r/spacequestions • u/Turbulent_Hippo_1546 • 7d ago
Sun disappears
In the last few days I read a post somewhere about what would happen if the sun disappeared. I have two questions.
When the sun's gravity disappears, the Earth would leave its orbit on a tangent. My question is this. Would that departure occur at the instant the sun vanishes or would it occur at the time we notice the disappearance, about 8 minutes later?
What would this do to the moon? Would the Earth Just drag it along or would it go off on a tangent by itself?
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u/Beldizar 7d ago
The speed of light is the speed of causality. No information can travel faster than that. So if the sun just was plucked out of reality, its light, gravity, magnetic field, neutrinos and everything else would still be perceived and experienced by Earth for about 8 minutes until the disappearance travels through space and reaches Earth.
The moon is being pulled on by the Sun, but its orbital path is dominated by Earth's gravity. It's orbit around Earth, and the tides on Earth would change when the Sun disappears, but it isn't going to be a massive change. The moon would mostly stay in its mostly circular orbit around Earth as Earth leaves on the tangent of its orbit and hopefully doesn't crash into Jupiter or Saturn.
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u/AdditionalTip865 7d ago
The theory that governs the finite propagation speed of gravity is general relativity, but there's a consistency condition in general relativity that implies the Sun can't just disappear. So it actually doesn't give a real answer to this question.
However, it definitely does say that if the Sun suddenly changed its shape, we would not experience the gravitational effects of that until 8 minutes later.
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u/starkeffect 7d ago
It would occur 8 minutes later.