天文學家發現宇宙最早恆星

Astronomers said on Wednesday that they had discovered a lost generation of monster stars that ushered light into the universe after the Big Bang and jump-started the creation of the elements needed for planets and life before disappearing forever.

天文學家在週三表示，他們發現了失蹤的一代巨型恆星，是它們在宇宙大爆炸之後將光照入宇宙，並在永遠消失之前，瞬間啓動了星球及生命所需要的所有元素的創造。

Modern-day stars like our sun have a healthy mix of heavy elements, known as metals, but in the aftermath of the Big Bang only hydrogen, helium and small traces of lithium were available to make the first stars.

太陽等現代恆星擁有大量重元素，也就是金屬元素，但在宇宙大爆炸之後，構成第一代恆星的元素只有氫、氦和少量鋰。

Such stars could have been hundreds or thousands of times as massive as the sun, according to calculations, burning brightly and dying quickly, only 200 million years after the universe began. Their explosions would have spewed into space the elements that started the chain of thermonuclear reactions by which subsequent generations of stars have gradually enriched the cosmos with elements like oxygen, carbon and iron.

根據計算，此類恆星的質量可能是太陽質量的數百或數千倍，這些形成於宇宙大爆炸後2億年的恆星猛烈燃燒，迅速消失。它們的爆炸應該向太空噴射了開啓一系列熱核反應的元素，後續的幾代恆星通過熱核反應逐漸爲宇宙增添氧、碳、鐵等元素。

Spotting the older stars in action is one of the prime missions of the James Webb Space Telescope, to be launched by NASA in 2018. The discovery of such stars “would be wonderful,” James Peebles, a Princeton professor and one of the fathers of modern cosmology, said recently.

尋找有活動的古老恆星是美國國家航空航天局(NASA)詹姆斯·韋伯太空望遠鏡的主要任務之一，該望遠鏡將於2018年發射。普林斯頓大學(Princeton)教授詹姆斯·佩布萊斯(James Peebles)最近表示，發現此類恆星“會是一件非常美妙的事情”，他是現代宇宙學奠基人之一。

Now, in a paper to be published in The Astrophysical Journal, an international crew of astronomers led by David Sobral of the University of Lisbon, in Portugal, and the Leiden Observatory, in the Netherlands, said they had spotted the signature of these first-generation stars in a recently discovered galaxy that existed when the universe was only about 800 million years old. Its light has been traveling to us for 12.9 billion years, while succeeding generations of stars have worked their magic to make the universe interesting.

在《天文物理期刊》(The Astrophysical Journal)即將刊登的一篇論文中，由葡萄牙里斯本大學(University of Lisbon)的戴維·索夫拉爾(David Sobral)、荷蘭萊頓天文臺(Leiden Observatory)帶領的國際天文學家小組表示，他們在最近發現的星系中找到了第一代恆星的識別標誌，該星系在宇宙只有大約8億年曆史的時候就出現了。該星系發出的光用了129億年纔到達地球，在此期間，後續的幾代恆星施展魔法，讓宇宙變得有趣。

The galaxy, known as CR7, is three times as luminous as any previously found from that time, the authors said. Within it is a bright blue cloud that seems to contain only hydrogen and helium.

作者表示，這個被稱爲CR7的星系的亮度是之前發現的同期星系的亮度的三倍。該星系裏面是一個似乎只包含氫和氦的亮藍色星雲。

In an email, Dr. Sobral called this the first direct evidence of the stars “that ultimately allowed us all to be here by fabricating heavy elements and changing the composition of the universe.”

索夫拉爾在郵件中稱，這是第一個直接證明這些恆星“通過創造重元素，改變宇宙的構成，最終使得我們得以存在”的證據。

In a statement from the European Southern Observatory, he said, “It doesn’t really get any more exciting than this.”

在歐洲南方天文臺(European Southern Observatory)發表的聲明中，他表示，“沒有什麼比這個更令人激動的了。”

Garth Illingworth, an astronomer at the University of California, Santa Cruz, and a veteran of the search for early galaxies, pointed out, however, that these stars were appearing far later in cosmic history than theory had predicted.

但加州大學聖克魯斯分校(University of California, Santa Cruz)天文學家加思·伊林沃思(Garth Illingworth)指出，這些恆星在宇宙歷史中出現的時間比理論預測的時間要晚得多。伊林沃思在尋找早期星系方面有豐富的經驗。

Dr. Sobral and his colleagues were using the Very Large Telescope of the Southern Observatory in Chile and the W. M. Keck Observatory in Hawaii, among other big telescopes, to build on an earlier search for glowing clouds of hydrogen that might represent very early galaxies. Galaxy CR7 — short for Cosmos Redshift 7, after the method by which distant objects in the universe are dated — stood out.

