Testing no-hair theorem by quasi-periodic oscillations: the quadrupole of GRO J1655-40

We perform an observational test of no-hair theorem using quasi-periodic oscillations within the relativistic precession model. Two well motivated metrics we apply are Kerr-Q and Hartle-Thorne metrics in which the quadrupole is the parameter that possibly encodes deviations from the Kerr black hole. The expressions for the quasi-periodic frequencies are derived before comparing the models with the observation. We encounter a degeneracy in constraining spin and quadrupole parameters that makes it difficult to measure their values. In particular, we here propose a novel test of no-hair theorem by adapting the Hartle-Thorne metric. We complement our study by doing a model comparison. We find that there is strong evidence that Kerr black hole is the source of the central object in GRO J1655-40 given the present observational precisions.

Automated summary

The study tests the no-hair theorem using quasi-periodic oscillations in the relativistic precession model, applying the Kerr-Q and Hartle-Thorne metrics to derive expressions for quasi-periodic frequencies. A degeneracy in constraining spin and quadrupole parameters complicates the measurement of their values. By proposing a novel test using the Hartle-Thorne metric, it is found that there is strong evidence suggesting the Kerr black hole as the source of the central object in GRO J1655-40.