星系差異為宇宙演化提供了線索（圖）
07-22
星系差異為宇宙演化提供了線索（圖）
這些用美國國家航空航天管理局的哈勃太空望遠鏡拍下的圖像，是四個星系的近景。圖像來自對附近星系的一次大規模觀測。
Galaxy Diversity Reveals Clues to Cosmic Evolution
| 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. | 長期以來，凝視宇宙深邃之處的天文學家們了解到，銀河系的相鄰星系只是表面上看起來相似。現在，美國國家航空航天管理局的哈勃太空望遠鏡提供了詳細觀測資料，資料顯示：那些星系隨著時間的推移而演化，併產生了差異。 |
| The ACS Nearby Galaxy Survey Treasury (ANGST) program zeroed in on14 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附近星系觀測資料庫（ANGST）計劃瞄準了69個附近星系中的1400萬顆恆星。這樣的星系距離近，哈勃的高解析度鏡頭能夠分離出最為明亮的恆星，而不會將其拍成模糊的一小片光亮。最重要的是，這樣可以幫助平息有關星系及其恆星形成方面的激烈爭執。 |
| "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." | 「我們不是挑選個別的星系來研究，而是觀察這個區域的『所有』星系，因此我們的觀測資料將是完整的，」ACS附近星系觀測資料庫西雅圖華盛頓大學觀測處主任朱莉安娜·達爾卡頓說，「這為我們提供了一幅多彩的畫面，展現出有關宇宙這一區域中所有恆星的形成時間和位置。」 |
| A galactic fossil record | 星系化石記錄 |
| 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). | 該觀測資料包括了距離地球650萬光年至130億光年的所有星系。一光年是光在一年當中所能夠穿行的距離，或者說大約相當於6萬億英里（10萬億公里）。 |
| 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. | 跟較遠星系中比較年輕的恆星相比，許多附近星系所包含的恆星實際上是處於瀕臨崩潰的狀態。根據附近較為老化的恆星，天文學家們可以推測出那些比較年輕的恆星會如何進行演化。 |
| "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為『化石記錄』，我們可以將它們跟遠處的年輕星系作對比，」達爾卡頓說，「這種對比可以為我們提供恆星形成的歷史，使我們更清楚地了解星系的質量、結構與環境。」 |
| 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. | 儘管越來越多的證據表明巨型星系的發展方式是跟較小的兄弟星繫結盟並融合，但是天文學家們對星系的形成仍然知之甚少。這種一步步演化而成為較大星系的說法，跟星系只不過是從無到有演化開來的理論是並存的。 |
| 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，一些觀察表明星系確實有快速擴張的能力。天文學家們曾經發現了一個距地球123億光年的恆星製造工廠，每年產出恆星4,000顆恆星，相比之下，我們銀河系每年才生產出10顆恆星。這種恆星製造活動的爆發表明，這樣的星系僅僅需要5,000萬年就可以成長為所觀察到的最大星系之一了。 |
| Stellar evolution | 恆星演化 |
| 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. | 一項獨立的新研究表明，很多這種大型漩渦星系在早期創造了多數恆星。同樣依據哈勃星系觀測資料，天文學家們考查了圓盤外側的星系M81。他們發現其中多數恆星形成於70多億年以前，即宇宙只有當前年齡的一半時。在如此巨大的星系中，巨型恆星作為超新星而滅亡，很快使得星系內充滿象碳這樣的重元素。 |
| "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. | 「這些元素形成的速度之快，以及隨後M81中大多數恆星形成速度的變化，都讓我們感到吃驚，」西雅圖華盛頓大學的天文學家本傑明·威廉姆斯說。 |
| 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，天文學家們認為，恆星群落在星系內的位置越遠就越年輕。然而，哈勃的資料表明較為老化的恆星也有可能潛伏於一個星系的外側旋臂中。最近的一次模擬研究提供了另外一個可能的解釋——恆星可以漫遊於整個漩渦星系中。這些觀測應該可以進一步提供資料，以充實當前的理論。 |
| "With this information, we will be able to trace the complete cycle of star formation in detail," Dalcanton said. | 達爾卡頓表示：「有了這些信息，我們將能夠仔細地跟蹤研究恆星形成的全過程。」 |
| 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. | 星系觀測結果提交到《天體物理學雜誌增刊》，等待發表。有關星系M81中恆星形成的研究論文已經提交給《天文學雜誌》。 |
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