Old Clusters

最古老的星团

Amateur Astronomer - - 宇宙奥秘 -

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。 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。

哈勃望远镜中的M 15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:E S A , Hubble,NASA

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