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Sprinkled throughout every galaxy are tightly packed balls of thousands or even millions of stars. And deep within the heart of just about all of these stellar clusters are strange populations of stars called blue stragglers, which appear much younger than their companions, even though they should all be the same age. Now astronomers think they have identified the secret of these stars, which, like Dorian Gray, refuse to grow old. |
成千上万颗、甚至几百万颗恒星密密麻麻地分布在每个星系中。在几乎所有星系团的中心部位，都深藏着一类奇特的恒星群体，它们被称为“蓝离散星”。尽管这些恒星都应该跟它们的同伴年龄相当，但它们看起来要年轻得多。现在天文学家们认为，他们发现了这些恒星象道林·格雷那样不会变老的秘密。 |
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As low-mass stars approach the end of their life cycles--at around 10 billion years old--most evolve first into red giants and then into white dwarfs. As they pass through those stages, the stars grow dimmer and cooler. But blue stragglers seem to follow a different path. Despite their advanced age--perhaps as old as 13 billion years--they burn hot and bright, just like a young star. Astronomers have hypothesized that these stars may owe their youthful looks to leaching from their neighbors. They may suck hydrogen away from nearby stars in a process called "mass transfer," or collide with them and absorb them whole. |
低质量的恒星在生命周期快要结束的时候大约为100亿岁，绝大部分恒星首先演化成红巨星，然后再变成白矮星，在这个过程中恒星亮度会变得较暗，温度变得较低。但是蓝离散星好象遵循着不同的演化途径。尽管蓝离散星年龄很高，可能达到130亿岁，但是它们跟年轻恒星似的，炽热而明亮地燃烧着。天文学家们提出假设：这些恒星的年轻面貌是从相邻的恒星那里获得的。它们可能通过“质量传递”的过程从附近恒星那里吸收氢气，或者与相邻的恒星相撞并将其全部吸收。 |
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In two papers appearing this week in Nature, astronomers report evidence for both processes. One team observed blue stragglers in NGC 188, a cluster located about 5000 light-years away in the northern constellation Cepheus. The other group studied Messier 30, about 26,000 light-years away in Capricorn. |
在本周《自然》杂志中的两篇文章里，天文学家们报道了上述两个过程的有关证据。一组天文学家观察了星系团NGC188中的蓝离散星，该星系团位于约5000光年之外的北天星座——仙王座；另一组天文学家研究了星系团“梅西尔30”，该星系团位于约2.6万光年之外的摩羯座。 |
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First, in the observation of Messier 30, astronomer Francesco Ferraro of the University of Bologna in Italy and colleagues confirmed that, in spite of their youthful appearance, blue stragglers are most likely quite old. Using data involving the temperature and brightness of the stars collected by the Hubble Space Telescope, they observed 44 blue stragglers among the cluster's many thousands of red-giant and white-dwarf stars. The data revealed that the stragglers are bright and hot, as would be expected for young suns. But these stars must be old, as they formed in the same place and, thus, at the same time as the other stars in the cluster. The absence of protostellar cloud material and the low velocity of the stars shows they could not have been born relatively recently or sailed in from elsewhere in the galaxy. |
在观察“梅西尔30”时，意大利博洛尼亚大学的天文学家弗朗西斯科·费拉罗及同事首先证实，尽管蓝离散星看起来年轻，但是它们很可能相当古老。利用哈勃太空望远镜收集的有关恒星温度和亮度的资料，研究人员观察了该星系团内部位于成千上万颗红巨星和白矮星当中的44颗蓝离散星。资料显示，蓝离散星明亮而炽热，如同年轻的恒星那样。然而，蓝离散星肯定是古老的，因为它们和星系团中的其他恒星形成于相同的区域，因此在形成时间上是一致的。星系中缺少原恒星物质云团，而且其中的恒星运转速度低，说明恒星不可能是在最近诞生的，也不会是从星系的其他地方飘然而入。 |
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Meanwhile, Robert Mathieu and Aaron Geller of the University of Wisconsin, Madison, used the telescope at the WIYN Observatory, near Tucson, Arizona, to track the motion and brightness of stars in a cluster called NGC 188 for nearly 15 years. The two astronomers found that about 75% of the blue stragglers in the cluster have partners that typically orbit at a distance similar to that between the sun and Jupiter. Such close proximity strongly suggests "that blue stragglers result from mass transfers, collisions, and mergers between two or more stars," Mathieu says. |
同时，威斯康星大学麦迪逊分校的罗伯特·马蒂厄和阿伦·盖勒，利用亚利桑那州图森市附近WIYN天文台的望远镜，花了近15年的时间，跟踪观察了一个被称为“NGC 188”的星系团。两位天文学家发现，该星系团中大约75%的蓝离散星都拥有伴星，这些伴星通常进行环绕运动，跟蓝离散星的距离相当于太阳跟木星的距离。马蒂厄说：“这么近的距离有力地说明，蓝离散星形成于质量传递、碰撞以及两颗或多颗恒星的合并。” |
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Together, the results confirm suspicions that the blue stragglers emerged from collisions and mass transfers, says astronomer Alison Sills of McMaster University in Hamilton, Canada. But there's still no direct evidence that shows exactly how an individual blue straggler was formed. The definitive answer, Sills says, could take another 10 to 15 years of observations. |
加拿大汉密尔顿市麦克马斯特大学的天文学家艾莉森·西尔斯称，这些结果证实了蓝离散星来自碰撞及质量传递。但是，仍然没有直接证据能够确切地说明一颗特定的蓝离散星是如何形成的。西尔斯说，要想获得明确的答案，可能需要再观察10至15年的时间。 |
