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1·Three generations of stars may exist based on metallicity.

以金属度划分，恒星有三个世代。

2·One clue comes from the metallicity of the disc's constituent stars.

一条线索来自于主盘内恒星的金属丰度。

3·Different theories predict how this metallicity gradient changes over billions of years.

已有几种不同的理论对金属丰度梯度在亿万年间如何变化作了推测。

4·Metallicity is a measure of the relative abundance in a star of elements other than hydrogen and helium.

金属丰度是对恒星内除氢和氦之外元素的相对丰度的度量(天文学中比氦重的元素都叫金属。——译者注)。

5·The metallicity of a star measures the amount of metals it has —that is, any element heavier than helium.

恒星的金属度用于表征它含有的“金属”的量——其实是所有比氦重的元素的量。

6·The metallicity of a star measures the amount of metals it has — that is, any element heavier than helium.

恒星的金属度用于表征它含有的“金属”的量——其实是所有比氦重的元素的量。

7·Thus, the disc begins its existence with a steep metallicity gradient, like the one in the distant galaxy in Leo.

因此，主盘在形成伊始有一个很大的丰度梯度，就像遥远的狮子座里的那个星系那样。

8·In this thesis, we study the relation between the critical accretion rate and the metallicity via AGB stars approach.

在本文中我们通过agb星研究了此临界吸积率和金属丰度之间的关系。

9·Because we see the galaxy when it was young, this result suggests spiral discs start off with steep metallicity gradients.

因为我们看到的它还处于早期，这个结果表明螺旋星系主盘开始时有着很大的金属丰度梯度。

10·Because stars congregate at a galaxy's centre, the metallicity in most nearby spirals is greatest there and drops toward the edge.

因为恒星聚集在星系的中心，其附近的金属丰度最高并沿边缘方向逐渐降低。