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。

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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。

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Benson says that the steep metallicity gradient agrees with the long-standing but unconfirmed idea that spiral galaxies form their discs of stars from the inside out.

Benson说，这个高梯度的结果与一个久已有之但一直未被证实的想法相符，这个想法就是螺旋星系的恒星主盘是由内而外形成的。

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