□ 曹 燕

雙語小知識（六）

□ 曹 燕

Milky Way Halo銀暈

There's a lot more to the Milky Way than meets the eye.

銀河，遠(yuǎn)比目之所及遼闊得多。

Most of what we think of as the Milky Way galaxy is contained in a thin disk of stars and gas that's about a hundred thousand lightyears wide. But there's a lot more material outside the disk than inside.

我們往往認(rèn)為銀河系就是包含在薄薄銀盤中的恒星和氣體，其跨度大約為十萬光年。但是，銀盤之外的物質(zhì)遠(yuǎn)比銀盤內(nèi)部多得多。

The region outside the disk is known as the halo. It forms a ball that completely surrounds the disk, and it's several times wider than the disk.

銀盤外部的區(qū)域被稱為銀暈。它形成了完全環(huán)繞銀盤的球形，比銀盤的寬度大出幾倍。

There aren't all that many individual stars in the halo. But the halo is home to the galaxy's globular clusters — tightly packed balls of hundreds of thousands of stars. Most of the clusters lie outside the disk, but even those that are inside the disk are just passing through — they belong to the halo.

銀暈中沒有那么多單獨(dú)的恒星，但是那里卻是球狀星團(tuán)的家園（球狀星團(tuán)是成千上萬顆恒星擁擠在一起形成的圓球）。絕大多數(shù)星團(tuán)居于銀盤外部，即便是那些身在銀盤內(nèi)部的星團(tuán)也僅僅是過客而已，它們終究屬于銀暈。

The stars in globular clusters are the oldest in the entire Milky Way.

球狀星團(tuán)中的恒星是整個(gè)銀河系中最古老的。

箭袋樹森林上方的銀河。影像拍攝于非洲納米比亞南部的一座箭袋樹森林，璀璨銀河與憨態(tài)可掬的箭袋樹相映成趣。當(dāng)然，圖片中可見的銀河僅僅是整個(gè)銀河的一部分。圖片來源：Florian Breuer攝影作品

A second component of the halo is hot gas. It produces an X-ray glow that was discovered a few years ago. The gas may equal the mass of all the stars in the galaxy — doubling the amount of the Milky Way's “normal” matter.

銀暈的另一個(gè)組成元素是熾熱的氣體。這形成了我們幾年前發(fā)現(xiàn)的X射線輝光。這些氣體可能與銀河系中所有的恒星質(zhì)量相當(dāng)，讓銀河的“總”物質(zhì)量翻了一倍。

Most of the stuff that makes up the Milky Way is dark matter, which is the halo's main component. Dark matter produces no energy, but its gravity tugs at the visible matter around it. It may consist of subatomic particles that are still awaiting discovery.

絕大多數(shù)裝扮銀河的物質(zhì)是暗物質(zhì)，這也是銀暈的主要組成成分。暗物質(zhì)并不產(chǎn)生能量，但其引力卻能把周圍的可見物質(zhì)拖曳過來。它可能由等待被發(fā)現(xiàn)的亞原子微粒組成。

The dark matter is several times more massive than all the galaxy's stars and gas combined — so there's a lot more to the Milky Way than meets the eye.

暗物質(zhì)可能比銀河系恒星和氣體的總和還要龐大上幾倍，正因?yàn)槿绱耍y河也比可見的大出許多。

Brightest Galaxy 最亮的星系

Our galaxy, the Milky Way, is bigger and brighter than most others. Its hundreds of billions of stars emit roughly 20 billion times the light of the Sun. But a few rare galaxies make our galactic home seem modest. The brightest galaxy yet seen, for example, is 10,000 times brighter than the entire Milky Way.

我們的星系——銀河系比其他星系更大也更亮，數(shù)千億顆恒星釋放出了大約200億倍于太陽的光亮。但是仍有一些星系讓我們的銀河系相形見絀。比如說，迄今為止見到的最亮的星系就要比整個(gè)銀河亮10,000倍。

This brilliant galaxy, which is identified only by a catalog name, is in the faint constellation Aquarius, which is low in the southeast at nightfall on these early autumn nights.

這個(gè)以編號來命名的最亮星系位于幽暗的寶瓶座。初秋日暮時(shí)分，它在東南方天幕低懸。

The galaxy is about 12-and-a-half billion light-years away, so we see it as it was when the universe was just 1.3 billion years old.

