在一个星团的类太阳的恒星周围发现行星 天文学家在一个叫Beehive star cluster 的两个和太阳类似的恒星的周围各发现一个行星。 这两颗行星都是hot Jupiters，它们是像木星一样的巨大气体行星，并且是围绕其恒星的轨道很近，因而其表面的温度很高。 
1，艺术家对这两颗行星的想像图。 这个叫蜂巢的星团是离太阳系最近的星团。它距太阳系大约是577光年。星团的中心明亮的直径大约22.8光年。在这样小的空间中，密布了大约1000颗恒星。在天文上，这样的恒星分布是非常密集的，所以把它称为“蜂巢”。比较一下，距我们最近的恒星大约是4光年多的距离。 在这样狭小的空间上，分布着如此众多的恒星，它们彼此间引力作用，绑缚住一起。这么多的恒星是一个巨大的星云凝聚而成的，它们是同时诞生的，它们的化学组成几乎是一样的。这些恒星的年龄大约是几亿年的数量级，这是很年轻的恒星。 这次发现的一个意义是：在一个恒星间引力互相作用的环境下，在恒星的周围像其它孤立的恒星一样会形成行星系统。这次发现为此类的理论提供了有力的证据。 
2，这两颗恒星在天空中的相对位置。版权为Stuart Heggie 拥有。 另一个意义是：灼热的类木星的行星围绕着宿主恒星在很近的轨道上旋转，其公转周期仅有几天。这对行星的形成的各种理论假设提供了新证据。按照理论推测，如此巨大的气体行星现在运行的轨道一定不是它诞生的地方。它必定是在更远的轨道上诞生的。由于引力的相互作用，这些行星会不断向更低的轨道迁移。因为这些恒星都是很年青的，目前的观察数据说明巨大的气体行星的轨道迁移已“完成”了，这表明了轨道迁移的速率是多么快。这为近一步了解太阳系的形成提供了可观测的“样本”。 我们推断，许多年龄较长的恒星周围的巨型气体行星大概被宿主恒星吞没了。 最后是两个图像的外链地址。 下面是NASA网站关于这个发现的报道原文。
PASADENA, Calif. -- NASA-funded astronomers have, for the first time, spotted planets orbiting sun-like stars in a crowded cluster of stars. The findings offer the best evidence yet that planets can sprout up in dense stellar environments. Although the newfound planets are not habitable, their skies would be starrier than what we see from Earth. The starry-skied planets are two so-called hot Jupiters, which are massive, gaseous orbs that are boiling hot because they orbit tightly around their parent stars. Each hot Jupiter circles a different sun-like star in the Beehive Cluster, also called the Praesepe, a collection of roughly 1,000 stars that appear to be swarming around a common center. The Beehive is an open cluster, or a grouping of stars born at about the same time and out of the same giant cloud of material. The stars therefore share a similar chemical composition. Unlike the majority of stars, which spread out shortly after birth, these young stars 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 new Beehive planets are called Pr0201b and Pr0211b. The star's name followed by a "b" is the standard naming convention for planets. "These are the first 'b's' in the Beehive," said Sam Quinn, a graduate student in astronomy at Georgia State University in Atlanta and the lead author of the paper describing the results, which was published in the Astrophysical Journal Letters. 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, Arizona to measure the slight gravitational wobble the orbiting planets induce upon their host stars. 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." 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," said 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." The research team suspects planets were 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. According to White, "Searches for planets around nearby stars suggest that these metals act like a 'planet fertilizer,' leading to an abundant crop of gas giant planets. 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 . http://www.nasa.gov/images/content/687507main_pia15802-43_800-600.jpg 艺术家的想像图地址。 http://www.nasa.gov/images/content/687314main_pia15801-43_946-710.jpg 恒星在天空中的位置地址。 版权为Stuart Heggie 拥有。
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