Astronomers have, for the first time, spotted planets orbiting sun-like stars in a crowded cluster – the best evidence yet that planets can form in dense stellar environments.
The planets in question – Pr0201b and Pr0211b – are two so-called hot Jupiters, orbiting tightly around their parent stars. Both are located in the Beehive Cluster, also called the Praesepe, a collection of roughly 1,000 stars that appear to be swarming around a common center.
“We are detecting more and more planets that can thrive in diverse and extreme environments like these nearby clusters,” says Mario R Perez, 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 planets were discovered using the 1.5-meter Tillinghast telescope at the Smithsonian Astrophysical Observatory’s Fred Lawrence Whipple Observatory near Amado, Arizona, which detected the slight gravitational wobble they givetheir host stars.
Previous searches of clusters had turned up two planets around massive stars – but none around stars like our own.
“This has been a big puzzle for planet hunters,” says Sam Quinn, a graduate student in astronomy at Georgia State University.
“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 results may help explain how hot Jupiters wind up so close to their stars. Most theories suggest that they 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,” says Russel White, the principal investigator on the NASA Origins of Solar Systems grant that funded this study.
“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.”