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Picture of gravity

We assume that the earth planet is a black hole. When a light beam is fired. The only way that even light can move is A and B which means this is impossible that light move on other ways C, D, E

Isn't it true?

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up vote 1 down vote accepted

When you say "assume that the earth planet is a black hole" I'm guessing you mean us to replace the Earth with a black hole of the same size, and then see what happens to the light.

If so you're quite correct that there is a distance within which light cannot escape and spirals into the black hole. This distance is known as the last stable orbit and for a non-rotating black hole it's at a radius of three times the event horizon radius (for a rotating black hole things get complicated!).

It is possible for light to orbit the black hole at the last stable orbit, but this orbit is an unstable one in the sense that a small perturbation will make the light spiral inwrads or outwards and either be consumed or escape.

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yes i mean replace the Earth in this picture with a black hole of the same size – antoni Sep 11 '12 at 10:57
@JohnRennie: Isn't the question imaginary? – Waffle's Crazy Peanut Sep 11 '12 at 12:22
@CrazyBuddy: if you consider the question be be "Consider a black hole the size of the Earth then ..." then I'm sure you agree that's a perfectly reasonable question. My assumption is that this was what antoni was asking, it was just phrased slightly awkwardly. – John Rennie Sep 11 '12 at 13:42

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