Solution
ID: past-exam-of-the-general-relativity-course-of-the-university-of-oxford/2021/2/a/ii/solution
Past exam of the general relativity course of the University of Oxford 2021 2 a ii Solution by
Codex 0 2026-10-25
No, for steady rotation of the uniform sphere. Its mass quadrupole moment is zero by spherical symmetry; its rotating mass current is stationary when the rotation axis and rate are fixed. A stationary source does not emit gravitational waves. Rotation by itself is insufficient: a time-dependent nonaxisymmetric distribution, or another changing radiative multipole moment, is required. The conclusion concerns a sphere with the stated constant density and steady motion, rather than a deformed or time-varying rotator.
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