A Schwarzschild Radius Heuristic

d=2GMv2 is the formula for computing in terms of any speed the distance at which the escape velocity is that speed in Newtonian physics. It is also true that for a Schwarzschild black hole, r=2GMc2


So, a black hole is present when the Newtonian escape velocity from an object exceeds the maximum velocity 
allowed by special relativity.

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