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stevebd1

Gold Member

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I'm currently looking at the various gravity gradients (tidal stresses) for black holes and I've realised that in respect of small stellar black holes, as you approach the event horizon, not only does the gravity increase but it (appears) to exceed c. For example, for a 3 sol black hole, the gravity at the event horizon, using GM/r^2, works out at 5.0845x10^12 m/s^2. With the notion that this is the rate of acceleration in every second, is it acceptable to use a figure like this to express something which is considered to travel as the same as c? I also noticed this only occurs with neutron stars and small black holes (and any other compact star that might exist in between). Doing some research, it seems acceptable to state that the surface gravity for neutron stars can range from 2x10^11 to 3x10^12 Earth g (which are in the same ball park). Also, working backwards, you can work out at what point the gravity exceeds 299,792,500 m/s^2, r = (GM/c)^0.5, for a 3 sol black hole this would be at 1152.2 km radius. Does this radius denote something significant? I'd appreciate any feedback.

regards

Steve

P.S. the gravity gradient at the event horizon for a 3 sol mass black hole increases at 1.1490x10^9 m/s^2 per metre which in itself appears to be superluminal (I'm aware that any object within a gravity field of this magnitude would not exceed c but be dragged by the gravity field to speeds very close to c). I'm also aware there are theories that propose that the speed of gravity exceeds c but this seems to be met with considerable skepticism.

regards

Steve

P.S. the gravity gradient at the event horizon for a 3 sol mass black hole increases at 1.1490x10^9 m/s^2 per metre which in itself appears to be superluminal (I'm aware that any object within a gravity field of this magnitude would not exceed c but be dragged by the gravity field to speeds very close to c). I'm also aware there are theories that propose that the speed of gravity exceeds c but this seems to be met with considerable skepticism.

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