双语小知识（六）

□ 曹 燕

双语小知识（六）

□ 曹 燕

Milky Way Halo银晕

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

银河，远比目之所及辽阔得多。

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.

我们往往认为银河系就是包含在薄薄银盘中的恒星和气体，其跨度大约为十万光年。但是，银盘之外的物质远比银盘内部多得多。

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.

银盘外部的区域被称为银晕。它形成了完全环绕银盘的球形，比银盘的宽度大出几倍。

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.

银晕中没有那么多单独的恒星，但是那里却是球状星团的家园（球状星团是成千上万颗恒星拥挤在一起形成的圆球）。绝大多数星团居于银盘外部，即便是那些身在银盘内部的星团也仅仅是过客而已，它们终究属于银晕。

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

球状星团中的恒星是整个银河系中最古老的。

箭袋树森林上方的银河。影像拍摄于非洲纳米比亚南部的一座箭袋树森林，璀璨银河与憨态可掬的箭袋树相映成趣。当然，图片中可见的银河仅仅是整个银河的一部分。图片来源：Florian Breuer摄影作品

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.

银晕的另一个组成元素是炽热的气体。这形成了我们几年前发现的X射线辉光。这些气体可能与银河系中所有的恒星质量相当，让银河的“总”物质量翻了一倍。

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.

绝大多数装扮银河的物质是暗物质，这也是银晕的主要组成成分。暗物质并不产生能量，但其引力却能把周围的可见物质拖曳过来。它可能由等待被发现的亚原子微粒组成。

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.

暗物质可能比银河系恒星和气体的总和还要庞大上几倍，正因为如此，银河也比可见的大出许多。

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.

我们的星系——银河系比其他星系更大也更亮，数千亿颗恒星释放出了大约200亿倍于太阳的光亮。但是仍有一些星系让我们的银河系相形见绌。比如说，迄今为止见到的最亮的星系就要比整个银河亮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.

这个以编号来命名的最亮星系位于幽暗的宝瓶座。初秋日暮时分，它在东南方天幕低悬。

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.

这一星系在距离大约125亿光年之外，所以我们看见的是当宇宙只有13亿岁时它的样貌。

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.

这一星系之所以能如此闪耀并非因为它的恒星，而是主要归功于黑洞，一个位于星系中心的巨型黑洞。当有气体进入时就会变得非常热，使其辐射增强。尘埃阻挡了我们观察这一星系的视线，但是尘埃本身也被加热并释放出红外光。实际上，天文学家就是通过空间红外望远镜发现这一星系的。

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.

我们不知道这一星系如今的样貌，但是当它还很年轻的时候就引领了如此加速的状态，它很可能会将其大部分气体吹跑，并将留下来的那部分转化成了诸多恒星。因而，如今的它很可能成了星系中较昏暗的一类——巨椭圆星系。如果真的是这样，之后它将不再拥有气体，没有年轻的恒星，也没有了它曾经是宇宙中最亮星系的所有痕迹。

Old Clusters 最古老的星团

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.

如果你同时拥有一片黑暗的天空和一个双筒望远镜的话，你就能在整个银河系中搜寻一些最古老的恒星了。这些恒星可能早在130亿年前就形成了，而那时候的宇宙也还不到10亿岁。

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

这些恒星属于位于银河系明亮银盘之外的、银晕中的球状星团。

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.

每个星团都是成千上万或者更多恒星挤在一起的圆球。而所有这些恒星在银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.

天文学家们通过测量恒星的组成成分来推断其年龄。宇宙里最初的恒星几乎全部是由氢和氦这两种宇宙大爆炸锻造的成分组成的。这类恒星的核反应制造了更重的元素。当恒星消亡，它们将一些重元素排放到宇宙空间里。

哈勃望远镜中的M15星团。图中的星星像蜜蜂一样挤在一起，这里的超过10万颗星星昭示了银河系早期的样子。图片来源：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.

经年累月，这些元素又成了新恒星的一部分，而新的恒星又反过来制造和贡献出更多的重元素。所以像太阳这样形成于宇宙大爆炸后数十亿年的恒星，包含了高浓度的重元素物质。但是，球状星团里的恒星们几乎没有这些物质，这也显示它们已经非常古老了。

特别说明：以上三篇文稿英文撰稿均为Damond Benningfield。文章来源于Star Date网站（https://stardate.org/），欢迎大家关注网站查看原文。

（责任编辑 张长喜）