Such stars eventually blow off the material of their outer layers, which creates an expanding shell of gas called a planetary nebula.

这样的恒星最终炸开了它们的外层物质，形成了向外扩展的气体盔甲，名为行星状星云。

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Hence, it is rare that an open cluster survives long enough for one of its members to form a planetary nebula.

因此，一个疏散星团很少能够存活到它内部的某个成员变成行星状星云。

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The hot core collapses and begins to pulsate, eventually shedding its outer layers of gas to set the stage for the birth of a planetary nebula.

恒星高温的核心坍缩，并开始有规律的振动，最终气体外层迸散，为行星星云的形成提供了有利条件。

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