The star that exploded that year was just on the edge of the theoretical mass limit for forming black holes, about 20 times the mass of the sun.

爆炸的恒星其质量接近形成黑洞的理论质量极限，即太阳质量的20倍左右。

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The known sample is not large enough to determine a firm upper mass limit, which would in turn give more detailed insight into the physics of such extremely dense forms of matter.

这些已知的样本还不足以确定一个严格的质量上限，而这个上限可以帮助我们进一步了解这些极高密度的物质的物理特性。

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We know there is no thing called a massless rope, but most ropes have a mass, but maybe negligible compared to the two blocks you are pulling, so we'll take the idealized limit where the mass of the rope is 0.

我们都知道无质量的绳子是不存在的,是绳子就有质量,但是相比于这两个物体就可以忽略不计了,所以我们有了这个理想的条件,即绳子的质量都是 0

耶鲁公开课 - 基础物理课程节选

All models were required to have a body mass index -- a ratio of height and weight -- above 18, the minimum limit considered healthy by the World Health Organization.

CNN: Young models dying to be skinny