BOONE—When Richard Gray looks at the stars, he sees more than just interesting bits of light in the night sky.

Gray, a professor in the Department of Physics and Astronomy at Appalachian State University, is part of an 11-member team looking for new planets. They have determined that planets may exist around twin or binary stars.

“We used to think that planets could only be found around single stars,” Gray said. “This is an interesting discovery because up until now, people have been skeptical about the possibility of planets with double stars. This project has shown is that it is possible for planets to exist around binary stars as well as single stars.”

Gray was invited to participate in the project because of his NASA-funded Nearby Stars project. Since 2000, Gray and a team of researchers have been collecting data on 3,600 nearby stars that may harbor planets.

Recently, a team of scientists led by David Trilling of the University of Arizona have studied debris disks found in the double-star systems using NASA’s Spitzer Space Telescope.

“The debris disks are made of dust and small particles which indicate that most probably planets have formed, or there is a good possibility that there are planets around these stars,” Gray explained.

“Binary systems were largely ignored before,” Trilling said. “They are more difficult to study, but they might be the most common sites for planet formation in our galaxy.”

Trilling, from the University of Arizona is the lead author of a paper about the NASA-funded research that has been published in the April 1 issue of the Astrophysical Journal. “There could be countless planets out there with two or more suns,” he said.

In the most comprehensive survey of its kind, the team looked for disks in 69 binary systems between about 50 and 200 light-years away from Earth. All of the stars are somewhat younger and more massive than our middle-aged sun. The data show that about 40 percent of the systems had disks, which is a bit higher than the frequency for a comparable sample of single stars. This means that planetary systems are at least as common around binary stars as they are around single stars.

In addition, the astronomers were shocked to find that discs were even more frequent (about 60 percent) around the tightest binaries in the study. These coziest of steller companions are between zero and three astronomical units apart. Spitzer detected disks orbiting both members of the star pairs, rather than just one. Extra-tight star systems like these are where planets, if they are present, would experience double sunsets such as the ones depicted on the fictional planet Tatooine in George Lucas’s “Star Wars.”

“We were very surprised to find that the tight group had more disks,” said Trilling. “This could mean that planet formation favors tight binaries over single stars, but it could also mean tight binaries are just dustier. Future observations should provide a better answer.”

As part of the survey, Gray helped analyze and classify stars in the binary systems by studying the spectra or light waves they emitted. He conducted his research using the 32-inch telescope at the university’s Dark Sky Observatory, a 90-inch telescope at Bok Steward Observatory telescope at Kitt Peak National Observatory in Arizona and software that he has developed while at Appalachian to determine the temperature, size, chemical composition and age of stars.

Gray says the scientists’ next step will be to observe the binary stars more closely and see if they can actually detect planets.

Additional information about the project is available at:
http://www.spitzer.caltech.edu/Media/releases/ssc2007-05/index.shtml
http://www.jpl.nasa.gov/news/spitzer-starwars.cfm

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