這一星系在距離大約125億光年之外，所以我們看見的是當(dāng)宇宙只有13億歲時(shí)它的樣貌。

The galaxy owes most of its brilliance not to its stars, but to a black hole. A supermassive black hole at the galaxy's center attracts gas. As the gas plunges in, it gets so hot that it radiates profusely. Dust blocks our view of the galaxy, but the dust itself gets heated and emits infrared light. In fact, astronomers discovered the galaxy with an infrared telescope in space.

這一星系之所以能如此閃耀并非因?yàn)樗暮阈?，而是主要?dú)w功于黑洞，一個(gè)位于星系中心的巨型黑洞。當(dāng)有氣體進(jìn)入時(shí)就會變得非常熱，使其輻射增強(qiáng)。塵埃阻擋了我們觀察這一星系的視線，但是塵埃本身也被加熱并釋放出紅外光。實(shí)際上，天文學(xué)家就是通過空間紅外望遠(yuǎn)鏡發(fā)現(xiàn)這一星系的。

We can't see what the galaxy looks like today. But it led such an accelerated lifestyle in its youth that it probably blew away much of its gas and converted the rest into stars. As a result, today it may be a dull type of galaxy known as a giant elliptical. If so, then it has no gas, no young stars, and no evidence that it once reigned as one of the brightest galaxies in the cosmos.

我們不知道這一星系如今的樣貌，但是當(dāng)它還很年輕的時(shí)候就引領(lǐng)了如此加速的狀態(tài)，它很可能會將其大部分氣體吹跑，并將留下來的那部分轉(zhuǎn)化成了諸多恒星。因而，如今的它很可能成了星系中較昏暗的一類——巨橢圓星系。如果真的是這樣，之后它將不再擁有氣體，沒有年輕的恒星，也沒有了它曾經(jīng)是宇宙中最亮星系的所有痕跡。

Old Clusters 最古老的星團(tuán)

If you have dark skies and a pair of binoculars, you can scan for some of the oldest stars in the entire galaxy. The stars may have formed as early as 13 billion years ago — when the universe was less than a billion years old.

如果你同時(shí)擁有一片黑暗的天空和一個(gè)雙筒望遠(yuǎn)鏡的話，你就能在整個(gè)銀河系中搜尋一些最古老的恒星了。這些恒星可能早在130億年前就形成了，而那時(shí)候的宇宙也還不到10億歲。

The stars belong to globular clusters, which reside in the Milky Way's halo, outside the galaxy's bright disk.

這些恒星屬于位于銀河系明亮銀盤之外的、銀暈中的球狀星團(tuán)。

Each cluster is a tightly packed ball of a hundred thousand stars or more. And all of those stars are among the most ancient in the galaxy.

每個(gè)星團(tuán)都是成千上萬或者更多恒星擠在一起的圓球。而所有這些恒星在銀河系里都是最古老的。

Astronomers infer a star's age by measuring its composition. The first stars in the universe consisted almost entirely of hydrogen and helium — elements forged in the Big Bang. Nuclear reactions in those stars made heavier elements. When the stars died, they expelled some of the heavy elements into space.

天文學(xué)家們通過測量恒星的組成成分來推斷其年齡。宇宙里最初的恒星幾乎全部是由氫和氦這兩種宇宙大爆炸鍛造的成分組成的。這類恒星的核反應(yīng)制造了更重的元素。當(dāng)恒星消亡，它們將一些重元素排放到宇宙空間里。

哈勃望遠(yuǎn)鏡中的M15星團(tuán)。圖中的星星像蜜蜂一樣擠在一起，這里的超過10萬顆星星昭示了銀河系早期的樣子。圖片來源：ESA, Hubble, NASA

Over time, those elements were incorporated into new stars, which in turn made and distributed even more heavy elements. So stars like the Sun, which formed billions of years after the Big Bang, contain fairly high concentrations of these elements. But the stars in globular clusters contain almost none, suggesting that they're extremely old.

經(jīng)年累月，這些元素又成了新恒星的一部分，而新的恒星又反過來制造和貢獻(xiàn)出更多的重元素。所以像太陽這樣形成于宇宙大爆炸后數(shù)十億年的恒星，包含了高濃度的重元素物質(zhì)。但是，球狀星團(tuán)里的恒星們幾乎沒有這些物質(zhì)，這也顯示它們已經(jīng)非常古老了。

特別說明：以上三篇文稿英文撰稿均為Damond Benningfield。文章來源于Star Date網(wǎng)站（https://stardate.org/），歡迎大家關(guān)注網(wǎng)站查看原文。

（責(zé)任編輯 張長喜）