A Myth about Black Holes

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Black holes irresistibly suck things in. That is a common misconception in science fiction. In fact, a spherical black hole of mass M attracts exterior mass no more strongly than a spherical star of mass M. Their exterior spacetimes are the same Schwarzschild geometry. But there is a sense in which it is more difficult to escape from close to a black hole than from a Newtonian center of acctraction of the same mass. Imagine using the thrust of a rocket to hover at a constant Schwarzschild coordinate radius R outside a spherical black hole of mass M. How much thrust would the rocket of mass m need to exert? Would it be infinitely larger as the radius R approaches 2M?
 
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George Jones
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Black holes irresistibly suck things in. That is a common misconception in science fiction. In fact, a spherical black home of mass M attracts exterior mass no more strongly than a spherical star of mass M. Their exterior spacetimes are the same Schwarzschild geometry.
Imagine using the thrust of a rocket to hover at a constant Schwarzschild coordinate radius R outside a spherical black hole of mass M. How much thrust would the rocket of mass m need to exert? Would it be infinitely larger as the radius R approaches 2M?
Yes, the thrust required approaches infinity as the event horizon is approached. See https://www.physicsforums.com/showpost.php?p=1633296&postcount=5".
 
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That's true, but the black hole is _deceptively_ massive. If you were approaching a red giant, because it was so large and so hot you'd know not to get so close that you'd be sucked in. If you were approaching a black hole, gravity would be felt much further away from the surface of the hole than it would from the surface of a star, and also there'd be no heat radiating from it, so you might not even know it was there until it was too late.
 

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