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steve asked the Naked Scientists: If the sun were suddenly to disappear without a trace, would all the planets fly off their orbits simultaneously, or in order of closeness to the sun, i.e. Mercury first, then Venus etc.
The problem with answering the question regarding whether planets would fly off instantaneously or after a time delay due to the speed of light limitation lies in the formulation of a question which has an impossible assertion; i.e. that the sun "suddenly" disappears. This can't happen. It could explode or somehow be moved away at finite speed but cannot disappear. From any normal event you can construct a model consistent with the physics. Anything that happens to the sun would propagate away from that event at the speed of light, whether a visual phenomena or some disturbance to its gravity field. I don't think you can formulate any viable solution for an event that has the sun "disappearing".
How about a black hole swallows the sun. Although that's not instantaneous', crossing the event horizon can't take that long. Now what happens - all the planets fly off simultaneously or one at a time? How long does it take for space-time to 'unbend'? Steve
If the Sun were to collapse into a black hole, the planets would keep on orbiting the black hole. From a distance, the strength of gravity is only sensitive to the total amount of mass, not to what particular form that mass is in.Monthly astronomy podcasts - www.thenakedscientists.com/astronomy
If we could (somehow) continue to provide energy to keep the world, light and warm, and feed ourselves (I realise it's a big if) - is there any reason why we could not continue to survive orbitting a black hole which had a similar mass to that of the sun?Matthew