PASADENA, Calif. and ATLANTA Georgia State University scientists and their colleagues have for the first time spotted planets orbiting sun-like stars in a crowded cluster of stars, offering the best evidence yet that planets can form in dense stellar environments.
A team led by Sam Quinn, a graduate student in astronomy under the direction of Russel White, assistant professor of astronomy, detected two planets, called “hot Jupiters” – massive gas giant planets that are extremely hot – around stars in the Beehive Cluster, also called Praesepe.
The research, funded by NASA’s Origins of Solar Systems project, was published in Astrophysical Journal Letters.
The cluster is a collection of about 1,000 stars that appear to be swarming around a common center. Called an “open cluster,” it is a grouping of stars born at about the same time and out of the same giant cloud of material, sharing a similar chemical composition.
Previous searches of clusters had turned up two planets around massive stars but none had been found around stars like our sun until now.
“This has been a big puzzle for planet hunters,” Quinn said. “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.”
“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 new Beehive planets are called Pr0201b and Pr0211b. The star’s name followed by a “b” is the standard naming convention for planets.
Quinn and his team, in collaboration with David Latham at the Harvard-Smithsonian Center for Astrophysics, discovered the planets by using the 1.5-meter Tillinghast telescope at the Smithsonian Astrophysical Observatory’s Fred Lawrence Whipple Observatory near Amado, Ariz. to measure the slight gravitational wobble the orbiting planets induce upon their host stars.
The results also are of interest to theorists who are trying to understand how hot Jupiters wind up so close to their stars. Most theories contend these blistering worlds 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,” White said. “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 research team suspects planets turned up in the Beehive cluster because it is rich in metals. Stars in the Beehive have more heavy elements such as 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.”
NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages NASA’s Exoplanet Exploration Program office. More information about exoplanets and NASA’s planet-finding program is available at: http://planetquest.jpl.nasa.gov.
For more information about astronomy at Georgia State, visit www.chara.gsu.edu.
Sept. 17, 2012