Solution

ID: past-exam-of-the-relativity-course-of-the-university-of-cambridge/2015/paper-1/1/b/solution

Assume an emitter at rest on the stellar surface and a static observer at infinity. Write . The time-translation Killing energy of a photon is conserved, while the locally measured photon energy is proportional to . Consequently
Using , , and ,
The Schwarzschild radius is approximately , below the given surface radius. The positive shift is therefore a gravitational redshift of an escaping photon, with received wavelength about times the emitted wavelength. A moving emitter would introduce an additional Doppler factor; that is outside this static-surface model. The weak-field estimate is insufficient at this compactness. These stated constants are numerical conventions, not a claim about an unavailable historical handbook's last digits.

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