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34. 蓝脱序星blue straggler的两种形成过程 Vampires and collisions rejuvenate stars Using the NASA/ESA Hubble Space Telescope, astronomers have uncovered two distinct kinds of rejuvenated stars in the globular cluster Messier 30. A new study shows that both stellar collisions and a process sometimes called vampirism are behind this cosmic face lift. The scientists also uncover evidence that both sorts of blue stragglers were produced during a critical dynamical event that occurred in Messier 30 a few billion years ago. Stars in globular clusters are generally extremely old, with ages of 12-13 billion years. However, a small fraction of them appear to be significantly younger than the average population and, because they seem to have been left behind by the stars that followed the normal path of stellar evolution and became red giants, have been dubbed blue stragglers . Blue stragglers appear to regress from old age back to a hotter and brighter youth, gaining a new lease on life in the process. A team of astronomers used Hubble to study the blue straggler star content in Messier 30, which formed 13 billion years ago and was discovered in 1764 by Charles Messier. Located about 28 000 light-years away from Earth, this globular clustera swarm of several hundred thousand starsis about 90 light-years across. Although blue stragglers have been known since the early 1950s, their formation process is still an unsolved puzzle in astrophysics. Its like seeing a few kids in the group picture of a rest-home for retired people. It is natural to wonder why they are there, says Francesco Ferraro from the University of Bologna in Italy, lead author of the study that will be published this week in Nature . Researchers have been studying these stars for many years and knew that blue stragglers are indeed old. They were thought to have arisen in a tight binary system . In such a pair, the less massive star acts as a vampire, siphoning fresh hydrogen from its more massive companion star. The new fuel supply allows the smaller star to heat up, growing bluer and hotterbehaving like a star at an earlier stage in its evolution. | 
