Rings of planet-forming dust have been discovered circling two "hypergiant" stars, indicating planet formation may be taking place in environments previously thought too hostile, according to research published on Wednesday.

In an article published in Astrophysical Journal Letters, astronomers concluded that planets can form around a wider range of stars than previously thought, including two "hypergiants" dubbed R66 and R126 that are 30- to 70-times the mass of the sun.

Flattened dust disks had previously been detected whirling around stars only about five times more massive than the sun.

Hypergiants "are tremendously hot and bright and have very strong winds, making the job of building planets difficult," the paper's lead author, Joel Kastner of the Rochester Institute of Technology, told Reuters.

Astronomers were surprised that data from NASA's Spitzer Space Telescope showed the micron-sized rocks comprising the dust rings were not blown out of the star systems by powerful stellar winds and intense ultraviolet radiation.

The Spitzer data, collected last summer, also appears to show that "fairly large" dust grains -- which could be precursors to planets -- have built up around the huge stars, located in the Milky Way's nearest neighbor galaxy, the Large Magellanic Cloud.

Complex hydrocarbons, a molecule commonly seen on Earth, have also been spotted by Spitzer's infrared spectrometer, indicating that complex molecules are being formed in the dust clouds. This process is similar to that which formed the Milky Way about 4.3 billion years ago, Kastner said.

The similar composition of both dust rings lead the astronomers to believe the material was not ejected from the stars, but built up over millions of years, Kastner said.

The stars, which have life spans counted in millions of years rather than billions for the sun, are about 180,000 light years from the Milky Way and probably will self-destruct as supernovae in fiery explosions that could blow the disks apart before they form planets.

"On the other hand, we can't really predict the future of these systems with much certainty," Kastner said, adding that the first planets found outside the Milky Way were orbiting a spinning dead stellar core called a pulsar.

Since then, astronomers have detected about 150 planetary systems, most with one planet that can be seen from Earth, said Geoff Bryden, an astronomer at NASA's Jet Propulsion Laboratory in Pasadena, Californa, which manages the Spitzer mission.

Launched in August of 2003, Spitzer trails the Earth in its orbit, obtaining images of the spectra and infrared energy radiated by objects in space.