GRE Reading Comprehension: JiJing 352-GRE阅读机经352篇 - 1P24NDQNHW8265A5K

Hotter and more massive than the Sun, stars called "stragglers" are puzzling to astronomers because such rapidly burning stars would not be expected to persist in ancient star clusters. Some researchers believe that the typical blue stragglers formed when two ancient, lower-mass stars collide, merge and form a more massive, hotter star. Peter Leonard theorizes alternatively that in low density globular clusters, where mergers between single stars occur too infrequently to account for the observed quantity of blue stragglers, these stragglers are created instead by a group of stars. He suggests that a pair of stars already orbiting each other presents a larger target for a third star or another pair. Once this new grouping forms, close encounters between the stars could prompt any two to merge as a blue straggler. Leonard's model predicts that each blue straggler has a distant orbiting companion – as appears true of many blue stragglers in the M67 cluster of the Milky Way galaxy.