| Astronomers peering out into our cosmic backyard have long understood that the Milky Way's galactic neighbors only seem similar on the surface. Now a detailed survey from NASA's Hubble Space Telescope has revealed the diversity of those galaxies as they evolve over time. |
长期以来，凝视宇宙深邃之处的天文学家们了解到，银河系的相邻星系只是表面上看起来相似。现在，美国国家航空航天管理局的哈勃太空望远镜提供了详细观测资料，资料显示：那些星系随着时间的推移而演化，并产生了差异。 |
| The ACS Nearby Galaxy Survey Treasury (ANGST) program zeroed in on 14 million stars in 69 nearby galaxies. Such galaxies sit close enough so that Hubble's sharp eyes could single out the brightest stars instead of seeing a giant smear of light, and may help settle raging debates over how galaxies and their stars form in the first place. |
ACS附近星系观测资料库（ANGST）计划瞄准了69个附近星系中的1400万颗恒星。这样的星系距离近，哈勃的高分辨率镜头能够分离出最为明亮的恒星，而不会将其拍成模糊的一小片光亮。最重要的是，这样可以帮助平息有关星系及其恒星形成方面的激烈争执。 |
| "Instead of picking and choosing particular galaxies to study, our survey will be complete by virtue of looking at 'all' the galaxies in the region," said Julianne Dalcanton, head of the ANGST survey at the University of Washington in Seattle. "This gives us a multi-color picture of when and where all the stars in the local universe formed." |
“我们不是挑选个别的星系来研究，而是观察这个区域的‘所有’星系，因此我们的观测资料将是完整的，”ACS附近星系观测资料库西雅图华盛顿大学观测处主任朱莉安娜·达尔卡顿说，“这为我们提供了一幅多彩的画面，展现出有关宇宙这一区域中所有恒星的形成时间和位置。” |
| A galactic fossil record |
星系化石记录 |
| The survey covered galaxies ranging 6.5 million light-years to 13 million light-years from Earth. A light-year is the distance light will travel in a year, or about 6 trillion miles (10 trillion kilometers). |
该观测资料包括了距离地球650万光年至130亿光年的所有星系。一光年是光在一年当中所能够穿行的距离，或者说大约相当于6万亿英里（10万亿公里）。 |
| Many nearby galaxies contain stars that are positive relics compared with the younger stars in more distant galaxies. Astronomers can guess how those younger stars may evolve based on the older nearby stars. |
跟较远星系中比较年轻的恒星相比，许多附近星系所包含的恒星实际上是处于濒临崩溃的状态。根据附近较为老化的恒星，天文学家们可以推测出那些比较年轻的恒星会如何进行演化。 |
| "Using the galaxies in the nearby universe as a 'fossil record,' we can compare them with young galaxies far away," Dalcanton said. "This comparison gives us a history of star formation and provides a better understanding of the masses, structures and environments of the galaxies." |
“利用宇宙中附近的星系作为‘化石记录’，我们可以将它们跟远处的年轻星系作对比，”达尔卡顿说，“这种对比可以为我们提供恒星形成的历史，使我们更清楚地了解星系的质量、结构与环境。” |
| The formation of galaxies remains poorly understood, although evidence is mounting that massive galaxies grow by clumping together and merging with smaller brethren. This step-by-step evolution of gradually larger galaxies competes with the theory that galaxies simply start from scratch. |
尽管越来越多的证据表明巨型星系的发展方式是跟较小的兄弟星系结盟并融合，但是天文学家们对星系的形成仍然知之甚少。这种一步步演化而成为较大星系的说法，跟星系只不过是从无到有演化开来的理论是并存的。 |
| However, some observations suggest that galaxies do have the power to expand rapidly. Astronomers found a star factory 12.3 billion light-years away that churns out 4,000 stars per year, compared with our Milky Way's 10 stars annually. That burst of star-making activity suggests such a galaxy would only need 50 million years to grow into one of the largest ever observed. |
然而，一些观察表明星系确实有快速扩张的能力。天文学家们曾经发现了一个距地球123亿光年的恒星制造工厂，每年产出恒星4,000颗恒星，相比之下，我们银河系每年才生产出10颗恒星。这种恒星制造活动的爆发表明，这样的星系仅仅需要5,000万年就可以成长为所观察到的最大星系之一了。 |
| Stellar evolution |
恒星演化 |
| Many such large spiral galaxies created most of their stars early on, according to a separate new study. Also relying on data from the Hubble galactic survey, the astronomers examined the outer disk of M81 and found that most stars formed more than 7 billion years ago, when the universe was half its current age. The supernova deaths of massive stars within such mammoth galaxies rapidly enriched them with heavy elements such as carbon. |
一项独立的新研究表明，很多这种大型漩涡星系在早期创造了多数恒星。同样依据哈勃星系观测资料，天文学家们考查了圆盘外侧的星系M81。他们发现其中多数恒星形成于70多亿年以前，即宇宙只有当前年龄的一半时。在如此巨大的星系中，巨型恒星作为超新星而灭亡，很快使得星系内充满象碳这样的重元素。 |
| "We were surprised by how quickly the elements formed and how the subsequent star-formation rate for the bulk of the stars in M81 changed after that," said Benjamin Williams, an astronomer at the University of Washington in Seattle. |
“这些元素形成的速度之快，以及随后M81中大多数恒星形成速度的变化，都让我们感到吃惊，”西雅图华盛顿大学的天文学家本杰明·威廉姆斯说。 |
| Astronomers had believed that star populations become increasingly younger further out within galaxies, but Hubble data indicated that older stars can also lurk in a galaxy's outer arms. Recent simulation work has presented another possible explanation — stars may wander all over spiral galaxies. The survey should provide further data to flesh out current theories. |
以前，天文学家们认为，恒星群落在星系内的位置越远就越年轻。然而，哈勃的资料表明较为老化的恒星也有可能潜伏于一个星系的外侧旋臂中。最近的一次模拟研究提供了另外一个可能的解释——恒星可以漫游于整个漩涡星系中。这些观测应该可以进一步提供资料，以充实当前的理论。 |
| "With this information, we will be able to trace the complete cycle of star formation in detail," Dalcanton said. |
达尔卡顿表示：“有了这些信息，我们将能够仔细地跟踪研究恒星形成的全过程。” |
| The galactic survey results were submitted for publication in The Astrophysical Journal Supplement Series. The research on M81's star-formation has been submitted to The Astronomical Journal. |
星系观测结果提交到《天体物理学杂志增刊》，等待发表。有关星系M81中恒星形成的研究论文已经提交给《天文学杂志》。 |
