September 15, 2012
Astronomers Find Planets Orbiting Sun-Like Stars In A Cluster
Lee Rannals for redOrbit.com - Your Universe Online
According to NASA-funded astronomers, planets can indeed form in dense stellar environments. This evidence comes from the recent discovery of planets that were observed orbiting sun-like stars in a crowded cluster of stars.The newfound planets are not habitable, and are considered to be two hot Jupiters, which are massive gas planets.
Each of the hot Jupiter planets circle a different sun-like star in the Beehive Cluster, which is a collection of about 1,000 stars that appear to be swarming around a common center.
This cluster of stars was born at about the same time and out of the same giant cloud of material. The stars born in the cluster share a similar chemical composition, and they remain loosely bound together by mutual gravitational attraction.
"We are detecting more and more planets that can thrive in diverse and extreme environments like these nearby clusters," said Mario R. Perez, the NASA astrophysics program scientist in the Origins of Solar Systems Program. "Our galaxy contains more than 1,000 of these open clusters, which potentially can present the physical conditions for harboring many more of these giant planets."
The two hot Jupiter planets, which have been named Pr0201b and Pr0211b, were discovered using the 5-foot Tillinghast telescope at the Smithsonian Astrophysical Observatory's Fred Lawrence Whipple Observatory.
"This has been a big puzzle for planet hunters," said Sam Quinn, a graduate student in astronomy at Georgia State University in Atlanta and the lead author of the paper published in the Astrophysical Journal Letters. "We know that most stars form in clustered environments like the Orion nebula, so unless this dense environment inhibits planet formation, at least some sun-like stars in open clusters should have planets. Now, we finally know they are indeed there."
The findings are of interest to theorists who are trying to understand how hot Jupiters wind up so close to their stars. Most theorists believe these planets start out much cooler and farther from their stars before migrating inward.
"The relatively young age of the Beehive cluster makes these planets among the youngest known," Russel White, the principal investigator on the NASA Origins of Solar Systems grant that funded this study, said in a press release. "And that's important because it sets a constraint on how quickly giant planets migrate inward -- and knowing how quickly they migrate is the first step to figuring out how they migrate."
The team believes planets were turned up in the Beehive cluster because it is rich in metals. Stars in the cluster have more heavy elements like iron than the sun has.
"Searches for planets around nearby stars suggest that these metals act like a 'planet fertilizer,' leading to an abundant crop of gas giant planets," White said. "Our results suggest this may be true in clusters as well."
Image 2 (below): This image of the Beehive star cluster points out the location of its first known planets, Pr0201b and Pr0211b, or, as astronomers call them, the first 'b's' in the Beehive. Image copyright: Stuart Heggie