Challenges testing the no-hair theorem with gravitational waves [CL]

http://arxiv.org/abs/1706.05152


General relativity’s no-hair theorem states that isolated astrophysical black holes are described by only two numbers: mass and spin. As a consequence, there are strict relationships between the frequency and damping time of the different modes of a perturbed Kerr black hole. Testing the no-hair theorem has been a longstanding goal of gravitational-wave astronomy. The recent detection of gravitational waves from black hole mergers would seem to make such tests imminent. We investigate how constraints on black hole ringdown parameters scale with the loudness of the ringdown signal–subject to the constraint that the post-merger remnant must be allowed to settle into a perturbative, Kerr-like state. In particular, we require that–for a given detector–the gravitational waveform predicted by numerical relativity is indistinguishable from an exponentially damped sine after time tcut. The investigation yields a surprising result: by requiring the post-merger remnant to settle into a perturbative state, constraints on ringdown parameters do not shrink monotonically with louder signals. Since the no-hair theorem describes black holes in the asymptotic t -> infinity limit, more sensitive measurements probe later times without necessarily providing tighter constraints on ringdown frequencies and damping times. As a result, there is no clear threshold beyond which gravitational-wave detectors can be said to have unambiguously validated the no-hair theorem, only a series of constraints probing later and later times following the merger. Preliminary investigations are unable to explain this result in terms of a numerical relativity artifact.

Read this paper on arXiv…

E. Thrane, P. Lasky and Y. Levin
Mon, 19 Jun 17
21/48

Comments: 5 pages, 2 figures