Escape velocity depends on mass, so how can there be black holes as big as the Sun?

Escape velocity depends on BOTH mass and distance:


                     1/2
   V    = ( 2 G M/ R)

If the mass of the Earth were shrunk to a ball 1 centimeter across, we would still have an escape velocity from it of 11 kilometers/sec at the distance we are from the center of the Earth right now of 6000 kilometers. If we were to travel to within 60 kilometers of this micro-earth, from the above equation you can see that the escape velocity would climb to 11 x ( 6000/60)^1/2 = 110 kilometers/sec.

Black holes 'work', because you eventually can get so close to their concentrated mass that the escape velocity becomes the speed of light.


Copyright 1997 Dr. Sten Odenwald
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