索夫拉爾和他的同事利用南方天文臺在智利設置的甚大望遠鏡(Very Large Telescope)、夏威夷的W·M·凱克天文臺(W. M. Keck Observatory)及其他大型望遠鏡，繼續之前尋找由氫組成的發光星雲的工作，這些星雲可能代表着早期的星系。他們發現了GR7星系——宇宙紅移7號(Cosmos Redshift 7)的縮寫，得名於追溯宇宙中遙遠物體所使用的方法。

In an expanding universe, the farther away or back in time an object is, the faster it is receding, which causes the wavelength of light from it to lengthen, the way the pitch of a siren sounds lower after it passes. In astronomy, this lengthening is known as redshifting.

在不斷膨脹的宇宙中，一個物體越久遠，消失的速度就越快，這導致物體發出的光的波長變長，就像救護車呼嘯經過後，警報器的音高會逐漸降低。在天文學上，這種延長被稱爲紅移。

The galaxy’s name, Dr. Sobral said, was also inspired by the great Portuguese soccer player Cristiano Ronaldo, a.k.a. CR7.

索夫拉爾表示，該星系的名稱——CR7還受到葡萄牙優秀的足球運動員克里斯蒂亞諾·羅納爾多(Cristiano Ronaldo)的啓發。

As in much of astronomy, the nomenclature of these star generations is awkwardly rooted in history and Earth-centered. Modern stars like the sun, with healthy abundances of so-called metals (anything heavier than helium), are now called Population I, mainly because they were the first known. They mostly inhabit the spiral arms and younger parts of galaxies like the Milky Way.

在天文學的主要領域，各代恆星的命名都尷尬地遵從歷史，是以地球爲中心的。太陽等現代恆星擁有充裕的金屬元素（比氦重的物質），它們現在被稱爲第一星族(Population I)，主要是因爲它們是首批被發現的恆星。它們主要位於銀河系(Milky Way)等星系的旋臂和年輕星團中。

In the middle of the 20th century, however, the astronomer Walter Baade noticed that the stars in older parts of the galaxy, like its core or globular clusters, are older and have fewer metals. He called them Population II.

但在20世紀中葉，天文學家瓦爾特·巴德(Walter Baade)注意到，該星系的古老星團——比如它的核心星團或球狀星團——中的恆星年代更爲久遠，金屬元素更少。他稱之爲第二星族(Population II)。

The advent of the Big Bang theory of the origin of the universe forced astronomers to realize that the first stars must have had no metals at all; those are known as Population III.

有關宇宙起源的大爆炸理論的出現，迫使天文學家認識到，第一代恆星肯定不包含金屬元素；它們被稱爲第三星族(Population III)。

Stars of both Population II and Population III are probably present in CR7, Dr. Sobral and his team report. While the blue cloud is metal-free, according to spectral measurements, the color of the rest of the galaxy is consistent with more evolved stars making up most of its mass. This suggests, they write, that the Population III stars there are late bloomers of a sort, forming from leftover clouds of pristine material as the galaxy was sending out its light 12.9 billion years ago.

索夫拉爾和他的團隊報告稱，CR7星系中可能存在第二星族和第三星族的恆星。雖然根據光譜測量，這個藍色星雲不包含金屬元素，但該星系剩餘部分的顏色與演化程度較高的、構成其大部分質量的恆星一致。他們寫道，這說明該星系中的第三星族恆星形成較晚，由該星系129億年前發出光線時的嶄新物質的殘餘星雲發展而成。

The only alternative explanation, Dr. Sobral said, is something so spectacular and unlikely that astronomers do not know if it has ever happened, namely a primordial cloud bypassing the star stage and collapsing directly into a black hole. That, he noted, is impossible to rule out because nobody really knows what it should look like.

索夫拉爾表示，除此之外的唯一解釋是，發生了一些驚人的、意想不到的事，天文學家還不知道這種事是否發生過，那就是原始星雲越過恆星階段，直接坍縮爲黑洞。他指出，不能排除這種可能性，因爲沒人真的知道它看上去是什麼樣子。

Further observations with the Hubble Space Telescope and the James Webb could help resolve the issue.

利用哈勃太空望遠鏡和詹姆斯·韋伯太空望遠鏡進一步觀察或許有助於這個問題的解決。