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I can't imagine such phenomenon. Would it becomes an ellipsoid, or maybe a straight line?

John Rennie
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Karthikreddy Dhanasiri
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    When you ask about a physical object moving at the speed of light, you're effectively asking, "What do the known laws of physics predict under conditions that violate the known laws of physics?" The answer is, the laws of physics predict nothing under those circumstances. Now if you asked, "...as the velocity approaches the speed of light?" then you might get an answer. (Maybe not from me though, 'cause I'm not a physicist.) – Solomon Slow Apr 19 '16 at 16:16
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    In this case, definitely not from me, but I do know that imagining the situation is the most you could ever hope to do. No real rigid object could ever withstand the internal stress that would result from spinning at relativistic speeds. – Solomon Slow Apr 19 '16 at 16:19
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    Related: http://physics.stackexchange.com/q/8659/2451 and links therein. See also Ehrenfest paradox on Wikipedia. – Qmechanic Apr 19 '16 at 17:14
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    The downvotes seem harsh as this is a perfectly reasonable question. As Qmechanic points out this is a variant of the Ehrenfest paradox. – John Rennie Apr 20 '16 at 07:45
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    Nuetron stars spin up to 24% the speed of light. – Xavier Apr 20 '16 at 12:23

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What you are referring to is a special case of the Ehrenfest Paradox

In its original formulation as presented by Paul Ehrenfest 1909 in relation to the concept of Born rigidity within special relativity,1 it discusses an ideally rigid cylinder that is made to rotate about its axis of symmetry. The radius R as seen in the laboratory frame is always perpendicular to its motion and should therefore be equal to its value R0 when stationary. However, the circumference (2πR) should appear Lorentz-contracted to a smaller value than at rest, by the usual factor γ. This leads to the contradiction that R=R0 and R

The paradox has been deepened further by Albert Einstein, who showed that since measuring rods aligned along the periphery and moving with it should appear contracted, more would fit around the circumference, which would thus measure greater than 2πR. This indicates that geometry is non-Euclidean for rotating observers, and was important for Einstein's development of general relativity.