We calculate the minimum distance at which one may approach a black hole in a free flyby. It corresponds to $r=4m$ for the Schwarzschild black hole for a probe that was non-relativistic at infinity. The problem is formulated in a way that is useful for teaching introductory general relativity.

中文翻译：

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黑洞飞越

我们计算了一个人在自由飞越中可以接近黑洞的最小距离。它对应于$r=4米$对于 Schwarzschild 黑洞，一个在无穷远非相对论的探测器。这个问题的表述方式对教授广义相对论的介绍很有用。